https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108789
--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-14 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:f9af4a05e027a8b797628f1a2c39ef0b28dc36d9 commit r14-10279-gf9af4a05e027a8b797628f1a2c39ef0b28dc36d9 Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Jun 4 12:28:01 2024 +0200 builtins: Force SAVE_EXPR for __builtin_{add,sub,mul}_overflow and __builtin{add,sub}c [PR108789] The following testcase is miscompiled, because we use save_expr on the .{ADD,SUB,MUL}_OVERFLOW call we are creating, but if the first two operands are not INTEGER_CSTs (in that case we just fold it right away) but are TREE_READONLY/!TREE_SIDE_EFFECTS, save_expr doesn't actually create a SAVE_EXPR at all and so we lower it to *arg2 = REALPART_EXPR (.ADD_OVERFLOW (arg0, arg1)), \ IMAGPART_EXPR (.ADD_OVERFLOW (arg0, arg1)) which evaluates the ifn twice and just hope it will be CSEd back. As *arg2 aliases *arg0, that is not the case. The builtins are really never const/pure as they store into what the third arguments points to, so after handling the INTEGER_CST+INTEGER_CST case, I think we should just always use SAVE_EXPR. Just building SAVE_EXPR by hand and setting TREE_SIDE_EFFECTS on it doesn't work, because c_fully_fold optimizes it away again, so the following patch marks the ifn calls as TREE_SIDE_EFFECTS (but doesn't do it for the __builtin_{add,sub,mul}_overflow_p case which were designed for use especially in constant expressions and don't really evaluate the realpart side, so we don't really need a SAVE_EXPR in that case). 2024-06-04 Jakub Jelinek <ja...@redhat.com> PR middle-end/108789 * builtins.cc (fold_builtin_arith_overflow): For ovf_only, don't call save_expr and don't build REALPART_EXPR, otherwise set TREE_SIDE_EFFECTS on call before calling save_expr. (fold_builtin_addc_subc): Set TREE_SIDE_EFFECTS on call before calling save_expr. * gcc.c-torture/execute/pr108789.c: New test. (cherry picked from commit b8e28381cb5c0cddfe5201faf799d8b27f5d7d6c)
