[llvm-commits] [llvm] r138932 - /llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp

[Duncan Sands]

Hi Bill,

> Resubmit with fix. Properly remove the instructions except for landingpad, which should be removed only when its invokes are.

same comment about the work list not really being needed.

Ciao, Duncan.

>
> Modified:
>      llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=138932&r1=138931&r2=138932&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Wed Aug 31 20:28:11 2011
> @@ -1574,22 +1574,41 @@
>       for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
>         if (!Visited.count(BB)) {
>           Instruction *Term = BB->getTerminator();
> -        while (Term != BB->begin()) {   // Remove instrs bottom-up
> -          BasicBlock::iterator I = Term; --I;
>
> -          DEBUG(errs()<<  "IC: DCE: "<<  *I<<  '\n');
> +        if (isa<TerminatorInst>(BB->begin()))
> +          continue;
> +
> +        // Delete the instructions backwards, as it has a reduced likelihood of
> +        // having to update as many def-use and use-def chains.
> +        std::vector<Instruction*>  WorkList;
> +        WorkList.reserve(BB->size());
> +        BasicBlock::iterator I = Term; --I;
> +
> +        while (true) {
> +          if (!I->getType()->isVoidTy())
> +            I->replaceAllUsesWith(UndefValue::get(I->getType()));
> +          WorkList.push_back(I);
> +          if (I == BB->begin())
> +            break;
> +          --I;
> +        }
> +
> +        for (std::vector<Instruction*>::iterator
> +               II = WorkList.begin(), IE = WorkList.end(); II != IE; ++II) {
> +          Instruction *Inst = *II;
> +          // Don't remove the landing pad. It should be removed only when its
> +          // invokes are removed.
> +          if (isa<LandingPadInst>(Inst))
> +            continue;
> +
>             // A debug intrinsic shouldn't force another iteration if we weren't
>             // going to do one without it.
> -          if (!isa<DbgInfoIntrinsic>(I)) {
> +          if (!isa<DbgInfoIntrinsic>(Inst)) {
>               ++NumDeadInst;
>               MadeIRChange = true;
>             }
>
> -          // If I is not void type then replaceAllUsesWith undef.
> -          // This allows ValueHandlers and custom metadata to adjust itself.
> -          if (!I->getType()->isVoidTy())
> -            I->replaceAllUsesWith(UndefValue::get(I->getType()));
> -          I->eraseFromParent();
> +          Inst->eraseFromParent();
>           }
>         }
>     }
>
>
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