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//===- LoadStoreVectorizer.cpp - GPU Load & Store Vectorizer --------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass merges loads/stores to/from sequential memory addresses into vector
// loads/stores. Although there's nothing GPU-specific in here, this pass is
// motivated by the microarchitectural quirks of nVidia and AMD GPUs.
//
// (For simplicity below we talk about loads only, but everything also applies
// to stores.)
//
// This pass is intended to be run late in the pipeline, after other
// vectorization opportunities have been exploited. So the assumption here is
// that immediately following our new vector load we'll need to extract out the
// individual elements of the load, so we can operate on them individually.
//
// On CPUs this transformation is usually not beneficial, because extracting the
// elements of a vector register is expensive on most architectures. It's
// usually better just to load each element individually into its own scalar
// register.
//
// However, nVidia and AMD GPUs don't have proper vector registers. Instead, a
// "vector load" loads directly into a series of scalar registers. In effect,
// extracting the elements of the vector is free. It's therefore always
// beneficial to vectorize a sequence of loads on these architectures.
//
// Vectorizing (perhaps a better name might be "coalescing") loads can have
// large performance impacts on GPU kernels, and opportunities for vectorizing
// are common in GPU code. This pass tries very hard to find such
// opportunities; its runtime is quadratic in the number of loads in a BB.
//
// Some CPU architectures, such as ARM, have instructions that load into
// multiple scalar registers, similar to a GPU vectorized load. In theory ARM
// could use this pass (with some modifications), but currently it implements
// its own pass to do something similar to what we do here.
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/MapVector.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/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/OrderedBasicBlock.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Vectorize.h"
#include "llvm/Transforms/Vectorize/LoadStoreVectorizer.h"
#include <algorithm>
#include <cassert>
#include <cstdlib>
#include <tuple>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "load-store-vectorizer"
STATISTIC(NumVectorInstructions, "Number of vector accesses generated");
STATISTIC(NumScalarsVectorized, "Number of scalar accesses vectorized");
// FIXME: Assuming stack alignment of 4 is always good enough
static const unsigned StackAdjustedAlignment = 4;
namespace {
/// ChainID is an arbitrary token that is allowed to be different only for the
/// accesses that are guaranteed to be considered non-consecutive by
/// Vectorizer::isConsecutiveAccess. It's used for grouping instructions
/// together and reducing the number of instructions the main search operates on
/// at a time, i.e. this is to reduce compile time and nothing else as the main
/// search has O(n^2) time complexity. The underlying type of ChainID should not
/// be relied upon.
using ChainID = const Value *;
using InstrList = SmallVector<Instruction *, 8>;
using InstrListMap = MapVector<ChainID, InstrList>;
class Vectorizer {
Function &F;
AliasAnalysis &AA;
DominatorTree &DT;
ScalarEvolution &SE;
TargetTransformInfo &TTI;
const DataLayout &DL;
IRBuilder<> Builder;
public:
Vectorizer(Function &F, AliasAnalysis &AA, DominatorTree &DT,
ScalarEvolution &SE, TargetTransformInfo &TTI)
: F(F), AA(AA), DT(DT), SE(SE), TTI(TTI),
DL(F.getParent()->getDataLayout()), Builder(SE.getContext()) {}
bool run();
private:
unsigned getPointerAddressSpace(Value *I);
unsigned getAlignment(LoadInst *LI) const {
unsigned Align = LI->getAlignment();
if (Align != 0)
return Align;
return DL.getABITypeAlignment(LI->getType());
}
unsigned getAlignment(StoreInst *SI) const {
unsigned Align = SI->getAlignment();
if (Align != 0)
return Align;
return DL.getABITypeAlignment(SI->getValueOperand()->getType());
}
static const unsigned MaxDepth = 3;
bool isConsecutiveAccess(Value *A, Value *B);
bool areConsecutivePointers(Value *PtrA, Value *PtrB, const APInt &PtrDelta,
unsigned Depth = 0) const;
bool lookThroughComplexAddresses(Value *PtrA, Value *PtrB, APInt PtrDelta,
unsigned Depth) const;
bool lookThroughSelects(Value *PtrA, Value *PtrB, const APInt &PtrDelta,
unsigned Depth) const;
/// After vectorization, reorder the instructions that I depends on
/// (the instructions defining its operands), to ensure they dominate I.
void reorder(Instruction *I);
/// Returns the first and the last instructions in Chain.
std::pair<BasicBlock::iterator, BasicBlock::iterator>
getBoundaryInstrs(ArrayRef<Instruction *> Chain);
/// Erases the original instructions after vectorizing.
void eraseInstructions(ArrayRef<Instruction *> Chain);
/// "Legalize" the vector type that would be produced by combining \p
/// ElementSizeBits elements in \p Chain. Break into two pieces such that the
/// total size of each piece is 1, 2 or a multiple of 4 bytes. \p Chain is
/// expected to have more than 4 elements.
std::pair<ArrayRef<Instruction *>, ArrayRef<Instruction *>>
splitOddVectorElts(ArrayRef<Instruction *> Chain, unsigned ElementSizeBits);
/// Finds the largest prefix of Chain that's vectorizable, checking for
/// intervening instructions which may affect the memory accessed by the
/// instructions within Chain.
///
/// The elements of \p Chain must be all loads or all stores and must be in
/// address order.
