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

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//===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs a simple dominator tree walk that eliminates trivially
// redundant instructions.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/EarlyCSE.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/ScopedHashTable.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/RecyclingAllocator.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include <deque>
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "early-cse"
STATISTIC(NumSimplify, "Number of instructions simplified or DCE'd");
STATISTIC(NumCSE, "Number of instructions CSE'd");
STATISTIC(NumCSELoad, "Number of load instructions CSE'd");
STATISTIC(NumCSECall, "Number of call instructions CSE'd");
STATISTIC(NumDSE, "Number of trivial dead stores removed");
//===----------------------------------------------------------------------===//
// SimpleValue
//===----------------------------------------------------------------------===//
namespace {
/// \brief Struct representing the available values in the scoped hash table.
struct SimpleValue {
Instruction *Inst;
SimpleValue(Instruction *I) : Inst(I) {
assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
}
bool isSentinel() const {
return Inst == DenseMapInfo<Instruction *>::getEmptyKey() ||
Inst == DenseMapInfo<Instruction *>::getTombstoneKey();
}
static bool canHandle(Instruction *Inst) {
// This can only handle non-void readnone functions.
if (CallInst *CI = dyn_cast<CallInst>(Inst))
return CI->doesNotAccessMemory() && !CI->getType()->isVoidTy();
return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) ||
isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst);
}
};
}
namespace llvm {
template <> struct DenseMapInfo<SimpleValue> {
static inline SimpleValue getEmptyKey() {
return DenseMapInfo<Instruction *>::getEmptyKey();
}
static inline SimpleValue getTombstoneKey() {
return DenseMapInfo<Instruction *>::getTombstoneKey();
}
static unsigned getHashValue(SimpleValue Val);
static bool isEqual(SimpleValue LHS, SimpleValue RHS);
};
}
unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
Instruction *Inst = Val.Inst;
// Hash in all of the operands as pointers.
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(Inst)) {
Value *LHS = BinOp->getOperand(0);
Value *RHS = BinOp->getOperand(1);
if (BinOp->isCommutative() && BinOp->getOperand(0) > BinOp->getOperand(1))
std::swap(LHS, RHS);
if (isa<OverflowingBinaryOperator>(BinOp)) {
// Hash the overflow behavior
unsigned Overflow =
BinOp->hasNoSignedWrap() * OverflowingBinaryOperator::NoSignedWrap |
BinOp->hasNoUnsignedWrap() *
OverflowingBinaryOperator::NoUnsignedWrap;
return hash_combine(BinOp->getOpcode(), Overflow, LHS, RHS);
}
return hash_combine(BinOp->getOpcode(), LHS, RHS);
}
if (CmpInst *CI = dyn_cast<CmpInst>(Inst)) {
Value *LHS = CI->getOperand(0);
Value *RHS = CI->getOperand(1);
CmpInst::Predicate Pred = CI->getPredicate();
if (Inst->getOperand(0) > Inst->getOperand(1)) {
std::swap(LHS, RHS);
Pred = CI->getSwappedPredicate();
}
return hash_combine(Inst->getOpcode(), Pred, LHS, RHS);
}
if (CastInst *CI = dyn_cast<CastInst>(Inst))
return hash_combine(CI->getOpcode(), CI->getType(), CI->getOperand(0));
if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst))
return hash_combine(EVI->getOpcode(), EVI->getOperand(0),
hash_combine_range(EVI->idx_begin(), EVI->idx_end()));
if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst))
return hash_combine(IVI->getOpcode(), IVI->getOperand(0),
IVI->getOperand(1),
hash_combine_range(IVI->idx_begin(), IVI->idx_end()));
assert((isa<CallInst>(Inst) || isa<BinaryOperator>(Inst) ||
isa<GetElementPtrInst>(Inst) || isa<SelectInst>(Inst) ||
isa<ExtractElementInst>(Inst) || isa<InsertElementInst>(Inst) ||
isa<ShuffleVectorInst>(Inst)) &&
"Invalid/unknown instruction");
// Mix in the opcode.
