https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103683
Bug ID: 103683
Summary: Redundant !__builtin_isnan not removed with
-fno-signaling-nans
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: tkoenig at gcc dot gnu.org
Target Milestone: ---
If x is a NaN, then x > 1 will fail, so the __builtin_isnan function
could be removed in comparisons like (!__builtin_isnan (x)) && x > 1
lwhen -fno-signaling-nans is in effect.
Test case:
#include <math.h>
#include <stdio.h>
_Bool foo (double x)
{
return (!__builtin_isnan (x)) && x > 1;
}
_Bool bar (double x)
{
return x > 1;
}
void chk(double x)
{
printf ("%f %x %x\n", x, foo(x), bar(x));
}
int main()
{
chk(-1.0);
chk(1.0);
chk(2.9);
chk(NAN);
return 0;
}
With "gcc -fno-signaling-nans -S -O3 nan.c", one gets for foo
foo:
.seh_endprologue
ucomisd %xmm0, %xmm0
jp .L3
comisd .LC0(%rip), %xmm0
seta %al
ret
and for bar
bar:
.seh_endprologue
comisd .LC0(%rip), %xmm0
seta %al
ret
.seh_endproc
