[BOLT] Improve file handling in NFC-Mode

This patch introduce the following improvements:
- Catch an exception when the CMakeCache.txt is not present
- Bail out gracefully when llvm-bolt did not build successfully the
  current or previous revision.

Author: paschalis-mpeis

bolt/utils/nfc-check-setup.py

@@ -80,18 +80,26 @@ def main():
 
     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")
+    try:
+        CMCacheFilename=f"{args.build_dir}/CMakeCache.txt"
+        with open(CMCacheFilename) 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:
+            raise Exception(f"Source directory not found: '{CMCacheFilename}'")
+    except Exception as e:
+        sys.exit(e)
 
     # build the current commit
     subprocess.run(
         shlex.split("cmake --build . --target llvm-bolt"), cwd=args.build_dir
     )
+
+    if not os.path.exists(bolt_path):
+        sys.exit(f"Failed to build the current revision: '{bolt_path}'")
+
     # rename llvm-bolt
     os.replace(bolt_path, f"{bolt_path}.new")
     # memorize the old hash for logging
@@ -122,12 +130,17 @@ def main():
     subprocess.run(shlex.split(f"git checkout -f {args.cmp_rev}"), 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
+    if not os.path.exists(bolt_path):
+        sys.exit(f"Failed to build the previous revision: '{bolt_path}'")
     os.replace(bolt_path, f"{bolt_path}.old")
+
     if args.switch_back:
         if stash:
             subprocess.run(shlex.split("git stash pop"), cwd=source_dir)