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llvm-project/llvm/lib/CodeGen/ExpandMemCmp.cpp

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//===--- ExpandMemCmp.cpp - Expand memcmp() to load/stores ----------------===//
//
// 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 tries to expand memcmp() calls into optimally-sized loads and
// compares for the target.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/LazyBlockFrequencyInfo.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/InitializePasses.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SizeOpts.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "expandmemcmp"
STATISTIC(NumMemCmpCalls, "Number of memcmp calls");
STATISTIC(NumMemCmpNotConstant, "Number of memcmp calls without constant size");
STATISTIC(NumMemCmpGreaterThanMax,
"Number of memcmp calls with size greater than max size");
STATISTIC(NumMemCmpInlined, "Number of inlined memcmp calls");
static cl::opt<unsigned> MemCmpEqZeroNumLoadsPerBlock(
"memcmp-num-loads-per-block", cl::Hidden, cl::init(1),
cl::desc("The number of loads per basic block for inline expansion of "
"memcmp that is only being compared against zero."));
static cl::opt<unsigned> MaxLoadsPerMemcmp(
"max-loads-per-memcmp", cl::Hidden,
cl::desc("Set maximum number of loads used in expanded memcmp"));
static cl::opt<unsigned> MaxLoadsPerMemcmpOptSize(
"max-loads-per-memcmp-opt-size", cl::Hidden,
cl::desc("Set maximum number of loads used in expanded memcmp for -Os/Oz"));
namespace {
// This class provides helper functions to expand a memcmp library call into an
// inline expansion.
class MemCmpExpansion {
struct ResultBlock {
BasicBlock *BB = nullptr;
PHINode *PhiSrc1 = nullptr;
PHINode *PhiSrc2 = nullptr;
ResultBlock() = default;
};
CallInst *const CI;
ResultBlock ResBlock;
const uint64_t Size;
unsigned MaxLoadSize;
uint64_t NumLoadsNonOneByte;
const uint64_t NumLoadsPerBlockForZeroCmp;
std::vector<BasicBlock *> LoadCmpBlocks;
BasicBlock *EndBlock;
PHINode *PhiRes;
const bool IsUsedForZeroCmp;
const DataLayout &DL;
IRBuilder<> Builder;
// Represents the decomposition in blocks of the expansion. For example,
// comparing 33 bytes on X86+sse can be done with 2x16-byte loads and
// 1x1-byte load, which would be represented as [{16, 0}, {16, 16}, {1, 32}.
struct LoadEntry {
LoadEntry(unsigned LoadSize, uint64_t Offset)
: LoadSize(LoadSize), Offset(Offset) {
}
// The size of the load for this block, in bytes.
unsigned LoadSize;
// The offset of this load from the base pointer, in bytes.
uint64_t Offset;
};
using LoadEntryVector = SmallVector<LoadEntry, 8>;
LoadEntryVector LoadSequence;
void createLoadCmpBlocks();
void createResultBlock();
void setupResultBlockPHINodes();
void setupEndBlockPHINodes();
Value *getCompareLoadPairs(unsigned BlockIndex, unsigned &LoadIndex);
void emitLoadCompareBlock(unsigned BlockIndex);
void emitLoadCompareBlockMultipleLoads(unsigned BlockIndex,
unsigned &LoadIndex);
void emitLoadCompareByteBlock(unsigned BlockIndex, unsigned OffsetBytes);
void emitMemCmpResultBlock();
Value *getMemCmpExpansionZeroCase();
Value *getMemCmpEqZeroOneBlock();
Value *getMemCmpOneBlock();
struct LoadPair {
Value *Lhs = nullptr;
Value *Rhs = nullptr;
};
LoadPair getLoadPair(Type *LoadSizeType, bool NeedsBSwap, Type *CmpSizeType,
unsigned OffsetBytes);
static LoadEntryVector
computeGreedyLoadSequence(uint64_t Size, llvm::ArrayRef<unsigned> LoadSizes,
unsigned MaxNumLoads, unsigned &NumLoadsNonOneByte);
static LoadEntryVector
computeOverlappingLoadSequence(uint64_t Size, unsigned MaxLoadSize,
unsigned MaxNumLoads,
unsigned &NumLoadsNonOneByte);
public:
MemCmpExpansion(CallInst *CI, uint64_t Size,
const TargetTransformInfo::MemCmpExpansionOptions &Options,
const bool IsUsedForZeroCmp, const DataLayout &TheDataLayout);
unsigned getNumBlocks();
uint64_t getNumLoads() const { return LoadSequence.size(); }
Value *getMemCmpExpansion();
};
MemCmpExpansion::LoadEntryVector MemCmpExpansion::computeGreedyLoadSequence(
uint64_t Size, llvm::ArrayRef<unsigned> LoadSizes,
const unsigned MaxNumLoads, unsigned &NumLoadsNonOneByte) {
NumLoadsNonOneByte = 0;
LoadEntryVector LoadSequence;
uint64_t Offset = 0;
while (Size && !LoadSizes.empty()) {
const unsigned LoadSize = LoadSizes.front();
const uint64_t NumLoadsForThisSize = Size / LoadSize;
if (LoadSequence.size() + NumLoadsForThisSize > MaxNumLoads) {
// Do not expand if the total number of loads is larger than what the
// target allows. Note that it's important that we exit before completing
// the expansion to avoid using a ton of memory to store the expansion for
// large sizes.
