Re: [PATCH 1/2] Change random seeds to 64bit and drop re-crcing

[Richard Guenther <richard dot guenther at gmail dot com>]

On Tue, Sep 27, 2011 at 11:30 PM, Andi Kleen <andi@firstfloor.org> wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> I had some trouble with random build failures in a large LTO project
> and it turned out to be random seed collisions in a highly parallel build
> (thanks to Honza for suggesting that)
>
> There were multiple problems:
> - The way to generate the random seed is pure (milli seconds plus pid)
> - It's only 32bit
> - Several users take the existing ascii seed and re-CRC32 it again, which
> doesn't exactly improve it.
>
> This patch changes that to:
> - Always use 64bit seeds as numbers (no re-crcing)
> - Change all users to use HOST_WIDE_INT
> - When the user specifies a random seed it's still crc32ed, but only in
> this case.
>
> Passes bootstrap + testsuite on x86_64-linux. Ok to commit?

Ok if there are no objections from other folks within 24h.

Thanks,
Richard.

> -Andi
>
> gcc/cp:
>
> 2011-09-26 ? Andi Kleen <ak@linux.intel.com>
>
> ? ? ? ?* repo.c (finish_repo): Use HOST_WIDE_INT_PRINT_HEX_PURE.
>
> gcc/:
>
> 2011-09-26 ? Andi Kleen <ak@linux.intel.com>
>
> ? ? ? ?* hwint.h (HOST_WIDE_INT_PRINT_HEX_PURE): Add.
> ? ? ? ?* lto-streamer.c (lto_get_section_name): Remove crc32_string.
> ? ? ? ?Handle numerical random seed.
> ? ? ? ?* lto-streamer.h (lto_file_decl_data): Change id to unsigned HOST_WIDE_INT.
> ? ? ? ?* toplev.c (random_seed): Add.
> ? ? ? ?(init_random_seed): Change for numerical random seed.
> ? ? ? ?(get_random_seed): Return as HOST_WIDE_INT.
> ? ? ? ?(set_random_seed): Crc32 existing string.
> ? ? ? ?* toplev.h (get_random_seed): Change to numercal return.
> ? ? ? ?* tree.c (get_file_function_name): Remove CRC. Handle numerical random seed.
>
> gcc/lto/:
>
> 2011-09-26 ? Andi Kleen <ak@linux.intel.com>
>
> ? ? ? ?* lto.c (lto_resolution_read): Remove id dumping.
> ? ? ? ?(lto_section_with_id): Turn id HOST_WIDE_ID.
> ? ? ? ?(create_subid_section_table): Dito.
> ---
> ?gcc/cp/repo.c ? ? ?| ? ?3 ++-
> ?gcc/hwint.h ? ? ? ?| ? ?1 +
> ?gcc/lto-streamer.c | ? ?8 ++++----
> ?gcc/lto-streamer.h | ? ?2 +-
> ?gcc/lto/lto.c ? ? ?| ? 11 ++++-------
> ?gcc/toplev.c ? ? ? | ? 23 ++++++++++++-----------
> ?gcc/toplev.h ? ? ? | ? ?2 +-
> ?gcc/tree.c ? ? ? ? | ? ?6 +++---
> ?8 files changed, 28 insertions(+), 28 deletions(-)
>
> diff --git a/gcc/cp/repo.c b/gcc/cp/repo.c
> index 16a192e..ca971b6 100644
> --- a/gcc/cp/repo.c
> +++ b/gcc/cp/repo.c
> @@ -263,7 +263,8 @@ finish_repo (void)
> ? ? ? ? anonymous namespaces will get the same mangling when this
> ? ? ? ? file is recompiled. ?*/
> ? ? ? if (!strstr (args, "'-frandom-seed="))
> - ? ? ? fprintf (repo_file, " '-frandom-seed=%s'", get_random_seed (false));
> + ? ? ? fprintf (repo_file, " '-frandom-seed=" HOST_WIDE_INT_PRINT_HEX_PURE "'",
> + ? ? ? ? ? ? ? ?get_random_seed (false));
> ? ? ? fprintf (repo_file, "\n");
> ? ? }
>
> diff --git a/gcc/hwint.h b/gcc/hwint.h
> index 2643aee..f5e0bee 100644
> --- a/gcc/hwint.h
> +++ b/gcc/hwint.h
> @@ -102,6 +102,7 @@ extern char sizeof_long_long_must_be_8[sizeof(long long) == 8 ? 1 : -1];
> ?#define HOST_WIDE_INT_PRINT_DEC_C HOST_WIDE_INT_PRINT_DEC HOST_WIDE_INT_PRINT_C
> ?#define HOST_WIDE_INT_PRINT_UNSIGNED "%" HOST_WIDE_INT_PRINT "u"
