fixdep: avoid parsing the same file over again

masahir0y · masahir0y · commit faa91c472be8 · 2023-01-22T23:43:33.000+09:00
The dep files (*.d files) emitted by C compilers usually contain the
deduplicated list of included files.

One exceptional case is when a header is included by the -include
command line option, and also by #include directive.

For example, the top Makefile adds the command line option,
"-include $(srctree)/include/linux/kconfig.h". You do not need to
include &lt;linux/kconfig.h&gt; in every source file.

In fact, include/linux/kconfig.h is listed twice in many .*.cmd files
due to include/linux/xarray.h having "#include &lt;linux/kconfig.h&gt;".
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 &lt;masahiroy@kernel.org&gt;
Acked-by: Miguel Ojeda &lt;ojeda@kernel.org&gt;
Tested-by: Miguel Ojeda &lt;ojeda@kernel.org&gt;
Reviewed-by: Vincenzo Palazzo &lt;vincenzopalazzodev@gmail.com&gt;
diff --git 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)
 {
@@ -365,14 +365,19 @@ 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;
 				printf("source_%s := %s\n\n", target, p);
 				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;
 		}