ArrayRef<Instruction *> getVectorizablePrefix(ArrayRef<Instruction *> Chain);
/// Collects load and store instructions to vectorize.
std::pair<InstrListMap, InstrListMap> collectInstructions(BasicBlock *BB);
/// Processes the collected instructions, the \p Map. The values of \p Map
/// should be all loads or all stores.
bool vectorizeChains(InstrListMap &Map);
/// Finds the load/stores to consecutive memory addresses and vectorizes them.
bool vectorizeInstructions(ArrayRef<Instruction *> Instrs);
/// Vectorizes the load instructions in Chain.
bool
vectorizeLoadChain(ArrayRef<Instruction *> Chain,
SmallPtrSet<Instruction *, 16> *InstructionsProcessed);
/// Vectorizes the store instructions in Chain.
bool
vectorizeStoreChain(ArrayRef<Instruction *> Chain,
SmallPtrSet<Instruction *, 16> *InstructionsProcessed);
/// Check if this load/store access is misaligned accesses.
bool accessIsMisaligned(unsigned SzInBytes, unsigned AddressSpace,
unsigned Alignment);
};
class LoadStoreVectorizerLegacyPass : public FunctionPass {
public:
static char ID;
LoadStoreVectorizerLegacyPass() : FunctionPass(ID) {
initializeLoadStoreVectorizerLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
StringRef getPassName() const override {
return "GPU Load and Store Vectorizer";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AAResultsWrapperPass>();
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.setPreservesCFG();
}
};
} // end anonymous namespace
char LoadStoreVectorizerLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(LoadStoreVectorizerLegacyPass, DEBUG_TYPE,
"Vectorize load and Store instructions", false, false)
INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_END(LoadStoreVectorizerLegacyPass, DEBUG_TYPE,
"Vectorize load and store instructions", false, false)
Pass *llvm::createLoadStoreVectorizerPass() {
return new LoadStoreVectorizerLegacyPass();
}
bool LoadStoreVectorizerLegacyPass::runOnFunction(Function &F) {
// Don't vectorize when the attribute NoImplicitFloat is used.
if (skipFunction(F) || F.hasFnAttribute(Attribute::NoImplicitFloat))
return false;
AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
TargetTransformInfo &TTI =
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
Vectorizer V(F, AA, DT, SE, TTI);
return V.run();
}
PreservedAnalyses LoadStoreVectorizerPass::run(Function &F, FunctionAnalysisManager &AM) {
// Don't vectorize when the attribute NoImplicitFloat is used.
if (F.hasFnAttribute(Attribute::NoImplicitFloat))
return PreservedAnalyses::all();
AliasAnalysis &AA = AM.getResult<AAManager>(F);
DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
ScalarEvolution &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
TargetTransformInfo &TTI = AM.getResult<TargetIRAnalysis>(F);
Vectorizer V(F, AA, DT, SE, TTI);
bool Changed = V.run();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return Changed ? PA : PreservedAnalyses::all();
}
// The real propagateMetadata expects a SmallVector<Value*>, but we deal in
// vectors of Instructions.
static void propagateMetadata(Instruction *I, ArrayRef<Instruction *> IL) {
SmallVector<Value *, 8> VL(IL.begin(), IL.end());
propagateMetadata(I, VL);
}
// Vectorizer Implementation
bool Vectorizer::run() {
bool Changed = false;
// Scan the blocks in the function in post order.
for (BasicBlock *BB : post_order(&F)) {
InstrListMap LoadRefs, StoreRefs;
std::tie(LoadRefs, StoreRefs) = collectInstructions(BB);
Changed |= vectorizeChains(LoadRefs);
Changed |= vectorizeChains(StoreRefs);
}
return Changed;
}
unsigned Vectorizer::getPointerAddressSpace(Value *I) {
if (LoadInst *L = dyn_cast<LoadInst>(I))
return L->getPointerAddressSpace();
if (StoreInst *S = dyn_cast<StoreInst>(I))
return S->getPointerAddressSpace();
return -1;
}
// FIXME: Merge with llvm::isConsecutiveAccess
bool Vectorizer::isConsecutiveAccess(Value *A, Value *B) {
Value *PtrA = getLoadStorePointerOperand(A);
Value *PtrB = getLoadStorePointerOperand(B);
unsigned ASA = getPointerAddressSpace(A);
unsigned ASB = getPointerAddressSpace(B);
// Check that the address spaces match and that the pointers are valid.
if (!PtrA || !PtrB || (ASA != ASB))
return false;
// Make sure that A and B are different pointers of the same size type.
Type *PtrATy = PtrA->getType()->getPointerElementType();
Type *PtrBTy = PtrB->getType()->getPointerElementType();
if (PtrA == PtrB ||
PtrATy->isVectorTy() != PtrBTy->isVectorTy() ||
DL.getTypeStoreSize(PtrATy) != DL.getTypeStoreSize(PtrBTy) ||
DL.getTypeStoreSize(PtrATy->getScalarType()) !=
DL.getTypeStoreSize(PtrBTy->getScalarType()))
return false;
unsigned PtrBitWidth = DL.getPointerSizeInBits(ASA);
APInt Size(PtrBitWidth, DL.getTypeStoreSize(PtrATy));
return areConsecutivePointers(PtrA, PtrB, Size);
}
bool Vectorizer::areConsecutivePointers(Value *PtrA, Value *PtrB,
const APInt &PtrDelta,
unsigned Depth) const {
unsigned PtrBitWidth = DL.getPointerTypeSizeInBits(PtrA->getType());
APInt OffsetA(PtrBitWidth, 0);
APInt OffsetB(PtrBitWidth, 0);
PtrA = PtrA->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetA);
PtrB = PtrB->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetB);
APInt OffsetDelta = OffsetB - OffsetA;
// Check if they are based on the same pointer. That makes the offsets
// sufficient.
if (PtrA == PtrB)
return OffsetDelta == PtrDelta;
// Compute the necessary base pointer delta to have the necessary final delta
// equal to the pointer delta requested.
