linux-kernel - Re: [PATCH] x86: always_inline wrapper for x86's test

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Message-ID: <20080413181642.GA8641@one.firstfloor.org>
Date:	Sun, 13 Apr 2008 20:16:42 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Alexander van Heukelum <heukelum@...tmail.fm>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: always_inline wrapper for x86's test_bit

> I have googled, but the only problem I found was concerning dead code 

It might come as a surprise, but google is still not omniscient.

> elimination, and in particular references to unavailable object from
> code that was expected to be discarded. The worst that can happen in 
> this case is that gcc might produce a strange construction where a
> runtime check will choose between the two alternative implementations of
> test_bit. Another is that it will select the 'wrong' implementation. 
> Both will result is some code-bloat, but at least the code should work
> properly.

Yes, but extreme code bloat can be fatal.

> I have not checked with 3.2. The oldest compiler I have available here
> is 3.3. That version compiles the functions as expected: I have found
> instances of either type in the objdump and I have not found strange
> constructions with both types there.

It would be good to check on 3.2 too to avoid potential nasty surprises.

> If you were thinking of another/bigger problem with gcc-3.2, could you 
> please give me a pointer?

Not sure what you mean here.

-Andi
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