https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84328
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Target| |x86_64-*-* i?86-*-*
Priority|P3 |P2
Component|c++ |target
Target Milestone|--- |6.5
Summary|[6 Regression] |[6/7/8 Regression]
|-finline-small-functions |-finline-small-functions
|and inline keyword lead to |and inline keyword lead to
|slowdown since version 6 |slowdown since version 6
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The loop is (fast)
.L3:
movzwl %bx, %eax
movl %eax, %edx
sall $8, %edx
orl %eax, %edx
movl %edx, %eax
andl $16711935, %eax
movl %eax, %edx
sall $4, %edx
orl %eax, %edx
andl $252645135, %edx
leal 0(,%rdx,4), %eax
orl %edx, %eax
andl $858993459, %eax
movl %eax, %edx
leal (%rax,%rax), %eax
orl %edx, %eax
andl $1431655765, %eax
orl $74565, %eax
xorl %eax, %ebx
subq $1, %rcx
jne .L3
vs. (slow)
.L3:
movl %ebx, %eax
andl $1023, %eax
movl %eax, %edx
sall $16, %edx
xorl %eax, %edx
movl %edx, %eax
andl $-16776961, %eax
movl %eax, %edx
sall $8, %edx
xorl %eax, %edx
andl $50393103, %edx
movl %edx, %eax
sall $4, %eax
xorl %edx, %eax
andl $51130563, %eax
movl %eax, %edx
leal 0(,%rax,4), %eax
xorl %edx, %eax
andl $153391689, %eax
orl $74565, %eax
xorl %eax, %ebx
subq $1, %rcx
jne .L3
I didn't try to confirm the actual slowdown. I think it has nothing to do with
inlining but with something x86 specific.
