* [Ada] Do not use 128-bit division for 64-bit fixed-point types
@ 2020-11-27 9:18 Pierre-Marie de Rodat
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From: Pierre-Marie de Rodat @ 2020-11-27 9:18 UTC (permalink / raw)
To: gcc-patches; +Cc: Eric Botcazou
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This restricts the use of 128-bit division for fixed-point types to
the cases where there is a 128-bit type in the source code, that is
to say this prevents the compiler from using it for 64-bit types.
This is done mainly for the sake of backward compatibility with earlier
compilers not supporting 128-bit fixed-point types, and because large
division operations generally require specific support routines.
Tested on x86_64-pc-linux-gnu, committed on trunk
gcc/ada/
* exp_fixd.adb (Build_Double_Divide): Only use a 128-bit
division if one of the operands is larger than 64 bits.
(Build_Double_Divide_Code): Likewise.
(Build_Scaled_Divide): Likewise.
(Build_Scaled_Divide_Code): Likewise.
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diff --git a/gcc/ada/exp_fixd.adb b/gcc/ada/exp_fixd.adb
--- a/gcc/ada/exp_fixd.adb
+++ b/gcc/ada/exp_fixd.adb
@@ -447,15 +447,22 @@ package body Exp_Fixd is
(N : Node_Id;
X, Y, Z : Node_Id) return Node_Id
is
+ X_Size : constant Nat := UI_To_Int (RM_Size (Etype (X)));
Y_Size : constant Nat := UI_To_Int (RM_Size (Etype (Y)));
Z_Size : constant Nat := UI_To_Int (RM_Size (Etype (Z)));
+ D_Size : constant Nat := Y_Size + Z_Size;
+ M_Size : constant Nat := Nat'Max (X_Size, Nat'Max (Y_Size, Z_Size));
Expr : Node_Id;
begin
-- If the denominator fits in Max_Integer_Size bits, we can build the
- -- operations directly without causing any intermediate overflow.
+ -- operations directly without causing any intermediate overflow. But
+ -- for backward compatibility reasons, we use a 128-bit divide only
+ -- if one of the operands is already larger than 64 bits.
- if Y_Size + Z_Size <= System_Max_Integer_Size then
+ if D_Size <= System_Max_Integer_Size
+ and then (D_Size <= 64 or else M_Size > 64)
+ then
return Build_Divide (N, X, Build_Multiply (N, Y, Z));
-- Otherwise we use the runtime routine
@@ -518,6 +525,7 @@ package body Exp_Fixd is
X_Size : constant Nat := UI_To_Int (RM_Size (Etype (X)));
Y_Size : constant Nat := UI_To_Int (RM_Size (Etype (Y)));
Z_Size : constant Nat := UI_To_Int (RM_Size (Etype (Z)));
+ M_Size : constant Nat := Nat'Max (X_Size, Nat'Max (Y_Size, Z_Size));
QR_Id : RE_Id;
QR_Siz : Nat;
@@ -546,17 +554,17 @@ package body Exp_Fixd is
QR_Typ := Standard_Integer_64;
QR_Id := RE_Null;
- elsif QR_Siz <= 128 and then System_Max_Integer_Size = 128 then
- QR_Typ := Standard_Integer_128;
- QR_Id := RE_Null;
-
- -- For more than Max_Integer_Size bits, we use the integer defined in
- -- Interfaces, so that it can be handled by the runtime routine.
+ -- For backward compatibility reasons, we use a 128-bit divide only
+ -- if one of the operands is already larger than 64 bits.
