https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96392
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:2d3c477599b02b06e338acd5f5098ee7a3fe6176 commit r12-7130-g2d3c477599b02b06e338acd5f5098ee7a3fe6176 Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Wed Feb 9 14:21:08 2022 +0000 [PATCH] PR tree-optimization/104420: Fix checks for constant folding X*0.0 This patch resolves PR tree-optimization/104420, which is a P1 regression where, as observed by Jakub Jelinek, the conditions for constant folding x*0.0 are incorrect (following my patch for PR tree-optimization/96392). The multiplication x*0.0 may yield a negative zero result, -0.0, if X is negative (not just if x may be negative zero). Hence (without -ffast-math) (int)x*0.0 can't be optimized to 0.0, but (unsigned)x*0.0 can be constant folded. This adds a bunch of test cases to confirm the desired behaviour, and removes an incorrect test from gcc.dg/pr96392.c which checked for the wrong behaviour. 2022-02-09 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog PR tree-optimization/104420 * match.pd (mult @0 real_zerop): Tweak conditions for constant folding X*0.0 (or X*-0.0) to HONOR_SIGNED_ZEROS when appropriate. gcc/testsuite/ChangeLog PR tree-optimization/104420 * gcc.dg/pr104420-1.c: New test case. * gcc.dg/pr104420-2.c: New test case. * gcc.dg/pr104420-3.c: New test case. * gcc.dg/pr104420-4.c: New test case. * gcc.dg/pr96392.c: Remove incorrect test.
