------- Comment #7 from fxcoudert at gcc dot gnu dot org 2007-09-11 09:55 ------- (In reply to comment #6) > Why? more precisely what are the rules behind this yes?
Short answer: the statements are treated independently in the front-end. When the front-end sees: "nearest(huge(1.0),1.0)", it parses the expression and then tries to simplify it. huge(1.0) will be replaced by its value, and the "nearest(xxxxxxx,1.0)" is simplified. (At that point, the front-end detects the overflow and errors out.) Normally, the inter-statement optimization is to be done by the middle-end. You will find that the following code: x = 2. x = sqrt(x) you will find that sqrt() is calculated at runtime for -O0, while the two statements are simplified (and sqrt(2.) is precomputed at compile-time) at -O1. For NEAREST, the middle-end doesn't perform the simplification because instead of translating the Fortran statement into C99 functions directly, we use call the libgfortran function gfortran_nearest_r4(), which the middle-end doesn't know and can't optimized away. (Doing so is a missed optimization, now filed as PR33387.) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33296
