/* Dead store elimination
- Copyright (C) 2004 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005 Free Software Foundation, Inc.
This file is part of GCC.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING. If not, write to
-the Free Software Foundation, 59 Temple Place - Suite 330,
-Boston, MA 02111-1307, USA. */
+the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+Boston, MA 02110-1301, USA. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
-#include "errors.h"
#include "ggc.h"
#include "tree.h"
#include "rtl.h"
bitmap stores;
};
+/* Basic blocks of the potentially dead store and the following
+ store, for memory_address_same. */
+struct address_walk_data
+{
+ basic_block store1_bb, store2_bb;
+};
+
static bool gate_dse (void);
-static void tree_ssa_dse (void);
+static unsigned int tree_ssa_dse (void);
static void dse_initialize_block_local_data (struct dom_walk_data *,
basic_block,
bool);
block_stmt_iterator);
static void dse_record_phis (struct dom_walk_data *, basic_block);
static void dse_finalize_block (struct dom_walk_data *, basic_block);
-static void fix_phi_uses (tree, tree);
-static void fix_stmt_v_may_defs (tree, tree);
static void record_voperand_set (bitmap, bitmap *, unsigned int);
-/* Function indicating whether we ought to include information for 'var'
- when calculating immediate uses. For this pass we only want use
- information for virtual variables. */
-
-static bool
-need_imm_uses_for (tree var)
-{
- return !is_gimple_reg (var);
-}
+static unsigned max_stmt_uid; /* Maximal uid of a statement. Uids to phi
+ nodes are assigned using the versions of
+ ssa names they define. */
+/* Returns uid of statement STMT. */
-/* Replace uses in PHI which match V_MAY_DEF_RESULTs in STMT with the
- corresponding V_MAY_DEF_OP in STMT. */
-
-static void
-fix_phi_uses (tree phi, tree stmt)
+static unsigned
+get_stmt_uid (tree stmt)
{
- stmt_ann_t ann = stmt_ann (stmt);
- v_may_def_optype v_may_defs;
- unsigned int i;
- int j;
-
- get_stmt_operands (stmt);
- v_may_defs = V_MAY_DEF_OPS (ann);
-
- /* Walk each V_MAY_DEF in STMT. */
- for (i = 0; i < NUM_V_MAY_DEFS (v_may_defs); i++)
- {
- tree v_may_def = V_MAY_DEF_RESULT (v_may_defs, i);
+ if (TREE_CODE (stmt) == PHI_NODE)
+ return SSA_NAME_VERSION (PHI_RESULT (stmt)) + max_stmt_uid;
- /* Find any uses in the PHI which match V_MAY_DEF and replace
- them with the appropriate V_MAY_DEF_OP. */
- for (j = 0; j < PHI_NUM_ARGS (phi); j++)
- if (v_may_def == PHI_ARG_DEF (phi, j))
- SET_PHI_ARG_DEF (phi, j, V_MAY_DEF_OP (v_may_defs, i));
- }
+ return stmt_ann (stmt)->uid;
}
-/* Replace the V_MAY_DEF_OPs in STMT1 which match V_MAY_DEF_RESULTs
- in STMT2 with the appropriate V_MAY_DEF_OPs from STMT2. */
-
-static void
-fix_stmt_v_may_defs (tree stmt1, tree stmt2)
-{
- stmt_ann_t ann1 = stmt_ann (stmt1);
- stmt_ann_t ann2 = stmt_ann (stmt2);
- v_may_def_optype v_may_defs1;
- v_may_def_optype v_may_defs2;
- unsigned int i, j;
-
- get_stmt_operands (stmt1);
- get_stmt_operands (stmt2);
- v_may_defs1 = V_MAY_DEF_OPS (ann1);
- v_may_defs2 = V_MAY_DEF_OPS (ann2);
-
- /* Walk each V_MAY_DEF_OP in stmt1. */
- for (i = 0; i < NUM_V_MAY_DEFS (v_may_defs1); i++)
- {
- tree v_may_def1 = V_MAY_DEF_OP (v_may_defs1, i);
-
- /* Find the appropriate V_MAY_DEF_RESULT in STMT2. */
- for (j = 0; j < NUM_V_MAY_DEFS (v_may_defs2); j++)
- {
- if (v_may_def1 == V_MAY_DEF_RESULT (v_may_defs2, j))
- {
- /* Update. */
- SET_V_MAY_DEF_OP (v_may_defs1, i, V_MAY_DEF_OP (v_may_defs2, j));
- break;
- }
- }
-
-#ifdef ENABLE_CHECKING
- /* If we did not find a corresponding V_MAY_DEF_RESULT, then something
- has gone terribly wrong. */
- if (j == NUM_V_MAY_DEFS (v_may_defs2))
- abort ();
-#endif
-
- }
-}
-
-
/* Set bit UID in bitmaps GLOBAL and *LOCAL, creating *LOCAL as needed. */
+
static void
record_voperand_set (bitmap global, bitmap *local, unsigned int uid)
