[lit] Avoid calling realpath() for every printed message

[arichardson]

Summary

I did some profiling of lit while trying to optimize the libc++ test
startup for remote hosts and it turns out that there is a realpath() call
for every message printed and this shows up in the profile.
The inspect.getframeinfo() function calls realpath() internally and
moreover we don't need most of the other information returned from it.
This patch uses inspect.getsourcefile() and os.path.normpath to remove
../ from the path instead. Not resolving symlinks reduces the startup time
for running a single test with lit by about 50ms for me.

[yln]

Just making sure I understand:
This is an implementation detail only and the message format stays the same (and it works on all platforms).
The only difference in behavior is that we don't resolve symlinks anymore; and we don't care about that.

LGTM, if the above is true.

Thanks!

[ldionne]

llvm/utils/lit/lit/LitConfig.py

168–171

I don't think you need to call normpath() after calling abspath(). From the Python docs:

os.path.abspath(path)
Return a normalized absolutized version of the pathname path. On most platforms, this is equivalent to calling the function normpath() as follows: normpath(join(os.getcwd(), path)).

[arichardson]

llvm/utils/lit/lit/LitConfig.py

168–171

Thanks I didn't read the docs and just assumed it would behave the same as pathlib Path.absolute():

>>> os.chdir("/usr/bin"); (os.getcwd(), os.path.abspath(".."), Path("..").absolute())
('/usr/bin', '/usr', PosixPath('/usr/bin/..'))

[yln]

llvm/utils/lit/lit/LitConfig.py

168–171

Good catch, thanks Louis!

[arichardson]

drop unncessary normpath

llvm/utils/lit/lit/LitConfig.py

def getToolsPath(self, dir, paths, tools):
 
         return dir
 
     def _write_message(self, kind, message):
         # Get the file/line where this message was generated.
         f = inspect.currentframe()
         # Step out of _write_message, and then out of wrapper.
         f = f.f_back.f_back
-        file,line,_,_,_ = inspect.getframeinfo(f)
-        location = '%s:%d' % (file, line)
-
-        sys.stderr.write('%s: %s: %s: %s\n' % (self.progname, location,
+        file = os.path.abspath(inspect.getsourcefile(f))
+        line = inspect.getlineno(f)
+        sys.stderr.write('%s: %s:%d: %s: %s\n' % (self.progname, file, line,
                                                   kind, message))
 
     def note(self, message):
         if not self.quiet:
             self._write_message('note', message)
 
     def warning(self, message):
         if not self.quiet:
             self._write_message('warning', message)