1 //===- GEPSplitter.cpp - Split complex GEPs into simple ones --------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This function breaks GEPs with more than 2 non-zero operands into smaller
11 // GEPs each with no more than 2 non-zero operands. This exposes redundancy
12 // between GEPs with common initial operand sequences.
14 //===----------------------------------------------------------------------===//
16 #define DEBUG_TYPE "split-geps"
17 #include "llvm/Transforms/Scalar.h"
18 #include "llvm/Constants.h"
19 #include "llvm/Function.h"
20 #include "llvm/Instructions.h"
21 #include "llvm/Pass.h"
25 class GEPSplitter : public FunctionPass {
26 virtual bool runOnFunction(Function &F);
27 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
29 static char ID; // Pass identification, replacement for typeid
30 explicit GEPSplitter() : FunctionPass(ID) {
31 initializeGEPSplitterPass(*PassRegistry::getPassRegistry());
36 char GEPSplitter::ID = 0;
37 INITIALIZE_PASS(GEPSplitter, "split-geps",
38 "split complex GEPs into simple GEPs", false, false)
40 FunctionPass *llvm::createGEPSplitterPass() {
41 return new GEPSplitter();
44 bool GEPSplitter::runOnFunction(Function &F) {
47 // Visit each GEP instruction.
48 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
49 for (BasicBlock::iterator II = I->begin(), IE = I->end(); II != IE; )
50 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(II++)) {
51 unsigned NumOps = GEP->getNumOperands();
52 // Ignore GEPs which are already simple.
55 bool FirstIndexIsZero = isa<ConstantInt>(GEP->getOperand(1)) &&
56 cast<ConstantInt>(GEP->getOperand(1))->isZero();
57 if (NumOps == 3 && FirstIndexIsZero)
59 // The first index is special and gets expanded with a 2-operand GEP
60 // (unless it's zero, in which case we can skip this).
61 Value *NewGEP = FirstIndexIsZero ?
63 GetElementPtrInst::Create(GEP->getOperand(0), GEP->getOperand(1),
65 // All remaining indices get expanded with a 3-operand GEP with zero
66 // as the second operand.
68 Idxs[0] = ConstantInt::get(Type::getInt64Ty(F.getContext()), 0);
69 for (unsigned i = 2; i != NumOps; ++i) {
70 Idxs[1] = GEP->getOperand(i);
71 NewGEP = GetElementPtrInst::Create(NewGEP, Idxs, Idxs+2, "tmp", GEP);
73 GEP->replaceAllUsesWith(NewGEP);
74 GEP->eraseFromParent();
81 void GEPSplitter::getAnalysisUsage(AnalysisUsage &AU) const {