Author: efriedma Date: Tue Feb 12 06:08:14 2008 New Revision: 47006 URL: http://llvm.org/viewvc/llvm-project?rev=47006&view=rev Log: Fix for bug 1996: optimize out loads of undef. This code basically just checks for a malloc/alloca immediately followed by a load.
Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=47006&r1=47005&r2=47006&view=diff ============================================================================== --- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original) +++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Tue Feb 12 06:08:14 2008 @@ -1010,7 +1010,34 @@ dep = MD.getDependency(L, dep); } } - + + if (dep != MemoryDependenceAnalysis::None && + dep != MemoryDependenceAnalysis::NonLocal && + isa<AllocationInst>(dep)) { + // Check that this load is actually from the + // allocation we found + Value* v = L->getOperand(0); + while (true) { + if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) + v = BC->getOperand(0); + else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) + v = GEP->getOperand(0); + else + break; + } + if (v == dep) { + // If this load depends directly on an allocation, there isn't + // anything stored there; therefore, we can optimize this load + // to undef. + MD.removeInstruction(L); + + L->replaceAllUsesWith(UndefValue::get(L->getType())); + toErase.push_back(L); + deletedLoad = true; + NumGVNLoad++; + } + } + if (!deletedLoad) last = L; _______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits