linux-kernel - Re: Compilers and RCU readers: Once more unto the breach!

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Date:	Wed, 20 May 2015 16:54:51 +0100
From:	Andrew Haley <aph@...hat.com>
To:	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"c++std-parallel@...u.org" <c++std-parallel@...u.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"gcc@....gnu.org" <gcc@....gnu.org>,
	p796231 <Peter.Sewell@...cam.ac.uk>,
	"mark.batty@...cam.ac.uk" <Mark.Batty@...cam.ac.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"michaelw@...ibm.com" <michaelw@...ibm.com>
Subject: Re: Compilers and RCU readers: Once more unto the breach!

On 05/20/2015 04:46 PM, Will Deacon wrote:
> I'm not sure... you'd require the compiler to perform static analysis of
> loops to determine the state of the machine when they exit (if they exit!)
> in order to show whether or not a dependency is carried to subsequent
> operations. If it can't prove otherwise, it would have to assume that a
> dependency *is* carried, and it's not clear to me how it would use this
> information to restrict any subsequent dependency removing optimisations.

It'd just convert consume to acquire.

Andrew.

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