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llvm-project/llvm/lib/Transforms/Scalar/NewGVN.cpp

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//===---- NewGVN.cpp - Global Value Numbering Pass --------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
/// This file implements the new LLVM's Global Value Numbering pass.
/// GVN partitions values computed by a function into congruence classes.
/// Values ending up in the same congruence class are guaranteed to be the same
/// for every execution of the program. In that respect, congruency is a
/// compile-time approximation of equivalence of values at runtime.
/// The algorithm implemented here uses a sparse formulation and it's based
/// on the ideas described in the paper:
/// "A Sparse Algorithm for Predicated Global Value Numbering" from
/// Karthik Gargi.
///
/// A brief overview of the algorithm: The algorithm is essentially the same as
/// the standard RPO value numbering algorithm (a good reference is the paper
/// "SCC based value numbering" by L. Taylor Simpson) with one major difference:
/// The RPO algorithm proceeds, on every iteration, to process every reachable
/// block and every instruction in that block. This is because the standard RPO
/// algorithm does not track what things have the same value number, it only
/// tracks what the value number of a given operation is (the mapping is
/// operation -> value number). Thus, when a value number of an operation
/// changes, it must reprocess everything to ensure all uses of a value number
/// get updated properly. In constrast, the sparse algorithm we use *also*
/// tracks what operations have a given value number (IE it also tracks the
/// reverse mapping from value number -> operations with that value number), so
/// that it only needs to reprocess the instructions that are affected when
/// something's value number changes. The rest of the algorithm is devoted to
/// performing symbolic evaluation, forward propagation, and simplification of
/// operations based on the value numbers deduced so far.
///
/// We also do not perform elimination by using any published algorithm. All
/// published algorithms are O(Instructions). Instead, we use a technique that
/// is O(number of operations with the same value number), enabling us to skip
/// trying to eliminate things that have unique value numbers.
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/NewGVN.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SparseBitVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/CFGPrinter.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/DebugCounter.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/GVNExpression.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PredicateInfo.h"
#include "llvm/Transforms/Utils/VNCoercion.h"
#include <numeric>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace llvm;
using namespace PatternMatch;
using namespace llvm::GVNExpression;
using namespace llvm::VNCoercion;
#define DEBUG_TYPE "newgvn"
STATISTIC(NumGVNInstrDeleted, "Number of instructions deleted");
STATISTIC(NumGVNBlocksDeleted, "Number of blocks deleted");
STATISTIC(NumGVNOpsSimplified, "Number of Expressions simplified");
STATISTIC(NumGVNPhisAllSame, "Number of PHIs whos arguments are all the same");
STATISTIC(NumGVNMaxIterations,
"Maximum Number of iterations it took to converge GVN");
STATISTIC(NumGVNLeaderChanges, "Number of leader changes");
STATISTIC(NumGVNSortedLeaderChanges, "Number of sorted leader changes");
STATISTIC(NumGVNAvoidedSortedLeaderChanges,
"Number of avoided sorted leader changes");
STATISTIC(NumGVNNotMostDominatingLeader,
"Number of times a member dominated it's new classes' leader");
STATISTIC(NumGVNDeadStores, "Number of redundant/dead stores eliminated");
DEBUG_COUNTER(VNCounter, "newgvn-vn",
"Controls which instructions are value numbered")
// Currently store defining access refinement is too slow due to basicaa being
// egregiously slow. This flag lets us keep it working while we work on this
// issue.
static cl::opt<bool> EnableStoreRefinement("enable-store-refinement",
cl::init(false), cl::Hidden);
//===----------------------------------------------------------------------===//
// GVN Pass
//===----------------------------------------------------------------------===//
// Anchor methods.
namespace llvm {
namespace GVNExpression {
Expression::~Expression() = default;
BasicExpression::~BasicExpression() = default;
CallExpression::~CallExpression() = default;
LoadExpression::~LoadExpression() = default;
StoreExpression::~StoreExpression() = default;
AggregateValueExpression::~AggregateValueExpression() = default;
PHIExpression::~PHIExpression() = default;
}
}
// Tarjan's SCC finding algorithm with Nuutila's improvements
// SCCIterator is actually fairly complex for the simple thing we want.
// It also wants to hand us SCC's that are unrelated to the phi node we ask
// about, and have us process them there or risk redoing work.
// Graph traits over a filter iterator also doesn't work that well here.
// This SCC finder is specialized to walk use-def chains, and only follows
// instructions,
// not generic values (arguments, etc).
struct TarjanSCC {
TarjanSCC() : Components(1) {}
void Start(const Instruction *Start) {
if (Root.lookup(Start) == 0)
FindSCC(Start);
}
const SmallPtrSetImpl<const Value *> &getComponentFor(const Value *V) const {
unsigned ComponentID = ValueToComponent.lookup(V);
assert(ComponentID > 0 &&
"Asking for a component for a value we never processed");
return Components[ComponentID];
}
private:
void FindSCC(const Instruction *I) {
Root[I] = ++DFSNum;
// Store the DFS Number we had before it possibly gets incremented.
unsigned int OurDFS = DFSNum;
for (auto &Op : I->operands()) {
if (auto *InstOp = dyn_cast<Instruction>(Op)) {
if (Root.lookup(Op) == 0)
FindSCC(InstOp);
if (!InComponent.count(Op))
Root[I] = std::min(Root.lookup(I), Root.lookup(Op));
}
}
// See if we really were the root of a component, by seeing if we still have
// our DFSNumber.
// If we do, we are the root of the component, and we have completed a
// component. If we do not,
// we are not the root of a component, and belong on the component stack.
if (Root.lookup(I) == OurDFS) {
unsigned ComponentID = Components.size();
Components.resize(Components.size() + 1);
auto &Component = Components.back();
Component.insert(I);
DEBUG(dbgs() << "Component root is " << *I << "\n");
InComponent.insert(I);
ValueToComponent[I] = ComponentID;
// Pop a component off the stack and label it.
while (!Stack.empty() && Root.lookup(Stack.back()) >= OurDFS) {
auto *Member = Stack.back();
DEBUG(dbgs() << "Component member is " << *Member << "\n");
Component.insert(Member);
InComponent.insert(Member);
ValueToComponent[Member] = ComponentID;
Stack.pop_back();
}
} else {
// Part of a component, push to stack
Stack.push_back(I);
}
}
unsigned int DFSNum = 1;
SmallPtrSet<const Value *, 8> InComponent;
DenseMap<const Value *, unsigned int> Root;
SmallVector<const Value *, 8> Stack;
// Store the components as vector of ptr sets, because we need the topo order
// of SCC's, but not individual member order
SmallVector<SmallPtrSet<const Value *, 8>, 8> Components;
DenseMap<const Value *, unsigned> ValueToComponent;
};
// Congruence classes represent the set of expressions/instructions
// that are all the same *during some scope in the function*.
// That is, because of the way we perform equality propagation, and
// because of memory value numbering, it is not correct to assume
// you can willy-nilly replace any member with any other at any
// point in the function.
//
// For any Value in the Member set, it is valid to replace any dominated member
// with that Value.
//
// Every congruence class has a leader, and the leader is used to symbolize
// instructions in a canonical way (IE every operand of an instruction that is a
// member of the same congruence class will always be replaced with leader
// during symbolization). To simplify symbolization, we keep the leader as a
// constant if class can be proved to be a constant value. Otherwise, the
// leader is the member of the value set with the smallest DFS number. Each
// congruence class also has a defining expression, though the expression may be
// null. If it exists, it can be used for forward propagation and reassociation
// of values.
// For memory, we also track a representative MemoryAccess, and a set of memory
// members for MemoryPhis (which have no real instructions). Note that for
// memory, it seems tempting to try to split the memory members into a
// MemoryCongruenceClass or something. Unfortunately, this does not work
// easily. The value numbering of a given memory expression depends on the
// leader of the memory congruence class, and the leader of memory congruence
// class depends on the value numbering of a given memory expression. This
// leads to wasted propagation, and in some cases, missed optimization. For
// example: If we had value numbered two stores together before, but now do not,
// we move them to a new value congruence class. This in turn will move at one
// of the memorydefs to a new memory congruence class. Which in turn, affects
// the value numbering of the stores we just value numbered (because the memory
// congruence class is part of the value number). So while theoretically
// possible to split them up, it turns out to be *incredibly* complicated to get
// it to work right, because of the interdependency. While structurally
// slightly messier, it is algorithmically much simpler and faster to do what we
// do here, and track them both at once in the same class.
// Note: The default iterators for this class iterate over values
class CongruenceClass {
public:
using MemberType = Value;
using MemberSet = SmallPtrSet<MemberType *, 4>;
using MemoryMemberType = MemoryPhi;
using MemoryMemberSet = SmallPtrSet<const MemoryMemberType *, 2>;
explicit CongruenceClass(unsigned ID) : ID(ID) {}
CongruenceClass(unsigned ID, Value *Leader, const Expression *E)
: ID(ID), RepLeader(Leader), DefiningExpr(E) {}
unsigned getID() const { return ID; }
// True if this class has no members left. This is mainly used for assertion
// purposes, and for skipping empty classes.
bool isDead() const {
// If it's both dead from a value perspective, and dead from a memory
// perspective, it's really dead.
return empty() && memory_empty();
}
// Leader functions
Value *getLeader() const { return RepLeader; }
void setLeader(Value *Leader) { RepLeader = Leader; }
const std::pair<Value *, unsigned int> &getNextLeader() const {
return NextLeader;
}
void resetNextLeader() { NextLeader = {nullptr, ~0}; }
void addPossibleNextLeader(std::pair<Value *, unsigned int> LeaderPair) {
if (LeaderPair.second < NextLeader.second)
NextLeader = LeaderPair;
}
Value *getStoredValue() const { return RepStoredValue; }
void setStoredValue(Value *Leader) { RepStoredValue = Leader; }
const MemoryAccess *getMemoryLeader() const { return RepMemoryAccess; }
void setMemoryLeader(const MemoryAccess *Leader) { RepMemoryAccess = Leader; }
// Forward propagation info
const Expression *getDefiningExpr() const { return DefiningExpr; }
// Value member set
bool empty() const { return Members.empty(); }
unsigned size() const { return Members.size(); }
MemberSet::const_iterator begin() const { return Members.begin(); }
MemberSet::const_iterator end() const { return Members.end(); }
void insert(MemberType *M) { Members.insert(M); }
void erase(MemberType *M) { Members.erase(M); }
void swap(MemberSet &Other) { Members.swap(Other); }
// Memory member set
bool memory_empty() const { return MemoryMembers.empty(); }
unsigned memory_size() const { return MemoryMembers.size(); }
MemoryMemberSet::const_iterator memory_begin() const {
return MemoryMembers.begin();
}
MemoryMemberSet::const_iterator memory_end() const {
return MemoryMembers.end();
}
iterator_range<MemoryMemberSet::const_iterator> memory() const {
return make_range(memory_begin(), memory_end());
}
void memory_insert(const MemoryMemberType *M) { MemoryMembers.insert(M); }
void memory_erase(const MemoryMemberType *M) { MemoryMembers.erase(M); }
// Store count
unsigned getStoreCount() const { return StoreCount; }
void incStoreCount() { ++StoreCount; }
void decStoreCount() {
assert(StoreCount != 0 && "Store count went negative");
--StoreCount;
}
// True if this class has no memory members.
bool definesNoMemory() const { return StoreCount == 0 && memory_empty(); }
// Return true if two congruence classes are equivalent to each other. This
// means
// that every field but the ID number and the dead field are equivalent.
bool isEquivalentTo(const CongruenceClass *Other) const {
if (!Other)
return false;
if (this == Other)
return true;
if (std::tie(StoreCount, RepLeader, RepStoredValue, RepMemoryAccess) !=
std::tie(Other->StoreCount, Other->RepLeader, Other->RepStoredValue,
Other->RepMemoryAccess))
return false;
if (DefiningExpr != Other->DefiningExpr)
if (!DefiningExpr || !Other->DefiningExpr ||
*DefiningExpr != *Other->DefiningExpr)
return false;
// We need some ordered set
std::set<Value *> AMembers(Members.begin(), Members.end());
std::set<Value *> BMembers(Members.begin(), Members.end());
return AMembers == BMembers;
}
private:
unsigned ID;
// Representative leader.
Value *RepLeader = nullptr;
// The most dominating leader after our current leader, because the member set
// is not sorted and is expensive to keep sorted all the time.
std::pair<Value *, unsigned int> NextLeader = {nullptr, ~0U};
// If this is represented by a store, the value of the store.
Value *RepStoredValue = nullptr;
// If this class contains MemoryDefs or MemoryPhis, this is the leading memory
// access.
const MemoryAccess *RepMemoryAccess = nullptr;
// Defining Expression.
const Expression *DefiningExpr = nullptr;
// Actual members of this class.
MemberSet Members;
// This is the set of MemoryPhis that exist in the class. MemoryDefs and
// MemoryUses have real instructions representing them, so we only need to
// track MemoryPhis here.
MemoryMemberSet MemoryMembers;
// Number of stores in this congruence class.
// This is used so we can detect store equivalence changes properly.
int StoreCount = 0;
};
namespace llvm {
template <> struct DenseMapInfo<const Expression *> {
static const Expression *getEmptyKey() {
auto Val = static_cast<uintptr_t>(-1);
Val <<= PointerLikeTypeTraits<const Expression *>::NumLowBitsAvailable;
return reinterpret_cast<const Expression *>(Val);
}
static const Expression *getTombstoneKey() {
auto Val = static_cast<uintptr_t>(~1U);
Val <<= PointerLikeTypeTraits<const Expression *>::NumLowBitsAvailable;
return reinterpret_cast<const Expression *>(Val);
}
static unsigned getHashValue(const Expression *V) {
return static_cast<unsigned>(V->getHashValue());
}
static bool isEqual(const Expression *LHS, const Expression *RHS) {
if (LHS == RHS)
return true;
if (LHS == getTombstoneKey() || RHS == getTombstoneKey() ||
LHS == getEmptyKey() || RHS == getEmptyKey())
return false;
return *LHS == *RHS;
}
};
} // end namespace llvm
namespace {
class NewGVN {
Function &F;
DominatorTree *DT;
const TargetLibraryInfo *TLI;
AliasAnalysis *AA;
MemorySSA *MSSA;
MemorySSAWalker *MSSAWalker;
const DataLayout &DL;
std::unique_ptr<PredicateInfo> PredInfo;
// These are the only two things the create* functions should have
// side-effects on due to allocating memory.
mutable BumpPtrAllocator ExpressionAllocator;
mutable ArrayRecycler<Value *> ArgRecycler;
mutable TarjanSCC SCCFinder;
const SimplifyQuery SQ;
// Number of function arguments, used by ranking
unsigned int NumFuncArgs;
// RPOOrdering of basic blocks
DenseMap<const DomTreeNode *, unsigned> RPOOrdering;
// Congruence class info.
// This class is called INITIAL in the paper. It is the class everything
// startsout in, and represents any value. Being an optimistic analysis,
// anything in the TOP class has the value TOP, which is indeterminate and
// equivalent to everything.
CongruenceClass *TOPClass;
std::vector<CongruenceClass *> CongruenceClasses;
unsigned NextCongruenceNum;
// Value Mappings.
DenseMap<Value *, CongruenceClass *> ValueToClass;
DenseMap<Value *, const Expression *> ValueToExpression;
// Mapping from predicate info we used to the instructions we used it with.
// In order to correctly ensure propagation, we must keep track of what
// comparisons we used, so that when the values of the comparisons change, we
// propagate the information to the places we used the comparison.
mutable DenseMap<const Value *, SmallPtrSet<Instruction *, 2>>
PredicateToUsers;
// the same reasoning as PredicateToUsers. When we skip MemoryAccesses for
// stores, we no longer can rely solely on the def-use chains of MemorySSA.
mutable DenseMap<const MemoryAccess *, SmallPtrSet<MemoryAccess *, 2>>
MemoryToUsers;
// A table storing which memorydefs/phis represent a memory state provably
// equivalent to another memory state.
// We could use the congruence class machinery, but the MemoryAccess's are
// abstract memory states, so they can only ever be equivalent to each other,
// and not to constants, etc.
