[Ada] Front-end support for OpenACC pragmas

This patch introduces the upper part of the Ada front-end support for a first
set of OpenACC directives (Acc_Kernels, Acc_Loop, Acc_Parallel, Acc_Data) and
their clauses.

The pragmas syntax is documented, pragmas are recognized and checked for
syntactic correctness, keyed on -fopenacc. A couple of new flags are defined
on loop statements in the GNAT tree.

2018-09-26  Olivier Hainque  <hainque@adacore.com>

gcc/ada/

	* opt.ads (OpenAcc_Enabled): New flag. False by default. True
	when OpenACC pragmas are requested to be honored, when -fopenacc
	is found on the command line.
	* back_end.adb (Scan_Compiler_Arguments): Set OpenACC_Enabled if
	-fopenacc is seen on the command line.
	* sinfo.adb, sinfo.ads (Is_OpenAcc_Environment): New
	flag/predicate on Loop statements which embed an Acc_Kernels,
	Acc_Parallel or Acc_Data pragma.
	(Is_OpenAcc_Loop): New flag/predicate on Loop statements which
	embed an Acc_Loop pragma.
	(Set_Is_OpenAcc_Environment, Set_Is_OpenAcc_Loop): Setters for
	the new flags.
	* par-prag.adb (Prag): Handle Acc_Data, Acc_Loop, Acc_Parallel
	and Acc_Kernels pragmas.  Nothing to do here, all handled by
	sem_prag.
	* sem_prag.adb (Acc_First, Acc_Next,
	Validate_Acc_Condition_Clause, Validate_Acc_Data_Clause,
	Validate_Acc_Int_Expr_Clause, Validate_Acc_Int_Expr_List_Clause,
	Validate_Acc_Loop_Collapse, Validate_Acc_Loop_Gang,
	Validate_Acc_Loop_Vector, Validate_Acc_Loop_Worker,
	Validate_Acc_Name_Reduction, Validate_Acc_Size_Expressions): New
	helper for Analyze_Pragma, to handle OpenACC pragmas.
	(Analyze_Pragma): Handle Acc_Data, Acc_Loop, Acc_Parallel and
	Acc_Kernels pragmas.
	* sem_ch5.adb (Disable_Constant): Unset Is_True_Constant on
	variable entity, action for ...
	(Disable_Constants): Helper for Analyze_Loop_Statement, to ...
	(Analyze_Loop_Statement): Disable True_Constant on variables
	referenced within an OpenACC environment.
	* snames.ads-tmpl: Declare Name_Ids for the OpenACC directives
	and clauses we can handle. Remove an exraneous whitespace before
	columns, preventing line length overflow in the generated spec
	with Ids now reaching beyond 999.
	* doc/gnat_rm/implementation_defined_pragmas.rst: Document
	pragma Acc_Parallel, Acc_Loop, Acc_Kernels and Acc_Data.
	* gnat_rm.texi: Regenerate.

