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Re: [patch] Make jump threading preserve loops
- From: Jeffrey Law <law at redhat dot com>
- To: Dorit Nuzman <DORIT at il dot ibm dot com>
- Cc: gcc-patches at gcc dot gnu dot org, Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- Date: Mon, 20 Nov 2006 13:01:47 -0500
- Subject: Re: [patch] Make jump threading preserve loops
- References: <OF2691608C.40713C19-ONC2257220.0043A848-C2257220.0045B8CE@il.ibm.com>
- Reply-to: law at redhat dot com
On Wed, 2006-11-08 at 14:41 +0200, Dorit Nuzman wrote:
> Two options to consider (beyond really calling vect_analyze_loop):
> - don't peel if -ftree-vectorize is on
> - maybe just check dependences in the loop, as a measure to evaluate
> vectorizability. it's an anlysis that is useful to have as a stand-alone
> anyhow (and mostly already is - compute_data_dependences_for_loop I guess).\
This is roughly what I was suggesting -- apply a set of simple tests
which can (cheaply) determine if a loop might be vectorizable -- erring
on the side of assuming the loop might be vectorizable.
I wouldn't be terribly surprised to find that there's a few tests we
can apply which would allow us to identify a significant portion of
the unvectorizable loops.
> this would still spoil the alignment, which is *very* unfortunate. People
> put a lot of attention to structuring their code such that the data would
> be aligned for vectorization (just two recent examples:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827#c56). I think we should
> strongly consider Jeff's comment above.