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reimplement LICM::sink to use SSAUpdater instead of PromoteMemToReg.

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This leads to much simpler code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112410 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-08-29 04:55:06 +00:00
parent ffd9beefb8
commit a6a36f59b4
1 changed files with 40 additions and 71 deletions
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111
lib/Transforms/Scalar/LICM.cpp
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@ -45,6 +45,7 @@
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/raw_ostream.h"
@ -477,7 +478,7 @@ void LICM::sink(Instruction &I) {
// If I has users in unreachable blocks, eliminate.
// If I is not void type then replaceAllUsesWith undef.
// This allows ValueHandlers and custom metadata to adjust itself.
if (!I.getType()->isVoidTy())
if (!I.use_empty())
I.replaceAllUsesWith(UndefValue::get(I.getType()));
I.eraseFromParent();
} else {
@ -496,82 +497,41 @@ void LICM::sink(Instruction &I) {
// If I has users in unreachable blocks, eliminate.
// If I is not void type then replaceAllUsesWith undef.
// This allows ValueHandlers and custom metadata to adjust itself.
if (!I.getType()->isVoidTy())
if (!I.use_empty())
I.replaceAllUsesWith(UndefValue::get(I.getType()));
I.eraseFromParent();
return;
}
// Otherwise, if we have multiple exits, use the PromoteMem2Reg function to
// do all of the hard work of inserting PHI nodes as necessary. We convert
// the value into a stack object to get it to do this.
// Firstly, we create a stack object to hold the value...
AllocaInst *AI = 0;
if (!I.getType()->isVoidTy()) {
AI = new AllocaInst(I.getType(), 0, I.getName(),
I.getParent()->getParent()->getEntryBlock().begin());
CurAST->add(AI);
}
// Secondly, insert load instructions for each use of the instruction
// outside of the loop.
while (!I.use_empty()) {
Instruction *U = cast<Instruction>(I.use_back());
// If the user is a PHI Node, we actually have to insert load instructions
// in all predecessor blocks, not in the PHI block itself!
if (PHINode *UPN = dyn_cast<PHINode>(U)) {
// Only insert into each predecessor once, so that we don't have
// different incoming values from the same block!
DenseMap<BasicBlock*, Value*> InsertedBlocks;
for (unsigned i = 0, e = UPN->getNumIncomingValues(); i != e; ++i) {
if (UPN->getIncomingValue(i) != &I) continue;
BasicBlock *Pred = UPN->getIncomingBlock(i);
Value *&PredVal = InsertedBlocks[Pred];
if (!PredVal) {
// Insert a new load instruction right before the terminator in
// the predecessor block.
PredVal = new LoadInst(AI, "", Pred->getTerminator());
CurAST->add(cast<LoadInst>(PredVal));
}
UPN->setIncomingValue(i, PredVal);
}
} else {
LoadInst *L = new LoadInst(AI, "", U);
U->replaceUsesOfWith(&I, L);
CurAST->add(L);
}
}
// Thirdly, insert a copy of the instruction in each exit block of the loop
// that is dominated by the instruction, storing the result into the memory
// location. Each exit block is known to only be in the ExitBlocks list once.
SmallPtrSet<BasicBlock*, 16> InsertedBlocks;
BasicBlock *InstOrigBB = I.getParent();
// Otherwise, if we have multiple exits, use the SSAUpdater to do all of the
// hard work of inserting PHI nodes as necessary.
SmallVector<PHINode*, 8> NewPHIs;
SSAUpdater SSA(&NewPHIs);
if (!I.use_empty())
SSA.Initialize(&I);
// Insert a copy of the instruction in each exit block of the loop that is
// dominated by the instruction. Each exit block is known to only be in the
// ExitBlocks list once.
BasicBlock *InstOrigBB = I.getParent();
unsigned NumInserted = 0;
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *ExitBlock = ExitBlocks[i];
if (!isExitBlockDominatedByBlockInLoop(ExitBlock, InstOrigBB))
continue;
// Insert the code after the last PHI node...
// Insert the code after the last PHI node.
BasicBlock::iterator InsertPt = ExitBlock->getFirstNonPHI();
// If this is the first exit block processed, just move the original
// instruction, otherwise clone the original instruction and insert
// the copy.
Instruction *New;
if (NumInserted == 0) {
I.removeFromParent();
ExitBlock->getInstList().insert(InsertPt, &I);
if (NumInserted++ == 0) {
I.moveBefore(InsertPt);
New = &I;
} else {
New = I.clone();
@ -581,24 +541,33 @@ void LICM::sink(Instruction &I) {
ExitBlock->getInstList().insert(InsertPt, New);
}
++NumInserted;
// Now that we have inserted the instruction, store it into the alloca
if (AI) new StoreInst(New, AI, InsertPt);
// Now that we have inserted the instruction, inform SSAUpdater.
if (!I.use_empty())
SSA.AddAvailableValue(ExitBlock, New);
}
// If the instruction doesn't dominate any exit blocks, it must be dead.
if (NumInserted == 0) {
CurAST->deleteValue(&I);
if (!I.use_empty())
I.replaceAllUsesWith(UndefValue::get(I.getType()));
I.eraseFromParent();
return;
}
// Finally, promote the fine value to SSA form.
if (AI) {
std::vector<AllocaInst*> Allocas;
Allocas.push_back(AI);
PromoteMemToReg(Allocas, *DT, *DF, CurAST);
// Next, rewrite uses of the instruction, inserting PHI nodes as needed.
for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); UI != UE; ) {
// Grab the use before incrementing the iterator.
Use &U = UI.getUse();
// Increment the iterator before removing the use from the list.
++UI;
SSA.RewriteUseAfterInsertions(U);
}
// Update CurAST for NewPHIs if I had pointer type.
if (I.getType()->isPointerTy())
for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
CurAST->copyValue(NewPHIs[i], &I);
}
/// hoist - When an instruction is found to only use loop invariant operands