[cfe-dev] Why clang needs to fork into itself?

[Manuel Klimek]

On Tue, Jan 28, 2014 at 9:11 PM, Ted Kremenek <kremenek at apple.com> wrote:

> On Jan 28, 2014, at 12:08 PM, Manuel Klimek <klimek at google.com> wrote:
>
> On Tue, Jan 28, 2014 at 2:38 AM, Richard Smith <metafoo at gmail.com> wrote:
>
>> On Mon Jan 27 2014 at 4:51:40 PM, Yuri <yuri at rawbw.com> wrote:
>>
>>> On 01/27/2014 16:37, Jean-Daniel Dupas wrote:
>>> > If you want to debug/profile clang, you can invoke it directly with
>>> the -cc1 flag, and passing the right arguments.
>>> >
>>> > To get the full command line used to invoke the real compilation
>>> process, you can use the -### argument:
>>> >
>>> > clang -### -c -emit-llvm c.cpp
>>> >
>>> > For the record, in the early days, the clang driver was a separate
>>> binary that used to invoke the compiler (which was called ccc IIRC).
>>> > Some time ago, the driver and the compiler were merged into a single
>>> clang binary, but it continue to work the same way it used to do. That
>>> explains why it executes itself.
>>>
>>> I see.
>>> So I wrote up my proposal to make this opt-in:
>>> http://llvm.org/bugs/show_bug.cgi?id=18638
>>
>>
>> I don't think the reasons why we spawn another binary have really been
>> captured in this thread. The biggest reason is that the clang driver
>> accepts multiple files to compile:
>>
>>    clang foo.c bar.c baz.c -o thing
>>
>> ... and runs one compile process for each source file (and in this case,
>> one link process for the binary). Crash recovery is just a nice side-effect
>> of having a separate driver and frontend. The main benefit is that we get a
>> consistent execution model regardless of the number of files passed to the
>> driver.
>>
>
> But nowadays with modules we also have in-process compilation steps of
> dependent modules without going through the whole driver enchilada, so is
> this becoming an obsolete argument?
>
>
> Clang forking itself remains quite useful for getting test cases for
> crashers.  If the forked clang crashes the parent clang process tries to
> generate a preprocessed source to serve as a test case.  We have found this
> to be invaluable for users to file useful test cases.
>

Will that still work if the crash comes from a dependent module?
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