From-SVN: r264617

gcc/ada/ChangeLog

+2018-09-26  Olivier Hainque  <hainque@adacore.com>
+
+	* opt.ads (OpenAcc_Enabled): New flag. False by default. True
+	when OpenACC pragmas are requested to be honored, when -fopenacc
+	is found on the command line.
+	* back_end.adb (Scan_Compiler_Arguments): Set OpenACC_Enabled if
+	-fopenacc is seen on the command line.
+	* sinfo.adb, sinfo.ads (Is_OpenAcc_Environment): New
+	flag/predicate on Loop statements which embed an Acc_Kernels,
+	Acc_Parallel or Acc_Data pragma.
+	(Is_OpenAcc_Loop): New flag/predicate on Loop statements which
+	embed an Acc_Loop pragma.
+	(Set_Is_OpenAcc_Environment, Set_Is_OpenAcc_Loop): Setters for
+	the new flags.
+	* par-prag.adb (Prag): Handle Acc_Data, Acc_Loop, Acc_Parallel
+	and Acc_Kernels pragmas.  Nothing to do here, all handled by
+	sem_prag.
+	* sem_prag.adb (Acc_First, Acc_Next,
+	Validate_Acc_Condition_Clause, Validate_Acc_Data_Clause,
+	Validate_Acc_Int_Expr_Clause, Validate_Acc_Int_Expr_List_Clause,
+	Validate_Acc_Loop_Collapse, Validate_Acc_Loop_Gang,
+	Validate_Acc_Loop_Vector, Validate_Acc_Loop_Worker,
+	Validate_Acc_Name_Reduction, Validate_Acc_Size_Expressions): New
+	helper for Analyze_Pragma, to handle OpenACC pragmas.
+	(Analyze_Pragma): Handle Acc_Data, Acc_Loop, Acc_Parallel and
+	Acc_Kernels pragmas.
+	* sem_ch5.adb (Disable_Constant): Unset Is_True_Constant on
+	variable entity, action for ...
+	(Disable_Constants): Helper for Analyze_Loop_Statement, to ...
+	(Analyze_Loop_Statement): Disable True_Constant on variables
+	referenced within an OpenACC environment.
+	* snames.ads-tmpl: Declare Name_Ids for the OpenACC directives
+	and clauses we can handle. Remove an exraneous whitespace before
+	columns, preventing line length overflow in the generated spec
+	with Ids now reaching beyond 999.
+	* doc/gnat_rm/implementation_defined_pragmas.rst: Document
+	pragma Acc_Parallel, Acc_Loop, Acc_Kernels and Acc_Data.
+	* gnat_rm.texi: Regenerate.
+
 2018-09-26  Ed Schonberg  <schonberg@adacore.com>
 
 	* sem_ch3.adb (Is_Onown_Limited): A derived type whose parent P

gcc/ada/back_end.adb

@@ -375,6 +375,9 @@ package body Back_End is
             elsif Is_Front_End_Switch (Argv) then
                Scan_Front_End_Switches (Argv, Args, Next_Arg);
 
+            elsif Argv (Argv'First + 1 .. Argv'Last) = "fopenacc" then
+               Opt.OpenAcc_Enabled := True;
+
             --  All non-front-end switches are back-end switches
 
             else

gcc/ada/doc/gnat_rm/implementation_defined_pragmas.rst

@@ -89,6 +89,158 @@ Syntax:
 For the semantics of this pragma, see the entry for aspect ``Abstract_State`` in
 the SPARK 2014 Reference Manual, section 7.1.4.
 