> ?#define HOST_WIDE_INT_PRINT_HEX "%#" HOST_WIDE_INT_PRINT "x"
> +#define HOST_WIDE_INT_PRINT_HEX_PURE "%" HOST_WIDE_INT_PRINT "x"
>
> ?/* Set HOST_WIDEST_INT. ?This is a 64-bit type unless the compiler
> ? ?in use has no 64-bit type at all; in that case it's 32 bits. ?*/
> diff --git a/gcc/lto-streamer.c b/gcc/lto-streamer.c
> index 633c3ce..e3ccb79 100644
> --- a/gcc/lto-streamer.c
> +++ b/gcc/lto-streamer.c
> @@ -166,13 +166,13 @@ lto_get_section_name (int section_type, const char *name, struct lto_file_decl_d
> ? ? ?doesn't confuse the reader with merged sections.
>
> ? ? ?For options don't add a ID, the option reader cannot deal with them
> - ? ? and merging should be ok here.
> -
> - ? ? XXX: use crc64 to minimize collisions? */
> + ? ? and merging should be ok here. */
> ? if (section_type == LTO_section_opts)
> ? ? strcpy (post, "");
> + ?else if (f != NULL)
> + ? ?sprintf (post, "." HOST_WIDE_INT_PRINT_HEX_PURE, f->id);
> ? else
> - ? ?sprintf (post, ".%x", f ? f->id : crc32_string(0, get_random_seed (false)));
> + ? ?sprintf (post, "." HOST_WIDE_INT_PRINT_HEX_PURE, get_random_seed (false));
> ? return concat (LTO_SECTION_NAME_PREFIX, sep, add, post, NULL);
> ?}
>
> diff --git a/gcc/lto-streamer.h b/gcc/lto-streamer.h
> index 190d6a3..2564bd2 100644
> --- a/gcc/lto-streamer.h
> +++ b/gcc/lto-streamer.h
> @@ -552,7 +552,7 @@ struct GTY(()) lto_file_decl_data
> ? struct lto_file_decl_data *next;
>
> ? /* Sub ID for merged objects. */
> - ?unsigned id;
> + ?unsigned HOST_WIDE_INT id;
>
> ? /* Symbol resolutions for this file */
> ? VEC(ld_plugin_symbol_resolution_t,heap) * GTY((skip)) resolutions;
> diff --git a/gcc/lto/lto.c b/gcc/lto/lto.c
> index 0b1dcb9..77eb1a1 100644
> --- a/gcc/lto/lto.c
> +++ b/gcc/lto/lto.c
> @@ -976,9 +976,6 @@ lto_resolution_read (splay_tree file_ids, FILE *resolution, lto_file *file)
> ? ? ? ?}
>
> ? ? ? file_data = (struct lto_file_decl_data *)nd->value;
> - ? ? ?if (cgraph_dump_file)
> - ? ? ? fprintf (cgraph_dump_file, "Adding resolution %u %u to id %x\n",
> - ? ? ? ? ? ? ? ?index, r, file_data->id);
> ? ? ? VEC_safe_grow_cleared (ld_plugin_symbol_resolution_t, heap,
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? file_data->resolutions,
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? max_index + 1);
> @@ -990,14 +987,14 @@ lto_resolution_read (splay_tree file_ids, FILE *resolution, lto_file *file)
> ?/* Is the name for a id'ed LTO section? */
>
> ?static int
> -lto_section_with_id (const char *name, unsigned *id)
> +lto_section_with_id (const char *name, unsigned HOST_WIDE_INT *id)
> ?{
> ? const char *s;
>
> ? if (strncmp (name, LTO_SECTION_NAME_PREFIX, strlen (LTO_SECTION_NAME_PREFIX)))
> ? ? return 0;
> ? s = strrchr (name, '.');
> - ?return s && sscanf (s, ".%x", id) == 1;
> + ?return s && sscanf (s, "." HOST_WIDE_INT_PRINT_HEX_PURE, id) == 1;
> ?}
>
> ?/* Create file_data of each sub file id */
> @@ -1008,7 +1005,7 @@ create_subid_section_table (void **slot, void *data)
> ? struct lto_section_slot s_slot, *new_slot;
> ? struct lto_section_slot *ls = *(struct lto_section_slot **)slot;
> ? splay_tree file_ids = (splay_tree)data;
> - ?unsigned id;
> + ?unsigned HOST_WIDE_INT id;
> ? splay_tree_node nd;
> ? void **hash_slot;
> ? char *new_name;
> @@ -1080,7 +1077,7 @@ static int lto_create_files_from_ids (splay_tree_node node, void *data)
