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llvm-mirror/lib/CodeGen/ExpandMemCmp.cpp
Chandler Carruth ae65e281f3 Update the file headers across all of the LLVM projects in the monorepo 
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636
2019-01-19 08:50:56 +00:00

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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/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"
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."));
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}, {32, 1}.
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();
Value *getPtrToElementAtOffset(Value *Source, Type *LoadSizeType,
uint64_t 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,
unsigned MaxNumLoads, const bool IsUsedForZeroCmp,
unsigned MaxLoadsPerBlockForZeroCmp, 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 unsigned MaxNumLoads, const bool IsUsedForZeroCmp,
const unsigned MaxLoadsPerBlockForZeroCmp, const DataLayout &TheDataLayout)
: CI(CI),
Size(Size),
MaxLoadSize(0),
NumLoadsNonOneByte(0),
NumLoadsPerBlockForZeroCmp(MaxLoadsPerBlockForZeroCmp),
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, MaxNumLoads,
GreedyNumLoadsNonOneByte);
NumLoadsNonOneByte = GreedyNumLoadsNonOneByte;
assert(LoadSequence.size() <= 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, MaxNumLoads, OverlappingNumLoadsNonOneByte);
if (!OverlappingLoads.empty() &&
(LoadSequence.empty() ||
OverlappingLoads.size() < LoadSequence.size())) {
LoadSequence = OverlappingLoads;
NumLoadsNonOneByte = OverlappingNumLoadsNonOneByte;
}
}
assert(LoadSequence.size() <= 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);
}
/// Return a pointer to an element of type `LoadSizeType` at offset
/// `OffsetBytes`.
Value *MemCmpExpansion::getPtrToElementAtOffset(Value *Source,
Type *LoadSizeType,
uint64_t OffsetBytes) {
if (OffsetBytes > 0) {
auto *ByteType = Type::getInt8Ty(CI->getContext());
Source = Builder.CreateGEP(
ByteType, Builder.CreateBitCast(Source, ByteType->getPointerTo()),
ConstantInt::get(ByteType, OffsetBytes));
}
return Builder.CreateBitCast(Source, LoadSizeType->getPointerTo());
}
// 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]);
Type *LoadSizeType = Type::getInt8Ty(CI->getContext());
Value *Source1 =
getPtrToElementAtOffset(CI->getArgOperand(0), LoadSizeType, OffsetBytes);
Value *Source2 =
getPtrToElementAtOffset(CI->getArgOperand(1), LoadSizeType, OffsetBytes);
Value *LoadSrc1 = Builder.CreateLoad(LoadSizeType, Source1);
Value *LoadSrc2 = Builder.CreateLoad(LoadSizeType, Source2);
LoadSrc1 = Builder.CreateZExt(LoadSrc1, Type::getInt32Ty(CI->getContext()));
LoadSrc2 = Builder.CreateZExt(LoadSrc2, Type::getInt32Ty(CI->getContext()));
Value *Diff = Builder.CreateSub(LoadSrc1, LoadSrc2);
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;
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];
IntegerType *LoadSizeType =
IntegerType::get(CI->getContext(), CurLoadEntry.LoadSize * 8);
Value *Source1 = getPtrToElementAtOffset(CI->getArgOperand(0), LoadSizeType,
CurLoadEntry.Offset);
Value *Source2 = getPtrToElementAtOffset(CI->getArgOperand(1), LoadSizeType,
CurLoadEntry.Offset);
// Get a constant or load a value for each source address.
Value *LoadSrc1 = nullptr;
if (auto *Source1C = dyn_cast<Constant>(Source1))
LoadSrc1 = ConstantFoldLoadFromConstPtr(Source1C, LoadSizeType, DL);
if (!LoadSrc1)
LoadSrc1 = Builder.CreateLoad(LoadSizeType, Source1);
Value *LoadSrc2 = nullptr;
if (auto *Source2C = dyn_cast<Constant>(Source2))
LoadSrc2 = ConstantFoldLoadFromConstPtr(Source2C, LoadSizeType, DL);
if (!LoadSrc2)
LoadSrc2 = Builder.CreateLoad(LoadSizeType, Source2);
if (NumLoads != 1) {
if (LoadSizeType != MaxLoadType) {
LoadSrc1 = Builder.CreateZExt(LoadSrc1, MaxLoadType);
LoadSrc2 = Builder.CreateZExt(LoadSrc2, MaxLoadType);
}
// If we have multiple loads per block, we need to generate a composite
// comparison using xor+or.
Diff = Builder.CreateXor(LoadSrc1, LoadSrc2);
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(LoadSrc1, LoadSrc2);
}
}
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);
}
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]);
Value *Source1 = getPtrToElementAtOffset(CI->getArgOperand(0), LoadSizeType,
CurLoadEntry.Offset);
Value *Source2 = getPtrToElementAtOffset(CI->getArgOperand(1), LoadSizeType,
CurLoadEntry.Offset);
// Load LoadSizeType from the base address.
