linux-kernel - [PATCH v2 1/9] gen_compile_commands: parse only the first line of .*.cmd files

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Date:   Sat, 22 Aug 2020 04:01:51 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     Nathan Huckleberry <nhuck@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Roeder <tmroeder@...gle.com>,
        clang-built-linux@...glegroups.com,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/9] gen_compile_commands: parse only the first line of .*.cmd files

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 rest.

With this optimization, now it runs 4 times faster.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
---

Changes in v2:
  - Remove the unneeded variable 'line'

 scripts/gen_compile_commands.py | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/scripts/gen_compile_commands.py b/scripts/gen_compile_commands.py
index c458696ef3a7..1bcf33a93cb9 100755
--- a/scripts/gen_compile_commands.py
+++ b/scripts/gen_compile_commands.py
@@ -125,11 +125,8 @@ 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
-
+                result = line_matcher.match(f.readline())
+                if result:
                     try:
                         entry = process_line(directory, dirpath,
                                              result.group(1), result.group(2))
-- 
2.25.1