RFC - COST of const_double for x86 prevents constant copy propagation in cse

[Andrew Pinski]

On Aug 25, 2005, at 2:09 PM, Fariborz Jahanian wrote:

> Compiled with -O1 -mdynamic-no-pic -march=pentium4 produces:
>
>         pxor    %xmm0, %xmm0
>         movsd   %xmm0, 16(%eax)
>         movsd   %xmm0, 8(%eax)
>         movsd   %xmm0, (%eax)
>
> But following code results in 7% performance gain in eon as reported 
> by one of Apple's performance people:
>
>         movl    $0, 16(%eax)
>         movl    $0, 20(%eax)
>         movl    $0, 8(%eax)
>         movl    $0, 12(%eax)
>         movl    $0, (%eax)
>         movl    $0, 4(%eax)

Actually that does not make sense for a real processor but then again 
this is x86 we
are talking about.  Because we have less complex instructions and less 
instructions
at that matter.

-- Pinski