We ICE on the following testcase when wi::multiple_of_p is called on widest_int 1 and -128 with UNSIGNED. I still need to work on the actual wide-int.cc issue, the latest patch attached to the PR regressed bitint-{38,39}.c, so will need to debug that, but there is a clear bug on the fold-const.cc side as well - widest_int is a signed representation by definition, using UNSIGNED with it certainly doesn't match what was intended, because -128 as the second operand effectively means unsigned 131072 bit 0xfffff............ffff80 integer, not the signed char -128 that appeared in the source. In the INTEGER_CST case a few lines above this we already use case INTEGER_CST: if (TREE_CODE (bottom) != INTEGER_CST || integer_zerop (bottom)) return false; return wi::multiple_of_p (wi::to_widest (top), wi::to_widest (bottom), SIGNED); so I think using SIGNED with widest_int is best there (compared to the other choices in the PR). 2023-11-29 Jakub Jelinek <jakub@redhat.com> PR middle-end/112733 * fold-const.cc (multiple_of_p): Pass SIGNED rather than UNSIGNED for wi::multiple_of_p on widest_int arguments. * gcc.dg/pr112733.c: New test.