return {};
}
if (NumLoadsForThisSize > 0) {
for (uint64_t I = 0; I < NumLoadsForThisSize; ++I) {
LoadSequence.push_back({LoadSize, Offset});
Offset += LoadSize;
}
if (LoadSize > 1)
++NumLoadsNonOneByte;
Size = Size % LoadSize;
}
LoadSizes = LoadSizes.drop_front();
}
return LoadSequence;
}
MemCmpExpansion::LoadEntryVector
MemCmpExpansion::computeOverlappingLoadSequence(uint64_t Size,
const unsigned MaxLoadSize,
const unsigned MaxNumLoads,
unsigned &NumLoadsNonOneByte) {
// These are already handled by the greedy approach.
if (Size < 2 || MaxLoadSize < 2)
return {};
// We try to do as many non-overlapping loads as possible starting from the
// beginning.
const uint64_t NumNonOverlappingLoads = Size / MaxLoadSize;
assert(NumNonOverlappingLoads && "there must be at least one load");
// There remain 0 to (MaxLoadSize - 1) bytes to load, this will be done with
// an overlapping load.
Size = Size - NumNonOverlappingLoads * MaxLoadSize;
// Bail if we do not need an overloapping store, this is already handled by
// the greedy approach.
if (Size == 0)
return {};
// Bail if the number of loads (non-overlapping + potential overlapping one)
// is larger than the max allowed.
if ((NumNonOverlappingLoads + 1) > MaxNumLoads)
return {};
// Add non-overlapping loads.
LoadEntryVector LoadSequence;
uint64_t Offset = 0;
for (uint64_t I = 0; I < NumNonOverlappingLoads; ++I) {
LoadSequence.push_back({MaxLoadSize, Offset});
Offset += MaxLoadSize;
}
// Add the last overlapping load.
assert(Size > 0 && Size < MaxLoadSize && "broken invariant");
LoadSequence.push_back({MaxLoadSize, Offset - (MaxLoadSize - Size)});
NumLoadsNonOneByte = 1;
return LoadSequence;
}
// Initialize the basic block structure required for expansion of memcmp call
// with given maximum load size and memcmp size parameter.
// This structure includes:
// 1. A list of load compare blocks - LoadCmpBlocks.
// 2. An EndBlock, split from original instruction point, which is the block to
// return from.
// 3. ResultBlock, block to branch to for early exit when a
// LoadCmpBlock finds a difference.
MemCmpExpansion::MemCmpExpansion(
CallInst *const CI, uint64_t Size,
const TargetTransformInfo::MemCmpExpansionOptions &Options,
const bool IsUsedForZeroCmp, const DataLayout &TheDataLayout)
: CI(CI), Size(Size), MaxLoadSize(0), NumLoadsNonOneByte(0),
NumLoadsPerBlockForZeroCmp(Options.NumLoadsPerBlock),
IsUsedForZeroCmp(IsUsedForZeroCmp), DL(TheDataLayout), Builder(CI) {
assert(Size > 0 && "zero blocks");
// Scale the max size down if the target can load more bytes than we need.
llvm::ArrayRef<unsigned> LoadSizes(Options.LoadSizes);
while (!LoadSizes.empty() && LoadSizes.front() > Size) {
LoadSizes = LoadSizes.drop_front();
}
assert(!LoadSizes.empty() && "cannot load Size bytes");
MaxLoadSize = LoadSizes.front();
// Compute the decomposition.
unsigned GreedyNumLoadsNonOneByte = 0;
LoadSequence = computeGreedyLoadSequence(Size, LoadSizes, Options.MaxNumLoads,
GreedyNumLoadsNonOneByte);
NumLoadsNonOneByte = GreedyNumLoadsNonOneByte;
assert(LoadSequence.size() <= Options.MaxNumLoads && "broken invariant");
// If we allow overlapping loads and the load sequence is not already optimal,
// use overlapping loads.
