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[Ada] Refine conditions for calling Copy_Bitfield

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Avoid calling Copy_Bitfield if there are volatile or independent
components that might be read or written. The test is conservative.

2019-09-17  Bob Duff  <duff@adacore.com>

gcc/ada/

	* exp_ch5.adb (Expand_Assign_Array_Loop_Or_Bitfield): Add tests
	for potential volatile or independent components.
	* libgnat/s-bituti.adb (Copy_Small_Bitfield,
	Copy_Large_Bitfield): Move declarations to more appropriate
	place.

From-SVN: r275768
This commit is contained in:
Bob Duff 2019-09-17 07:59:11 +00:00 committed by Pierre-Marie de Rodat
parent 8ba9c127cd
commit 38b06e7a19
3 changed files with 51 additions and 28 deletions
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8
gcc/ada/ChangeLog
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@ -1,3 +1,11 @@
2019-09-17 Bob Duff <duff@adacore.com>
* exp_ch5.adb (Expand_Assign_Array_Loop_Or_Bitfield): Add tests
for potential volatile or independent components.
* libgnat/s-bituti.adb (Copy_Small_Bitfield,
Copy_Large_Bitfield): Move declarations to more appropriate
place.
2019-09-13 Maciej W. Rozycki <macro@wdc.com>
* make.adb (Scan_Make_Arg): Also accept `--sysroot=' for the

25
gcc/ada/exp_ch5.adb
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@ -1451,20 +1451,35 @@ package body Exp_Ch5 is
begin
-- Determine whether Copy_Bitfield is appropriate (will work, and will
-- be more efficient than component-by-component copy). Copy_Bitfield
-- doesn't work for reversed storage orders. It is efficient only for
-- slices of bit-packed arrays.
-- doesn't work for reversed storage orders. It is efficient for slices
-- of bit-packed arrays. Copy_Bitfield can read and write bits that are
-- not part of the objects being copied, so we don't want to use it if
-- there are volatile or independent components. If the Prefix of the
-- slice is a selected component (etc, see below), then it might be a
-- component of an object with some other volatile or independent
-- components, so we disable the optimization in that case as well.
-- We could complicate this code by actually looking for such volatile
-- and independent components.
-- Note that Expand_Assign_Array_Bitfield is disabled for now
-- Note that Expand_Assign_Array_Bitfield is disabled for now.
if False -- ???
if False and then -- ???
RTE_Available (RE_Copy_Bitfield)
and then Is_Bit_Packed_Array (L_Type)
and then Is_Bit_Packed_Array (R_Type)
and then RTE_Available (RE_Copy_Bitfield)
and then not Reverse_Storage_Order (L_Type)
and then not Reverse_Storage_Order (R_Type)
and then Ndim = 1
and then not Rev
and then Slices
and then not Has_Volatile_Component (L_Type)
and then not Has_Volatile_Component (R_Type)
and then not Has_Independent_Components (L_Type)
and then not Has_Independent_Components (R_Type)
and then not Nkind_In (Prefix (Name (N)),
N_Selected_Component,
N_Indexed_Component,
N_Slice)
then
return Expand_Assign_Array_Bitfield
(N, Larray, Rarray, L_Type, R_Type, Rev);

46
gcc/ada/libgnat/s-bituti.adb
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@ -71,6 +71,29 @@ package body System.Bitfield_Utils is
-- set to Src_Value. Src_Value must have high order bits (Size and
-- above) zero. The result is returned as the function result.
procedure Copy_Small_Bitfield
(Src_Address : Address;
Src_Offset : Bit_Offset;
Dest_Address : Address;
Dest_Offset : Bit_Offset;
Size : Small_Size);
-- Copy_Bitfield in the case where Size <= Val'Size.
-- The Address values must be aligned as for Val and Val_2.
-- This works for overlapping bit fields.
procedure Copy_Large_Bitfield
(Src_Address : Address;
Src_Offset : Bit_Offset;
Dest_Address : Address;
Dest_Offset : Bit_Offset;
Size : Bit_Size);
-- Copy_Bitfield in the case where Size > Val'Size.
-- The Address values must be aligned as for Val and Val_2.
-- This works for overlapping bit fields only if the source
-- bit address is greater than or equal to the destination
-- bit address, because it copies forward (from lower to higher
-- bit addresses).
function Get_Bitfield
(Src : Val_2; Src_Offset : Bit_Offset; Size : Small_Size)
return Val
@ -115,29 +138,6 @@ package body System.Bitfield_Utils is
return Result;
end Set_Bitfield;
procedure Copy_Small_Bitfield
(Src_Address : Address;
Src_Offset : Bit_Offset;
Dest_Address : Address;
Dest_Offset : Bit_Offset;
Size : Small_Size);
-- Copy_Bitfield in the case where Size <= Val'Size.
-- The Address values must be aligned as for Val and Val_2.
-- This works for overlapping bit fields.
procedure Copy_Large_Bitfield
(Src_Address : Address;
Src_Offset : Bit_Offset;
Dest_Address : Address;
Dest_Offset : Bit_Offset;
Size : Bit_Size);
-- Copy_Bitfield in the case where Size > Val'Size.
-- The Address values must be aligned as for Val and Val_2.
-- This works for overlapping bit fields only if the source
-- bit address is greater than or equal to the destination
-- bit address, because it copies forward (from lower to higher
-- bit addresses).
procedure Copy_Small_Bitfield
(Src_Address : Address;
Src_Offset : Bit_Offset;