decl2.c (decl_constant_var_p): New fn.

	* decl2.c (decl_constant_var_p): New fn.
	(decl_maybe_constant_var_p): New fn.
	(mark_used): Rework instantiation of things needed for constant
	expressions.
	* cp-tree.h: Declare new fns.
	* pt.c (instantiate_decl): Handle cp_unevaluated_operand.
	(always_instantiate_p): Use decl_maybe_constant_var_p.
	(instantiate_decl): Don't defer constexpr functions.
	* repo.c (repo_emit_p): Use decl_maybe_constant_var_p.
	* semantics.c (finish_id_expression): Use decl_constant_var_p.
	Check for valid name in constant expr after mark_used.

From-SVN: r166164

gcc/cp/ChangeLog

+2010-11-01  Jason Merrill  <jason@redhat.com>
+
+	* decl2.c (decl_constant_var_p): New fn.
+	(decl_maybe_constant_var_p): New fn.
+	(mark_used): Rework instantiation of things needed for constant
+	expressions.
+	* cp-tree.h: Declare new fns.
+	* pt.c (instantiate_decl): Handle cp_unevaluated_operand.
+	(always_instantiate_p): Use decl_maybe_constant_var_p.
+	(instantiate_decl): Don't defer constexpr functions.
+	* repo.c (repo_emit_p): Use decl_maybe_constant_var_p.
+	* semantics.c (finish_id_expression): Use decl_constant_var_p.
+	Check for valid name in constant expr after mark_used.
+
 2010-10-31  Jason Merrill  <jason@redhat.com>
 
 	* class.c (is_really_empty_class): Work when type is not complete.

gcc/cp/cp-tree.h

@@ -4882,6 +4882,8 @@ extern void constrain_class_visibility		(tree);
 extern void import_export_decl			(tree);
 extern tree build_cleanup			(tree);
 extern tree build_offset_ref_call_from_tree	(tree, VEC(tree,gc) **);
+extern bool decl_constant_var_p			(tree);
+extern bool decl_maybe_constant_var_p		(tree);
 extern void check_default_args			(tree);
 extern void mark_used				(tree);
 extern void finish_static_data_member_decl	(tree, tree, bool, tree, int);

gcc/cp/decl2.c

@@ -3526,6 +3526,60 @@ decl_defined_p (tree decl)
     }
 }
 
+/* Nonzero for a VAR_DECL whose value can be used in a constant expression.
+
+      [expr.const]
+
+      An integral constant-expression can only involve ... const
+      variables of integral or enumeration types initialized with
+      constant expressions ...
+
+      C++0x also allows constexpr variables and temporaries initialized
+      with constant expressions.  We handle the former here, but the latter
+      are just folded away in cxx_eval_constant_expression.
+
+   The standard does not require that the expression be non-volatile.
+   G++ implements the proposed correction in DR 457.  */
+
+bool
+decl_constant_var_p (tree decl)
+{
+  bool ret;
+  tree type = TREE_TYPE (decl);
+  if (TREE_CODE (decl) != VAR_DECL)
+    return false;
+  if (DECL_DECLARED_CONSTEXPR_P (decl))
+    ret = true;
+  else if (CP_TYPE_CONST_NON_VOLATILE_P (type)
+	   && INTEGRAL_OR_ENUMERATION_TYPE_P (type))
+    {
+      /* We don't know if a template static data member is initialized with
+	 a constant expression until we instantiate its initializer.  */
+      mark_used (decl);
+      ret = DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl);
+    }
+  else
+    ret = false;
+
+  gcc_assert (!ret || DECL_INITIAL (decl));
+  return ret;
+}
+
+/* Returns true if DECL could be a symbolic constant variable, depending on
+   its initializer.  */
+
+bool
+decl_maybe_constant_var_p (tree decl)
+{
+  tree type = TREE_TYPE (decl);
+  if (TREE_CODE (decl) != VAR_DECL)
+    return false;
+  if (DECL_DECLARED_CONSTEXPR_P (decl))
+    return true;
+  return (CP_TYPE_CONST_NON_VOLATILE_P (type)
+	  && INTEGRAL_OR_ENUMERATION_TYPE_P (type));
+}
+
 /* Complain that DECL uses a type with no linkage but is never defined.  */
 