if (Options.AllowOverlappingLoads &&
(LoadSequence.empty() || LoadSequence.size() > 2)) {
unsigned OverlappingNumLoadsNonOneByte = 0;
auto OverlappingLoads = computeOverlappingLoadSequence(
Size, MaxLoadSize, Options.MaxNumLoads, OverlappingNumLoadsNonOneByte);
if (!OverlappingLoads.empty() &&
(LoadSequence.empty() ||
OverlappingLoads.size() < LoadSequence.size())) {
LoadSequence = OverlappingLoads;
NumLoadsNonOneByte = OverlappingNumLoadsNonOneByte;
}
}
assert(LoadSequence.size() <= Options.MaxNumLoads && "broken invariant");
}
unsigned MemCmpExpansion::getNumBlocks() {
if (IsUsedForZeroCmp)
return getNumLoads() / NumLoadsPerBlockForZeroCmp +
(getNumLoads() % NumLoadsPerBlockForZeroCmp != 0 ? 1 : 0);
return getNumLoads();
}
void MemCmpExpansion::createLoadCmpBlocks() {
for (unsigned i = 0; i < getNumBlocks(); i++) {
BasicBlock *BB = BasicBlock::Create(CI->getContext(), "loadbb",
EndBlock->getParent(), EndBlock);
LoadCmpBlocks.push_back(BB);
}
}
void MemCmpExpansion::createResultBlock() {
ResBlock.BB = BasicBlock::Create(CI->getContext(), "res_block",
EndBlock->getParent(), EndBlock);
}
MemCmpExpansion::LoadPair MemCmpExpansion::getLoadPair(Type *LoadSizeType,
bool NeedsBSwap,
Type *CmpSizeType,
unsigned OffsetBytes) {
// Get the memory source at offset `OffsetBytes`.
Value *LhsSource = CI->getArgOperand(0);
Value *RhsSource = CI->getArgOperand(1);
Align LhsAlign = LhsSource->getPointerAlignment(DL);
Align RhsAlign = RhsSource->getPointerAlignment(DL);
if (OffsetBytes > 0) {
auto *ByteType = Type::getInt8Ty(CI->getContext());
LhsSource = Builder.CreateConstGEP1_64(
ByteType, Builder.CreateBitCast(LhsSource, ByteType->getPointerTo()),
OffsetBytes);
RhsSource = Builder.CreateConstGEP1_64(
ByteType, Builder.CreateBitCast(RhsSource, ByteType->getPointerTo()),
OffsetBytes);
LhsAlign = commonAlignment(LhsAlign, OffsetBytes);
RhsAlign = commonAlignment(RhsAlign, OffsetBytes);
}
LhsSource = Builder.CreateBitCast(LhsSource, LoadSizeType->getPointerTo());
RhsSource = Builder.CreateBitCast(RhsSource, LoadSizeType->getPointerTo());
// Create a constant or a load from the source.
Value *Lhs = nullptr;
if (auto *C = dyn_cast<Constant>(LhsSource))
Lhs = ConstantFoldLoadFromConstPtr(C, LoadSizeType, DL);
if (!Lhs)
Lhs = Builder.CreateAlignedLoad(LoadSizeType, LhsSource, LhsAlign);
Value *Rhs = nullptr;
if (auto *C = dyn_cast<Constant>(RhsSource))
Rhs = ConstantFoldLoadFromConstPtr(C, LoadSizeType, DL);
if (!Rhs)
Rhs = Builder.CreateAlignedLoad(LoadSizeType, RhsSource, RhsAlign);
// Swap bytes if required.
if (NeedsBSwap) {
Function *Bswap = Intrinsic::getDeclaration(CI->getModule(),
Intrinsic::bswap, LoadSizeType);
Lhs = Builder.CreateCall(Bswap, Lhs);
Rhs = Builder.CreateCall(Bswap, Rhs);
}
// Zero extend if required.
if (CmpSizeType != nullptr && CmpSizeType != LoadSizeType) {
Lhs = Builder.CreateZExt(Lhs, CmpSizeType);
Rhs = Builder.CreateZExt(Rhs, CmpSizeType);
}
return {Lhs, Rhs};
}
// This function creates the IR instructions for loading and comparing 1 byte.
