From: Jason Merrill <jason@redhat.com>
Date: Fri, 22 Sep 2023 09:54:28 +0000 (+0100)
Subject: c++: constexpr and designated initializer
X-Git-Tag: basepoints/gcc-15~5909
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=22cda0ca5fb406f22925bbf51ab152a958e3319d;p=thirdparty%2Fgcc.git

c++: constexpr and designated initializer

The change of active member being non-constant (before C++20) results in a
CONSTRUCTOR with a null value for the first field, don't crash.

gcc/cp/ChangeLog:

	* constexpr.cc (free_constructor): Handle null ce->value.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/constexpr-union7.C: New test.
---

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index a673a6022f17..2a6601c0cbca 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1753,7 +1753,7 @@ free_constructor (tree t)
 	{
 	  constructor_elt *ce;
 	  for (HOST_WIDE_INT i = 0; vec_safe_iterate (elts, i, &ce); ++i)
-	    if (TREE_CODE (ce->value) == CONSTRUCTOR)
+	    if (ce->value && TREE_CODE (ce->value) == CONSTRUCTOR)
 	      vec_safe_push (ctors, ce->value);
 	  ggc_free (elts);
 	}
diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-union7.C b/gcc/testsuite/g++.dg/cpp2a/constexpr-union7.C
new file mode 100644
index 000000000000..230fa6e7d063
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-union7.C
@@ -0,0 +1,6 @@
+// { dg-do compile { target c++14 } }
+// { dg-options "" }
+
+union U { int i; float f; };
+constexpr auto g (U u) { return (u.i = 42); } // { dg-error "active member" "" { target c++17_down } }
+static_assert (g({.f = 3.14}) == 42); // { dg-error "non-constant" "" { target c++17_down } }