+Pragma Acc_Parallel
+===================
+Syntax:
+
+.. code-block:: ada
+
+  pragma Acc_Parallel [( ACC_PARALLEL_CLAUSE [, ACC_PARALLEL_CLAUSE... ])];
+
+  ACC_PARALLEL_CLAUSE ::=
+      Acc_If        => boolean_EXPRESSION
+    | Acc_Private   => IDENTIFIERS
+    | Async         => integer_EXPRESSION
+    | Copy          => IDENTIFIERS
+    | Copy_In       => IDENTIFIERS
+    | Copy_Out      => IDENTIFIERS
+    | Create        => IDENTIFIERS
+    | Default       => None
+    | Device_Ptr    => IDENTIFIERS
+    | First_Private => IDENTIFIERS
+    | Num_Gangs     => integer_EXPRESSION
+    | Num_Workers   => integer_EXPRESSION
+    | Present       => IDENTIFIERS
+    | Reduction     => (REDUCTION_RECORD)
+    | Vector_Length => integer_EXPRESSION
+    | Wait          => INTEGERS
+
+  REDUCTION_RECORD ::=
+      "+"   => IDENTIFIERS
+    | "*"   => IDENTIFIERS
+    | "min" => IDENTIFIERS
+    | "max" => IDENTIFIERS
+    | "or"  => IDENTIFIERS
+    | "and" => IDENTIFIERS
+
+  IDENTIFIERS ::=
+    | IDENTIFIER
+    | (IDENTIFIER, IDENTIFIERS)
+
+  INTEGERS ::=
+    | integer_EXPRESSION
+    | (integer_EXPRESSION, INTEGERS)
+
+Requires the :switch:`-fopenacc` flag.
+
+Equivalent to the ``parallel`` directive of the OpenAcc standard. This pragma
+should be placed in loops. It offloads the content of the loop to an
+accelerator device.
+
+For more information about the effect of the clauses, see the OpenAcc
+specification.
+
+Pragma Acc_Loop
+===============
+Syntax:
+
+.. code-block:: ada
+
+  pragma Acc_Loop [( ACC_LOOP_CLAUSE [, ACC_LOOP_CLAUSE... ])];
+
+  ACC_LOOP_CLAUSE ::=
+      Auto
+    | Collapse        => INTEGER_LITERAL
+    | Gang            [=> GANG_ARG]
+    | Independent
+    | Private         => IDENTIFIERS
+    | Reduction       => (REDUCTION_RECORD)
+    | Seq
+    | Tile            => SIZE_EXPRESSION
+    | Vector          [=> integer_EXPRESSION]
+    | Worker          [=> integer_EXPRESSION]
+
+  GANG_ARG ::=
+      integer_EXPRESSION
+    | Static => SIZE_EXPRESSION
+
+  SIZE_EXPRESSION ::=
+      *
+    | integer_EXPRESSION
+
+Requires the :switch:`-fopenacc` flag.
+
+Equivalent to the ``loop`` directive of the OpenAcc standard. This pragma
+should be placed in for loops after the "Acc_Parallel" pragma. It tells the
+compiler how to parallelize the loop.
+
+For more information about the effect of the clauses, see the OpenAcc
+specification.
+
+Pragma Acc_Kernels
+==================
+Syntax:
+
+.. code-block:: ada
+
+  pragma Acc_Kernels [( ACC_KERNELS_CLAUSE [, ACC_KERNELS_CLAUSE...])];
+
+  ACC_KERNELS_CLAUSE ::=
+      Acc_If        => boolean_EXPRESSION
+    | Async         => integer_EXPRESSION
+    | Copy          => IDENTIFIERS
+    | Copy_In       => IDENTIFIERS
+    | Copy_Out      => IDENTIFIERS
+    | Create        => IDENTIFIERS
+    | Default       => None
+    | Device_Ptr    => IDENTIFIERS
+    | Num_Gangs     => integer_EXPRESSION
+    | Num_Workers   => integer_EXPRESSION
+    | Present       => IDENTIFIERS
+    | Vector_Length => integer_EXPRESSION
+    | Wait          => INTEGERS
+
+  IDENTIFIERS ::=
+    | IDENTIFIER
+    | (IDENTIFIER, IDENTIFIERS)
+
+  INTEGERS ::=
+    | integer_EXPRESSION
+    | (integer_EXPRESSION, INTEGERS)
+
+Requires the :switch:`-fopenacc` flag.
+
+Equivalent to the kernels directive of the OpenAcc standard. This pragma should
+be placed in loops.
+
+For more information about the effect of the clauses, see the OpenAcc
+specification.
+
+Pragma Acc_Data
+===============
+Syntax:
+
+.. code-block:: ada
+
+  pragma Acc_Data ([ ACC_DATA_CLAUSE [, ACC_DATA_CLAUSE...]]);
+
+  ACC_DATA_CLAUSE ::=
+      Copy          => IDENTIFIERS
+    | Copy_In       => IDENTIFIERS
+    | Copy_Out      => IDENTIFIERS
+    | Create        => IDENTIFIERS
+    | Device_Ptr    => IDENTIFIERS
+    | Present       => IDENTIFIERS
+
+Requires the :switch:`-fopenacc` flag.
+
+Equivalent to the ``data`` directive of the OpenAcc standard. This pragma
+should be placed in loops.
+
+For more information about the effect of the clauses, see the OpenAcc
+specification.
+
+
 Pragma Ada_83
 =============
 

gcc/ada/opt.ads

@@ -2335,6 +2335,15 @@ package Opt is
 
    --    The only special comment sequence allowed is --!
 
