https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94800
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:144aee70b80de50f96a97ee64edd2f1c237c4906 commit r11-65-g144aee70b80de50f96a97ee64edd2f1c237c4906 Author: Jakub Jelinek <ja...@redhat.com> Date: Tue May 5 11:36:47 2020 +0200 match.pd: Canonicalize (x + (x << cst)) into (x * cst2) [PR94800] The popcount* testcases show yet another creative way to write popcount, but rather than adjusting the popcount matcher to deal with it, I think we just should canonicalize those (X + (X << C) to X * (1 + (1 << C)) and (X << C1) + (X << C2) to X * ((1 << C1) + (1 << C2)), because for multiplication we already have simplification rules that can handle nested multiplication (X * CST1 * CST2), while the the shifts and adds we have nothing like that. And user could have written the multiplication anyway, so if we don't emit the fastest or smallest code for the multiplication by constant, we should improve that. At least on the testcases seems the emitted code is reasonable according to cost, except that perhaps we could in some cases try to improve expansion of vector multiplication by uniform constant. 2020-05-05 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/94800 * match.pd (X + (X << C) to X * (1 + (1 << C)), (X << C1) + (X << C2) to X * ((1 << C1) + (1 << C2))): New canonicalizations. * gcc.dg/tree-ssa/pr94800.c: New test. * gcc.dg/tree-ssa/popcount5.c: New test. * gcc.dg/tree-ssa/popcount5l.c: New test. * gcc.dg/tree-ssa/popcount5ll.c: New test.
