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[Ada] Improve optimization of "=" on bit-packed arrays

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This patch fixes a performance regression, introduced by a previous bug
fix.  That fix had the unintended side effect of removing the
optimization in cases where the two operands are of two different
compiler-generated modular types.

gcc/ada/

	* exp_pakd.adb (Expand_Packed_Eq): Replace the check for *same*
	modular type, with a check for any modular type, and assert that
	the two types have the same modulus and so on.
	* exp_pakd.ads: Minor comment improvements.
This commit is contained in:
Bob Duff 2022-04-07 13:23:20 -04:00 committed by Pierre-Marie de Rodat
parent 5cc07f401a
commit 88f7b07de7
2 changed files with 17 additions and 8 deletions
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12
gcc/ada/exp_pakd.adb
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@ -1930,9 +1930,17 @@ package body Exp_Pakd is
-- modular case we guarantee that the unused bits are always zeroes.
-- We do have to compare the lengths because we could be comparing
-- two different subtypes of the same base type. We can only do this
-- if the PATs on both sides are the same.
-- if the PATs on both sides are modular (in which case they are
-- necessarily structurally the same -- same Modulus and so on);
-- otherwise, we have a case where the right operand is not of
-- compile time known size.
if Is_Modular_Integer_Type (PAT)
and then Is_Modular_Integer_Type (Etype (R))
then
pragma Assert (RM_Size (Etype (R)) = RM_Size (PAT));
pragma Assert (Modulus (Etype (R)) = Modulus (PAT));
if Is_Modular_Integer_Type (PAT) and then PAT = Etype (R) then
Rewrite (N,
Make_And_Then (Loc,
Left_Opnd =>

13
gcc/ada/exp_pakd.ads
View File

@ -41,7 +41,8 @@ package Exp_Pakd is
-- This packed array type has the name xxxPn, where xxx is the name
-- of the packed type, and n is the component size. The expanded
-- declaration declares a type that is one of the following:
-- declaration declares a type that is one of the following (sizes
-- below are in bytes):
-- For an unconstrained array with component size 1,2,4 or any other
-- odd component size. These are the cases in which we do not need
@ -49,10 +50,10 @@ package Exp_Pakd is
-- type xxxPn is new Packed_Bytes1;
-- For an unconstrained array with component size that is divisible
-- by 2, but not divisible by 4 (other than 2 itself). These are the
-- cases in which we can generate better code if the underlying array
-- is 2-byte aligned (see System.Pack_14 in file s-pack14 for example).
-- For an unconstrained array with component size greater than 2, that is
-- divisible by 2, but not divisible by 4. These are the cases in which
-- we can generate better code if the underlying array is 2-byte aligned
-- (see System.Pack_14 in file s-pack14 for example).
-- type xxxPn is new Packed_Bytes2;
@ -942,7 +943,7 @@ package Exp_Pakd is
-- N is an N_Op_Eq node where the operands are packed arrays whose
-- representation is an array-of-bytes type (the case where a modular
-- type is used for the representation does not require any special
-- handling, because in the modular case, unused bits are zeroes.
-- handling, because in the modular case, unused bits are zeroes).
procedure Expand_Packed_Not (N : Node_Id);
-- N is an N_Op_Not node where the operand is packed array of Boolean