https://gcc.gnu.org/g:144b6099cdaa9ac1b298687c0cfdb06a970e338b
commit r15-2118-g144b6099cdaa9ac1b298687c0cfdb06a970e338b
Author: Patrick Palka <ppa...@redhat.com>
Date: Wed Jul 17 20:57:54 2024 -0400
c++: missing -Wunused-value for !<expr> [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 <ja...@redhat.com>
Diff:
---
gcc/cp/cvt.cc | 2 ++
gcc/testsuite/g++.dg/warn/Wunused-20.C | 19 +++++++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index db086c017e89..d95e01c118c4 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 000000000000..31b1920adcdd
--- /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
