1 files changed, 68 insertions, 11 deletions

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 397d383f650..32154108107 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -5805,6 +5805,40 @@ cxx_bind_parameters_in_call (const constexpr_call *old_call, tree t,
     }
 }
 
+/* Variables and functions to manage constexpr call expansion context.
+   These do not need to be marked for PCH or GC.  */
+
+static VEC(tree,heap) *call_stack = NULL;
+static int call_stack_tick;
+static int last_cx_error_tick;
+
+static void
+push_cx_call_context (tree call)
+{
+  ++call_stack_tick;
+  if (!EXPR_HAS_LOCATION (call))
+    SET_EXPR_LOCATION (call, input_location);
+  VEC_safe_push (tree, heap, call_stack, call);
+}
+
+static void
+pop_cx_call_context (void)
+{
+  ++call_stack_tick;
+  VEC_pop (tree, call_stack);
+}
+
+VEC(tree,heap) *
+cx_error_context (void)
+{
+  VEC(tree,heap) *r = NULL;
+  if (call_stack_tick != last_cx_error_tick
+      && !VEC_empty (tree, call_stack))
+    r = call_stack;
+  last_cx_error_tick = call_stack_tick;
+  return r;
+}
+
 /* Subroutine of cxx_eval_constant_expression.
    Evaluate the call expression tree T in the context of OLD_CALL expression
    evaluation.  */
@@ -5814,13 +5848,11 @@ cxx_eval_call_expression (const constexpr_call *old_call, tree t,
 			  bool allow_non_constant, bool addr,
 			  bool *non_constant_p)
 {
-  location_t loc = EXPR_LOCATION (t);
+  location_t loc = EXPR_LOC_OR_HERE (t);
   tree fun = get_function_named_in_call (t);
   tree result;
   constexpr_call new_call = { NULL, NULL, NULL, 0 };
   constexpr_call **slot;
-  if (loc == UNKNOWN_LOCATION)
-    loc = input_location;
   if (TREE_CODE (fun) != FUNCTION_DECL)
     {
       /* Might be a constexpr function pointer.  */
@@ -5875,6 +5907,8 @@ cxx_eval_call_expression (const constexpr_call *old_call, tree t,
   if (*non_constant_p)
     return t;
 
+  push_cx_call_context (t);
+
   new_call.hash
     = iterative_hash_template_arg (new_call.bindings,
 				   constexpr_fundef_hash (new_call.fundef));
@@ -5933,13 +5967,7 @@ cxx_eval_call_expression (const constexpr_call *old_call, tree t,
 	}
     }
 
-  if (result == error_mark_node)
-    {
-      if (!allow_non_constant)
-	error_at (loc, "in expansion of %qE", t);
-      *non_constant_p = true;
-      result = t;
-    }
+  pop_cx_call_context ();
   return result;
 }
 
@@ -6513,7 +6541,36 @@ cxx_eval_constant_expression (const constexpr_call *call, tree t,
       if (DECL_P (r))
 	{
 	  if (!allow_non_constant)
-	    error ("%qD cannot appear in a constant expression", r);
+	    {
+	      tree type = TREE_TYPE (r);
+	      error ("the value of %qD is not usable in a constant "
+		     "expression", r);
+	      if (INTEGRAL_OR_ENUMERATION_TYPE_P (type))
+		{
+		  if (!CP_TYPE_CONST_P (type))
+		    inform (DECL_SOURCE_LOCATION (r),
+			    "%q#D is not const", r);
+		  else if (CP_TYPE_VOLATILE_P (type))
+		    inform (DECL_SOURCE_LOCATION (r),
+			    "%q#D is volatile", r);
+		  else if (!DECL_INITIAL (r))
+		    inform (DECL_SOURCE_LOCATION (r),
+			    "%qD was not initialized with a constant "
+			    "expression", r);
+		  else
+		    gcc_unreachable ();
+		}
+	      else
+		{
+		  if (cxx_dialect >= cxx0x && !DECL_DECLARED_CONSTEXPR_P (r))
+		    inform (DECL_SOURCE_LOCATION (r),
+			    "%qD was not declared %<constexpr%>", r);
+		  else
+		    inform (DECL_SOURCE_LOCATION (r),
+			    "%qD does not have integral or enumeration type",
+			    r);
+		}
+	    }
 	  *non_constant_p = true;
 	}
       break;