[LLVMdev] CodeExtractor.cpp potential bug?

[Vu Le]

I forgot to cc llvmdev.
Here is my original message.

I'm a bit confused on DominatorTreeBase::Split() (
http://llvm.org/docs/doxygen/html/Dominators_8h_source.html#l00229)
If a basic block A splits into A->B, when I call Split(), which is NewBB? A
or B?

The semantics shows that NewBB is the newly split basic block B.
But the assertion at line 229 doesn't seem right.

00229     assert(std::distance(GraphT::child_begin(NewBB),
00230                          GraphT::child_end(NewBB)) == 1 &&
00231            "NewBB should have a single successor!");

If A has 2 successors C, D, after it split to A->NewBB, NewBB should have 2
successors.
Hope anyone could explain this to me.
Thanks,
Vu

On Sat, Jan 22, 2011 at 10:28 PM, Vu Le <vmle at ucdavis.edu> wrote:

> Hi Cameron,
> I'm a bit confused on DominatorTreeBase::Split() (
> http://llvm.org/docs/doxygen/html/Dominators_8h_source.html#l00229)
> If a basic block A splits into A->B, when I call Split(), which is NewBB?
> A or B.
> Thanks,
> Vu
>
>
> On Mon, Jan 3, 2011 at 1:25 PM, Cameron Zwarich <zwarich at apple.com> wrote:
>
>> On Dec 31, 2010, at 11:20 AM, Vu Le wrote:
>>
>> > There might be a misuse of DominatorTree::splitBasicBlock in
>> CodeExtractor.cpp, line 145.
>> > Header is splited into two (OldPred->NewBB).
>> >
>> > Line 145 updates the dominator tree by calling
>> DT->splitBasicBlock(NewBB).
>> > I think it should be DT->splitBasicBlock(OldPred).
>> >
>> > When I tried to extract a code region whose header has 2 successors, my
>> pass crashed.
>> > It was because header (or OldPred) is the block that was splited, not
>> NewBB.
>> > DominatorTree::splitBasicBlock(BB) requires BB to have one successor.
>>
>>
>> The code in Dominator::splitBasicBlock() looks correct, but I think the
>> comment and assert may not be. I was writing a patch where I hit the same
>> issue.
>>
>> Cameron
>
>
>
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