-no-pthread option for mingw-w64

[martell]

Summary

When compiling mingw-w64 gcc provides us with a -no-pthreads option because it is linked in by default
If we want to build mingw-w64 with clang and not gcc we must not link to pthreads
clang currently fails at building mingw-w64 because it errors out for unknown argument.

The handling of the argument in the driver is superficial atm because we don't link to it by default

[yaron.keren]

The issue is that gcc accepts -no-pthread while clang errors on it. We may wish to accept -no-pthread even if it has no tunction just for gcc compatibility.

The driver patch does not make any sense, it will trigger only if -pthread -no-pthread are *both* provided.

What I don't understand, what do you mean by "gcc provides us with -no-pthread"? if oyu build using clang gcc is not used at all, how does it enters the picture? -no-pthread comes from a makefile, or??

[martell]

In D11087#202605, @yaron.keren wrote:

The issue is that gcc accepts -no-pthread while clang errors on it. We may wish to accept -no-pthread even if it has no tunction just for gcc compatibility.

Yes that would make sense to me also and this is my use case

In D11087#202605, @yaron.keren wrote:

The driver patch does not make any sense, it will trigger only if -pthread -no-pthread are *both* provided.

Yes the issue here is mingw.org doesn't have libpthread while mingw-w64 links to it by default
For mingw-w64 we would just have

if (!Args.hasArg(options::OPT_no_pthread))
  CmdArgs.push_back("-lpthread");

In D11087#202605, @yaron.keren wrote:

What I don't understand, what do you mean by "gcc provides us with -no-pthread"? if oyu build using clang gcc is not used at all, how does it enters the picture? -no-pthread comes from a makefile, or??

It comes from the autotools scripts from within mingw-w64's source code.
It is not an option they would remove from the scripts because mingw-w64 assumes libpthread is linked by default.

Is there a way for us to detect if clang is targetting mingw-w64 or mingw.org?
It seems like we are doing this in the constructor of the driver class.
Could we store this somehow to support both cases?

[yaron.keren]

I see, mingw-w64-v4.0.2\mingw-w64-libraries\winpthreads\Makefile.am indeed passes -no-pthread when building winpthreads since pthreads is not available at that time and it is linked by default. clang does not link by default but errors on -no-pthread. I'll commit this switch to avoid the error but we may ignore it otherwise.

[martell]

Updated the diff to reflect this

[martell]

For reference this is a mingw-w64 bootstrap issue.
It should have c11 threading and should not link to pthreads by default.
If I have time I will work on that from within the mingw-w64 project :)

[yaron.keren]

Committed revision 241929.

[martell]

Thanks yaron :)

include/clang/Driver/Options.td

 def pthreads : Flag<["-"], "pthreads">;
 def pthread : Flag<["-"], "pthread">, Flags<[CC1Option]>,
   HelpText<"Support POSIX threads in generated code">;
+def no_pthread : Flag<["-"], "no-pthread">, Flags<[CC1Option]>;
 def p : Flag<["-"], "p">;
 def pie : Flag<["-"], "pie">;
 def read__only__relocs : Separate<["-"], "read_only_relocs">;