[PATCH] support static nested constructors in bitfields (1/2)

[Olivier Hainque <hainque at adacore dot com>]

Hello,

This is a first patch out of two to implement support for output of
static nested constructors within bitfields, pretty common and easy to
get in Ada, for instance:

  <<
  type u1 is mod 2**1;
  type u8 is mod 2**8;

  type HI_Record is record
    A, B : U8;
  end record;
  pragma Suppress_Initialization (HI_Record);

  type Blob is record
     Bit : U1;
     Agg : HI_Record;
  end record;
  pragma Suppress_Initialization (Blob);

  for Blob use record
     Bit at 0 range  0 .. 0;
     Agg at 0 range  1 .. 16; -- bits 1 to 16 from start byte 0
  end record;

  K0 : Blob := (Bit => 0, Agg => (A => 3, B => 7));
  >>

The goal is to let such constructs generate a static initializer
instead of hairy run-time elaboration code with shifts, masks and so
on.

The bulk of the overall support is in output_constructor.

As this is a complex function already, this first patch is a
suggestion to split three helpers out of it, one for each case
of processed element kind in the current code:

   << if (index && TREE_CODE (index) == RANGE_EXPR)
        [...]

      else if (field == 0 || !DECL_BIT_FIELD (field))
	[... An element that is not a bit-field ...]

      else if (val != 0 && TREE_CODE (val) != INTEGER_CST)
	error ("invalid initial value for member %qs",

      else
        [... INTEGER_CST bitfield ...]
   >>

The split is performed by introducing a simple datastructure to
represent the local state and use an instance of it to communicate
with the helpers.

Bootstrapped and regression tested on x86_64-suse-linux.

We are also using this internally with a GCC 4.3 base on a number of
other targets.

Thanks in advance,

Olivier

	2008-07-23  Olivier Hainque  <hainque@adacore.com>

	* varasm.c (oc_local_state): New structure, output_constructor
	local state to support communication with helpers.
	(output_constructor_array_range): New output_constructor helper,
	extracted code for an array range element.
	(output_constructor_regular_field): New output_constructor helper,
	extracted code for an element that is not a bitfield.
	(output_constructor_bitfield): New output_constructor helper,
	extracted code for a bitfield element.
	(output_constructor): Rework to use helpers.

Attachment: oc-split.dif
Description: Text document