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Re: g++ and aliasing bools
- From: dewar at gnat dot com (Robert Dewar)
- To: dan at dberlin dot org, dewar at gnat dot com
- Cc: gcc at gcc dot gnu dot org, kenner at vlsi1 dot ultra dot nyu dot edu
- Date: Fri, 25 Jan 2002 11:05:37 -0500 (EST)
- Subject: Re: g++ and aliasing bools
<<The language semantics don't necessarily give you enough to be able to
place all types in the right sets. If it doesn't, you are back to
undecidability.
>>
Of course it is undecidable in the dynamic sense, but there we are not
interested in "the right sets", we are interested in sets that we can
prove are disjoint. It is quite "right" to put everything in the same
set, just not very efficient. We are NOT looking for an optimal solution,
here, that's obvious to anyone that that's unattainable.
What we are looking for is improved, verifiable, principles for splitting
the sets more finely.
Sometimes I really think they should not teach anyone about undecidability.
It always ends up with people looking at a perfectly simple problem like
this one (simple conceptually, not simple to get good solutions to), and
worrying about undecidability when it is a complete red herring.
If you propose that two items are not aliased, and it is undecidable whether
they are aliased, that's fine, it just means they go in the same alias set,
no big deal!