https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79173
--- Comment #25 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:f8f68c4ca622a24c2e8cf2b5f2f9fdcd47a7b369 commit r14-2001-gf8f68c4ca622a24c2e8cf2b5f2f9fdcd47a7b369 Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Jun 20 20:17:41 2023 +0200 tree-ssa-math-opts: Small uaddc/usubc pattern matching improvement [PR79173] In the following testcase we fail to pattern recognize the least significant .UADDC call. The reason is that arg3 in that case is _3 = .ADD_OVERFLOW (...); _2 = __imag__ _3; _1 = _2 != 0; arg3 = (unsigned long) _1; and while before the changes arg3 has a single use in some .ADD_OVERFLOW later on, we add a .UADDC call next to it (and gsi_remove/gsi_replace only what is strictly necessary and leave quite a few dead stmts around which next DCE cleans up) and so it all of sudden isn't used just once, but twice (.ADD_OVERFLOW and .UADDC) and so uaddc_cast fails. While we could tweak uaddc_cast and not require has_single_use in these uses, there is also no vrp that would figure out that because __imag__ _3 is in [0, 1] range, it can just use arg3 = __imag__ _3; and drop the comparison and cast. We already search if either arg2 or arg3 is ultimately set from __imag__ of .{{ADD,SUB}_OVERFLOW,U{ADD,SUB}C} call, so the following patch just remembers the lhs of __imag__ from that case and uses it later. 2023-06-20 Jakub Jelinek <ja...@redhat.com> PR middle-end/79173 * tree-ssa-math-opts.cc (match_uaddc_usubc): Remember lhs of IMAGPART_EXPR of arg2/arg3 and use that as arg3 if it has the right type. * g++.target/i386/pr79173-1.C: New test.
