[Ada] Reduce -Wstack-usage false positives on variant records

Message ID 1621213.tUdijo6jlR@polaris
State New
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  • [Ada] Reduce -Wstack-usage false positives on variant records
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Commit Message

Eric Botcazou July 7, 2018, 10:37 a.m.
This reduces the number of false positives of -Wstack-usage in the presence of 
variables whose nominal subtype is a discriminated record with a variant part.

Tested on x86-64/Linux, applied on the mainline.


2018-07-07  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/decl.c (gnat_to_gnu_entity): Add GNAT_DECL local
	variable and use it throughout.
	<E_Variable>: If the nominal subtype of the object is unconstrained,
	compute the Ada size separately and put in on the padding type if the
	size is not fixed.
	<E_Record_Type>: Minor tweak.
	* gcc-interface/misc.c (gnat_type_max_size): Rename max_size_unit
	into max_size_unit throughout.


2018-07-07  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/stack_usage6.adb: New test.
	* gnat.dg/stack_usage6_pkg.ads: New helper.

Patch

Index: gcc-interface/decl.c
===================================================================
--- gcc-interface/decl.c	(revision 262497)
+++ gcc-interface/decl.c	(working copy)
@@ -273,7 +273,9 @@  static bool intrin_profiles_compatible_p
 tree
 gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 {
-  /* Contains the kind of the input GNAT node.  */
+  /* The construct that declared the entity.  */
+  const Node_Id gnat_decl = Declaration_Node (gnat_entity);
+  /* The kind of the entity.  */
   const Entity_Kind kind = Ekind (gnat_entity);
   /* True if this is a type.  */
   const bool is_type = IN (kind, Type_Kind);
@@ -578,7 +580,7 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
       if (definition
 	  && !gnu_expr
 	  && No (Address_Clause (gnat_entity))
-	  && !No_Initialization (Declaration_Node (gnat_entity))
+	  && !No_Initialization (gnat_decl)
 	  && No (Renamed_Object (gnat_entity)))
 	{
 	  gnu_decl = error_mark_node;
@@ -611,9 +613,9 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
 	 may contain N_Expression_With_Actions nodes and thus declarations of
 	 objects from other units that we need to discard.  */
       if (!definition
-	  && !No_Initialization (Declaration_Node (gnat_entity))
+	  && !No_Initialization (gnat_decl)
 	  && !Is_Dispatch_Table_Entity (gnat_entity)
-	  && Present (gnat_temp = Expression (Declaration_Node (gnat_entity)))
+	  && Present (gnat_temp = Expression (gnat_decl))
 	  && Nkind (gnat_temp) != N_Allocator
 	  && (!type_annotate_only || Compile_Time_Known_Value (gnat_temp)))
 	gnu_expr = gnat_to_gnu_external (gnat_temp);
@@ -634,9 +636,8 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
 	     && !(kind == E_Variable
 		  && Present (Linker_Section_Pragma (gnat_entity)))
 	     && !Treat_As_Volatile (gnat_entity)
-	     && (((Nkind (Declaration_Node (gnat_entity))
-		   == N_Object_Declaration)
-		  && Present (Expression (Declaration_Node (gnat_entity))))
+	     && (((Nkind (gnat_decl) == N_Object_Declaration)
+		  && Present (Expression (gnat_decl)))
 		 || Present (Renamed_Object (gnat_entity))
 		 || imported_p));
 	bool inner_const_flag = const_flag;
@@ -650,7 +651,7 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
 	bool used_by_ref = false;
 	tree gnu_ext_name = NULL_TREE;
 	tree renamed_obj = NULL_TREE;
-	tree gnu_object_size;
+	tree gnu_ada_size = NULL_TREE;
 
