[libcxx] Disable tautological-type-limit-compare warning

[bcain]

Summary

Clang change to "cripple" the warning (rC321691) was not effective for libcxx because we opt-in to Wextra

But since the warning is partitioned now, we could opt-out of this specific one?

[lebedev.ri]

Note that it won't help for the cases where libc++ is used, and -Wextra -Wsystem-headers is specified.

[bcain]

In D41727#967371, @lebedev.ri wrote:

Note that it won't help for the cases where libc++ is used, and -Wextra -Wsystem-headers is specified.

I think that's acceptable and I think we should have known/expected that as of the change to clang.

The only real way to mitigate that is with a local pragma to disable the warning for those spots, correct? And I believe that had been proposed and rejected before.

[lebedev.ri]

libcxx/utils/libcxx/test/config.py

904

Why not self.cxx.addWarningFlagIfSupported('-Wno-tautological-type-limit-compare'), like seen on the next lines ?

[EricWF]

LGTM with the change mentioned by @lebedev.ri .

[bcain]

In D41727#979404, @EricWF wrote:

LGTM with the change mentioned by @lebedev.ri .

I agree that the change suggested is a good one but from the cfe-dev discussion this change may be obsolete. It sounds like the plan is to remove the warning from Wextra.

[EricWF]

@bcain Can we land it and then revert it once Clang decides what it's up to? That way we can get the 32bit builder green?

[hans]

In D41727#979506, @EricWF wrote:

@bcain Can we land it and then revert it once Clang decides what it's up to? That way we can get the 32bit builder green?

+Nico who's I believe working on moving the bad flag out of -Wextra.

[bcain]

Changed per review

[bcain]

I think this is now obsolete due to clang changing the warning.

libcxx/utils/libcxx/test/config.py

def configure_warnings(self):
         enable_warnings = self.get_lit_bool('enable_warnings',
                                             default_enable_warnings)
         self.cxx.useWarnings(enable_warnings)
         self.cxx.warning_flags += [
             '-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER',
             '-Wall', '-Wextra', '-Werror'
         ]
         if self.cxx.hasWarningFlag('-Wuser-defined-warnings'):
             self.cxx.warning_flags += ['-Wuser-defined-warnings']
             self.config.available_features.add('diagnose-if-support')
+        self.cxx.addWarningFlagIfSupported('-Wno-tautological-type-limit-compare')
         self.cxx.addWarningFlagIfSupported('-Wshadow')
         self.cxx.addWarningFlagIfSupported('-Wno-unused-command-line-argument')
         self.cxx.addWarningFlagIfSupported('-Wno-attributes')
         self.cxx.addWarningFlagIfSupported('-Wno-pessimizing-move')
         self.cxx.addWarningFlagIfSupported('-Wno-c++11-extensions')
         self.cxx.addWarningFlagIfSupported('-Wno-user-defined-literals')
         self.cxx.addWarningFlagIfSupported('-Wno-noexcept-type')
         self.cxx.addWarningFlagIfSupported('-Wno-aligned-allocation-unavailable')