https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107172
--- Comment #19 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to H.J. Lu from comment #18)
> (In reply to Segher Boessenkool from comment #16)
> > Hi Roger,
> >
> > (In reply to Roger Sayle from comment #15)
> > > Yes, a COMPARE rtx can be used to set various flags on x86, but many other
> > > operations also legitimately set and/or use MODE_CC, often in a parallel
> > > with the primary operation.
> >
> > *Any* MODE_CC setter sets the flags as-if from a compare. This is what
> > MODE_CC *is*.
> >
> > Setting something as ne:CC and then using it as somethingelse:CC has no
> > defined meaning.
>
> This
>
> (parallel [
> (set (reg:SI 97)
> (neg:SI (ltu:SI (reg:CCC 17 flags)
> (const_int 0 [0]))))
> (clobber (reg:CC 17 flags))
> ])
>
> still won't work correctly if reg:CCC 17 flags is set by a compare of
> 2 known values.
I guess Segher means it should be NE instead of LTU in the
x86_mov<mode>cc_0_m1_neg, since the setters is NE to const 0.
(ne:CCC (reg:SI 87 [ a_lsm.8 ])
(const_int 0 [0])))
(define_expand "x86_mov<mode>cc_0_m1_neg"
[(parallel
[(set (match_operand:SWI48 0 "register_operand")
- (neg:SWI48 (ltu:SWI48 (reg:CCC FLAGS_REG) (const_int 0))))
+ (neg:SWI48 (ne:SWI48 (reg:CCC FLAGS_REG) (const_int 0))))
(clobber (reg:CC FLAGS_REG))])])
It can pass the PR, but failed pr101617.c, the f1 case.
generate:
testl %edi, %edi
movl $1, %edx
movl $-1, %eax
cmove %edx, %eax
origin:
negl %edi
sbbl %eax, %eax
orl $1, %eax
