https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90204
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2019-04-23
CC| |hjl.tools at gmail dot com,
| |jakub at gcc dot gnu.org,
| |uros at gcc dot gnu.org
Component|c |target
Target Milestone|--- |8.4
Summary|[8 Regression] C code is |[8/9 Regression] C code is
|optimized worse than C++ |optimized worse than C++
Ever confirmed|0 |1
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r257505. A smaller regression happened already earlier with
r254855. Before the latter, we emitted:
pushq %rbp
movq %rdi, %rax
movq %rsp, %rbp
andq $-64, %rsp
vmovdqu32 16(%rbp), %zmm1
vpaddd 80(%rbp), %zmm1, %zmm0
vmovdqa64 %zmm0, -64(%rsp)
vmovdqa64 -64(%rsp), %xmm2
vmovdqa64 -48(%rsp), %xmm3
vmovdqa64 -32(%rsp), %xmm4
vmovdqa64 -16(%rsp), %xmm5
vmovups %xmm2, (%rdi)
vmovups %xmm3, 16(%rdi)
vmovups %xmm4, 32(%rdi)
vmovups %xmm5, 48(%rdi)
vzeroupper
leave
ret
r254855 then changed it into:
pushq %rbp
movq %rsp, %rbp
andq $-32, %rsp
movq %rdi, %rax
vmovdqu32 16(%rbp), %ymm2
vpaddd 80(%rbp), %ymm2, %ymm0
vmovq %xmm0, %rdx
vmovdqa64 %ymm0, -64(%rsp)
vmovdqu32 48(%rbp), %ymm3
vpaddd 112(%rbp), %ymm3, %ymm0
vmovdqa64 %ymm0, -32(%rsp)
movq %rdx, (%rdi)
movq -56(%rsp), %rdx
movq %rdx, 8(%rdi)
movq -48(%rsp), %rdx
movq %rdx, 16(%rdi)
movq -40(%rsp), %rdx
movq %rdx, 24(%rdi)
vmovq %xmm0, 32(%rax)
movq -24(%rsp), %rdx
movq %rdx, 40(%rdi)
movq -16(%rsp), %rdx
movq %rdx, 48(%rdi)
movq -8(%rsp), %rdx
movq %rdx, 56(%rdi)
vzeroupper
leave
ret
After the r257505 we seem to be versioning for alignment or so, that can't be
right for a loop with just 16 iterations.
