------- Additional Comments From athena at fftw dot org 2005-02-16 20:37 ------- (In reply to comment #3) > Ok, this is the patch which caused this code generation regression: > 2004-02-07 Roger Sayle <[EMAIL PROTECTED]> > > * fold-const.c (negate_expr_p, negate_expr): Optimize -(A+B) into > either (-A)-B or (-B)-A, if A or B is easily negated respectively. > (fold) <MINUS_EXPR>: Optimize (A*C) - (B*C) -> (A-B)*C for both > integer types and floating point with unsafe_math_optimizations. > Add similar optimization for (A*C1) - (A*C2) -> A*(C1-C2). > Optimize A - B as A + (-B), if B is easily negated.
Note that the straightforward transformation -(A+B) => (-A)-B is illegal according to the ieee-754 standard. For A=-0 and B=+0, -(A+B) = -(+0) = -0, whereas (-A)-B = +0 - +0 = +0 + -0 = +0. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19988
