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[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.

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.

From-SVN: r275941
This commit is contained in:
Eric Botcazou 2019-09-19 08:13:29 +00:00 committed by Pierre-Marie de Rodat
parent c4f372c54f
commit 1dd3915be1
2 changed files with 96 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
gcc/ada/ChangeLog
View File

@ -1,3 +1,10 @@
2019-09-19 Eric Botcazou <ebotcazou@adacore.com>
* 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.
2019-09-19 Piotr Trojanek <trojanek@adacore.com>
* exp_dbug.ads, exp_dbug.adb (Get_Homonym_Number): Remove.

124
gcc/ada/exp_ch4.adb
View File

@ -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);
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.
Append_To (Bodies, Func_Body);
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;
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;
-----------------------------