When Diego committed rev 119760 he basically disabled the codepath
that switched virtual symbols to full rewrite. Basically because
you could still trigger it by --param virtual-mappings-ratio=0.
As the code has not been excercised in the last 6(!) years I
opted to remove it as the underlying issue, very many virtual operands
vanished with the merge of alias-improvements.
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
Richard.
2012-07-27 Richard Guenther <rguent...@suse.de>
* doc/invoke.texi (min-virtual-mappings, virtual-mappings-ratio):
Remove param documentation.
* params.def (PARAM_MIN_VIRTUAL_MAPPINGS,
PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO): Remove.
* tree-flow.h (mark_set_for_renaming): Remove.
* tree-into-ssa.c (struct update_ssa_stats_d): Remove.
(add_new_name_mapping): Remove bookkeeping code.
(dump_update_ssa): Remove stats dumping code.
(init_update_ssa): Remove stats allocation code.
(delete_update_ssa): Remove stats freeing code.
(mark_set_for_renaming): Remove.
(switch_virtuals_to_full_rewrite_p): Likewise.
(switch_virtuals_to_full_rewrite): Likewise.
(update_ssa): Do not call switch_virtuals_to_full_rewrite.
Index: trunk/gcc/doc/invoke.texi
===================================================================
*** trunk.orig/gcc/doc/invoke.texi 2012-07-26 10:46:37.000000000 +0200
--- trunk/gcc/doc/invoke.texi 2012-07-27 12:52:05.774891497 +0200
*************** Small integer constants can use a shared
*** 9156,9173 ****
compiler's memory usage and increasing its speed. This sets the maximum
value of a shared integer constant. The default value is 256.
- @item min-virtual-mappings
- Specifies the minimum number of virtual mappings in the incremental
- SSA updater that should be registered to trigger the virtual mappings
- heuristic defined by virtual-mappings-ratio. The default value is
- 100.
-
- @item virtual-mappings-ratio
- If the number of virtual mappings is virtual-mappings-ratio bigger
- than the number of virtual symbols to be updated, then the incremental
- SSA updater switches to a full update for those symbols. The default
- ratio is 3.
-
@item ssp-buffer-size
The minimum size of buffers (i.e.@: arrays) that receive stack smashing
protection when @option{-fstack-protection} is used.
--- 9156,9161 ----
Index: trunk/gcc/params.def
===================================================================
*** trunk.orig/gcc/params.def 2012-06-06 11:40:57.000000000 +0200
--- trunk/gcc/params.def 2012-07-27 12:51:33.096892630 +0200
*************** DEFPARAM (PARAM_INTEGER_SHARE_LIMIT,
*** 644,673 ****
"The upper bound for sharing integer constants",
256, 2, 2)
- /* Incremental SSA updates for virtual operands may be very slow if
- there is a large number of mappings to process. In those cases, it
- is faster to rewrite the virtual symbols from scratch as if they
- had been recently introduced. This heuristic cannot be applied to
- SSA mappings for real SSA names, only symbols kept in FUD chains.
-
- PARAM_MIN_VIRTUAL_MAPPINGS specifies the minimum number of virtual
- mappings that should be registered to trigger the heuristic.
