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Re: Abstracting pointer arithmetic
- To: lars dot spam at nocrew dot org
- Subject: Re: Abstracting pointer arithmetic
- From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Date: Mon, 29 Jan 01 08:12:01 EST
- Cc: gcc at gcc dot gnu dot org
I'm writing a back end for a word-adressed machine. For this machine,
pointer arithmetic doesn't quite work like integer arithmetic.
Pointers to sub-word objects have a word address in the low bits, and
a byte selector in the top bits, and are incremented using a special
instruction. Subtracting or comparing these pointers takes several
instructions. Pointers to words are incremented by adding 1*<number
of words>, not 4*<number of words>, but otherwise behave as integers.
It seems to be that the back end would have to handle or provide
information about a few pointer operations.
For *those* machines you can define Pmode as a different class. I thought
you were proposing doing it for *all* machines in order to support those.