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Re: [PATCH, GCC/LRA] Teach LRA to not use same register value for multiple output operands of an insn


On Thursday 14 July 2016 10:32:48 Thomas Preudhomme wrote:
> On Friday 08 July 2016 09:05:55 Mike Stump wrote:
> > On Jul 8, 2016, at 8:07 AM, Thomas Preudhomme
> 
> <thomas.preudhomme@foss.arm.com> wrote:
> > > While investigating the root cause a testsuite regression for the
> > > ARM/embedded-5-branch GCC in gcc.dg/vect/slp-perm-5.c, we found that the
> > > bug seems to also affect trunk.
> > 
> > Hum...  If in 6.x, and safe to back port to 6, a back port would be
> > nice...
> > I use LRA in 6.x, and seems like I'd be susceptible to this sort of thing,
> > but, I didn't test it.
> 
> It should affect 6.x as well yes since there is no special protection
> against it in the code being modified. However I only ever managed to
> reproduce this on the ARM/embedded-5-branch.

I've created PR71878 for this problem with more details on how to reproduce 
the issue. it only requires to backport a single commit to gcc-5-branch, build 
gcc for arm-none-eabi (make all-gcc is enough) and compile the testcase 
attached in the PR with the given options.

Please let me know if you need any more details.

Best regards,

Thomas


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