DenseMap<const MemoryAccess *, CongruenceClass *> MemoryAccessToClass;
// We could, if we wanted, build MemoryPhiExpressions and
// MemoryVariableExpressions, etc, and value number them the same way we value
// number phi expressions. For the moment, this seems like overkill. They
// can only exist in one of three states: they can be TOP (equal to
// everything), Equivalent to something else, or unique. Because we do not
// create expressions for them, we need to simulate leader change not just
// when they change class, but when they change state. Note: We can do the
// same thing for phis, and avoid having phi expressions if we wanted, We
// should eventually unify in one direction or the other, so this is a little
// bit of an experiment in which turns out easier to maintain.
enum MemoryPhiState { MPS_Invalid, MPS_TOP, MPS_Equivalent, MPS_Unique };
DenseMap<const MemoryPhi *, MemoryPhiState> MemoryPhiState;
enum PhiCycleState { PCS_Unknown, PCS_CycleFree, PCS_Cycle };
mutable DenseMap<const PHINode *, PhiCycleState> PhiCycleState;
// Expression to class mapping.
using ExpressionClassMap = DenseMap<const Expression *, CongruenceClass *>;
ExpressionClassMap ExpressionToClass;
// Which values have changed as a result of leader changes.
SmallPtrSet<Value *, 8> LeaderChanges;
// Reachability info.
using BlockEdge = BasicBlockEdge;
DenseSet<BlockEdge> ReachableEdges;
SmallPtrSet<const BasicBlock *, 8> ReachableBlocks;
// This is a bitvector because, on larger functions, we may have
// thousands of touched instructions at once (entire blocks,
// instructions with hundreds of uses, etc). Even with optimization
// for when we mark whole blocks as touched, when this was a
// SmallPtrSet or DenseSet, for some functions, we spent >20% of all
// the time in GVN just managing this list. The bitvector, on the
// other hand, efficiently supports test/set/clear of both
// individual and ranges, as well as "find next element" This
// enables us to use it as a worklist with essentially 0 cost.
BitVector TouchedInstructions;
DenseMap<const BasicBlock *, std::pair<unsigned, unsigned>> BlockInstRange;
#ifndef NDEBUG
// Debugging for how many times each block and instruction got processed.
DenseMap<const Value *, unsigned> ProcessedCount;
#endif
// DFS info.
// This contains a mapping from Instructions to DFS numbers.
// The numbering starts at 1. An instruction with DFS number zero
// means that the instruction is dead.
DenseMap<const Value *, unsigned> InstrDFS;
// This contains the mapping DFS numbers to instructions.
SmallVector<Value *, 32> DFSToInstr;
// Deletion info.
SmallPtrSet<Instruction *, 8> InstructionsToErase;
public:
NewGVN(Function &F, DominatorTree *DT, AssumptionCache *AC,
TargetLibraryInfo *TLI, AliasAnalysis *AA, MemorySSA *MSSA,
const DataLayout &DL)
: F(F), DT(DT), TLI(TLI), AA(AA), MSSA(MSSA), DL(DL),
PredInfo(make_unique<PredicateInfo>(F, *DT, *AC)), SQ(DL, TLI, DT, AC) {
}
bool runGVN();
private:
// Expression handling.
const Expression *createExpression(Instruction *) const;
const Expression *createBinaryExpression(unsigned, Type *, Value *,
Value *) const;
PHIExpression *createPHIExpression(Instruction *, bool &HasBackEdge,
bool &AllConstant) const;
const VariableExpression *createVariableExpression(Value *) const;
const ConstantExpression *createConstantExpression(Constant *) const;
const Expression *createVariableOrConstant(Value *V) const;
const UnknownExpression *createUnknownExpression(Instruction *) const;
const StoreExpression *createStoreExpression(StoreInst *,
const MemoryAccess *) const;
LoadExpression *createLoadExpression(Type *, Value *, LoadInst *,
const MemoryAccess *) const;
const CallExpression *createCallExpression(CallInst *,
const MemoryAccess *) const;
const AggregateValueExpression *
createAggregateValueExpression(Instruction *) const;
bool setBasicExpressionInfo(Instruction *, BasicExpression *) const;
// Congruence class handling.
CongruenceClass *createCongruenceClass(Value *Leader, const Expression *E) {
auto *result = new CongruenceClass(NextCongruenceNum++, Leader, E);
CongruenceClasses.emplace_back(result);
return result;
}
CongruenceClass *createMemoryClass(MemoryAccess *MA) {
auto *CC = createCongruenceClass(nullptr, nullptr);
CC->setMemoryLeader(MA);
return CC;
}
CongruenceClass *ensureLeaderOfMemoryClass(MemoryAccess *MA) {
auto *CC = getMemoryClass(MA);
if (CC->getMemoryLeader() != MA)
CC = createMemoryClass(MA);
return CC;
}
CongruenceClass *createSingletonCongruenceClass(Value *Member) {
CongruenceClass *CClass = createCongruenceClass(Member, nullptr);
CClass->insert(Member);
ValueToClass[Member] = CClass;
return CClass;
}
void initializeCongruenceClasses(Function &F);
// Value number an Instruction or MemoryPhi.
void valueNumberMemoryPhi(MemoryPhi *);
void valueNumberInstruction(Instruction *);
// Symbolic evaluation.
const Expression *checkSimplificationResults(Expression *, Instruction *,
Value *) const;
const Expression *performSymbolicEvaluation(Value *) const;
const Expression *performSymbolicLoadCoercion(Type *, Value *, LoadInst *,
Instruction *,
MemoryAccess *) const;
const Expression *performSymbolicLoadEvaluation(Instruction *) const;
const Expression *performSymbolicStoreEvaluation(Instruction *) const;
const Expression *performSymbolicCallEvaluation(Instruction *) const;
const Expression *performSymbolicPHIEvaluation(Instruction *) const;
const Expression *performSymbolicAggrValueEvaluation(Instruction *) const;
const Expression *performSymbolicCmpEvaluation(Instruction *) const;
const Expression *performSymbolicPredicateInfoEvaluation(Instruction *) const;
// Congruence finding.
bool someEquivalentDominates(const Instruction *, const Instruction *) const;
Value *lookupOperandLeader(Value *) const;
void performCongruenceFinding(Instruction *, const Expression *);
void moveValueToNewCongruenceClass(Instruction *, const Expression *,
CongruenceClass *, CongruenceClass *);
void moveMemoryToNewCongruenceClass(Instruction *, MemoryAccess *,
CongruenceClass *, CongruenceClass *);
Value *getNextValueLeader(CongruenceClass *) const;
const MemoryAccess *getNextMemoryLeader(CongruenceClass *) const;
bool setMemoryClass(const MemoryAccess *From, CongruenceClass *To);
CongruenceClass *getMemoryClass(const MemoryAccess *MA) const;
const MemoryAccess *lookupMemoryLeader(const MemoryAccess *) const;
bool isMemoryAccessTop(const MemoryAccess *) const;
// Ranking
unsigned int getRank(const Value *) const;
bool shouldSwapOperands(const Value *, const Value *) const;
// Reachability handling.
void updateReachableEdge(BasicBlock *, BasicBlock *);
void processOutgoingEdges(TerminatorInst *, BasicBlock *);
Value *findConditionEquivalence(Value *) const;
// Elimination.
struct ValueDFS;
void convertClassToDFSOrdered(const CongruenceClass &,
SmallVectorImpl<ValueDFS> &,
DenseMap<const Value *, unsigned int> &,
SmallPtrSetImpl<Instruction *> &) const;
void convertClassToLoadsAndStores(const CongruenceClass &,
SmallVectorImpl<ValueDFS> &) const;
bool eliminateInstructions(Function &);
void replaceInstruction(Instruction *, Value *);
void markInstructionForDeletion(Instruction *);
void deleteInstructionsInBlock(BasicBlock *);
// New instruction creation.
void handleNewInstruction(Instruction *){};
// Various instruction touch utilities
void markUsersTouched(Value *);
void markMemoryUsersTouched(const MemoryAccess *);
void markMemoryDefTouched(const MemoryAccess *);
void markPredicateUsersTouched(Instruction *);
void markValueLeaderChangeTouched(CongruenceClass *CC);
void markMemoryLeaderChangeTouched(CongruenceClass *CC);
void addPredicateUsers(const PredicateBase *, Instruction *) const;
void addMemoryUsers(const MemoryAccess *To, MemoryAccess *U) const;
// Main loop of value numbering
void iterateTouchedInstructions();
// Utilities.
void cleanupTables();
std::pair<unsigned, unsigned> assignDFSNumbers(BasicBlock *, unsigned);
void updateProcessedCount(Value *V);
void verifyMemoryCongruency() const;
void verifyIterationSettled(Function &F);
void verifyStoreExpressions() const;
bool singleReachablePHIPath(SmallPtrSet<const MemoryAccess *, 8> &,
const MemoryAccess *, const MemoryAccess *) const;
BasicBlock *getBlockForValue(Value *V) const;
void deleteExpression(const Expression *E) const;
unsigned InstrToDFSNum(const Value *V) const {
assert(isa<Instruction>(V) && "This should not be used for MemoryAccesses");
return InstrDFS.lookup(V);
}
unsigned InstrToDFSNum(const MemoryAccess *MA) const {
return MemoryToDFSNum(MA);
}
Value *InstrFromDFSNum(unsigned DFSNum) { return DFSToInstr[DFSNum]; }
// Given a MemoryAccess, return the relevant instruction DFS number. Note:
// This deliberately takes a value so it can be used with Use's, which will
// auto-convert to Value's but not to MemoryAccess's.
unsigned MemoryToDFSNum(const Value *MA) const {
assert(isa<MemoryAccess>(MA) &&
"This should not be used with instructions");
return isa<MemoryUseOrDef>(MA)
? InstrToDFSNum(cast<MemoryUseOrDef>(MA)->getMemoryInst())
: InstrDFS.lookup(MA);
}
bool isCycleFree(const PHINode *PN) const;
template <class T, class Range> T *getMinDFSOfRange(const Range &) const;
// Debug counter info. When verifying, we have to reset the value numbering
// debug counter to the same state it started in to get the same results.
std::pair<int, int> StartingVNCounter;
};
} // end anonymous namespace
template <typename T>
static bool equalsLoadStoreHelper(const T &LHS, const Expression &RHS) {
if (!isa<LoadExpression>(RHS) && !isa<StoreExpression>(RHS))
return false;
return LHS.MemoryExpression::equals(RHS);
}
bool LoadExpression::equals(const Expression &Other) const {
return equalsLoadStoreHelper(*this, Other);
}
bool StoreExpression::equals(const Expression &Other) const {
if (!equalsLoadStoreHelper(*this, Other))
return false;
// Make sure that store vs store includes the value operand.
if (const auto *S = dyn_cast<StoreExpression>(&Other))
if (getStoredValue() != S->getStoredValue())
return false;
return true;
}
#ifndef NDEBUG
static std::string getBlockName(const BasicBlock *B) {
return DOTGraphTraits<const Function *>::getSimpleNodeLabel(B, nullptr);
}
#endif
// Get the basic block from an instruction/memory value.
BasicBlock *NewGVN::getBlockForValue(Value *V) const {
if (auto *I = dyn_cast<Instruction>(V))
return I->getParent();
else if (auto *MP = dyn_cast<MemoryPhi>(V))
return MP->getBlock();
llvm_unreachable("Should have been able to figure out a block for our value");
return nullptr;
}
// Delete a definitely dead expression, so it can be reused by the expression
// allocator. Some of these are not in creation functions, so we have to accept
// const versions.
void NewGVN::deleteExpression(const Expression *E) const {
assert(isa<BasicExpression>(E));
auto *BE = cast<BasicExpression>(E);
const_cast<BasicExpression *>(BE)->deallocateOperands(ArgRecycler);
ExpressionAllocator.Deallocate(E);
}
PHIExpression *NewGVN::createPHIExpression(Instruction *I, bool &HasBackedge,
bool &AllConstant) const {
BasicBlock *PHIBlock = I->getParent();
auto *PN = cast<PHINode>(I);
auto *E =
new (ExpressionAllocator) PHIExpression(PN->getNumOperands(), PHIBlock);
E->allocateOperands(ArgRecycler, ExpressionAllocator);
E->setType(I->getType());
E->setOpcode(I->getOpcode());
unsigned PHIRPO = RPOOrdering.lookup(DT->getNode(PHIBlock));
// NewGVN assumes the operands of a PHI node are in a consistent order across
// PHIs. LLVM doesn't seem to always guarantee this. While we need to fix
// this in LLVM at some point we don't want GVN to find wrong congruences.
// Therefore, here we sort uses in predecessor order.
// We're sorting the values by pointer. In theory this might be cause of
// non-determinism, but here we don't rely on the ordering for anything
// significant, e.g. we don't create new instructions based on it so we're
// fine.
SmallVector<const Use *, 4> PHIOperands;
for (const Use &U : PN->operands())
PHIOperands.push_back(&U);
std::sort(PHIOperands.begin(), PHIOperands.end(),
[&](const Use *U1, const Use *U2) {
return PN->getIncomingBlock(*U1) < PN->getIncomingBlock(*U2);
});
// Filter out unreachable phi operands.
auto Filtered = make_filter_range(PHIOperands, [&](const Use *U) {
return ReachableEdges.count({PN->getIncomingBlock(*U), PHIBlock});
});
std::transform(Filtered.begin(), Filtered.end(), op_inserter(E),
[&](const Use *U) -> Value * {
auto *BB = PN->getIncomingBlock(*U);
auto *DTN = DT->getNode(BB);
if (RPOOrdering.lookup(DTN) >= PHIRPO)
HasBackedge = true;
AllConstant &= isa<UndefValue>(*U) || isa<Constant>(*U);
// Don't try to transform self-defined phis.
if (*U == PN)
return PN;
return lookupOperandLeader(*U);
});
return E;
}
// Set basic expression info (Arguments, type, opcode) for Expression
// E from Instruction I in block B.
bool NewGVN::setBasicExpressionInfo(Instruction *I, BasicExpression *E) const {
bool AllConstant = true;
if (auto *GEP = dyn_cast<GetElementPtrInst>(I))
E->setType(GEP->getSourceElementType());
else
E->setType(I->getType());
E->setOpcode(I->getOpcode());
E->allocateOperands(ArgRecycler, ExpressionAllocator);
// Transform the operand array into an operand leader array, and keep track of
// whether all members are constant.
std::transform(I->op_begin(), I->op_end(), op_inserter(E), [&](Value *O) {
auto Operand = lookupOperandLeader(O);
AllConstant &= isa<Constant>(Operand);
return Operand;
});
return AllConstant;
}
const Expression *NewGVN::createBinaryExpression(unsigned Opcode, Type *T,
Value *Arg1,
Value *Arg2) const {
auto *E = new (ExpressionAllocator) BasicExpression(2);
E->setType(T);
E->setOpcode(Opcode);
E->allocateOperands(ArgRecycler, ExpressionAllocator);
if (Instruction::isCommutative(Opcode)) {
// Ensure that commutative instructions that only differ by a permutation
// of their operands get the same value number by sorting the operand value
// numbers. Since all commutative instructions have two operands it is more
// efficient to sort by hand rather than using, say, std::sort.
if (shouldSwapOperands(Arg1, Arg2))
std::swap(Arg1, Arg2);
}
E->op_push_back(lookupOperandLeader(Arg1));
E->op_push_back(lookupOperandLeader(Arg2));
Value *V = SimplifyBinOp(Opcode, E->getOperand(0), E->getOperand(1), SQ);
if (const Expression *SimplifiedE = checkSimplificationResults(E, nullptr, V))
return SimplifiedE;
return E;
}
// Take a Value returned by simplification of Expression E/Instruction
// I, and see if it resulted in a simpler expression. If so, return
// that expression.
// TODO: Once finished, this should not take an Instruction, we only
// use it for printing.
const Expression *NewGVN::checkSimplificationResults(Expression *E,
Instruction *I,
Value *V) const {
if (!V)
return nullptr;
if (auto *C = dyn_cast<Constant>(V)) {
if (I)
DEBUG(dbgs() << "Simplified " << *I << " to "
<< " constant " << *C << "\n");
NumGVNOpsSimplified++;
assert(isa<BasicExpression>(E) &&
"We should always have had a basic expression here");
deleteExpression(E);
return createConstantExpression(C);
} else if (isa<Argument>(V) || isa<GlobalVariable>(V)) {
if (I)
DEBUG(dbgs() << "Simplified " << *I << " to "
<< " variable " << *V << "\n");
deleteExpression(E);
return createVariableExpression(V);
}
CongruenceClass *CC = ValueToClass.lookup(V);
if (CC && CC->getDefiningExpr()) {
if (I)
DEBUG(dbgs() << "Simplified " << *I << " to "
<< " expression " << *V << "\n");
NumGVNOpsSimplified++;
deleteExpression(E);
return CC->getDefiningExpr();
}
return nullptr;
}
const Expression *NewGVN::createExpression(Instruction *I) const {
auto *E = new (ExpressionAllocator) BasicExpression(I->getNumOperands());
bool AllConstant = setBasicExpressionInfo(I, E);
if (I->isCommutative()) {
// Ensure that commutative instructions that only differ by a permutation
// of their operands get the same value number by sorting the operand value
// numbers. Since all commutative instructions have two operands it is more
// efficient to sort by hand rather than using, say, std::sort.
assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!");
if (shouldSwapOperands(E->getOperand(0), E->getOperand(1)))
E->swapOperands(0, 1);
}
// Perform simplificaiton
// TODO: Right now we only check to see if we get a constant result.
