From d89d9ecceb541ca824f7fb5f57f747a31c7ce9a5 Mon Sep 17 00:00:00 2001 From: Claire Dross Date: Fri, 21 Jan 2022 10:42:49 +0100 Subject: [PATCH] [Ada] Accept Structural in aspect Subprogram_Variant and pragma Loop_Variant Add a new form of variants to ensure termination of loops or recursive subprograms. Structural variants correspond to objects which designate a part of the data-structure they used to designate in the previous loop iteration or recursive call. They only imply termination if the data-structure is acyclic, which is the case in SPARK but not in Ada in general. The fact that these variants are correct is only verified formally by the proof tool and not by the compiler or dynamically at execution like other forms of variants. gcc/ada/ * snames.ads-tmpl: Add "Structural" as a name. * sem_prag.adb: (Analyze_Pragma): Accept modifier "Structural" in pragmas Loop_Variant and Subprogram_Variant. Check that items associated to Structural occur alone in the pragma associations. (Analyze_Subprogram_Variant_In_Decl_Part): Idem. * exp_prag.adb (Expand_Pragma_Loop_Variant): Discard structural variants. (Expand_Pragma_Subprogram_Variant): Idem. gcc/testsuite/ * gnat.dg/loopvar.adb: Update expected error message. --- gcc/ada/exp_prag.adb | 25 ++++++++++------ gcc/ada/sem_prag.adb | 61 +++++++++++++++++++++++++++++---------- gcc/ada/snames.ads-tmpl | 1 + gcc/testsuite/gnat.dg/loopvar.adb | 2 +- 4 files changed, 64 insertions(+), 25 deletions(-) diff --git a/gcc/ada/exp_prag.adb b/gcc/ada/exp_prag.adb index 0fe8bff..bf2d297 100644 --- a/gcc/ada/exp_prag.adb +++ b/gcc/ada/exp_prag.adb @@ -2694,10 +2694,15 @@ package body Exp_Prag is -- If pragma is not enabled, rewrite as Null statement. If pragma is -- disabled, it has already been rewritten as a Null statement. -- - -- Likewise, do this in CodePeer mode, because the expanded code is too + -- Likewise, ignore structural variants for execution. + -- + -- Also do this in CodePeer mode, because the expanded code is too -- complicated for CodePeer to analyse. - if Is_Ignored (N) or else CodePeer_Mode then + if Is_Ignored (N) + or else Chars (Last_Var) = Name_Structural + or else CodePeer_Mode + then Rewrite (N, Make_Null_Statement (Loc)); Analyze (N); return; @@ -3058,10 +3063,12 @@ package body Exp_Prag is Loc : constant Source_Ptr := Sloc (Prag); - Aggr : Node_Id; + Aggr : constant Node_Id := + Expression (First (Pragma_Argument_Associations (Prag))); Formal_Map : Elist_Id; Last : Node_Id; - Last_Variant : Node_Id; + Last_Variant : constant Node_Id := + Nlists.Last (Component_Associations (Aggr)); Proc_Bod : Node_Id; Proc_Decl : Node_Id; Proc_Id : Entity_Id; @@ -3069,14 +3076,15 @@ package body Exp_Prag is Variant : Node_Id; begin - -- Do nothing if pragma is not present or is disabled + -- Do nothing if pragma is not present or is disabled. + -- Also ignore structural variants for execution. - if Is_Ignored (Prag) then + if Is_Ignored (Prag) + or else Chars (Nlists.Last (Choices (Last_Variant))) = Name_Structural + then return; end if; - Aggr := Expression (First (Pragma_Argument_Associations (Prag))); - -- The expansion of Subprogram Variant is quite distributed as it -- produces various statements to capture and compare the arguments. -- To preserve the original context, set the Is_Assertion_Expr flag. @@ -3115,7 +3123,6 @@ package body Exp_Prag is Last := Proc_Decl; Curr_Decls := New_List; - Last_Variant := Nlists.Last (Component_Associations (Aggr)); Variant := First (Component_Associations (Aggr)); while Present (Variant) loop diff --git a/gcc/ada/sem_prag.adb b/gcc/ada/sem_prag.adb index 9ef3a06..57a74db 100644 --- a/gcc/ada/sem_prag.adb +++ b/gcc/ada/sem_prag.adb @@ -19423,7 +19423,8 @@ package body Sem_Prag is if Chars (Variant) = No_Name then Error_Pragma_Arg_Ident ("expect name `Increases`", Variant); - elsif Chars (Variant) not in Name_Decreases | Name_Increases + elsif Chars (Variant) not in + Name_Decreases | Name_Increases | Name_Structural then declare Name : String := Get_Name_String (Chars (Variant)); @@ -19448,11 +19449,24 @@ package body Sem_Prag is Error_Pragma_Arg_Ident ("expect name `Decreases`", Variant); + elsif Name'Length >= 4 + and then Name (1 .. 