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

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//===- GVNSink.cpp - sink expressions into successors ---------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \file GVNSink.cpp
/// This pass attempts to sink instructions into successors, reducing static
/// instruction count and enabling if-conversion.
///
/// We use a variant of global value numbering to decide what can be sunk.
/// Consider:
///
/// [ %a1 = add i32 %b, 1 ] [ %c1 = add i32 %d, 1 ]
/// [ %a2 = xor i32 %a1, 1 ] [ %c2 = xor i32 %c1, 1 ]
/// \ /
/// [ %e = phi i32 %a2, %c2 ]
/// [ add i32 %e, 4 ]
///
///
/// GVN would number %a1 and %c1 differently because they compute different
/// results - the VN of an instruction is a function of its opcode and the
/// transitive closure of its operands. This is the key property for hoisting
/// and CSE.
///
/// What we want when sinking however is for a numbering that is a function of
/// the *uses* of an instruction, which allows us to answer the question "if I
/// replace %a1 with %c1, will it contribute in an equivalent way to all
/// successive instructions?". The PostValueTable class in GVN provides this
/// mapping.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/ArrayRecycler.h"
#include "llvm/Support/AtomicOrdering.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/GVN.h"
#include "llvm/Transforms/Scalar/GVNExpression.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "gvn-sink"
STATISTIC(NumRemoved, "Number of instructions removed");
namespace llvm {
namespace GVNExpression {
LLVM_DUMP_METHOD void Expression::dump() const {
print(dbgs());
dbgs() << "\n";
}
} // end namespace GVNExpression
} // end namespace llvm
namespace {
static bool isMemoryInst(const Instruction *I) {
return isa<LoadInst>(I) || isa<StoreInst>(I) ||
(isa<InvokeInst>(I) && !cast<InvokeInst>(I)->doesNotAccessMemory()) ||
(isa<CallInst>(I) && !cast<CallInst>(I)->doesNotAccessMemory());
}
/// Iterates through instructions in a set of blocks in reverse order from the
/// first non-terminator. For example (assume all blocks have size n):
/// LockstepReverseIterator I([B1, B2, B3]);
/// *I-- = [B1[n], B2[n], B3[n]];
/// *I-- = [B1[n-1], B2[n-1], B3[n-1]];
/// *I-- = [B1[n-2], B2[n-2], B3[n-2]];
/// ...
///
/// It continues until all blocks have been exhausted. Use \c getActiveBlocks()
/// to
/// determine which blocks are still going and the order they appear in the
/// list returned by operator*.
class LockstepReverseIterator {
ArrayRef<BasicBlock *> Blocks;
SmallSetVector<BasicBlock *, 4> ActiveBlocks;
SmallVector<Instruction *, 4> Insts;
bool Fail;
public:
LockstepReverseIterator(ArrayRef<BasicBlock *> Blocks) : Blocks(Blocks) {
reset();
}
void reset() {
Fail = false;
ActiveBlocks.clear();
for (BasicBlock *BB : Blocks)
ActiveBlocks.insert(BB);
Insts.clear();
for (BasicBlock *BB : Blocks) {
if (BB->size() <= 1) {
// Block wasn't big enough - only contained a terminator.
ActiveBlocks.remove(BB);
continue;
}
Insts.push_back(BB->getTerminator()->getPrevNode());
}
if (Insts.empty())
Fail = true;
}
bool isValid() const { return !Fail; }
ArrayRef<Instruction *> operator*() const { return Insts; }
// Note: This needs to return a SmallSetVector as the elements of
// ActiveBlocks will be later copied to Blocks using std::copy. The
// resultant order of elements in Blocks needs to be deterministic.
// Using SmallPtrSet instead causes non-deterministic order while
// copying. And we cannot simply sort Blocks as they need to match the
// corresponding Values.