// We may get a less than constant, but still better, result for
// some operations.
// IE
// add 0, x -> x
// and x, x -> x
// We should handle this by simply rewriting the expression.
if (auto *CI = dyn_cast<CmpInst>(I)) {
// Sort the operand value numbers so x<y and y>x get the same value
// number.
CmpInst::Predicate Predicate = CI->getPredicate();
if (shouldSwapOperands(E->getOperand(0), E->getOperand(1))) {
E->swapOperands(0, 1);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
E->setOpcode((CI->getOpcode() << 8) | Predicate);
// TODO: 25% of our time is spent in SimplifyCmpInst with pointer operands
assert(I->getOperand(0)->getType() == I->getOperand(1)->getType() &&
"Wrong types on cmp instruction");
assert((E->getOperand(0)->getType() == I->getOperand(0)->getType() &&
E->getOperand(1)->getType() == I->getOperand(1)->getType()));
Value *V =
SimplifyCmpInst(Predicate, E->getOperand(0), E->getOperand(1), SQ);
if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
return SimplifiedE;
} else if (isa<SelectInst>(I)) {
if (isa<Constant>(E->getOperand(0)) ||
E->getOperand(0) == E->getOperand(1)) {
assert(E->getOperand(1)->getType() == I->getOperand(1)->getType() &&
E->getOperand(2)->getType() == I->getOperand(2)->getType());
Value *V = SimplifySelectInst(E->getOperand(0), E->getOperand(1),
E->getOperand(2), SQ);
if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
return SimplifiedE;
}
} else if (I->isBinaryOp()) {
Value *V =
SimplifyBinOp(E->getOpcode(), E->getOperand(0), E->getOperand(1), SQ);
if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
return SimplifiedE;
} else if (auto *BI = dyn_cast<BitCastInst>(I)) {
Value *V =
SimplifyCastInst(BI->getOpcode(), BI->getOperand(0), BI->getType(), SQ);
if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
return SimplifiedE;
} else if (isa<GetElementPtrInst>(I)) {
Value *V = SimplifyGEPInst(
E->getType(), ArrayRef<Value *>(E->op_begin(), E->op_end()), SQ);
if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
return SimplifiedE;
} else if (AllConstant) {
// We don't bother trying to simplify unless all of the operands
// were constant.
// TODO: There are a lot of Simplify*'s we could call here, if we
// wanted to. The original motivating case for this code was a
// zext i1 false to i8, which we don't have an interface to
// simplify (IE there is no SimplifyZExt).
SmallVector<Constant *, 8> C;
for (Value *Arg : E->operands())
C.emplace_back(cast<Constant>(Arg));
if (Value *V = ConstantFoldInstOperands(I, C, DL, TLI))
if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
return SimplifiedE;
}
return E;
}
const AggregateValueExpression *
NewGVN::createAggregateValueExpression(Instruction *I) const {
if (auto *II = dyn_cast<InsertValueInst>(I)) {
auto *E = new (ExpressionAllocator)
AggregateValueExpression(I->getNumOperands(), II->getNumIndices());
setBasicExpressionInfo(I, E);
E->allocateIntOperands(ExpressionAllocator);
std::copy(II->idx_begin(), II->idx_end(), int_op_inserter(E));
return E;
} else if (auto *EI = dyn_cast<ExtractValueInst>(I)) {
auto *E = new (ExpressionAllocator)
AggregateValueExpression(I->getNumOperands(), EI->getNumIndices());
setBasicExpressionInfo(EI, E);
E->allocateIntOperands(ExpressionAllocator);
std::copy(EI->idx_begin(), EI->idx_end(), int_op_inserter(E));
return E;
}
llvm_unreachable("Unhandled type of aggregate value operation");
}
const VariableExpression *NewGVN::createVariableExpression(Value *V) const {
auto *E = new (ExpressionAllocator) VariableExpression(V);
E->setOpcode(V->getValueID());
return E;
}
const Expression *NewGVN::createVariableOrConstant(Value *V) const {
if (auto *C = dyn_cast<Constant>(V))
return createConstantExpression(C);
return createVariableExpression(V);
}
const ConstantExpression *NewGVN::createConstantExpression(Constant *C) const {
auto *E = new (ExpressionAllocator) ConstantExpression(C);
E->setOpcode(C->getValueID());
return E;
}
const UnknownExpression *NewGVN::createUnknownExpression(Instruction *I) const {
auto *E = new (ExpressionAllocator) UnknownExpression(I);
E->setOpcode(I->getOpcode());
return E;
}
const CallExpression *
NewGVN::createCallExpression(CallInst *CI, const MemoryAccess *MA) const {
// FIXME: Add operand bundles for calls.
auto *E =
new (ExpressionAllocator) CallExpression(CI->getNumOperands(), CI, MA);
setBasicExpressionInfo(CI, E);
return E;
}
// Return true if some equivalent of instruction Inst dominates instruction U.
bool NewGVN::someEquivalentDominates(const Instruction *Inst,
const Instruction *U) const {
auto *CC = ValueToClass.lookup(Inst);
// This must be an instruction because we are only called from phi nodes
// in the case that the value it needs to check against is an instruction.
// The most likely candiates for dominance are the leader and the next leader.
// The leader or nextleader will dominate in all cases where there is an
// equivalent that is higher up in the dom tree.
// We can't *only* check them, however, because the
// dominator tree could have an infinite number of non-dominating siblings
// with instructions that are in the right congruence class.
// A
// B C D E F G
// |
// H
// Instruction U could be in H, with equivalents in every other sibling.
// Depending on the rpo order picked, the leader could be the equivalent in
// any of these siblings.
if (!CC)
return false;
if (DT->dominates(cast<Instruction>(CC->getLeader()), U))
return true;
if (CC->getNextLeader().first &&
DT->dominates(cast<Instruction>(CC->getNextLeader().first), U))
return true;
return llvm::any_of(*CC, [&](const Value *Member) {
return Member != CC->getLeader() &&
DT->dominates(cast<Instruction>(Member), U);
});
}
// See if we have a congruence class and leader for this operand, and if so,
// return it. Otherwise, return the operand itself.
Value *NewGVN::lookupOperandLeader(Value *V) const {
CongruenceClass *CC = ValueToClass.lookup(V);
if (CC) {
// Everything in TOP is represneted by undef, as it can be any value.
// We do have to make sure we get the type right though, so we can't set the
// RepLeader to undef.
if (CC == TOPClass)
return UndefValue::get(V->getType());
return CC->getStoredValue() ? CC->getStoredValue() : CC->getLeader();
}
return V;
}
const MemoryAccess *NewGVN::lookupMemoryLeader(const MemoryAccess *MA) const {
auto *CC = getMemoryClass(MA);
assert(CC->getMemoryLeader() &&
"Every MemoryAccess should be mapped to a congruence class with a "
"representative memory access");
return CC->getMemoryLeader();
}
// Return true if the MemoryAccess is really equivalent to everything. This is
// equivalent to the lattice value "TOP" in most lattices. This is the initial
// state of all MemoryAccesses.
bool NewGVN::isMemoryAccessTop(const MemoryAccess *MA) const {
return getMemoryClass(MA) == TOPClass;
}
LoadExpression *NewGVN::createLoadExpression(Type *LoadType, Value *PointerOp,
LoadInst *LI,
const MemoryAccess *MA) const {
auto *E =
new (ExpressionAllocator) LoadExpression(1, LI, lookupMemoryLeader(MA));
E->allocateOperands(ArgRecycler, ExpressionAllocator);
E->setType(LoadType);
// Give store and loads same opcode so they value number together.
E->setOpcode(0);
E->op_push_back(PointerOp);
if (LI)
E->setAlignment(LI->getAlignment());
// TODO: Value number heap versions. We may be able to discover
// things alias analysis can't on it's own (IE that a store and a
// load have the same value, and thus, it isn't clobbering the load).
return E;
}
const StoreExpression *
NewGVN::createStoreExpression(StoreInst *SI, const MemoryAccess *MA) const {
auto *StoredValueLeader = lookupOperandLeader(SI->getValueOperand());
auto *E = new (ExpressionAllocator)
StoreExpression(SI->getNumOperands(), SI, StoredValueLeader, MA);
E->allocateOperands(ArgRecycler, ExpressionAllocator);
E->setType(SI->getValueOperand()->getType());
// Give store and loads same opcode so they value number together.
E->setOpcode(0);
E->op_push_back(lookupOperandLeader(SI->getPointerOperand()));
// TODO: Value number heap versions. We may be able to discover
// things alias analysis can't on it's own (IE that a store and a
// load have the same value, and thus, it isn't clobbering the load).
return E;
}
const Expression *NewGVN::performSymbolicStoreEvaluation(Instruction *I) const {
// Unlike loads, we never try to eliminate stores, so we do not check if they
// are simple and avoid value numbering them.
auto *SI = cast<StoreInst>(I);
auto *StoreAccess = MSSA->getMemoryAccess(SI);
// Get the expression, if any, for the RHS of the MemoryDef.
const MemoryAccess *StoreRHS = StoreAccess->getDefiningAccess();
if (EnableStoreRefinement)
StoreRHS = MSSAWalker->getClobberingMemoryAccess(StoreAccess);
// If we bypassed the use-def chains, make sure we add a use.
if (StoreRHS != StoreAccess->getDefiningAccess())
addMemoryUsers(StoreRHS, StoreAccess);
StoreRHS = lookupMemoryLeader(StoreRHS);
// If we are defined by ourselves, use the live on entry def.
if (StoreRHS == StoreAccess)
StoreRHS = MSSA->getLiveOnEntryDef();
if (SI->isSimple()) {
// See if we are defined by a previous store expression, it already has a
// value, and it's the same value as our current store. FIXME: Right now, we
// only do this for simple stores, we should expand to cover memcpys, etc.
const auto *LastStore = createStoreExpression(SI, StoreRHS);
const auto *LastCC = ExpressionToClass.lookup(LastStore);
// Basically, check if the congruence class the store is in is defined by a
// store that isn't us, and has the same value. MemorySSA takes care of
// ensuring the store has the same memory state as us already.
// The RepStoredValue gets nulled if all the stores disappear in a class, so
// we don't need to check if the class contains a store besides us.
if (LastCC &&
LastCC->getStoredValue() == lookupOperandLeader(SI->getValueOperand()))
return LastStore;
deleteExpression(LastStore);
// Also check if our value operand is defined by a load of the same memory
// location, and the memory state is the same as it was then (otherwise, it
// could have been overwritten later. See test32 in
// transforms/DeadStoreElimination/simple.ll).
if (auto *LI =
dyn_cast<LoadInst>(lookupOperandLeader(SI->getValueOperand()))) {
if ((lookupOperandLeader(LI->getPointerOperand()) ==
lookupOperandLeader(SI->getPointerOperand())) &&
(lookupMemoryLeader(MSSA->getMemoryAccess(LI)->getDefiningAccess()) ==
StoreRHS))
return createVariableExpression(LI);
}
}
// If the store is not equivalent to anything, value number it as a store that
// produces a unique memory state (instead of using it's MemoryUse, we use
// it's MemoryDef).
return createStoreExpression(SI, StoreAccess);
}
// See if we can extract the value of a loaded pointer from a load, a store, or
// a memory instruction.
const Expression *
NewGVN::performSymbolicLoadCoercion(Type *LoadType, Value *LoadPtr,
LoadInst *LI, Instruction *DepInst,
MemoryAccess *DefiningAccess) const {
assert((!LI || LI->isSimple()) && "Not a simple load");
if (auto *DepSI = dyn_cast<StoreInst>(DepInst)) {
// Can't forward from non-atomic to atomic without violating memory model.
// Also don't need to coerce if they are the same type, we will just
// propogate..
if (LI->isAtomic() > DepSI->isAtomic() ||
LoadType == DepSI->getValueOperand()->getType())
return nullptr;
int Offset = analyzeLoadFromClobberingStore(LoadType, LoadPtr, DepSI, DL);
if (Offset >= 0) {
if (auto *C = dyn_cast<Constant>(
lookupOperandLeader(DepSI->getValueOperand()))) {
DEBUG(dbgs() << "Coercing load from store " << *DepSI << " to constant "
<< *C << "\n");
return createConstantExpression(
getConstantStoreValueForLoad(C, Offset, LoadType, DL));
}
}
} else if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
// Can't forward from non-atomic to atomic without violating memory model.
if (LI->isAtomic() > DepLI->isAtomic())
return nullptr;
int Offset = analyzeLoadFromClobberingLoad(LoadType, LoadPtr, DepLI, DL);
if (Offset >= 0) {
// We can coerce a constant load into a load
if (auto *C = dyn_cast<Constant>(lookupOperandLeader(DepLI)))
if (auto *PossibleConstant =
getConstantLoadValueForLoad(C, Offset, LoadType, DL)) {
DEBUG(dbgs() << "Coercing load from load " << *LI << " to constant "
<< *PossibleConstant << "\n");
return createConstantExpression(PossibleConstant);
}
}
} else if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInst)) {
int Offset = analyzeLoadFromClobberingMemInst(LoadType, LoadPtr, DepMI, DL);
if (Offset >= 0) {
if (auto *PossibleConstant =
getConstantMemInstValueForLoad(DepMI, Offset, LoadType, DL)) {
DEBUG(dbgs() << "Coercing load from meminst " << *DepMI
<< " to constant " << *PossibleConstant << "\n");
return createConstantExpression(PossibleConstant);
}
}
}
// All of the below are only true if the loaded pointer is produced
// by the dependent instruction.
if (LoadPtr != lookupOperandLeader(DepInst) &&
!AA->isMustAlias(LoadPtr, DepInst))
return nullptr;
// If this load really doesn't depend on anything, then we must be loading an
// undef value. This can happen when loading for a fresh allocation with no
// intervening stores, for example. Note that this is only true in the case
// that the result of the allocation is pointer equal to the load ptr.
if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) {
return createConstantExpression(UndefValue::get(LoadType));
}
// If this load occurs either right after a lifetime begin,
// then the loaded value is undefined.
else if (auto *II = dyn_cast<IntrinsicInst>(DepInst)) {
if (II->getIntrinsicID() == Intrinsic::lifetime_start)
return createConstantExpression(UndefValue::get(LoadType));
}
// If this load follows a calloc (which zero initializes memory),
// then the loaded value is zero
else if (isCallocLikeFn(DepInst, TLI)) {
return createConstantExpression(Constant::getNullValue(LoadType));
}
return nullptr;
}
const Expression *NewGVN::performSymbolicLoadEvaluation(Instruction *I) const {
auto *LI = cast<LoadInst>(I);
// We can eliminate in favor of non-simple loads, but we won't be able to
// eliminate the loads themselves.
if (!LI->isSimple())
return nullptr;
Value *LoadAddressLeader = lookupOperandLeader(LI->getPointerOperand());
// Load of undef is undef.
if (isa<UndefValue>(LoadAddressLeader))
return createConstantExpression(UndefValue::get(LI->getType()));
MemoryAccess *DefiningAccess = MSSAWalker->getClobberingMemoryAccess(I);
if (!MSSA->isLiveOnEntryDef(DefiningAccess)) {
if (auto *MD = dyn_cast<MemoryDef>(DefiningAccess)) {
Instruction *DefiningInst = MD->getMemoryInst();
// If the defining instruction is not reachable, replace with undef.
if (!ReachableBlocks.count(DefiningInst->getParent()))
return createConstantExpression(UndefValue::get(LI->getType()));
// This will handle stores and memory insts. We only do if it the
// defining access has a different type, or it is a pointer produced by
// certain memory operations that cause the memory to have a fixed value
// (IE things like calloc).
if (const auto *CoercionResult =
performSymbolicLoadCoercion(LI->getType(), LoadAddressLeader, LI,
DefiningInst, DefiningAccess))
return CoercionResult;
}
}
const Expression *E = createLoadExpression(LI->getType(), LoadAddressLeader,
LI, DefiningAccess);
return E;
}
const Expression *
NewGVN::performSymbolicPredicateInfoEvaluation(Instruction *I) const {
auto *PI = PredInfo->getPredicateInfoFor(I);
if (!PI)
return nullptr;
DEBUG(dbgs() << "Found predicate info from instruction !\n");
auto *PWC = dyn_cast<PredicateWithCondition>(PI);
if (!PWC)
return nullptr;
auto *CopyOf = I->getOperand(0);
auto *Cond = PWC->Condition;
// If this a copy of the condition, it must be either true or false depending
// on the predicate info type and edge
if (CopyOf == Cond) {
// We should not need to add predicate users because the predicate info is
// already a use of this operand.
if (isa<PredicateAssume>(PI))
return createConstantExpression(ConstantInt::getTrue(Cond->getType()));
if (auto *PBranch = dyn_cast<PredicateBranch>(PI)) {
if (PBranch->TrueEdge)
return createConstantExpression(ConstantInt::getTrue(Cond->getType()));
return createConstantExpression(ConstantInt::getFalse(Cond->getType()));
}
if (auto *PSwitch = dyn_cast<PredicateSwitch>(PI))
return createConstantExpression(cast<Constant>(PSwitch->CaseValue));
}
// Not a copy of the condition, so see what the predicates tell us about this
// value. First, though, we check to make sure the value is actually a copy
// of one of the condition operands. It's possible, in certain cases, for it
// to be a copy of a predicateinfo copy. In particular, if two branch
// operations use the same condition, and one branch dominates the other, we
// will end up with a copy of a copy. This is currently a small deficiency in
// predicateinfo. What will end up happening here is that we will value
// number both copies the same anyway.