// It loads 1 byte from each source of the memcmp parameters with the given
// GEPIndex. It then subtracts the two loaded values and adds this result to the
// final phi node for selecting the memcmp result.
void MemCmpExpansion::emitLoadCompareByteBlock(unsigned BlockIndex,
unsigned OffsetBytes) {
Builder.SetInsertPoint(LoadCmpBlocks[BlockIndex]);
const LoadPair Loads =
getLoadPair(Type::getInt8Ty(CI->getContext()), /*NeedsBSwap=*/false,
Type::getInt32Ty(CI->getContext()), OffsetBytes);
Value *Diff = Builder.CreateSub(Loads.Lhs, Loads.Rhs);
PhiRes->addIncoming(Diff, LoadCmpBlocks[BlockIndex]);
if (BlockIndex < (LoadCmpBlocks.size() - 1)) {
// Early exit branch if difference found to EndBlock. Otherwise, continue to
// next LoadCmpBlock,
Value *Cmp = Builder.CreateICmp(ICmpInst::ICMP_NE, Diff,
ConstantInt::get(Diff->getType(), 0));
BranchInst *CmpBr =
BranchInst::Create(EndBlock, LoadCmpBlocks[BlockIndex + 1], Cmp);
Builder.Insert(CmpBr);
} else {
// The last block has an unconditional branch to EndBlock.
BranchInst *CmpBr = BranchInst::Create(EndBlock);
Builder.Insert(CmpBr);
}
}
/// Generate an equality comparison for one or more pairs of loaded values.
/// This is used in the case where the memcmp() call is compared equal or not
/// equal to zero.
Value *MemCmpExpansion::getCompareLoadPairs(unsigned BlockIndex,
unsigned &LoadIndex) {
assert(LoadIndex < getNumLoads() &&
"getCompareLoadPairs() called with no remaining loads");
std::vector<Value *> XorList, OrList;
Value *Diff = nullptr;
const unsigned NumLoads =
std::min(getNumLoads() - LoadIndex, NumLoadsPerBlockForZeroCmp);
// For a single-block expansion, start inserting before the memcmp call.
if (LoadCmpBlocks.empty())
Builder.SetInsertPoint(CI);
else
Builder.SetInsertPoint(LoadCmpBlocks[BlockIndex]);
Value *Cmp = nullptr;
// If we have multiple loads per block, we need to generate a composite
// comparison using xor+or. The type for the combinations is the largest load
// type.
IntegerType *const MaxLoadType =
NumLoads == 1 ? nullptr
: IntegerType::get(CI->getContext(), MaxLoadSize * 8);
for (unsigned i = 0; i < NumLoads; ++i, ++LoadIndex) {
const LoadEntry &CurLoadEntry = LoadSequence[LoadIndex];
const LoadPair Loads = getLoadPair(
IntegerType::get(CI->getContext(), CurLoadEntry.LoadSize * 8),
/*NeedsBSwap=*/false, MaxLoadType, CurLoadEntry.Offset);
if (NumLoads != 1) {
// If we have multiple loads per block, we need to generate a composite
// comparison using xor+or.
Diff = Builder.CreateXor(Loads.Lhs, Loads.Rhs);
Diff = Builder.CreateZExt(Diff, MaxLoadType);
XorList.push_back(Diff);
} else {
// If there's only one load per block, we just compare the loaded values.
Cmp = Builder.CreateICmpNE(Loads.Lhs, Loads.Rhs);
}
}
auto pairWiseOr = [&](std::vector<Value *> &InList) -> std::vector<Value *> {
std::vector<Value *> OutList;
for (unsigned i = 0; i < InList.size() - 1; i = i + 2) {
Value *Or = Builder.CreateOr(InList[i], InList[i + 1]);
OutList.push_back(Or);
}
if (InList.size() % 2 != 0)
OutList.push_back(InList.back());
return OutList;
};
if (!Cmp) {
// Pairwise OR the XOR results.
OrList = pairWiseOr(XorList);
// Pairwise OR the OR results until one result left.
while (OrList.size() != 1) {
OrList = pairWiseOr(OrList);
}
assert(Diff && "Failed to find comparison diff");
Cmp = Builder.CreateICmpNE(OrList[0], ConstantInt::get(Diff->getType(), 0));
}
return Cmp;
}
void MemCmpExpansion::emitLoadCompareBlockMultipleLoads(unsigned BlockIndex,
unsigned &LoadIndex) {
Value *Cmp = getCompareLoadPairs(BlockIndex, LoadIndex);
BasicBlock *NextBB = (BlockIndex == (LoadCmpBlocks.size() - 1))
? EndBlock
: LoadCmpBlocks[BlockIndex + 1];
// Early exit branch if difference found to ResultBlock. Otherwise,
// continue to next LoadCmpBlock or EndBlock.
