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Re: [PATCH][4/n] Remove GENERIC stmt combining from SCCVN

From: Jeff Law <law at redhat dot com>
To: Richard Biener <rguenther at suse dot de>
Cc: gcc-patches at gcc dot gnu dot org
Date: Mon, 13 Jul 2015 15:41:00 -0600
Subject: Re: [PATCH][4/n] Remove GENERIC stmt combining from SCCVN
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On 07/13/2015 01:47 AM, Richard Biener wrote:


The path duplication to expose redundancies is one of the things I'd like to
get out of a Bodik-esque scheme.  One of the things Bodik's work does is
identify the minimal set of blocks that need to be copied to expose each path
specific redundancy that it finds.


I see - so this could be then also used to compute a better idea of
a cost to duplicate such a path then?  That is, you don't commit
to creating all of those paths.

Correct.

The identification step with Bodik is a backwards substitution with aform of GVN to capture a secondary effect. Once the redundancies areidentified, you run a totally separate analysis to identify the minimalregion of blocks that need to be copied to expose the redundancy. Thenyou can look at the size of those regions vs the redundancy and make adecision about the cost/benefit.

So are you fine with the idea (or even implementation) of the patch
to go forward with moving fold_{widening,sign_change}_comparison to
match.pd?

Yes -- I'm pretty sure we can fix the immediate issue of themissed-optimization in the threader without major surgery.


jeff

References:
- Re: [PATCH][4/n] Remove GENERIC stmt combining from SCCVN
  - From: Jeff Law
- Re: [PATCH][4/n] Remove GENERIC stmt combining from SCCVN
  - From: Richard Biener

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