https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91384
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmpf. So the following was not optimized ever:
void foo (void);
void bar (void);
int
test (int a)
{
int r = -a;
if (a == 0)
foo ();
else
bar ();
return r;
}
Note this is also about canonicalization if you consider both jump forms
appearing in the source and the ability to thread them.
But yes, the CC re-using form is better (in case r is not dead otherwise).
On GIMPLE this shows we lack modeling of CCs. I'm not sure doing
_1 = __IFN_NEGATE_WITH_CCZ (a_2);
r_3 = __real _1;
_4 = __imag _1;
if (_4 != 0)
foo ();
else
bar ();
is the way to go though (that would be possible with current infrastructure).
A "nicer"/leaner way would be to generalize SSA projections so we do not
have to abuse COMPLEX and could allow
_1 = __IFN_NEGATE_WITH_CC (a_2);
r_3 = __value _1;
if (__CCZ _1 != 0);
foo ();
else
bar ();
but then doing this on GIMPLE is of course prone to CC spilling.
Note "fixing" the above testcase on GIMPLE is as hard as fixing it on RTL.
