https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98865
--- Comment #8 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:8fb94fc6097c0a934aac0d89c9c5e2038da67655 commit r13-793-g8fb94fc6097c0a934aac0d89c9c5e2038da67655 Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Fri May 27 08:57:46 2022 +0100 Canonicalize X&-Y as X*Y in match.pd when Y is [0,1]. "For every pessimization, there's an equal and opposite optimization". In the review of my original patch for PR middle-end/98865, Richard Biener pointed out that match.pd shouldn't be transforming X*Y into X&-Y as the former is considered cheaper by tree-ssa's cost model (operator count). A corollary of this is that we should instead be transforming X&-Y into the cheaper X*Y as a preferred canonical form (especially as RTL expansion now intelligently selects the appropriate implementation based on the target's costs). With this patch we now generate identical code for: int foo(int x, int y) { return -(x&1) & y; } int bar(int x, int y) { return (x&1) * y; } specifically on x86_64-pc-linux-gnu both use and/neg/and with -O2, but both use and/mul with -Os. One minor wrinkle/improvement is that this patch includes three additional optimizations (that account for the change in canonical form) to continue to optimize PR92834 and PR94786. 2022-05-27 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog * match.pd (match_zero_one_valued_p): New predicate. (mult @0 @1): Use zero_one_valued_p for optimization to the expression "bit_and @0 @1". (bit_and (negate zero_one_valued_p@0) @1): Optimize to MULT_EXPR. (plus @0 (mult (minus @1 @0) zero_one_valued_p@2)): New transform. (minus @0 (mult (minus @0 @1) zero_one_valued_p@2)): Likewise. (bit_xor @0 (mult (bit_xor @0 @1) zero_one_valued_p@2)): Likewise. Remove three redundant transforms obsoleted by the three above. gcc/testsuite/ChangeLog * gcc.dg/pr98865.c: New test case.
