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llvm-6502/lib/Target/NVPTX/NVPTXLowerAggrCopies.cpp
Eli Bendersky 27bd1ca0d9 Use inbounds GEPs for memcpy and memset lowering 
Follow-up on discussion in http://reviews.llvm.org/D11220


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242542 91177308-0d34-0410-b5e6-96231b3b80d8
2015-07-17 16:42:33 +00:00

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//===- NVPTXLowerAggrCopies.cpp - ------------------------------*- C++ -*--===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// \file
// Lower aggregate copies, memset, memcpy, memmov intrinsics into loops when
// the size is large or is not a compile-time constant.
//
//===----------------------------------------------------------------------===//
#include "NVPTXLowerAggrCopies.h"
#include "llvm/CodeGen/MachineFunctionAnalysis.h"
#include "llvm/CodeGen/StackProtector.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#define DEBUG_TYPE "nvptx"
using namespace llvm;
namespace {
// actual analysis class, which is a functionpass
struct NVPTXLowerAggrCopies : public FunctionPass {
static char ID;
NVPTXLowerAggrCopies() : FunctionPass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addPreserved<MachineFunctionAnalysis>();
AU.addPreserved<StackProtector>();
}
bool runOnFunction(Function &F) override;
static const unsigned MaxAggrCopySize = 128;
const char *getPassName() const override {
return "Lower aggregate copies/intrinsics into loops";
}
};
char NVPTXLowerAggrCopies::ID = 0;
// Lower memcpy to loop.
void convertMemCpyToLoop(Instruction *ConvertedInst, Value *SrcAddr,
Value *DstAddr, Value *CopyLen, bool SrcIsVolatile,
bool DstIsVolatile, LLVMContext &Context,
Function &F) {
Type *TypeOfCopyLen = CopyLen->getType();
BasicBlock *OrigBB = ConvertedInst->getParent();
BasicBlock *NewBB =
ConvertedInst->getParent()->splitBasicBlock(ConvertedInst, "split");
BasicBlock *LoopBB = BasicBlock::Create(Context, "loadstoreloop", &F, NewBB);
OrigBB->getTerminator()->setSuccessor(0, LoopBB);
IRBuilder<> Builder(OrigBB, OrigBB->getTerminator());
// SrcAddr and DstAddr are expected to be pointer types,
// so no check is made here.
unsigned SrcAS = cast<PointerType>(SrcAddr->getType())->getAddressSpace();
unsigned DstAS = cast<PointerType>(DstAddr->getType())->getAddressSpace();
// Cast pointers to (char *)
SrcAddr = Builder.CreateBitCast(SrcAddr, Builder.getInt8PtrTy(SrcAS));
DstAddr = Builder.CreateBitCast(DstAddr, Builder.getInt8PtrTy(DstAS));
IRBuilder<> LoopBuilder(LoopBB);
PHINode *LoopIndex = LoopBuilder.CreatePHI(TypeOfCopyLen, 0);
LoopIndex->addIncoming(ConstantInt::get(TypeOfCopyLen, 0), OrigBB);
// load from SrcAddr+LoopIndex
// TODO: we can leverage the align parameter of llvm.memcpy for more efficient
// word-sized loads and stores.
Value *Element =
LoopBuilder.CreateLoad(LoopBuilder.CreateInBoundsGEP(
LoopBuilder.getInt8Ty(), SrcAddr, LoopIndex),
SrcIsVolatile);
// store at DstAddr+LoopIndex
LoopBuilder.CreateStore(Element,
LoopBuilder.CreateInBoundsGEP(LoopBuilder.getInt8Ty(),
DstAddr, LoopIndex),
DstIsVolatile);
// The value for LoopIndex coming from backedge is (LoopIndex + 1)
Value *NewIndex =
LoopBuilder.CreateAdd(LoopIndex, ConstantInt::get(TypeOfCopyLen, 1));
LoopIndex->addIncoming(NewIndex, LoopBB);
LoopBuilder.CreateCondBr(LoopBuilder.CreateICmpULT(NewIndex, CopyLen), LoopBB,
NewBB);
}
// Lower memmove to IR. memmove is required to correctly copy overlapping memory
// regions; therefore, it has to check the relative positions of the source and
// destination pointers and choose the copy direction accordingly.
//
// The code below is an IR rendition of this C function:
//
// void* memmove(void* dst, const void* src, size_t n) {
// unsigned char* d = dst;
// const unsigned char* s = src;
// if (s < d) {
// // copy backwards
// while (n--) {
// d[n] = s[n];
// }
// } else {
// // copy forward
// for (size_t i = 0; i < n; ++i) {
// d[i] = s[i];
// }
// }
// return dst;
// }
void convertMemMoveToLoop(Instruction *ConvertedInst, Value *SrcAddr,
Value *DstAddr, Value *CopyLen, bool SrcIsVolatile,
bool DstIsVolatile, LLVMContext &Context,
Function &F) {
Type *TypeOfCopyLen = CopyLen->getType();
BasicBlock *OrigBB = ConvertedInst->getParent();
// Create the a comparison of src and dst, based on which we jump to either
// the forward-copy part of the function (if src >= dst) or the backwards-copy
// part (if src < dst).
