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[Ada] Streamline comparison for equality of 2-element arrays
- From: Pierre-Marie de Rodat <derodat at adacore dot com>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Eric Botcazou <ebotcazou at adacore dot com>
- Date: Thu, 19 Sep 2019 09:28:19 -0400
- Subject: [Ada] Streamline comparison for equality of 2-element arrays
In the general case, the comparison for equality of array objects is
implemented by a local function that contains, among other things, a
loop running over the elements, comparing them one by one and exiting
as soon as an element is not the same in the two array objects.
For the specific case of constrained 2-element arrays, this is rather
heavy and unnecessarily obfuscates the control flow of the program,
so this change implements a simple conjunction of comparisons for it.
Running these commands:
gcc -c p.ads -O -gnatD
grep loop p.ads.dg
On the following sources:
package P is
type Rec is record
Re : Float;
Im : Float;
end record;
type Arr is array (1 .. 2) of Rec;
function Equal (A, B : Arr) return Boolean is (A = B);
end P;
Should execute silently.
Tested on x86_64-pc-linux-gnu, committed on trunk
2019-09-19 Eric Botcazou <ebotcazou@adacore.com>
gcc/ada/
* exp_ch4.adb (Expand_Array_Equality): If optimization is
enabled, generate a simple conjunction of comparisons for the
specific case of constrained 1-dimensional 2-element arrays.
Fix formatting.--- gcc/ada/exp_ch4.adb
+++ gcc/ada/exp_ch4.adb
@@ -1582,7 +1582,7 @@ package body Exp_Ch4 is
Index_List1 : constant List_Id := New_List;
Index_List2 : constant List_Id := New_List;
- Actuals : List_Id;
+ First_Idx : Node_Id;
Formals : List_Id;
Func_Name : Entity_Id;
Func_Body : Node_Id;
@@ -1594,6 +1594,10 @@ package body Exp_Ch4 is
Rtyp : Entity_Id;
-- The parameter types to be used for the formals
+ New_Lhs : Node_Id;
+ New_Rhs : Node_Id;
+ -- The LHS and RHS converted to the parameter types
+
function Arr_Attr
(Arr : Entity_Id;
Nam : Name_Id;
@@ -1962,6 +1966,82 @@ package body Exp_Ch4 is
pragma Assert (Ltyp = Rtyp);
end if;
+ -- If the array type is distinct from the type of the arguments, it
+ -- is the full view of a private type. Apply an unchecked conversion
+ -- to ensure that analysis of the code below succeeds.
+
+ if No (Etype (Lhs))
+ or else Base_Type (Etype (Lhs)) /= Base_Type (Ltyp)
+ then
+ New_Lhs := OK_Convert_To (Ltyp, Lhs);
+ else
+ New_Lhs := Lhs;
+ end if;
+
+ if No (Etype (Rhs))
+ or else Base_Type (Etype (Rhs)) /= Base_Type (Rtyp)
+ then
+ New_Rhs := OK_Convert_To (Rtyp, Rhs);
+ else
+ New_Rhs := Rhs;
+ end if;
+
+ First_Idx := First_Index (Ltyp);
+
+ -- If optimization is enabled and the array boils down to a couple of
+ -- consecutive elements, generate a simple conjunction of comparisons
+ -- which should be easier to optimize by the code generator.
+
+ if Optimization_Level > 0
+ and then Ltyp = Rtyp
+ and then Is_Constrained (Ltyp)
+ and then Number_Dimensions (Ltyp) = 1
+ and then Nkind (First_Idx) = N_Range
+ and then Compile_Time_Known_Value (Low_Bound (First_Idx))
+ and then Compile_Time_Known_Value (High_Bound (First_Idx))
+ and then Expr_Value (High_Bound (First_Idx)) =
+ Expr_Value (Low_Bound (First_Idx)) + 1
+ then
+ declare
+ Ctyp : constant Entity_Id := Component_Type (Ltyp);
+ L, R : Node_Id;
+ TestL, TestH : Node_Id;
+ Index_List : List_Id;
+
+ begin
+ Index_List := New_List (New_Copy_Tree (Low_Bound (First_Idx)));
+
+ L :=
+ Make_Indexed_Component (Loc,
+ Prefix => New_Copy_Tree (New_Lhs),
+ Expressions => Index_List);
+
+ R :=
+ Make_Indexed_Component (Loc,
+ Prefix => New_Copy_Tree (New_Rhs),
+ Expressions => Index_List);
+
+ TestL := Expand_Composite_Equality (Nod, Ctyp, L, R, Bodies);
+
+ Index_List := New_List (New_Copy_Tree (High_Bound (First_Idx)));
+
+ L :=
+ Make_Indexed_Component (Loc,
+ Prefix => New_Lhs,
+ Expressions => Index_List);
+
+ R :=
+ Make_Indexed_Component (Loc,
+ Prefix => New_Rhs,
+ Expressions => Index_List);
+
+ TestH := Expand_Composite_Equality (Nod, Ctyp, L, R, Bodies);
+
+ return
+ Make_And_Then (Loc, Left_Opnd => TestL, Right_Opnd => TestH);
+ end;
+ end if;
+
-- Build list of formals for function
Formals := New_List (
@@ -2004,46 +2084,20 @@ package body Exp_Ch4 is
Make_Simple_Return_Statement (Loc,
Expression => New_Occurrence_Of (Standard_False, Loc)))),
- Handle_One_Dimension (1, First_Index (Ltyp)),
+ Handle_One_Dimension (1, First_Idx),
Make_Simple_Return_Statement (Loc,
Expression => New_Occurrence_Of (Standard_True, Loc)))));
- Set_Has_Completion (Func_Name, True);
- Set_Is_Inlined (Func_Name);
-
- -- If the array type is distinct from the type of the arguments, it
- -- is the full view of a private type. Apply an unchecked conversion
- -- to ensure that analysis of the call succeeds.
-
- declare
- L, R : Node_Id;
-
- begin
- L := Lhs;
- R := Rhs;
-
- if No (Etype (Lhs))
- or else Base_Type (Etype (Lhs)) /= Base_Type (Ltyp)
- then
- L := OK_Convert_To (Ltyp, Lhs);
- end if;
-
- if No (Etype (Rhs))
- or else Base_Type (Etype (Rhs)) /= Base_Type (Rtyp)
- then
- R := OK_Convert_To (Rtyp, Rhs);
- end if;
-
- Actuals := New_List (L, R);
- end;
+ Set_Has_Completion (Func_Name, True);
+ Set_Is_Inlined (Func_Name);
- Append_To (Bodies, Func_Body);
+ Append_To (Bodies, Func_Body);
- return
- Make_Function_Call (Loc,
- Name => New_Occurrence_Of (Func_Name, Loc),
- Parameter_Associations => Actuals);
+ return
+ Make_Function_Call (Loc,
+ Name => New_Occurrence_Of (Func_Name, Loc),
+ Parameter_Associations => New_List (New_Lhs, New_Rhs));
end Expand_Array_Equality;
-----------------------------