On Thursday 06 January 2011 09:01:09 Erik Cederstrand wrote: > Den 05/01/2011 kl. 20.36 skrev Jilles Tjoelker: >> On Wed, Jan 05, 2011 at 05:55:45PM +0100, Ulrich Spörlein wrote: >>> On Wed, 05.01.2011 at 09:34:49 -0500, John Baldwin wrote: >>>> These are all marked as __dead2, so the compiler should "know" that these >>>> do >>>> not return. >>> >>> And clang did the right thing here in the past. Beware that it does no >>> inter-procedural analysis yet, so it will usually miss that usage() >>> calls exit unconditionally. >>> >>> *But*, it should grok that for err(3) and exit(3). Now there are some >>> possible remedies: >>> >>> - get IPA to work with clang, or at least file a bug >>> - mark functions as __dead2 (please don't do that) >> >> Why not? > > Because the analyzer is supposed to find bugs. Only the function that > really doesn't return should be marked as such. If we begin spewing > __dead2's everywhere, it's bound to silence a valid bug somewhere > down the line when e.g. a conditional in a print_help() function is > changed subtly so it doesn't always reach exit().
On the other hand you can't really expect the compiler/analyser to know what a procedure in another file does, so in that case you need __dead2 anyway. For procedures in the same file it would be nice if the compiler automatically optimised non-returning calls, but I'm not sure the analyser should do that. If the code relies on the fact that a procedure doesn't return, which is the case here, it's a good thing to declare it as such exactly to prevent bugs from creeping in. You can't add a return statement to a non-returning procedure without the compiler complaining about it and I'm sure the analyser would complain about it as well. So you won't be hiding other bugs by adding __dead2 here and there.
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