http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32629
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2012-06-06
Ever Confirmed|0 |1
--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-06-06
10:05:57 UTC ---
Confirmed with -Os on trunk (4.8). With -O2 we unroll completely to
f:
.LFB0:
.cfi_startproc
movq $0, (%rdi)
movq $0, 8(%rdi)
movq $0, 16(%rdi)
movq $0, 24(%rdi)
movq $0, 32(%rdi)
movq $0, 40(%rdi)
movq $0, 48(%rdi)
movq $0, 56(%rdi)
movq $0, 64(%rdi)
movq $0, 72(%rdi)
ret
which lacks the size optimization to use a zeroed %rax. Likewise
for -Os which now looks like
0: 48 8d 57 30 lea 0x30(%rdi),%rdx
4: 48 c7 07 00 00 00 00 movq $0x0,(%rdi)
b: 48 c7 47 08 00 00 00 movq $0x0,0x8(%rdi)
12: 00
13: 48 c7 47 10 00 00 00 movq $0x0,0x10(%rdi)
1a: 00
1b: 48 c7 47 18 00 00 00 movq $0x0,0x18(%rdi)
22: 00
23: b9 08 00 00 00 mov $0x8,%ecx
28: 48 c7 47 20 00 00 00 movq $0x0,0x20(%rdi)
2f: 00
30: 48 c7 47 28 00 00 00 movq $0x0,0x28(%rdi)
37: 00
38: 31 c0 xor %eax,%eax
3a: 48 89 d7 mov %rdx,%rdi
3d: f3 ab rep stos %eax,%es:(%rdi)
3f: c3 retq
I suppose with -Os we use rep stosl because that's one byte smaller ...(?)
I suppose doing the $0x0 optimization should be done post-reload.
