https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121264
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-15 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:46860078a0dc147b76ad0cc660b021c6e5b7bb81 commit r15-10169-g46860078a0dc147b76ad0cc660b021c6e5b7bb81 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Jul 31 12:10:02 2025 +0200 change get_best_mode args int -> HOST_WIDE_INT [PR121264] The following testcase is miscompiled, because byte 0x20000000 is bit 0x100000000 and ifcombine incorrectly combines the two loads into a BIT_FIELD_REF even when they are very far away. The problem is that gimple-fold.cc ifcombine uses get_best_mode heavily, and that function has just int bitsize and int bitpos arguments, so when called e.g. with if (get_best_mode (end_bit - first_bit, first_bit, 0, ll_end_region, ll_align, BITS_PER_WORD, volatilep, &lnmode)) where end_bit - first_bit doesn't fit into int, it is silently truncated. If there was just a single problematic get_best_mode call, I would probably just check for overflows in the caller, but there are many. And the two arguments are used solely as arguments to bit_field_mode_iterator constructor which has HOST_WIDE_INT arguments, so I think the easiest fix is just make the get_best_mode arguments also HOST_WIDE_INT. 2025-07-31 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/121264 * machmode.h (get_best_mode): Change type of first 2 arguments from int to HOST_WIDE_INT. * stor-layout.cc (get_best_mode): Likewise. * gcc.dg/tree-ssa/pr121264.c: New test. (cherry picked from commit e624d5559d21992c9e5da85b4ae75629a61afc2c)