APInt BaseDelta = PtrDelta - OffsetDelta;
// Compute the distance with SCEV between the base pointers.
const SCEV *PtrSCEVA = SE.getSCEV(PtrA);
const SCEV *PtrSCEVB = SE.getSCEV(PtrB);
const SCEV *C = SE.getConstant(BaseDelta);
const SCEV *X = SE.getAddExpr(PtrSCEVA, C);
if (X == PtrSCEVB)
return true;
// The above check will not catch the cases where one of the pointers is
// factorized but the other one is not, such as (C + (S * (A + B))) vs
// (AS + BS). Get the minus scev. That will allow re-combining the expresions
// and getting the simplified difference.
const SCEV *Dist = SE.getMinusSCEV(PtrSCEVB, PtrSCEVA);
if (C == Dist)
return true;
// Sometimes even this doesn't work, because SCEV can't always see through
// patterns that look like (gep (ext (add (shl X, C1), C2))). Try checking
// things the hard way.
return lookThroughComplexAddresses(PtrA, PtrB, BaseDelta, Depth);
}
bool Vectorizer::lookThroughComplexAddresses(Value *PtrA, Value *PtrB,
APInt PtrDelta,
unsigned Depth) const {
auto *GEPA = dyn_cast<GetElementPtrInst>(PtrA);
auto *GEPB = dyn_cast<GetElementPtrInst>(PtrB);
if (!GEPA || !GEPB)
return lookThroughSelects(PtrA, PtrB, PtrDelta, Depth);
// Look through GEPs after checking they're the same except for the last
// index.
if (GEPA->getNumOperands() != GEPB->getNumOperands() ||
GEPA->getPointerOperand() != GEPB->getPointerOperand())
return false;
gep_type_iterator GTIA = gep_type_begin(GEPA);
gep_type_iterator GTIB = gep_type_begin(GEPB);
for (unsigned I = 0, E = GEPA->getNumIndices() - 1; I < E; ++I) {
if (GTIA.getOperand() != GTIB.getOperand())
return false;
++GTIA;
++GTIB;
}
Instruction *OpA = dyn_cast<Instruction>(GTIA.getOperand());
Instruction *OpB = dyn_cast<Instruction>(GTIB.getOperand());
if (!OpA || !OpB || OpA->getOpcode() != OpB->getOpcode() ||
OpA->getType() != OpB->getType())
return false;
if (PtrDelta.isNegative()) {
if (PtrDelta.isMinSignedValue())
return false;
PtrDelta.negate();
std::swap(OpA, OpB);
}
uint64_t Stride = DL.getTypeAllocSize(GTIA.getIndexedType());
if (PtrDelta.urem(Stride) != 0)
return false;
unsigned IdxBitWidth = OpA->getType()->getScalarSizeInBits();
APInt IdxDiff = PtrDelta.udiv(Stride).zextOrSelf(IdxBitWidth);
// Only look through a ZExt/SExt.
if (!isa<SExtInst>(OpA) && !isa<ZExtInst>(OpA))
return false;
bool Signed = isa<SExtInst>(OpA);
// At this point A could be a function parameter, i.e. not an instruction
Value *ValA = OpA->getOperand(0);
OpB = dyn_cast<Instruction>(OpB->getOperand(0));
if (!OpB || ValA->getType() != OpB->getType())
return false;
// Now we need to prove that adding IdxDiff to ValA won't overflow.
bool Safe = false;
// First attempt: if OpB is an add with NSW/NUW, and OpB is IdxDiff added to
// ValA, we're okay.
if (OpB->getOpcode() == Instruction::Add &&
isa<ConstantInt>(OpB->getOperand(1)) &&
IdxDiff.sle(cast<ConstantInt>(OpB->getOperand(1))->getSExtValue())) {
if (Signed)
Safe = cast<BinaryOperator>(OpB)->hasNoSignedWrap();
else
Safe = cast<BinaryOperator>(OpB)->hasNoUnsignedWrap();
}
unsigned BitWidth = ValA->getType()->getScalarSizeInBits();
// Second attempt:
// If all set bits of IdxDiff or any higher order bit other than the sign bit
// are known to be zero in ValA, we can add Diff to it while guaranteeing no
// overflow of any sort.
if (!Safe) {
OpA = dyn_cast<Instruction>(ValA);
if (!OpA)
return false;
KnownBits Known(BitWidth);
computeKnownBits(OpA, Known, DL, 0, nullptr, OpA, &DT);
APInt BitsAllowedToBeSet = Known.Zero.zext(IdxDiff.getBitWidth());
if (Signed)
BitsAllowedToBeSet.clearBit(BitWidth - 1);
if (BitsAllowedToBeSet.ult(IdxDiff))
return false;
}
const SCEV *OffsetSCEVA = SE.getSCEV(ValA);
const SCEV *OffsetSCEVB = SE.getSCEV(OpB);
const SCEV *C = SE.getConstant(IdxDiff.trunc(BitWidth));
const SCEV *X = SE.getAddExpr(OffsetSCEVA, C);
return X == OffsetSCEVB;
}
bool Vectorizer::lookThroughSelects(Value *PtrA, Value *PtrB,
const APInt &PtrDelta,
unsigned Depth) const {
if (Depth++ == MaxDepth)
return false;
if (auto *SelectA = dyn_cast<SelectInst>(PtrA)) {
if (auto *SelectB = dyn_cast<SelectInst>(PtrB)) {
return SelectA->getCondition() == SelectB->getCondition() &&
areConsecutivePointers(SelectA->getTrueValue(),
SelectB->getTrueValue(), PtrDelta, Depth) &&
areConsecutivePointers(SelectA->getFalseValue(),
SelectB->getFalseValue(), PtrDelta, Depth);
}
}
return false;
}
void Vectorizer::reorder(Instruction *I) {
OrderedBasicBlock OBB(I->getParent());
SmallPtrSet<Instruction *, 16> InstructionsToMove;
SmallVector<Instruction *, 16> Worklist;
Worklist.push_back(I);
while (!Worklist.empty()) {
Instruction *IW = Worklist.pop_back_val();
int NumOperands = IW->getNumOperands();
for (int i = 0; i < NumOperands; i++) {
Instruction *IM = dyn_cast<Instruction>(IW->getOperand(i));
if (!IM || IM->getOpcode() == Instruction::PHI)
continue;
// If IM is in another BB, no need to move it, because this pass only
// vectorizes instructions within one BB.