 	/* We need to translate the renamed object even though we are only
 	   referencing the renaming.  But it may contain a call for which
@@ -755,8 +756,9 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
 	  {
 	    if (gnu_expr && kind == E_Constant)
 	      {
-		tree size = TYPE_SIZE (TREE_TYPE (gnu_expr));
-		if (CONTAINS_PLACEHOLDER_P (size))
+		gnu_size = TYPE_SIZE (TREE_TYPE (gnu_expr));
+		gnu_ada_size = TYPE_ADA_SIZE (TREE_TYPE (gnu_expr));
+		if (CONTAINS_PLACEHOLDER_P (gnu_size))
 		  {
 		    /* If the initializing expression is itself a constant,
 		       despite having a nominal type with self-referential
@@ -768,27 +770,38 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
 			&& (TREE_READONLY (TREE_OPERAND (gnu_expr, 0))
 			    || DECL_READONLY_ONCE_ELAB
 			       (TREE_OPERAND (gnu_expr, 0))))
-		      gnu_size = DECL_SIZE (TREE_OPERAND (gnu_expr, 0));
+		      {
+			gnu_size = DECL_SIZE (TREE_OPERAND (gnu_expr, 0));
+			gnu_ada_size = gnu_size;
+		      }
 		    else
-		      gnu_size
-			= SUBSTITUTE_PLACEHOLDER_IN_EXPR (size, gnu_expr);
+		      {
+			gnu_size
+			  = SUBSTITUTE_PLACEHOLDER_IN_EXPR (gnu_size,
+							    gnu_expr);
+			gnu_ada_size
+			  = SUBSTITUTE_PLACEHOLDER_IN_EXPR (gnu_ada_size,
+							    gnu_expr);
+		      }
 		  }
-		else
-		  gnu_size = size;
 	      }
 	    /* We may have no GNU_EXPR because No_Initialization is
 	       set even though there's an Expression.  */
 	    else if (kind == E_Constant
-		     && (Nkind (Declaration_Node (gnat_entity))
-			 == N_Object_Declaration)
-		     && Present (Expression (Declaration_Node (gnat_entity))))
-	      gnu_size
-		= TYPE_SIZE (gnat_to_gnu_type
-			     (Etype
-			      (Expression (Declaration_Node (gnat_entity)))));
+		     && Nkind (gnat_decl) == N_Object_Declaration
+		     && Present (Expression (gnat_decl)))
+	      {
+		tree gnu_expr_type
+		  = gnat_to_gnu_type (Etype (Expression (gnat_decl)));
+		gnu_size = TYPE_SIZE (gnu_expr_type);
+		gnu_ada_size = TYPE_ADA_SIZE (gnu_expr_type);
+	      }
 	    else
 	      {
 		gnu_size = max_size (TYPE_SIZE (gnu_type), true);
+		/* We can be called on unconstrained arrays in this mode.  */
+		if (!type_annotate_only)
+		  gnu_ada_size = max_size (TYPE_ADA_SIZE (gnu_type), true);
 		mutable_p = true;
 	      }
 
@@ -904,7 +917,7 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
 	/* Make a new type with the desired size and alignment, if needed.
 	   But do not take into account alignment promotions to compute the
 	   size of the object.  */
-	gnu_object_size = gnu_size ? gnu_size : TYPE_SIZE (gnu_type);
+	tree gnu_object_size = gnu_size ? gnu_size : TYPE_SIZE (gnu_type);
 	if (gnu_size || align > 0)
 	  {
 	    tree orig_type = gnu_type;
@@ -912,6 +925,13 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
 	    gnu_type = maybe_pad_type (gnu_type, gnu_size, align, gnat_entity,
 				       false, false, definition, true);
 
