[Bug middle-end/44382] New: Slow integer multiply

[hjl dot tools at gmail dot com]

For

---
extern int a, b, c, d, e, f;

void
foo ()
{
  a = f * b * c * d;
}
---

on Linux/x86-64, gcc generates:

        movl    b(%rip), %eax
        imull   f(%rip), %eax
        imull   c(%rip), %eax
        imull   d(%rip), %eax
        movl    %eax, a(%rip)
        ret

Icc generates:

        movl      c(%rip), %eax                                 #6.15
        movl      f(%rip), %edx                                 #6.7
        imull     d(%rip), %eax                                 #6.19
        imull     b(%rip), %edx                                 #6.11
        imull     %eax, %edx                                    #6.15
        movl      %edx, a(%rip)                                 #6.3
        ret                                                     #7.1

Icc version is faster since 2 multiplications may
be issued at the same time.


-- 
           Summary: Slow integer multiply
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hjl dot tools at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44382