[llvm-commits] [llvm] r132022 - /llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp

[Cameron Zwarich]

On 2011-05-24, at 4:12 PM, Evan Cheng wrote:

> @@ -910,12 +916,27 @@
>     // successor if they become single-entry, those PHI nodes may
>     // be in the Users list.
> 
> +    BasicBlock *Switch = SI->getParent();
> +    BasicBlock *SISucc = SI->getSuccessor(DeadCase);
> +    BasicBlock *Latch = L->getLoopLatch();
> +    // If the DeadCase successor dominates all of the predecessors of the
> +    // loop latch, then the transformation isn't safe since it will delete
> +    // the predecessor edges to the latch.
> +    if (Latch) {
> +      bool DominateAll = true;
> +      for (pred_iterator PI = pred_begin(Latch), PE = pred_end(Latch);
> +           DominateAll && PI != PE; ++PI)
> +        if (!DT->dominates(SISucc, *PI))
> +          DominateAll = false;
> +      if (DominateAll)
> +        continue;
> +    }

You only need to check whether SISucc dominates Latch here. Also, you should be change this check in RemoveBlockIfDead to be a dominance check rather than an equality check and avoid skipping the optimization:

  // If this is the edge to the header block for a loop, remove the loop and
  // promote all subloops.
  if (Loop *BBLoop = LI->getLoopFor(BB)) {
    if (BBLoop->getLoopLatch() == BB)
      RemoveLoopFromHierarchy(BBLoop);
  }

Cameron