 static void
@@ -4074,8 +4128,6 @@ possibly_inlined_p (tree decl)
 void
 mark_used (tree decl)
 {
-  HOST_WIDE_INT saved_processing_template_decl = 0;
-
   /* If DECL is a BASELINK for a single function, then treat it just
      like the DECL for the function.  Otherwise, if the BASELINK is
      for an overloaded function, we don't know which function was
@@ -4113,9 +4165,6 @@ mark_used (tree decl)
 	error_at (DECL_SOURCE_LOCATION (decl), "declared here");
       return;
     }
-  /* If we don't need a value, then we don't need to synthesize DECL.  */
-  if (cp_unevaluated_operand != 0)
-    return;
 
   /* We can only check DECL_ODR_USED on variables or functions with
      DECL_LANG_SPECIFIC set, and these are also the only decls that we
@@ -4139,31 +4188,39 @@ mark_used (tree decl)
       return;
     }
 
-  /* Normally, we can wait until instantiation-time to synthesize
-     DECL.  However, if DECL is a static data member initialized with
-     a constant, we need the value right now because a reference to
-     such a data member is not value-dependent.  */
-  if (TREE_CODE (decl) == VAR_DECL
-      && DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl)
-      && DECL_CLASS_SCOPE_P (decl))
+  /* Normally, we can wait until instantiation-time to synthesize DECL.
+     However, if DECL is a static data member initialized with a constant
+     or a constexpr function, we need it right now because a reference to
+     such a data member or a call to such function is not value-dependent.  */
+  if ((decl_maybe_constant_var_p (decl)
+       || (TREE_CODE (decl) == FUNCTION_DECL
+	   && DECL_DECLARED_CONSTEXPR_P (decl)))
+      && !DECL_INITIAL (decl)
+      && DECL_LANG_SPECIFIC (decl)
+      && DECL_TEMPLATE_INSTANTIATION (decl))
     {
-      /* Don't try to instantiate members of dependent types.  We
-	 cannot just use dependent_type_p here because this function
-	 may be called from fold_non_dependent_expr, and then we may
-	 see dependent types, even though processing_template_decl
-	 will not be set.  */
-      if (CLASSTYPE_TEMPLATE_INFO ((DECL_CONTEXT (decl)))
-	  && uses_template_parms (CLASSTYPE_TI_ARGS (DECL_CONTEXT (decl))))
-	return;
-      /* Pretend that we are not in a template, even if we are, so
-	 that the static data member initializer will be processed.  */
-      saved_processing_template_decl = processing_template_decl;
-      processing_template_decl = 0;
+      /* Instantiating a function will result in garbage collection.  We
+	 must treat this situation as if we were within the body of a
+	 function so as to avoid collecting live data only referenced from
+	 the stack (such as overload resolution candidates).  */
+      ++function_depth;
+      instantiate_decl (decl, /*defer_ok=*/false,
+			/*expl_inst_class_mem_p=*/false);
+      --function_depth;
     }
 
+  /* If we don't need a value, then we don't need to synthesize DECL.  */
+  if (cp_unevaluated_operand != 0)
+    return;
+
   if (processing_template_decl)
     return;
 
+  /* Check this too in case we're within fold_non_dependent_expr.  */
+  if (DECL_TEMPLATE_INFO (decl)
+      && uses_template_parms (DECL_TI_ARGS (decl)))
+    return;
+
   DECL_ODR_USED (decl) = 1;
   if (DECL_CLONED_FUNCTION_P (decl))
     DECL_ODR_USED (DECL_CLONED_FUNCTION (decl)) = 1;
@@ -4233,8 +4290,6 @@ mark_used (tree decl)
        need.  Therefore, we always try to defer instantiation.  */
     instantiate_decl (decl, /*defer_ok=*/true,
 		      /*expl_inst_class_mem_p=*/false);
-
-  processing_template_decl = saved_processing_template_decl;
 }
 
