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Re: bounded pointers in RTL


On Wed, Oct 13, 1999 at 01:49:58PM -1000, Greg McGary wrote:
> My original implementation of bounded pointers in gcc-2.7.2
> instituted a new set of machine modes like so:
> 
> /* Bounded pointers are aggregates of three pointers: value, base & extent */
> DEF_MACHMODE (BQImode, "BQI", MODE_BOUNDED_PTR, 1, 1, BHImode)
> DEF_MACHMODE (BHImode, "BHI", MODE_BOUNDED_PTR, 2, 2, BSImode)
> DEF_MACHMODE (BSImode, "BSI", MODE_BOUNDED_PTR, 12, 4, BDImode)
> DEF_MACHMODE (BDImode, "BDI", MODE_BOUNDED_PTR, 24, 8, VOIDmode)

I wonder if we can make do with only one such mode "BPmode".  I've
wanted to make Pmode it's own entity...

> Without going into too much detail yet, I'm seeking some "spiritual
> advice" on this subject.  Are bounded-pointer modes acceptable, or is
> there a greater salvation in going "modeless" for which I should
> accept the pain and suffering to adapt the RTL layer?

I have no advice here.  I'd go with the one that turns out to be
less gross in implementation.

> In the past there has been some
> discussion about the desirability of treating structs/classes as
> collections if values independently assignable to registers, but
> nothing about the implementation details.  Has anyone thought much
> about this?

Not past "we should do this sometime".



r~


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