From 596334fa040094c772965ff1998d171fe3e00348 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Wed, 15 Jan 2020 14:45:24 -0500
Subject: PR c++/93257 - consteval void function.

A prvalue can have void type, and if it doesn't do anything prohibited in a
constant expression, it's vacuously constant.

	* constexpr.c (verify_constant): Allow void_node.
---
 gcc/cp/ChangeLog                             |  3 +++
 gcc/cp/constexpr.c                           |  3 ++-
 gcc/testsuite/g++.dg/cpp2a/consteval-void1.C | 10 ++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-void1.C

(limited to 'gcc')

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 78eb834..95eb2a7 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,8 @@
 2020-01-15  Jason Merrill  <jason@redhat.com>
 
+	PR c++/93257 - consteval void function.
+	* constexpr.c (verify_constant): Allow void_node.
+
 	PR c++/92871 - bad code with xvalue and GNU ?: extension.
 	* call.c (prevent_lifetime_extension): New.
 	(build_conditional_expr_1): Use it.
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index bb126a9..17b04d7 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -2609,7 +2609,8 @@ static bool
 verify_constant (tree t, bool allow_non_constant, bool *non_constant_p,
 		 bool *overflow_p)
 {
-  if (!*non_constant_p && !reduced_constant_expression_p (t))
+  if (!*non_constant_p && !reduced_constant_expression_p (t)
+      && t != void_node)
     {
       if (!allow_non_constant)
 	error ("%q+E is not a constant expression", t);
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-void1.C b/gcc/testsuite/g++.dg/cpp2a/consteval-void1.C
new file mode 100644
index 0000000..783cf4c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-void1.C
@@ -0,0 +1,10 @@
+// PR c++/93257
+// { dg-do compile { target c++2a } }
+
+template <bool, typename>
+consteval void test() {}
+
+int main() {
+    test<false, int>();
+    return 0;
+}
-- 
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