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Re: [PATCH] Fix predcom ICE introduced by var clobber changes (PR tree-optimization/51246)
- From: Michael Matz <matz at suse dot de>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Thu, 24 Nov 2011 17:28:00 +0100 (CET)
- Subject: Re: [PATCH] Fix predcom ICE introduced by var clobber changes (PR tree-optimization/51246)
- References: <20111124150804.GI27242@tyan-ft48-01.lab.bos.redhat.com>
Hi,
On Thu, 24 Nov 2011, Jakub Jelinek wrote:
> When stmt is mem = {v} {CLOBBER};, then lhs is neither
> SSA_NAME, but it doesn't satisfy gimple_assign_copy_p either.
> With this patch it will set the new_tree also to the clobber,
> making it clear that the next iteration uses unitialized variable.
Hmm. My guts don't like clobbers on the RHS of normal ssa operations.
Usually our uninitialized values are the default defs of SSA names that
aren't PARM_DECLs. I don't like having two ways of expressing
uninitializedness.
As the default defs are already automatically handled by all our ssa
infrastructure (including warning and propagation machinery) I think it
would be best to generate such one instead of a clobber for the RHS.
Ciao,
Michael.