I have a -ffast-math (missing?) optimization question. I noticed on MIPS
that if I compiled:
#include <math.h>
extern x;
void foo() { x = sin(log(x)); }
GCC will extend 'x' to double precision, call the double precision log and sin
functions and then truncate the result to single precision.
If instead, I have:
#include <math.h>
extern x;
void foo() { x = log(x); x = sin(x); }
Then GCC will call the single precision log and sin functions and not do
any extensions or truncations. In addition to avoiding the extend/trunc
instructions the single precision log and sin functions are presumably
faster then the double precision ones making the entire code much faster.
Is there a reason why GCC couldn't (under -ffast-math) call the single
precision routines for the first case?
Steve Ellcey
[email protected]
