Bootstrapped andrregtested on x86_64-pc-linux-gnu, does this look
OK for trunk?
-- >8 --
Here we're neglecting to emit a -Wunused-value for eligible ! 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
consider warning for TRUTH_NOT_EXPR as well.
PR c++/114104
gcc/cp/ChangeLog:
* cvt.cc (convert_to_void): Call warn_if_unused_value for
TRUTH_NOT_EXPR as well.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wunused-20.C: New test.
---
gcc/cp/cvt.cc | 1 +
gcc/testsuite/g++.dg/warn/Wunused-20.C | 17 +++++++++++++++++
2 files changed, 18 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..ebff6db2ea9 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -1664,6 +1664,7 @@ 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 == 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..6d7838fab13
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wunused-20.C
@@ -0,0 +1,17 @@
+// PR c++/114104
+// { dg-additional-options "-Wunused-value" }
+
+bool f();
+
+void g() {
+ !f(); // { dg-warning "value computed is not used" }
+}
+
+#if __cplusplus >= 202002L
+struct A { };
+[[nodiscard]] bool operator==(A, int);
+
+void g(A a) {
+ a != 0; // { dg-warning "value computed is not used" "" { target c++20 } }
+}
+#endif
--
2.46.0.rc0.35.gad850ef1cf
