On Wed, Mar 07, 2018 at 05:39:41PM +0000, Kyrill Tkachov wrote:
> Hi all,
> 
> In this wrong-code PR the combine pass ends up moving a CC-using instruction 
> past a *compare_cstore<mode>_insn
> insn_and_split. After reload the *compare_cstore<mode>_insn splitter ends up 
> generating a SUBS instruction that
> clobbers the condition flags, and things go bad.
> 
> The solution is simple, the *compare_cstore<mode>_insn pattern should specify 
> that it clobbers the CC register
> so that combine (or any other pass) does not assume that it can move CC-using 
> patterns across it.
> 
> This patch does that and fixes the testcase.
> 
> The testcase FAILs on GCC 8 only, but the buggy pattern is in GCC 6 onwards, 
> so we should backport this as
> a latent bug fix after it's had some time to bake in trunk.
> 
> Bootstrapped and tested on aarch64-none-linux-gnu.
> 
> Ok for trunk and later backports?

OK.

Thanks,
James

> 2018-03-07  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>
> 
>      PR target/84748
>      * config/aarch64/aarch64.md (*compare_cstore<mode>_insn): Mark pattern
>      as clobbering CC_REGNUM.
> 
> 2018-03-07  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>
> 
>      PR target/84748
>      * gcc.c-torture/execute/pr84748.c: New test.

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