if (IM->getParent() != I->getParent())
continue;
if (!OBB.dominates(IM, I)) {
InstructionsToMove.insert(IM);
Worklist.push_back(IM);
}
}
}
// All instructions to move should follow I. Start from I, not from begin().
for (auto BBI = I->getIterator(), E = I->getParent()->end(); BBI != E;
++BBI) {
if (!InstructionsToMove.count(&*BBI))
continue;
Instruction *IM = &*BBI;
--BBI;
IM->removeFromParent();
IM->insertBefore(I);
}
}
std::pair<BasicBlock::iterator, BasicBlock::iterator>
Vectorizer::getBoundaryInstrs(ArrayRef<Instruction *> Chain) {
Instruction *C0 = Chain[0];
BasicBlock::iterator FirstInstr = C0->getIterator();
BasicBlock::iterator LastInstr = C0->getIterator();
BasicBlock *BB = C0->getParent();
unsigned NumFound = 0;
for (Instruction &I : *BB) {
if (!is_contained(Chain, &I))
continue;
++NumFound;
if (NumFound == 1) {
FirstInstr = I.getIterator();
}
if (NumFound == Chain.size()) {
LastInstr = I.getIterator();
break;
}
}
// Range is [first, last).
return std::make_pair(FirstInstr, ++LastInstr);
}
void Vectorizer::eraseInstructions(ArrayRef<Instruction *> Chain) {
SmallVector<Instruction *, 16> Instrs;
for (Instruction *I : Chain) {
Value *PtrOperand = getLoadStorePointerOperand(I);
assert(PtrOperand && "Instruction must have a pointer operand.");
Instrs.push_back(I);
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(PtrOperand))
Instrs.push_back(GEP);
}
// Erase instructions.
for (Instruction *I : Instrs)
if (I->use_empty())
I->eraseFromParent();
}
std::pair<ArrayRef<Instruction *>, ArrayRef<Instruction *>>
Vectorizer::splitOddVectorElts(ArrayRef<Instruction *> Chain,
unsigned ElementSizeBits) {
unsigned ElementSizeBytes = ElementSizeBits / 8;
unsigned SizeBytes = ElementSizeBytes * Chain.size();
unsigned NumLeft = (SizeBytes - (SizeBytes % 4)) / ElementSizeBytes;
if (NumLeft == Chain.size()) {
if ((NumLeft & 1) == 0)
NumLeft /= 2; // Split even in half
else
--NumLeft; // Split off last element
} else if (NumLeft == 0)
NumLeft = 1;
return std::make_pair(Chain.slice(0, NumLeft), Chain.slice(NumLeft));
}
ArrayRef<Instruction *>
Vectorizer::getVectorizablePrefix(ArrayRef<Instruction *> Chain) {
// These are in BB order, unlike Chain, which is in address order.
SmallVector<Instruction *, 16> MemoryInstrs;
SmallVector<Instruction *, 16> ChainInstrs;
bool IsLoadChain = isa<LoadInst>(Chain[0]);
LLVM_DEBUG({
for (Instruction *I : Chain) {
if (IsLoadChain)
assert(isa<LoadInst>(I) &&
"All elements of Chain must be loads, or all must be stores.");
else
assert(isa<StoreInst>(I) &&
"All elements of Chain must be loads, or all must be stores.");
}
});
for (Instruction &I : make_range(getBoundaryInstrs(Chain))) {
if (isa<LoadInst>(I) || isa<StoreInst>(I)) {
if (!is_contained(Chain, &I))
MemoryInstrs.push_back(&I);
else
ChainInstrs.push_back(&I);
} else if (isa<IntrinsicInst>(&I) &&
cast<IntrinsicInst>(&I)->getIntrinsicID() ==
Intrinsic::sideeffect) {
// Ignore llvm.sideeffect calls.
} else if (IsLoadChain && (I.mayWriteToMemory() || I.mayThrow())) {
LLVM_DEBUG(dbgs() << "LSV: Found may-write/throw operation: " << I
<< '\n');
break;
} else if (!IsLoadChain && (I.mayReadOrWriteMemory() || I.mayThrow())) {
LLVM_DEBUG(dbgs() << "LSV: Found may-read/write/throw operation: " << I
<< '\n');
break;
}
}
OrderedBasicBlock OBB(Chain[0]->getParent());
// Loop until we find an instruction in ChainInstrs that we can't vectorize.
unsigned ChainInstrIdx = 0;
Instruction *BarrierMemoryInstr = nullptr;
for (unsigned E = ChainInstrs.size(); ChainInstrIdx < E; ++ChainInstrIdx) {
Instruction *ChainInstr = ChainInstrs[ChainInstrIdx];
// If a barrier memory instruction was found, chain instructions that follow
// will not be added to the valid prefix.
if (BarrierMemoryInstr && OBB.dominates(BarrierMemoryInstr, ChainInstr))
break;
// Check (in BB order) if any instruction prevents ChainInstr from being
// vectorized. Find and store the first such "conflicting" instruction.
for (Instruction *MemInstr : MemoryInstrs) {
// If a barrier memory instruction was found, do not check past it.
if (BarrierMemoryInstr && OBB.dominates(BarrierMemoryInstr, MemInstr))
break;
auto *MemLoad = dyn_cast<LoadInst>(MemInstr);
auto *ChainLoad = dyn_cast<LoadInst>(ChainInstr);
if (MemLoad && ChainLoad)
continue;
// We can ignore the alias if the we have a load store pair and the load
// is known to be invariant. The load cannot be clobbered by the store.
