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

[Evan Cheng]

On May 25, 2011, at 1:45 AM, Cameron Zwarich wrote:

> 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:

Of course. Done: r132071.

Evan

> 
>  // 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