re PR c++/79520 (Spurious caching for constexpr arguments)

	PR c++/79520
	* g++.dg/cpp1y/constexpr-79520.C: New test.

From-SVN: r274214

gcc/testsuite/ChangeLog

+2019-08-08  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/79520
+	* g++.dg/cpp1y/constexpr-79520.C: New test.
+
 2019-08-08  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* gcc.dg/pr79983.c (enum E): Don't allow an error about nested

gcc/testsuite/g++.dg/cpp1y/constexpr-79520.C

+// PR c++/79520
+// { dg-do compile { target c++14 } }
+
+constexpr int f(int const& x) { return x; }
+
+constexpr struct S {
+    int x = 0;
+    constexpr S() {(void)f(x); x = 1;}
+} s;
+
+static_assert(f(s.x) == 1, "");