[Bug target/105206] mis-optimization with -ffast-math and __builtin_powf

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105206

--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 11 Apr 2022, kargl at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105206
> 
> --- Comment #3 from kargl at gcc dot gnu.org ---
> (In reply to Richard Biener from comment #2)
> > Hm, it works for me on linux with glibc, can you be more specific as to what
> > OS/libc (version) you are using?
> > 
> > foof:
> > .LFB0:
> >         .cfi_startproc
> >         mulss   .LC0(%rip), %xmm0
> >         jmp     expf
> > 
> > food:
> > .LFB1:
> >         .cfi_startproc
> >         mulsd   .LC1(%rip), %xmm0
> >         jmp     exp
> 
> Richard, I'm using x86_64-*-freebsd.  I just checked with powl(), and got 
> fool:
> .LFB5:
>         .cfi_startproc
>         pushq   %rbp
>         .cfi_def_cfa_offset 16
>         .cfi_offset 6, -16
>         movq    %rsp, %rbp
>         .cfi_def_cfa_register 6
>         subq    $16, %rsp
>         flds    .LC0(%rip)
>         pushq   24(%rbp)
>         pushq   16(%rbp)
>         fstpt   -16(%rbp)
>         movq    -16(%rbp), %rax
>         movl    -8(%rbp), %edx
>         pushq   %rdx
>         pushq   %rax
>         call    powl
>         addq    $32, %rsp
>         leave
>         .cfi_def_cfa 7, 8
>         ret
>         .cfi_endproc
> 
> with -ffast-math.
> 
> This might be related to PR89125.  The patch I attached to that PR has never
> found its way into the repository.  I'll do some more testing later today.

Ah, yeah - that old issue, indeed good to revisit that.