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Allowing inlining of "rarely-mutated" top-level variables

From: Mark H Weaver
Subject: Allowing inlining of "rarely-mutated" top-level variables
Date: Wed, 21 Sep 2011 14:51:50 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux)

Hello all,

Peval's potential (and that of the optimizer in general) will be
significantly reduced if it cannot inline top-level variable references.
It seems to me that there's a way to enjoy the benefits of both
optimization and dynamism at the same time.

I propose that we allow code to declare that a given top-level variable
is "rarely-mutated".  Semantically, this would give Guile permission to
use a representation of the variable for which mutations are very
expensive, in the hope that references can be made much cheaper.

Rarely-mutated variables would be treated as constants by the optimizer.
However, associated with each rarely-mutated variable would be a list of
compiled code segments that have inlined its value.

Then when a rarely-mutated variable is set!, the associated list of
compiled code segments would be immediately invalidated.  Obviously,
this would require an implementation of on-stack replacement.

What do you think?


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