SmallSetVector<BasicBlock *, 4> &getActiveBlocks() { return ActiveBlocks; }
void restrictToBlocks(SmallSetVector<BasicBlock *, 4> &Blocks) {
for (auto II = Insts.begin(); II != Insts.end();) {
if (std::find(Blocks.begin(), Blocks.end(), (*II)->getParent()) ==
Blocks.end()) {
ActiveBlocks.remove((*II)->getParent());
II = Insts.erase(II);
} else {
++II;
}
}
}
void operator--() {
if (Fail)
return;
SmallVector<Instruction *, 4> NewInsts;
for (auto *Inst : Insts) {
if (Inst == &Inst->getParent()->front())
ActiveBlocks.remove(Inst->getParent());
else
NewInsts.push_back(Inst->getPrevNode());
}
if (NewInsts.empty()) {
Fail = true;
return;
}
Insts = NewInsts;
}
};
//===----------------------------------------------------------------------===//
/// Candidate solution for sinking. There may be different ways to
/// sink instructions, differing in the number of instructions sunk,
/// the number of predecessors sunk from and the number of PHIs
/// required.
struct SinkingInstructionCandidate {
unsigned NumBlocks;
unsigned NumInstructions;
unsigned NumPHIs;
unsigned NumMemoryInsts;
int Cost = -1;
SmallVector<BasicBlock *, 4> Blocks;
void calculateCost(unsigned NumOrigPHIs, unsigned NumOrigBlocks) {
unsigned NumExtraPHIs = NumPHIs - NumOrigPHIs;
unsigned SplitEdgeCost = (NumOrigBlocks > NumBlocks) ? 2 : 0;
Cost = (NumInstructions * (NumBlocks - 1)) -
(NumExtraPHIs *
NumExtraPHIs) // PHIs are expensive, so make sure they're worth it.
- SplitEdgeCost;
}
bool operator>(const SinkingInstructionCandidate &Other) const {
return Cost > Other.Cost;
}
};
#ifndef NDEBUG
raw_ostream &operator<<(raw_ostream &OS, const SinkingInstructionCandidate &C) {
OS << "<Candidate Cost=" << C.Cost << " #Blocks=" << C.NumBlocks
<< " #Insts=" << C.NumInstructions << " #PHIs=" << C.NumPHIs << ">";
return OS;
}
#endif
//===----------------------------------------------------------------------===//
/// Describes a PHI node that may or may not exist. These track the PHIs
/// that must be created if we sunk a sequence of instructions. It provides
/// a hash function for efficient equality comparisons.
class ModelledPHI {
SmallVector<Value *, 4> Values;
SmallVector<BasicBlock *, 4> Blocks;
public:
ModelledPHI() = default;
ModelledPHI(const PHINode *PN) {
// BasicBlock comes first so we sort by basic block pointer order, then by value pointer order.
SmallVector<std::pair<BasicBlock *, Value *>, 4> Ops;
for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I)
Ops.push_back({PN->getIncomingBlock(I), PN->getIncomingValue(I)});
std::sort(Ops.begin(), Ops.end());
for (auto &P : Ops) {
Blocks.push_back(P.first);
Values.push_back(P.second);
}
}
/// Create a dummy ModelledPHI that will compare unequal to any other ModelledPHI
/// without the same ID.
/// \note This is specifically for DenseMapInfo - do not use this!
static ModelledPHI createDummy(size_t ID) {
ModelledPHI M;
M.Values.push_back(reinterpret_cast<Value*>(ID));
return M;
}
/// Create a PHI from an array of incoming values and incoming blocks.
template <typename VArray, typename BArray>
ModelledPHI(const VArray &V, const BArray &B) {
std::copy(V.begin(), V.end(), std::back_inserter(Values));
std::copy(B.begin(), B.end(), std::back_inserter(Blocks));
}
/// Create a PHI from [I[OpNum] for I in Insts].
template <typename BArray>
ModelledPHI(ArrayRef<Instruction *> Insts, unsigned OpNum, const BArray &B) {
std::copy(B.begin(), B.end(), std::back_inserter(Blocks));
for (auto *I : Insts)
Values.push_back(I->getOperand(OpNum));
}
/// Restrict the PHI's contents down to only \c NewBlocks.
