re PR c++/77907 (Add "const" to argument of constexpr constructor causes the…

re PR c++/77907 (Add "const" to argument of constexpr constructor causes the object to be left in unconstructed state)

	PR c++/77907
	* cp-gimplify.c (cp_fold) <case CALL_EXPR>: When calling constructor
	and maybe_constant_value returns non-CALL_EXPR, create INIT_EXPR
	with the object on lhs and maybe_constant_value returned expr on rhs.

	* g++.dg/cpp0x/pr77907.C: New test.

From-SVN: r242790

gcc/cp/ChangeLog

 2016-11-23  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/77907
+	* cp-gimplify.c (cp_fold) <case CALL_EXPR>: When calling constructor
+	and maybe_constant_value returns non-CALL_EXPR, create INIT_EXPR
+	with the object on lhs and maybe_constant_value returned expr on rhs.
+
 	PR c++/71450
 	* pt.c (tsubst_copy): Return error_mark_node when mark_used
 	fails, even when complain & tf_error.

gcc/cp/cp-gimplify.c

@@ -2340,11 +2340,18 @@ cp_fold (tree x)
 	   constant, but the call followed by an INDIRECT_REF is.  */
 	if (callee && DECL_DECLARED_CONSTEXPR_P (callee)
 	    && !flag_no_inline)
-          r = maybe_constant_value (x);
+	  r = maybe_constant_value (x);
 	optimize = sv;
 
         if (TREE_CODE (r) != CALL_EXPR)
 	  {
+	    if (DECL_CONSTRUCTOR_P (callee))
+	      {
+		loc = EXPR_LOCATION (x);
+		tree s = build_fold_indirect_ref_loc (loc,
+						      CALL_EXPR_ARG (x, 0));
+		r = build2_loc (loc, INIT_EXPR, TREE_TYPE (s), s, r);
+	      }
 	    x = r;
 	    break;
 	  }

gcc/testsuite/ChangeLog

+2016-11-23  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/77907
+	* g++.dg/cpp0x/pr77907.C: New test.
+
 2016-11-23  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
 
 	PR middle-end/78153

gcc/testsuite/g++.dg/cpp0x/pr77907.C

+// PR c++/77907
+// { dg-do run { target c++11 } }
+// { dg-options "-O2" }
+
+struct A {
+  int foo () { return 1; }
+};
+
+struct B {
+  using C = int (A::*) ();
+  constexpr explicit B (const C x) : b{x} {}
+  C b;
+};
+
+B b{&A::foo};
+
+int
+main ()
+{
+  if (!b.b)
+    __builtin_abort ();
+}