{
bitmap_set_bit (*local, uid);
bitmap_set_bit (global, uid);
}
+
/* Initialize block local data structures. */
static void
bool recycled)
{
struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
+ = VEC_last (void_p, walk_data->block_data_stack);
/* If we are given a recycled block local data structure, ensure any
bitmap associated with the block is cleared. */
}
}
+/* Helper function for memory_address_same via walk_tree. Returns
+ non-NULL if it finds an SSA_NAME which is part of the address,
+ such that the definition of the SSA_NAME post-dominates the store
+ we want to delete but not the store that we believe makes it
+ redundant. This indicates that the address may change between
+ the two stores. */
+
+static tree
+memory_ssa_name_same (tree *expr_p, int *walk_subtrees ATTRIBUTE_UNUSED,
+ void *data)
+{
+ struct address_walk_data *walk_data = data;
+ tree expr = *expr_p;
+ tree def_stmt;
+ basic_block def_bb;
+
+ if (TREE_CODE (expr) != SSA_NAME)
+ return NULL_TREE;
+
+ /* If we've found a default definition, then there's no problem. Both
+ stores will post-dominate it. And def_bb will be NULL. */
+ if (expr == default_def (SSA_NAME_VAR (expr)))
+ return NULL_TREE;
+
+ def_stmt = SSA_NAME_DEF_STMT (expr);
+ def_bb = bb_for_stmt (def_stmt);
+
+ /* DEF_STMT must dominate both stores. So if it is in the same
+ basic block as one, it does not post-dominate that store. */
+ if (walk_data->store1_bb != def_bb
+ && dominated_by_p (CDI_POST_DOMINATORS, walk_data->store1_bb, def_bb))
+ {
+ if (walk_data->store2_bb == def_bb
+ || !dominated_by_p (CDI_POST_DOMINATORS, walk_data->store2_bb,
+ def_bb))
+ /* Return non-NULL to stop the walk. */
+ return def_stmt;
+ }
+
+ return NULL_TREE;
+}
+
+/* Return TRUE if the destination memory address in STORE1 and STORE2
+ might be modified after STORE1, before control reaches STORE2. */
+
+static bool
+memory_address_same (tree store1, tree store2)
+{
+ struct address_walk_data walk_data;
+
+ walk_data.store1_bb = bb_for_stmt (store1);
+ walk_data.store2_bb = bb_for_stmt (store2);
+
+ return (walk_tree (&TREE_OPERAND (store1, 0), memory_ssa_name_same,
+ &walk_data, NULL)
+ == NULL);
+}
+
/* Attempt to eliminate dead stores in the statement referenced by BSI.
A dead store is a store into a memory location which will later be
block_stmt_iterator bsi)
{
struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
+ = VEC_last (void_p, walk_data->block_data_stack);
struct dse_global_data *dse_gd = walk_data->global_data;
tree stmt = bsi_stmt (bsi);
stmt_ann_t ann = stmt_ann (stmt);
- v_may_def_optype v_may_defs;
-
- get_stmt_operands (stmt);
- v_may_defs = V_MAY_DEF_OPS (ann);
- /* If this statement has no virtual uses, then there is nothing
+ /* If this statement has no virtual defs, then there is nothing
to do. */
- if (NUM_V_MAY_DEFS (v_may_defs) == 0)
+ if (ZERO_SSA_OPERANDS (stmt, (SSA_OP_VMAYDEF|SSA_OP_VMUSTDEF)))
return;
/* We know we have virtual definitions. If this is a MODIFY_EXPR that's
not also a function call, then record it into our table. */
if (get_call_expr_in (stmt))
return;
+
+ if (ann->has_volatile_ops)
+ return;
+
if (TREE_CODE (stmt) == MODIFY_EXPR)
{
- dataflow_t df = get_immediate_uses (stmt);
- unsigned int num_uses = num_immediate_uses (df);
- tree use;
- tree skipped_phi;
+ use_operand_p first_use_p = NULL_USE_OPERAND_P;
+ use_operand_p use_p = NULL;
+ tree use, use_stmt, temp;
+ tree defvar = NULL_TREE, usevar = NULL_TREE;
+ bool fail = false;
+ use_operand_p var2;
+ def_operand_p var1;
+ ssa_op_iter op_iter;
+
+ /* We want to verify that each virtual definition in STMT has
+ precisely one use and that all the virtual definitions are
+ used by the same single statement. When complete, we
+ want USE_STMT to refer to the one statement which uses
+ all of the virtual definitions from STMT. */
+ use_stmt = NULL;