// Everything below relies on the condition being a comparison.
auto *Cmp = dyn_cast<CmpInst>(Cond);
if (!Cmp)
return nullptr;
if (CopyOf != Cmp->getOperand(0) && CopyOf != Cmp->getOperand(1)) {
DEBUG(dbgs() << "Copy is not of any condition operands!\n");
return nullptr;
}
Value *FirstOp = lookupOperandLeader(Cmp->getOperand(0));
Value *SecondOp = lookupOperandLeader(Cmp->getOperand(1));
bool SwappedOps = false;
// Sort the ops
if (shouldSwapOperands(FirstOp, SecondOp)) {
std::swap(FirstOp, SecondOp);
SwappedOps = true;
}
CmpInst::Predicate Predicate =
SwappedOps ? Cmp->getSwappedPredicate() : Cmp->getPredicate();
if (isa<PredicateAssume>(PI)) {
// If the comparison is true when the operands are equal, then we know the
// operands are equal, because assumes must always be true.
if (CmpInst::isTrueWhenEqual(Predicate)) {
addPredicateUsers(PI, I);
return createVariableOrConstant(FirstOp);
}
}
if (const auto *PBranch = dyn_cast<PredicateBranch>(PI)) {
// If we are *not* a copy of the comparison, we may equal to the other
// operand when the predicate implies something about equality of
// operations. In particular, if the comparison is true/false when the
// operands are equal, and we are on the right edge, we know this operation
// is equal to something.
if ((PBranch->TrueEdge && Predicate == CmpInst::ICMP_EQ) ||
(!PBranch->TrueEdge && Predicate == CmpInst::ICMP_NE)) {
addPredicateUsers(PI, I);
return createVariableOrConstant(FirstOp);
}
// Handle the special case of floating point.
if (((PBranch->TrueEdge && Predicate == CmpInst::FCMP_OEQ) ||
(!PBranch->TrueEdge && Predicate == CmpInst::FCMP_UNE)) &&
isa<ConstantFP>(FirstOp) && !cast<ConstantFP>(FirstOp)->isZero()) {
addPredicateUsers(PI, I);
return createConstantExpression(cast<Constant>(FirstOp));
}
}
return nullptr;
}
// Evaluate read only and pure calls, and create an expression result.
const Expression *NewGVN::performSymbolicCallEvaluation(Instruction *I) const {
auto *CI = cast<CallInst>(I);
if (auto *II = dyn_cast<IntrinsicInst>(I)) {
// Instrinsics with the returned attribute are copies of arguments.
if (auto *ReturnedValue = II->getReturnedArgOperand()) {
if (II->getIntrinsicID() == Intrinsic::ssa_copy)
if (const auto *Result = performSymbolicPredicateInfoEvaluation(I))
return Result;
return createVariableOrConstant(ReturnedValue);
}
}
if (AA->doesNotAccessMemory(CI)) {
return createCallExpression(CI, TOPClass->getMemoryLeader());
} else if (AA->onlyReadsMemory(CI)) {
MemoryAccess *DefiningAccess = MSSAWalker->getClobberingMemoryAccess(CI);
return createCallExpression(CI, DefiningAccess);
}
return nullptr;
}
// Retrieve the memory class for a given MemoryAccess.
CongruenceClass *NewGVN::getMemoryClass(const MemoryAccess *MA) const {
auto *Result = MemoryAccessToClass.lookup(MA);
assert(Result && "Should have found memory class");
return Result;
}
// Update the MemoryAccess equivalence table to say that From is equal to To,
// and return true if this is different from what already existed in the table.
bool NewGVN::setMemoryClass(const MemoryAccess *From,
CongruenceClass *NewClass) {
assert(NewClass &&
"Every MemoryAccess should be getting mapped to a non-null class");
DEBUG(dbgs() << "Setting " << *From);
DEBUG(dbgs() << " equivalent to congruence class ");
DEBUG(dbgs() << NewClass->getID() << " with current MemoryAccess leader ");
DEBUG(dbgs() << *NewClass->getMemoryLeader() << "\n");
auto LookupResult = MemoryAccessToClass.find(From);
bool Changed = false;
// If it's already in the table, see if the value changed.
if (LookupResult != MemoryAccessToClass.end()) {
auto *OldClass = LookupResult->second;
if (OldClass != NewClass) {
// If this is a phi, we have to handle memory member updates.
if (auto *MP = dyn_cast<MemoryPhi>(From)) {
OldClass->memory_erase(MP);
NewClass->memory_insert(MP);
// This may have killed the class if it had no non-memory members
if (OldClass->getMemoryLeader() == From) {
if (OldClass->definesNoMemory()) {
OldClass->setMemoryLeader(nullptr);
} else {
OldClass->setMemoryLeader(getNextMemoryLeader(OldClass));
DEBUG(dbgs() << "Memory class leader change for class "
<< OldClass->getID() << " to "
<< *OldClass->getMemoryLeader()
<< " due to removal of a memory member " << *From
<< "\n");
markMemoryLeaderChangeTouched(OldClass);
}
}
}
// It wasn't equivalent before, and now it is.
LookupResult->second = NewClass;
Changed = true;
}
}
return Changed;
}
// Determine if a phi is cycle-free. That means the values in the phi don't
// depend on any expressions that can change value as a result of the phi.
// For example, a non-cycle free phi would be v = phi(0, v+1).
bool NewGVN::isCycleFree(const PHINode *PN) const {
// In order to compute cycle-freeness, we do SCC finding on the phi, and see
// what kind of SCC it ends up in. If it is a singleton, it is cycle-free.
// If it is not in a singleton, it is only cycle free if the other members are
// all phi nodes (as they do not compute anything, they are copies). TODO:
// There are likely a few other intrinsics or expressions that could be
// included here, but this happens so infrequently already that it is not
// likely to be worth it.
auto PCS = PhiCycleState.lookup(PN);
if (PCS == PCS_Unknown) {
SCCFinder.Start(PN);
auto &SCC = SCCFinder.getComponentFor(PN);
// It's cycle free if it's size 1 or or the SCC is *only* phi nodes.
if (SCC.size() == 1)
PhiCycleState.insert({PN, PCS_CycleFree});
else {
bool AllPhis =
llvm::all_of(SCC, [](const Value *V) { return isa<PHINode>(V); });
PCS = AllPhis ? PCS_CycleFree : PCS_Cycle;
for (auto *Member : SCC)
if (auto *MemberPhi = dyn_cast<PHINode>(Member))
PhiCycleState.insert({MemberPhi, PCS});
}
}
if (PCS == PCS_Cycle)
return false;
return true;
}
// Evaluate PHI nodes symbolically, and create an expression result.
const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
// True if one of the incoming phi edges is a backedge.
bool HasBackedge = false;
// All constant tracks the state of whether all the *original* phi operands
// were constant. This is really shorthand for "this phi cannot cycle due
// to forward propagation", as any change in value of the phi is guaranteed
// not to later change the value of the phi.
// IE it can't be v = phi(undef, v+1)
bool AllConstant = true;
auto *E =
cast<PHIExpression>(createPHIExpression(I, HasBackedge, AllConstant));
// We match the semantics of SimplifyPhiNode from InstructionSimplify here.
// See if all arguments are the same.
// We track if any were undef because they need special handling.
bool HasUndef = false;
auto Filtered = make_filter_range(E->operands(), [&](const Value *Arg) {
if (Arg == I)
return false;
if (isa<UndefValue>(Arg)) {
HasUndef = true;
return false;
}
return true;
});
// If we are left with no operands, it's undef
if (Filtered.begin() == Filtered.end()) {
DEBUG(dbgs() << "Simplified PHI node " << *I << " to undef"
<< "\n");
deleteExpression(E);
return createConstantExpression(UndefValue::get(I->getType()));
}
unsigned NumOps = 0;
Value *AllSameValue = *(Filtered.begin());
++Filtered.begin();
// Can't use std::equal here, sadly, because filter.begin moves.
if (llvm::all_of(Filtered, [AllSameValue, &NumOps](const Value *V) {
++NumOps;
return V == AllSameValue;
})) {
// In LLVM's non-standard representation of phi nodes, it's possible to have
// phi nodes with cycles (IE dependent on other phis that are .... dependent
// on the original phi node), especially in weird CFG's where some arguments
// are unreachable, or uninitialized along certain paths. This can cause
// infinite loops during evaluation. We work around this by not trying to
// really evaluate them independently, but instead using a variable
// expression to say if one is equivalent to the other.
// We also special case undef, so that if we have an undef, we can't use the
// common value unless it dominates the phi block.
if (HasUndef) {
// If we have undef and at least one other value, this is really a
// multivalued phi, and we need to know if it's cycle free in order to
// evaluate whether we can ignore the undef. The other parts of this are
// just shortcuts. If there is no backedge, or all operands are
// constants, or all operands are ignored but the undef, it also must be
// cycle free.
if (!AllConstant && HasBackedge && NumOps > 0 &&
!isa<UndefValue>(AllSameValue) && !isCycleFree(cast<PHINode>(I)))
return E;
// Only have to check for instructions
if (auto *AllSameInst = dyn_cast<Instruction>(AllSameValue))
if (!someEquivalentDominates(AllSameInst, I))
return E;
}
NumGVNPhisAllSame++;
DEBUG(dbgs() << "Simplified PHI node " << *I << " to " << *AllSameValue
<< "\n");
deleteExpression(E);
return createVariableOrConstant(AllSameValue);
}
return E;
}
const Expression *
NewGVN::performSymbolicAggrValueEvaluation(Instruction *I) const {
if (auto *EI = dyn_cast<ExtractValueInst>(I)) {
auto *II = dyn_cast<IntrinsicInst>(EI->getAggregateOperand());
if (II && EI->getNumIndices() == 1 && *EI->idx_begin() == 0) {
unsigned Opcode = 0;
// EI might be an extract from one of our recognised intrinsics. If it
// is we'll synthesize a semantically equivalent expression instead on
// an extract value expression.
switch (II->getIntrinsicID()) {
case Intrinsic::sadd_with_overflow:
case Intrinsic::uadd_with_overflow:
Opcode = Instruction::Add;
break;
case Intrinsic::ssub_with_overflow:
case Intrinsic::usub_with_overflow:
Opcode = Instruction::Sub;
break;
case Intrinsic::smul_with_overflow:
case Intrinsic::umul_with_overflow:
Opcode = Instruction::Mul;
break;
default:
break;
}
if (Opcode != 0) {
// Intrinsic recognized. Grab its args to finish building the
// expression.
assert(II->getNumArgOperands() == 2 &&
"Expect two args for recognised intrinsics.");
return createBinaryExpression(
Opcode, EI->getType(), II->getArgOperand(0), II->getArgOperand(1));
}
}
}
return createAggregateValueExpression(I);
}
const Expression *NewGVN::performSymbolicCmpEvaluation(Instruction *I) const {
auto *CI = dyn_cast<CmpInst>(I);
// See if our operands are equal to those of a previous predicate, and if so,
// if it implies true or false.
auto Op0 = lookupOperandLeader(CI->getOperand(0));
auto Op1 = lookupOperandLeader(CI->getOperand(1));
auto OurPredicate = CI->getPredicate();
if (shouldSwapOperands(Op0, Op1)) {
std::swap(Op0, Op1);
OurPredicate = CI->getSwappedPredicate();
}
// Avoid processing the same info twice
const PredicateBase *LastPredInfo = nullptr;
// See if we know something about the comparison itself, like it is the target
// of an assume.
auto *CmpPI = PredInfo->getPredicateInfoFor(I);
if (dyn_cast_or_null<PredicateAssume>(CmpPI))
return createConstantExpression(ConstantInt::getTrue(CI->getType()));
if (Op0 == Op1) {
// This condition does not depend on predicates, no need to add users
if (CI->isTrueWhenEqual())
return createConstantExpression(ConstantInt::getTrue(CI->getType()));
else if (CI->isFalseWhenEqual())
return createConstantExpression(ConstantInt::getFalse(CI->getType()));
}
// NOTE: Because we are comparing both operands here and below, and using
// previous comparisons, we rely on fact that predicateinfo knows to mark
// comparisons that use renamed operands as users of the earlier comparisons.
// It is *not* enough to just mark predicateinfo renamed operands as users of
// the earlier comparisons, because the *other* operand may have changed in a
// previous iteration.
// Example:
// icmp slt %a, %b
// %b.0 = ssa.copy(%b)
// false branch:
// icmp slt %c, %b.0
// %c and %a may start out equal, and thus, the code below will say the second
// %icmp is false. c may become equal to something else, and in that case the
// %second icmp *must* be reexamined, but would not if only the renamed
// %operands are considered users of the icmp.
// *Currently* we only check one level of comparisons back, and only mark one
// level back as touched when changes appen . If you modify this code to look
// back farther through comparisons, you *must* mark the appropriate
// comparisons as users in PredicateInfo.cpp, or you will cause bugs. See if
// we know something just from the operands themselves
// See if our operands have predicate info, so that we may be able to derive
// something from a previous comparison.
for (const auto &Op : CI->operands()) {
auto *PI = PredInfo->getPredicateInfoFor(Op);
if (const auto *PBranch = dyn_cast_or_null<PredicateBranch>(PI)) {
if (PI == LastPredInfo)
continue;
LastPredInfo = PI;
// TODO: Along the false edge, we may know more things too, like icmp of
// same operands is false.
// TODO: We only handle actual comparison conditions below, not and/or.
auto *BranchCond = dyn_cast<CmpInst>(PBranch->Condition);
if (!BranchCond)
continue;
auto *BranchOp0 = lookupOperandLeader(BranchCond->getOperand(0));
auto *BranchOp1 = lookupOperandLeader(BranchCond->getOperand(1));
auto BranchPredicate = BranchCond->getPredicate();
if (shouldSwapOperands(BranchOp0, BranchOp1)) {
std::swap(BranchOp0, BranchOp1);
BranchPredicate = BranchCond->getSwappedPredicate();
}
if (BranchOp0 == Op0 && BranchOp1 == Op1) {
if (PBranch->TrueEdge) {
// If we know the previous predicate is true and we are in the true
// edge then we may be implied true or false.
if (CmpInst::isImpliedTrueByMatchingCmp(BranchPredicate,
OurPredicate)) {
addPredicateUsers(PI, I);
return createConstantExpression(
ConstantInt::getTrue(CI->getType()));
}
if (CmpInst::isImpliedFalseByMatchingCmp(BranchPredicate,
OurPredicate)) {
addPredicateUsers(PI, I);
return createConstantExpression(
ConstantInt::getFalse(CI->getType()));
}
} else {
// Just handle the ne and eq cases, where if we have the same
// operands, we may know something.
if (BranchPredicate == OurPredicate) {
addPredicateUsers(PI, I);
// Same predicate, same ops,we know it was false, so this is false.
return createConstantExpression(
ConstantInt::getFalse(CI->getType()));
} else if (BranchPredicate ==
CmpInst::getInversePredicate(OurPredicate)) {
addPredicateUsers(PI, I);
// Inverse predicate, we know the other was false, so this is true.
return createConstantExpression(
ConstantInt::getTrue(CI->getType()));
}
}
}
}
}
// Create expression will take care of simplifyCmpInst
return createExpression(I);
}
// Substitute and symbolize the value before value numbering.
const Expression *NewGVN::performSymbolicEvaluation(Value *V) const {
const Expression *E = nullptr;
if (auto *C = dyn_cast<Constant>(V))
E = createConstantExpression(C);
else if (isa<Argument>(V) || isa<GlobalVariable>(V)) {
E = createVariableExpression(V);
} else {
// TODO: memory intrinsics.