return hash_combine(
Inst->getOpcode(),
hash_combine_range(Inst->value_op_begin(), Inst->value_op_end()));
}
bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
if (LHS.isSentinel() || RHS.isSentinel())
return LHSI == RHSI;
if (LHSI->getOpcode() != RHSI->getOpcode())
return false;
if (LHSI->isIdenticalTo(RHSI))
return true;
// If we're not strictly identical, we still might be a commutable instruction
if (BinaryOperator *LHSBinOp = dyn_cast<BinaryOperator>(LHSI)) {
if (!LHSBinOp->isCommutative())
return false;
assert(isa<BinaryOperator>(RHSI) &&
"same opcode, but different instruction type?");
BinaryOperator *RHSBinOp = cast<BinaryOperator>(RHSI);
// Check overflow attributes
if (isa<OverflowingBinaryOperator>(LHSBinOp)) {
assert(isa<OverflowingBinaryOperator>(RHSBinOp) &&
"same opcode, but different operator type?");
if (LHSBinOp->hasNoUnsignedWrap() != RHSBinOp->hasNoUnsignedWrap() ||
LHSBinOp->hasNoSignedWrap() != RHSBinOp->hasNoSignedWrap())
return false;
}
// Commuted equality
return LHSBinOp->getOperand(0) == RHSBinOp->getOperand(1) &&
LHSBinOp->getOperand(1) == RHSBinOp->getOperand(0);
}
if (CmpInst *LHSCmp = dyn_cast<CmpInst>(LHSI)) {
assert(isa<CmpInst>(RHSI) &&
"same opcode, but different instruction type?");
CmpInst *RHSCmp = cast<CmpInst>(RHSI);
// Commuted equality
return LHSCmp->getOperand(0) == RHSCmp->getOperand(1) &&
LHSCmp->getOperand(1) == RHSCmp->getOperand(0) &&
LHSCmp->getSwappedPredicate() == RHSCmp->getPredicate();
}
return false;
}
//===----------------------------------------------------------------------===//
// CallValue
//===----------------------------------------------------------------------===//
namespace {
/// \brief Struct representing the available call values in the scoped hash
/// table.
struct CallValue {
Instruction *Inst;
CallValue(Instruction *I) : Inst(I) {
assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
}
bool isSentinel() const {
return Inst == DenseMapInfo<Instruction *>::getEmptyKey() ||
Inst == DenseMapInfo<Instruction *>::getTombstoneKey();
}
static bool canHandle(Instruction *Inst) {
// Don't value number anything that returns void.
if (Inst->getType()->isVoidTy())
return false;
CallInst *CI = dyn_cast<CallInst>(Inst);
if (!CI || !CI->onlyReadsMemory())
return false;
return true;
}
};
}
namespace llvm {
template <> struct DenseMapInfo<CallValue> {
static inline CallValue getEmptyKey() {
return DenseMapInfo<Instruction *>::getEmptyKey();
}
static inline CallValue getTombstoneKey() {
return DenseMapInfo<Instruction *>::getTombstoneKey();
}
static unsigned getHashValue(CallValue Val);
static bool isEqual(CallValue LHS, CallValue RHS);
};
}
unsigned DenseMapInfo<CallValue>::getHashValue(CallValue Val) {
Instruction *Inst = Val.Inst;
// Hash all of the operands as pointers and mix in the opcode.
return hash_combine(
Inst->getOpcode(),
hash_combine_range(Inst->value_op_begin(), Inst->value_op_end()));
}
bool DenseMapInfo<CallValue>::isEqual(CallValue LHS, CallValue RHS) {
Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
if (LHS.isSentinel() || RHS.isSentinel())
return LHSI == RHSI;
return LHSI->isIdenticalTo(RHSI);
}
//===----------------------------------------------------------------------===//
// EarlyCSE implementation
//===----------------------------------------------------------------------===//
namespace {
/// \brief A simple and fast domtree-based CSE pass.
///
/// This pass does a simple depth-first walk over the dominator tree,
/// eliminating trivially redundant instructions and using instsimplify to
/// canonicalize things as it goes. It is intended to be fast and catch obvious
/// cases so that instcombine and other passes are more effective. It is
/// expected that a later pass of GVN will catch the interesting/hard cases.
class EarlyCSE {
public:
Function &F;
const TargetLibraryInfo &TLI;
const TargetTransformInfo &TTI;
DominatorTree &DT;
AssumptionCache &AC;
typedef RecyclingAllocator<
BumpPtrAllocator, ScopedHashTableVal<SimpleValue, Value *>> AllocatorTy;
typedef ScopedHashTable<SimpleValue, Value *, DenseMapInfo<SimpleValue>,
AllocatorTy> ScopedHTType;
/// \brief A scoped hash table of the current values of all of our simple
/// scalar expressions.
///
/// As we walk down the domtree, we look to see if instructions are in this:
/// if so, we replace them with what we find, otherwise we insert them so
/// that dominated values can succeed in their lookup.
