rs6000.c warnings

[David Edelsohn <dje at watson dot ibm dot com>]

[I am explicitly cc'ing Zack and Kaveh because they have a lot of
experience with warnings and seem to have opinions about this subject :-]

	rs6000.c currently produces

warning: signed and unsigned type in conditional expression

because of the RS6000_ARG_SIZE macro:

#define RS6000_ARG_SIZE(MODE, TYPE)                                   \
((MODE) != BLKmode                                                    \
 ? (GET_MODE_SIZE (MODE) + (UNITS_PER_WORD - 1)) / UNITS_PER_WORD     \
 : ((unsigned HOST_WIDE_INT) int_size_in_bytes (TYPE)                 \
    + (UNITS_PER_WORD - 1)) / UNITS_PER_WORD)

	The warning occurs because UNITS_PER_WORD is an integer constant
assumed signed and int_size_in_bytes is not constant.  The code in
c-typeck.c to build a conditional expression skips the warning if the
expression is constant, but the function call defeats that exception.
This appears to be GCC being a little overly-aggressize with warnings.

	I can remove the warning by REMOVING the cast of int_size_in_bytes
to unsigned H_W_I.  This macro only is used to set or modify "int", so
making the expression signed isn't a problem.  I could change
UNITS_PER_WORD to constants with "u" appended (which also fixes the
warning), but that is not too appealing.

	I am not sure what promotion will occur.  Removing the cast makes
one part of the expression unsigned (GET_MODE_SIZE) and the other part
signed (int_size_in_bytes).  A warning that encourages me to make an
expression asymmeric seems like a bad warning.

	Does removing the cast seem like a reasonable solution?  Is there
a way for GCC to ignore the signedness of non-negative constant integers
combined with variable expressions?

Thanks, David