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//===- LowerMemIntrinsics.cpp ----------------------------------*- C++ -*--===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/LowerMemIntrinsics.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
void llvm::createMemCpyLoop(Instruction *InsertBefore,
Value *SrcAddr, Value *DstAddr, Value *CopyLen,
unsigned SrcAlign, unsigned DestAlign,
bool SrcIsVolatile, bool DstIsVolatile) {
Type *TypeOfCopyLen = CopyLen->getType();
BasicBlock *OrigBB = InsertBefore->getParent();
Function *F = OrigBB->getParent();
BasicBlock *NewBB =
InsertBefore->getParent()->splitBasicBlock(InsertBefore, "split");
BasicBlock *LoopBB = BasicBlock::Create(F->getContext(), "loadstoreloop",
F, NewBB);
OrigBB->getTerminator()->setSuccessor(0, LoopBB);
IRBuilder<> Builder(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;
// }
static void createMemMoveLoop(Instruction *InsertBefore,
Value *SrcAddr, Value *DstAddr, Value *CopyLen,
unsigned SrcAlign, unsigned DestAlign,
bool SrcIsVolatile, bool DstIsVolatile) {
Type *TypeOfCopyLen = CopyLen->getType();
BasicBlock *OrigBB = InsertBefore->getParent();
Function *F = OrigBB->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(InsertBefore, ICmpInst::ICMP_ULT,
SrcAddr, DstAddr, "compare_src_dst");
TerminatorInst *ThenTerm, *ElseTerm;
SplitBlockAndInsertIfThenElse(PtrCompare, InsertBefore, &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 = InsertBefore->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(F->getContext(), "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(F->getContext(), "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();
}
static void createMemSetLoop(Instruction *InsertBefore,
Value *DstAddr, Value *CopyLen, Value *SetValue,
unsigned Align, bool IsVolatile) {
BasicBlock *OrigBB = InsertBefore->getParent();
Function *F = OrigBB->getParent();
BasicBlock *NewBB =
OrigBB->splitBasicBlock(InsertBefore, "split");
BasicBlock *LoopBB
= BasicBlock::Create(F->getContext(), "loadstoreloop", F, NewBB);
OrigBB->getTerminator()->setSuccessor(0, LoopBB);
IRBuilder<> Builder(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),
IsVolatile);
Value *NewIndex =
LoopBuilder.CreateAdd(LoopIndex, ConstantInt::get(CopyLen->getType(), 1));
LoopIndex->addIncoming(NewIndex, LoopBB);
LoopBuilder.CreateCondBr(LoopBuilder.CreateICmpULT(NewIndex, CopyLen), LoopBB,
NewBB);
}
void llvm::expandMemCpyAsLoop(MemCpyInst *Memcpy) {
createMemCpyLoop(/* InsertBefore */ Memcpy,
/* SrcAddr */ Memcpy->getRawSource(),
/* DstAddr */ Memcpy->getRawDest(),
/* CopyLen */ Memcpy->getLength(),
/* SrcAlign */ Memcpy->getAlignment(),
/* DestAlign */ Memcpy->getAlignment(),
/* SrcIsVolatile */ Memcpy->isVolatile(),
/* DstIsVolatile */ Memcpy->isVolatile());
}
void llvm::expandMemMoveAsLoop(MemMoveInst *Memmove) {
createMemMoveLoop(/* InsertBefore */ Memmove,
/* SrcAddr */ Memmove->getRawSource(),
/* DstAddr */ Memmove->getRawDest(),
/* CopyLen */ Memmove->getLength(),
/* SrcAlign */ Memmove->getAlignment(),
/* DestAlign */ Memmove->getAlignment(),
/* SrcIsVolatile */ Memmove->isVolatile(),
/* DstIsVolatile */ Memmove->isVolatile());
}
void llvm::expandMemSetAsLoop(MemSetInst *Memset) {
createMemSetLoop(/* InsertBefore */ Memset,
/* DstAddr */ Memset->getRawDest(),
/* CopyLen */ Memset->getLength(),
/* SetValue */ Memset->getValue(),
/* Alignment */ Memset->getAlignment(),
Memset->isVolatile());
}
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