https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98947
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:f0f62557c3de0313673d7c0527277e86231ee95b commit r10-9684-gf0f62557c3de0313673d7c0527277e86231ee95b Author: Marek Polacek <pola...@redhat.com> Date: Wed Feb 3 17:57:22 2021 -0500 c++: Fix bogus -Wvolatile warning in C++20 [PR98947] Since most of volatile is deprecated in C++20, we are required to warn for compound assignments to volatile variables and so on. But here we have volatile int x, y, z; (b ? x : y) = 1; and we shouldn't warn, because simple assignments like x = 24; should not provoke the warning when they are a discarded-value expression. We warn here because when ?: is used as an lvalue, we transform it in cp_build_modify_expr/COND_EXPR from (a ? b : c) = rhs to (a ? (b = rhs) : (c = rhs)) and build_conditional_expr then calls mark_lvalue_use for the new artificial assignments, which then evokes the warning. The calls to mark_lvalue_use were added in r160289 to suppress warnings in Wunused-var-10.c, but looks like they're no longer needed. To warn on (b ? (x = 2) : y) = 1; (b ? x : (y = 5)) = 1; I've tweaked a check in mark_use/MODIFY_EXPR. I'd argue this is a regression because GCC 9 doesn't warn. gcc/cp/ChangeLog: PR c++/98947 * call.c (build_conditional_expr_1): Don't call mark_lvalue_use on arg2/arg3. * expr.c (mark_use) <case MODIFY_EXPR>: Don't check read_p when issuing the -Wvolatile warning. Only set TREE_THIS_VOLATILE if a warning was emitted. gcc/testsuite/ChangeLog: PR c++/98947 * g++.dg/cpp2a/volatile5.C: New test. (cherry picked from commit 7a18bc4ae62081021f4fd90d591a588cac931f77)
