C++ PATCH for c++/65525 (ICE with trivial assignment)

[Jason Merrill]

It's simple enough to make potential_constant_expression_1 handle MEM_REF.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit c25738941b9d32a9653bca90a896407667685d91
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Mar 26 13:11:13 2015 -0400

    	PR c++/65525
    	* constexpr.c (potential_constant_expression_1): Handle MEM_REF.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 37b619d..2f09472 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -4395,6 +4395,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
     case ARRAY_RANGE_REF:
     case MEMBER_REF:
     case DOTSTAR_EXPR:
+    case MEM_REF:
     binary:
       for (i = 0; i < 2; ++i)
 	if (!RECUR (TREE_OPERAND (t, i), want_rval))
diff --git a/gcc/testsuite/g++.dg/parse/assign1.C b/gcc/testsuite/g++.dg/parse/assign1.C
new file mode 100644
index 0000000..c0138c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/assign1.C
@@ -0,0 +1,22 @@
+// PR c++/65525
+
+struct A
+{
+    int x;
+    char y; // Actually, short and bool (types smaller than int?) trigger this ICE too
+    // Also: the problem doesn't occur if you put the smaller type first, e.g. "char x; int y;"
+
+    A(int x) {} // custom ctor needed for ICE
+};
+
+int main()
+{
+    A a(0), x(1), y(2);
+
+    x = a; // OK
+    y = a; // OK
+    x = y = a; // ICE: sorry, unimplemented: unexpected AST of kind mem_ref
+    // internal compiler error: in potential_constant_expression_1, at cp/constexpr.c:4432
+
+    return 0;
+}