http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58963
--- Comment #3 from Cong Hou <congh at google dot com> --- Suppose there is a third-party complex library, which is written in the same way as <complex>. Then GCC could not recognize that as complex type, and will not use builtin calls to calculate multiplication and division. So why there should be a difference when I use the third-party complex lib and the standard library lib. After all, <complex> is all written in source code. <complex> is not the same as _Complex in C99. If we can use _Complex in C++, it is fine. But C does not have <complex>: we won't meet the situation that building the same file t.c using gcc and g++, and g++ is faster. gcc cannot recognize <complex>.
