Re: Modes on CONST_INTs

[Jeffrey A Law <law at redhat dot com>]

  In message <Pine.LNX.4.21.0011240956520.12759-100000@host117.cygnus>you write
:
  > It seems that every now and then, we run into bugs involving a lack of mode
  > information on CONST_INTs.  So far everyone I've asked has agreed that we
  > really should have a mode for constants, but no one ever bothered because
  > the change is going to be huge.
Yes.

  > Even if the change is going to be huge, I don't see how it can be any more
  > painful than the recurring problems we have because of the lack of mode
  > information.  So, I'm looking for viable ways to gradually transform the
  > compiler towards using modes on constants.
OK.  Personally I feel the change (as a whole) is too big for GCC 3.0, but if
there are safe stepping stones we can put in now we can go forward them them.


  > Here's what I have in mind so far:
  > 1. Create a new macro GENMINT (MODE, INTVAL).  This macro will at first
  >    ignore the MODE argument.
  >    Replace all uses of GEN_INT with GENMINT.  Once done, remove the old
  >    GEN_INT and rename GENMINT to GEN_INT.  (I'm open to suggestions for
  >    a better name than GENMINT, but it should have 7 characters to avoid
  >    reformatting madness).
Basically Ok.  However GEN_INT is (IMHO) a well-known interface provided
to front & backends.  We should either remove it, or keep it, but produce
an error.  I don't think we want to add another argument GEN_INT.

  > 2. In a similar way, replace uses of const0_rtx etc. with CONST0_RTX(MODE).
  >    We'll also need a few new macros, e.g. CONSTM1_RTX(MODE) etc.
Similarly.  It might even be able to happen independently of #1.  In fact,
I generally prefer to write  CONST0_RTX(MODE) over const0_rtx already :-)
Note that initially 

  > I haven't quite figured out yet what mode should be used for variable shift
  > counts.
word_mode, unless there is some notable benefit in using a smaller mode.

jeff