// TODO: Some day, we should do the forward propagation and reassociation
// parts of the algorithm.
auto *I = cast<Instruction>(V);
switch (I->getOpcode()) {
case Instruction::ExtractValue:
case Instruction::InsertValue:
E = performSymbolicAggrValueEvaluation(I);
break;
case Instruction::PHI:
E = performSymbolicPHIEvaluation(I);
break;
case Instruction::Call:
E = performSymbolicCallEvaluation(I);
break;
case Instruction::Store:
E = performSymbolicStoreEvaluation(I);
break;
case Instruction::Load:
E = performSymbolicLoadEvaluation(I);
break;
case Instruction::BitCast: {
E = createExpression(I);
} break;
case Instruction::ICmp:
case Instruction::FCmp: {
E = performSymbolicCmpEvaluation(I);
} break;
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::PtrToInt:
case Instruction::IntToPtr:
case Instruction::Select:
case Instruction::ExtractElement:
case Instruction::InsertElement:
case Instruction::ShuffleVector:
case Instruction::GetElementPtr:
E = createExpression(I);
break;
default:
return nullptr;
}
}
return E;
}
void NewGVN::markUsersTouched(Value *V) {
// Now mark the users as touched.
for (auto *User : V->users()) {
assert(isa<Instruction>(User) && "Use of value not within an instruction?");
TouchedInstructions.set(InstrToDFSNum(User));
}
}
void NewGVN::addMemoryUsers(const MemoryAccess *To, MemoryAccess *U) const {
DEBUG(dbgs() << "Adding memory user " << *U << " to " << *To << "\n");
MemoryToUsers[To].insert(U);
}
void NewGVN::markMemoryDefTouched(const MemoryAccess *MA) {
TouchedInstructions.set(MemoryToDFSNum(MA));
}
void NewGVN::markMemoryUsersTouched(const MemoryAccess *MA) {
if (isa<MemoryUse>(MA))
return;
for (auto U : MA->users())
TouchedInstructions.set(MemoryToDFSNum(U));
const auto Result = MemoryToUsers.find(MA);
if (Result != MemoryToUsers.end()) {
for (auto *User : Result->second)
TouchedInstructions.set(MemoryToDFSNum(User));
MemoryToUsers.erase(Result);
}
}
// Add I to the set of users of a given predicate.
void NewGVN::addPredicateUsers(const PredicateBase *PB, Instruction *I) const {
if (auto *PBranch = dyn_cast<PredicateBranch>(PB))
PredicateToUsers[PBranch->Condition].insert(I);
else if (auto *PAssume = dyn_cast<PredicateBranch>(PB))
PredicateToUsers[PAssume->Condition].insert(I);
}
// Touch all the predicates that depend on this instruction.
void NewGVN::markPredicateUsersTouched(Instruction *I) {
const auto Result = PredicateToUsers.find(I);
if (Result != PredicateToUsers.end()) {
for (auto *User : Result->second)
TouchedInstructions.set(InstrToDFSNum(User));
PredicateToUsers.erase(Result);
}
}
// Mark users affected by a memory leader change.
void NewGVN::markMemoryLeaderChangeTouched(CongruenceClass *CC) {
for (auto M : CC->memory())
markMemoryDefTouched(M);
}
// Touch the instructions that need to be updated after a congruence class has a
// leader change, and mark changed values.
void NewGVN::markValueLeaderChangeTouched(CongruenceClass *CC) {
for (auto M : *CC) {
if (auto *I = dyn_cast<Instruction>(M))
TouchedInstructions.set(InstrToDFSNum(I));
LeaderChanges.insert(M);
}
}
// Give a range of things that have instruction DFS numbers, this will return
// the member of the range with the smallest dfs number.
template <class T, class Range>
T *NewGVN::getMinDFSOfRange(const Range &R) const {
std::pair<T *, unsigned> MinDFS = {nullptr, ~0U};
for (const auto X : R) {
auto DFSNum = InstrToDFSNum(X);
if (DFSNum < MinDFS.second)
MinDFS = {X, DFSNum};
}
return MinDFS.first;
}
// This function returns the MemoryAccess that should be the next leader of
// congruence class CC, under the assumption that the current leader is going to
// disappear.
const MemoryAccess *NewGVN::getNextMemoryLeader(CongruenceClass *CC) const {
// TODO: If this ends up to slow, we can maintain a next memory leader like we
// do for regular leaders.
// Make sure there will be a leader to find
assert(!CC->definesNoMemory() && "Can't get next leader if there is none");
if (CC->getStoreCount() > 0) {
if (auto *NL = dyn_cast_or_null<StoreInst>(CC->getNextLeader().first))
return MSSA->getMemoryAccess(NL);
// Find the store with the minimum DFS number.
auto *V = getMinDFSOfRange<Value>(make_filter_range(
*CC, [&](const Value *V) { return isa<StoreInst>(V); }));
return MSSA->getMemoryAccess(cast<StoreInst>(V));
}
assert(CC->getStoreCount() == 0);
// Given our assertion, hitting this part must mean
// !OldClass->memory_empty()
if (CC->memory_size() == 1)
return *CC->memory_begin();
return getMinDFSOfRange<const MemoryPhi>(CC->memory());
}
// This function returns the next value leader of a congruence class, under the
// assumption that the current leader is going away. This should end up being
// the next most dominating member.
Value *NewGVN::getNextValueLeader(CongruenceClass *CC) const {
// We don't need to sort members if there is only 1, and we don't care about
// sorting the TOP class because everything either gets out of it or is
// unreachable.
if (CC->size() == 1 || CC == TOPClass) {
return *(CC->begin());
} else if (CC->getNextLeader().first) {
++NumGVNAvoidedSortedLeaderChanges;
return CC->getNextLeader().first;
} else {
++NumGVNSortedLeaderChanges;
// NOTE: If this ends up to slow, we can maintain a dual structure for
// member testing/insertion, or keep things mostly sorted, and sort only
// here, or use SparseBitVector or ....
return getMinDFSOfRange<Value>(*CC);
}
}
// Move a MemoryAccess, currently in OldClass, to NewClass, including updates to
// the memory members, etc for the move.
//
// The invariants of this function are:
//
// I must be moving to NewClass from OldClass The StoreCount of OldClass and
// NewClass is expected to have been updated for I already if it is is a store.
// The OldClass memory leader has not been updated yet if I was the leader.
void NewGVN::moveMemoryToNewCongruenceClass(Instruction *I,
MemoryAccess *InstMA,
CongruenceClass *OldClass,
CongruenceClass *NewClass) {
// If the leader is I, and we had a represenative MemoryAccess, it should
// be the MemoryAccess of OldClass.
assert((!InstMA || !OldClass->getMemoryLeader() ||
OldClass->getLeader() != I ||
OldClass->getMemoryLeader() == InstMA) &&
"Representative MemoryAccess mismatch");
// First, see what happens to the new class
if (!NewClass->getMemoryLeader()) {
// Should be a new class, or a store becoming a leader of a new class.
assert(NewClass->size() == 1 ||
(isa<StoreInst>(I) && NewClass->getStoreCount() == 1));
NewClass->setMemoryLeader(InstMA);
// Mark it touched if we didn't just create a singleton
DEBUG(dbgs() << "Memory class leader change for class " << NewClass->getID()
<< " due to new memory instruction becoming leader\n");
markMemoryLeaderChangeTouched(NewClass);
}
setMemoryClass(InstMA, NewClass);
// Now, fixup the old class if necessary
if (OldClass->getMemoryLeader() == InstMA) {
if (!OldClass->definesNoMemory()) {
OldClass->setMemoryLeader(getNextMemoryLeader(OldClass));
DEBUG(dbgs() << "Memory class leader change for class "
<< OldClass->getID() << " to "
<< *OldClass->getMemoryLeader()
<< " due to removal of old leader " << *InstMA << "\n");
markMemoryLeaderChangeTouched(OldClass);
} else
OldClass->setMemoryLeader(nullptr);
}
}
// Move a value, currently in OldClass, to be part of NewClass
// Update OldClass and NewClass for the move (including changing leaders, etc).
void NewGVN::moveValueToNewCongruenceClass(Instruction *I, const Expression *E,
CongruenceClass *OldClass,
CongruenceClass *NewClass) {
if (I == OldClass->getNextLeader().first)
OldClass->resetNextLeader();
// It's possible, though unlikely, for us to discover equivalences such
// that the current leader does not dominate the old one.
// This statistic tracks how often this happens.
// We assert on phi nodes when this happens, currently, for debugging, because
// we want to make sure we name phi node cycles properly.
if (isa<Instruction>(NewClass->getLeader()) && NewClass->getLeader() &&
I != NewClass->getLeader()) {
auto *IBB = I->getParent();
auto *NCBB = cast<Instruction>(NewClass->getLeader())->getParent();
bool Dominated =
IBB == NCBB && InstrToDFSNum(I) < InstrToDFSNum(NewClass->getLeader());
Dominated = Dominated || DT->properlyDominates(IBB, NCBB);
if (Dominated) {
++NumGVNNotMostDominatingLeader;
assert(
!isa<PHINode>(I) &&
"New class for instruction should not be dominated by instruction");
}
}
if (NewClass->getLeader() != I)
NewClass->addPossibleNextLeader({I, InstrToDFSNum(I)});
OldClass->erase(I);
NewClass->insert(I);
// Handle our special casing of stores.
if (auto *SI = dyn_cast<StoreInst>(I)) {
OldClass->decStoreCount();
// Okay, so when do we want to make a store a leader of a class?
// If we have a store defined by an earlier load, we want the earlier load
// to lead the class.
// If we have a store defined by something else, we want the store to lead
// the class so everything else gets the "something else" as a value.
// If we have a store as the single member of the class, we want the store
// as the leader
if (NewClass->getStoreCount() == 0 && !NewClass->getStoredValue()) {
// If it's a store expression we are using, it means we are not equivalent
// to something earlier.
if (auto *SE = dyn_cast<StoreExpression>(E)) {
assert(SE->getStoredValue() != NewClass->getLeader());
NewClass->setStoredValue(SE->getStoredValue());
markValueLeaderChangeTouched(NewClass);
// Shift the new class leader to be the store
DEBUG(dbgs() << "Changing leader of congruence class "
<< NewClass->getID() << " from " << *NewClass->getLeader()
<< " to " << *SI << " because store joined class\n");
// If we changed the leader, we have to mark it changed because we don't
// know what it will do to symbolic evlauation.
NewClass->setLeader(SI);
}
// We rely on the code below handling the MemoryAccess change.
}
NewClass->incStoreCount();
}
// True if there is no memory instructions left in a class that had memory
// instructions before.
// If it's not a memory use, set the MemoryAccess equivalence
auto *InstMA = dyn_cast_or_null<MemoryDef>(MSSA->getMemoryAccess(I));
if (InstMA)
moveMemoryToNewCongruenceClass(I, InstMA, OldClass, NewClass);
ValueToClass[I] = NewClass;
// See if we destroyed the class or need to swap leaders.
if (OldClass->empty() && OldClass != TOPClass) {
if (OldClass->getDefiningExpr()) {
DEBUG(dbgs() << "Erasing expression " << *OldClass->getDefiningExpr()
<< " from table\n");
ExpressionToClass.erase(OldClass->getDefiningExpr());
}
} else if (OldClass->getLeader() == I) {
// When the leader changes, the value numbering of
// everything may change due to symbolization changes, so we need to
// reprocess.
DEBUG(dbgs() << "Value class leader change for class " << OldClass->getID()
<< "\n");
++NumGVNLeaderChanges;
// Destroy the stored value if there are no more stores to represent it.
// Note that this is basically clean up for the expression removal that
// happens below. If we remove stores from a class, we may leave it as a
// class of equivalent memory phis.
if (OldClass->getStoreCount() == 0) {
if (OldClass->getStoredValue())
OldClass->setStoredValue(nullptr);
}
OldClass->setLeader(getNextValueLeader(OldClass));
OldClass->resetNextLeader();
markValueLeaderChangeTouched(OldClass);
}
}
// Perform congruence finding on a given value numbering expression.
void NewGVN::performCongruenceFinding(Instruction *I, const Expression *E) {
// This is guaranteed to return something, since it will at least find
// TOP.
CongruenceClass *IClass = ValueToClass[I];
assert(IClass && "Should have found a IClass");
// Dead classes should have been eliminated from the mapping.
assert(!IClass->isDead() && "Found a dead class");
CongruenceClass *EClass;
if (const auto *VE = dyn_cast<VariableExpression>(E)) {
EClass = ValueToClass[VE->getVariableValue()];
} else {
auto lookupResult = ExpressionToClass.insert({E, nullptr});
// If it's not in the value table, create a new congruence class.
if (lookupResult.second) {
CongruenceClass *NewClass = createCongruenceClass(nullptr, E);
auto place = lookupResult.first;
place->second = NewClass;
// Constants and variables should always be made the leader.
if (const auto *CE = dyn_cast<ConstantExpression>(E)) {
NewClass->setLeader(CE->getConstantValue());
} else if (const auto *SE = dyn_cast<StoreExpression>(E)) {
StoreInst *SI = SE->getStoreInst();
NewClass->setLeader(SI);
NewClass->setStoredValue(SE->getStoredValue());
// The RepMemoryAccess field will be filled in properly by the
// moveValueToNewCongruenceClass call.
} else {
NewClass->setLeader(I);
}
assert(!isa<VariableExpression>(E) &&
"VariableExpression should have been handled already");
EClass = NewClass;
DEBUG(dbgs() << "Created new congruence class for " << *I
<< " using expression " << *E << " at " << NewClass->getID()
<< " and leader " << *(NewClass->getLeader()));
if (NewClass->getStoredValue())
DEBUG(dbgs() << " and stored value " << *(NewClass->getStoredValue()));
DEBUG(dbgs() << "\n");
} else {
EClass = lookupResult.first->second;
if (isa<ConstantExpression>(E))
assert((isa<Constant>(EClass->getLeader()) ||
(EClass->getStoredValue() &&
isa<Constant>(EClass->getStoredValue()))) &&
"Any class with a constant expression should have a "
"constant leader");
assert(EClass && "Somehow don't have an eclass");
assert(!EClass->isDead() && "We accidentally looked up a dead class");
}
}
bool ClassChanged = IClass != EClass;
bool LeaderChanged = LeaderChanges.erase(I);
if (ClassChanged || LeaderChanged) {
DEBUG(dbgs() << "New class " << EClass->getID() << " for expression " << *E
<< "\n");
if (ClassChanged)
moveValueToNewCongruenceClass(I, E, IClass, EClass);
markUsersTouched(I);
if (MemoryAccess *MA = MSSA->getMemoryAccess(I))
markMemoryUsersTouched(MA);
if (auto *CI = dyn_cast<CmpInst>(I))
markPredicateUsersTouched(CI);
}
// If we changed the class of the store, we want to ensure nothing finds the
// old store expression. In particular, loads do not compare against stored
// value, so they will find old store expressions (and associated class
// mappings) if we leave them in the table.
if (ClassChanged && isa<StoreInst>(I)) {
auto *OldE = ValueToExpression.lookup(I);
// It could just be that the old class died. We don't want to erase it if we
// just moved classes.
if (OldE && isa<StoreExpression>(OldE) && *E != *OldE)
ExpressionToClass.erase(OldE);
}
ValueToExpression[I] = E;
}
// Process the fact that Edge (from, to) is reachable, including marking
// any newly reachable blocks and instructions for processing.
void NewGVN::updateReachableEdge(BasicBlock *From, BasicBlock *To) {
// Check if the Edge was reachable before.
if (ReachableEdges.insert({From, To}).second) {
// If this block wasn't reachable before, all instructions are touched.
if (ReachableBlocks.insert(To).second) {
DEBUG(dbgs() << "Block " << getBlockName(To) << " marked reachable\n");
const auto &InstRange = BlockInstRange.lookup(To);
TouchedInstructions.set(InstRange.first, InstRange.second);
} else {
DEBUG(dbgs() << "Block " << getBlockName(To)
<< " was reachable, but new edge {" << getBlockName(From)
<< "," << getBlockName(To) << "} to it found\n");
// We've made an edge reachable to an existing block, which may
// impact predicates. Otherwise, only mark the phi nodes as touched, as
// they are the only thing that depend on new edges. Anything using their
// values will get propagated to if necessary.
if (MemoryAccess *MemPhi = MSSA->getMemoryAccess(To))
TouchedInstructions.set(InstrToDFSNum(MemPhi));
auto BI = To->begin();
while (isa<PHINode>(BI)) {
TouchedInstructions.set(InstrToDFSNum(&*BI));
++BI;
}
}
}
}
// Given a predicate condition (from a switch, cmp, or whatever) and a block,
// see if we know some constant value for it already.
