https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81803
Chen Qi <qi.chen at windriver dot com> changed:
What |Removed |Added
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CC| |qi.chen at windriver dot com
--- Comment #11 from Chen Qi <qi.chen at windriver dot com> ---
mpf,
I'm working on Yocto project. I also encountered a similar problem.
In brief, on qemumips64, `systemctl status <xxx>' has the output of `systemctl
show <xxx>'. I debugged a little bit and found that it's not the code logic's
problem. Instead it's gcc optimization problem. With '-O1', the problem is
reproduced; with '-O0', the problem is gone.
Please see https://bugzilla.yoctoproject.org/show_bug.cgi?id=12266 for more
details.
I used the patch you created in attachment. And things work correctly with
'-O2'.
Is there any plan sending the patch to gcc mailing list?
Is there any known problem about the patch?
Best Regards,
Chen Qi
(In reply to mpf from comment #9)
> Created attachment 42075 [details]
> Proposed fix
>
> Off-thread James pointed out that one of my patches I did last year appeared
> to fix this issue but it was one I reverted owing to breaking ARM (and
> probably others). The thread was:
>
> https://gcc.gnu.org/ml/gcc-patches/2017-02/msg00518.html
>
> At the time I thought I had fixed the same problem twice and that the
> changes to simplify_operand_subreg were sufficient. It occurs to me however
> that simplify_operand_subreg only has the opportunity to fix
> WORD_REGISTER_OPERATIONS issues affecting subreg(mem) patterns not
> subreg(reg) patterns where reg is a pseudo that may yet be spilled.
>
> I can't say that I am 100% convinced yet with my thinking here but I've
> attached an updated version of the original patch with some changes:
>
> * Incorporated Eric's feedback on the original patch to check
> GET_MODE_PRECISION instead of GET_MODE_SIZE for comparing whether a mode is
> strictly narrower
> * Limited the test to word sized inner modes or smaller
> * Limited the test to OP_OUT or OP_INOUT as I can't see any reason why it
> would matter if we do a narrower input reload
>
> This is barely tested but does fix testcase-c which is the only one I can
> get to trigger.