// SplitBlockAndInsertIfThenElse conveniently creates the basic if-then-else
// structure. Its block terminators (unconditional branches) are replaced by
// the appropriate conditional branches when the loop is built.
ICmpInst *PtrCompare = new ICmpInst(ConvertedInst, ICmpInst::ICMP_ULT,
SrcAddr, DstAddr, "compare_src_dst");
TerminatorInst *ThenTerm, *ElseTerm;
SplitBlockAndInsertIfThenElse(PtrCompare, ConvertedInst, &ThenTerm,
&ElseTerm);
// Each part of the function consists of two blocks:
// copy_backwards: used to skip the loop when n == 0
// copy_backwards_loop: the actual backwards loop BB
// copy_forward: used to skip the loop when n == 0
// copy_forward_loop: the actual forward loop BB
BasicBlock *CopyBackwardsBB = ThenTerm->getParent();
CopyBackwardsBB->setName("copy_backwards");
BasicBlock *CopyForwardBB = ElseTerm->getParent();
CopyForwardBB->setName("copy_forward");
BasicBlock *ExitBB = ConvertedInst->getParent();
ExitBB->setName("memmove_done");
// Initial comparison of n == 0 that lets us skip the loops altogether. Shared
// between both backwards and forward copy clauses.
ICmpInst *CompareN =
new ICmpInst(OrigBB->getTerminator(), ICmpInst::ICMP_EQ, CopyLen,
ConstantInt::get(TypeOfCopyLen, 0), "compare_n_to_0");
// Copying backwards.
BasicBlock *LoopBB =
BasicBlock::Create(Context, "copy_backwards_loop", &F, CopyForwardBB);
IRBuilder<> LoopBuilder(LoopBB);
PHINode *LoopPhi = LoopBuilder.CreatePHI(TypeOfCopyLen, 0);
Value *IndexPtr = LoopBuilder.CreateSub(
LoopPhi, ConstantInt::get(TypeOfCopyLen, 1), "index_ptr");
Value *Element = LoopBuilder.CreateLoad(
LoopBuilder.CreateInBoundsGEP(SrcAddr, IndexPtr), "element");
LoopBuilder.CreateStore(Element,
LoopBuilder.CreateInBoundsGEP(DstAddr, IndexPtr));
LoopBuilder.CreateCondBr(
LoopBuilder.CreateICmpEQ(IndexPtr, ConstantInt::get(TypeOfCopyLen, 0)),
ExitBB, LoopBB);
LoopPhi->addIncoming(IndexPtr, LoopBB);
LoopPhi->addIncoming(CopyLen, CopyBackwardsBB);
BranchInst::Create(ExitBB, LoopBB, CompareN, ThenTerm);
ThenTerm->eraseFromParent();
// Copying forward.
BasicBlock *FwdLoopBB =
BasicBlock::Create(Context, "copy_forward_loop", &F, ExitBB);
IRBuilder<> FwdLoopBuilder(FwdLoopBB);
PHINode *FwdCopyPhi = FwdLoopBuilder.CreatePHI(TypeOfCopyLen, 0, "index_ptr");
Value *FwdElement = FwdLoopBuilder.CreateLoad(
FwdLoopBuilder.CreateInBoundsGEP(SrcAddr, FwdCopyPhi), "element");
FwdLoopBuilder.CreateStore(
FwdElement, FwdLoopBuilder.CreateInBoundsGEP(DstAddr, FwdCopyPhi));
Value *FwdIndexPtr = FwdLoopBuilder.CreateAdd(
FwdCopyPhi, ConstantInt::get(TypeOfCopyLen, 1), "index_increment");
FwdLoopBuilder.CreateCondBr(FwdLoopBuilder.CreateICmpEQ(FwdIndexPtr, CopyLen),
ExitBB, FwdLoopBB);
FwdCopyPhi->addIncoming(FwdIndexPtr, FwdLoopBB);
FwdCopyPhi->addIncoming(ConstantInt::get(TypeOfCopyLen, 0), CopyForwardBB);
BranchInst::Create(ExitBB, FwdLoopBB, CompareN, ElseTerm);
ElseTerm->eraseFromParent();
}
// Lower memset to loop.
