Re: FDO patch -- make ic related vars TLS if target allows

[David Edelsohn <dje dot gcc at gmail dot com>]

Hi, David

The front-end drivers use -pthread and that often adds -lpthread. But
-pthread is not passed to cc1, etc.

I am not certain if there is a way for the compiler to ascertain that
it is being invoked to compile a file intended for a multi-threaded
application. It knows bout OpenMP and __thread, but that does not
encompass all pthreads applications.

Thanks, David

On Fri, Dec 28, 2012 at 2:08 PM, Xinliang David Li <davidxl@google.com> wrote:
> Is there a way to tell if the program is going to be multi-threaded?
> If not, it might be useful to introduce a compiler option such as -fmt
> which also enables -lpthread.  Using tricks like weakrefs can
> introduce unnecessary runtime overhead.
>
> David
>
> On Fri, Dec 28, 2012 at 8:26 AM, David Edelsohn <dje.gcc@gmail.com> wrote:
>> David,
>>
>> Support for native TLS on AIX exposed a problem with this patch.  A
>> similar problem exists on Solaris 9.
>>
>> Some helper functions for TLS on AIX and Solaris 9 only are provided
>> by libpthread. Promoting ic related variables to TLS breaks profiling
>> of non-pthread appications.  I completely agree with reducing race
>> conditions and improving support for profiling of pthread
>> applications, but why should this change be enabled for applications
>> not built and run as multi-threaded? This feature should test more
>> than the existence of target TLS support.
>>
>> Thanks, David