[Ada] Suppress Base_Address call on init of activation record components
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Message ID 20191213095501.GA13971@adacore.com
State New
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  • [Ada] Suppress Base_Address call on init of activation record components
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Commit Message

Pierre-Marie de Rodat Dec. 13, 2019, 9:55 a.m. UTC
In the special case of an Address attribute that is used to initialize a
component of an activation record object (for handling unnesting in back
ends that don't support nested subprograms directly, such as LLVM), we
don't want the attribute to be passed to the Base_Address function (that
performs pointer displacement for interface objects). The expansion of
such a call is suppressed in that case, since we want the address
assigned as-is to the AREC component.

Tested on x86_64-pc-linux-gnu, committed on trunk

2019-12-13  Gary Dismukes  <dismukes@adacore.com>

gcc/ada/

	* exp_attr.adb (Expand_N_Attribute_Reference,
	Attribute_Address): Suppress generation of a call to
	Base_Address in the case where the Address attribute is being
	used to initialize a corresponding component of an activation
	record.
	(Is_Unnested_Component_Init): New function to determine whether
	an attribute reference for Address is used to initialized a
	component of an activation record object that corresponds to the
	object denoted by the prefix of the attribute (an assignment
	used in support of unnesting for back ends like LLVM).

Patch
diff mbox series

--- gcc/ada/exp_attr.adb
+++ gcc/ada/exp_attr.adb
@@ -2316,6 +2316,24 @@  package body Exp_Attr is
       when Attribute_Address => Address : declare
          Task_Proc : Entity_Id;
 
+         function Is_Unnested_Component_Init (N : Node_Id) return Boolean;
+         --  Returns True if N is being used to initialize a component of
+         --  an activation record object where the component corresponds to
+         --  the object denoted by the prefix of the attribute N.
+
+         function Is_Unnested_Component_Init (N : Node_Id) return Boolean is
+         begin
+            return Present (Parent (N))
+              and then Nkind (Parent (N)) = N_Assignment_Statement
+              and then Is_Entity_Name (Pref)
+              and then Present (Activation_Record_Component (Entity (Pref)))
+              and then Nkind (Name (Parent (N))) = N_Selected_Component
+              and then Entity (Selector_Name (Name (Parent (N)))) =
+                         Activation_Record_Component (Entity (Pref));
+         end Is_Unnested_Component_Init;
+
+      --  Start of processing for Address
+
       begin
          --  If the prefix is a task or a task type, the useful address is that
          --  of the procedure for the task body, i.e. the actual program unit.
@@ -2379,13 +2397,19 @@  package body Exp_Attr is
          --  "displaced" to reference the tag associated with the interface
          --  type. In order to obtain the real address of such objects we
          --  generate a call to a run-time subprogram that returns the base
-         --  address of the object.
+         --  address of the object. This call is not generated in cases where
+         --  the attribute is being used to initialize a component of an
+         --  activation record object where the component corresponds to
+         --  prefix of the attribute (for back ends that require "unnesting"
+         --  of nested subprograms), since the address needs to be assigned
+         --  as-is to such components.
 
          elsif Is_Class_Wide_Type (Ptyp)
            and then Is_Interface (Underlying_Type (Ptyp))
            and then Tagged_Type_Expansion
            and then not (Nkind (Pref) in N_Has_Entity
                           and then Is_Subprogram (Entity (Pref)))
+           and then not Is_Unnested_Component_Init (N)
          then
             Rewrite (N,
               Make_Function_Call (Loc,