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Re: CSE optimization question
- From: law at redhat dot com
- To: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Cc: gcc at gcc dot gnu dot org
- Date: Thu, 10 Jan 2002 07:36:36 -0700
- Subject: Re: CSE optimization question
- Reply-to: law at redhat dot com
> 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. 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.
jeff