https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99588
--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:b1fc1f1c4b2e9005c40ed476b067577da2d2ce84 commit r10-9619-gb1fc1f1c4b2e9005c40ed476b067577da2d2ce84 Author: Jakub Jelinek <ja...@redhat.com> Date: Fri Mar 19 22:54:31 2021 +0100 c: Fix up -Wunused-but-set-* warnings for _Atomics [PR99588] As the following testcases show, compared to -D_Atomic= case we have many -Wunused-but-set-* warning false positives. When an _Atomic variable/parameter is read, we call mark_exp_read on it in convert_lvalue_to_rvalue, but build_atomic_assign does not. For consistency with the non-_Atomic case where we mark_exp_read the lhs for lhs op= ... but not for lhs = ..., this patch does that too. But furthermore we need to pattern match the trees emitted by _Atomic store, so that _Atomic store itself is not marked as being a variable read, but when the result of the store is used, we mark it. 2021-03-19 Jakub Jelinek <ja...@redhat.com> PR c/99588 * c-typeck.c (mark_exp_read): Recognize what build_atomic_assign with modifycode NOP_EXPR produces and mark the _Atomic var as read if found. (build_atomic_assign): For modifycode of NOP_EXPR, use COMPOUND_EXPRs rather than STATEMENT_LIST. Otherwise call mark_exp_read on lhs. Set TREE_SIDE_EFFECTS on the TARGET_EXPR. * gcc.dg/Wunused-var-5.c: New test. * gcc.dg/Wunused-var-6.c: New test.