>
> ? lto_file_finalize (file_data, lw->file);
> ? if (cgraph_dump_file)
> - ? ?fprintf (cgraph_dump_file, "Creating file %s with sub id %x\n",
> + ? ?fprintf (cgraph_dump_file, "Creating file %s with sub id " HOST_WIDE_INT_PRINT_HEX "\n",
> ? ? ? ? ? ? file_data->file_name, file_data->id);
> ? file_data->next = *lw->file_data;
> ? *lw->file_data = file_data;
> diff --git a/gcc/toplev.c b/gcc/toplev.c
> index 3688c09..e1a8b35 100644
> --- a/gcc/toplev.c
> +++ b/gcc/toplev.c
> @@ -141,6 +141,9 @@ static const char *flag_random_seed;
> ? ?user has specified a particular random seed. ?*/
> ?unsigned local_tick;
>
> +/* Random number for this compilation */
> +HOST_WIDE_INT random_seed;
> +
> ?/* -f flags. ?*/
>
> ?/* Generate code for GNU or NeXT Objective-C runtime environment. ?*/
> @@ -251,7 +254,7 @@ announce_function (tree decl)
> ? ? }
> ?}
>
> -/* Initialize local_tick with the time of day, or -1 if
> +/* Initialize local_tick with a random number or -1 if
> ? ?flag_random_seed is set. ?*/
>
> ?static void
> @@ -286,24 +289,21 @@ init_local_tick (void)
> ?static void
> ?init_random_seed (void)
> ?{
> - ?unsigned HOST_WIDE_INT value;
> - ?static char random_seed[HOST_BITS_PER_WIDE_INT / 4 + 3];
> -
> - ?value = local_tick ^ getpid ();
> -
> - ?sprintf (random_seed, HOST_WIDE_INT_PRINT_HEX, value);
> - ?flag_random_seed = random_seed;
> + ?if (flag_random_seed)
> + ? ?random_seed = crc32_string (0, flag_random_seed);
> + ?else if (!random_seed)
> + ? ?random_seed = local_tick ^ getpid (); ?/* Old racey fallback method */
> ?}
>
> -/* Obtain the random_seed string. ?Unless NOINIT, initialize it if
> +/* Obtain the random_seed. ?Unless NOINIT, initialize it if
> ? ?it's not provided in the command line. ?*/
>
> -const char *
> +HOST_WIDE_INT
> ?get_random_seed (bool noinit)
> ?{
> ? if (!flag_random_seed && !noinit)
> ? ? init_random_seed ();
> - ?return flag_random_seed;
> + ?return random_seed;
> ?}
>
> ?/* Modify the random_seed string to VAL. ?Return its previous
> @@ -314,6 +314,7 @@ set_random_seed (const char *val)
> ?{
> ? const char *old = flag_random_seed;
> ? flag_random_seed = val;
> + ?random_seed = crc32_string (0, flag_random_seed);
> ? return old;
> ?}
>
> diff --git a/gcc/toplev.h b/gcc/toplev.h
> index 2455dc0..588cfdb 100644
> --- a/gcc/toplev.h
> +++ b/gcc/toplev.h
> @@ -77,7 +77,7 @@ extern bool set_src_pwd ? ? ? ? ? ? ? ? ? ? ?(const char *);
>
> ?/* Functions used to manipulate the random seed. ?*/
>
> -extern const char *get_random_seed (bool);
> +extern HOST_WIDE_INT get_random_seed (bool);
> ?extern const char *set_random_seed (const char *);
>
> ?#endif /* ! GCC_TOPLEV_H */
> diff --git a/gcc/tree.c b/gcc/tree.c
> index a53c9f4..6a2e9fb 100644
> --- a/gcc/tree.c
> +++ b/gcc/tree.c
> @@ -8749,11 +8749,11 @@ get_file_function_name (const char *type)
> ? ? ? ?file = input_filename;
>
> ? ? ? len = strlen (file);
> - ? ? ?q = (char *) alloca (9 * 2 + len + 1);
> + ? ? ?q = (char *) alloca (9 + 17 + len + 1);
> ? ? ? memcpy (q, file, len + 1);
>
> - ? ? ?sprintf (q + len, "_%08X_%08X", crc32_string (0, name),
> - ? ? ? ? ? ? ?crc32_string (0, get_random_seed (false)));
> + ? ? ?snprintf (q + len, 9 + 17 + 1, "_%08X_" HOST_WIDE_INT_PRINT_HEX,
> + ? ? ? ? ? ? ? crc32_string (0, name), get_random_seed (false));
>
> ? ? ? p = q;
> ? ? }
> --
> 1.7.5.4
>
>