- elsif System_Max_Integer_Size < 128 then
+ elsif System_Max_Integer_Size < 128 or else M_Size <= 64 then
QR_Typ := RTE (RE_Integer_64);
QR_Id := RE_Double_Divide64;
+ elsif QR_Siz <= 128 then
+ QR_Typ := Standard_Integer_128;
+ QR_Id := RE_Null;
+
else
QR_Typ := RTE (RE_Integer_128);
QR_Id := RE_Double_Divide128;
@@ -571,9 +579,9 @@ package body Exp_Fixd is
Set_Etype (Qnn, QR_Typ);
Set_Etype (Rnn, QR_Typ);
- -- Case that we can compute the denominator in Max_Integer_Size bits
+ -- Case where we can compute the denominator in Max_Integer_Size bits
- if QR_Siz <= System_Max_Integer_Size then
+ if QR_Id = RE_Null then
-- Create temporaries for numerator and denominator and set Etypes,
-- so that New_Occurrence_Of picks them up for Build_xxx calls.
@@ -829,13 +837,20 @@ package body Exp_Fixd is
is
X_Size : constant Nat := UI_To_Int (RM_Size (Etype (X)));
Y_Size : constant Nat := UI_To_Int (RM_Size (Etype (Y)));
+ Z_Size : constant Nat := UI_To_Int (RM_Size (Etype (Z)));
+ N_Size : constant Nat := X_Size + Y_Size;
+ M_Size : constant Nat := Nat'Max (X_Size, Nat'Max (Y_Size, Z_Size));
Expr : Node_Id;
begin
-- If the numerator fits in Max_Integer_Size bits, we can build the
- -- operations directly without causing any intermediate overflow.
+ -- operations directly without causing any intermediate overflow. But
+ -- for backward compatibility reasons, we use a 128-bit divide only
+ -- if one of the operands is already larger than 64 bits.
- if X_Size + Y_Size <= System_Max_Integer_Size then
+ if N_Size <= System_Max_Integer_Size
+ and then (N_Size <= 64 or else M_Size > 64)
+ then
return Build_Divide (N, Build_Multiply (N, X, Y), Z);
-- Otherwise we use the runtime routine
@@ -895,6 +910,7 @@ package body Exp_Fixd is
X_Size : constant Nat := UI_To_Int (RM_Size (Etype (X)));
Y_Size : constant Nat := UI_To_Int (RM_Size (Etype (Y)));
Z_Size : constant Nat := UI_To_Int (RM_Size (Etype (Z)));
+ M_Size : constant Nat := Nat'Max (X_Size, Nat'Max (Y_Size, Z_Size));
QR_Id : RE_Id;
QR_Siz : Nat;
@@ -923,17 +939,17 @@ package body Exp_Fixd is
QR_Typ := Standard_Integer_64;
QR_Id := RE_Null;
- elsif QR_Siz <= 128 and then System_Max_Integer_Size = 128 then
- QR_Typ := Standard_Integer_128;
- QR_Id := RE_Null;
-
- -- For more than Max_Integer_Size bits, we use the integer defined in
- -- Interfaces, so that it can be handled by the runtime routine.
+ -- For backward compatibility reasons, we use a 128-bit divide only
+ -- if one of the operands is already larger than 64 bits.
- elsif System_Max_Integer_Size < 128 then
+ elsif System_Max_Integer_Size < 128 or else M_Size <= 64 then
QR_Typ := RTE (RE_Integer_64);
QR_Id := RE_Scaled_Divide64;
+ elsif QR_Siz <= 128 then
+ QR_Typ := Standard_Integer_128;
+ QR_Id := RE_Null;
+
else
QR_Typ := RTE (RE_Integer_128);
QR_Id := RE_Scaled_Divide128;
@@ -948,9 +964,9 @@ package body Exp_Fixd is
Set_Etype (Qnn, QR_Typ);
Set_Etype (Rnn, QR_Typ);
- -- Case that we can compute the numerator in Max_Integer_Size bits
+ -- Case where we can compute the numerator in Max_Integer_Size bits
- if QR_Siz <= System_Max_Integer_Size then
+ if QR_Id = RE_Null then
Nnn := Make_Temporary (Loc, 'N');
Dnn := Make_Temporary (Loc, 'D');
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2020-11-27 9:18 [Ada] Do not use 128-bit division for 64-bit fixed-point types Pierre-Marie de Rodat
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