[llvm-commits] [llvm] r138890 - /llvm/trunk/lib/Transforms/Scalar/SCCP.cpp

[Duncan Sands]

Hi Bill, why do you need a worklist?  Basic blocks can be big, so pushing the
whole basic block into a worklist seems like a bad idea to me if it can be
avoided.  Here I think you can get the same effect without a work list by
moving the iterator appropriately when you see a landingpad instruction.

Ciao, Duncan.


> Make sure we aren't deleting the landingpad instruction.
>
> The landingpad instruction is required in the landing pad block. Because we're
> not deleting terminating instructions, the invoke may still jump to here (see
> Transforms/SCCP/2004-11-16-DeadInvoke.ll). Remove all uses of the landingpad
> instruction, but keep it around until code-gen can remove the basic block.
>
> Modified:
>      llvm/trunk/lib/Transforms/Scalar/SCCP.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/SCCP.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SCCP.cpp?rev=138890&r1=138889&r2=138890&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/SCCP.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/SCCP.cpp Wed Aug 31 15:55:20 2011
> @@ -1681,15 +1681,31 @@
>   static void DeleteInstructionInBlock(BasicBlock *BB) {
>     DEBUG(dbgs()<<  "  BasicBlock Dead:"<<  *BB);
>     ++NumDeadBlocks;
> -
> +
> +  // Check to see if there are non-terminating instructions to delete.
> +  if (isa<TerminatorInst>(BB->begin()))
> +    return;
> +
>     // Delete the instructions backwards, as it has a reduced likelihood of
>     // having to update as many def-use and use-def chains.
> -  while (!isa<TerminatorInst>(BB->begin())) {
> -    Instruction *I = --BasicBlock::iterator(BB->getTerminator());
> -
> +  std::vector<Instruction*>  WorkList;
> +  WorkList.reserve(BB->size());
> +  BasicBlock::iterator I = --BasicBlock::iterator(BB->getTerminator());
> +
> +  while (true) {
>       if (!I->use_empty())
>         I->replaceAllUsesWith(UndefValue::get(I->getType()));
> -    BB->getInstList().erase(I);
> +    WorkList.push_back(I);
> +    if (I == BB->begin())
> +      break;
> +    --I;
> +  }
> +
> +  for (std::vector<Instruction*>::iterator
> +         II = WorkList.begin(), IE = WorkList.end(); II != IE; ++II) {
> +    if (isa<LandingPadInst>(*II))
> +      continue;
> +    BB->getInstList().erase(*II);
>       ++NumInstRemoved;
>     }
>   }
>
>
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