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Re: [PATCH 2/2] shrink-wrap: Rewrite try_shrink_wrapping

From: Bernd Schmidt <bschmidt at redhat dot com>
To: Segher Boessenkool <segher at kernel dot crashing dot org>
Cc: gcc-patches at gcc dot gnu dot org
Date: Fri, 11 Sep 2015 14:46:14 +0200
Subject: Re: [PATCH 2/2] shrink-wrap: Rewrite try_shrink_wrapping
Authentication-results: sourceware.org; auth=none
References: <5503d4c7cce8849f8a2901b540b388411b6b6a5a dot 1441893071 dot git dot segher at kernel dot crashing dot org> <c66f1521d7ec462efb6683f4b44beecaf7e3553f dot 1441893071 dot git dot segher at kernel dot crashing dot org> <55F29CAC dot 7030302 at redhat dot com> <20150911123622 dot GC24204 at gate dot crashing dot org>

On 09/11/2015 02:36 PM, Segher Boessenkool wrote:

I'm wondering how your new algorithm prevents the prologue from being
placed inside a loop. Can you have a situation where this picks a
predecessor that is reachable but not dominated by PRO?


It doesn't prevent it!

The prologue will not be _inside_ the loop: there is one prologue, and it
is executed exactly once for any block needing it.  But the code can copy
part of the first iteration of a loop, if there are early exits.  Example
(from the testsuite, pr39943.c, -Os I think):

I was wondering if that was the intention. This also ought to be spelledout in the comments.



Bernd

References:
- [PATCH 1/2] shrink-wrap: Header hygiene
  - From: Segher Boessenkool
- [PATCH 2/2] shrink-wrap: Rewrite try_shrink_wrapping
  - From: Segher Boessenkool
- Re: [PATCH 2/2] shrink-wrap: Rewrite try_shrink_wrapping
  - From: Bernd Schmidt
- Re: [PATCH 2/2] shrink-wrap: Rewrite try_shrink_wrapping
  - From: Segher Boessenkool

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