[Ada] Improve efficiency of small slice assignments of packed arrays

gcc/ada/

	* rtsfind.ads, libgnat/s-bitfie.ads, libgnat/s-bituti.adb,
	libgnat/s-bituti.ads (Fast_Copy_Bitfield): New run-time library
	function to copy bit fields faster than Copy_Bitfield. Cannot be
	called with zero-size bit fields.  Remove obsolete ??? comments
	from s-bituti.adb; we already do "avoid calling this if
	Forwards_OK is False".
	* exp_ch5.adb (Expand_Assign_Array_Loop_Or_Bitfield,
	Expand_Assign_Array_Bitfield_Fast): Generate calls to
	Fast_Copy_Bitfield when appropriate.
	* sem_util.adb, sem_util.ads (Get_Index_Bounds): Two new
	functions for getting the index bounds. These are more
	convenient than the procedure of the same name, because they can
	be used to initialize constants.

1 files changed, 15 insertions, 1 deletions

diff --git a/gcc/ada/libgnat/s-bituti.ads b/gcc/ada/libgnat/s-bituti.ads
index c9c4b91..8afee24 100644
--- a/gcc/ada/libgnat/s-bituti.ads
+++ b/gcc/ada/libgnat/s-bituti.ads
@@ -54,7 +54,7 @@ package System.Bitfield_Utils is
    --  generic formal, or on a type derived from a generic formal, so they have
    --  to be passed in.
    --
-   --  Endian indicates whether we're on little-endian or big-endian machine.
+   --  Endian indicates whether we're on a little- or big-endian machine.
 
    pragma Elaborate_Body;
 
@@ -127,6 +127,20 @@ package System.Bitfield_Utils is
       --        D (D_First)'Address, D (D_First)'Bit,
       --        Size);
 
+      function Fast_Copy_Bitfield
+        (Src         : Val_2;
+         Src_Offset  : Bit_Offset;
+         Dest        : Val_2;
+         Dest_Offset : Bit_Offset;
+         Size        : Small_Size)
+        return Val_2 with Inline;
+      --  Faster version of Copy_Bitfield, with a different calling convention.
+      --  In particular, we pass by copy rather than passing Addresses. The bit
+      --  field must fit in Val_Bits. Src and Dest must be properly aligned.
+      --  The result is supposed to be assigned back into Dest, as in:
+      --
+      --     Dest := Fast_Copy_Bitfield (Src, ..., Dest, ..., ...);
+
    end G;
 
 end System.Bitfield_Utils;