 #include "gt-cp-decl2.h"

gcc/cp/pt.c

@@ -16714,7 +16714,7 @@ always_instantiate_p (tree decl)
 	     their initializers are available in integral constant
 	     expressions.  */
 	  || (TREE_CODE (decl) == VAR_DECL
-	      && DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl)));
+	      && decl_maybe_constant_var_p (decl)));
 }
 
 /* Produce the definition of D, a _DECL generated from a template.  If
@@ -16750,7 +16750,8 @@ instantiate_decl (tree d, int defer_ok,
      case that an expression refers to the value of the variable --
      if the variable has a constant value the referring expression can
      take advantage of that fact.  */
-  if (TREE_CODE (d) == VAR_DECL)
+  if (TREE_CODE (d) == VAR_DECL
+      || DECL_DECLARED_CONSTEXPR_P (d))
     defer_ok = 0;
 
   /* Don't instantiate cloned functions.  Instead, instantiate the
@@ -16926,6 +16927,11 @@ instantiate_decl (tree d, int defer_ok,
 	permerror (input_location,  "explicit instantiation of %qD "
 		   "but no definition available", d);
 
+      /* If we're in unevaluated context, we just wanted to get the
+	 constant value; this isn't an odr use, so don't queue
+	 a full instantiation.  */
+      if (cp_unevaluated_operand != 0)
+	goto out;
       /* ??? Historically, we have instantiated inline functions, even
 	 when marked as "extern template".  */
       if (!(external_p && TREE_CODE (d) == VAR_DECL))

gcc/cp/repo.c

@@ -319,7 +319,7 @@ repo_emit_p (tree decl)
 	 available.  Still record them into *.rpo files, so if they
 	 weren't actually emitted and collect2 requests them, they can
 	 be provided.  */
-      if (DECL_INTEGRAL_CONSTANT_VAR_P (decl)
+      if (decl_maybe_constant_var_p (decl)
 	  && DECL_CLASS_SCOPE_P (decl))
 	ret = 2;
     }

gcc/cp/semantics.c

@@ -2826,7 +2826,7 @@ finish_id_expression (tree id_expression,
 	     the complexity of the problem"
 
 	     FIXME update for final resolution of core issue 696.  */
-	  if (DECL_INTEGRAL_CONSTANT_VAR_P (decl))
+	  if (decl_constant_var_p (decl))
 	    return integral_constant_value (decl);
 
 	  if (TYPE_P (context))
@@ -3077,21 +3077,6 @@ finish_id_expression (tree id_expression,
 	  return id_expression;
 	}
 
-      /* Only certain kinds of names are allowed in constant
-	 expression.  Enumerators and template parameters have already
-	 been handled above.  */
-      if (integral_constant_expression_p
-	  && ! DECL_INTEGRAL_CONSTANT_VAR_P (decl)
-	  && ! builtin_valid_in_constant_expr_p (decl))
-	{
-	  if (!allow_non_integral_constant_expression_p)
-	    {
-	      error ("%qD cannot appear in a constant-expression", decl);
-	      return error_mark_node;
-	    }
-	  *non_integral_constant_expression_p = true;
-	}
-
       if (TREE_CODE (decl) == NAMESPACE_DECL)
 	{
 	  error ("use of namespace %qD as expression", decl);
@@ -3118,6 +3103,21 @@ finish_id_expression (tree id_expression,
 	  || TREE_CODE (decl) == RESULT_DECL)
 	mark_used (decl);
 
+      /* Only certain kinds of names are allowed in constant
+	 expression.  Enumerators and template parameters have already
+	 been handled above.  */
+      if (integral_constant_expression_p
+	  && ! decl_constant_var_p (decl)
+	  && ! builtin_valid_in_constant_expr_p (decl))
+	{
+	  if (!allow_non_integral_constant_expression_p)
+	    {
+	      error ("%qD cannot appear in a constant-expression", decl);
+	      return error_mark_node;
+	    }
+	  *non_integral_constant_expression_p = true;
+	}
+
       if (scope)
 	{
 	  decl = (adjust_result_of_qualified_name_lookup