/* Dead store elimination
- Copyright (C) 2004, 2005 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2, or (at your option)
+the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful,
GNU General Public License for more details.
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. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
#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);
bool recycled)
{
struct dse_block_local_data *bd
- = VEC_last (void_p, walk_data->block_data_stack);
+ = (struct dse_block_local_data *)
+ 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 = (struct address_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 (SSA_NAME_IS_DEFAULT_DEF (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 (&GIMPLE_STMT_OPERAND (store1, 0), memory_ssa_name_same,
+ &walk_data, NULL)
+ == NULL);
+}
+
+/* Return true if there is a stmt that kills the lhs of STMT and is in the
+ virtual def-use chain of STMT without a use inbetween the kill and STMT.
+ Returns false if no such stmt is found.
+ *FIRST_USE_P is set to the first use of the single virtual def of
+ STMT. *USE_P is set to the vop killed by *USE_STMT. */
+
+static bool
+get_kill_of_stmt_lhs (tree stmt,
+ use_operand_p * first_use_p,
+ use_operand_p * use_p, tree * use_stmt)
+{
+ tree lhs;
+
+ gcc_assert (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT);
+
+ lhs = GIMPLE_STMT_OPERAND (stmt, 0);
+
+ /* We now walk the chain of single uses of the single VDEFs.
+ We succeeded finding a kill if the lhs of the use stmt is
+ equal to the original lhs. We can keep walking to the next
+ use if there are no possible uses of the original lhs in
+ the stmt. */
+ do
+ {
+ tree use_lhs, use_rhs;
+ def_operand_p def_p;
+
+ /* The stmt must have a single VDEF. */
+ def_p = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_VDEF);
+ if (def_p == NULL_DEF_OPERAND_P)
+ return false;
+
+ /* Get the single immediate use of the def. */
+ if (!single_imm_use (DEF_FROM_PTR (def_p), first_use_p, &stmt))
+ return false;
+ first_use_p = use_p;
+
+ /* If there are possible hidden uses, give up. */
+ if (TREE_CODE (stmt) != GIMPLE_MODIFY_STMT)
+ return false;
+ use_rhs = GIMPLE_STMT_OPERAND (stmt, 1);
+ if (TREE_CODE (use_rhs) == CALL_EXPR
+ || (!is_gimple_min_invariant (use_rhs)
+ && TREE_CODE (use_rhs) != SSA_NAME))
+ return false;
+
+ /* If the use stmts lhs matches the original lhs we have
+ found the kill, otherwise continue walking. */
+ use_lhs = GIMPLE_STMT_OPERAND (stmt, 0);
+ if (operand_equal_p (use_lhs, lhs, 0))
+ {
+ *use_stmt = stmt;
+ return true;
+ }
+ }
+ while (1);
+}
+
+/* A helper of dse_optimize_stmt.
+ Given a GIMPLE_MODIFY_STMT in STMT, check that each VDEF has one
+ use, and that one use is another VDEF clobbering the first one.
+
+ Return TRUE if the above conditions are met, otherwise FALSE. */
+
+static bool
+dse_possible_dead_store_p (tree stmt,
+ use_operand_p *first_use_p,
+ use_operand_p *use_p,
+ tree *use_stmt,
+ struct dse_global_data *dse_gd,
+ struct dse_block_local_data *bd)
+{
+ ssa_op_iter op_iter;
+ bool fail = false;
+ def_operand_p var1;
+ vuse_vec_p vv;
+ tree defvar = NULL_TREE, temp;
+ tree prev_defvar = NULL_TREE;
+ stmt_ann_t ann = stmt_ann (stmt);
+
+ /* 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_VDEF_OPERAND (var1, vv, stmt, op_iter)
+ {
+ defvar = DEF_FROM_PTR (var1);
+
+ /* If this virtual def does not have precisely one use, then
+ we will not be able to eliminate STMT. */
+ if (!has_single_use (defvar))
+ {
+ fail = true;
+ break;
+ }
+
+ /* 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;
+
+ /* In the case of memory partitions, we may get:
+
+ # MPT.764_162 = VDEF <MPT.764_161(D)>
+ x = {};
+ # MPT.764_167 = VDEF <MPT.764_162>
+ y = {};
+
+ So we must make sure we're talking about the same LHS.
