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Re: [tree-ssa] Lazy updating of stmt operands
- From: Chris Lattner <sabre at nondot dot org>
- To: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- Cc: Andrew MacLeod <amacleod at redhat dot com>, Jeff Law <law at redhat dot com>,Diego Novillo <dnovillo at redhat dot com>,gcc mailing list <gcc at gcc dot gnu dot org>
- Date: Mon, 15 Dec 2003 14:31:36 -0600 (CST)
- Subject: Re: [tree-ssa] Lazy updating of stmt operands
Zdenek Dvorak wrote:
> suppose a statement is changed. To update the immediate uses of this
> statement, you would need to go to the defining statement for each
> variable, find yourself in a (possibly very long) list of uses and
> make the update. This would be a disaster for the performance.
This is exactly what I was talking about here:
http://gcc.gnu.org/ml/gcc/2003-12/msg00691.html
Imagine if the value you are using is the constant "0". If you represent
use chains of the 0, there may be "several" instructions on the list. The
lists can get large. In LLVM, this is a constant time operation.
-Chris
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