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SubjectRe: [PATCH 5/6] fixdep: avoid parsing the same file over again
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Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

On Sat Dec 31, 2022 at 7:42 AM CET, Masahiro Yamada wrote:
> 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@kernel.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

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