BranchInst *CmpBr = BranchInst::Create(ResBlock.BB, NextBB, Cmp);
Builder.Insert(CmpBr);
// Add a phi edge for the last LoadCmpBlock to Endblock with a value of 0
// since early exit to ResultBlock was not taken (no difference was found in
// any of the bytes).
if (BlockIndex == LoadCmpBlocks.size() - 1) {
Value *Zero = ConstantInt::get(Type::getInt32Ty(CI->getContext()), 0);
PhiRes->addIncoming(Zero, LoadCmpBlocks[BlockIndex]);
}
}
// This function creates the IR intructions for loading and comparing using the
// given LoadSize. It loads the number of bytes specified by LoadSize from each
// source of the memcmp parameters. It then does a subtract to see if there was
// a difference in the loaded values. If a difference is found, it branches
// with an early exit to the ResultBlock for calculating which source was
// larger. Otherwise, it falls through to the either the next LoadCmpBlock or
// the EndBlock if this is the last LoadCmpBlock. Loading 1 byte is handled with
// a special case through emitLoadCompareByteBlock. The special handling can
// simply subtract the loaded values and add it to the result phi node.
void MemCmpExpansion::emitLoadCompareBlock(unsigned BlockIndex) {
// There is one load per block in this case, BlockIndex == LoadIndex.
const LoadEntry &CurLoadEntry = LoadSequence[BlockIndex];
if (CurLoadEntry.LoadSize == 1) {
MemCmpExpansion::emitLoadCompareByteBlock(BlockIndex, CurLoadEntry.Offset);
return;
}
Type *LoadSizeType =
IntegerType::get(CI->getContext(), CurLoadEntry.LoadSize * 8);
Type *MaxLoadType = IntegerType::get(CI->getContext(), MaxLoadSize * 8);
assert(CurLoadEntry.LoadSize <= MaxLoadSize && "Unexpected load type");
Builder.SetInsertPoint(LoadCmpBlocks[BlockIndex]);
const LoadPair Loads =
getLoadPair(LoadSizeType, /*NeedsBSwap=*/DL.isLittleEndian(), MaxLoadType,
CurLoadEntry.Offset);
// Add the loaded values to the phi nodes for calculating memcmp result only
// if result is not used in a zero equality.
if (!IsUsedForZeroCmp) {
ResBlock.PhiSrc1->addIncoming(Loads.Lhs, LoadCmpBlocks[BlockIndex]);
ResBlock.PhiSrc2->addIncoming(Loads.Rhs, LoadCmpBlocks[BlockIndex]);
}
Value *Cmp = Builder.CreateICmp(ICmpInst::ICMP_EQ, Loads.Lhs, Loads.Rhs);
BasicBlock *NextBB = (BlockIndex == (LoadCmpBlocks.size() - 1))
? EndBlock
: LoadCmpBlocks[BlockIndex + 1];
// Early exit branch if difference found to ResultBlock. Otherwise, continue
// to next LoadCmpBlock or EndBlock.
BranchInst *CmpBr = BranchInst::Create(NextBB, ResBlock.BB, Cmp);
Builder.Insert(CmpBr);
// Add a phi edge for the last LoadCmpBlock to Endblock with a value of 0
// since early exit to ResultBlock was not taken (no difference was found in
// any of the bytes).
if (BlockIndex == LoadCmpBlocks.size() - 1) {
Value *Zero = ConstantInt::get(Type::getInt32Ty(CI->getContext()), 0);
PhiRes->addIncoming(Zero, LoadCmpBlocks[BlockIndex]);
}
}
// This function populates the ResultBlock with a sequence to calculate the
// memcmp result. It compares the two loaded source values and returns -1 if
// src1 < src2 and 1 if src1 > src2.
void MemCmpExpansion::emitMemCmpResultBlock() {
// Special case: if memcmp result is used in a zero equality, result does not
// need to be calculated and can simply return 1.
if (IsUsedForZeroCmp) {
BasicBlock::iterator InsertPt = ResBlock.BB->getFirstInsertionPt();
Builder.SetInsertPoint(ResBlock.BB, InsertPt);
Value *Res = ConstantInt::get(Type::getInt32Ty(CI->getContext()), 1);
PhiRes->addIncoming(Res, ResBlock.BB);
BranchInst *NewBr = BranchInst::Create(EndBlock);
Builder.Insert(NewBr);
return;
}
BasicBlock::iterator InsertPt = ResBlock.BB->getFirstInsertionPt();
Builder.SetInsertPoint(ResBlock.BB, InsertPt);
Value *Cmp = Builder.CreateICmp(ICmpInst::ICMP_ULT, ResBlock.PhiSrc1,
ResBlock.PhiSrc2);
Value *Res =
Builder.CreateSelect(Cmp, ConstantInt::get(Builder.getInt32Ty(), -1),
ConstantInt::get(Builder.getInt32Ty(), 1));
BranchInst *NewBr = BranchInst::Create(EndBlock);
Builder.Insert(NewBr);
PhiRes->addIncoming(Res, ResBlock.BB);
}
void MemCmpExpansion::setupResultBlockPHINodes() {
Type *MaxLoadType = IntegerType::get(CI->getContext(), MaxLoadSize * 8);
Builder.SetInsertPoint(ResBlock.BB);
// Note: this assumes one load per block.
