Messages in this thread | | | From | "Alexander van Heukelum" <> | Subject | Re: [PATCH] x86: always_inline wrapper for x86's test_bit | Date | Mon, 14 Apr 2008 14:24:05 +0200 |
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On Sun, 13 Apr 2008 20:16:42 +0200, "Andi Kleen" <andi@firstfloor.org> said: > > 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.
Hi,
It's just not always easy to think of the right question to ask the oracle ;).
> > 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.
Checked with a stock 3.2.3 form gcc.gnu.org (compiled using debian's gcc-2.95). It gets it right: places that should get the C version get the C version and places that should get the inline-assembly version get the inline-assembly version. No funny things at all.
B.T.W., debian and ubuntu don't provide gcc-3.2 packages. Is there a good reason why gcc-3.2.3 (5 years old in a week) should still be supported?
> > 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.
I just thought you might have been thinking of a specific problem. A bug-report or something like that would have been convenient to have. Looking for a problem is easier than looking for no problems ;).
Greetings, Alexander
> -Andi -- Alexander van Heukelum heukelum@fastmail.fm
-- http://www.fastmail.fm - Does exactly what it says on the tin
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