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05a91cc09f
GEPs (more than one non-zero index) into simple GEPs (at most one non-zero index). In some simple experiments using this it's not uncommon to see 3% overall code size wins, because it exposes redundancies that can be eliminated, however it's tricky to use because instcombine aggressively undoes the work that this pass does. llvm-svn: 85144
82 lines
2.9 KiB
C++
82 lines
2.9 KiB
C++
//===- GEPSplitter.cpp - Split complex GEPs into simple ones --------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This function breaks GEPs with more than 2 non-zero operands into smaller
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// GEPs each with no more than 2 non-zero operands. This exposes redundancy
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// between GEPs with common initial operand sequences.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "split-geps"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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using namespace llvm;
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namespace {
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class GEPSplitter : public FunctionPass {
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virtual bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const;
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit GEPSplitter() : FunctionPass(&ID) {}
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};
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}
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char GEPSplitter::ID = 0;
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static RegisterPass<GEPSplitter> X("split-geps",
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"split complex GEPs into simple GEPs");
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FunctionPass *llvm::createGEPSplitterPass() {
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return new GEPSplitter();
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}
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bool GEPSplitter::runOnFunction(Function &F) {
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bool Changed = false;
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// Visit each GEP instruction.
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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for (BasicBlock::iterator II = I->begin(), IE = I->end(); II != IE; )
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(II++)) {
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unsigned NumOps = GEP->getNumOperands();
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// Ignore GEPs which are already simple.
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if (NumOps <= 2)
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continue;
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bool FirstIndexIsZero = isa<ConstantInt>(GEP->getOperand(1)) &&
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cast<ConstantInt>(GEP->getOperand(1))->isZero();
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if (NumOps == 3 && FirstIndexIsZero)
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continue;
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// The first index is special and gets expanded with a 2-operand GEP
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// (unless it's zero, in which case we can skip this).
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Value *NewGEP = FirstIndexIsZero ?
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GEP->getOperand(0) :
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GetElementPtrInst::Create(GEP->getOperand(0), GEP->getOperand(1),
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"tmp", GEP);
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// All remaining indices get expanded with a 3-operand GEP with zero
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// as the second operand.
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Value *Idxs[2];
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Idxs[0] = ConstantInt::get(Type::getInt64Ty(F.getContext()), 0);
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for (unsigned i = 2; i != NumOps; ++i) {
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Idxs[1] = GEP->getOperand(i);
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NewGEP = GetElementPtrInst::Create(NewGEP, Idxs, Idxs+2, "tmp", GEP);
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}
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GEP->replaceAllUsesWith(NewGEP);
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GEP->eraseFromParent();
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Changed = true;
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}
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return Changed;
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}
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void GEPSplitter::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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}
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