/// \c NewBlocks must be a subset of \c this->Blocks.
void restrictToBlocks(const SmallSetVector<BasicBlock *, 4> &NewBlocks) {
auto BI = Blocks.begin();
auto VI = Values.begin();
while (BI != Blocks.end()) {
assert(VI != Values.end());
if (std::find(NewBlocks.begin(), NewBlocks.end(), *BI) ==
NewBlocks.end()) {
BI = Blocks.erase(BI);
VI = Values.erase(VI);
} else {
++BI;
++VI;
}
}
assert(Blocks.size() == NewBlocks.size());
}
ArrayRef<Value *> getValues() const { return Values; }
bool areAllIncomingValuesSame() const {
return llvm::all_of(Values, [&](Value *V) { return V == Values[0]; });
}
bool areAllIncomingValuesSameType() const {
return llvm::all_of(
Values, [&](Value *V) { return V->getType() == Values[0]->getType(); });
}
bool areAnyIncomingValuesConstant() const {
return llvm::any_of(Values, [&](Value *V) { return isa<Constant>(V); });
}
// Hash functor
unsigned hash() const {
return (unsigned)hash_combine_range(Values.begin(), Values.end());
}
bool operator==(const ModelledPHI &Other) const {
return Values == Other.Values && Blocks == Other.Blocks;
}
};
template <typename ModelledPHI> struct DenseMapInfo {
static inline ModelledPHI &getEmptyKey() {
static ModelledPHI Dummy = ModelledPHI::createDummy(0);
return Dummy;
}
static inline ModelledPHI &getTombstoneKey() {
static ModelledPHI Dummy = ModelledPHI::createDummy(1);
return Dummy;
}
static unsigned getHashValue(const ModelledPHI &V) { return V.hash(); }
static bool isEqual(const ModelledPHI &LHS, const ModelledPHI &RHS) {
return LHS == RHS;
}
};
using ModelledPHISet = DenseSet<ModelledPHI, DenseMapInfo<ModelledPHI>>;
//===----------------------------------------------------------------------===//
// ValueTable
//===----------------------------------------------------------------------===//
// This is a value number table where the value number is a function of the
// *uses* of a value, rather than its operands. Thus, if VN(A) == VN(B) we know
// that the program would be equivalent if we replaced A with PHI(A, B).
//===----------------------------------------------------------------------===//
/// A GVN expression describing how an instruction is used. The operands
/// field of BasicExpression is used to store uses, not operands.
///
/// This class also contains fields for discriminators used when determining
/// equivalence of instructions with sideeffects.
class InstructionUseExpr : public GVNExpression::BasicExpression {
unsigned MemoryUseOrder = -1;
bool Volatile = false;
public:
InstructionUseExpr(Instruction *I, ArrayRecycler<Value *> &R,
BumpPtrAllocator &A)
: GVNExpression::BasicExpression(I->getNumUses()) {
allocateOperands(R, A);
setOpcode(I->getOpcode());
setType(I->getType());
for (auto &U : I->uses())
op_push_back(U.getUser());
std::sort(op_begin(), op_end());
}
void setMemoryUseOrder(unsigned MUO) { MemoryUseOrder = MUO; }
void setVolatile(bool V) { Volatile = V; }
hash_code getHashValue() const override {
return hash_combine(GVNExpression::BasicExpression::getHashValue(),
MemoryUseOrder, Volatile);
}
template <typename Function> hash_code getHashValue(Function MapFn) {
hash_code H =
hash_combine(getOpcode(), getType(), MemoryUseOrder, Volatile);
for (auto *V : operands())
H = hash_combine(H, MapFn(V));
return H;
}
};
class ValueTable {
DenseMap<Value *, uint32_t> ValueNumbering;
DenseMap<GVNExpression::Expression *, uint32_t> ExpressionNumbering;
DenseMap<size_t, uint32_t> HashNumbering;
BumpPtrAllocator Allocator;
ArrayRecycler<Value *> Recycler;
uint32_t nextValueNumber = 1;
/// Create an expression for I based on its opcode and its uses. If I
/// touches or reads memory, the expression is also based upon its memory
/// order - see \c getMemoryUseOrder().
