Re: remove wrong code in immed_double_const

[Richard Sandiford <rdsandiford@googlemail.com>]

Mike Stump <mikestump@comcast.net> writes:
> This removes some wrong code.
>
> Ok?
>
> Index: gcc/emit-rtl.c
> ===================================================================
> --- gcc/emit-rtl.c      (revision 184563)
> +++ gcc/emit-rtl.c      (working copy)
> @@ -540,8 +540,6 @@ immed_double_const (HOST_WIDE_INT i0, HO
>  
>        if (GET_MODE_BITSIZE (mode) <= HOST_BITS_PER_WIDE_INT)
>         return gen_int_mode (i0, mode);
> -
> -      gcc_assert (GET_MODE_BITSIZE (mode) == 2 * HOST_BITS_PER_WIDE_INT);
>      }
>  
>    /* If this integer fits in one word, return a CONST_INT.  */

Is this because you have an integer mode between HOST_BITS_PER_WIDE_INT and
2 * HOST_BITS_PER_WIDE_INT?  (I.e. a partial one?)  If so, I can see an
argument for changing the "==" to "<=", although we'd need to think
carefully about what CONST_DOUBLE means in that case.  (Endianness, etc.)

Or is this because you have an integer mode wider than
2*OST_BITS_PER_WIDE_INT?  We currently only support constant integer
widths <= 2*HOST_BITS_PER_WIDE_INT, and the assert is correctly
triggering if we try to build a wider constant.  Obviously it'd be
nice if we supported arbitrary widths, e.g. by replacing CONST_INT and
CONST_DOUBLE with a single n-HOST_WIDE_INT rtx (and immed_double_const
with some kind of nary builder, etc.).  It won't be easy though.

Removing the assert seems like papering over the problem.

FWIW, here's another case where this came up:

    http://gcc.gnu.org/ml/gcc-patches/2011-03/msg01220.html

Richard