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Re: Modes on CONST_INTs
- To: Michael Meissner <meissner at cygnus dot com>
- Subject: Re: Modes on CONST_INTs
- From: Bernd Schmidt <bernds at redhat dot com>
- Date: Mon, 27 Nov 2000 15:04:50 +0000 (GMT)
- cc: gcc at gcc dot gnu dot org
On Mon, 27 Nov 2000, Michael Meissner wrote:
> Ummm, as desirable as the change may be, I suspect we probably want to delay
> doing this until after GCC 3.0 ships.
Oh, I'm not suggesting we immediately make the constants have modes. The
first steps should be purely adding infrastructure while still keeping
VOIDmode for constants. Then, once all the dubious code has been cleaned
up, we can make the switch. It may even be possible during a transition
phase to add a target macro that says whether a port has been converted
to use proper modes. Then we wouldn't have to update all the ports at
> Secondarily, I would prefer to see a more encompassing approach that handles
> multi-word integers, including the ability to create 128 bit integer constants
> on 32-bit machines.
How would you suggest to do this? By eliminating CONST_INT entirely and just
using CONST_DOUBLE for everything?
> Third, we still haven't solved the sign-extends/zero-extends problem. To
> really solve that problem, I think we either need a bit in the
> CONST_INT/CONST_whatever that says to apply zero extension or we need unsigned
> varients of all of the basic/vector integer types.
I don't see yet why this is necessary. Surely we have no such problem for
other rtx objects such as REG or MEM; why should constants be different? If
any piece of code needs a wider version of a given constant, doesn't it also
have to know whether it wants a sign extension or a zero extension?
Comparisons shouldn't be a problem either, since we distinguish between
unsigned and signed variants.
> > 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.
> Delete const0_rtx and friends so that the change is more apparent.
Eventually, yes, once everything has been converted.