https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94589
--- Comment #20 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:ad96c867e173c1ebcfc201b201adac5095683a08 commit r12-559-gad96c867e173c1ebcfc201b201adac5095683a08 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu May 6 10:15:40 2021 +0200 phiopt: Optimize (x <=> y) cmp z [PR94589] genericize_spaceship genericizes i <=> j to approximately ({ int c; if (i == j) c = 0; else if (i < j) c = -1; else c = 1; c; }) for strong ordering and ({ int c; if (i == j) c = 0; else if (i < j) c = -1; else if (i > j) c = 1; else c = 2; c; }) for partial ordering. The C++ standard supports then == or != comparisons of that against strong/partial ordering enums, or </<=/==/!=/>/>= comparisons of <=> result against literal 0. In some cases we already optimize that but in many cases we keep performing all the 2 or 3 comparisons, compute the spaceship value and then compare that. The following patch recognizes those patterns if the <=> operands are integral types or floating point (the latter only for -ffast-math) and optimizes it to the single comparison that is needed (plus adds debug stmts if needed for the spaceship result). There is one thing I'd like to address in a follow-up: the pr94589-2.C testcase should be matching just 12 times each, but runs into operator>=(partial_ordering, unspecified) being defined as (_M_value&1)==_M_value rather than _M_value>=0. When not honoring NaNs, the 2 case should be unreachable and so (_M_value&1)==_M_value is then equivalent to _M_value>=0, but is not a single use but two uses. I'll need to pattern match that case specially. 2021-05-06 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/94589 * tree-ssa-phiopt.c (tree_ssa_phiopt_worker): Call spaceship_replacement. (cond_only_block_p, spaceship_replacement): New functions. * gcc.dg/pr94589-1.c: New test. * gcc.dg/pr94589-2.c: New test. * gcc.dg/pr94589-3.c: New test. * gcc.dg/pr94589-4.c: New test. * g++.dg/opt/pr94589-1.C: New test. * g++.dg/opt/pr94589-2.C: New test. * g++.dg/opt/pr94589-3.C: New test. * g++.dg/opt/pr94589-4.C: New test.
