Re: Patch: darwin specific

[Per Bothner <per at bothner dot com>]

Dale Johannesen wrote:

> This uses the TREE_TYPE and TREE_CHAIN field of some IDENTIFIER nodes,
> which
> are currently idle.  Per Bothner is working on IDENTIFIERs and knows about
> this new usage.
What I'm working on is replacing all or most of the language-specific
fields like C's IDENTIFIER_GLOBAL_VALUE and IDENTIFIER_LOCAL_VALUE by
"properties" stored a single shared field.  An enum (stolen from
cpp_hashnode) indicates which "property" is the value of the field.
If an identifier has more than one non-NULL property, then the field
instead points to an extension tree_vec.

The idea is that most identifiers have no language-specific properties,
and for the rest most of them only have a single property.  So we can
save a lot of space in each identifier.

A refinement of this idea is to use the normally unused TREE_TYPE or
TREE_CHAIN fields of the identifier, saving more space.  This of
course would conflict with Dale's patch.  One possible solution to
that is allow "target-specific properties"; Dale's patch could be
fairly easily modified to work that way.  Mainly it's a matter of
modifying macros like DARWIN_ID_TO_NON_LAZY_PTR, though we'd also
need to add lvalue versions, like SET_DARWIN_ID_TO_NON_LAZY_PTR.

I did a trial implemntation (without the target properties), but
I decided (from a trial run) that for C++ it probably makes more
sense to use a separate field for IDENTIFIER_NAMESPACE_BINDINGS.
This is free if we use TREE_CHAIN (say), while using (say)
TREE_TYPE for the selected property value.

This is taking a little longer than expected to get working, partly
due to multi-tasking.  Not really knowing much about the C++
front-end isn't helping, of course.
--
	--Per Bothner
per@bothner.com   http://www.bothner.com/per/