auto IsInvariantLoad = [](const LoadInst *LI) -> bool {
return LI->getMetadata(LLVMContext::MD_invariant_load);
};
// We can ignore the alias as long as the load comes before the store,
// because that means we won't be moving the load past the store to
// vectorize it (the vectorized load is inserted at the location of the
// first load in the chain).
if (isa<StoreInst>(MemInstr) && ChainLoad &&
(IsInvariantLoad(ChainLoad) || OBB.dominates(ChainLoad, MemInstr)))
continue;
// Same case, but in reverse.
if (MemLoad && isa<StoreInst>(ChainInstr) &&
(IsInvariantLoad(MemLoad) || OBB.dominates(MemLoad, ChainInstr)))
continue;
if (!AA.isNoAlias(MemoryLocation::get(MemInstr),
MemoryLocation::get(ChainInstr))) {
LLVM_DEBUG({
dbgs() << "LSV: Found alias:\n"
" Aliasing instruction and pointer:\n"
<< " " << *MemInstr << '\n'
<< " " << *getLoadStorePointerOperand(MemInstr) << '\n'
<< " Aliased instruction and pointer:\n"
<< " " << *ChainInstr << '\n'
<< " " << *getLoadStorePointerOperand(ChainInstr) << '\n';
});
// Save this aliasing memory instruction as a barrier, but allow other
// instructions that precede the barrier to be vectorized with this one.
BarrierMemoryInstr = MemInstr;
break;
}
}
// Continue the search only for store chains, since vectorizing stores that
// precede an aliasing load is valid. Conversely, vectorizing loads is valid
// up to an aliasing store, but should not pull loads from further down in
// the basic block.
if (IsLoadChain && BarrierMemoryInstr) {
// The BarrierMemoryInstr is a store that precedes ChainInstr.
assert(OBB.dominates(BarrierMemoryInstr, ChainInstr));
break;
}
}
// Find the largest prefix of Chain whose elements are all in
// ChainInstrs[0, ChainInstrIdx). This is the largest vectorizable prefix of
// Chain. (Recall that Chain is in address order, but ChainInstrs is in BB
// order.)
SmallPtrSet<Instruction *, 8> VectorizableChainInstrs(
ChainInstrs.begin(), ChainInstrs.begin() + ChainInstrIdx);
unsigned ChainIdx = 0;
for (unsigned ChainLen = Chain.size(); ChainIdx < ChainLen; ++ChainIdx) {
if (!VectorizableChainInstrs.count(Chain[ChainIdx]))
break;
}
return Chain.slice(0, ChainIdx);
}
static ChainID getChainID(const Value *Ptr, const DataLayout &DL) {
const Value *ObjPtr = GetUnderlyingObject(Ptr, DL);
if (const auto *Sel = dyn_cast<SelectInst>(ObjPtr)) {
// The select's themselves are distinct instructions even if they share the
// same condition and evaluate to consecutive pointers for true and false
// values of the condition. Therefore using the select's themselves for
// grouping instructions would put consecutive accesses into different lists
// and they won't be even checked for being consecutive, and won't be
// vectorized.
return Sel->getCondition();
}
return ObjPtr;
}
std::pair<InstrListMap, InstrListMap>
Vectorizer::collectInstructions(BasicBlock *BB) {
InstrListMap LoadRefs;
InstrListMap StoreRefs;
for (Instruction &I : *BB) {
if (!I.mayReadOrWriteMemory())
continue;
if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
if (!LI->isSimple())
continue;
// Skip if it's not legal.
if (!TTI.isLegalToVectorizeLoad(LI))
continue;
Type *Ty = LI->getType();
if (!VectorType::isValidElementType(Ty->getScalarType()))
continue;
// Skip weird non-byte sizes. They probably aren't worth the effort of
// handling correctly.
unsigned TySize = DL.getTypeSizeInBits(Ty);
if ((TySize % 8) != 0)
continue;
// Skip vectors of pointers. The vectorizeLoadChain/vectorizeStoreChain
// functions are currently using an integer type for the vectorized
// load/store, and does not support casting between the integer type and a
// vector of pointers (e.g. i64 to <2 x i16*>)
if (Ty->isVectorTy() && Ty->isPtrOrPtrVectorTy())
continue;
Value *Ptr = LI->getPointerOperand();
unsigned AS = Ptr->getType()->getPointerAddressSpace();
unsigned VecRegSize = TTI.getLoadStoreVecRegBitWidth(AS);
unsigned VF = VecRegSize / TySize;
VectorType *VecTy = dyn_cast<VectorType>(Ty);
// No point in looking at these if they're too big to vectorize.
if (TySize > VecRegSize / 2 ||
(VecTy && TTI.getLoadVectorFactor(VF, TySize, TySize / 8, VecTy) == 0))
continue;
// Make sure all the users of a vector are constant-index extracts.
if (isa<VectorType>(Ty) && !llvm::all_of(LI->users(), [](const User *U) {
const ExtractElementInst *EEI = dyn_cast<ExtractElementInst>(U);
return EEI && isa<ConstantInt>(EEI->getOperand(1));
}))
continue;
// Save the load locations.
const ChainID ID = getChainID(Ptr, DL);
LoadRefs[ID].push_back(LI);
} else if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
if (!SI->isSimple())
continue;
// Skip if it's not legal.
if (!TTI.isLegalToVectorizeStore(SI))
continue;
Type *Ty = SI->getValueOperand()->getType();
if (!VectorType::isValidElementType(Ty->getScalarType()))
continue;
// Skip vectors of pointers. The vectorizeLoadChain/vectorizeStoreChain
// functions are currently using an integer type for the vectorized
// load/store, and does not support casting between the integer type and a
// vector of pointers (e.g. i64 to <2 x i16*>)
if (Ty->isVectorTy() && Ty->isPtrOrPtrVectorTy())
continue;
// Skip weird non-byte sizes. They probably aren't worth the effort of
// handling correctly.
