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[Ada] Handle implicit moves in SPARK ownership pointer support
- From: Pierre-Marie de Rodat <derodat at adacore dot com>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Yannick Moy <moy at adacore dot com>
- Date: Tue, 9 Jul 2019 03:52:00 -0400
- Subject: [Ada] Handle implicit moves in SPARK ownership pointer support
Allocator expressions and sub-expressions of (extension) aggregates are
implicitly the source of assignments in Ada. Thus, they should be moved
when of a deep type when checking ownership rules in SPARK.
There is no impact on compilation.
Tested on x86_64-pc-linux-gnu, committed on trunk
2019-07-09 Yannick Moy <moy@adacore.com>
gcc/ada/
* sem_spark.adb (Check_Expression): Handle correctly implicit
assignments as part of allocators and (extension) aggregates.
(Get_Root_Object): Adapt for new path expressions.
(Is_Path_Expression): Return True for (extension) aggregate.
--- gcc/ada/sem_spark.adb
+++ gcc/ada/sem_spark.adb
@@ -1436,6 +1436,13 @@ package body Sem_SPARK is
function Is_Type_Name (Expr : Node_Id) return Boolean;
-- Detect when a path expression is in fact a type name
+ procedure Move_Expression (Expr : Node_Id);
+ -- Some subexpressions are only analyzed in Move mode. This is a
+ -- specialized version of Check_Expression for that case.
+
+ procedure Move_Expression_List (L : List_Id);
+ -- Call Move_Expression on every expression in the list L
+
procedure Read_Expression (Expr : Node_Id);
-- Most subexpressions are only analyzed in Read mode. This is a
-- specialized version of Check_Expression for that case.
@@ -1459,6 +1466,36 @@ package body Sem_SPARK is
end Is_Type_Name;
---------------------
+ -- Move_Expression --
+ ---------------------
+
+ -- Distinguish the case where the argument is a path expression that
+ -- needs explicit moving.
+
+ procedure Move_Expression (Expr : Node_Id) is
+ begin
+ if Is_Path_Expression (Expr) then
+ Check_Expression (Expr, Move);
+ else
+ Read_Expression (Expr);
+ end if;
+ end Move_Expression;
+
+ --------------------------
+ -- Move_Expression_List --
+ --------------------------
+
+ procedure Move_Expression_List (L : List_Id) is
+ N : Node_Id;
+ begin
+ N := First (L);
+ while Present (N) loop
+ Move_Expression (N);
+ Next (N);
+ end loop;
+ end Move_Expression_List;
+
+ ---------------------
-- Read_Expression --
---------------------
@@ -1489,7 +1526,26 @@ package body Sem_SPARK is
-- Local subprograms
+ function Is_Singleton_Choice (Choices : List_Id) return Boolean;
+ -- Return whether Choices is a singleton choice
+
procedure Read_Param (Formal : Entity_Id; Actual : Node_Id);
+ -- Call Read_Expression on the actual
+
+ -------------------------
+ -- Is_Singleton_Choice --
+ -------------------------
+
+ function Is_Singleton_Choice (Choices : List_Id) return Boolean is
+ Choice : constant Node_Id := First (Choices);
+ begin
+ return List_Length (Choices) = 1
+ and then Nkind (Choice) /= N_Others_Choice
+ and then not Nkind_In (Choice, N_Subtype_Indication, N_Range)
+ and then not
+ (Nkind_In (Choice, N_Identifier, N_Expanded_Name)
+ and then Is_Type (Entity (Choice)));
+ end Is_Singleton_Choice;
----------------
-- Read_Param --
@@ -1526,8 +1582,11 @@ package body Sem_SPARK is
Read_Indexes (Prefix (Expr));
Read_Expression (Discrete_Range (Expr));
+ -- The argument of an allocator is moved as part of the implicit
+ -- assignment.
+
when N_Allocator =>
- Read_Expression (Expression (Expr));
+ Move_Expression (Expression (Expr));
when N_Function_Call =>
Read_Params (Expr);
@@ -1539,6 +1598,91 @@ package body Sem_SPARK is
=>
Read_Indexes (Expression (Expr));
+ when N_Aggregate =>
+ declare
+ Assocs : constant List_Id := Component_Associations (Expr);
+ CL : List_Id;
+ Assoc : Node_Id := Nlists.First (Assocs);
+ Choice : Node_Id;
+
+ begin
+ -- The subexpressions of an aggregate are moved as part
+ -- of the implicit assignments. Handle the positional
+ -- components first.
+
+ Move_Expression_List (Expressions (Expr));
+
+ -- Handle the named components next.
+
+ while Present (Assoc) loop
+ CL := Choices (Assoc);
+
+ -- For an array aggregate, we should also check that the
+ -- expressions used in choices are readable.
