From d5f8684b16057df73771b23e293b400cb327e079 Mon Sep 17 00:00:00 2001 From: Owen Anderson Date: Thu, 23 Dec 2010 20:57:35 +0000 Subject: [PATCH] It is possible for SimplifyCFG to cause PHI nodes to become redundant too late in the optimization pipeline to be caught by instcombine, and it's not feasible to catch them in SimplifyCFG because the use-lists are in an inconsistent state at the point where it could know that it need to simplify them. Instead, have CodeGenPrepare look for trivially redundant PHIs as part of its general cleanup effort. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122516 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/CodeGenPrepare.cpp | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp index 60c7f7565eb..1f0930df06c 100644 --- a/lib/Transforms/Scalar/CodeGenPrepare.cpp +++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp @@ -22,6 +22,7 @@ #include "llvm/Instructions.h" #include "llvm/IntrinsicInst.h" #include "llvm/Pass.h" +#include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/ProfileInfo.h" #include "llvm/Target/TargetData.h" #include "llvm/Target/TargetLowering.h" @@ -959,7 +960,15 @@ bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) { for (BasicBlock::iterator BBI = BB.begin(), E = BB.end(); BBI != E; ) { Instruction *I = BBI++; - if (CastInst *CI = dyn_cast(I)) { + if (PHINode *P = dyn_cast(I)) { + // It is possible for very late stage optimizations (such as SimplifyCFG) + // to introduce PHI nodes too late to be cleaned up. If we detect such a + // trivial PHI, go ahead and zap it here. + if (Value *V = SimplifyInstruction(P)) { + P->replaceAllUsesWith(V); + P->eraseFromParent(); + } + } else if (CastInst *CI = dyn_cast(I)) { // If the source of the cast is a constant, then this should have // already been constant folded. The only reason NOT to constant fold // it is if something (e.g. LSR) was careful to place the constant