PATCH: Allow BITS_PER_UNIT != 8

[Lars Brinkhoff]

The function get_mode_alignment() in stor-layout.c doesn't work if
BITS_PER_UNIT isn't 2^n.

2001-01-13  lars brinkhoff  <lars@brinkhoff.se>

        * stor-layout.c (get_mode_alignment): Remove the restriction
        that BITS_PER_UNIT must be a power of 2.

Index: stor-layout.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/stor-layout.c,v
retrieving revision 1.92
diff -u -r1.92 stor-layout.c
--- stor-layout.c       2000/12/17 17:22:41     1.92
+++ stor-layout.c       2001/01/15 13:08:48
@@ -1795,10 +1795,11 @@
 get_mode_alignment (mode)
      enum machine_mode mode;
 {
-  unsigned int alignment = GET_MODE_UNIT_SIZE (mode) * BITS_PER_UNIT;
+  unsigned int alignment = GET_MODE_UNIT_SIZE (mode);

   /* Extract the LSB of the size.  */
   alignment = alignment & -alignment;
+  alignment *= BITS_PER_UNIT;

   alignment = MIN (BIGGEST_ALIGNMENT, MAX (1, alignment));
   return alignment;



lars@brinkhoff.se writes:

> I'm writing a new processor backend.  When porting the backend from
> GCC 2.95.2 to the current CVS tree I stumbled accross this code, which
> does not work on processors which does not have 2^n word length.
> 
>    /* Return the alignment of MODE. This will be bounded by 1 and
>       BIGGEST_ALIGNMENT.  */
>    
>    unsigned int
>    get_mode_alignment (mode)
>         enum machine_mode mode;
>    {
>      unsigned int alignment = GET_MODE_UNIT_SIZE (mode) * BITS_PER_UNIT;
>    
>      /* Extract the LSB of the size.  */
>      alignment = alignment & -alignment;
>    
>      alignment = MIN (BIGGEST_ALIGNMENT, MAX (1, alignment));
>      return alignment;
>    }
> 
> Here's the corresponding ChangeLog entry:
> 
>    2000-02-24  Nathan Sidwell  <nathan@codesourcery.com>
>    
>            * machmode.h (get_mode_alignment): Declare.
>            (GET_MODE_ALIGNMENT): Call it.
>            * stor-layout.c (get_mode_alignment): New function. Make
>            sure alignment is always power of 2.
> 
> A tentative patch would thus be:
> 
> 2001-01-13  lars brinkhoff  <lars@brinkhoff.se>
> 
>         * stor-layout.c (get_mode_alignment): Remove the restriction
>         that alignment is always a power of 2.
> 
> diff -u -r1.92 stor-layout.c
> --- stor-layout.c       2000/12/17 17:22:41     1.92
> +++ stor-layout.c       2001/01/13 09:24:50
> @@ -1797,9 +1797,6 @@
>  {
>    unsigned int alignment = GET_MODE_UNIT_SIZE (mode) * BITS_PER_UNIT;
> 
> -  /* Extract the LSB of the size.  */
> -  alignment = alignment & -alignment;
> -
>    alignment = MIN (BIGGEST_ALIGNMENT, MAX (1, alignment));
>    return alignment;
>  }
> 

-- 
http://lars.nocrew.org/