https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98172
--- Comment #8 from H.J. Lu <hjl.tools at gmail dot com> ---
-mtune=generic -mavx2 -mfma generates awful code:
[hjl@gnu-skx-1 tmp]$ cat y.c
#define DATA_ENTRIES 256
extern double *a, *x, *y, *z;
void work()
{
int i;
for (i = 0; i < DATA_ENTRIES; ++i)
z[i] = a[i] * x[i] + y[i];
}
[hjl@gnu-skx-1 tmp]$ gcc -S -O3 y.c -mavx2 -mfma
[hjl@gnu-skx-1 tmp]$ cat y.s
.file "y.c"
.text
.p2align 4
.globl work
.type work, @function
work:
.LFB0:
.cfi_startproc
movq z(%rip), %rdx
movq x(%rip), %rsi
movq a(%rip), %rcx
movq y(%rip), %rdi
leaq 8(%rsi), %r8
movq %rdx, %rax
subq %r8, %rax
leaq 8(%rcx), %r9
cmpq $16, %rax
movq %rdx, %rax
seta %r8b
subq %r9, %rax
cmpq $16, %rax
seta %al
testb %al, %r8b
je .L5
leaq 8(%rdi), %r8
movq %rdx, %rax
subq %r8, %rax
cmpq $16, %rax
jbe .L5
xorl %eax, %eax
.p2align 4,,10
.p2align 3
.L3:
vmovupd (%rcx,%rax), %xmm3
vmovupd (%rsi,%rax), %xmm4
vinsertf128 $0x1, 16(%rcx,%rax), %ymm3, %ymm0
vinsertf128 $0x1, 16(%rsi,%rax), %ymm4, %ymm2
vmovupd (%rdi,%rax), %xmm5
vinsertf128 $0x1, 16(%rdi,%rax), %ymm5, %ymm1
vfmadd132pd %ymm2, %ymm1, %ymm0
vmovupd %xmm0, (%rdx,%rax)
vextractf128 $0x1, %ymm0, 16(%rdx,%rax)
addq $32, %rax
cmpq $2048, %rax
jne .L3
vzeroupper
ret
.L5:
xorl %eax, %eax
.p2align 4,,10
.p2align 3
.L2:
vmovsd (%rcx,%rax), %xmm0
vmovsd (%rdi,%rax), %xmm6
vfmadd132sd (%rsi,%rax), %xmm6, %xmm0
vmovsd %xmm0, (%rdx,%rax)
addq $8, %rax
cmpq $2048, %rax
jne .L2
ret
.cfi_endproc
.LFE0:
.size work, .-work
.ident "GCC: (GNU) 10.2.1 20210119 (Red Hat 10.2.1-10)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-skx-1 tmp]$ gcc -S -O3 y.c -mavx2 -mfma -mtune=haswell
[hjl@gnu-skx-1 tmp]$ cat y.s
.file "y.c"
.text
.p2align 4
.globl work
.type work, @function
work:
.LFB0:
.cfi_startproc
movq z(%rip), %rdx
movq x(%rip), %rsi
movq a(%rip), %rcx
movq y(%rip), %rdi
leaq 8(%rsi), %r8
movq %rdx, %rax
subq %r8, %rax
leaq 8(%rcx), %r9
cmpq $16, %rax
movq %rdx, %rax
seta %r8b
subq %r9, %rax
cmpq $16, %rax
seta %al
testb %al, %r8b
je .L5
leaq 8(%rdi), %r8
movq %rdx, %rax
subq %r8, %rax
cmpq $16, %rax
jbe .L5
xorl %eax, %eax
.p2align 4,,10
.p2align 3
.L3:
vmovupd (%rcx,%rax), %ymm0
vmovupd (%rdi,%rax), %ymm1
vfmadd132pd (%rsi,%rax), %ymm1, %ymm0
vmovupd %ymm0, (%rdx,%rax)
addq $32, %rax
cmpq $2048, %rax
jne .L3
vzeroupper
ret
.L5:
xorl %eax, %eax
.p2align 4,,10
.p2align 3
.L2:
vmovsd (%rcx,%rax), %xmm0
vmovsd (%rdi,%rax), %xmm2
vfmadd132sd (%rsi,%rax), %xmm2, %xmm0
vmovsd %xmm0, (%rdx,%rax)
addq $8, %rax
cmpq $2048, %rax
jne .L2
ret
.cfi_endproc
.LFE0:
.size work, .-work
.ident "GCC: (GNU) 10.2.1 20210119 (Red Hat 10.2.1-10)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-skx-1 tmp]$
