From: mpolacek <mpolacek@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Sat, 22 Jun 2019 14:43:00 +0000 (+0000)
Subject: 	PR c++/90881 - bogus -Wunused-value in unevaluated context.
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4a74b19c1f56056041fde79d61dfaca5d6c0ca9e;p=thirdparty%2Fgcc.git

	PR c++/90881 - bogus -Wunused-value in unevaluated context.
	* cvt.c (convert_to_void): Don't emit unused warnings in
	an unevaluated context.

	* g++.dg/cpp0x/Wunused-value1.C: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@272585 138bc75d-0d04-0410-961f-82ee72b054a4
---

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 93b4875de7a4..31336f954c34 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2019-06-22  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/90881 - bogus -Wunused-value in unevaluated context.
+	* cvt.c (convert_to_void): Don't emit unused warnings in
+	an unevaluated context.
+
 2019-06-22  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* decl.c (grokdeclarator): Use id_loc, typespec_loc, and
diff --git a/gcc/cp/cvt.c b/gcc/cp/cvt.c
index 1c405ecd7b62..23d2aabc4836 100644
--- a/gcc/cp/cvt.c
+++ b/gcc/cp/cvt.c
@@ -1518,7 +1518,8 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain)
       if (implicit != ICV_CAST
 	  && warn_unused_value
 	  && !TREE_NO_WARNING (expr)
-	  && !processing_template_decl)
+	  && !processing_template_decl
+	  && !cp_unevaluated_operand)
 	{
 	  /* The middle end does not warn about expressions that have
 	     been explicitly cast to void, so we must do so here.  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 80ea5916fcc7..b0b1d4ba9122 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-06-22  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/90881 - bogus -Wunused-value in unevaluated context.
+	* g++.dg/cpp0x/Wunused-value1.C: New test.
+
 2019-06-22  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* g++.dg/diagnostic/auto-storage-1.C: New.
diff --git a/gcc/testsuite/g++.dg/cpp0x/Wunused-value1.C b/gcc/testsuite/g++.dg/cpp0x/Wunused-value1.C
new file mode 100644
index 000000000000..a0683b693a1d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/Wunused-value1.C
@@ -0,0 +1,20 @@
+// PR c++/90881
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wall" }
+
+namespace std {
+  struct true_type { static const bool value = true; };
+  struct false_type { static const bool value = false; };
+}
+
+template <typename T, typename = void> struct status : std::false_type{};
+
+template <typename T> struct status<T, decltype(T::member, void())> : std::true_type {}; // { dg-bogus "left operand of comma operator has no effect" }
+
+struct s1{int member;};
+struct s2{int _member;};
+
+int main(){
+	static_assert(status<s1>::value, "has member");
+	static_assert(!status<s2>::value, "has no member");
+}