[PATCH] Provide macro to override limiting field alignment

[Fred Forsman <forsman at apple dot com>]

This patch introduces a macro (LIMIT_FIELD_ALIGN) to limit the alignment 
of fields to maximum_field_alignment.  This macro does not change the 
behavior of the compiler unless the macro is defined to do something 
else.  The macro provides a hook to override the normal alignment 
behavior, needed on the PowerPC to handle vector data.  This macro 
functions in much the same way as the other macros allowing 
target-specific handling of alignment.

Fred Forsman
Apple Computer, Inc.


2001-12-10  Fred Forsman   <forsman@apple.com>

         Provide a macro for limiting the alignment of fields to
         allow overriding of this behavior (needed for PowerPC vector
         data alignment).
         * stor-layout.c: Define LIMIT_FIELD_ALIGN macro if not
         already defined.
         (layout_decl): Use LIMIT_FIELD_ALIGN macro.
         (place_field): Use LIMIT_FIELD_ALIGN macro (2 cases).

Index: stor-layout.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/stor-layout.c,v
retrieving revision 1.114
diff -c -3 -p -r1.114 stor-layout.c
*** stor-layout.c	2001/12/08 19:43:07	1.114
--- stor-layout.c	2001/12/10 23:16:38
*************** tree sizetype_tab[(int) TYPE_KIND_LAST];
*** 46,51 ****
--- 46,59 ----
      The value is measured in bits.  */
   unsigned int maximum_field_alignment;

+ /* Macro to limit the alignment of fields to maximum_field_alignment.
+    It also provides an opportunity to override this behavior in cases
+    that require something other than the usual maximum alignment.  */
+ #ifndef LIMIT_FIELD_ALIGN
+ #define LIMIT_FIELD_ALIGN(DESIRED_ALIGN)		\
+ 		MIN (DESIRED_ALIGN, (unsigned) maximum_field_alignment)
+ #endif
+
   /* If non-zero, the alignment of a bitstring or (power-)set value, in 
bits.
      May be overridden by front-ends.  */
   unsigned int set_alignment = 0;
*************** layout_decl (decl, known_align)
*** 388,394 ****
       {
         DECL_BIT_FIELD_TYPE (decl) = DECL_BIT_FIELD (decl) ? type : 0;
         if (maximum_field_alignment != 0)
! 	DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), maximum_field_alignment);
         else if (DECL_PACKED (decl))
   	{
   	  DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), BITS_PER_UNIT);
--- 396,402 ----
       {
         DECL_BIT_FIELD_TYPE (decl) = DECL_BIT_FIELD (decl) ? type : 0;
         if (maximum_field_alignment != 0)
! 	DECL_ALIGN (decl) = LIMIT_FIELD_ALIGN (DECL_ALIGN (decl));
         else if (DECL_PACKED (decl))
   	{
   	  DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), BITS_PER_UNIT);
*************** place_field (rli, field)
*** 800,806 ****
   	  unsigned int type_align = TYPE_ALIGN (type);

   	  if (maximum_field_alignment != 0)
! 	    type_align = MIN (type_align, maximum_field_alignment);
   	  else if (DECL_PACKED (field))
   	    type_align = MIN (type_align, BITS_PER_UNIT);

--- 808,814 ----
   	  unsigned int type_align = TYPE_ALIGN (type);

   	  if (maximum_field_alignment != 0)
! 	    type_align = LIMIT_FIELD_ALIGN (type_align);
   	  else if (DECL_PACKED (field))
   	    type_align = MIN (type_align, BITS_PER_UNIT);

*************** place_field (rli, field)
*** 915,921 ****
         HOST_WIDE_INT bit_offset = tree_low_cst (rli->bitpos, 0);

         if (maximum_field_alignment != 0)
! 	type_align = MIN (type_align, maximum_field_alignment);
         /* ??? This test is opposite the test in the containing if
   	 statement, so this code is unreachable currently.  */
         else if (DECL_PACKED (field))
--- 923,929 ----
         HOST_WIDE_INT bit_offset = tree_low_cst (rli->bitpos, 0);

         if (maximum_field_alignment != 0)
! 	type_align = LIMIT_FIELD_ALIGN (type_align);
         /* ??? This test is opposite the test in the containing if
   	 statement, so this code is unreachable currently.  */
         else if (DECL_PACKED (field))