Value *NewGVN::findConditionEquivalence(Value *Cond) const {
auto Result = lookupOperandLeader(Cond);
if (isa<Constant>(Result))
return Result;
return nullptr;
}
// Process the outgoing edges of a block for reachability.
void NewGVN::processOutgoingEdges(TerminatorInst *TI, BasicBlock *B) {
// Evaluate reachability of terminator instruction.
BranchInst *BR;
if ((BR = dyn_cast<BranchInst>(TI)) && BR->isConditional()) {
Value *Cond = BR->getCondition();
Value *CondEvaluated = findConditionEquivalence(Cond);
if (!CondEvaluated) {
if (auto *I = dyn_cast<Instruction>(Cond)) {
const Expression *E = createExpression(I);
if (const auto *CE = dyn_cast<ConstantExpression>(E)) {
CondEvaluated = CE->getConstantValue();
}
} else if (isa<ConstantInt>(Cond)) {
CondEvaluated = Cond;
}
}
ConstantInt *CI;
BasicBlock *TrueSucc = BR->getSuccessor(0);
BasicBlock *FalseSucc = BR->getSuccessor(1);
if (CondEvaluated && (CI = dyn_cast<ConstantInt>(CondEvaluated))) {
if (CI->isOne()) {
DEBUG(dbgs() << "Condition for Terminator " << *TI
<< " evaluated to true\n");
updateReachableEdge(B, TrueSucc);
} else if (CI->isZero()) {
DEBUG(dbgs() << "Condition for Terminator " << *TI
<< " evaluated to false\n");
updateReachableEdge(B, FalseSucc);
}
} else {
updateReachableEdge(B, TrueSucc);
updateReachableEdge(B, FalseSucc);
}
} else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
// For switches, propagate the case values into the case
// destinations.
// Remember how many outgoing edges there are to every successor.
SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
Value *SwitchCond = SI->getCondition();
Value *CondEvaluated = findConditionEquivalence(SwitchCond);
// See if we were able to turn this switch statement into a constant.
if (CondEvaluated && isa<ConstantInt>(CondEvaluated)) {
auto *CondVal = cast<ConstantInt>(CondEvaluated);
// We should be able to get case value for this.
auto Case = *SI->findCaseValue(CondVal);
if (Case.getCaseSuccessor() == SI->getDefaultDest()) {
// We proved the value is outside of the range of the case.
// We can't do anything other than mark the default dest as reachable,
// and go home.
updateReachableEdge(B, SI->getDefaultDest());
return;
}
// Now get where it goes and mark it reachable.
BasicBlock *TargetBlock = Case.getCaseSuccessor();
updateReachableEdge(B, TargetBlock);
} else {
for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
BasicBlock *TargetBlock = SI->getSuccessor(i);
++SwitchEdges[TargetBlock];
updateReachableEdge(B, TargetBlock);
}
}
} else {
// Otherwise this is either unconditional, or a type we have no
// idea about. Just mark successors as reachable.
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
BasicBlock *TargetBlock = TI->getSuccessor(i);
updateReachableEdge(B, TargetBlock);
}
// This also may be a memory defining terminator, in which case, set it
// equivalent only to itself.
//
auto *MA = MSSA->getMemoryAccess(TI);
if (MA && !isa<MemoryUse>(MA)) {
auto *CC = ensureLeaderOfMemoryClass(MA);
if (setMemoryClass(MA, CC))
markMemoryUsersTouched(MA);
}
}
}
// The algorithm initially places the values of the routine in the TOP
// congruence class. The leader of TOP is the undetermined value `undef`.
// When the algorithm has finished, values still in TOP are unreachable.
void NewGVN::initializeCongruenceClasses(Function &F) {
NextCongruenceNum = 0;
// Note that even though we use the live on entry def as a representative
// MemoryAccess, it is *not* the same as the actual live on entry def. We
// have no real equivalemnt to undef for MemoryAccesses, and so we really
// should be checking whether the MemoryAccess is top if we want to know if it
// is equivalent to everything. Otherwise, what this really signifies is that
// the access "it reaches all the way back to the beginning of the function"
// Initialize all other instructions to be in TOP class.
TOPClass = createCongruenceClass(nullptr, nullptr);
TOPClass->setMemoryLeader(MSSA->getLiveOnEntryDef());
// The live on entry def gets put into it's own class
MemoryAccessToClass[MSSA->getLiveOnEntryDef()] =
createMemoryClass(MSSA->getLiveOnEntryDef());
for (auto DTN : nodes(DT)) {
BasicBlock *BB = DTN->getBlock();
// All MemoryAccesses are equivalent to live on entry to start. They must
// be initialized to something so that initial changes are noticed. For
// the maximal answer, we initialize them all to be the same as
// liveOnEntry.
auto *MemoryBlockDefs = MSSA->getBlockDefs(BB);
if (MemoryBlockDefs)
for (const auto &Def : *MemoryBlockDefs) {
MemoryAccessToClass[&Def] = TOPClass;
auto *MD = dyn_cast<MemoryDef>(&Def);
// Insert the memory phis into the member list.
if (!MD) {
const MemoryPhi *MP = cast<MemoryPhi>(&Def);
TOPClass->memory_insert(MP);
MemoryPhiState.insert({MP, MPS_TOP});
}
if (MD && isa<StoreInst>(MD->getMemoryInst()))
TOPClass->incStoreCount();
}
for (auto &I : *BB) {
// Don't insert void terminators into the class. We don't value number
// them, and they just end up sitting in TOP.
if (isa<TerminatorInst>(I) && I.getType()->isVoidTy())
continue;
TOPClass->insert(&I);
ValueToClass[&I] = TOPClass;
}
}
// Initialize arguments to be in their own unique congruence classes
for (auto &FA : F.args())
createSingletonCongruenceClass(&FA);
}
void NewGVN::cleanupTables() {
for (unsigned i = 0, e = CongruenceClasses.size(); i != e; ++i) {
DEBUG(dbgs() << "Congruence class " << CongruenceClasses[i]->getID()
<< " has " << CongruenceClasses[i]->size() << " members\n");
// Make sure we delete the congruence class (probably worth switching to
// a unique_ptr at some point.
delete CongruenceClasses[i];
CongruenceClasses[i] = nullptr;
}
ValueToClass.clear();
ArgRecycler.clear(ExpressionAllocator);
ExpressionAllocator.Reset();
CongruenceClasses.clear();
ExpressionToClass.clear();
ValueToExpression.clear();
ReachableBlocks.clear();
ReachableEdges.clear();
#ifndef NDEBUG
ProcessedCount.clear();
#endif
InstrDFS.clear();
InstructionsToErase.clear();
DFSToInstr.clear();
BlockInstRange.clear();
TouchedInstructions.clear();
MemoryAccessToClass.clear();
PredicateToUsers.clear();
MemoryToUsers.clear();
}
std::pair<unsigned, unsigned> NewGVN::assignDFSNumbers(BasicBlock *B,
unsigned Start) {
unsigned End = Start;
if (MemoryAccess *MemPhi = MSSA->getMemoryAccess(B)) {
InstrDFS[MemPhi] = End++;
DFSToInstr.emplace_back(MemPhi);
}
for (auto &I : *B) {
// There's no need to call isInstructionTriviallyDead more than once on
// an instruction. Therefore, once we know that an instruction is dead
// we change its DFS number so that it doesn't get value numbered.
if (isInstructionTriviallyDead(&I, TLI)) {
InstrDFS[&I] = 0;
DEBUG(dbgs() << "Skipping trivially dead instruction " << I << "\n");
markInstructionForDeletion(&I);
continue;
}
InstrDFS[&I] = End++;
DFSToInstr.emplace_back(&I);
}
// All of the range functions taken half-open ranges (open on the end side).
// So we do not subtract one from count, because at this point it is one
// greater than the last instruction.
return std::make_pair(Start, End);
}
void NewGVN::updateProcessedCount(Value *V) {
#ifndef NDEBUG
if (ProcessedCount.count(V) == 0) {
ProcessedCount.insert({V, 1});
} else {
++ProcessedCount[V];
assert(ProcessedCount[V] < 100 &&
"Seem to have processed the same Value a lot");
}
#endif
}
// Evaluate MemoryPhi nodes symbolically, just like PHI nodes
void NewGVN::valueNumberMemoryPhi(MemoryPhi *MP) {
// If all the arguments are the same, the MemoryPhi has the same value as the
// argument.
// Filter out unreachable blocks and self phis from our operands.
const BasicBlock *PHIBlock = MP->getBlock();
auto Filtered = make_filter_range(MP->operands(), [&](const Use &U) {
return lookupMemoryLeader(cast<MemoryAccess>(U)) != MP &&
!isMemoryAccessTop(cast<MemoryAccess>(U)) &&
ReachableEdges.count({MP->getIncomingBlock(U), PHIBlock});
});
// If all that is left is nothing, our memoryphi is undef. We keep it as
// InitialClass. Note: The only case this should happen is if we have at
// least one self-argument.
if (Filtered.begin() == Filtered.end()) {
if (setMemoryClass(MP, TOPClass))
markMemoryUsersTouched(MP);
return;
}
// Transform the remaining operands into operand leaders.
// FIXME: mapped_iterator should have a range version.
auto LookupFunc = [&](const Use &U) {
return lookupMemoryLeader(cast<MemoryAccess>(U));
};
auto MappedBegin = map_iterator(Filtered.begin(), LookupFunc);
auto MappedEnd = map_iterator(Filtered.end(), LookupFunc);
// and now check if all the elements are equal.
// Sadly, we can't use std::equals since these are random access iterators.
const auto *AllSameValue = *MappedBegin;
++MappedBegin;
bool AllEqual = std::all_of(
MappedBegin, MappedEnd,
[&AllSameValue](const MemoryAccess *V) { return V == AllSameValue; });
if (AllEqual)
DEBUG(dbgs() << "Memory Phi value numbered to " << *AllSameValue << "\n");
else
DEBUG(dbgs() << "Memory Phi value numbered to itself\n");
// If it's equal to something, it's in that class. Otherwise, it has to be in
// a class where it is the leader (other things may be equivalent to it, but
// it needs to start off in its own class, which means it must have been the
// leader, and it can't have stopped being the leader because it was never
// removed).
CongruenceClass *CC =
AllEqual ? getMemoryClass(AllSameValue) : ensureLeaderOfMemoryClass(MP);
auto OldState = MemoryPhiState.lookup(MP);
assert(OldState != MPS_Invalid && "Invalid memory phi state");
auto NewState = AllEqual ? MPS_Equivalent : MPS_Unique;
MemoryPhiState[MP] = NewState;
if (setMemoryClass(MP, CC) || OldState != NewState)
markMemoryUsersTouched(MP);
}
// Value number a single instruction, symbolically evaluating, performing
// congruence finding, and updating mappings.
void NewGVN::valueNumberInstruction(Instruction *I) {
DEBUG(dbgs() << "Processing instruction " << *I << "\n");
if (!I->isTerminator()) {
const Expression *Symbolized = nullptr;
if (DebugCounter::shouldExecute(VNCounter)) {
Symbolized = performSymbolicEvaluation(I);
} else {
// Mark the instruction as unused so we don't value number it again.
InstrDFS[I] = 0;
}
// If we couldn't come up with a symbolic expression, use the unknown
// expression
if (Symbolized == nullptr) {
Symbolized = createUnknownExpression(I);
}
performCongruenceFinding(I, Symbolized);
} else {
// Handle terminators that return values. All of them produce values we
// don't currently understand. We don't place non-value producing
// terminators in a class.
if (!I->getType()->isVoidTy()) {
auto *Symbolized = createUnknownExpression(I);
performCongruenceFinding(I, Symbolized);
}
processOutgoingEdges(dyn_cast<TerminatorInst>(I), I->getParent());
}
}
// Check if there is a path, using single or equal argument phi nodes, from
// First to Second.
bool NewGVN::singleReachablePHIPath(
SmallPtrSet<const MemoryAccess *, 8> &Visited, const MemoryAccess *First,
const MemoryAccess *Second) const {
if (First == Second)
return true;
if (MSSA->isLiveOnEntryDef(First))
return false;
// This is not perfect, but as we're just verifying here, we can live with
// the loss of precision. The real solution would be that of doing strongly
// connected component finding in this routine, and it's probably not worth
// the complexity for the time being. So, we just keep a set of visited
// MemoryAccess and return true when we hit a cycle.
if (Visited.count(First))
return true;
Visited.insert(First);
const auto *EndDef = First;
for (auto *ChainDef : optimized_def_chain(First)) {
if (ChainDef == Second)
return true;
if (MSSA->isLiveOnEntryDef(ChainDef))
return false;
EndDef = ChainDef;
}
auto *MP = cast<MemoryPhi>(EndDef);
auto ReachableOperandPred = [&](const Use &U) {
return ReachableEdges.count({MP->getIncomingBlock(U), MP->getBlock()});
};
auto FilteredPhiArgs =
make_filter_range(MP->operands(), ReachableOperandPred);
SmallVector<const Value *, 32> OperandList;
std::copy(FilteredPhiArgs.begin(), FilteredPhiArgs.end(),
std::back_inserter(OperandList));
bool Okay = OperandList.size() == 1;
if (!Okay)
Okay =
std::equal(OperandList.begin(), OperandList.end(), OperandList.begin());
if (Okay)
return singleReachablePHIPath(Visited, cast<MemoryAccess>(OperandList[0]),
Second);
return false;
}
// Verify the that the memory equivalence table makes sense relative to the
// congruence classes. Note that this checking is not perfect, and is currently
// subject to very rare false negatives. It is only useful for
// testing/debugging.
void NewGVN::verifyMemoryCongruency() const {
#ifndef NDEBUG
// Verify that the memory table equivalence and memory member set match
for (const auto *CC : CongruenceClasses) {
if (CC == TOPClass || CC->isDead())
continue;
if (CC->getStoreCount() != 0) {
assert((CC->getStoredValue() || !isa<StoreInst>(CC->getLeader())) &&
"Any class with a store as a leader should have a "
"representative stored value");
assert(CC->getMemoryLeader() &&
"Any congruence class with a store should have a "
"representative access");
}
if (CC->getMemoryLeader())
assert(MemoryAccessToClass.lookup(CC->getMemoryLeader()) == CC &&
"Representative MemoryAccess does not appear to be reverse "
"mapped properly");
for (auto M : CC->memory())
assert(MemoryAccessToClass.lookup(M) == CC &&
"Memory member does not appear to be reverse mapped properly");
}
// Anything equivalent in the MemoryAccess table should be in the same
// congruence class.
