diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index b326220499d..cbfb81bf05a 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -4671,6 +4671,39 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) { SPI->replaceAllUsesWith(PrevSPI); return EraseInstFromFunction(CI); } + } else { + switch (II->getIntrinsicID()) { + default: break; + case Intrinsic::stackrestore: { + // If the save is right next to the restore, remove the restore. This can + // happen when variable allocas are DCE'd. + if (IntrinsicInst *SS = dyn_cast(II->getOperand(1))) { + if (SS->getIntrinsicID() == Intrinsic::stacksave) { + BasicBlock::iterator BI = SS; + if (&*++BI == II) + return EraseInstFromFunction(CI); + } + } + + // If the stack restore is in a return/unwind block and if there are no + // allocas or calls between the restore and the return, nuke the restore. + TerminatorInst *TI = II->getParent()->getTerminator(); + if (isa(TI) || isa(TI)) { + BasicBlock::iterator BI = II; + bool CannotRemove = false; + for (++BI; &*BI != TI; ++BI) { + if (isa(BI) || + (isa(BI) && !isa(BI))) { + CannotRemove = true; + break; + } + } + if (!CannotRemove) + return EraseInstFromFunction(CI); + } + break; + } + } } return visitCallSite(II);