-
- PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO specifies the ratio between
- mappings and symbols. If the number of virtual mappings is
- PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO bigger than the number of
- virtual symbols to be updated, then the updater switches to a full
- update for those symbols. */
- DEFPARAM (PARAM_MIN_VIRTUAL_MAPPINGS,
- "min-virtual-mappings",
- "Minimum number of virtual mappings to consider switching to full
virtual renames",
- 100, 0, 0)
-
- DEFPARAM (PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO,
- "virtual-mappings-ratio",
- "Ratio between virtual mappings and virtual symbols to do full
virtual renames",
- 3, 0, 0)
-
DEFPARAM (PARAM_SSP_BUFFER_SIZE,
"ssp-buffer-size",
"The lower bound for a buffer to be considered for stack smashing
protection",
--- 644,649 ----
Index: trunk/gcc/tree-flow.h
===================================================================
*** trunk.orig/gcc/tree-flow.h 2012-07-26 15:47:35.000000000 +0200
--- trunk/gcc/tree-flow.h 2012-07-27 12:46:26.098903253 +0200
*************** bool name_registered_for_update_p (tree)
*** 575,581 ****
void release_ssa_name_after_update_ssa (tree);
void compute_global_livein (bitmap, bitmap);
void mark_sym_for_renaming (tree);
- void mark_set_for_renaming (bitmap);
bool symbol_marked_for_renaming (tree);
tree get_current_def (tree);
void set_current_def (tree, tree);
--- 575,580 ----
Index: trunk/gcc/tree-into-ssa.c
===================================================================
*** trunk.orig/gcc/tree-into-ssa.c 2012-07-27 12:44:02.000000000 +0200
--- trunk/gcc/tree-into-ssa.c 2012-07-27 12:52:09.835891373 +0200
*************** static htab_t repl_tbl;
*** 145,165 ****
NULL if they need to be initialized by register_new_name_mapping. */
static struct function *update_ssa_initialized_fn = NULL;
- /* Statistics kept by update_ssa to use in the virtual mapping
- heuristic. If the number of virtual mappings is beyond certain
- threshold, the updater will switch from using the mappings into
- renaming the virtual symbols from scratch. In some cases, the
- large number of name mappings for virtual names causes significant
- slowdowns in the PHI insertion code. */
- struct update_ssa_stats_d
- {
- unsigned num_virtual_mappings;
- unsigned num_total_mappings;
- bitmap virtual_symbols;
- unsigned num_virtual_symbols;
- };
- static struct update_ssa_stats_d update_ssa_stats;
-
/* Global data to attach to the main dominator walk structure. */
struct mark_def_sites_global_data
{
--- 145,150 ----
*************** add_new_name_mapping (tree new_tree, tre
*** 667,692 ****
/* OLD and NEW_TREE must be different SSA names for the same symbol. */
gcc_assert (new_tree != old && SSA_NAME_VAR (new_tree) == SSA_NAME_VAR
(old));
- /* If this mapping is for virtual names, we will need to update
- virtual operands. If this is a mapping for .MEM, then we gather
- the symbols associated with each name. */
- if (!is_gimple_reg (new_tree))
- {
- tree sym;
-
- update_ssa_stats.num_virtual_mappings++;
- update_ssa_stats.num_virtual_symbols++;
-
- /* Keep counts of virtual mappings and symbols to use in the
- virtual mapping heuristic. If we have large numbers of
- virtual mappings for a relatively low number of symbols, it
- will make more sense to rename the symbols from scratch.
- Otherwise, the insertion of PHI nodes for each of the old
- names in these mappings will be very slow. */
- sym = SSA_NAME_VAR (new_tree);
- bitmap_set_bit (update_ssa_stats.virtual_symbols, DECL_UID (sym));
- }
-
/* We may need to grow NEW_SSA_NAMES and OLD_SSA_NAMES because our
caller may have created new names since the set was created. */
if (new_ssa_names->n_bits <= num_ssa_names - 1)
--- 652,657 ----
*************** add_new_name_mapping (tree new_tree, tre
*** 709,717 ****
SET_BIT (new_ssa_names, SSA_NAME_VERSION (new_tree));
SET_BIT (old_ssa_names, SSA_NAME_VERSION (old));
- /* Update mapping counter to use in the virtual mapping heuristic. */
- update_ssa_stats.num_total_mappings++;
-
timevar_pop (TV_TREE_SSA_INCREMENTAL);
}
--- 674,679 ----
*************** dump_update_ssa (FILE *file)
*** 2831,2848 ****
EXECUTE_IF_SET_IN_SBITMAP (new_ssa_names, 0, i, sbi)
dump_names_replaced_by (file, ssa_name (i));
-
- fprintf (file, "\n");
- fprintf (file, "Number of virtual NEW -> OLD mappings: %7u\n",
- update_ssa_stats.num_virtual_mappings);
