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Re: [tree-ssa] Lazy updating of stmt operands
- From: Diego Novillo <dnovillo at redhat dot com>
- To: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Sun, 07 Dec 2003 11:55:55 -0500
- Subject: Re: [tree-ssa] Lazy updating of stmt operands
- Organization: Red Hat Canada
- References: <20031207161929.GA10638@atrey.karlin.mff.cuni.cz>
On Sun, 2003-12-07 at 11:19, Zdenek Dvorak wrote:
> what is the purpose of having lists of stmt operands updated on demand?
>
Performance. If the statement hasn't changed, no point re-scanning it.
> I thought that it is for performance reasons, but this seems not to be
> the case as all the statements are anyway scanned in the final dce pass,
> so they end up in updated forms and we cannot gain anything elsewhere.
>
The call to get_stmt_operands doesn't necessarily mean that the
statement will be re-scanned.
> Why I am interested in this is that it prevents us from having also
> def-use edges (immediate uses) provided explicitly, which would be
> convenient in two cases I have encountered recently.
>
tree-dfa.c:compute_immediate_uses()
Diego.