Re: Setting precision for a PSImode type

[Bernd Schmidt <bernds at codesourcery dot com>]

On 04/11/2012 07:31 PM, Peter Bigot wrote:
> The biggest one is that widening from 20-bit to 32-bit is an extremely
> expensive operation: it was a 16-bit ISA, but some newer MCUs support
> an extension with 20 bits in each register and a set of new
> instructions that must be used to preserve the upper 4 bits.  Getting
> bits 19..16 of a 20-bit register down into the low bits of a 16 bit
> register requires a five-position rotate-through-carry.  The 20-bit
> enhancement to the ISA was really intended only to support a larger
> address space; to simplify validation of the machine description I've
> chosen to allow it to be used for any integer operation, but I have no
> reason to think that'll be common.

Ok. So these are pointer modes, essentially? For the target I'm working
on, I'm using the following patch, see if that helps you any. It seems
to apply to trunk, so I might as well ask for an OK if it bootstraps and
tests ok (but it has little use while these ports remain out-of-tree).


Bernd

Attachment: modeptr.diff
Description: Text document