ResBlock.PhiSrc1 =
Builder.CreatePHI(MaxLoadType, NumLoadsNonOneByte, "phi.src1");
ResBlock.PhiSrc2 =
Builder.CreatePHI(MaxLoadType, NumLoadsNonOneByte, "phi.src2");
}
void MemCmpExpansion::setupEndBlockPHINodes() {
Builder.SetInsertPoint(&EndBlock->front());
PhiRes = Builder.CreatePHI(Type::getInt32Ty(CI->getContext()), 2, "phi.res");
}
Value *MemCmpExpansion::getMemCmpExpansionZeroCase() {
unsigned LoadIndex = 0;
// This loop populates each of the LoadCmpBlocks with the IR sequence to
// handle multiple loads per block.
for (unsigned I = 0; I < getNumBlocks(); ++I) {
emitLoadCompareBlockMultipleLoads(I, LoadIndex);
}
emitMemCmpResultBlock();
return PhiRes;
}
/// A memcmp expansion that compares equality with 0 and only has one block of
/// load and compare can bypass the compare, branch, and phi IR that is required
/// in the general case.
Value *MemCmpExpansion::getMemCmpEqZeroOneBlock() {
unsigned LoadIndex = 0;
Value *Cmp = getCompareLoadPairs(0, LoadIndex);
assert(LoadIndex == getNumLoads() && "some entries were not consumed");
return Builder.CreateZExt(Cmp, Type::getInt32Ty(CI->getContext()));
}
/// A memcmp expansion that only has one block of load and compare can bypass
/// the compare, branch, and phi IR that is required in the general case.
Value *MemCmpExpansion::getMemCmpOneBlock() {
Type *LoadSizeType = IntegerType::get(CI->getContext(), Size * 8);
bool NeedsBSwap = DL.isLittleEndian() && Size != 1;
// The i8 and i16 cases don't need compares. We zext the loaded values and
// subtract them to get the suitable negative, zero, or positive i32 result.
if (Size < 4) {
const LoadPair Loads =
getLoadPair(LoadSizeType, NeedsBSwap, Builder.getInt32Ty(),
/*Offset*/ 0);
return Builder.CreateSub(Loads.Lhs, Loads.Rhs);
}
const LoadPair Loads = getLoadPair(LoadSizeType, NeedsBSwap, LoadSizeType,
/*Offset*/ 0);
// The result of memcmp is negative, zero, or positive, so produce that by
// subtracting 2 extended compare bits: sub (ugt, ult).
// If a target prefers to use selects to get -1/0/1, they should be able
// to transform this later. The inverse transform (going from selects to math)
// may not be possible in the DAG because the selects got converted into
// branches before we got there.
Value *CmpUGT = Builder.CreateICmpUGT(Loads.Lhs, Loads.Rhs);
Value *CmpULT = Builder.CreateICmpULT(Loads.Lhs, Loads.Rhs);
Value *ZextUGT = Builder.CreateZExt(CmpUGT, Builder.getInt32Ty());
Value *ZextULT = Builder.CreateZExt(CmpULT, Builder.getInt32Ty());
return Builder.CreateSub(ZextUGT, ZextULT);
}
// This function expands the memcmp call into an inline expansion and returns
// the memcmp result.
Value *MemCmpExpansion::getMemCmpExpansion() {
// Create the basic block framework for a multi-block expansion.
if (getNumBlocks() != 1) {
BasicBlock *StartBlock = CI->getParent();
EndBlock = StartBlock->splitBasicBlock(CI, "endblock");
setupEndBlockPHINodes();
createResultBlock();
// If return value of memcmp is not used in a zero equality, we need to
// calculate which source was larger. The calculation requires the
// two loaded source values of each load compare block.
// These will be saved in the phi nodes created by setupResultBlockPHINodes.
if (!IsUsedForZeroCmp) setupResultBlockPHINodes();
// Create the number of required load compare basic blocks.
createLoadCmpBlocks();
// Update the terminator added by splitBasicBlock to branch to the first
// LoadCmpBlock.
StartBlock->getTerminator()->setSuccessor(0, LoadCmpBlocks[0]);
}
Builder.SetCurrentDebugLocation(CI->getDebugLoc());
if (IsUsedForZeroCmp)
return getNumBlocks() == 1 ? getMemCmpEqZeroOneBlock()
: getMemCmpExpansionZeroCase();
if (getNumBlocks() == 1)
return getMemCmpOneBlock();
for (unsigned I = 0; I < getNumBlocks(); ++I) {
emitLoadCompareBlock(I);
}
emitMemCmpResultBlock();
return PhiRes;
}
// This function checks to see if an expansion of memcmp can be generated.
