On Wed, Feb 9, 2022 at 12:20 AM Roger Sayle <ro...@nextmovesoftware.com> wrote: > > > 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. > > This patch has been tested on x86_64-pc-linux-gnu with make bootstrap and > make -k check no new failures. Ok for mainline?
OK. Thanks, Richard. > 2022-02-08 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. > > Thanks in advance (and sorry for the breakage/thinko). > Roger > -- >
