https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86029
--- Comment #5 from Tavian Barnes <tavianator at gmail dot com> ---
(In reply to Zsolt from comment #3)
> What is the difference between gcc's and clang's __mulsc3?
The important difference is that Clang (and GCC trunk) expand the fastpath
inline, and fall back on __mulsc3 for the more complicated cases. So instead
of
complex float a = b * c;
expanding to
complex float a = __mulsc3(crealf(b), cimagf(b), crealf(c), cimagf(c));
it's more like
complex float a = (crealf(b)*crealf(c) - cimagf(b)*cimagf(c) +
I*(crealf(b)*cimagf(c) + cimagf(b)*crealf(c));
if (isunordered(crealf(a), cimagf(a))) {
a = __mulsc3(crealf(b), cimagf(b), crealf(c), cimagf(c));
}
The fastpath and unlikely branch tends to be faster than the function call.