InstructionUseExpr *createExpr(Instruction *I) {
InstructionUseExpr *E =
new (Allocator) InstructionUseExpr(I, Recycler, Allocator);
if (isMemoryInst(I))
E->setMemoryUseOrder(getMemoryUseOrder(I));
if (CmpInst *C = dyn_cast<CmpInst>(I)) {
CmpInst::Predicate Predicate = C->getPredicate();
E->setOpcode((C->getOpcode() << 8) | Predicate);
}
return E;
}
/// Helper to compute the value number for a memory instruction
/// (LoadInst/StoreInst), including checking the memory ordering and
/// volatility.
template <class Inst> InstructionUseExpr *createMemoryExpr(Inst *I) {
if (isStrongerThanUnordered(I->getOrdering()) || I->isAtomic())
return nullptr;
InstructionUseExpr *E = createExpr(I);
E->setVolatile(I->isVolatile());
return E;
}
public:
ValueTable() = default;
/// Returns the value number for the specified value, assigning
/// it a new number if it did not have one before.
uint32_t lookupOrAdd(Value *V) {
auto VI = ValueNumbering.find(V);
if (VI != ValueNumbering.end())
return VI->second;
if (!isa<Instruction>(V)) {
ValueNumbering[V] = nextValueNumber;
return nextValueNumber++;
}
Instruction *I = cast<Instruction>(V);
InstructionUseExpr *exp = nullptr;
switch (I->getOpcode()) {
case Instruction::Load:
exp = createMemoryExpr(cast<LoadInst>(I));
break;
case Instruction::Store:
exp = createMemoryExpr(cast<StoreInst>(I));
break;
case Instruction::Call:
case Instruction::Invoke:
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::ICmp:
case Instruction::FCmp:
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::BitCast:
case Instruction::Select:
case Instruction::ExtractElement:
case Instruction::InsertElement:
case Instruction::ShuffleVector:
case Instruction::InsertValue:
case Instruction::GetElementPtr:
exp = createExpr(I);
break;
default:
break;
}
if (!exp) {
ValueNumbering[V] = nextValueNumber;
return nextValueNumber++;
}
uint32_t e = ExpressionNumbering[exp];
if (!e) {
hash_code H = exp->getHashValue([=](Value *V) { return lookupOrAdd(V); });
auto I = HashNumbering.find(H);
if (I != HashNumbering.end()) {
e = I->second;
} else {
e = nextValueNumber++;
HashNumbering[H] = e;
ExpressionNumbering[exp] = e;
}
}
ValueNumbering[V] = e;
return e;
}
/// Returns the value number of the specified value. Fails if the value has
/// not yet been numbered.
uint32_t lookup(Value *V) const {
auto VI = ValueNumbering.find(V);
assert(VI != ValueNumbering.end() && "Value not numbered?");
return VI->second;
}
/// Removes all value numberings and resets the value table.
void clear() {
ValueNumbering.clear();
ExpressionNumbering.clear();
HashNumbering.clear();
Recycler.clear(Allocator);
nextValueNumber = 1;
}
/// \c Inst uses or touches memory. Return an ID describing the memory state
/// at \c Inst such that if getMemoryUseOrder(I1) == getMemoryUseOrder(I2),
/// the exact same memory operations happen after I1 and I2.
///
/// This is a very hard problem in general, so we use domain-specific
/// knowledge that we only ever check for equivalence between blocks sharing a
/// single immediate successor that is common, and when determining if I1 ==
/// I2 we will have already determined that next(I1) == next(I2). This
/// inductive property allows us to simply return the value number of the next
/// instruction that defines memory.
uint32_t getMemoryUseOrder(Instruction *Inst) {
auto *BB = Inst->getParent();
for (auto I = std::next(Inst->getIterator()), E = BB->end();
I != E && !I->isTerminator(); ++I) {
if (!isMemoryInst(&*I))
continue;
if (isa<LoadInst>(&*I))
continue;
CallInst *CI = dyn_cast<CallInst>(&*I);
if (CI && CI->onlyReadsMemory())
continue;
InvokeInst *II = dyn_cast<InvokeInst>(&*I);
if (II && II->onlyReadsMemory())
continue;
return lookupOrAdd(&*I);
}
return 0;
}
};
//===----------------------------------------------------------------------===//
class GVNSink {
public:
GVNSink() = default;
bool run(Function &F) {
DEBUG(dbgs() << "GVNSink: running on function @" << F.getName() << "\n");
unsigned NumSunk = 0;
ReversePostOrderTraversal<Function*> RPOT(&F);
for (auto *N : RPOT)
NumSunk += sinkBB(N);
return NumSunk > 0;
}
private:
ValueTable VN;
bool isInstructionBlacklisted(Instruction *I) {
// These instructions may change or break semantics if moved.
if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
I->getType()->isTokenTy())
return true;
return false;
}
/// The main heuristic function. Analyze the set of instructions pointed to by
/// LRI and return a candidate solution if these instructions can be sunk, or
/// None otherwise.