void convertMemSetToLoop(Instruction *ConvertedInst, Value *DstAddr,
Value *CopyLen, Value *SetValue, LLVMContext &Context,
Function &F) {
BasicBlock *OrigBB = ConvertedInst->getParent();
BasicBlock *NewBB =
ConvertedInst->getParent()->splitBasicBlock(ConvertedInst, "split");
BasicBlock *LoopBB = BasicBlock::Create(Context, "loadstoreloop", &F, NewBB);
OrigBB->getTerminator()->setSuccessor(0, LoopBB);
IRBuilder<> Builder(OrigBB, OrigBB->getTerminator());
// Cast pointer to the type of value getting stored
unsigned dstAS = cast<PointerType>(DstAddr->getType())->getAddressSpace();
DstAddr = Builder.CreateBitCast(DstAddr,
PointerType::get(SetValue->getType(), dstAS));
IRBuilder<> LoopBuilder(LoopBB);
PHINode *LoopIndex = LoopBuilder.CreatePHI(CopyLen->getType(), 0);
LoopIndex->addIncoming(ConstantInt::get(CopyLen->getType(), 0), OrigBB);
LoopBuilder.CreateStore(
SetValue,
LoopBuilder.CreateInBoundsGEP(SetValue->getType(), DstAddr, LoopIndex),
false);
Value *NewIndex =
LoopBuilder.CreateAdd(LoopIndex, ConstantInt::get(CopyLen->getType(), 1));
LoopIndex->addIncoming(NewIndex, LoopBB);
LoopBuilder.CreateCondBr(LoopBuilder.CreateICmpULT(NewIndex, CopyLen), LoopBB,
NewBB);
}
bool NVPTXLowerAggrCopies::runOnFunction(Function &F) {
SmallVector<LoadInst *, 4> AggrLoads;
SmallVector<MemIntrinsic *, 4> MemCalls;
const DataLayout &DL = F.getParent()->getDataLayout();
LLVMContext &Context = F.getParent()->getContext();
// Collect all aggregate loads and mem* calls.
for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;
++II) {
if (LoadInst *LI = dyn_cast<LoadInst>(II)) {
if (!LI->hasOneUse())
continue;
if (DL.getTypeStoreSize(LI->getType()) < MaxAggrCopySize)
continue;
if (StoreInst *SI = dyn_cast<StoreInst>(LI->user_back())) {
if (SI->getOperand(0) != LI)
continue;
AggrLoads.push_back(LI);
}
} else if (MemIntrinsic *IntrCall = dyn_cast<MemIntrinsic>(II)) {
// Convert intrinsic calls with variable size or with constant size
// larger than the MaxAggrCopySize threshold.
if (ConstantInt *LenCI = dyn_cast<ConstantInt>(IntrCall->getLength())) {
if (LenCI->getZExtValue() >= MaxAggrCopySize) {
MemCalls.push_back(IntrCall);
}
} else {
MemCalls.push_back(IntrCall);
}
}
}
}
if (AggrLoads.size() == 0 && MemCalls.size() == 0) {
return false;
}
//
// Do the transformation of an aggr load/copy/set to a loop
//
for (LoadInst *LI : AggrLoads) {
StoreInst *SI = dyn_cast<StoreInst>(*LI->user_begin());
Value *SrcAddr = LI->getOperand(0);
Value *DstAddr = SI->getOperand(1);
unsigned NumLoads = DL.getTypeStoreSize(LI->getType());
Value *CopyLen = ConstantInt::get(Type::getInt32Ty(Context), NumLoads);
convertMemCpyToLoop(/* ConvertedInst */ SI,
/* SrcAddr */ SrcAddr, /* DstAddr */ DstAddr,
/* CopyLen */ CopyLen,
/* SrcIsVolatile */ LI->isVolatile(),
/* DstIsVolatile */ SI->isVolatile(),
/* Context */ Context,
/* Function F */ F);
SI->eraseFromParent();
LI->eraseFromParent();
}
// Transform mem* intrinsic calls.
for (MemIntrinsic *MemCall : MemCalls) {
if (MemCpyInst *Memcpy = dyn_cast<MemCpyInst>(MemCall)) {
convertMemCpyToLoop(/* ConvertedInst */ Memcpy,
/* SrcAddr */ Memcpy->getRawSource(),
/* DstAddr */ Memcpy->getRawDest(),
/* CopyLen */ Memcpy->getLength(),
/* SrcIsVolatile */ Memcpy->isVolatile(),
/* DstIsVolatile */ Memcpy->isVolatile(),
/* Context */ Context,
/* Function F */ F);
} else if (MemMoveInst *Memmove = dyn_cast<MemMoveInst>(MemCall)) {
convertMemMoveToLoop(/* ConvertedInst */ Memmove,
/* SrcAddr */ Memmove->getRawSource(),
/* DstAddr */ Memmove->getRawDest(),
/* CopyLen */ Memmove->getLength(),
/* SrcIsVolatile */ Memmove->isVolatile(),
/* DstIsVolatile */ Memmove->isVolatile(),
/* Context */ Context,
/* Function F */ F);
} else if (MemSetInst *Memset = dyn_cast<MemSetInst>(MemCall)) {
convertMemSetToLoop(/* ConvertedInst */ Memset,
/* DstAddr */ Memset->getRawDest(),
/* CopyLen */ Memset->getLength(),
/* SetValue */ Memset->getValue(),
/* Context */ Context,
/* Function F */ F);
}
MemCall->eraseFromParent();
}
return true;
}
} // namespace
namespace llvm {
void initializeNVPTXLowerAggrCopiesPass(PassRegistry &);
}
INITIALIZE_PASS(NVPTXLowerAggrCopies, "nvptx-lower-aggr-copies",
"Lower aggregate copies, and llvm.mem* intrinsics into loops",
false, false)
FunctionPass *llvm::createLowerAggrCopies() {
return new NVPTXLowerAggrCopies();
}
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