ScopedHTType AvailableValues;
/// \brief A scoped hash table of the current values of loads.
///
/// This allows us to get efficient access to dominating loads when we have
/// a fully redundant load. In addition to the most recent load, we keep
/// track of a generation count of the read, which is compared against the
/// current generation count. The current generation count is incremented
/// after every possibly writing memory operation, which ensures that we only
/// CSE loads with other loads that have no intervening store.
struct LoadValue {
Value *Data;
unsigned Generation;
int MatchingId;
LoadValue() : Data(nullptr), Generation(0), MatchingId(-1) {}
LoadValue(Value *Data, unsigned Generation, unsigned MatchingId)
: Data(Data), Generation(Generation), MatchingId(MatchingId) {}
};
typedef RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<Value *, LoadValue>>
LoadMapAllocator;
typedef ScopedHashTable<Value *, LoadValue, DenseMapInfo<Value *>,
LoadMapAllocator> LoadHTType;
LoadHTType AvailableLoads;
/// \brief A scoped hash table of the current values of read-only call
/// values.
///
/// It uses the same generation count as loads.
typedef ScopedHashTable<CallValue, std::pair<Value *, unsigned>> CallHTType;
CallHTType AvailableCalls;
/// \brief This is the current generation of the memory value.
unsigned CurrentGeneration;
/// \brief Set up the EarlyCSE runner for a particular function.
EarlyCSE(Function &F, const TargetLibraryInfo &TLI,
const TargetTransformInfo &TTI, DominatorTree &DT,
AssumptionCache &AC)
: F(F), TLI(TLI), TTI(TTI), DT(DT), AC(AC), CurrentGeneration(0) {}
bool run();
private:
// Almost a POD, but needs to call the constructors for the scoped hash
// tables so that a new scope gets pushed on. These are RAII so that the
// scope gets popped when the NodeScope is destroyed.
class NodeScope {
public:
NodeScope(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads,
CallHTType &AvailableCalls)
: Scope(AvailableValues), LoadScope(AvailableLoads),
CallScope(AvailableCalls) {}
private:
NodeScope(const NodeScope &) = delete;
void operator=(const NodeScope &) = delete;
ScopedHTType::ScopeTy Scope;
LoadHTType::ScopeTy LoadScope;
CallHTType::ScopeTy CallScope;
};
// Contains all the needed information to create a stack for doing a depth
// first tranversal of the tree. This includes scopes for values, loads, and
// calls as well as the generation. There is a child iterator so that the
// children do not need to be store spearately.
class StackNode {
public:
StackNode(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads,
CallHTType &AvailableCalls, unsigned cg, DomTreeNode *n,
DomTreeNode::iterator child, DomTreeNode::iterator end)
: CurrentGeneration(cg), ChildGeneration(cg), Node(n), ChildIter(child),
EndIter(end), Scopes(AvailableValues, AvailableLoads, AvailableCalls),
Processed(false) {}
// Accessors.
unsigned currentGeneration() { return CurrentGeneration; }
unsigned childGeneration() { return ChildGeneration; }
void childGeneration(unsigned generation) { ChildGeneration = generation; }
DomTreeNode *node() { return Node; }
DomTreeNode::iterator childIter() { return ChildIter; }
DomTreeNode *nextChild() {
DomTreeNode *child = *ChildIter;
++ChildIter;
return child;
}
DomTreeNode::iterator end() { return EndIter; }
bool isProcessed() { return Processed; }
void process() { Processed = true; }
private:
StackNode(const StackNode &) = delete;
void operator=(const StackNode &) = delete;
// Members.
unsigned CurrentGeneration;
unsigned ChildGeneration;
DomTreeNode *Node;
DomTreeNode::iterator ChildIter;
DomTreeNode::iterator EndIter;
NodeScope Scopes;
bool Processed;
};
/// \brief Wrapper class to handle memory instructions, including loads,
/// stores and intrinsic loads and stores defined by the target.