unsigned TySize = DL.getTypeSizeInBits(Ty);
if ((TySize % 8) != 0)
continue;
Value *Ptr = SI->getPointerOperand();
unsigned AS = Ptr->getType()->getPointerAddressSpace();
unsigned VecRegSize = TTI.getLoadStoreVecRegBitWidth(AS);
unsigned VF = VecRegSize / TySize;
VectorType *VecTy = dyn_cast<VectorType>(Ty);
// No point in looking at these if they're too big to vectorize.
if (TySize > VecRegSize / 2 ||
(VecTy && TTI.getStoreVectorFactor(VF, TySize, TySize / 8, VecTy) == 0))
continue;
if (isa<VectorType>(Ty) && !llvm::all_of(SI->users(), [](const User *U) {
const ExtractElementInst *EEI = dyn_cast<ExtractElementInst>(U);
return EEI && isa<ConstantInt>(EEI->getOperand(1));
}))
continue;
// Save store location.
const ChainID ID = getChainID(Ptr, DL);
StoreRefs[ID].push_back(SI);
}
}
return {LoadRefs, StoreRefs};
}
bool Vectorizer::vectorizeChains(InstrListMap &Map) {
bool Changed = false;
for (const std::pair<ChainID, InstrList> &Chain : Map) {
unsigned Size = Chain.second.size();
if (Size < 2)
continue;
LLVM_DEBUG(dbgs() << "LSV: Analyzing a chain of length " << Size << ".\n");
// Process the stores in chunks of 64.
for (unsigned CI = 0, CE = Size; CI < CE; CI += 64) {
unsigned Len = std::min<unsigned>(CE - CI, 64);
ArrayRef<Instruction *> Chunk(&Chain.second[CI], Len);
Changed |= vectorizeInstructions(Chunk);
}
}
return Changed;
}
bool Vectorizer::vectorizeInstructions(ArrayRef<Instruction *> Instrs) {
LLVM_DEBUG(dbgs() << "LSV: Vectorizing " << Instrs.size()
<< " instructions.\n");
SmallVector<int, 16> Heads, Tails;
int ConsecutiveChain[64];
// Do a quadratic search on all of the given loads/stores and find all of the
// pairs of loads/stores that follow each other.
for (int i = 0, e = Instrs.size(); i < e; ++i) {
ConsecutiveChain[i] = -1;
for (int j = e - 1; j >= 0; --j) {
if (i == j)
continue;
if (isConsecutiveAccess(Instrs[i], Instrs[j])) {
if (ConsecutiveChain[i] != -1) {
int CurDistance = std::abs(ConsecutiveChain[i] - i);
int NewDistance = std::abs(ConsecutiveChain[i] - j);
if (j < i || NewDistance > CurDistance)
continue; // Should not insert.
}
Tails.push_back(j);
Heads.push_back(i);
ConsecutiveChain[i] = j;
}
}
}
bool Changed = false;
SmallPtrSet<Instruction *, 16> InstructionsProcessed;
for (int Head : Heads) {
if (InstructionsProcessed.count(Instrs[Head]))
continue;
bool LongerChainExists = false;
for (unsigned TIt = 0; TIt < Tails.size(); TIt++)
if (Head == Tails[TIt] &&
!InstructionsProcessed.count(Instrs[Heads[TIt]])) {
LongerChainExists = true;
break;
}
if (LongerChainExists)
continue;
// We found an instr that starts a chain. Now follow the chain and try to
// vectorize it.
SmallVector<Instruction *, 16> Operands;
int I = Head;
while (I != -1 && (is_contained(Tails, I) || is_contained(Heads, I))) {
if (InstructionsProcessed.count(Instrs[I]))
break;
Operands.push_back(Instrs[I]);
I = ConsecutiveChain[I];
}
bool Vectorized = false;
if (isa<LoadInst>(*Operands.begin()))
Vectorized = vectorizeLoadChain(Operands, &InstructionsProcessed);
else
Vectorized = vectorizeStoreChain(Operands, &InstructionsProcessed);
Changed |= Vectorized;
}
return Changed;
}
bool Vectorizer::vectorizeStoreChain(
ArrayRef<Instruction *> Chain,
SmallPtrSet<Instruction *, 16> *InstructionsProcessed) {
StoreInst *S0 = cast<StoreInst>(Chain[0]);
// If the vector has an int element, default to int for the whole store.
Type *StoreTy = nullptr;
for (Instruction *I : Chain) {
StoreTy = cast<StoreInst>(I)->getValueOperand()->getType();
if (StoreTy->isIntOrIntVectorTy())
break;
if (StoreTy->isPtrOrPtrVectorTy()) {
StoreTy = Type::getIntNTy(F.getParent()->getContext(),
DL.getTypeSizeInBits(StoreTy));
break;
}
}
assert(StoreTy && "Failed to find store type");
unsigned Sz = DL.getTypeSizeInBits(StoreTy);
unsigned AS = S0->getPointerAddressSpace();
unsigned VecRegSize = TTI.getLoadStoreVecRegBitWidth(AS);
unsigned VF = VecRegSize / Sz;
unsigned ChainSize = Chain.size();
unsigned Alignment = getAlignment(S0);
if (!isPowerOf2_32(Sz) || VF < 2 || ChainSize < 2) {
InstructionsProcessed->insert(Chain.begin(), Chain.end());
return false;
}
ArrayRef<Instruction *> NewChain = getVectorizablePrefix(Chain);
if (NewChain.empty()) {
// No vectorization possible.
InstructionsProcessed->insert(Chain.begin(), Chain.end());
return false;
}
if (NewChain.size() == 1) {
// Failed after the first instruction. Discard it and try the smaller chain.
