https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86352
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
As for the memset issue with vectors, with -march=skylake on the trunk we get:
BucketMap::acquireBucket():
movq %rdi, %rax
movq %rsi, %rcx
.L2:
movq (%rsi), %rdx
andl $1, %edx
lock btsq %rdx, (%rcx)
jc .L2
vpxor %xmm15, %xmm15, %xmm15
vmovdqu %ymm15, (%rax)
vmovdqu %ymm15, 32(%rax)
vmovdqu %ymm15, 64(%rax)
vmovdqu %ymm15, 96(%rax)
ret
Which I think is close to the best code, there are two extra moves which is due
to the way atomics are represented but otherwise still decent code.
Which is much better than LLVM can do:
BucketMap::acquireBucket(): # @BucketMap::acquireBucket()
movq %rdi, %r8
movl $1, %ecx
.LBB1_1: # =>This Loop Header: Depth=1
# Child Loop BB1_2 Depth 2
movq (%rsi), %rax
andb $1, %al
shlxq %rax, %rcx, %rdx
movq (%rsi), %rax
.p2align 4, 0x90
.LBB1_2: # Parent Loop BB1_1 Depth=1
# => This Inner Loop Header: Depth=2
movq %rax, %rdi
orq %rdx, %rdi
lock cmpxchgq %rdi, (%rsi)
jne .LBB1_2
# %bb.3: # in Loop: Header=BB1_1 Depth=1
testl %eax, %edx
jne .LBB1_1
# %bb.4:
vxorps %xmm0, %xmm0, %xmm0
vmovups %ymm0, 96(%r8)
vmovups %ymm0, 64(%r8)
vmovups %ymm0, 32(%r8)
vmovups %ymm0, (%r8)
movq %r8, %rax
vzeroupper
ret
So many things badly wrong with the above LLVM code, compare xchange loop vs
btsq, extra vzeroupper which is not needed as the upper parts of the ymm
registers are already zero.
