[Bug rtl-optimization/48037] Missed optimization: unnecessary register moves

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48037

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |glisse at gcc dot gnu.org

--- Comment #9 from Marc Glisse <glisse at gcc dot gnu.org> 2012-10-23 18:42:28 UTC ---
(In reply to comment #8)
> The useless reg-reg moves prevail:
> 
> _Z6vsqrt2U8__vectord:
> .LFB520:
>         .cfi_startproc
>         sqrtsd  %xmm0, %xmm1
>         unpckhpd        %xmm0, %xmm0
>         movapd  %xmm1, %xmm2
>         sqrtsd  %xmm0, %xmm0
>         unpcklpd        %xmm0, %xmm2
>         movapd  %xmm2, %xmm0
>         ret
> 
> both movapds can be avoided by better register allocation.

With LRA we get one mov less:

_Z6vsqrt2U8__vectord:
.LFB521:
    .cfi_startproc
    sqrtsd    %xmm0, %xmm2
    unpckhpd    %xmm0, %xmm0
    sqrtsd    %xmm0, %xmm1
    movapd    %xmm2, %xmm0
    unpcklpd    %xmm1, %xmm0
    ret