[Bug target/122948] sh: comparison is miscompiled

[olegendo at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122948

--- Comment #4 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to celeriyacon from comment #3)
> The T flag calculation part of the "subc" insn in sh.md looks wrong:
> 
>       (gtu:SI (minus:SI (minus:SI (match_dup 1) (match_dup 2))
>                         (reg:SI T_REG))
>               (match_dup 1)))]
> 
> 
> I think it should instead be something like:
> 
>       (gtu:SI (plus:DI (zero_extend:DI (match_dup:SI 2))
>                        (zero_extend:DI (reg:SI T_REG)))
>               (zero_extend:DI (match_dup:SI 1))))]

Thanks for reporting this.

Have you tried to change the pattern to see if it fixes the problem?

I would be surprised if the T-bit calculation expression of "subc" (or of addc)
is actually used.