Optional<SinkingInstructionCandidate> analyzeInstructionForSinking(
LockstepReverseIterator &LRI, unsigned &InstNum, unsigned &MemoryInstNum,
ModelledPHISet &NeededPHIs, SmallPtrSetImpl<Value *> &PHIContents);
/// Create a ModelledPHI for each PHI in BB, adding to PHIs.
void analyzeInitialPHIs(BasicBlock *BB, ModelledPHISet &PHIs,
SmallPtrSetImpl<Value *> &PHIContents) {
for (auto &I : *BB) {
auto *PN = dyn_cast<PHINode>(&I);
if (!PN)
return;
auto MPHI = ModelledPHI(PN);
PHIs.insert(MPHI);
for (auto *V : MPHI.getValues())
PHIContents.insert(V);
}
}
/// The main instruction sinking driver. Set up state and try and sink
/// instructions into BBEnd from its predecessors.
unsigned sinkBB(BasicBlock *BBEnd);
/// Perform the actual mechanics of sinking an instruction from Blocks into
/// BBEnd, which is their only successor.
void sinkLastInstruction(ArrayRef<BasicBlock *> Blocks, BasicBlock *BBEnd);
/// Remove PHIs that all have the same incoming value.
void foldPointlessPHINodes(BasicBlock *BB) {
auto I = BB->begin();
while (PHINode *PN = dyn_cast<PHINode>(I++)) {
if (!llvm::all_of(PN->incoming_values(), [&](const Value *V) {
return V == PN->getIncomingValue(0);
}))
continue;
if (PN->getIncomingValue(0) != PN)
PN->replaceAllUsesWith(PN->getIncomingValue(0));
else
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
PN->eraseFromParent();
}
}
};
Optional<SinkingInstructionCandidate> GVNSink::analyzeInstructionForSinking(
LockstepReverseIterator &LRI, unsigned &InstNum, unsigned &MemoryInstNum,
ModelledPHISet &NeededPHIs, SmallPtrSetImpl<Value *> &PHIContents) {
auto Insts = *LRI;
DEBUG(dbgs() << " -- Analyzing instruction set: [\n"; for (auto *I
: Insts) {
I->dump();
} dbgs() << " ]\n";);
DenseMap<uint32_t, unsigned> VNums;
for (auto *I : Insts) {
uint32_t N = VN.lookupOrAdd(I);
DEBUG(dbgs() << " VN=" << utohexstr(N) << " for" << *I << "\n");
if (N == ~0U)
return None;
VNums[N]++;
}
unsigned VNumToSink =
std::max_element(VNums.begin(), VNums.end(),
[](const std::pair<uint32_t, unsigned> &I,
const std::pair<uint32_t, unsigned> &J) {
return I.second < J.second;
})
->first;
if (VNums[VNumToSink] == 1)
// Can't sink anything!
return None;
// Now restrict the number of incoming blocks down to only those with
// VNumToSink.
auto &ActivePreds = LRI.getActiveBlocks();
unsigned InitialActivePredSize = ActivePreds.size();
SmallVector<Instruction *, 4> NewInsts;
for (auto *I : Insts) {
if (VN.lookup(I) != VNumToSink)
ActivePreds.remove(I->getParent());
else
NewInsts.push_back(I);
}
for (auto *I : NewInsts)
if (isInstructionBlacklisted(I))
return None;
// If we've restricted the incoming blocks, restrict all needed PHIs also
// to that set.
bool RecomputePHIContents = false;
if (ActivePreds.size() != InitialActivePredSize) {
ModelledPHISet NewNeededPHIs;
for (auto P : NeededPHIs) {
P.restrictToBlocks(ActivePreds);
NewNeededPHIs.insert(P);
}
NeededPHIs = NewNeededPHIs;
LRI.restrictToBlocks(ActivePreds);
RecomputePHIContents = true;
}
// The sunk instruction's results.
