https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104912
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'm noting that for skylake cost we have
_28 * _33 1 times scalar_stmt costs 16 in prologue
and
_28 * _33 1 times vector_stmt costs 16 in body
but the load/store costs are just 12, compared to znver2 this tips the bias
over to allow vectorization while for znver2 I currently see no vectorization.
For generic I also see vectorization.
Note that costing currently assumes that the cost model niter check is
performed first and short-cuts all the versioning conditions. But since
we emit
_248 = (unsigned int) mk_113;
_247 = _248 + 4294967295;
_246 = _247 > 2;
_245 = stride.4_74 != 0;
_244 = _245 & _246;
...
_183 = _184 | _211;
_182 = _183 & _244;
if (_182 != 0)
goto <bb 27>; [80.00%]
else
goto <bb 28>; [20.00%]
on GIMPLE how things are expanded depends on some luck and with the standalone
testcase and -Ofast with generic tuning we emit the > 2 cost model check
quite late:
addq $1, %rdi
imulq %r13, %rdi
leaq (%rax,%rdi), %rcx
movq 32(%rsp), %rax
leaq (%rax,%rcx), %rsi
movq (%rsp), %rax
leaq 0(,%rsi,8), %rdx
addq %rax, %rcx
leaq 0(,%rcx,8), %rax
addq %r13, %rcx
salq $3, %rcx
cmpq %rcx, %rdx
setg %cl
addq %r13, %rsi
salq $3, %rsi
cmpq %rsi, %rax
setg %sil
orb %cl, %sil
je .L8
movl -100(%rsp), %esi
leal -1(%rsi), %ecx
cmpl $2, %ecx <-----
movl 112(%rsp), %ecx
seta %sil
testl %ecx, %ecx
setg %cl
testb %cl, %sil
je .L8
let me try to hack^Wfix this.
