https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98095
Bug ID: 98095
Summary: Optimize __builtin_unordered (...) ||
__builtin_is{less,greater}{,equal}
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ubizjak at gmail dot com
Target Milestone: ---
These two functions are equivalent:
int t3 (float a, float b)
{
return __builtin_isless (a, b) || __builtin_isunordered (a, b);
}
int t4 (float a, float b)
{
return !__builtin_isgreaterequal (a, b);
}
gcc -O2:
t3:
ucomiss %xmm0, %xmm1
seta %al
ucomiss %xmm1, %xmm0
setp %dl
orl %edx, %eax
movzbl %al, %eax
ret
t4:
xorl %eax, %eax
ucomiss %xmm1, %xmm0
setb %al
ret
Proof:
for ordered operands:
the result of t3 is (a < b); the result of t4 is !(a >= b) = (a < b)
for unordered operands:
the result of the t3 is true; the result of t4 is !false = true.
q.e.d.
The above equivalence is true for all relations. I didn't check
__builtin_islessgreater; although gcc provides UNEQ, it doesn't provide
__builtin_isequal builtin function.