+ FOR_EACH_SSA_MUST_AND_MAY_DEF_OPERAND (var1, var2, stmt, op_iter)
+ {
+ defvar = DEF_FROM_PTR (var1);
+ usevar = USE_FROM_PTR (var2);
+ /* If this virtual def does not have precisely one use, then
+ we will not be able to eliminate STMT. */
+ if (num_imm_uses (defvar) != 1)
+ {
+ fail = true;
+ break;
+ }
- /* If there are no uses then there is nothing left to do. */
- if (num_uses == 0)
+ /* Get the one and only immediate use of DEFVAR. */
+ single_imm_use (defvar, &use_p, &temp);
+ gcc_assert (use_p != NULL_USE_OPERAND_P);
+ first_use_p = use_p;
+ use = USE_FROM_PTR (use_p);
+
+ /* If the immediate use of DEF_VAR is not the same as the
+ previously find immediate uses, then we will not be able
+ to eliminate STMT. */
+ if (use_stmt == NULL)
+ use_stmt = temp;
+ else if (temp != use_stmt)
+ {
+ fail = true;
+ break;
+ }
+ }
+
+ if (fail)
{
record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
return;
}
- use = immediate_use (df, 0);
- skipped_phi = NULL;
-
/* Skip through any PHI nodes we have already seen if the PHI
represents the only use of this store.
Note this does not handle the case where the store has
- multiple V_MAY_DEFs which all reach a set of PHI nodes in the
+ multiple V_{MAY,MUST}_DEFs which all reach a set of PHI nodes in the
same block. */
- while (num_uses == 1
- && TREE_CODE (use) == PHI_NODE
- && bitmap_bit_p (dse_gd->stores, stmt_ann (use)->uid))
+ while (use_p != NULL_USE_OPERAND_P
+ && TREE_CODE (use_stmt) == PHI_NODE
+ && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt)))
{
- /* Record the first PHI we skip so that we can fix its
- uses if we find that STMT is a dead store. */
- if (!skipped_phi)
- skipped_phi = use;
+ /* A PHI node can both define and use the same SSA_NAME if
+ the PHI is at the top of a loop and the PHI_RESULT is
+ a loop invariant and copies have not been fully propagated.
+
+ The safe thing to do is exit assuming no optimization is
+ possible. */
+ if (SSA_NAME_DEF_STMT (PHI_RESULT (use_stmt)) == use_stmt)
+ return;
/* Skip past this PHI and loop again in case we had a PHI
chain. */
- df = get_immediate_uses (use);
- num_uses = num_immediate_uses (df);
- use = immediate_use (df, 0);
+ if (single_imm_use (PHI_RESULT (use_stmt), &use_p, &use_stmt))
+ use = USE_FROM_PTR (use_p);
}
/* If we have precisely one immediate use at this point, then we may
- have found redundant store. */
- if (num_uses == 1
- && bitmap_bit_p (dse_gd->stores, stmt_ann (use)->uid)
+ have found redundant store. Make sure that the stores are to
+ the same memory location. This includes checking that any
+ SSA-form variables in the address will have the same values. */
+ if (use_p != NULL_USE_OPERAND_P
+ && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
&& operand_equal_p (TREE_OPERAND (stmt, 0),
- TREE_OPERAND (use, 0), 0))
+ TREE_OPERAND (use_stmt, 0), 0)
+ && memory_address_same (stmt, use_stmt))
{
- /* We need to fix the operands if either the first PHI we
- skipped, or the store which we are not deleting if we did
- not skip any PHIs. */
- if (skipped_phi)
- fix_phi_uses (skipped_phi, stmt);
- else
- fix_stmt_v_may_defs (use, stmt);
+ /* Make sure we propagate the ABNORMAL bit setting. */
+ if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (first_use_p)))
+ SSA_NAME_OCCURS_IN_ABNORMAL_PHI (usevar) = 1;
if (dump_file && (dump_flags & TDF_DETAILS))
{
print_generic_expr (dump_file, bsi_stmt (bsi), dump_flags);
fprintf (dump_file, "'\n");
}
+ /* Then we need to fix the operand of the consuming stmt. */
+ FOR_EACH_SSA_MUST_AND_MAY_DEF_OPERAND (var1, var2, stmt, op_iter)
+ {
+ single_imm_use (DEF_FROM_PTR (var1), &use_p, &temp);
+ SET_USE (use_p, USE_FROM_PTR (var2));
+ }
+ /* Remove the dead store. */
+ bsi_remove (&bsi, true);
- /* Any immediate uses which reference STMT need to instead
- reference the new consumer, either SKIPPED_PHI or USE.