ModelledPHI NewPHI(NewInsts, ActivePreds);
// Does sinking this instruction render previous PHIs redundant?
if (NeededPHIs.find(NewPHI) != NeededPHIs.end()) {
NeededPHIs.erase(NewPHI);
RecomputePHIContents = true;
}
if (RecomputePHIContents) {
// The needed PHIs have changed, so recompute the set of all needed
// values.
PHIContents.clear();
for (auto &PHI : NeededPHIs)
PHIContents.insert(PHI.getValues().begin(), PHI.getValues().end());
}
// Is this instruction required by a later PHI that doesn't match this PHI?
// if so, we can't sink this instruction.
for (auto *V : NewPHI.getValues())
if (PHIContents.count(V))
// V exists in this PHI, but the whole PHI is different to NewPHI
// (else it would have been removed earlier). We cannot continue
// because this isn't representable.
return None;
// Which operands need PHIs?
// FIXME: If any of these fail, we should partition up the candidates to
// try and continue making progress.
Instruction *I0 = NewInsts[0];
for (unsigned OpNum = 0, E = I0->getNumOperands(); OpNum != E; ++OpNum) {
ModelledPHI PHI(NewInsts, OpNum, ActivePreds);
if (PHI.areAllIncomingValuesSame())
continue;
if (!canReplaceOperandWithVariable(I0, OpNum))
// We can 't create a PHI from this instruction!
return None;
if (NeededPHIs.count(PHI))
continue;
if (!PHI.areAllIncomingValuesSameType())
return None;
// Don't create indirect calls! The called value is the final operand.
if ((isa<CallInst>(I0) || isa<InvokeInst>(I0)) && OpNum == E - 1 &&
PHI.areAnyIncomingValuesConstant())
return None;
NeededPHIs.reserve(NeededPHIs.size());
NeededPHIs.insert(PHI);
PHIContents.insert(PHI.getValues().begin(), PHI.getValues().end());
}
if (isMemoryInst(NewInsts[0]))
++MemoryInstNum;
SinkingInstructionCandidate Cand;
Cand.NumInstructions = ++InstNum;
Cand.NumMemoryInsts = MemoryInstNum;
Cand.NumBlocks = ActivePreds.size();
Cand.NumPHIs = NeededPHIs.size();
for (auto *C : ActivePreds)
Cand.Blocks.push_back(C);
return Cand;
}
unsigned GVNSink::sinkBB(BasicBlock *BBEnd) {
DEBUG(dbgs() << "GVNSink: running on basic block ";
BBEnd->printAsOperand(dbgs()); dbgs() << "\n");
SmallVector<BasicBlock *, 4> Preds;
for (auto *B : predecessors(BBEnd)) {
auto *T = B->getTerminator();
if (isa<BranchInst>(T) || isa<SwitchInst>(T))
Preds.push_back(B);
else
return 0;
}
if (Preds.size() < 2)
return 0;
std::sort(Preds.begin(), Preds.end());
unsigned NumOrigPreds = Preds.size();
// We can only sink instructions through unconditional branches.
for (auto I = Preds.begin(); I != Preds.end();) {
if ((*I)->getTerminator()->getNumSuccessors() != 1)
I = Preds.erase(I);
else
++I;
}
LockstepReverseIterator LRI(Preds);
SmallVector<SinkingInstructionCandidate, 4> Candidates;
unsigned InstNum = 0, MemoryInstNum = 0;
ModelledPHISet NeededPHIs;
SmallPtrSet<Value *, 4> PHIContents;
analyzeInitialPHIs(BBEnd, NeededPHIs, PHIContents);
unsigned NumOrigPHIs = NeededPHIs.size();
while (LRI.isValid()) {
auto Cand = analyzeInstructionForSinking(LRI, InstNum, MemoryInstNum,
NeededPHIs, PHIContents);
if (!Cand)
break;
Cand->calculateCost(NumOrigPHIs, Preds.size());
Candidates.emplace_back(*Cand);
--LRI;
}
std::stable_sort(
Candidates.begin(), Candidates.end(),
[](const SinkingInstructionCandidate &A,
const SinkingInstructionCandidate &B) { return A > B; });
DEBUG(dbgs() << " -- Sinking candidates:\n"; for (auto &C
: Candidates) dbgs()
<< " " << C << "\n";);
// Pick the top candidate, as long it is positive!
