llvm dev - May 2014 - [LLVMdev] Regression in 3.4's register allocator?

Hi,

The RoboVM project recently upgraded from LLVM 3.3 to 3.4 and with the new
version we are sometimes seeing "ran out of registers during register
allocation" errors when targeting x86 32-bit that we haven't seen
before.
Nothing has changed in our bitcode generator. I have attached an IR file
which can be used to reproduce this problem. The problem occurs with -O2
and -disable-fp-elim specified.

Running llc from 3.3 works without problems:
$ ~/Downloads/clang+llvm-3.3-x86_64-apple-darwin12/bin/llc -mtriple
i386-unknown-macosx -O2 -disable-fp-elim reg-alloc-test.ll

While llc from 3.4 fails:
$ ~/Downloads/clang+llvm-3.4-x86_64-apple-darwin10.9/bin/llc -mtriple
i386-unknown-macosx -O2 -disable-fp-elim reg-alloc-test.ll
LLVM ERROR: ran out of registers during register allocation

I haven't been able to test this with the latest trunk but I got the same
error when trying with the 3.4.1 branch.

Has anyone else seen this? Is it a known bug? Or should I report it?

Regards,
Niklas
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Hi Niklas,

This works for me with trunk r207129.

We did fix some register allocation issues recently, don’t know which change
fixes the issue though.

Thanks,
-Quentin

On Apr 24, 2014, at 1:07 PM, Niklas Therning <niklas at therning.org>
wrote:
> Hi,
> 
> The RoboVM project recently upgraded from LLVM 3.3 to 3.4 and with the new
version we are sometimes seeing "ran out of registers during register
allocation" errors when targeting x86 32-bit that we haven't seen
before. Nothing has changed in our bitcode generator. I have attached an IR file
which can be used to reproduce this problem. The problem occurs with -O2 and
-disable-fp-elim specified.
> 
> Running llc from 3.3 works without problems:
> $ ~/Downloads/clang+llvm-3.3-x86_64-apple-darwin12/bin/llc -mtriple
i386-unknown-macosx -O2 -disable-fp-elim reg-alloc-test.ll
> 
> While llc from 3.4 fails:
> $ ~/Downloads/clang+llvm-3.4-x86_64-apple-darwin10.9/bin/llc -mtriple
i386-unknown-macosx -O2 -disable-fp-elim reg-alloc-test.ll
> LLVM ERROR: ran out of registers during register allocation
> 
> I haven't been able to test this with the latest trunk but I got the
same error when trying with the 3.4.1 branch.
> 
> Has anyone else seen this? Is it a known bug? Or should I report it?
> 
> Regards,
> Niklas
> <reg-alloc-test.ll>_______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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I can confirm that this regression has been fixed in trunk. Should I report
this as a bug in 3.4?


On Thu, Apr 24, 2014 at 10:17 PM, Quentin Colombet <qcolombet at
apple.com>wrote:
> Hi Niklas,
>
> This works for me with trunk r207129.
>
> We did fix some register allocation issues recently, don’t know which
> change fixes the issue though.
>
> Thanks,
> -Quentin
>
> On Apr 24, 2014, at 1:07 PM, Niklas Therning <niklas at therning.org>
wrote:
>
> Hi,
>
> The RoboVM project recently upgraded from LLVM 3.3 to 3.4 and with the new
> version we are sometimes seeing "ran out of registers during register
> allocation" errors when targeting x86 32-bit that we haven't seen
before.
> Nothing has changed in our bitcode generator. I have attached an IR file
> which can be used to reproduce this problem. The problem occurs with -O2
> and -disable-fp-elim specified.
>
> Running llc from 3.3 works without problems:
> $ ~/Downloads/clang+llvm-3.3-x86_64-apple-darwin12/bin/llc -mtriple
> i386-unknown-macosx -O2 -disable-fp-elim reg-alloc-test.ll
>
> While llc from 3.4 fails:
> $ ~/Downloads/clang+llvm-3.4-x86_64-apple-darwin10.9/bin/llc -mtriple
> i386-unknown-macosx -O2 -disable-fp-elim reg-alloc-test.ll
> LLVM ERROR: ran out of registers during register allocation
>
> I haven't been able to test this with the latest trunk but I got the
same
> error when trying with the 3.4.1 branch.
>
> Has anyone else seen this? Is it a known bug? Or should I report it?
>
> Regards,
> Niklas
> <reg-alloc-test.ll>_______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
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