r207696 - PR19601: std::remove_if does not really remove the elements.

[Arnaud Allard de Grandmaison]

I have not been able to come up with a testcase which does better than what
test/Tooling/multi-jobs.cpp already does.

The current test status:
 1. no remove_if (and thus no erase) : multi-jobs fails
 2. remove_if : multi-jobs pass
 3. remove_if + erase : multi-jobs pass

Invoking clang-check with '-v' shows that in cases 2 & 3 the
-no-integrated-as has been dropped. I feel a bit like hunting a red herring
there : depending on the argument position, it gets dropped or not.
Jordan's hypothesis is probably right.

Cheers,
--
Arnaud





On Wed, Apr 30, 2014 at 11:30 PM, Jordan Rose <jordan_rose at apple.com> wrote:

> My hypothesis for how this was working: std::remove_if reorders elements
> using std::move, so we were getting lucky that -no-integrated-as wasn't the
> last argument and something else got moved on top of it. We'd have
> duplicates of the last few arguments (because they got moved earlier), but
> that wouldn't show -no-integrated-as.
>
> Jordan
>
>
> On Apr 30, 2014, at 14:09, Richard Smith <richard at metafoo.co.uk> wrote:
>
> This needs a test case. This code has already been committed, incorrectly,
> twice before this revision; the existing test case clearly doesn't actually
> cover it properly.
>
>
> On Wed, Apr 30, 2014 at 12:59 PM, Arnaud A. de Grandmaison <
> arnaud.adegm at gmail.com> wrote:
>
>> Author: aadg
>> Date: Wed Apr 30 14:59:22 2014
>> New Revision: 207696
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=207696&view=rev
>> Log:
>> PR19601: std::remove_if does not really remove the elements.
>>
>> It moves them at the end of the range instead, so an extra erase is
>> needed.
>>
>> It is strange that this code works without the erase. On the other hand,
>> removing the remove_if will make fail some tests.
>>
>> Modified:
>>     cfe/trunk/lib/Tooling/CompilationDatabase.cpp
>>
>> Modified: cfe/trunk/lib/Tooling/CompilationDatabase.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Tooling/CompilationDatabase.cpp?rev=207696&r1=207695&r2=207696&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Tooling/CompilationDatabase.cpp (original)
>> +++ cfe/trunk/lib/Tooling/CompilationDatabase.cpp Wed Apr 30 14:59:22 2014
>> @@ -238,8 +238,9 @@ static bool stripPositionalArgs(std::vec
>>
>>    // Remove -no-integrated-as; it's not used for syntax checking,
>>    // and it confuses targets which don't support this option.
>> -  std::remove_if(Args.begin(), Args.end(),
>> -                 MatchesAny(std::string("-no-integrated-as")));
>> +  Args.erase(std::remove_if(Args.begin(), Args.end(),
>> +
>>  MatchesAny(std::string("-no-integrated-as"))),
>> +             Args.end());
>>
>>    const std::unique_ptr<driver::Compilation> Compilation(
>>        NewDriver->BuildCompilation(Args));
>>
>>
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