+	    /* If the nominal subtype of the object is unconstrained and its
+	       size is not fixed, compute the Ada size from the Ada size of
+	       the subtype and/or the expression; this will make it possible
+	       for gnat_type_max_size to easily compute a maximum size.  */
+	    if (gnu_ada_size && gnu_size && !TREE_CONSTANT (gnu_size))
+	      SET_TYPE_ADA_SIZE (gnu_type, gnu_ada_size);
+
 	    /* If a padding record was made, declare it now since it will
 	       never be declared otherwise.  This is necessary to ensure
 	       that its subtrees are properly marked.  */
@@ -2941,23 +2961,19 @@  gnat_to_gnu_entity (Entity_Id gnat_entit
        the tree.  */
 
     case E_Record_Type:
-      if (Has_Complex_Representation (gnat_entity))
-	{
-	  gnu_type
-	    = build_complex_type
-	      (get_unpadded_type
-	       (Etype (Defining_Entity
-		       (First (Component_Items
-			       (Component_List
-				(Type_Definition
-				 (Declaration_Node (gnat_entity)))))))));
+      {
+	Node_Id record_definition = Type_Definition (gnat_decl);
 
-	  break;
-	}
+	if (Has_Complex_Representation (gnat_entity))
+	  {
+	    const Node_Id first_component
+	      = First (Component_Items (Component_List (record_definition)));
+	    tree gnu_component_type
+	      = get_unpadded_type (Etype (Defining_Entity (first_component)));
+	    gnu_type = build_complex_type (gnu_component_type);
+	    break;
+	  }
 
-      {
-	Node_Id full_definition = Declaration_Node (gnat_entity);
-	Node_Id record_definition = Type_Definition (full_definition);
 	Node_Id gnat_constr;
 	Entity_Id gnat_field, gnat_parent_type;
 	tree gnu_field, gnu_field_list = NULL_TREE;
Index: gcc-interface/misc.c
===================================================================
--- gcc-interface/misc.c	(revision 262468)
+++ gcc-interface/misc.c	(working copy)
@@ -736,25 +736,25 @@  gnat_type_max_size (const_tree gnu_type)
   /* First see what we can get from TYPE_SIZE_UNIT, which might not
      be constant even for simple expressions if it has already been
      elaborated and possibly replaced by a VAR_DECL.  */
-  tree max_unitsize = max_size (TYPE_SIZE_UNIT (gnu_type), true);
+  tree max_size_unit = max_size (TYPE_SIZE_UNIT (gnu_type), true);
 
   /* If we don't have a constant, try to look at attributes which should have
      stayed untouched.  */
-  if (!tree_fits_uhwi_p (max_unitsize))
+  if (!tree_fits_uhwi_p (max_size_unit))
     {
       /* For record types, see what we can get from TYPE_ADA_SIZE.  */
       if (RECORD_OR_UNION_TYPE_P (gnu_type)
 	  && !TYPE_FAT_POINTER_P (gnu_type)
 	  && TYPE_ADA_SIZE (gnu_type))
 	{
-	  tree max_adasize = max_size (TYPE_ADA_SIZE (gnu_type), true);
+	  tree max_ada_size = max_size (TYPE_ADA_SIZE (gnu_type), true);
 
 	  /* If we have succeeded in finding a constant, round it up to the
 	     type's alignment and return the result in units.  */
-	  if (tree_fits_uhwi_p (max_adasize))
-	    max_unitsize
+	  if (tree_fits_uhwi_p (max_ada_size))
+	    max_size_unit
 	      = size_binop (CEIL_DIV_EXPR,
-			    round_up (max_adasize, TYPE_ALIGN (gnu_type)),
+			    round_up (max_ada_size, TYPE_ALIGN (gnu_type)),
 			    bitsize_unit_node);
 	}
 
@@ -784,7 +784,7 @@  gnat_type_max_size (const_tree gnu_type)
 		    = fold_build2 (PLUS_EXPR, ctype,
 				   fold_build2 (MINUS_EXPR, ctype, hb, lb),
 				   build_int_cst (ctype, 1));
-		  max_unitsize
+		  max_size_unit
 		    = fold_build2 (MULT_EXPR, sizetype,
 				   fold_convert (sizetype, length),
 				   TYPE_SIZE_UNIT (TREE_TYPE (gnu_type)));
@@ -793,7 +793,7 @@  gnat_type_max_size (const_tree gnu_type)
 	}
     }
 
-  return max_unitsize;
+  return max_size_unit;
 }
 
 static tree get_array_bit_stride (tree);