https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96272
--- Comment #7 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:fe78528c05fdd562f21e12675781473b0fbe892e commit r11-5957-gfe78528c05fdd562f21e12675781473b0fbe892e Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Dec 12 14:48:47 2020 +0100 widening_mul: Recognize another form of ADD_OVERFLOW [PR96272] The following patch recognizes another form of hand written __builtin_add_overflow (this time _p), in particular when the code does unsigned if (x > ~0U - y) or if (x <= ~0U - y) it can be optimized (if the subtraction turned into ~y is single use) into if (__builtin_add_overflow_p (x, y, 0U)) or if (!__builtin_add_overflow_p (x, y, 0U)) and generate better code, e.g. for the first function in the testcase: - movl %esi, %eax addl %edi, %esi - notl %eax - cmpl %edi, %eax - movl $-1, %eax - cmovnb %esi, %eax + jc .L3 + movl %esi, %eax + ret +.L3: + orl $-1, %eax ret on x86_64. As for the jumps vs. conditional move case, that is some CE issue with complex branch patterns we should fix up no matter what, but in this case I'm actually not sure if branchy code isn't better, overflow is something that isn't that common. 2020-12-12 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/96272 * tree-ssa-math-opts.c (uaddsub_overflow_check_p): Add OTHER argument. Handle BIT_NOT_EXPR. (match_uaddsub_overflow): Optimize unsigned a > ~b into __imag__ .ADD_OVERFLOW (a, b). (math_opts_dom_walker::after_dom_children): Call match_uaddsub_overflow even for BIT_NOT_EXPR. * gcc.dg/tree-ssa/pr96272.c: New test.