if (Candidates.empty() || Candidates.front().Cost <= 0)
return 0;
auto C = Candidates.front();
DEBUG(dbgs() << " -- Sinking: " << C << "\n");
BasicBlock *InsertBB = BBEnd;
if (C.Blocks.size() < NumOrigPreds) {
DEBUG(dbgs() << " -- Splitting edge to "; BBEnd->printAsOperand(dbgs());
dbgs() << "\n");
InsertBB = SplitBlockPredecessors(BBEnd, C.Blocks, ".gvnsink.split");
if (!InsertBB) {
DEBUG(dbgs() << " -- FAILED to split edge!\n");
// Edge couldn't be split.
return 0;
}
}
for (unsigned I = 0; I < C.NumInstructions; ++I)
sinkLastInstruction(C.Blocks, InsertBB);
return C.NumInstructions;
}
void GVNSink::sinkLastInstruction(ArrayRef<BasicBlock *> Blocks,
BasicBlock *BBEnd) {
SmallVector<Instruction *, 4> Insts;
for (BasicBlock *BB : Blocks)
Insts.push_back(BB->getTerminator()->getPrevNode());
Instruction *I0 = Insts.front();
SmallVector<Value *, 4> NewOperands;
for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) {
bool NeedPHI = llvm::any_of(Insts, [&I0, O](const Instruction *I) {
return I->getOperand(O) != I0->getOperand(O);
});
if (!NeedPHI) {
NewOperands.push_back(I0->getOperand(O));
continue;
}
// Create a new PHI in the successor block and populate it.
auto *Op = I0->getOperand(O);
assert(!Op->getType()->isTokenTy() && "Can't PHI tokens!");
auto *PN = PHINode::Create(Op->getType(), Insts.size(),
Op->getName() + ".sink", &BBEnd->front());
for (auto *I : Insts)
PN->addIncoming(I->getOperand(O), I->getParent());
NewOperands.push_back(PN);
}
// Arbitrarily use I0 as the new "common" instruction; remap its operands
// and move it to the start of the successor block.
for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O)
I0->getOperandUse(O).set(NewOperands[O]);
I0->moveBefore(&*BBEnd->getFirstInsertionPt());
// Update metadata and IR flags.
for (auto *I : Insts)
if (I != I0) {
combineMetadataForCSE(I0, I);
I0->andIRFlags(I);
}
for (auto *I : Insts)
if (I != I0)
I->replaceAllUsesWith(I0);
foldPointlessPHINodes(BBEnd);
// Finally nuke all instructions apart from the common instruction.
for (auto *I : Insts)
if (I != I0)
I->eraseFromParent();
NumRemoved += Insts.size() - 1;
}
////////////////////////////////////////////////////////////////////////////////
// Pass machinery / boilerplate
class GVNSinkLegacyPass : public FunctionPass {
public:
static char ID;
GVNSinkLegacyPass() : FunctionPass(ID) {
initializeGVNSinkLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
GVNSink G;
return G.run(F);
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addPreserved<GlobalsAAWrapperPass>();
}
};
} // end anonymous namespace
PreservedAnalyses GVNSinkPass::run(Function &F, FunctionAnalysisManager &AM) {
GVNSink G;
if (!G.run(F))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<GlobalsAA>();
return PA;
}
char GVNSinkLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(GVNSinkLegacyPass, "gvn-sink",
"Early GVN sinking of Expressions", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)
INITIALIZE_PASS_END(GVNSinkLegacyPass, "gvn-sink",
"Early GVN sinking of Expressions", false, false)
FunctionPass *llvm::createGVNSinkPass() { return new GVNSinkLegacyPass(); }
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