llvm dev - Jun 2012 - [LLVMdev] Strong PHI elimination asserts in RegisterCoalescer.C:1388

I've started using the strong PHI elimination pass, and it seems to work 
beautifully (producing much better placement of copy instructions) - 
though I'm seeing that it triggers an assert in debug+assert builds.  
The assertion is on line 1388 of RegisterCoalescer.C.  Attached is the 
-debug output from the machine optimization part of the optimizer, for 
the simplest test case I could create that triggers this behavior.

Any idea what might be going wrong?  Are there known issues with strong 
PHI elimination?

Andrew
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: log_debug_coalescing
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20120620/b1fc4878/attachment.ksh>

I'm the person who wrote it, and it's not really maintained, as we
decided we wanted to go in a different direction long-term by having fewer
passes making independent coalescing decisions rather than more. At the time I
stopped working on it, it worked fine on x86 but caused problems with armv7 NEON
code.

If you file a PR with a test case, I am happy to take a quick look and try to
fix it. There have been some changes to the backend that might not have been
updated correctly in StrongPHIElimination.

Cameron

On Jun 20, 2012, at 3:47 PM, Andrew Clinton wrote:
> I've started using the strong PHI elimination pass, and it seems to
work beautifully (producing much better placement of copy instructions) - though
I'm seeing that it triggers an assert in debug+assert builds.  The assertion
is on line 1388 of RegisterCoalescer.C.  Attached is the -debug output from the
machine optimization part of the optimizer, for the simplest test case I could
create that triggers this behavior.
> 
> Any idea what might be going wrong?  Are there known issues with strong PHI
elimination?
> 
> Andrew
>
<log_debug_coalescing.txt>_______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

I will try to make a standalone test case but the one that is failing 
uses a custom back end, so it's not really portable.

So is the plan to have the strong PHI elimination behavior rolled into 
other passes?

Andrew

On 06/20/2012 06:54 PM, Cameron Zwarich wrote:
> I'm the person who wrote it, and it's not really maintained, as we
decided we wanted to go in a different direction long-term by having fewer
passes making independent coalescing decisions rather than more. At the time I
stopped working on it, it worked fine on x86 but caused problems with armv7 NEON
code.
>
> If you file a PR with a test case, I am happy to take a quick look and try
to fix it. There have been some changes to the backend that might not have been
updated correctly in StrongPHIElimination.
>
> Cameron
>
> On Jun 20, 2012, at 3:47 PM, Andrew Clinton wrote:
>
>> I've started using the strong PHI elimination pass, and it seems to
work beautifully (producing much better placement of copy instructions) - though
I'm seeing that it triggers an assert in debug+assert builds.  The assertion
is on line 1388 of RegisterCoalescer.C.  Attached is the -debug output from the
machine optimization part of the optimizer, for the simplest test case I could
create that triggers this behavior.
>>
>> Any idea what might be going wrong?  Are there known issues with strong
PHI elimination?
>>
>> Andrew
>>
<log_debug_coalescing.txt>_______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev