http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55180
Bug #: 55180
Summary: Missed optimization abs(-x) -> abs(x)
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: gli...@gcc.gnu.org
double f(double x){
double y=-x;
return __builtin_fabs(y);
}
The negation doesn't disappear, even at -Ofast, I still see both "xor" and
"and" in the asm. (I don't think this optimization requires any unsafe math
option, but I am not completely sure about the trapping behavior)
Note that if I write __builtin_fabs(-x), the negation is removed before it has
a chance to appear in a dump.