Value *LoadSrc1 = Builder.CreateLoad(LoadSizeType, Source1);
Value *LoadSrc2 = Builder.CreateLoad(LoadSizeType, Source2);
if (DL.isLittleEndian()) {
Function *Bswap = Intrinsic::getDeclaration(CI->getModule(),
Intrinsic::bswap, LoadSizeType);
LoadSrc1 = Builder.CreateCall(Bswap, LoadSrc1);
LoadSrc2 = Builder.CreateCall(Bswap, LoadSrc2);
}
if (LoadSizeType != MaxLoadType) {
LoadSrc1 = Builder.CreateZExt(LoadSrc1, MaxLoadType);
LoadSrc2 = Builder.CreateZExt(LoadSrc2, MaxLoadType);
}
// 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(LoadSrc1, LoadCmpBlocks[BlockIndex]);
ResBlock.PhiSrc2->addIncoming(LoadSrc2, LoadCmpBlocks[BlockIndex]);
}
Value *Cmp = Builder.CreateICmp(ICmpInst::ICMP_EQ, LoadSrc1, LoadSrc2);
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);
Value *Source1 = CI->getArgOperand(0);
Value *Source2 = CI->getArgOperand(1);
// Cast source to LoadSizeType*.
if (Source1->getType() != LoadSizeType)
Source1 = Builder.CreateBitCast(Source1, LoadSizeType->getPointerTo());
if (Source2->getType() != LoadSizeType)
Source2 = Builder.CreateBitCast(Source2, LoadSizeType->getPointerTo());
// Load LoadSizeType from the base address.
Value *LoadSrc1 = Builder.CreateLoad(LoadSizeType, Source1);
Value *LoadSrc2 = Builder.CreateLoad(LoadSizeType, Source2);
if (DL.isLittleEndian() && Size != 1) {
Function *Bswap = Intrinsic::getDeclaration(CI->getModule(),
Intrinsic::bswap, LoadSizeType);
LoadSrc1 = Builder.CreateCall(Bswap, LoadSrc1);
LoadSrc2 = Builder.CreateCall(Bswap, LoadSrc2);
}
if (Size < 4) {
// 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.
LoadSrc1 = Builder.CreateZExt(LoadSrc1, Builder.getInt32Ty());
LoadSrc2 = Builder.CreateZExt(LoadSrc2, Builder.getInt32Ty());
return Builder.CreateSub(LoadSrc1, LoadSrc2);
}
// 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(LoadSrc1, LoadSrc2);
Value *CmpULT = Builder.CreateICmpULT(LoadSrc1, LoadSrc2);
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) {
NumMemCmpCalls++;
// Early exit from expansion if -Oz.
if (CI->getFunction()->optForMinSize())
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);
const auto *const Options = TTI->enableMemCmpExpansion(IsUsedForZeroCmp);
if (!Options) return false;
const unsigned MaxNumLoads =
TLI->getMaxExpandSizeMemcmp(CI->getFunction()->optForSize());
unsigned NumLoadsPerBlock = MemCmpEqZeroNumLoadsPerBlock.getNumOccurrences()
? MemCmpEqZeroNumLoadsPerBlock
: TLI->getMemcmpEqZeroLoadsPerBlock();
MemCmpExpansion Expansion(CI, SizeVal, *Options, MaxNumLoads,
IsUsedForZeroCmp, NumLoadsPerBlock, *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();
const TargetTransformInfo *TTI =
&getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto PA = runImpl(F, TLI, TTI, TL);
return !PA.areAllPreserved();
}
private:
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
FunctionPass::getAnalysisUsage(AU);
}
PreservedAnalyses runImpl(Function &F, const TargetLibraryInfo *TLI,
const TargetTransformInfo *TTI,
const TargetLowering* TL);
// Returns true if a change was made.
bool runOnBlock(BasicBlock &BB, const TargetLibraryInfo *TLI,
const TargetTransformInfo *TTI, const TargetLowering* TL,
const DataLayout& DL);
};
bool ExpandMemCmpPass::runOnBlock(
BasicBlock &BB, const TargetLibraryInfo *TLI,
const TargetTransformInfo *TTI, const TargetLowering* TL,
const DataLayout& DL) {
for (Instruction& I : BB) {
CallInst *CI = dyn_cast<CallInst>(&I);
if (!CI) {
continue;
}
LibFunc Func;
if (TLI->getLibFunc(ImmutableCallSite(CI), Func) &&
Func == LibFunc_memcmp && expandMemCmp(CI, TTI, TL, &DL)) {
return true;
}
}
return false;
}
PreservedAnalyses ExpandMemCmpPass::runImpl(
Function &F, const TargetLibraryInfo *TLI, const TargetTransformInfo *TTI,
const TargetLowering* TL) {
const DataLayout& DL = F.getParent()->getDataLayout();
bool MadeChanges = false;
for (auto BBIt = F.begin(); BBIt != F.end();) {
if (runOnBlock(*BBIt, TLI, TTI, TL, DL)) {
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;
}
}
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_END(ExpandMemCmpPass, "expandmemcmp",
"Expand memcmp() to load/stores", false, false)
FunctionPass *llvm::createExpandMemCmpPass() {
return new ExpandMemCmpPass();
}
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