class ParseMemoryInst {
public:
ParseMemoryInst(Instruction *Inst, const TargetTransformInfo &TTI)
: Load(false), Store(false), Vol(false), MayReadFromMemory(false),
MayWriteToMemory(false), MatchingId(-1), Ptr(nullptr) {
MayReadFromMemory = Inst->mayReadFromMemory();
MayWriteToMemory = Inst->mayWriteToMemory();
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
MemIntrinsicInfo Info;
if (!TTI.getTgtMemIntrinsic(II, Info))
return;
if (Info.NumMemRefs == 1) {
Store = Info.WriteMem;
Load = Info.ReadMem;
MatchingId = Info.MatchingId;
MayReadFromMemory = Info.ReadMem;
MayWriteToMemory = Info.WriteMem;
Vol = Info.Vol;
Ptr = Info.PtrVal;
}
} else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
Load = true;
Vol = !LI->isSimple();
Ptr = LI->getPointerOperand();
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
Store = true;
Vol = !SI->isSimple();
Ptr = SI->getPointerOperand();
}
}
bool isLoad() const { return Load; }
bool isStore() const { return Store; }
bool isVolatile() const { return Vol; }
bool isMatchingMemLoc(const ParseMemoryInst &Inst) const {
return Ptr == Inst.Ptr && MatchingId == Inst.MatchingId;
}
bool isValid() const { return Ptr != nullptr; }
int getMatchingId() const { return MatchingId; }
Value *getPtr() const { return Ptr; }
bool mayReadFromMemory() const { return MayReadFromMemory; }
bool mayWriteToMemory() const { return MayWriteToMemory; }
private:
bool Load;
bool Store;
bool Vol;
bool MayReadFromMemory;
bool MayWriteToMemory;
// For regular (non-intrinsic) loads/stores, this is set to -1. For
// intrinsic loads/stores, the id is retrieved from the corresponding
// field in the MemIntrinsicInfo structure. That field contains
// non-negative values only.
int MatchingId;
Value *Ptr;
};
bool processNode(DomTreeNode *Node);
Value *getOrCreateResult(Value *Inst, Type *ExpectedType) const {
if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
return LI;
else if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
return SI->getValueOperand();
assert(isa<IntrinsicInst>(Inst) && "Instruction not supported");
return TTI.getOrCreateResultFromMemIntrinsic(cast<IntrinsicInst>(Inst),
ExpectedType);
}
};
}
bool EarlyCSE::processNode(DomTreeNode *Node) {
BasicBlock *BB = Node->getBlock();
// If this block has a single predecessor, then the predecessor is the parent
// of the domtree node and all of the live out memory values are still current
// in this block. If this block has multiple predecessors, then they could
// have invalidated the live-out memory values of our parent value. For now,
// just be conservative and invalidate memory if this block has multiple
// predecessors.
if (!BB->getSinglePredecessor())
++CurrentGeneration;
// If this node has a single predecessor which ends in a conditional branch,
// we can infer the value of the branch condition given that we took this
// path. We need the single predeccesor to ensure there's not another path
// which reaches this block where the condition might hold a different
// value. Since we're adding this to the scoped hash table (like any other
// def), it will have been popped if we encounter a future merge block.
if (BasicBlock *Pred = BB->getSinglePredecessor())
if (auto *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
if (BI->isConditional())
if (auto *CondInst = dyn_cast<Instruction>(BI->getCondition()))
if (SimpleValue::canHandle(CondInst)) {
assert(BI->getSuccessor(0) == BB || BI->getSuccessor(1) == BB);
auto *ConditionalConstant = (BI->getSuccessor(0) == BB) ?
ConstantInt::getTrue(BB->getContext()) :
ConstantInt::getFalse(BB->getContext());
AvailableValues.insert(CondInst, ConditionalConstant);
DEBUG(dbgs() << "EarlyCSE CVP: Add conditional value for '"
<< CondInst->getName() << "' as " << *ConditionalConstant
<< " in " << BB->getName() << "\n");
// Replace all dominated uses with the known value
replaceDominatedUsesWith(CondInst, ConditionalConstant, DT,
BasicBlockEdge(Pred, BB));
}
/// LastStore - Keep track of the last non-volatile store that we saw... for
/// as long as there in no instruction that reads memory. If we see a store
/// to the same location, we delete the dead store. This zaps trivial dead
/// stores which can occur in bitfield code among other things.
