[llvm-commits] [llvm] r168829 - /llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp

[Bill Wendling]

On Dec 5, 2012, at 4:23 PM, Nick Lewycky <nlewycky at google.com> wrote:

> On 28 November 2012 15:23, Bill Wendling <isanbard at gmail.com> wrote:
> Author: void
> Date: Wed Nov 28 17:23:48 2012
> New Revision: 168829
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=168829&view=rev
> Log:
> When we delete a dead basic block, see if any of its successors are dead and
> delete those as well.
> 
> Modified:
>     llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp
> 
> Modified: llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp?rev=168829&r1=168828&r2=168829&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp Wed Nov 28 17:23:48 2012
> @@ -194,9 +194,19 @@
>            WorkList.insert(*II);
>      }
> 
> -    for (SmallPtrSet<BasicBlock*, 8>::iterator
> -           I = WorkList.begin(), E = WorkList.end(); I != E; ++I)
> -      DeleteDeadBlock(*I);
> +    // Delete the dead blocks and any of their dead successors.
> +    while (!WorkList.empty()) {
> +      BasicBlock *BB = *WorkList.begin();
> +      WorkList.erase(BB);
> +      SmallVector<BasicBlock*, 2> Successors(succ_begin(BB), succ_end(BB));
> +
> +      DeleteDeadBlock(BB);
> 
> I think you need to set MadeChange = true here. I think this bug could actually manifest because we use MadeChange later on to decide whether we need to recalculate the domtree.
> 
Okay.

> +
> +      for (SmallVectorImpl<BasicBlock*>::iterator
> +             II = Successors.begin(), IE = Successors.end(); II != IE; ++II)
> +        if (pred_begin(*II) == pred_end(*II))
> 
> What if the block includes a branch to itself?
> 
Won't the predecessor list be non-empty then?

-bw