[BOLT][UTILS] Add nfc-check-setup --switch-back option

[Amir]

Summary

Add an option to switch repo revision back, handling stashing automatically.

[rafauler]

LGTM

bolt/utils/nfc-check-setup.py

 
 def main():
     parser = argparse.ArgumentParser(description=textwrap.dedent('''
             This script builds two versions of BOLT (with the current and
             previous revision) and sets up symlink for llvm-bolt-wrapper.
             Passes the options through to llvm-bolt-wrapper.
             '''))
     parser.add_argument('build_dir', nargs='?', default=os.getcwd(),
-                        help='Path to BOLT build directory, default is current directory')
+                        help='Path to BOLT build directory, default is current '
+                             'directory')
+    parser.add_argument('--switch-back', default=False, action='store_true',
+                        help='Checkout back to the starting revision')
     args, wrapper_args = parser.parse_known_args()
     bolt_path = f'{args.build_dir}/bin/llvm-bolt'
 
     source_dir = None
     # find the repo directory
     with open(f'{args.build_dir}/CMakeCache.txt') as f:
         for line in f:
             m = re.match(r'LLVM_SOURCE_DIR:STATIC=(.*)', line)
             if m:
                 source_dir = m.groups()[0]
     if not source_dir:
         sys.exit("Source directory is not found")
 
     script_dir = os.path.dirname(os.path.abspath(__file__))
     wrapper_path = f'{script_dir}/llvm-bolt-wrapper.py'
     # build the current commit
     subprocess.run(shlex.split("cmake --build . --target llvm-bolt"),
                    cwd=args.build_dir)
     # rename llvm-bolt
     os.replace(bolt_path, f'{bolt_path}.new')
     # memorize the old hash for logging
     old_ref = get_git_ref_or_rev(source_dir)
 
+    # determine whether a stash is needed
+    stash = subprocess.run(shlex.split("git status --porcelain"), cwd=source_dir,
+                           stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
+                           text=True).stdout
+    if stash:
         # save local changes before checkout
         subprocess.run(shlex.split("git stash"), cwd=source_dir)
     # check out the previous commit
     subprocess.run(shlex.split("git checkout -f HEAD^"), cwd=source_dir)
     # get the parent commit hash for logging
     new_ref = get_git_ref_or_rev(source_dir)
     # build the previous commit
     subprocess.run(shlex.split("cmake --build . --target llvm-bolt"),
                    cwd=args.build_dir)
     # rename llvm-bolt
     os.replace(bolt_path, f'{bolt_path}.old')
     # set up llvm-bolt-wrapper.ini
     ini = subprocess.check_output(
         shlex.split(
             f"{wrapper_path} {bolt_path}.old {bolt_path}.new") + wrapper_args,
             text=True)
     with open(f'{args.build_dir}/bin/llvm-bolt-wrapper.ini', 'w') as f:
         f.write(ini)
     # symlink llvm-bolt-wrapper
     os.symlink(wrapper_path, bolt_path)
-    print(f"The repository {source_dir} has been switched from rev {old_ref} "
+    if args.switch_back:
+        if stash:
+            subprocess.run(shlex.split("git stash pop"), cwd=source_dir)
+        subprocess.run(shlex.split(f"git checkout {old_ref}"), cwd=source_dir)
+    else:
+        print(f"The repository {source_dir} has been switched from {old_ref} "
               f"to {new_ref}. Local changes were stashed. Switch back using\n\t"
-          f"git checkout {old_ref}\n"
-          "Current build directory is ready to run BOLT tests, e.g.\n\t"
-          "bin/llvm-lit -sv tools/bolt/test\nor\n\t"
-          "bin/llvm-lit -sv tools/bolttests")
+              f"git checkout {old_ref}\n")
+    print(f"Build directory {args.build_dir} is ready to run BOLT tests, e.g.\n"
+          "\tbin/llvm-lit -sv tools/bolt/test\nor\n"
+          "\tbin/llvm-lit -sv tools/bolttests")
 
 
 if __name__ == "__main__":
     main()