linux-kernel - Re: [RFC][PATCH 0/5] arch: atomic rework

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Message-ID: <Pine.LNX.4.64.1402212206040.16563@digraph.polyomino.org.uk>
Date:	Fri, 21 Feb 2014 22:10:54 +0000
From:	"Joseph S. Myers" <joseph@...esourcery.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	Michael Matz <matz@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Torvald Riegel <triegel@...hat.com>,
	Will Deacon <will.deacon@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
	David Howells <dhowells@...hat.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"gcc@....gnu.org" <gcc@....gnu.org>
Subject: Re: [RFC][PATCH 0/5] arch: atomic rework

On Fri, 21 Feb 2014, Paul E. McKenney wrote:

> This needs to be as follows:
> 
> [[carries_dependency]] int getzero(int i [[carries_dependency]])
> {
> 	return i - i;
> }
> 
> Otherwise dependencies won't get carried through it.

C11 doesn't have attributes at all (and no specification regarding calls 
and dependencies that I can see).  And the way I read the C++11 
specification of carries_dependency is that specifying carries_dependency 
is purely about increasing optimization of the caller: that if it isn't 
specified, then the caller doesn't know what dependencies might be 
carried.  "Note: The carries_dependency attribute does not change the 
meaning of the program, but may result in generation of more efficient 
code. - end note".

-- 
Joseph S. Myers
joseph@...esourcery.com
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