// Filter out the unreachable and trivially dead entries, because they may
// never have been updated if the instructions were not processed.
auto ReachableAccessPred =
[&](const std::pair<const MemoryAccess *, CongruenceClass *> Pair) {
bool Result = ReachableBlocks.count(Pair.first->getBlock());
if (!Result || MSSA->isLiveOnEntryDef(Pair.first) ||
MemoryToDFSNum(Pair.first) == 0)
return false;
if (auto *MemDef = dyn_cast<MemoryDef>(Pair.first))
return !isInstructionTriviallyDead(MemDef->getMemoryInst());
// We could have phi nodes which operands are all trivially dead,
// so we don't process them.
if (auto *MemPHI = dyn_cast<MemoryPhi>(Pair.first)) {
for (auto &U : MemPHI->incoming_values()) {
if (Instruction *I = dyn_cast<Instruction>(U.get())) {
if (!isInstructionTriviallyDead(I))
return true;
}
}
return false;
}
return true;
};
auto Filtered = make_filter_range(MemoryAccessToClass, ReachableAccessPred);
for (auto KV : Filtered) {
assert(KV.second != TOPClass &&
"Memory not unreachable but ended up in TOP");
if (auto *FirstMUD = dyn_cast<MemoryUseOrDef>(KV.first)) {
auto *SecondMUD = dyn_cast<MemoryUseOrDef>(KV.second->getMemoryLeader());
if (FirstMUD && SecondMUD) {
SmallPtrSet<const MemoryAccess *, 8> VisitedMAS;
assert((singleReachablePHIPath(VisitedMAS, FirstMUD, SecondMUD) ||
ValueToClass.lookup(FirstMUD->getMemoryInst()) ==
ValueToClass.lookup(SecondMUD->getMemoryInst())) &&
"The instructions for these memory operations should have "
"been in the same congruence class or reachable through"
"a single argument phi");
}
} else if (auto *FirstMP = dyn_cast<MemoryPhi>(KV.first)) {
// We can only sanely verify that MemoryDefs in the operand list all have
// the same class.
auto ReachableOperandPred = [&](const Use &U) {
return ReachableEdges.count(
{FirstMP->getIncomingBlock(U), FirstMP->getBlock()}) &&
isa<MemoryDef>(U);
};
// All arguments should in the same class, ignoring unreachable arguments
auto FilteredPhiArgs =
make_filter_range(FirstMP->operands(), ReachableOperandPred);
SmallVector<const CongruenceClass *, 16> PhiOpClasses;
std::transform(FilteredPhiArgs.begin(), FilteredPhiArgs.end(),
std::back_inserter(PhiOpClasses), [&](const Use &U) {
const MemoryDef *MD = cast<MemoryDef>(U);
return ValueToClass.lookup(MD->getMemoryInst());
});
assert(std::equal(PhiOpClasses.begin(), PhiOpClasses.end(),
PhiOpClasses.begin()) &&
"All MemoryPhi arguments should be in the same class");
}
}
#endif
}
// Verify that the sparse propagation we did actually found the maximal fixpoint
// We do this by storing the value to class mapping, touching all instructions,
// and redoing the iteration to see if anything changed.
void NewGVN::verifyIterationSettled(Function &F) {
#ifndef NDEBUG
DEBUG(dbgs() << "Beginning iteration verification\n");
if (DebugCounter::isCounterSet(VNCounter))
DebugCounter::setCounterValue(VNCounter, StartingVNCounter);
// Note that we have to store the actual classes, as we may change existing
// classes during iteration. This is because our memory iteration propagation
// is not perfect, and so may waste a little work. But it should generate
// exactly the same congruence classes we have now, with different IDs.
std::map<const Value *, CongruenceClass> BeforeIteration;
for (auto &KV : ValueToClass) {
if (auto *I = dyn_cast<Instruction>(KV.first))
// Skip unused/dead instructions.
if (InstrToDFSNum(I) == 0)
continue;
BeforeIteration.insert({KV.first, *KV.second});
}
TouchedInstructions.set();
TouchedInstructions.reset(0);
iterateTouchedInstructions();
DenseSet<std::pair<const CongruenceClass *, const CongruenceClass *>>
EqualClasses;
for (const auto &KV : ValueToClass) {
if (auto *I = dyn_cast<Instruction>(KV.first))
// Skip unused/dead instructions.
if (InstrToDFSNum(I) == 0)
continue;
// We could sink these uses, but i think this adds a bit of clarity here as
// to what we are comparing.
auto *BeforeCC = &BeforeIteration.find(KV.first)->second;
auto *AfterCC = KV.second;
// Note that the classes can't change at this point, so we memoize the set
// that are equal.
if (!EqualClasses.count({BeforeCC, AfterCC})) {
assert(BeforeCC->isEquivalentTo(AfterCC) &&
"Value number changed after main loop completed!");
EqualClasses.insert({BeforeCC, AfterCC});
}
}
#endif
}
// Verify that for each store expression in the expression to class mapping,
// only the latest appears, and multiple ones do not appear.
// Because loads do not use the stored value when doing equality with stores,
// if we don't erase the old store expressions from the table, a load can find
// a no-longer valid StoreExpression.
void NewGVN::verifyStoreExpressions() const {
#ifndef NDEBUG
DenseSet<std::pair<const Value *, const Value *>> StoreExpressionSet;
for (const auto &KV : ExpressionToClass) {
if (auto *SE = dyn_cast<StoreExpression>(KV.first)) {
// Make sure a version that will conflict with loads is not already there
auto Res =
StoreExpressionSet.insert({SE->getOperand(0), SE->getMemoryLeader()});
assert(Res.second &&
"Stored expression conflict exists in expression table");
auto *ValueExpr = ValueToExpression.lookup(SE->getStoreInst());
assert(ValueExpr && ValueExpr->equals(*SE) &&
"StoreExpression in ExpressionToClass is not latest "
"StoreExpression for value");
}
}
#endif
}
// This is the main value numbering loop, it iterates over the initial touched
// instruction set, propagating value numbers, marking things touched, etc,
// until the set of touched instructions is completely empty.
void NewGVN::iterateTouchedInstructions() {
unsigned int Iterations = 0;
// Figure out where touchedinstructions starts
int FirstInstr = TouchedInstructions.find_first();
// Nothing set, nothing to iterate, just return.
if (FirstInstr == -1)
return;
BasicBlock *LastBlock = getBlockForValue(InstrFromDFSNum(FirstInstr));
while (TouchedInstructions.any()) {
++Iterations;
// Walk through all the instructions in all the blocks in RPO.
// TODO: As we hit a new block, we should push and pop equalities into a
// table lookupOperandLeader can use, to catch things PredicateInfo
// might miss, like edge-only equivalences.
for (unsigned InstrNum : TouchedInstructions.set_bits()) {
// This instruction was found to be dead. We don't bother looking
// at it again.
if (InstrNum == 0) {
TouchedInstructions.reset(InstrNum);
continue;
}
Value *V = InstrFromDFSNum(InstrNum);
BasicBlock *CurrBlock = getBlockForValue(V);
// If we hit a new block, do reachability processing.
if (CurrBlock != LastBlock) {
LastBlock = CurrBlock;
bool BlockReachable = ReachableBlocks.count(CurrBlock);
const auto &CurrInstRange = BlockInstRange.lookup(CurrBlock);
// If it's not reachable, erase any touched instructions and move on.
if (!BlockReachable) {
TouchedInstructions.reset(CurrInstRange.first, CurrInstRange.second);
DEBUG(dbgs() << "Skipping instructions in block "
<< getBlockName(CurrBlock)
<< " because it is unreachable\n");
continue;
}
updateProcessedCount(CurrBlock);
}
if (auto *MP = dyn_cast<MemoryPhi>(V)) {
DEBUG(dbgs() << "Processing MemoryPhi " << *MP << "\n");
valueNumberMemoryPhi(MP);
} else if (auto *I = dyn_cast<Instruction>(V)) {
valueNumberInstruction(I);
} else {
llvm_unreachable("Should have been a MemoryPhi or Instruction");
}
updateProcessedCount(V);
// Reset after processing (because we may mark ourselves as touched when
// we propagate equalities).
TouchedInstructions.reset(InstrNum);
}
}
NumGVNMaxIterations = std::max(NumGVNMaxIterations.getValue(), Iterations);
}
// This is the main transformation entry point.
bool NewGVN::runGVN() {
if (DebugCounter::isCounterSet(VNCounter))
StartingVNCounter = DebugCounter::getCounterValue(VNCounter);
bool Changed = false;
NumFuncArgs = F.arg_size();
MSSAWalker = MSSA->getWalker();
// Count number of instructions for sizing of hash tables, and come
// up with a global dfs numbering for instructions.
unsigned ICount = 1;
// Add an empty instruction to account for the fact that we start at 1
DFSToInstr.emplace_back(nullptr);
// Note: We want ideal RPO traversal of the blocks, which is not quite the
// same as dominator tree order, particularly with regard whether backedges
// get visited first or second, given a block with multiple successors.
// If we visit in the wrong order, we will end up performing N times as many
// iterations.
// The dominator tree does guarantee that, for a given dom tree node, it's
// parent must occur before it in the RPO ordering. Thus, we only need to sort
// the siblings.
ReversePostOrderTraversal<Function *> RPOT(&F);
unsigned Counter = 0;
for (auto &B : RPOT) {
auto *Node = DT->getNode(B);
assert(Node && "RPO and Dominator tree should have same reachability");
RPOOrdering[Node] = ++Counter;
}
// Sort dominator tree children arrays into RPO.
for (auto &B : RPOT) {
auto *Node = DT->getNode(B);
if (Node->getChildren().size() > 1)
std::sort(Node->begin(), Node->end(),
[&](const DomTreeNode *A, const DomTreeNode *B) {
return RPOOrdering[A] < RPOOrdering[B];
});
}
// Now a standard depth first ordering of the domtree is equivalent to RPO.
for (auto DTN : depth_first(DT->getRootNode())) {
BasicBlock *B = DTN->getBlock();
const auto &BlockRange = assignDFSNumbers(B, ICount);
BlockInstRange.insert({B, BlockRange});
ICount += BlockRange.second - BlockRange.first;
}
TouchedInstructions.resize(ICount);
// Ensure we don't end up resizing the expressionToClass map, as
// that can be quite expensive. At most, we have one expression per
// instruction.
ExpressionToClass.reserve(ICount);
// Initialize the touched instructions to include the entry block.
const auto &InstRange = BlockInstRange.lookup(&F.getEntryBlock());
TouchedInstructions.set(InstRange.first, InstRange.second);
ReachableBlocks.insert(&F.getEntryBlock());
initializeCongruenceClasses(F);
iterateTouchedInstructions();
verifyMemoryCongruency();
verifyIterationSettled(F);
verifyStoreExpressions();
Changed |= eliminateInstructions(F);
// Delete all instructions marked for deletion.
for (Instruction *ToErase : InstructionsToErase) {
if (!ToErase->use_empty())
ToErase->replaceAllUsesWith(UndefValue::get(ToErase->getType()));
ToErase->eraseFromParent();
}
// Delete all unreachable blocks.
auto UnreachableBlockPred = [&](const BasicBlock &BB) {
return !ReachableBlocks.count(&BB);
};
for (auto &BB : make_filter_range(F, UnreachableBlockPred)) {
DEBUG(dbgs() << "We believe block " << getBlockName(&BB)
<< " is unreachable\n");
deleteInstructionsInBlock(&BB);
Changed = true;
}
cleanupTables();
return Changed;
}
// Return true if V is a value that will always be available (IE can
// be placed anywhere) in the function. We don't do globals here
// because they are often worse to put in place.
// TODO: Separate cost from availability
static bool alwaysAvailable(Value *V) {
return isa<Constant>(V) || isa<Argument>(V);
}
struct NewGVN::ValueDFS {
int DFSIn = 0;
int DFSOut = 0;
int LocalNum = 0;
// Only one of Def and U will be set.
// The bool in the Def tells us whether the Def is the stored value of a
// store.
PointerIntPair<Value *, 1, bool> Def;
Use *U = nullptr;
bool operator<(const ValueDFS &Other) const {
// It's not enough that any given field be less than - we have sets
// of fields that need to be evaluated together to give a proper ordering.
// For example, if you have;
// DFS (1, 3)
// Val 0
// DFS (1, 2)
// Val 50
// We want the second to be less than the first, but if we just go field
// by field, we will get to Val 0 < Val 50 and say the first is less than
// the second. We only want it to be less than if the DFS orders are equal.
//
// Each LLVM instruction only produces one value, and thus the lowest-level
// differentiator that really matters for the stack (and what we use as as a
// replacement) is the local dfs number.
// Everything else in the structure is instruction level, and only affects
// the order in which we will replace operands of a given instruction.
//
// For a given instruction (IE things with equal dfsin, dfsout, localnum),
// the order of replacement of uses does not matter.
// IE given,
// a = 5
// b = a + a
// When you hit b, you will have two valuedfs with the same dfsin, out, and
// localnum.
// The .val will be the same as well.
// The .u's will be different.
// You will replace both, and it does not matter what order you replace them
// in (IE whether you replace operand 2, then operand 1, or operand 1, then
// operand 2).
// Similarly for the case of same dfsin, dfsout, localnum, but different
// .val's
// a = 5
// b = 6
// c = a + b
// in c, we will a valuedfs for a, and one for b,with everything the same
// but .val and .u.
// It does not matter what order we replace these operands in.
// You will always end up with the same IR, and this is guaranteed.
return std::tie(DFSIn, DFSOut, LocalNum, Def, U) <
std::tie(Other.DFSIn, Other.DFSOut, Other.LocalNum, Other.Def,
Other.U);
}
};
// This function converts the set of members for a congruence class from values,
// to sets of defs and uses with associated DFS info. The total number of
// reachable uses for each value is stored in UseCount, and instructions that
// seem
// dead (have no non-dead uses) are stored in ProbablyDead.
void NewGVN::convertClassToDFSOrdered(
const CongruenceClass &Dense, SmallVectorImpl<ValueDFS> &DFSOrderedSet,
DenseMap<const Value *, unsigned int> &UseCounts,
SmallPtrSetImpl<Instruction *> &ProbablyDead) const {
for (auto D : Dense) {
// First add the value.
BasicBlock *BB = getBlockForValue(D);
// Constants are handled prior to ever calling this function, so
// we should only be left with instructions as members.
assert(BB && "Should have figured out a basic block for value");
ValueDFS VDDef;
DomTreeNode *DomNode = DT->getNode(BB);
VDDef.DFSIn = DomNode->getDFSNumIn();
VDDef.DFSOut = DomNode->getDFSNumOut();
// If it's a store, use the leader of the value operand, if it's always
// available, or the value operand. TODO: We could do dominance checks to
// find a dominating leader, but not worth it ATM.
if (auto *SI = dyn_cast<StoreInst>(D)) {
auto Leader = lookupOperandLeader(SI->getValueOperand());
if (alwaysAvailable(Leader)) {
VDDef.Def.setPointer(Leader);
} else {
VDDef.Def.setPointer(SI->getValueOperand());
VDDef.Def.setInt(true);
}
} else {
VDDef.Def.setPointer(D);
}
assert(isa<Instruction>(D) &&
"The dense set member should always be an instruction");
VDDef.LocalNum = InstrToDFSNum(D);
DFSOrderedSet.emplace_back(VDDef);
Instruction *Def = cast<Instruction>(D);
unsigned int UseCount = 0;
// Now add the uses.
for (auto &U : Def->uses()) {
if (auto *I = dyn_cast<Instruction>(U.getUser())) {
// Don't try to replace into dead uses
if (InstructionsToErase.count(I))
continue;
ValueDFS VDUse;
// Put the phi node uses in the incoming block.
BasicBlock *IBlock;
if (auto *P = dyn_cast<PHINode>(I)) {
IBlock = P->getIncomingBlock(U);
// Make phi node users appear last in the incoming block
// they are from.
VDUse.LocalNum = InstrDFS.size() + 1;
} else {
IBlock = I->getParent();
VDUse.LocalNum = InstrToDFSNum(I);
}
// Skip uses in unreachable blocks, as we're going
// to delete them.
if (ReachableBlocks.count(IBlock) == 0)
continue;
DomTreeNode *DomNode = DT->getNode(IBlock);
VDUse.DFSIn = DomNode->getDFSNumIn();
VDUse.DFSOut = DomNode->getDFSNumOut();
VDUse.U = &U;
++UseCount;
DFSOrderedSet.emplace_back(VDUse);
}
}
// If there are no uses, it's probably dead (but it may have side-effects,
// so not definitely dead. Otherwise, store the number of uses so we can
// track if it becomes dead later).
if (UseCount == 0)
ProbablyDead.insert(Def);
else
UseCounts[Def] = UseCount;
}
}
// This function converts the set of members for a congruence class from values,
// to the set of defs for loads and stores, with associated DFS info.
void NewGVN::convertClassToLoadsAndStores(
const CongruenceClass &Dense,
SmallVectorImpl<ValueDFS> &LoadsAndStores) const {
for (auto D : Dense) {
if (!isa<LoadInst>(D) && !isa<StoreInst>(D))
continue;
BasicBlock *BB = getBlockForValue(D);
ValueDFS VD;
DomTreeNode *DomNode = DT->getNode(BB);
VD.DFSIn = DomNode->getDFSNumIn();
VD.DFSOut = DomNode->getDFSNumOut();
VD.Def.setPointer(D);
// If it's an instruction, use the real local dfs number.
if (auto *I = dyn_cast<Instruction>(D))
VD.LocalNum = InstrToDFSNum(I);
else
llvm_unreachable("Should have been an instruction");
LoadsAndStores.emplace_back(VD);
}
}
static void patchReplacementInstruction(Instruction *I, Value *Repl) {
auto *ReplInst = dyn_cast<Instruction>(Repl);
if (!ReplInst)
return;
// Patch the replacement so that it is not more restrictive than the value
// being replaced.
// Note that if 'I' is a load being replaced by some operation,
// for example, by an arithmetic operation, then andIRFlags()
// would just erase all math flags from the original arithmetic
// operation, which is clearly not wanted and not needed.
if (!isa<LoadInst>(I))
ReplInst->andIRFlags(I);
// FIXME: If both the original and replacement value are part of the
// same control-flow region (meaning that the execution of one
// guarantees the execution of the other), then we can combine the
// noalias scopes here and do better than the general conservative
// answer used in combineMetadata().
