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Re: Question about how to fix PR69052

From: Bernd Schmidt <bernds_cb1 at t-online dot de>
To: Jeff Law <law at redhat dot com>, "Bin.Cheng" <amker dot cheng at gmail dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
Date: Mon, 25 Jan 2016 21:05:43 +0100
Subject: Re: Question about how to fix PR69052
Authentication-results: sourceware.org; auth=none
References: <CAHFci280ObgaSxzCBiKKBfKONeYsXOue8i84hH=pDwynhC4PNQ at mail dot gmail dot com> <56A67CD9 dot 70405 at redhat dot com>

On 01/25/2016 08:51 PM, Jeff Law wrote:

No, the combiner works within a basic block only.  There was a group, I
believe in Moscow, that worked on a cross-block combiner.  It was
discussed at the Cauldron in California a few years back.  I don't know
if they did any further work on those ideas.

Is the issue here not knowing when the loop invariant can be forward
propagated back into the memory reference -- and for complex RTL like
you cited, you ultimately determine that no it can't be propagated and
thus increase its invariant cost?

Is this just a pass ordering problem? What happens if you doloop-invariant after combine?



Bernd

Follow-Ups:
- Re: Question about how to fix PR69052
  - From: Bin.Cheng

References:
- Question about how to fix PR69052
  - From: Bin.Cheng
- Re: Question about how to fix PR69052
  - From: Jeff Law

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