[Bug rtl-optimization/17236] inefficient code for long long multiply on x86

[ubizjak at gmail dot com]

------- Comment #22 from ubizjak at gmail dot com  2007-12-19 13:11 -------
(In reply to comment #21)

> Indeed, if I only use the regclass.c and local-alloc.c hunks, I get only one
> spill!
> 
>         pushl   %ebx
>         movl    8(%esp), %edx
>         movl    16(%esp), %eax
>         movl    20(%esp), %ecx
>         imull   %edx, %ecx
>         movl    12(%esp), %ebx
>         imull   %eax, %ebx
>         addl    %ebx, %ecx
>         mull    %edx
>         leal    (%ecx,%edx), %edx
>         popl    %ebx
> 
> and no reg-reg move.

Excellent!

I think that we should fwprop stack arguments into the insns to further
optimize the code. According to pentopt.pdf, there is no penalty at all (at
least for P4+) when one of the insn operands is a memory reference. This would
relieve register pressure considerably.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17236