+   -------------
+   -- OpenAcc --
+   -------------
+
+   OpenAcc_Enabled : Boolean := False;
+   --  GNAT
+   --  Indicates whether OpenAcc pragmas should be taken into account.
+   --  Set True by use of -fopenacc.
+
    --------------------------
    -- Private Declarations --
    --------------------------

gcc/ada/par-prag.adb

@@ -1516,6 +1516,10 @@ begin
          | Pragma_Warning_As_Error
          | Pragma_Weak_External
          | Pragma_Validity_Checks
+         | Pragma_Acc_Data
+         | Pragma_Acc_Kernels
+         | Pragma_Acc_Loop
+         | Pragma_Acc_Parallel
       =>
          null;
 

gcc/ada/sem_ch5.adb

@@ -3361,6 +3361,9 @@ package body Sem_Ch5 is
 
    procedure Analyze_Loop_Statement (N : Node_Id) is
 
+      function Disable_Constant (N : Node_Id) return Traverse_Result;
+      --  If N represents an E_Variable entity, set Is_True_Constant To False
+
       function Is_Container_Iterator (Iter : Node_Id) return Boolean;
       --  Given a loop iteration scheme, determine whether it is an Ada 2012
       --  container iteration.
@@ -3371,6 +3374,25 @@ package body Sem_Ch5 is
       --  iterators. Prevents infinite recursion when block is analyzed.
       --  Routine is a noop if loop is single statement within source block.
 
+      ----------------------
+      -- Disable_Constant --
+      ----------------------
+
+      function Disable_Constant (N : Node_Id) return Traverse_Result is
+      begin
+         if Is_Entity_Name (N)
+            and then Present (Entity (N))
+            and then Ekind (Entity (N)) = E_Variable
+         then
+            Set_Is_True_Constant (Entity (N), False);
+         end if;
+         return OK;
+      end Disable_Constant;
+
+      procedure Disable_Constants is new Traverse_Proc (Disable_Constant);
+      --  Helper for Analyze_Loop_Statement, to unset Is_True_Constant on
+      --  variables referenced within an OpenACC environment.
+
       ---------------------------
       -- Is_Container_Iterator --
       ---------------------------
@@ -3812,6 +3834,15 @@ package body Sem_Ch5 is
       if No (Iter) and then not Has_Exit (Ent) then
          Check_Unreachable_Code (Stmt);
       end if;
+
+      --  Variables referenced within a loop subject to possible OpenACC
+      --  offloading may be implicitly written to as part of the OpenACC
+      --  transaction.  Clear flags possibly conveying that they are constant,
+      --  set for example when the code does not explicitly assign them.
+
+      if Is_OpenAcc_Environment (Stmt) then
+         Disable_Constants (Stmt);
+      end if;
    end Analyze_Loop_Statement;
 
    ----------------------------

gcc/ada/sinfo.adb

@@ -2069,6 +2069,22 @@ package body Sinfo is
       return Flag16 (N);
    end Is_Null_Loop;
 
+   function Is_OpenAcc_Environment
+      (N : Node_Id) return Boolean is
+   begin
+      pragma Assert (False
+        or else NT (N).Nkind = N_Loop_Statement);
+      return Flag13 (N);
+   end Is_OpenAcc_Environment;
+
+   function Is_OpenAcc_Loop
+      (N : Node_Id) return Boolean is
+   begin
+      pragma Assert (False
+        or else NT (N).Nkind = N_Loop_Statement);
+      return Flag14 (N);
+   end Is_OpenAcc_Loop;
+
    function Is_Overloaded
       (N : Node_Id) return Boolean is
    begin
@@ -5527,6 +5543,22 @@ package body Sinfo is
       Set_Flag16 (N, Val);
    end Set_Is_Null_Loop;
 