4) = "stru" + then + Error_Pragma_Arg_Ident + ("expect name `Structural`", Variant); + else Error_Pragma_Arg_Ident - ("expect name `Increases` or `Decreases`", Variant); + ("expect name `Increases`, `Decreases`," + & " or `Structural`", Variant); end if; end; + + elsif Chars (Variant) = Name_Structural + and then List_Length (Pragma_Argument_Associations (N)) > 1 + then + Error_Pragma_Arg_Ident + ("Structural variant shall be the only variant", Variant); end if; -- Preanalyze_Assert_Expression, but without enforcing any of @@ -19460,9 +19474,12 @@ package body Sem_Prag is Preanalyze_Assert_Expression (Expression (Variant)); - -- Expression of a discrete type is allowed + -- Expression of a discrete type is allowed. Nothing to + -- check for structural variants. - if Is_Discrete_Type (Etype (Expression (Variant))) then + if Chars (Variant) = Name_Structural + or else Is_Discrete_Type (Etype (Expression (Variant))) + then null; -- Expression of a Big_Integer type (or its ghost variant) is @@ -24227,13 +24244,16 @@ package body Sem_Prag is -- Subprogram_Variant -- ------------------------ - -- pragma Subprogram_Variant ( SUBPROGRAM_VARIANT_ITEM - -- {, SUBPROGRAM_VARIANT_ITEM } ); - - -- SUBPROGRAM_VARIANT_ITEM ::= - -- CHANGE_DIRECTION => discrete_EXPRESSION + -- pragma Subprogram_Variant ( SUBPROGRAM_VARIANT_LIST ); - -- CHANGE_DIRECTION ::= Increases | Decreases + -- SUBPROGRAM_VARIANT_LIST ::= STRUCTURAL_SUBPROGRAM_VARIANT_ITEM + -- | NUMERIC_SUBPROGRAM_VARIANT_ITEMS + -- NUMERIC_SUBPROGRAM_VARIANT_ITEMS ::= + -- NUMERIC_SUBPROGRAM_VARIANT_ITEM + -- {, NUMERIC_SUBPROGRAM_VARIANT_ITEM} + -- NUMERIC_SUBPROGRAM_VARIANT_ITEM ::= CHANGE_DIRECTION => EXPRESSION + -- STRUCTURAL_SUBPROGRAM_VARIANT_ITEM ::= Structural => EXPRESSION + -- CHANGE_DIRECTION ::= Increases | Decreases -- Characteristics: @@ -29435,9 +29455,9 @@ package body Sem_Prag is -- Check placement of OTHERS if available (SPARK RM 6.1.3(1)) if Nkind (Direction) = N_Identifier then - if Chars (Direction) /= Name_Decreases - and then - Chars (Direction) /= Name_Increases + if Chars (Direction) not in Name_Decreases + | Name_Increases + | Name_Structural then Error_Msg_N ("wrong direction", Direction); end if; @@ -29452,9 +29472,12 @@ package body Sem_Prag is Preanalyze_Assert_Expression (Expr); - -- Expression of a discrete type is allowed + -- Expression of a discrete type is allowed. Nothing more to check + -- for structural variants. - if Is_Discrete_Type (Etype (Expr)) then + if Is_Discrete_Type (Etype (Expr)) + or else Chars (Direction) = Name_Structural + then null; -- Expression of a Big_Integer type (or its ghost variant) is only @@ -29561,6 +29584,14 @@ package body Sem_Prag is Variant := First (Component_Associations (Variants)); while Present (Variant) loop Analyze_Variant (Variant); + + if Chars (First (Choices (Variant))) = Name_Structural + and then List_Length (Component_Associations (Variants)) > 1 + then + Error_Msg_N + ("Structural variant shall be the only variant", Variant); + end if; + Next (Variant); end loop; diff --git a/gcc/ada/snames.ads-tmpl b/gcc/ada/snames.ads-tmpl index fa7ac8a..5f7d6b7 100644 --- a/gcc/ada/snames.ads-tmpl +++ b/gcc/ada/snames.ads-tmpl @@ -875,6 +875,7 @@ package Snames is Name_Static : constant Name_Id := N + $; Name_Stack_Size : constant Name_Id := N + $; Name_Strict : constant Name_Id := N + $; + Name_Structural : constant Name_Id := N + $; Name_Subunit_File_Name : constant Name_Id := N + $; Name_Suppressible : constant Name_Id := N + $; Name_Synchronous : constant Name_Id := N + $; diff --git a/gcc/testsuite/gnat.dg/loopvar.adb b/gcc/testsuite/gnat.dg/loopvar.adb index f85402a..e98d20d 100644 --- a/gcc/testsuite/gnat.dg/loopvar.adb +++ b/gcc/testsuite/gnat.dg/loopvar.adb @@ -9,7 +9,7 @@ begin pragma Loop_Variant (J + 1); -- { dg-error "expect name \"Increases\"" } pragma Loop_Variant (incr => -J + 1); -- { dg-error "expect name \"Increases\"" } pragma Loop_Variant (decr => -J + 1); -- { dg-error "expect name \"Decreases\"" } - pragma Loop_Variant (foof => -J + 1); -- { dg-error "expect name \"Increases\" or \"Decreases\"" } + pragma Loop_Variant (foof => -J + 1); -- { dg-error "expect name \"Increases\", \"Decreases\", or \"Structural\"" } J := J + 2; end loop; end Loopvar; -- 2.7.4