https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103973
--- Comment #9 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:463d9108766dcbb6a1051985e6c840a46897fe10 commit r12-6637-g463d9108766dcbb6a1051985e6c840a46897fe10 Author: Jakub Jelinek <ja...@redhat.com> Date: Mon Jan 17 13:39:05 2022 +0100 widening_mul, i386: Improve spaceship expansion on x86 [PR103973] C++20: #include <compare> auto cmp4way(double a, double b) { return a <=> b; } expands to: ucomisd %xmm1, %xmm0 jp .L8 movl $0, %eax jne .L8 .L2: ret .p2align 4,,10 .p2align 3 .L8: comisd %xmm0, %xmm1 movl $-1, %eax ja .L2 ucomisd %xmm1, %xmm0 setbe %al addl $1, %eax ret That is 3 comparisons of the same operands. The following patch improves it to just one comparison: comisd %xmm1, %xmm0 jp .L4 seta %al movl $0, %edx leal -1(%rax,%rax), %eax cmove %edx, %eax ret .L4: movl $2, %eax ret While a <=> b expands to a == b ? 0 : a < b ? -1 : a > b ? 1 : 2 where the first comparison is equality and this shouldn't raise exceptions on qNaN operands, if the operands aren't equal (which includes unordered cases), then it immediately performs < or > comparison and that raises exceptions even on qNaNs, so we can just perform a single comparison that raises exceptions on qNaN. As the 4 different cases are encoded as ZF CF PF 1 1 1 a unordered b 0 0 0 a > b 0 1 0 a < b 1 0 0 a == b we can emit optimal sequence of comparions, first jp for the unordered case, then je for the == case and finally jb for the < case. The patch pattern recognizes spaceship-like comparisons during widening_mul if the spaceship optab is implemented, and replaces those comparisons with comparisons of .SPACESHIP ifn which returns -1/0/1/2 based on the comparison. This seems to work well both for the case of just returning the -1/0/1/2 (when we have just a common successor with a PHI) or when the different cases are handled with various other basic blocks. The testcases cover both of those cases, the latter with different function calls in those. 2022-01-17 Jakub Jelinek <ja...@redhat.com> PR target/103973 * tree-cfg.h (cond_only_block_p): Declare. * tree-ssa-phiopt.c (cond_only_block_p): Move function to ... * tree-cfg.c (cond_only_block_p): ... here. No longer static. * optabs.def (spaceship_optab): New optab. * internal-fn.def (SPACESHIP): New internal function. * internal-fn.h (expand_SPACESHIP): Declare. * internal-fn.c (expand_PHI): Formatting fix. (expand_SPACESHIP): New function. * tree-ssa-math-opts.c (optimize_spaceship): New function. (math_opts_dom_walker::after_dom_children): Use it. * config/i386/i386.md (spaceship<mode>3): New define_expand. * config/i386/i386-protos.h (ix86_expand_fp_spaceship): Declare. * config/i386/i386-expand.c (ix86_expand_fp_spaceship): New function. * doc/md.texi (spaceship@var{m}3): Document. * gcc.target/i386/pr103973-1.c: New test. * gcc.target/i386/pr103973-2.c: New test. * gcc.target/i386/pr103973-3.c: New test. * gcc.target/i386/pr103973-4.c: New test. * gcc.target/i386/pr103973-5.c: New test. * gcc.target/i386/pr103973-6.c: New test. * gcc.target/i386/pr103973-7.c: New test. * gcc.target/i386/pr103973-8.c: New test. * gcc.target/i386/pr103973-9.c: New test. * gcc.target/i386/pr103973-10.c: New test. * gcc.target/i386/pr103973-11.c: New test. * gcc.target/i386/pr103973-12.c: New test. * gcc.target/i386/pr103973-13.c: New test. * gcc.target/i386/pr103973-14.c: New test. * gcc.target/i386/pr103973-15.c: New test. * gcc.target/i386/pr103973-16.c: New test. * gcc.target/i386/pr103973-17.c: New test. * gcc.target/i386/pr103973-18.c: New test. * gcc.target/i386/pr103973-19.c: New test. * gcc.target/i386/pr103973-20.c: New test. * g++.target/i386/pr103973-1.C: New test. * g++.target/i386/pr103973-2.C: New test. * g++.target/i386/pr103973-3.C: New test. * g++.target/i386/pr103973-4.C: New test. * g++.target/i386/pr103973-5.C: New test. * g++.target/i386/pr103973-6.C: New test. * g++.target/i386/pr103973-7.C: New test. * g++.target/i386/pr103973-8.C: New test. * g++.target/i386/pr103973-9.C: New test. * g++.target/i386/pr103973-10.C: New test. * g++.target/i386/pr103973-11.C: New test. * g++.target/i386/pr103973-12.C: New test. * g++.target/i386/pr103973-13.C: New test. * g++.target/i386/pr103973-14.C: New test. * g++.target/i386/pr103973-15.C: New test. * g++.target/i386/pr103973-16.C: New test. * g++.target/i386/pr103973-17.C: New test. * g++.target/i386/pr103973-18.C: New test. * g++.target/i386/pr103973-19.C: New test. * g++.target/i386/pr103973-20.C: New test.