+   procedure Set_Is_OpenAcc_Environment
+      (N : Node_Id; Val : Boolean := True) is
+   begin
+      pragma Assert (False
+        or else NT (N).Nkind = N_Loop_Statement);
+      Set_Flag13 (N, Val);
+   end Set_Is_OpenAcc_Environment;
+
+   procedure Set_Is_OpenAcc_Loop
+      (N : Node_Id; Val : Boolean := True) is
+   begin
+      pragma Assert (False
+        or else NT (N).Nkind = N_Loop_Statement);
+      Set_Flag14 (N, Val);
+   end Set_Is_OpenAcc_Loop;
+
    procedure Set_Is_Overloaded
       (N : Node_Id; Val : Boolean := True) is
    begin

gcc/ada/sinfo.ads

@@ -1896,6 +1896,14 @@ package Sinfo is
    --    can be determined to be null at compile time. This is used to remove
    --    the loop entirely at expansion time.
 
+   --  Is_OpenAcc_Environment (Flag13-Sem)
+   --    This flag is set in an N_Loop_Statement node if it contains an
+   --    Acc_Data, Acc_Parallel or Add_Kernels pragma.
+
+   --  Is_OpenAcc_Loop (Flag14-Sem)
+   --    This flag is set in an N_Loop_Statement node if it contains an
+   --    OpenAcc_Loop pragma.
+
    --  Is_Overloaded (Flag5-Sem)
    --    A flag present in all expression nodes. Used temporarily during
    --    overloading determination. The setting of this flag is not relevant
@@ -5129,6 +5137,8 @@ package Sinfo is
       --  Has_Created_Identifier (Flag15)
       --  Is_Null_Loop (Flag16)
       --  Suppress_Loop_Warnings (Flag17)
+      --  Is_OpenAcc_Environment (Flag13-Sem)
+      --  Is_OpenAcc_Loop (Flag14-Sem)
 
       --  Note: the parser fills in the Identifier field if there is an
       --  explicit loop identifier. Otherwise the parser leaves this field
@@ -9847,6 +9857,12 @@ package Sinfo is
    function Is_Null_Loop
      (N : Node_Id) return Boolean;    -- Flag16
 
+   function Is_OpenAcc_Environment
+     (N : Node_Id) return Boolean;    -- Flag13
+
+   function Is_OpenAcc_Loop
+     (N : Node_Id) return Boolean;    -- Flag14
+
    function Is_Overloaded
      (N : Node_Id) return Boolean;    -- Flag5
 
@@ -10945,6 +10961,12 @@ package Sinfo is
    procedure Set_Is_Null_Loop
      (N : Node_Id; Val : Boolean := True);    -- Flag16
 
+   procedure Set_Is_OpenAcc_Environment
+     (N : Node_Id; Val : Boolean := True);    -- Flag13
+
+   procedure Set_Is_OpenAcc_Loop
+     (N : Node_Id; Val : Boolean := True);    -- Flag14
+
    procedure Set_Is_Overloaded
      (N : Node_Id; Val : Boolean := True);    -- Flag5
 
@@ -13450,6 +13472,8 @@ package Sinfo is
    pragma Inline (Is_Known_Guaranteed_ABE);
    pragma Inline (Is_Machine_Number);
    pragma Inline (Is_Null_Loop);
+   pragma Inline (Is_OpenAcc_Environment);
+   pragma Inline (Is_OpenAcc_Loop);
    pragma Inline (Is_Overloaded);
    pragma Inline (Is_Power_Of_2_For_Shift);
    pragma Inline (Is_Prefixed_Call);
@@ -13812,6 +13836,8 @@ package Sinfo is
    pragma Inline (Set_Is_Known_Guaranteed_ABE);
    pragma Inline (Set_Is_Machine_Number);
    pragma Inline (Set_Is_Null_Loop);
+   pragma Inline (Set_Is_OpenAcc_Environment);
+   pragma Inline (Set_Is_OpenAcc_Loop);
    pragma Inline (Set_Is_Overloaded);
    pragma Inline (Set_Is_Power_Of_2_For_Shift);
    pragma Inline (Set_Is_Prefixed_Call);