// In general, GVN unifies expressions over different control-flow
// regions, and so we need a conservative combination of the noalias
// scopes.
static const unsigned KnownIDs[] = {
LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
LLVMContext::MD_noalias, LLVMContext::MD_range,
LLVMContext::MD_fpmath, LLVMContext::MD_invariant_load,
LLVMContext::MD_invariant_group};
combineMetadata(ReplInst, I, KnownIDs);
}
static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) {
patchReplacementInstruction(I, Repl);
I->replaceAllUsesWith(Repl);
}
void NewGVN::deleteInstructionsInBlock(BasicBlock *BB) {
DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
++NumGVNBlocksDeleted;
// Delete the instructions backwards, as it has a reduced likelihood of having
// to update as many def-use and use-def chains. Start after the terminator.
auto StartPoint = BB->rbegin();
++StartPoint;
// Note that we explicitly recalculate BB->rend() on each iteration,
// as it may change when we remove the first instruction.
for (BasicBlock::reverse_iterator I(StartPoint); I != BB->rend();) {
Instruction &Inst = *I++;
if (!Inst.use_empty())
Inst.replaceAllUsesWith(UndefValue::get(Inst.getType()));
if (isa<LandingPadInst>(Inst))
continue;
Inst.eraseFromParent();
++NumGVNInstrDeleted;
}
// Now insert something that simplifycfg will turn into an unreachable.
Type *Int8Ty = Type::getInt8Ty(BB->getContext());
new StoreInst(UndefValue::get(Int8Ty),
Constant::getNullValue(Int8Ty->getPointerTo()),
BB->getTerminator());
}
void NewGVN::markInstructionForDeletion(Instruction *I) {
DEBUG(dbgs() << "Marking " << *I << " for deletion\n");
InstructionsToErase.insert(I);
}
void NewGVN::replaceInstruction(Instruction *I, Value *V) {
DEBUG(dbgs() << "Replacing " << *I << " with " << *V << "\n");
patchAndReplaceAllUsesWith(I, V);
// We save the actual erasing to avoid invalidating memory
// dependencies until we are done with everything.
markInstructionForDeletion(I);
}
namespace {
// This is a stack that contains both the value and dfs info of where
// that value is valid.
class ValueDFSStack {
public:
Value *back() const { return ValueStack.back(); }
std::pair<int, int> dfs_back() const { return DFSStack.back(); }
void push_back(Value *V, int DFSIn, int DFSOut) {
ValueStack.emplace_back(V);
DFSStack.emplace_back(DFSIn, DFSOut);
}
bool empty() const { return DFSStack.empty(); }
bool isInScope(int DFSIn, int DFSOut) const {
if (empty())
return false;
return DFSIn >= DFSStack.back().first && DFSOut <= DFSStack.back().second;
}
void popUntilDFSScope(int DFSIn, int DFSOut) {
// These two should always be in sync at this point.
assert(ValueStack.size() == DFSStack.size() &&
"Mismatch between ValueStack and DFSStack");
while (
!DFSStack.empty() &&
!(DFSIn >= DFSStack.back().first && DFSOut <= DFSStack.back().second)) {
DFSStack.pop_back();
ValueStack.pop_back();
}
}
private:
SmallVector<Value *, 8> ValueStack;
SmallVector<std::pair<int, int>, 8> DFSStack;
};
}
bool NewGVN::eliminateInstructions(Function &F) {
// This is a non-standard eliminator. The normal way to eliminate is
// to walk the dominator tree in order, keeping track of available
// values, and eliminating them. However, this is mildly
// pointless. It requires doing lookups on every instruction,
// regardless of whether we will ever eliminate it. For
// instructions part of most singleton congruence classes, we know we
// will never eliminate them.
// Instead, this eliminator looks at the congruence classes directly, sorts
// them into a DFS ordering of the dominator tree, and then we just
// perform elimination straight on the sets by walking the congruence
// class member uses in order, and eliminate the ones dominated by the
// last member. This is worst case O(E log E) where E = number of
// instructions in a single congruence class. In theory, this is all
// instructions. In practice, it is much faster, as most instructions are
// either in singleton congruence classes or can't possibly be eliminated
// anyway (if there are no overlapping DFS ranges in class).
// When we find something not dominated, it becomes the new leader
// for elimination purposes.
// TODO: If we wanted to be faster, We could remove any members with no
// overlapping ranges while sorting, as we will never eliminate anything
// with those members, as they don't dominate anything else in our set.
bool AnythingReplaced = false;
// Since we are going to walk the domtree anyway, and we can't guarantee the
// DFS numbers are updated, we compute some ourselves.
DT->updateDFSNumbers();
for (auto &B : F) {
if (!ReachableBlocks.count(&B)) {
for (const auto S : successors(&B)) {
for (auto II = S->begin(); isa<PHINode>(II); ++II) {
auto &Phi = cast<PHINode>(*II);
DEBUG(dbgs() << "Replacing incoming value of " << *II << " for block "
<< getBlockName(&B)
<< " with undef due to it being unreachable\n");
for (auto &Operand : Phi.incoming_values())
if (Phi.getIncomingBlock(Operand) == &B)
Operand.set(UndefValue::get(Phi.getType()));
}
}
}
}
// Map to store the use counts
DenseMap<const Value *, unsigned int> UseCounts;
for (CongruenceClass *CC : reverse(CongruenceClasses)) {
// Track the equivalent store info so we can decide whether to try
// dead store elimination.
SmallVector<ValueDFS, 8> PossibleDeadStores;
SmallPtrSet<Instruction *, 8> ProbablyDead;
if (CC->isDead() || CC->empty())
continue;
// Everything still in the TOP class is unreachable or dead.
if (CC == TOPClass) {
#ifndef NDEBUG
for (auto M : *CC)
assert((!ReachableBlocks.count(cast<Instruction>(M)->getParent()) ||
InstructionsToErase.count(cast<Instruction>(M))) &&
"Everything in TOP should be unreachable or dead at this "
"point");
#endif
continue;
}
assert(CC->getLeader() && "We should have had a leader");
// If this is a leader that is always available, and it's a
// constant or has no equivalences, just replace everything with
// it. We then update the congruence class with whatever members
// are left.
Value *Leader =
CC->getStoredValue() ? CC->getStoredValue() : CC->getLeader();
if (alwaysAvailable(Leader)) {
CongruenceClass::MemberSet MembersLeft;
for (auto M : *CC) {
Value *Member = M;
// Void things have no uses we can replace.
if (Member == Leader || !isa<Instruction>(Member) ||
Member->getType()->isVoidTy()) {
MembersLeft.insert(Member);
continue;
}
DEBUG(dbgs() << "Found replacement " << *(Leader) << " for " << *Member
<< "\n");
auto *I = cast<Instruction>(Member);
assert(Leader != I && "About to accidentally remove our leader");
replaceInstruction(I, Leader);
AnythingReplaced = true;
}
CC->swap(MembersLeft);
} else {
DEBUG(dbgs() << "Eliminating in congruence class " << CC->getID()
<< "\n");
// If this is a singleton, we can skip it.
if (CC->size() != 1) {
// This is a stack because equality replacement/etc may place
// constants in the middle of the member list, and we want to use
// those constant values in preference to the current leader, over
// the scope of those constants.
ValueDFSStack EliminationStack;
// Convert the members to DFS ordered sets and then merge them.
SmallVector<ValueDFS, 8> DFSOrderedSet;
convertClassToDFSOrdered(*CC, DFSOrderedSet, UseCounts, ProbablyDead);
// Sort the whole thing.
std::sort(DFSOrderedSet.begin(), DFSOrderedSet.end());
for (auto &VD : DFSOrderedSet) {
int MemberDFSIn = VD.DFSIn;
int MemberDFSOut = VD.DFSOut;
Value *Def = VD.Def.getPointer();
bool FromStore = VD.Def.getInt();
Use *U = VD.U;
// We ignore void things because we can't get a value from them.
if (Def && Def->getType()->isVoidTy())
continue;
if (EliminationStack.empty()) {
DEBUG(dbgs() << "Elimination Stack is empty\n");
} else {
DEBUG(dbgs() << "Elimination Stack Top DFS numbers are ("
<< EliminationStack.dfs_back().first << ","
<< EliminationStack.dfs_back().second << ")\n");
}
DEBUG(dbgs() << "Current DFS numbers are (" << MemberDFSIn << ","
<< MemberDFSOut << ")\n");
// First, we see if we are out of scope or empty. If so,
// and there equivalences, we try to replace the top of
// stack with equivalences (if it's on the stack, it must
// not have been eliminated yet).
// Then we synchronize to our current scope, by
// popping until we are back within a DFS scope that
// dominates the current member.
// Then, what happens depends on a few factors
// If the stack is now empty, we need to push
// If we have a constant or a local equivalence we want to
// start using, we also push.
// Otherwise, we walk along, processing members who are
// dominated by this scope, and eliminate them.
bool ShouldPush = Def && EliminationStack.empty();
bool OutOfScope =
!EliminationStack.isInScope(MemberDFSIn, MemberDFSOut);
if (OutOfScope || ShouldPush) {
// Sync to our current scope.
EliminationStack.popUntilDFSScope(MemberDFSIn, MemberDFSOut);
bool ShouldPush = Def && EliminationStack.empty();
if (ShouldPush) {
EliminationStack.push_back(Def, MemberDFSIn, MemberDFSOut);
}
}
// Skip the Def's, we only want to eliminate on their uses. But mark
// dominated defs as dead.
if (Def) {
// For anything in this case, what and how we value number
// guarantees that any side-effets that would have occurred (ie
// throwing, etc) can be proven to either still occur (because it's
// dominated by something that has the same side-effects), or never
// occur. Otherwise, we would not have been able to prove it value
// equivalent to something else. For these things, we can just mark
// it all dead. Note that this is different from the "ProbablyDead"
// set, which may not be dominated by anything, and thus, are only
// easy to prove dead if they are also side-effect free. Note that
// because stores are put in terms of the stored value, we skip
// stored values here. If the stored value is really dead, it will
// still be marked for deletion when we process it in its own class.
if (!EliminationStack.empty() && Def != EliminationStack.back() &&
isa<Instruction>(Def) && !FromStore)
markInstructionForDeletion(cast<Instruction>(Def));
continue;
}
// At this point, we know it is a Use we are trying to possibly
// replace.
assert(isa<Instruction>(U->get()) &&
"Current def should have been an instruction");
assert(isa<Instruction>(U->getUser()) &&
"Current user should have been an instruction");
// If the thing we are replacing into is already marked to be dead,
// this use is dead. Note that this is true regardless of whether
// we have anything dominating the use or not. We do this here
// because we are already walking all the uses anyway.
Instruction *InstUse = cast<Instruction>(U->getUser());
if (InstructionsToErase.count(InstUse)) {
auto &UseCount = UseCounts[U->get()];
if (--UseCount == 0) {
ProbablyDead.insert(cast<Instruction>(U->get()));
}
}
// If we get to this point, and the stack is empty we must have a use
// with nothing we can use to eliminate this use, so just skip it.
if (EliminationStack.empty())
continue;
Value *DominatingLeader = EliminationStack.back();
auto *II = dyn_cast<IntrinsicInst>(DominatingLeader);
if (II && II->getIntrinsicID() == Intrinsic::ssa_copy)
DominatingLeader = II->getOperand(0);
// Don't replace our existing users with ourselves.
if (U->get() == DominatingLeader)
continue;
DEBUG(dbgs() << "Found replacement " << *DominatingLeader << " for "
<< *U->get() << " in " << *(U->getUser()) << "\n");
// If we replaced something in an instruction, handle the patching of
// metadata. Skip this if we are replacing predicateinfo with its
// original operand, as we already know we can just drop it.
auto *ReplacedInst = cast<Instruction>(U->get());
auto *PI = PredInfo->getPredicateInfoFor(ReplacedInst);
if (!PI || DominatingLeader != PI->OriginalOp)
patchReplacementInstruction(ReplacedInst, DominatingLeader);
U->set(DominatingLeader);
// This is now a use of the dominating leader, which means if the
// dominating leader was dead, it's now live!
auto &LeaderUseCount = UseCounts[DominatingLeader];
// It's about to be alive again.
if (LeaderUseCount == 0 && isa<Instruction>(DominatingLeader))
ProbablyDead.erase(cast<Instruction>(DominatingLeader));
if (LeaderUseCount == 0 && II)
ProbablyDead.insert(II);
++LeaderUseCount;
AnythingReplaced = true;
}
}
}
// At this point, anything still in the ProbablyDead set is actually dead if
// would be trivially dead.
for (auto *I : ProbablyDead)
if (wouldInstructionBeTriviallyDead(I))
markInstructionForDeletion(I);
// Cleanup the congruence class.
CongruenceClass::MemberSet MembersLeft;
for (auto *Member : *CC)
if (!isa<Instruction>(Member) ||
!InstructionsToErase.count(cast<Instruction>(Member)))
MembersLeft.insert(Member);
CC->swap(MembersLeft);
// If we have possible dead stores to look at, try to eliminate them.
if (CC->getStoreCount() > 0) {
convertClassToLoadsAndStores(*CC, PossibleDeadStores);
std::sort(PossibleDeadStores.begin(), PossibleDeadStores.end());
ValueDFSStack EliminationStack;
for (auto &VD : PossibleDeadStores) {
int MemberDFSIn = VD.DFSIn;
int MemberDFSOut = VD.DFSOut;
Instruction *Member = cast<Instruction>(VD.Def.getPointer());
if (EliminationStack.empty() ||
!EliminationStack.isInScope(MemberDFSIn, MemberDFSOut)) {
// Sync to our current scope.
EliminationStack.popUntilDFSScope(MemberDFSIn, MemberDFSOut);
if (EliminationStack.empty()) {
EliminationStack.push_back(Member, MemberDFSIn, MemberDFSOut);
continue;
}
}
// We already did load elimination, so nothing to do here.
if (isa<LoadInst>(Member))
continue;
assert(!EliminationStack.empty());
Instruction *Leader = cast<Instruction>(EliminationStack.back());
(void)Leader;
assert(DT->dominates(Leader->getParent(), Member->getParent()));
// Member is dominater by Leader, and thus dead
DEBUG(dbgs() << "Marking dead store " << *Member
<< " that is dominated by " << *Leader << "\n");
markInstructionForDeletion(Member);
CC->erase(Member);
++NumGVNDeadStores;
}
}
}
return AnythingReplaced;
}
// This function provides global ranking of operations so that we can place them
// in a canonical order. Note that rank alone is not necessarily enough for a
// complete ordering, as constants all have the same rank. However, generally,
// we will simplify an operation with all constants so that it doesn't matter
// what order they appear in.
unsigned int NewGVN::getRank(const Value *V) const {
// Prefer undef to anything else
if (isa<UndefValue>(V))
return 0;
if (isa<Constant>(V))
return 1;
else if (auto *A = dyn_cast<Argument>(V))
return 2 + A->getArgNo();
// Need to shift the instruction DFS by number of arguments + 3 to account for
// the constant and argument ranking above.
unsigned Result = InstrToDFSNum(V);
if (Result > 0)
return 3 + NumFuncArgs + Result;
// Unreachable or something else, just return a really large number.
return ~0;
}
// This is a function that says whether two commutative operations should
// have their order swapped when canonicalizing.
bool NewGVN::shouldSwapOperands(const Value *A, const Value *B) const {
// Because we only care about a total ordering, and don't rewrite expressions
// in this order, we order by rank, which will give a strict weak ordering to
// everything but constants, and then we order by pointer address.
return std::make_pair(getRank(A), A) > std::make_pair(getRank(B), B);
}
class NewGVNLegacyPass : public FunctionPass {
public:
static char ID; // Pass identification, replacement for typeid.
NewGVNLegacyPass() : FunctionPass(ID) {
initializeNewGVNLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
private:
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<MemorySSAWrapperPass>();
AU.addRequired<AAResultsWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
}
};
bool NewGVNLegacyPass::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
return NewGVN(F, &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
&getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
&getAnalysis<AAResultsWrapperPass>().getAAResults(),
&getAnalysis<MemorySSAWrapperPass>().getMSSA(),
F.getParent()->getDataLayout())
.runGVN();
}
INITIALIZE_PASS_BEGIN(NewGVNLegacyPass, "newgvn", "Global Value Numbering",
false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
INITIALIZE_PASS_END(NewGVNLegacyPass, "newgvn", "Global Value Numbering", false,
false)
char NewGVNLegacyPass::ID = 0;
// createGVNPass - The public interface to this file.
FunctionPass *llvm::createNewGVNPass() { return new NewGVNLegacyPass(); }
PreservedAnalyses NewGVNPass::run(Function &F, AnalysisManager<Function> &AM) {
// Apparently the order in which we get these results matter for
// the old GVN (see Chandler's comment in GVN.cpp). I'll keep
// the same order here, just in case.
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &AA = AM.getResult<AAManager>(F);
auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
bool Changed =
NewGVN(F, &DT, &AC, &TLI, &AA, &MSSA, F.getParent()->getDataLayout())
.runGVN();
if (!Changed)
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<DominatorTreeAnalysis>();
PA.preserve<GlobalsAA>();
return PA;
}
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