Instruction *LastStore = nullptr;
bool Changed = false;
const DataLayout &DL = BB->getModule()->getDataLayout();
// See if any instructions in the block can be eliminated. If so, do it. If
// not, add them to AvailableValues.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
Instruction *Inst = I++;
// Dead instructions should just be removed.
if (isInstructionTriviallyDead(Inst, &TLI)) {
DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
Inst->eraseFromParent();
Changed = true;
++NumSimplify;
continue;
}
// Skip assume intrinsics, they don't really have side effects (although
// they're marked as such to ensure preservation of control dependencies),
// and this pass will not disturb any of the assumption's control
// dependencies.
if (match(Inst, m_Intrinsic<Intrinsic::assume>())) {
DEBUG(dbgs() << "EarlyCSE skipping assumption: " << *Inst << '\n');
continue;
}
// If the instruction can be simplified (e.g. X+0 = X) then replace it with
// its simpler value.
if (Value *V = SimplifyInstruction(Inst, DL, &TLI, &DT, &AC)) {
DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n');
Inst->replaceAllUsesWith(V);
Inst->eraseFromParent();
Changed = true;
++NumSimplify;
continue;
}
// If this is a simple instruction that we can value number, process it.
if (SimpleValue::canHandle(Inst)) {
// See if the instruction has an available value. If so, use it.
if (Value *V = AvailableValues.lookup(Inst)) {
DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n');
Inst->replaceAllUsesWith(V);
Inst->eraseFromParent();
Changed = true;
++NumCSE;
continue;
}
// Otherwise, just remember that this value is available.
AvailableValues.insert(Inst, Inst);
continue;
}
ParseMemoryInst MemInst(Inst, TTI);
// If this is a non-volatile load, process it.
if (MemInst.isValid() && MemInst.isLoad()) {
// Ignore volatile loads.
if (MemInst.isVolatile()) {
LastStore = nullptr;
// Don't CSE across synchronization boundaries.
if (Inst->mayWriteToMemory())
++CurrentGeneration;
continue;
}
// If we have an available version of this load, and if it is the right
// generation, replace this instruction.
LoadValue InVal = AvailableLoads.lookup(MemInst.getPtr());
if (InVal.Data != nullptr && InVal.Generation == CurrentGeneration &&
InVal.MatchingId == MemInst.getMatchingId()) {
Value *Op = getOrCreateResult(InVal.Data, Inst->getType());
if (Op != nullptr) {
DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst
<< " to: " << *InVal.Data << '\n');
if (!Inst->use_empty())
Inst->replaceAllUsesWith(Op);
Inst->eraseFromParent();
Changed = true;
++NumCSELoad;
continue;
}
}
// Otherwise, remember that we have this instruction.
AvailableLoads.insert(
MemInst.getPtr(),
LoadValue(Inst, CurrentGeneration, MemInst.getMatchingId()));
LastStore = nullptr;
continue;
}
// If this instruction may read from memory, forget LastStore.
// Load/store intrinsics will indicate both a read and a write to
// memory. The target may override this (e.g. so that a store intrinsic
// does not read from memory, and thus will be treated the same as a
// regular store for commoning purposes).
if (Inst->mayReadFromMemory() &&
!(MemInst.isValid() && !MemInst.mayReadFromMemory()))
LastStore = nullptr;
// If this is a read-only call, process it.
if (CallValue::canHandle(Inst)) {
// If we have an available version of this call, and if it is the right
// generation, replace this instruction.
std::pair<Value *, unsigned> InVal = AvailableCalls.lookup(Inst);
if (InVal.first != nullptr && InVal.second == CurrentGeneration) {
DEBUG(dbgs() << "EarlyCSE CSE CALL: " << *Inst
<< " to: " << *InVal.first << '\n');
if (!Inst->use_empty())
Inst->replaceAllUsesWith(InVal.first);
Inst->eraseFromParent();
Changed = true;
++NumCSECall;
continue;
}
// Otherwise, remember that we have this instruction.
AvailableCalls.insert(
Inst, std::pair<Value *, unsigned>(Inst, CurrentGeneration));
continue;
}
// A release fence requires that all stores complete before it, but does
// not prevent the reordering of following loads 'before' the fence. As a
// result, we don't need to consider it as writing to memory and don't need
// to advance the generation. We do need to prevent DSE across the fence,
// but that's handled above.
if (FenceInst *FI = dyn_cast<FenceInst>(Inst))
if (FI->getOrdering() == Release) {
assert(Inst->mayReadFromMemory() && "relied on to prevent DSE above");
continue;
}
// Okay, this isn't something we can CSE at all. Check to see if it is
// something that could modify memory. If so, our available memory values
// cannot be used so bump the generation count.
if (Inst->mayWriteToMemory()) {
++CurrentGeneration;
if (MemInst.isValid() && MemInst.isStore()) {
// We do a trivial form of DSE if there are two stores to the same
// location with no intervening loads. Delete the earlier store.
if (LastStore) {
ParseMemoryInst LastStoreMemInst(LastStore, TTI);
if (LastStoreMemInst.isMatchingMemLoc(MemInst)) {
DEBUG(dbgs() << "EarlyCSE DEAD STORE: " << *LastStore
<< " due to: " << *Inst << '\n');
LastStore->eraseFromParent();
Changed = true;
++NumDSE;
LastStore = nullptr;
}
// fallthrough - we can exploit information about this store
}
// Okay, we just invalidated anything we knew about loaded values. Try
// to salvage *something* by remembering that the stored value is a live
// version of the pointer. It is safe to forward from volatile stores
// to non-volatile loads, so we don't have to check for volatility of
// the store.