- fprintf (file, "Number of real NEW -> OLD mappings: %7u\n",
- update_ssa_stats.num_total_mappings
- - update_ssa_stats.num_virtual_mappings);
- fprintf (file, "Number of total NEW -> OLD mappings: %7u\n",
- update_ssa_stats.num_total_mappings);
-
- fprintf (file, "\nNumber of virtual symbols: %u\n",
- update_ssa_stats.num_virtual_symbols);
}
if (!bitmap_empty_p (SYMS_TO_RENAME (cfun)))
--- 2793,2798 ----
*************** init_update_ssa (struct function *fn)
*** 2890,2897 ****
repl_tbl = htab_create (20, repl_map_hash, repl_map_eq, repl_map_free);
names_to_release = NULL;
- memset (&update_ssa_stats, 0, sizeof (update_ssa_stats));
- update_ssa_stats.virtual_symbols = BITMAP_ALLOC (NULL);
update_ssa_initialized_fn = fn;
}
--- 2840,2845 ----
*************** delete_update_ssa (void)
*** 2914,2920 ****
repl_tbl = NULL;
bitmap_clear (SYMS_TO_RENAME (update_ssa_initialized_fn));
- BITMAP_FREE (update_ssa_stats.virtual_symbols);
if (names_to_release)
{
--- 2862,2867 ----
*************** mark_sym_for_renaming (tree sym)
*** 2998,3019 ****
}
- /* Register all the symbols in SET to be renamed by update_ssa. */
-
- void
- mark_set_for_renaming (bitmap set)
- {
- bitmap_iterator bi;
- unsigned i;
-
- if (set == NULL || bitmap_empty_p (set))
- return;
-
- EXECUTE_IF_SET_IN_BITMAP (set, 0, i, bi)
- mark_sym_for_renaming (referenced_var (i));
- }
-
-
/* Return true if there is any work to be done by update_ssa
for function FN. */
--- 2945,2950 ----
*************** insert_updated_phi_nodes_for (tree var,
*** 3175,3247 ****
}
- /* Heuristic to determine whether SSA name mappings for virtual names
- should be discarded and their symbols rewritten from scratch. When
- there is a large number of mappings for virtual names, the
- insertion of PHI nodes for the old names in the mappings takes
- considerable more time than if we inserted PHI nodes for the
- symbols instead.
-
- Currently the heuristic takes these stats into account:
-
- - Number of mappings for virtual SSA names.
- - Number of distinct virtual symbols involved in those mappings.
-
- If the number of virtual mappings is much larger than the number of
- virtual symbols, then it will be faster to compute PHI insertion
- spots for the symbols. Even if this involves traversing the whole
- CFG, which is what happens when symbols are renamed from scratch. */
-
- static bool
- switch_virtuals_to_full_rewrite_p (void)
- {
- if (update_ssa_stats.num_virtual_mappings < (unsigned) MIN_VIRTUAL_MAPPINGS)
- return false;
-
- if (update_ssa_stats.num_virtual_mappings
- > (unsigned) VIRTUAL_MAPPINGS_TO_SYMS_RATIO
- * update_ssa_stats.num_virtual_symbols)
- return true;
-
- return false;
- }
-
-
- /* Remove every virtual mapping and mark all the affected virtual
- symbols for renaming. */
-
- static void
- switch_virtuals_to_full_rewrite (void)
- {
- unsigned i = 0;
- sbitmap_iterator sbi;
-
- if (dump_file)
- {
- fprintf (dump_file, "\nEnabled virtual name mapping heuristic.\n");
- fprintf (dump_file, "\tNumber of virtual mappings: %7u\n",
- update_ssa_stats.num_virtual_mappings);
- fprintf (dump_file, "\tNumber of unique virtual symbols: %7u\n",
- update_ssa_stats.num_virtual_symbols);
- fprintf (dump_file, "Updating FUD-chains from top of CFG will be "
- "faster than processing\nthe name mappings.\n\n");
- }
-
- /* Remove all virtual names from NEW_SSA_NAMES and OLD_SSA_NAMES.
- Note that it is not really necessary to remove the mappings from
- REPL_TBL, that would only waste time. */
- EXECUTE_IF_SET_IN_SBITMAP (new_ssa_names, 0, i, sbi)
- if (!is_gimple_reg (ssa_name (i)))
- RESET_BIT (new_ssa_names, i);
-
- EXECUTE_IF_SET_IN_SBITMAP (old_ssa_names, 0, i, sbi)
- if (!is_gimple_reg (ssa_name (i)))
- RESET_BIT (old_ssa_names, i);
-
- mark_set_for_renaming (update_ssa_stats.virtual_symbols);
- }
-
-
/* Given a set of newly created SSA names (NEW_SSA_NAMES) and a set of
existing SSA names (OLD_SSA_NAMES), update the SSA form so that:
--- 3106,3111 ----
*************** update_ssa (unsigned update_flags)
*** 3370,3380 ****
def_blocks = NULL;
}
- /* Heuristic to avoid massive slow downs when the replacement
- mappings include lots of virtual names. */
- if (insert_phi_p && switch_virtuals_to_full_rewrite_p ())
- switch_virtuals_to_full_rewrite ();
-
/* If there are names defined in the replacement table, prepare
definition and use sites for all the names in NEW_SSA_NAMES and
OLD_SSA_NAMES. */
--- 3234,3239 ----
