From 144b6099cdaa9ac1b298687c0cfdb06a970e338b Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Wed, 17 Jul 2024 20:57:54 -0400 Subject: [PATCH] c++: missing -Wunused-value for ! [PR114104] Here we're neglecting to issue a -Wunused-value warning for suitable ! operator expressions, and in turn for != operator expressions that are rewritten as !(x == y), only because we don't call warn_if_unused_value on TRUTH_NOT_EXPR since its class is tcc_expression. This patch makes us also consider warning for TRUTH_NOT_EXPR and also for ADDR_EXPR. PR c++/114104 gcc/cp/ChangeLog: * cvt.cc (convert_to_void): Call warn_if_unused_value for TRUTH_NOT_EXPR and ADDR_EXPR as well. gcc/testsuite/ChangeLog: * g++.dg/warn/Wunused-20.C: New test. Reviewed-by: Jason Merrill --- gcc/cp/cvt.cc | 2 ++ gcc/testsuite/g++.dg/warn/Wunused-20.C | 19 +++++++++++++++++++ 2 files changed, 21 insertions(+) create mode 100644 gcc/testsuite/g++.dg/warn/Wunused-20.C diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc index db086c017e8..d95e01c118c 100644 --- a/gcc/cp/cvt.cc +++ b/gcc/cp/cvt.cc @@ -1664,6 +1664,8 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain) if (tclass == tcc_comparison || tclass == tcc_unary || tclass == tcc_binary + || code == TRUTH_NOT_EXPR + || code == ADDR_EXPR || code == VEC_PERM_EXPR || code == VEC_COND_EXPR) warn_if_unused_value (e, loc); diff --git a/gcc/testsuite/g++.dg/warn/Wunused-20.C b/gcc/testsuite/g++.dg/warn/Wunused-20.C new file mode 100644 index 00000000000..31b1920adcd --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/Wunused-20.C @@ -0,0 +1,19 @@ +// PR c++/114104 +// { dg-additional-options "-Wunused-value" } + +bool f(); +struct A { int i; }; +A& g(); + +void h() { + !f(); // { dg-warning "value computed is not used" } + &g().i; // { dg-warning "value computed is not used" } +} + +#if __cplusplus >= 202002L +[[nodiscard]] bool operator==(A&, int); + +void h(A a) { + a != 0; // { dg-warning "value computed is not used" "" { target c++20 } } +} +#endif