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Re: CSE optimization question
- From: Daniel Berlin <dan at dberlin dot org>
- To: law at redhat dot com
- Cc: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner), gcc at gcc dot gnu dot org
- Date: Thu, 10 Jan 2002 09:52:20 -0500
- Subject: Re: CSE optimization question
On Thursday, January 10, 2002, at 09:36 AM, law@redhat.com wrote:
>> I asked this before, but why isn't GCSE making that obsolete now? It
>> isn't,
>> but I don't understand *why* it isn't.
> There's a lot of code in cse that doesn't exist in gcse -- for example
> cse
> does a lot of simplifications that gcse knows nothing about.
>
> But more importantly gcse is based on common subexpression elimination
> while cse is actually a derivative of value numbering.
Right.
In fact, it does little CSE, if any, at all.
> Meaning they're
> based on completely different concepts for identifying expressions which
> are redundant. And finally, gcse doesn't handle redundancies which
> occur
> within a single basic block.
This could be fixed pretty easily by doing it during local availability
computation, no?
>
> jeff