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

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Date:   Fri, 06 Jan 2023 10:31:49 +0100
From:   "Vincenzo" <vincenzopalazzodev@...il.com>
To:     "Masahiro Yamada" <masahiroy@...nel.org>,
        <linux-kbuild@...r.kernel.org>
Cc:     <linux-kernel@...r.kernel.org>, "Miguel Ojeda" <ojeda@...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: Re: [PATCH 5/6] fixdep: avoid parsing the same file over again

Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@...il.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@...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