From: Jason Merrill <jason@redhat.com>
Date: Wed, 9 Dec 2020 02:47:11 +0000 (-0500)
Subject: c++: Avoid [[nodiscard]] warning in requires-expr [PR98019]
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=c3a63fb3854392af65a191154e3586e7f5a1066e;p=gcc.git

c++: Avoid [[nodiscard]] warning in requires-expr [PR98019]

If we aren't really evaluating the expression, it doesn't matter that the
return value is discarded.

gcc/cp/ChangeLog:

	PR c++/98019
	* cvt.c (maybe_warn_nodiscard): Check c_inhibit_evaluation_warnings.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-nodiscard1.C: Remove xfail.
---

diff --git a/gcc/cp/cvt.c b/gcc/cp/cvt.c
index bcd7c5af81c..29ceaeb24ce 100644
--- a/gcc/cp/cvt.c
+++ b/gcc/cp/cvt.c
@@ -1031,6 +1031,9 @@ cp_get_callee_fndecl_nofold (tree call)
 static void
 maybe_warn_nodiscard (tree expr, impl_conv_void implicit)
 {
+  if (!warn_unused_result || c_inhibit_evaluation_warnings)
+    return;
+
   tree call = expr;
   if (TREE_CODE (expr) == TARGET_EXPR)
     call = TARGET_EXPR_INITIAL (expr);
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-nodiscard1.C b/gcc/testsuite/g++.dg/cpp2a/concepts-nodiscard1.C
index 907e68b1fc2..3d5cd85bc94 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-nodiscard1.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-nodiscard1.C
@@ -1,6 +1,6 @@
 // PR c++/98019
 // { dg-do compile { target c++20 } }
-// { dg-excess-errors *-*-* }
+// Don't give [[nodiscard]] warning for an expression requirement.
 
 template <class T, class U> concept same_as = __is_same_as (T, U);