- This allows us to cascade dead stores. */
- redirect_immediate_uses (stmt, skipped_phi ? skipped_phi : use);
-
- /* Finally remove the dead store. */
- bsi_remove (&bsi);
+ /* And release any SSA_NAMEs set in this statement back to the
+ SSA_NAME manager. */
+ release_defs (stmt);
}
record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
dse_record_phis (struct dom_walk_data *walk_data, basic_block bb)
{
struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
+ = VEC_last (void_p, walk_data->block_data_stack);
struct dse_global_data *dse_gd = walk_data->global_data;
tree phi;
for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
- if (need_imm_uses_for (PHI_RESULT (phi)))
+ if (!is_gimple_reg (PHI_RESULT (phi)))
record_voperand_set (dse_gd->stores,
&bd->stores,
- get_stmt_ann (phi)->uid);
+ get_stmt_uid (phi));
}
static void
basic_block bb ATTRIBUTE_UNUSED)
{
struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
+ = VEC_last (void_p, walk_data->block_data_stack);
struct dse_global_data *dse_gd = walk_data->global_data;
bitmap stores = dse_gd->stores;
unsigned int i;
+ bitmap_iterator bi;
/* Unwind the stores noted in this basic block. */
if (bd->stores)
- EXECUTE_IF_SET_IN_BITMAP (bd->stores, 0, i, bitmap_clear_bit (stores, i););
+ EXECUTE_IF_SET_IN_BITMAP (bd->stores, 0, i, bi)
+ {
+ bitmap_clear_bit (stores, i);
+ }
}
-static void
+static unsigned int
tree_ssa_dse (void)
{
struct dom_walk_data walk_data;
struct dse_global_data dse_gd;
- unsigned int uid = 0;
basic_block bb;
/* Create a UID for each statement in the function. Ordering of the
UIDs is not important for this pass. */
+ max_stmt_uid = 0;
FOR_EACH_BB (bb)
{
block_stmt_iterator bsi;
- tree phi;
for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- stmt_ann (bsi_stmt (bsi))->uid = uid++;
-
- for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
- stmt_ann (phi)->uid = uid++;
+ stmt_ann (bsi_stmt (bsi))->uid = max_stmt_uid++;
}
/* We might consider making this a property of each pass so that it
dominators. */
calculate_dominance_info (CDI_POST_DOMINATORS);
- /* We also need immediate use information for virtual operands. */
- compute_immediate_uses (TDFA_USE_VOPS, need_imm_uses_for);
-
/* Dead store elimination is fundamentally a walk of the post-dominator
tree and a backwards walk of statements within each block. */
walk_data.walk_stmts_backward = true;
walk_data.after_dom_children_before_stmts = NULL;
walk_data.after_dom_children_walk_stmts = NULL;
walk_data.after_dom_children_after_stmts = dse_finalize_block;
+ walk_data.interesting_blocks = NULL;
walk_data.block_local_data_size = sizeof (struct dse_block_local_data);
/* This is the main hash table for the dead store elimination pass. */
- dse_gd.stores = BITMAP_XMALLOC ();
+ dse_gd.stores = BITMAP_ALLOC (NULL);
walk_data.global_data = &dse_gd;
/* Initialize the dominator walker. */
fini_walk_dominator_tree (&walk_data);
/* Release the main bitmap. */
- BITMAP_XFREE (dse_gd.stores);
-
- /* Free dataflow information. It's probably out of date now anyway. */
- free_df ();
+ BITMAP_FREE (dse_gd.stores);
/* For now, just wipe the post-dominator information. */
free_dominance_info (CDI_POST_DOMINATORS);
+ return 0;
}
static bool
NULL, /* next */
0, /* static_pass_number */
TV_TREE_DSE, /* tv_id */
- PROP_cfg | PROP_ssa
+ PROP_cfg
+ | PROP_ssa
| PROP_alias, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */
- | TODO_verify_ssa,
- 0 /* letter */
+ TODO_dump_func
+ | TODO_ggc_collect
+ | TODO_verify_ssa, /* todo_flags_finish */
+ 0 /* letter */
};
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