https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108540
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think
int
foo (int x, double d)
{
if (x == 42)
d = -0.0;
if (d == 0.0)
return 42;
return 12;
}
behaves similarly with threading. The above function is basically return (x ==
42 || d == 0.0) ? 42 : 12;
In forwprop1 at -O2 we still have correct:
<bb 2> :
if (x_3(D) == 42)
goto <bb 3>; [INV]
else
goto <bb 4>; [INV]
<bb 3> :
<bb 4> :
# d_1 = PHI <d_4(D)(2), -0.0(3)>
if (d_1 == 0.0)
goto <bb 5>; [INV]
else
goto <bb 6>; [INV]
<bb 5> :
// predicted unlikely by early return (on trees) predictor.
<bb 6> :
# RANGE [irange] int [-INF, +INF] NONZERO 0x2e
# _2 = PHI <42(5), 12(4)>
but then comes ethread and turns that into:
<bb 2> :
if (x_3(D) == 42)
goto <bb 3>; [INV]
else
goto <bb 4>; [INV]
<bb 3> :
# d_5 = PHI <-0.0(2)>
goto <bb 6>; [100.00%]
<bb 4> :
# d_1 = PHI <d_4(D)(2)>
if (d_1 == 0.0)
goto <bb 5>; [INV]
else
goto <bb 6>; [INV]
<bb 5> :
// predicted unlikely by early return (on trees) predictor.
<bb 6> :
# RANGE [irange] int [-INF, +INF] NONZERO 0x2e
# _2 = PHI <42(5), 12(4), 12(3)>
as if -0.0 == 0.0 was false rather than true.
