[gcc r11-2160] [Ada] Adjust heuristics about size of static aggregates
Pierre-Marie de Rodat
pmderodat@gcc.gnu.org
Thu Jul 16 09:22:08 GMT 2020
https://gcc.gnu.org/g:eaf6e63a647b8604de960d2fa992c7dd57a5d553
commit r11-2160-geaf6e63a647b8604de960d2fa992c7dd57a5d553
Author: Bob Duff <duff@adacore.com>
Date: Tue Jun 9 19:04:56 2020 -0400
[Ada] Adjust heuristics about size of static aggregates
gcc/ada/
* exp_aggr.adb (Max_Aggregate_Size): Use the small size of 64
when copying is needed (for example, for the initialization of a
local variable, and for assignment statements). Use the larger
size when static allocation can be done without copying.
Diff:
---
gcc/ada/exp_aggr.adb | 96 +++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 77 insertions(+), 19 deletions(-)
diff --git a/gcc/ada/exp_aggr.adb b/gcc/ada/exp_aggr.adb
index 29d3f149095..0ca1af4abfa 100644
--- a/gcc/ada/exp_aggr.adb
+++ b/gcc/ada/exp_aggr.adb
@@ -252,7 +252,7 @@ package body Exp_Aggr is
function Aggr_Assignment_OK_For_Backend (N : Node_Id) return Boolean;
-- Returns true if an aggregate assignment can be done by the back end
- function Aggr_Size_OK (N : Node_Id; Typ : Entity_Id) return Boolean;
+ function Aggr_Size_OK (N : Node_Id) return Boolean;
-- Very large static aggregates present problems to the back-end, and are
-- transformed into assignments and loops. This function verifies that the
-- total number of components of an aggregate is acceptable for rewriting
@@ -328,10 +328,10 @@ package body Exp_Aggr is
-- is a two dimensional bit packed array with component size 1, 2, or 4.
function Max_Aggregate_Size
- (Typ : Entity_Id;
+ (N : Node_Id;
Default_Size : Nat := 5000) return Nat;
- -- Return the max size for a static aggregate of the given Typ.
- -- Return Default_Size if no other special criteria trigger.
+ -- Return the max size for a static aggregate N. Return Default_Size if no
+ -- other special criteria trigger.
function Packed_Array_Aggregate_Handled (N : Node_Id) return Boolean;
-- Given an array aggregate, this function handles the case of a packed
@@ -593,7 +593,8 @@ package body Exp_Aggr is
-- Aggr_Size_OK --
------------------
- function Aggr_Size_OK (N : Node_Id; Typ : Entity_Id) return Boolean is
+ function Aggr_Size_OK (N : Node_Id) return Boolean is
+ Typ : constant Entity_Id := Etype (N);
Lo : Node_Id;
Hi : Node_Id;
Indx : Node_Id;
@@ -688,9 +689,9 @@ package body Exp_Aggr is
if No (Expressions (N))
and then No (Next (First (Component_Associations (N))))
then
- Max_Aggr_Size := Max_Aggregate_Size (Typ);
+ Max_Aggr_Size := Max_Aggregate_Size (N);
else
- Max_Aggr_Size := Max_Aggregate_Size (Typ, 500_000);
+ Max_Aggr_Size := Max_Aggregate_Size (N, 500_000);
end if;
Size := UI_From_Int (Component_Count (Component_Type (Typ)));
@@ -4955,7 +4956,7 @@ package body Exp_Aggr is
is
Typ : constant Entity_Id := Etype (N);
Dims : constant Nat := Number_Dimensions (Typ);
- Max_Others_Replicate : constant Nat := Max_Aggregate_Size (Typ);
+ Max_Others_Replicate : constant Nat := Max_Aggregate_Size (N);
Static_Components : Boolean := True;
@@ -5475,7 +5476,7 @@ package body Exp_Aggr is
-- compatible with the upper bound of the type, and therefore it is
-- worth flattening such aggregates as well.
- if Aggr_Size_OK (N, Typ)
+ if Aggr_Size_OK (N)
and then
Flatten (N, Dims, First_Index (Typ), First_Index (Base_Type (Typ)))
then
@@ -8315,8 +8316,69 @@ package body Exp_Aggr is
------------------------
function Max_Aggregate_Size
- (Typ : Entity_Id;
- Default_Size : Nat := 5000) return Nat is
+ (N : Node_Id;
+ Default_Size : Nat := 5000) return Nat
+ is
+ Typ : constant Entity_Id := Etype (N);
+
+ function Use_Small_Size (N : Node_Id) return Boolean;
+ -- True if we should return a very small size, which means large
+ -- aggregates will be implemented as a loop when possible (potentially
+ -- transformed to memset calls).
+
+ function Aggr_Context (N : Node_Id) return Node_Id;
+ -- Return the context in which the aggregate appears, not counting
+ -- qualified expressions and similar.
+
+ function Aggr_Context (N : Node_Id) return Node_Id is
+ Result : Node_Id := Parent (N);
+ begin
+ if Nkind_In (Result, N_Qualified_Expression,
+ N_Type_Conversion,
+ N_Unchecked_Type_Conversion,
+ N_If_Expression,
+ N_Case_Expression,
+ N_Component_Association,
+ N_Aggregate)
+ then
+ Result := Aggr_Context (Result);
+ end if;
+
+ return Result;
+ end Aggr_Context;
+
+ function Use_Small_Size (N : Node_Id) return Boolean is
+ C : constant Node_Id := Aggr_Context (N);
+ -- The decision depends on the context in which the aggregate occurs,
+ -- and for variable declarations, whether we are nested inside a
+ -- subprogram.
+ begin
+ case Nkind (C) is
+ -- True for assignment statements and similar
+
+ when N_Assignment_Statement
+ | N_Simple_Return_Statement
+ | N_Allocator
+ | N_Attribute_Reference
+ =>
+ return True;
+
+ -- True for nested variable declarations. False for library level
+ -- variables, and for constants (whether or not nested).
+
+ when N_Object_Declaration =>
+ return not Constant_Present (C)
+ and then Ekind (Current_Scope) in Subprogram_Kind;
+
+ -- False for all other contexts
+
+ when others =>
+ return False;
+ end case;
+ end Use_Small_Size;
+
+ -- Start of processing for Max_Aggregate_Size
+
begin
-- We use a small limit in CodePeer mode where we favor loops
-- instead of thousands of single assignments (from large aggregates).
@@ -8332,10 +8394,6 @@ package body Exp_Aggr is
-- if components are static it is much more efficient to construct a
-- one-dimensional equivalent array with static components.
- -- Finally we also use a small limit when we're within a subprogram
- -- since we want to favor loops (potentially transformed to memset
- -- calls) in this context.
-
if CodePeer_Mode then
return 100;
elsif Restriction_Active (No_Elaboration_Code)
@@ -8345,11 +8403,11 @@ package body Exp_Aggr is
and then Static_Elaboration_Desired (Current_Scope))
then
return 2 ** 24;
- elsif Ekind (Current_Scope) in Subprogram_Kind then
+ elsif Use_Small_Size (N) then
return 64;
- else
- return Default_Size;
end if;
+
+ return Default_Size;
end Max_Aggregate_Size;
-----------------------
@@ -9153,7 +9211,7 @@ package body Exp_Aggr is
return False;
end if;
- if not Aggr_Size_OK (N, Typ) then
+ if not Aggr_Size_OK (N) then
return False;
end if;
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