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Re: [tree-ssa] CCP and non-destructive folding problems
- From: Diego Novillo <dnovillo at redhat dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: 25 Feb 2003 13:22:33 -0500
- Subject: Re: [tree-ssa] CCP and non-destructive folding problems
- References: <200302251818.h1PIIM8p020602@localhost.redhat.com>
On Tue, 2003-02-25 at 13:18, law at redhat dot com wrote:
> We must be talking past each other.
>
We? Talking past each other? ;)
Yes, now we are on the same page. It's fine for evaluate_stmt() to
return VARYING when it can't fold for whatever reason. If it couldn't
fold because of a limitation in the non-destructive folder then (a) it's
just a mis-optimization bug, and (b) we will likely fail in the final
replace and fold stage.
At that point we can decide whether to fix the non-destructive folder or
live with the mis-optimization.
> Now in the case where all the operands are constants, but we failed to
> fold the expression we have a "soft" failure if we return VARYING. ie,
> we fail to optimize the code as much as we should. Investigating to see
> how many of these are still lurking would be a good thing to do.
>
Agreed.
Diego.