AvailableLoads.insert(
MemInst.getPtr(),
LoadValue(Inst, CurrentGeneration, MemInst.getMatchingId()));
// Remember that this was the last store we saw for DSE.
if (!MemInst.isVolatile())
LastStore = Inst;
}
}
}
return Changed;
}
bool EarlyCSE::run() {
// Note, deque is being used here because there is significant performance
// gains over vector when the container becomes very large due to the
// specific access patterns. For more information see the mailing list
// discussion on this:
// http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20120116/135228.html
std::deque<StackNode *> nodesToProcess;
bool Changed = false;
// Process the root node.
nodesToProcess.push_back(new StackNode(
AvailableValues, AvailableLoads, AvailableCalls, CurrentGeneration,
DT.getRootNode(), DT.getRootNode()->begin(), DT.getRootNode()->end()));
// Save the current generation.
unsigned LiveOutGeneration = CurrentGeneration;
// Process the stack.
while (!nodesToProcess.empty()) {
// Grab the first item off the stack. Set the current generation, remove
// the node from the stack, and process it.
StackNode *NodeToProcess = nodesToProcess.back();
// Initialize class members.
CurrentGeneration = NodeToProcess->currentGeneration();
// Check if the node needs to be processed.
if (!NodeToProcess->isProcessed()) {
// Process the node.
Changed |= processNode(NodeToProcess->node());
NodeToProcess->childGeneration(CurrentGeneration);
NodeToProcess->process();
} else if (NodeToProcess->childIter() != NodeToProcess->end()) {
// Push the next child onto the stack.
DomTreeNode *child = NodeToProcess->nextChild();
nodesToProcess.push_back(
new StackNode(AvailableValues, AvailableLoads, AvailableCalls,
NodeToProcess->childGeneration(), child, child->begin(),
child->end()));
} else {
// It has been processed, and there are no more children to process,
// so delete it and pop it off the stack.
delete NodeToProcess;
nodesToProcess.pop_back();
}
} // while (!nodes...)
// Reset the current generation.
CurrentGeneration = LiveOutGeneration;
return Changed;
}
PreservedAnalyses EarlyCSEPass::run(Function &F,
AnalysisManager<Function> *AM) {
auto &TLI = AM->getResult<TargetLibraryAnalysis>(F);
auto &TTI = AM->getResult<TargetIRAnalysis>(F);
auto &DT = AM->getResult<DominatorTreeAnalysis>(F);
auto &AC = AM->getResult<AssumptionAnalysis>(F);
EarlyCSE CSE(F, TLI, TTI, DT, AC);
if (!CSE.run())
return PreservedAnalyses::all();
// CSE preserves the dominator tree because it doesn't mutate the CFG.
// FIXME: Bundle this with other CFG-preservation.
PreservedAnalyses PA;
PA.preserve<DominatorTreeAnalysis>();
return PA;
}
namespace {
/// \brief A simple and fast domtree-based CSE pass.
///
/// This pass does a simple depth-first walk over the dominator tree,
/// eliminating trivially redundant instructions and using instsimplify to
/// canonicalize things as it goes. It is intended to be fast and catch obvious
/// cases so that instcombine and other passes are more effective. It is
/// expected that a later pass of GVN will catch the interesting/hard cases.
class EarlyCSELegacyPass : public FunctionPass {
public:
static char ID;
EarlyCSELegacyPass() : FunctionPass(ID) {
initializeEarlyCSELegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipOptnoneFunction(F))
return false;
auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
EarlyCSE CSE(F, TLI, TTI, DT, AC);
return CSE.run();
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.setPreservesCFG();
}
};
}
char EarlyCSELegacyPass::ID = 0;
FunctionPass *llvm::createEarlyCSEPass() { return new EarlyCSELegacyPass(); }
INITIALIZE_PASS_BEGIN(EarlyCSELegacyPass, "early-cse", "Early CSE", false,
false)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(EarlyCSELegacyPass, "early-cse", "Early CSE", false, false)
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