[llvm-commits] [llvm] r133512 - /llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp

[Frits van Bommel]

On 21 June 2011 13:57, Jay Foad <jay.foad at gmail.com> wrote:
> On 21 June 2011 12:41, Frits van Bommel <fvbommel at gmail.com> wrote:
>> On 21 June 2011 12:02, Jay Foad <jay.foad at gmail.com> wrote:
>>> Log:
>>> Don't use PN->replaceUsesOfWith() to change a PHINode's incoming blocks,
>>> because it won't work after my phi operand changes, because the incoming
>>> blocks will no longer be Uses.
>>
>>>   while (PHINode* P = dyn_cast<PHINode>(BI)) {
>>> -    P->replaceUsesOfWith(exitingBlock, preheader);
>>> +    int j = P->getBasicBlockIndex(exitingBlock);
>>> +    assert(j >= 0 && "Can't find exiting block in exit block's phi node!");
>>> +    P->setIncomingBlock(j, preheader);
>>
>> replaceUsesOfWith() can handle multiple uses of the same value, but
>> this version only handles a single use. Are you sure there can only be
>> a single incoming edge from each basic block here?
>
> exitingBlock is an arbitrarily chosen member of exitingBlocks[]. The
> code goes on to say:
>
>    for (unsigned i = 1; i < exitingBlocks.size(); ++i)
>      P->removeIncomingValue(exitingBlocks[i]);
>
> which will only remove one incoming edge for each of the other members
> of exitingBlocks[]. So yes, I'm fairly sure that either there's only a
> single incoming edge from each exitingBlock, or the code was already
> broken.

Huh. Don't know how I missed that. It's all right there in the diff, even.