// It checks for constant compare size that is less than the max inline size.
// If an expansion cannot occur, returns false to leave as a library call.
// Otherwise, the library call is replaced with a new IR instruction sequence.
/// We want to transform:
/// %call = call signext i32 @memcmp(i8* %0, i8* %1, i64 15)
/// To:
/// loadbb:
/// %0 = bitcast i32* %buffer2 to i8*
/// %1 = bitcast i32* %buffer1 to i8*
/// %2 = bitcast i8* %1 to i64*
/// %3 = bitcast i8* %0 to i64*
/// %4 = load i64, i64* %2
/// %5 = load i64, i64* %3
/// %6 = call i64 @llvm.bswap.i64(i64 %4)
/// %7 = call i64 @llvm.bswap.i64(i64 %5)
/// %8 = sub i64 %6, %7
/// %9 = icmp ne i64 %8, 0
/// br i1 %9, label %res_block, label %loadbb1
/// res_block: ; preds = %loadbb2,
/// %loadbb1, %loadbb
/// %phi.src1 = phi i64 [ %6, %loadbb ], [ %22, %loadbb1 ], [ %36, %loadbb2 ]
/// %phi.src2 = phi i64 [ %7, %loadbb ], [ %23, %loadbb1 ], [ %37, %loadbb2 ]
/// %10 = icmp ult i64 %phi.src1, %phi.src2
/// %11 = select i1 %10, i32 -1, i32 1
/// br label %endblock
/// loadbb1: ; preds = %loadbb
/// %12 = bitcast i32* %buffer2 to i8*
/// %13 = bitcast i32* %buffer1 to i8*
/// %14 = bitcast i8* %13 to i32*
/// %15 = bitcast i8* %12 to i32*
/// %16 = getelementptr i32, i32* %14, i32 2
/// %17 = getelementptr i32, i32* %15, i32 2
/// %18 = load i32, i32* %16
/// %19 = load i32, i32* %17
/// %20 = call i32 @llvm.bswap.i32(i32 %18)
/// %21 = call i32 @llvm.bswap.i32(i32 %19)
/// %22 = zext i32 %20 to i64
/// %23 = zext i32 %21 to i64
/// %24 = sub i64 %22, %23
/// %25 = icmp ne i64 %24, 0
/// br i1 %25, label %res_block, label %loadbb2
/// loadbb2: ; preds = %loadbb1
/// %26 = bitcast i32* %buffer2 to i8*
/// %27 = bitcast i32* %buffer1 to i8*
/// %28 = bitcast i8* %27 to i16*
/// %29 = bitcast i8* %26 to i16*
/// %30 = getelementptr i16, i16* %28, i16 6
/// %31 = getelementptr i16, i16* %29, i16 6
/// %32 = load i16, i16* %30
/// %33 = load i16, i16* %31
/// %34 = call i16 @llvm.bswap.i16(i16 %32)
/// %35 = call i16 @llvm.bswap.i16(i16 %33)
/// %36 = zext i16 %34 to i64
/// %37 = zext i16 %35 to i64
/// %38 = sub i64 %36, %37
/// %39 = icmp ne i64 %38, 0
/// br i1 %39, label %res_block, label %loadbb3
/// loadbb3: ; preds = %loadbb2
/// %40 = bitcast i32* %buffer2 to i8*
/// %41 = bitcast i32* %buffer1 to i8*
/// %42 = getelementptr i8, i8* %41, i8 14
/// %43 = getelementptr i8, i8* %40, i8 14
/// %44 = load i8, i8* %42
/// %45 = load i8, i8* %43
/// %46 = zext i8 %44 to i32
/// %47 = zext i8 %45 to i32
/// %48 = sub i32 %46, %47
/// br label %endblock
/// endblock: ; preds = %res_block,
/// %loadbb3
/// %phi.res = phi i32 [ %48, %loadbb3 ], [ %11, %res_block ]
/// ret i32 %phi.res
static bool expandMemCmp(CallInst *CI, const TargetTransformInfo *TTI,
const TargetLowering *TLI, const DataLayout *DL,
ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI) {
NumMemCmpCalls++;
// Early exit from expansion if -Oz.
if (CI->getFunction()->hasMinSize())
return false;
// Early exit from expansion if size is not a constant.
