[PATCH 1/3] gen_compile_commands: parse only the first line of .*.cmd files

From: Masahiro Yamada <masahiroy@kernel.org>
To: linux-kbuild@vger.kernel.org
Cc: Nathan Huckleberry <nhuck@google.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Tom Roeder <tmroeder@google.com>,
	clang-built-linux@googlegroups.com,
	Masahiro Yamada <masahiroy@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: [PATCH 1/3] gen_compile_commands: parse only the first line of .*.cmd files
Date: Thu, 13 Aug 2020 02:39:56 +0900	[thread overview]
Message-ID: <20200812173958.2307251-2-masahiroy@kernel.org> (raw)
In-Reply-To: <20200812173958.2307251-1-masahiroy@kernel.org>

After the allmodconfig build, this script takes about 5 sec on my
machine. Most of the run-time is consumed for needless regex matching.

We know the format of .*.cmd file; the first line is the build command.
There is no need to parse the remaining.

With this optimization, now it runs in about 1 sec with the allmodconfig
build.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 scripts/gen_compile_commands.py | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/scripts/gen_compile_commands.py b/scripts/gen_compile_commands.py
index c458696ef3a7..19c7338740e7 100755
--- a/scripts/gen_compile_commands.py
+++ b/scripts/gen_compile_commands.py
@@ -125,11 +125,9 @@ def main():
             filepath = os.path.join(dirpath, filename)
 
             with open(filepath, 'rt') as f:
-                for line in f:
-                    result = line_matcher.match(line)
-                    if not result:
-                        continue
-
+                line = f.readline()
+                result = line_matcher.match(line)
+                if result:
                     try:
                         entry = process_line(directory, dirpath,
                                              result.group(1), result.group(2))
-- 
2.25.1

