linux-kernel - [PATCH 5/6] fixdep: avoid parsing the same file over again

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Date:   Sat, 31 Dec 2022 15:42:02 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        rust-for-linux@...r.kernel.org
Subject: [PATCH 5/6] fixdep: avoid parsing the same file over again

The dep files (*.d files) emitted by C compilers usually contain the
deduplicated list of included files.

There is an exceptional case; if a header is included by the -include
command line option, and also by #include directive, it appears twice
in the *.d file.

For example, the top Makefile specifies the command line option,
-include $(srctree)/include/linux/kconfig.h. You do not need to
add #include <linux/kconfig.h> in every source file.

In fact, include/linux/kconfig.h is listed twice in many .*.cmd files
due to include/linux/xarray.h including <linux/kconfig.h>.
I did not fix that since it is a small redundancy.

However, this is more annoying for rustc. rustc emits the dependency
for each emission type.

For example, cmd_rustc_library emits dep-info, obj, and metadata.
So, the emitted *.d file contains the dependency for those 3 targets,
which makes fixdep parse the same file 3 times.

  $ grep rust/alloc/raw_vec.rs rust/.alloc.o.cmd
    rust/alloc/raw_vec.rs \
    rust/alloc/raw_vec.rs \
    rust/alloc/raw_vec.rs \

To skip the second parsing, this commit adds a hash table for parsed
files, just like we did for CONFIG options.

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

 scripts/basic/fixdep.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index b20777b888d7..cc8f6d34c2ca 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -113,7 +113,7 @@ struct item {
 };
 
 #define HASHSZ 256
-static struct item *config_hashtab[HASHSZ];
+static struct item *config_hashtab[HASHSZ], *file_hashtab[HASHSZ];
 
 static unsigned int strhash(const char *str, unsigned int sz)
 {
@@ -361,6 +361,10 @@ static void parse_dep_file(char *p, const char *target)
 			 * name, which will be the original one, and ignore any
 			 * other source names, which will be intermediate
 			 * temporary files.
+			 *
+			 * rustc emits the same dependency list for each
+			 * emission type. It is enough to list the source name
+			 * just once.
 			 */
 			if (!saw_any_target) {
 				saw_any_target = true;
@@ -368,7 +372,8 @@ static void parse_dep_file(char *p, const char *target)
 				printf("deps_%s := \\\n", target);
 				need_parse = true;
 			}
-		} else if (!is_ignored_file(p, q - p)) {
+		} else if (!is_ignored_file(p, q - p) &&
+			   !in_hashtable(p, q - p, file_hashtab)) {
 			printf("  %s \\\n", p);
 			need_parse = true;
 		}
-- 
2.34.1