Re: Why I've Dropped In

MitchAlsup1 [2025-06-17 21:18:29] wrote:

On Tue, 17 Jun 2025 20:43:00 +0000, Stefan Monnier wrote:

What do you mean by "a few instructions later"?  The above was stated in
the context of a register allocator based on something like Chaitin's
algorithm, which does not proceed "instruction by instruction" but
instead takes a whole function (or basic bloc), builds an interference
graph from it, then chooses registers for the vars looking only at that
interference graph.

>
I am regurgitating conversations I have had with compile people over
the last 40 years. Noting I have seen in ISA design has moderated
these problems--but I, personally, have not been inside a compiler
for 41 years, either (1983). So, find a compiler writer to set this
record straight.  I continue to be told: it is enough harder that you
should design ISA so you don't need pairing or sharing, ever.

Ah, well, pairing is a different problem than the "incomplete register
specifiers" I'm talking about.  Indeed, it can be much more difficult to
adapt a Chaitin-style allocator to handle pairing because it can't be
expressed simply in the interference graph.


        Stefan