http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55342
--- Comment #9 from Yuri Rumyantsev <ysrumyan at gmail dot com> ---
The issue still exists in 4.9 compiler but we got another 30% degradation after
r202165 fix. It can be reproduced with modified test-case which as attached
with any 4.9 compiler, namely code produced for inner loop looks like:
.L8:
movl %esi, %ecx
movl %esi, %edi
movzbl 3(%esp), %edx
cmpb %cl, %dl
movl %edx, %ecx
cmovbe %ecx, %edi
.L4:
movl %esi, %edx
movl %edi, %ecx
subl %ecx, %edx
movl 28(%esp), %ecx
movl 28(%esp), %esi
addl $4, 28(%esp)
movb %dl, (%ecx)
movl %edi, %ecx
subl %ecx, %ebx
movl %edi, %edx
movzbl 3(%esp), %ecx
movb %bl, 1(%esi)
subl %edx, %ecx
movl %edi, %ebx
movb %cl, 2(%esi)
movl 28(%esp), %esi
cmpl %ebp, %eax
movb %bl, -1(%esi)
je .L1
.L5:
movzbl (%eax), %esi
leal 3(%eax), %eax
movzbl -2(%eax), %ebx
notl %esi
notl %ebx
movl %esi, %edx
movzbl -1(%eax), %ecx
cmpb %bl, %dl
movb %cl, 3(%esp)
notb 3(%esp)
jb .L8
movzbl 3(%esp), %edx
movl %ebx, %edi
cmpb %bl, %dl
cmovbe %edx, %edi
jmp .L4
and you can see that (1) there are 2 additional moves on top of blocks marked
with .L4 and .L8; (2) redundant spill/fills of 'write' base in block marked
with .L4 (28(%esp)).
To reproduce it is sufficient to compile modified test-case with '-m32
-march=atom' options.
