https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111151
--- Comment #15 from GCC 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:c4f2c84e8fa369856aee76679590eb613724bfb0 commit r14-9668-gc4f2c84e8fa369856aee76679590eb613724bfb0 Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Mar 26 11:21:38 2024 +0100 fold-const: Punt on MULT_EXPR in extract_muldiv MIN/MAX_EXPR case [PR111151] As I've tried to explain in the comments, the extract_muldiv_1 MIN/MAX_EXPR optimization is wrong for code == MULT_EXPR. If the multiplication is done in unsigned type or in signed type with -fwrapv, it is fairly obvious that max (a, b) * c in many cases isn't equivalent to max (a * c, b * c) (or min if c is negative) due to overflows, but even for signed with undefined overflow, the optimization could turn something without UB in it (where say a * c invokes UB, but max (or min) picks the other operand where b * c doesn't). As for division/modulo, I think it is in most cases safe, except if the problematic INT_MIN / -1 case could be triggered, but we can just punt for MAX_EXPR because for MIN_EXPR if one operand is INT_MIN, we'd pick that operand already. It is just for completeness, match.pd already has an optimization which turns x / -1 into -x, so the division by zero is mostly theoretical. That is also why in the testcase the i case isn't actually miscompiled without the patch, while the c and f cases are. 2024-03-26 Jakub Jelinek <ja...@redhat.com> PR middle-end/111151 * fold-const.cc (extract_muldiv_1) <case MAX_EXPR>: Punt for MULT_EXPR altogether, or for MAX_EXPR if c is -1. * gcc.c-torture/execute/pr111151.c: New test.
