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

Sean Silva silvas at purdue.edu
Wed Jan 29 12:06:17 PST 2014

On Tue, Jan 28, 2014 at 12:45 PM, Nico Weber <thakis at chromium.org> wrote:

> I believe there was a thread about not forking the driver a while ago, but
> I'm unable to find it. As far as I remember, Chris Lattner wanted to get
> rid of it for aesthetic reasons and to save the milliseconds of overhead it
> adds (I think doing this has originally been the plan, see the "fork/exec"
> section on
> http://lists.cs.uiuc.edu/pipermail/cfe-dev/2009-December/007211.html). At
> the end, the decision was made to keep the subprocess for cc1, but I don't
> remember all the reasons. I think crash reporting was part of the
> discussion, but there was half a plan to keep that feature with in-process
> crash reporting somehow.
> Maybe someone still has a copy of that thread in their inbox? Keywords
> "lattner dgregor cc1 crash fork exec" or similar might find it.

The thread you linked to predates my LLVM involvement, but I remember
another thread (long time ago) that I was involved in where basically it
was asked "is this a measurable slowdown?" (my me or someone else, I
forget) and nobody could provide real numbers supporting that it was a
measurable slowdown (even on Windows). Can't see to find the thread in my
email though.

Do we have real performance numbers demonstrating a slowdown at this point?

-- Sean Silva

> On Tue, Jan 28, 2014 at 7:19 AM, Rafael EspĂ­ndola <
> rafael.espindola at gmail.com> wrote:
>> On 27 January 2014 17:27, Reid Kleckner <rnk at google.com> wrote:
>> > As an alternative, on Windows we could rig up some kind of SEH filter
>> to do
>> > crash recovery.  Then we could save the subprocess invocation and speed
>> > things up.
>> Breakpad is used by both chrome and firefox for this. If going this
>> path, please make sure the same technique is used for all systems.
>> Cheers,
>> Rafale
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