ConstantInt *SizeCast = dyn_cast<ConstantInt>(CI->getArgOperand(2));
if (!SizeCast) {
NumMemCmpNotConstant++;
return false;
}
const uint64_t SizeVal = SizeCast->getZExtValue();
if (SizeVal == 0) {
return false;
}
// TTI call to check if target would like to expand memcmp. Also, get the
// available load sizes.
const bool IsUsedForZeroCmp = isOnlyUsedInZeroEqualityComparison(CI);
bool OptForSize = CI->getFunction()->hasOptSize() ||
llvm::shouldOptimizeForSize(CI->getParent(), PSI, BFI);
auto Options = TTI->enableMemCmpExpansion(OptForSize,
IsUsedForZeroCmp);
if (!Options) return false;
if (MemCmpEqZeroNumLoadsPerBlock.getNumOccurrences())
Options.NumLoadsPerBlock = MemCmpEqZeroNumLoadsPerBlock;
if (OptForSize &&
MaxLoadsPerMemcmpOptSize.getNumOccurrences())
Options.MaxNumLoads = MaxLoadsPerMemcmpOptSize;
if (!OptForSize && MaxLoadsPerMemcmp.getNumOccurrences())
Options.MaxNumLoads = MaxLoadsPerMemcmp;
MemCmpExpansion Expansion(CI, SizeVal, Options, IsUsedForZeroCmp, *DL);
// Don't expand if this will require more loads than desired by the target.
if (Expansion.getNumLoads() == 0) {
NumMemCmpGreaterThanMax++;
return false;
}
NumMemCmpInlined++;
Value *Res = Expansion.getMemCmpExpansion();
// Replace call with result of expansion and erase call.
CI->replaceAllUsesWith(Res);
CI->eraseFromParent();
return true;
}
class ExpandMemCmpPass : public FunctionPass {
public:
static char ID;
ExpandMemCmpPass() : FunctionPass(ID) {
initializeExpandMemCmpPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F)) return false;
auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
if (!TPC) {
return false;
}
const TargetLowering* TL =
TPC->getTM<TargetMachine>().getSubtargetImpl(F)->getTargetLowering();
const TargetLibraryInfo *TLI =
&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
const TargetTransformInfo *TTI =
&getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
auto *BFI = (PSI && PSI->hasProfileSummary()) ?
&getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() :
nullptr;
auto PA = runImpl(F, TLI, TTI, TL, PSI, BFI);
return !PA.areAllPreserved();
}
private:
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addRequired<ProfileSummaryInfoWrapperPass>();
LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU);
FunctionPass::getAnalysisUsage(AU);
}
PreservedAnalyses runImpl(Function &F, const TargetLibraryInfo *TLI,
const TargetTransformInfo *TTI,
const TargetLowering* TL,
ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI);
// Returns true if a change was made.
bool runOnBlock(BasicBlock &BB, const TargetLibraryInfo *TLI,
const TargetTransformInfo *TTI, const TargetLowering* TL,
const DataLayout& DL, ProfileSummaryInfo *PSI,
BlockFrequencyInfo *BFI);
};
bool ExpandMemCmpPass::runOnBlock(
BasicBlock &BB, const TargetLibraryInfo *TLI,
const TargetTransformInfo *TTI, const TargetLowering* TL,
const DataLayout& DL, ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI) {
for (Instruction& I : BB) {
CallInst *CI = dyn_cast<CallInst>(&I);
if (!CI) {
continue;
}
LibFunc Func;
if (TLI->getLibFunc(*CI, Func) &&
(Func == LibFunc_memcmp || Func == LibFunc_bcmp) &&
expandMemCmp(CI, TTI, TL, &DL, PSI, BFI)) {
return true;
}
}
return false;
}
PreservedAnalyses ExpandMemCmpPass::runImpl(
Function &F, const TargetLibraryInfo *TLI, const TargetTransformInfo *TTI,
const TargetLowering* TL, ProfileSummaryInfo *PSI,
BlockFrequencyInfo *BFI) {
const DataLayout& DL = F.getParent()->getDataLayout();
bool MadeChanges = false;
for (auto BBIt = F.begin(); BBIt != F.end();) {
if (runOnBlock(*BBIt, TLI, TTI, TL, DL, PSI, BFI)) {
MadeChanges = true;
// If changes were made, restart the function from the beginning, since
// the structure of the function was changed.
BBIt = F.begin();
} else {
++BBIt;
}
}
if (MadeChanges)
for (BasicBlock &BB : F)
SimplifyInstructionsInBlock(&BB);
return MadeChanges ? PreservedAnalyses::none() : PreservedAnalyses::all();
}
} // namespace
char ExpandMemCmpPass::ID = 0;
INITIALIZE_PASS_BEGIN(ExpandMemCmpPass, "expandmemcmp",
"Expand memcmp() to load/stores", false, false)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LazyBlockFrequencyInfoPass)
INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
INITIALIZE_PASS_END(ExpandMemCmpPass, "expandmemcmp",
"Expand memcmp() to load/stores", false, false)
FunctionPass *llvm::createExpandMemCmpPass() {
return new ExpandMemCmpPass();
}
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