InstructionsProcessed->insert(NewChain.front());
return false;
}
// Update Chain to the valid vectorizable subchain.
Chain = NewChain;
ChainSize = Chain.size();
// Check if it's legal to vectorize this chain. If not, split the chain and
// try again.
unsigned EltSzInBytes = Sz / 8;
unsigned SzInBytes = EltSzInBytes * ChainSize;
VectorType *VecTy;
VectorType *VecStoreTy = dyn_cast<VectorType>(StoreTy);
if (VecStoreTy)
VecTy = VectorType::get(StoreTy->getScalarType(),
Chain.size() * VecStoreTy->getNumElements());
else
VecTy = VectorType::get(StoreTy, Chain.size());
// If it's more than the max vector size or the target has a better
// vector factor, break it into two pieces.
unsigned TargetVF = TTI.getStoreVectorFactor(VF, Sz, SzInBytes, VecTy);
if (ChainSize > VF || (VF != TargetVF && TargetVF < ChainSize)) {
LLVM_DEBUG(dbgs() << "LSV: Chain doesn't match with the vector factor."
" Creating two separate arrays.\n");
return vectorizeStoreChain(Chain.slice(0, TargetVF),
InstructionsProcessed) |
vectorizeStoreChain(Chain.slice(TargetVF), InstructionsProcessed);
}
LLVM_DEBUG({
dbgs() << "LSV: Stores to vectorize:\n";
for (Instruction *I : Chain)
dbgs() << " " << *I << "\n";
});
// We won't try again to vectorize the elements of the chain, regardless of
// whether we succeed below.
InstructionsProcessed->insert(Chain.begin(), Chain.end());
// If the store is going to be misaligned, don't vectorize it.
if (accessIsMisaligned(SzInBytes, AS, Alignment)) {
if (S0->getPointerAddressSpace() != DL.getAllocaAddrSpace()) {
auto Chains = splitOddVectorElts(Chain, Sz);
return vectorizeStoreChain(Chains.first, InstructionsProcessed) |
vectorizeStoreChain(Chains.second, InstructionsProcessed);
}
unsigned NewAlign = getOrEnforceKnownAlignment(S0->getPointerOperand(),
StackAdjustedAlignment,
DL, S0, nullptr, &DT);
if (NewAlign != 0)
Alignment = NewAlign;
}
if (!TTI.isLegalToVectorizeStoreChain(SzInBytes, Alignment, AS)) {
auto Chains = splitOddVectorElts(Chain, Sz);
return vectorizeStoreChain(Chains.first, InstructionsProcessed) |
vectorizeStoreChain(Chains.second, InstructionsProcessed);
}
BasicBlock::iterator First, Last;
std::tie(First, Last) = getBoundaryInstrs(Chain);
Builder.SetInsertPoint(&*Last);
Value *Vec = UndefValue::get(VecTy);
if (VecStoreTy) {
unsigned VecWidth = VecStoreTy->getNumElements();
for (unsigned I = 0, E = Chain.size(); I != E; ++I) {
StoreInst *Store = cast<StoreInst>(Chain[I]);
for (unsigned J = 0, NE = VecStoreTy->getNumElements(); J != NE; ++J) {
unsigned NewIdx = J + I * VecWidth;
Value *Extract = Builder.CreateExtractElement(Store->getValueOperand(),
Builder.getInt32(J));
if (Extract->getType() != StoreTy->getScalarType())
Extract = Builder.CreateBitCast(Extract, StoreTy->getScalarType());
Value *Insert =
Builder.CreateInsertElement(Vec, Extract, Builder.getInt32(NewIdx));
Vec = Insert;
}
}
} else {
for (unsigned I = 0, E = Chain.size(); I != E; ++I) {
StoreInst *Store = cast<StoreInst>(Chain[I]);
Value *Extract = Store->getValueOperand();
if (Extract->getType() != StoreTy->getScalarType())
Extract =
Builder.CreateBitOrPointerCast(Extract, StoreTy->getScalarType());
Value *Insert =
Builder.CreateInsertElement(Vec, Extract, Builder.getInt32(I));
Vec = Insert;
}
}
StoreInst *SI = Builder.CreateAlignedStore(
Vec,
Builder.CreateBitCast(S0->getPointerOperand(), VecTy->getPointerTo(AS)),
Alignment);
propagateMetadata(SI, Chain);
eraseInstructions(Chain);
++NumVectorInstructions;
NumScalarsVectorized += Chain.size();
return true;
}
bool Vectorizer::vectorizeLoadChain(
ArrayRef<Instruction *> Chain,
SmallPtrSet<Instruction *, 16> *InstructionsProcessed) {
LoadInst *L0 = cast<LoadInst>(Chain[0]);
// If the vector has an int element, default to int for the whole load.
Type *LoadTy;
for (const auto &V : Chain) {
LoadTy = cast<LoadInst>(V)->getType();
if (LoadTy->isIntOrIntVectorTy())
break;
if (LoadTy->isPtrOrPtrVectorTy()) {
LoadTy = Type::getIntNTy(F.getParent()->getContext(),
DL.getTypeSizeInBits(LoadTy));
break;
}
}
unsigned Sz = DL.getTypeSizeInBits(LoadTy);
unsigned AS = L0->getPointerAddressSpace();
unsigned VecRegSize = TTI.getLoadStoreVecRegBitWidth(AS);
unsigned VF = VecRegSize / Sz;
unsigned ChainSize = Chain.size();
unsigned Alignment = getAlignment(L0);
if (!isPowerOf2_32(Sz) || VF < 2 || ChainSize < 2) {
InstructionsProcessed->insert(Chain.begin(), Chain.end());
return false;
}
ArrayRef<Instruction *> NewChain = getVectorizablePrefix(Chain);
if (NewChain.empty()) {
// No vectorization possible.
