[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

diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 1f3128e178a13f85cbc5c46be83ad6a624f4ef53..37576aaee5c08861796e65e098b2e3df4c4f42cd 100644 (file)
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -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.

diff --git a/gcc/ada/exp_ch4.adb b/gcc/ada/exp_ch4.adb
index a20469cfa7c7985589adb7212da27404970134e9..82145b42a197392aed2ca129e6417c8a69506cc8 100644 (file)
--- a/gcc/ada/exp_ch4.adb
+++ b/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;
 
    -----------------------------