llvm dev - Aug 2009 - [LLVMdev] SimplifyCFG

Hello,

in the description of SimplifyCFG, it says that it can "Eliminates PHI 
nodes for basic blocks with a single predecessor."

I tested this pass with a program that has phi nodes with a single 
predecessor and it did not remove it. I also looked in the code and 
found nothing to remove it. I'm I missing something, or it does not 
remove phis with a single predecessor?

My sample is attached.

-- 
Andre Tavares
Master Student in Computer Science - UFMG - Brasil
http://dcc.ufmg.br/~andrelct

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2009/8/28 Andre Tavares <andrelct at dcc.ufmg.br>
> Hello,
>
> in the description of SimplifyCFG, it says that it can "Eliminates PHI
> nodes for basic blocks with a single predecessor."
>
> I tested this pass with a program that has phi nodes with a single
> predecessor and it did not remove it. I also looked in the code and found
> nothing to remove it. I'm I missing something, or it does not remove
phis
> with a single predecessor?

This is probably better discussed in a bug report. I only took a brief look,
but it looks like the problem is triggered by the CFG being diamond-shaped.
The attached x.bc is a simpler testcase that also demonstrates the
missed-optimization.

Nick
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