InstructionsProcessed->insert(Chain.begin(), Chain.end());
return false;
}
if (NewChain.size() == 1) {
// Failed after the first instruction. Discard it and try the smaller chain.
InstructionsProcessed->insert(NewChain.front());
return false;
}
// Update Chain to the valid vectorizable subchain.
Chain = NewChain;
ChainSize = Chain.size();
// Check if it's legal to vectorize this chain. If not, split the chain and
// try again.
unsigned EltSzInBytes = Sz / 8;
unsigned SzInBytes = EltSzInBytes * ChainSize;
VectorType *VecTy;
VectorType *VecLoadTy = dyn_cast<VectorType>(LoadTy);
if (VecLoadTy)
VecTy = VectorType::get(LoadTy->getScalarType(),
Chain.size() * VecLoadTy->getNumElements());
else
VecTy = VectorType::get(LoadTy, Chain.size());
// If it's more than the max vector size or the target has a better
// vector factor, break it into two pieces.
unsigned TargetVF = TTI.getLoadVectorFactor(VF, Sz, SzInBytes, VecTy);
if (ChainSize > VF || (VF != TargetVF && TargetVF < ChainSize)) {
LLVM_DEBUG(dbgs() << "LSV: Chain doesn't match with the vector factor."
" Creating two separate arrays.\n");
return vectorizeLoadChain(Chain.slice(0, TargetVF), InstructionsProcessed) |
vectorizeLoadChain(Chain.slice(TargetVF), InstructionsProcessed);
}
// We won't try again to vectorize the elements of the chain, regardless of
// whether we succeed below.
InstructionsProcessed->insert(Chain.begin(), Chain.end());
// If the load is going to be misaligned, don't vectorize it.
if (accessIsMisaligned(SzInBytes, AS, Alignment)) {
if (L0->getPointerAddressSpace() != DL.getAllocaAddrSpace()) {
auto Chains = splitOddVectorElts(Chain, Sz);
return vectorizeLoadChain(Chains.first, InstructionsProcessed) |
vectorizeLoadChain(Chains.second, InstructionsProcessed);
}
unsigned NewAlign = getOrEnforceKnownAlignment(L0->getPointerOperand(),
StackAdjustedAlignment,
DL, L0, nullptr, &DT);
if (NewAlign != 0)
Alignment = NewAlign;
Alignment = NewAlign;
}
if (!TTI.isLegalToVectorizeLoadChain(SzInBytes, Alignment, AS)) {
auto Chains = splitOddVectorElts(Chain, Sz);
return vectorizeLoadChain(Chains.first, InstructionsProcessed) |
vectorizeLoadChain(Chains.second, InstructionsProcessed);
}
LLVM_DEBUG({
dbgs() << "LSV: Loads to vectorize:\n";
for (Instruction *I : Chain)
I->dump();
});
// getVectorizablePrefix already computed getBoundaryInstrs. The value of
// Last may have changed since then, but the value of First won't have. If it
// matters, we could compute getBoundaryInstrs only once and reuse it here.
BasicBlock::iterator First, Last;
std::tie(First, Last) = getBoundaryInstrs(Chain);
Builder.SetInsertPoint(&*First);
Value *Bitcast =
Builder.CreateBitCast(L0->getPointerOperand(), VecTy->getPointerTo(AS));
LoadInst *LI = Builder.CreateAlignedLoad(VecTy, Bitcast, Alignment);
propagateMetadata(LI, Chain);
if (VecLoadTy) {
SmallVector<Instruction *, 16> InstrsToErase;
unsigned VecWidth = VecLoadTy->getNumElements();
for (unsigned I = 0, E = Chain.size(); I != E; ++I) {
for (auto Use : Chain[I]->users()) {
// All users of vector loads are ExtractElement instructions with
// constant indices, otherwise we would have bailed before now.
Instruction *UI = cast<Instruction>(Use);
unsigned Idx = cast<ConstantInt>(UI->getOperand(1))->getZExtValue();
unsigned NewIdx = Idx + I * VecWidth;
Value *V = Builder.CreateExtractElement(LI, Builder.getInt32(NewIdx),
UI->getName());
if (V->getType() != UI->getType())
V = Builder.CreateBitCast(V, UI->getType());
// Replace the old instruction.
UI->replaceAllUsesWith(V);
InstrsToErase.push_back(UI);
}
}
// Bitcast might not be an Instruction, if the value being loaded is a
// constant. In that case, no need to reorder anything.
if (Instruction *BitcastInst = dyn_cast<Instruction>(Bitcast))
reorder(BitcastInst);
for (auto I : InstrsToErase)
I->eraseFromParent();
} else {
for (unsigned I = 0, E = Chain.size(); I != E; ++I) {
Value *CV = Chain[I];
Value *V =
Builder.CreateExtractElement(LI, Builder.getInt32(I), CV->getName());
if (V->getType() != CV->getType()) {
V = Builder.CreateBitOrPointerCast(V, CV->getType());
}
// Replace the old instruction.
CV->replaceAllUsesWith(V);
}
if (Instruction *BitcastInst = dyn_cast<Instruction>(Bitcast))
reorder(BitcastInst);
}
eraseInstructions(Chain);
++NumVectorInstructions;
NumScalarsVectorized += Chain.size();
return true;
}
bool Vectorizer::accessIsMisaligned(unsigned SzInBytes, unsigned AddressSpace,
unsigned Alignment) {
if (Alignment % SzInBytes == 0)
return false;
bool Fast = false;
bool Allows = TTI.allowsMisalignedMemoryAccesses(F.getParent()->getContext(),
SzInBytes * 8, AddressSpace,
Alignment, &Fast);
LLVM_DEBUG(dbgs() << "LSV: Target said misaligned is allowed? " << Allows
<< " and fast? " << Fast << "\n";);
return !Allows || !Fast;
}