------- Comment #2 from hjl dot tools at gmail dot com 2010-06-04 13:08 -------
(In reply to comment #1)
> Because our tree reassoc doesn't re-associate them.
>
The tree reassoc pass makes it slower:
[...@gnu-6 44382]$ cat x.i
extern int a, b, c, d, e, f;
void
foo ()
{
a = (b * c) * (d * e);
}
[...@gnu-6 44382]$ gcc -S -O2 x.i
[...@gnu-6 44382]$ cat x.s
.file "x.i"
.text
.p2align 4,,15
.globl foo
.type foo, @function
foo:
.LFB0:
.cfi_startproc
movl c(%rip), %eax
imull b(%rip), %eax
imull d(%rip), %eax
imull e(%rip), %eax
movl %eax, a(%rip)
ret
[...@gnu-6 44382]$ gcc -S -O2 x.i -fno-tree-reassoc
[...@gnu-6 44382]$ cat x.s
.file "x.i"
.text
.p2align 4,,15
.globl foo
.type foo, @function
foo:
.LFB0:
.cfi_startproc
movl b(%rip), %eax
movl d(%rip), %edx
imull c(%rip), %eax
imull e(%rip), %edx
imull %edx, %eax
movl %eax, a(%rip)
ret
[...@gnu-6 44382]$
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44382
