------- Additional Comments From roger at eyesopen dot com 2005-02-19 05:41
-------
Re: comment #5
For floating point expressions, -(A+B) is only transformed into (-A)-B or
(-B)-A when the user explicitly specifies -ffast-math, i.e. only when
flag_unsafe_math_optimizations is true.
Re: comment #6
Interesting. Although on a handful of rs6000 cores (mpccore, 601 and 603),
a fused-multiply-add is more expensive that an addition, its always a win
to perform two fma's rather than a mult and two adds. It might be possible
(with some work) to teach combine to un-CSE the following:
double x;
double y;
void foo(double p, double q, double r, double s)
{
double t = p * q;
x = t + r;
y = t + s;
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19988
