[LLVMdev] Behaviour of outs()?

[mats petersson]

I too tried replicating this, by running gdb on a unchanged [but quite
old] clang (-cc1 and stuff), with a breakpoint on `outs`, and it is
never called called.

So, I will have to investigate if something in our code is calling
llvm::outs(), without actually writing anything.

(By the way, at some point in the past, someone [1] had altered this
code to have shouldClose to false, I changed it back to true as that
is how upstream is, and then found out "the hard way" that this is not
a good change - it passed all sorts of local testing and regression
tests, only some time later someone discovered that some benchmarks
were no longer producing output)

[1] the history is murky due to changes in our process&version control
system, so can't say who, and it's quite possibly someone that is no
longer working here anyway, so can't really ask "why is it this way".

--
Mats

On 23 January 2015 at 19:12, Duncan P. N. Exon Smith
<dexonsmith at apple.com> wrote:
> Both of those SGTM.
>
>> On 2015-Jan-23, at 10:32, Reid Kleckner <rnk at google.com> wrote:
>>
>> We've had this argument before. IMO LLVM should not be in the business of closing stdout, and no code in lib/ should print to stdout because users may expect output there (-o -).
>>
>> On Fri, Jan 23, 2015 at 10:20 AM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
>>
>> > On 2015-Jan-23, at 09:52, mats petersson <mats at planetcatfish.com> wrote:
>> >
>> > I was just fixing a bug that was caused by `stdout` being closed
>> > before the runtime has done `fflush(stdout)` [or however this is
>> > implemented in the runtime].
>> >
>> > The cause of this seems to be that `outs()` returns a static object
>> > created from `raw_fd_stream(STDOUT_FILENO, true)` - the `true` being
>> > the `shouldClose` parameter.
>> >
>> > Surely LLVM is not supposed to close `stdout` as part of its operations?
>>
>> Looks like this was added in r111643:
>>
>> commit 5d56d9df928c48571980efe8d4205de8ab557b7c
>> Author: Dan Gohman <gohman at apple.com>
>> Date:   Fri Aug 20 16:44:56 2010 +0000
>>
>>     Make outs() close its file when its stream is destructed, so that
>>     pending output errors are detected.
>>
>>
>>     git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111643 91177308-0d34-0410-b5e6-96231b3b80d8
>>
>> Certainly looks intentional.  Comment in the code is:
>>
>>     // Delete the file descriptor when the program exits, forcing error
>>     // detection. If you don't want this behavior, don't use outs().
>>
>> I don't really have an opinion on whether this is a good idea, but it
>> does suggest that any use of `outs()` in `lib/` is a bug.
>>
>> $ git grep -l 'outs()' -- lib/
>> lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp
>> lib/IR/GCOV.cpp
>> lib/Support/CommandLine.cpp
>> lib/Support/FormattedStream.cpp
>> lib/Support/TargetRegistry.cpp
>> lib/Support/raw_ostream.cpp
>> lib/Target/CppBackend/CPPBackend.cpp
>>
>> All of these cases seem to be for outputting help text of some sort.  But
>> probably they should be passed a reference to a `raw_ostream`, so that the
>> caller gets to choose whether or not to use `outs()`.
>>
>> Were you hitting one of these?
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>