[Bug tree-optimization/79389] [7 Regression] 30% performance regression in SciMark2 MonteCarlo

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79389

--- Comment #8 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #6)
> Well, at least in the -O2 case, it clearly shows that (RTL) if-conversion
> does happen.
> If SETCC + ZEXT + ADD is always a win compared to LEAL x+1 + CMOV*, then we
> should just expand the cmov in that case to that or combine or peephole it
> to that.
> Now, with -m32 -march=i586 -O2 (so that cmov can't be used), I see
> noce_try_addcc (which is exactly that, SETCC + ZEXT + ADD) fails because the
> condition is complex:
> (ne (and:QI (subreg:QI (zero_extract:SI (reg:HI 100)
>                 (const_int 8 [0x8])
>                 (const_int 8 [0x8])) 0)
>         (const_int 5 [0x5]))
>     (const_int 0 [0]))

You can use -march=i686, so fcomi will be emitted instead of fcomp/fnstsw/test.