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Re: [PATCH] Remove unnecessary jump threading restriction

From: Jeff Law <law at redhat dot com>
To: Richard Biener <rguenther at suse dot de>, gcc-patches at gcc dot gnu dot org
Date: Fri, 5 Aug 2016 14:43:18 -0600
Subject: Re: [PATCH] Remove unnecessary jump threading restriction
Authentication-results: sourceware.org; auth=none
References: <alpine.LSU.2.11.1608050944270.26629@t29.fhfr.qr>

On 08/05/2016 01:45 AM, Richard Biener wrote:


There is no need to avoid threading to a loop header, the threading
code can cope with this just fine.  Noticed when working on PR72772.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2016-08-05  Richard Biener  <rguenther@suse.de>

	* tree-ssa-threadupdate.c (thread_block_1): Remove unnecessary
	restriction on threading to a loop header.

This restriction exists to help prevent threading through a loop headerinto the loop which can easily create an irreducible region.

In fact what you've done is revert the fix for 58343. Now there is ofcourse a test for 58343 in the regression suite.

It's entirely possible that 58343 is just latent now or other changes intree-ssa-threadupdate.c prevent the problems that we saw with 58343.


Jeff

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References:
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  - From: Richard Biener

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