https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107846
--- Comment #11 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:db1405ddf566fe6129328229579b3f98a574b34c commit r13-6474-gdb1405ddf566fe6129328229579b3f98a574b34c Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Mar 4 10:14:33 2023 +0100 c-family: Account for integral promotions of left shifts for -Wshift-overflow warning [PR107846] The r13-1100-gacb1e6f43dc2bbedd124 change added match.pd narrowing of left shifts, and while I believe the C++ FE calls the warning on unfolded trees, the C FE folds them and so left shifts where integral promotion happened and so were done in int type will be usually narrowed back to char/signed char/unsigned char/short/unsigned short left shifts if the shift count is constant and fits into the precision of the var being shifted. One possibility would be to restrict the match.pd optimization to GIMPLE only, another don't fold in C FE before this warning (well, we need to fold the shift count operand to constant if possible), the following patch just takes integral promotion into account in the warning code. 2023-03-04 Jakub Jelinek <ja...@redhat.com> PR c/107846 * c-warn.cc: Include langhooks.h. (maybe_warn_shift_overflow): Set type0 to what TREE_TYPE (op0) promotes to rather than TREE_TYPE (op0) itself, if TREE_TYPE (op0) is narrower than type0 and unsigned, use wi::min_precision with UNSIGNED and fold_convert op0 to type0 before emitting the warning. * gcc.dg/pr107846.c: New test.