+
+ if Is_Array_Type (Etype (Expr)) then
+ Choice := Nlists.First (CL);
+ while Present (Choice) loop
+ if Nkind (Choice) /= N_Others_Choice then
+ Read_Expression (Choice);
+ end if;
+ Next (Choice);
+ end loop;
+ end if;
+
+ -- There can be only one element for a value of deep type
+ -- in order to avoid aliasing.
+
+ if Is_Deep (Etype (Expression (Assoc)))
+ and then not Is_Singleton_Choice (CL)
+ then
+ Error_Msg_F ("singleton choice required"
+ & " to prevent aliasing", First (CL));
+ end if;
+
+ -- The subexpressions of an aggregate are moved as part
+ -- of the implicit assignments.
+
+ Move_Expression (Expression (Assoc));
+
+ Next (Assoc);
+ end loop;
+ end;
+
+ when N_Extension_Aggregate =>
+ declare
+ Exprs : constant List_Id := Expressions (Expr);
+ Assocs : constant List_Id := Component_Associations (Expr);
+ CL : List_Id;
+ Assoc : Node_Id := Nlists.First (Assocs);
+
+ begin
+ Move_Expression (Ancestor_Part (Expr));
+
+ -- No positional components allowed at this stage
+
+ if Present (Exprs) then
+ raise Program_Error;
+ end if;
+
+ while Present (Assoc) loop
+ CL := Choices (Assoc);
+
+ -- Only singleton components allowed at this stage
+
+ if not Is_Singleton_Choice (CL) then
+ raise Program_Error;
+ end if;
+
+ -- The subexpressions of an aggregate are moved as part
+ -- of the implicit assignments.
+
+ Move_Expression (Expression (Assoc));
+
+ Next (Assoc);
+ end loop;
+ end;
+
when others =>
raise Program_Error;
end case;
@@ -1759,45 +1903,6 @@ package body Sem_SPARK is
Read_Expression (Condition (Expr));
end;
- when N_Aggregate =>
- declare
- Assocs : constant List_Id := Component_Associations (Expr);
- Assoc : Node_Id := First (Assocs);
- CL : List_Id;
- Choice : Node_Id;
-
- begin
- while Present (Assoc) loop
-
- -- An array aggregate with a single component association
- -- may have a nonstatic choice expression that needs to be
- -- analyzed. This can only occur for a single choice that
- -- is not the OTHERS one.
-
- if Is_Array_Type (Etype (Expr)) then
- CL := Choices (Assoc);
- if List_Length (CL) = 1 then
- Choice := First (CL);
- if Nkind (Choice) /= N_Others_Choice then
- Read_Expression (Choice);
- end if;
- end if;
- end if;
-
- -- The expression in the component association also needs to
- -- be analyzed.
-
- Read_Expression (Expression (Assoc));
- Next (Assoc);
- end loop;
-
- Read_Expression_List (Expressions (Expr));
- end;
-
- when N_Extension_Aggregate =>
- Read_Expression (Ancestor_Part (Expr));
- Read_Expression_List (Expressions (Expr));
-
when N_Character_Literal
| N_Numeric_Or_String_Literal
| N_Operator_Symbol
@@ -1818,9 +1923,11 @@ package body Sem_SPARK is
-- Path expressions are handled before this point
- when N_Allocator
+ when N_Aggregate
+ | N_Allocator
| N_Expanded_Name
| N_Explicit_Dereference
+ | N_Extension_Aggregate
| N_Function_Call
| N_Identifier
| N_Indexed_Component
@@ -3283,7 +3390,7 @@ package body Sem_SPARK is
return (R => Unfolded, Tree_Access => C);
end;
- -- For a non-terminal path, we get the permission tree of its
+ -- For a nonterminal path, we get the permission tree of its
-- prefix, and then get the subtree associated with the extension,
-- if unfolded. If folded, we return the permission associated with
-- children.
@@ -3389,9 +3496,12 @@ package body Sem_SPARK is
=>
return Get_Root_Object (Prefix (Expr), Through_Traversal);
- -- There is no root object for an allocator or NULL
+ -- There is no root object for an (extension) aggregate, allocator,
+ -- or NULL.
- when N_Allocator
+ when N_Aggregate
+ | N_Allocator
+ | N_Extension_Aggregate
| N_Null
=>
return Empty;
@@ -3596,10 +3706,12 @@ package body Sem_SPARK is
when N_Null =>
return True;
- -- Object returned by a allocator or function call corresponds to
- -- a path.
+ -- Object returned by an (extension) aggregate, an allocator, or
+ -- a function call corresponds to a path.
- when N_Allocator
+ when N_Aggregate
+ | N_Allocator
+ | N_Extension_Aggregate
| N_Function_Call
=>
return True;
@@ -4763,7 +4875,7 @@ package body Sem_SPARK is
return C;
end;
- -- For a non-terminal path, we set the permission tree of its prefix,
+ -- For a nonterminal path, we set the permission tree of its prefix,
-- and then we extract from the returned pointer the subtree and
-- assign an adequate permission to it, if unfolded. If folded,
-- we unroll the tree one level.