https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68105
--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to zboson from comment #0) > In addition, the following equations are always true even without > associative math. > > 2*a = a + a > 3*a = a + a + a > 4*a = a + a + a + a > 5*a = a + a + a + a + a > > It turns out that GCC does simplify a + a + a + a to 4*a but only with > associative math enabled e.g. with -Ofast when it could do it with -O3. This "always true" needs some qualification. It is wrong with -frounding-math, where you have to stop at 3 IIRC. (In reply to kugan from comment #2) > Looks like a duplicate of PR63586. I am not convinced this is completely a dup. The patch https://gcc.gnu.org/ml/gcc-patches/2016-05/msg00368.html would probably close PR63586, but not this one since all of the testcases about float in that patch use -ffast-math.