+ */
+ if (TREE_CODE (temp) == GIMPLE_MODIFY_STMT)
+ {
+ tree base1 = get_base_address (GIMPLE_STMT_OPERAND (stmt, 0));
+ tree base2 = get_base_address (GIMPLE_STMT_OPERAND (temp, 0));
+
+ while (base1 && INDIRECT_REF_P (base1))
+ base1 = TREE_OPERAND (base1, 0);
+ while (base2 && INDIRECT_REF_P (base2))
+ base2 = TREE_OPERAND (base2, 0);
+
+ if (base1 != base2)
+ {
+ fail = true;
+ break;
+ }
+ }
+
+ /* 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;
+ prev_defvar = defvar;
+ }
+ else if (temp != *use_stmt)
+ {
+ fail = true;
+ break;
+ }
+ }
+
+ if (fail)
+ {
+ record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
+ return false;
+ }
+
+ /* 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 VDEFs which all reach a set of PHI nodes in the same block. */
+ while (*use_p != NULL_USE_OPERAND_P
+ && TREE_CODE (*use_stmt) == PHI_NODE
+ && bitmap_bit_p (dse_gd->stores, get_stmt_uid (*use_stmt)))
+ {
+ /* 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 false;
+
+ /* Skip past this PHI and loop again in case we had a PHI
+ chain. */
+ single_imm_use (PHI_RESULT (*use_stmt), use_p, use_stmt);
+ }
+
+ return true;
+}
+
+
/* 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
- = VEC_last (void_p, walk_data->block_data_stack);
- struct dse_global_data *dse_gd = walk_data->global_data;
+ = (struct dse_block_local_data *)
+ VEC_last (void_p, walk_data->block_data_stack);
+ struct dse_global_data *dse_gd
+ = (struct dse_global_data *) walk_data->global_data;
tree stmt = bsi_stmt (bsi);
stmt_ann_t ann = stmt_ann (stmt);
/* If this statement has no virtual defs, then there is nothing
to do. */
- if (ZERO_SSA_OPERANDS (stmt, (SSA_OP_VMAYDEF|SSA_OP_VMUSTDEF)))
+ if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VDEF))
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. */
+ /* We know we have virtual definitions. If this is a GIMPLE_MODIFY_STMT
+ 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)
+ if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT)
{
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);
+ tree use_stmt;
- /* 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;
- }
-
- /* 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;
- }
-
- /* 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,MUST}_DEFs which all reach a set of PHI nodes in the
- same block. */
- while (use_p != NULL_USE_OPERAND_P
- && TREE_CODE (use_stmt) == PHI_NODE
- && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt)))
- {
- /* Skip past this PHI and loop again in case we had a PHI
- chain. */
- if (single_imm_use (PHI_RESULT (use_stmt), &use_p, &use_stmt))
- use = USE_FROM_PTR (use_p);
- }
+ if (!dse_possible_dead_store_p (stmt, &first_use_p, &use_p, &use_stmt,
+ dse_gd, bd))
+ return;
/* If we have precisely one immediate use at this point, then we may
- have found redundant store. */
+ 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 (GIMPLE_STMT_OPERAND (stmt, 0),
+ GIMPLE_STMT_OPERAND (use_stmt, 0), 0)
+ && memory_address_same (stmt, use_stmt))
+ {
+ /* If we have precisely one immediate use at this point, but
+ the stores are not to the same memory location then walk the
+ virtual def-use chain to get the stmt which stores to that same
+ memory location. */
+ if (!get_kill_of_stmt_lhs (stmt, &first_use_p, &use_p, &use_stmt))
+ {
+ record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
+ return;
+ }
+ }
+
+ /* If we have precisely one immediate use at this point and the
+ stores are to the same memory location or there is a chain of
+ virtual uses from stmt and the stmt which stores to that same
+ memory location, then we may have found redundant store. */
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_stmt, 0), 0))
+ && operand_equal_p (GIMPLE_STMT_OPERAND (stmt, 0),
+ GIMPLE_STMT_OPERAND (use_stmt, 0), 0)
+ && memory_address_same (stmt, use_stmt))
{
- tree def;
- ssa_op_iter iter;
-
- /* 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;
- /* Then we need to fix the operand of the consuming stmt. */
- SET_USE (first_use_p, usevar);
+ ssa_op_iter op_iter;
+ def_operand_p var1;
+ vuse_vec_p vv;
+ tree stmt_lhs;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "'\n");
}
- /* Remove the dead store. */
- bsi_remove (&bsi);
+ /* Then we need to fix the operand of the consuming stmt. */
+ stmt_lhs = USE_FROM_PTR (first_use_p);
+ FOR_EACH_SSA_VDEF_OPERAND (var1, vv, stmt, op_iter)
+ {
+ tree usevar, temp;
- /* The virtual defs for the dead statement will need to be
- updated. Since these names are going to disappear,
- FUD chains for uses downstream need to be updated. */
- FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_VIRTUAL_DEFS)
- mark_sym_for_renaming (SSA_NAME_VAR (def));
+ single_imm_use (DEF_FROM_PTR (var1), &use_p, &temp);
+ gcc_assert (VUSE_VECT_NUM_ELEM (*vv) == 1);
+ usevar = VUSE_ELEMENT_VAR (*vv, 0);
+ SET_USE (use_p, usevar);
+
+ /* Make sure we propagate the ABNORMAL bit setting. */
+ if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (stmt_lhs))
+ SSA_NAME_OCCURS_IN_ABNORMAL_PHI (usevar) = 1;
+ }
+
+ /* Remove the dead store. */
+ bsi_remove (&bsi, true);
/* And release any SSA_NAMEs set in this statement back to the
SSA_NAME manager. */
dse_record_phis (struct dom_walk_data *walk_data, basic_block bb)
{
struct dse_block_local_data *bd
- = VEC_last (void_p, walk_data->block_data_stack);
- struct dse_global_data *dse_gd = walk_data->global_data;
+ = (struct dse_block_local_data *)
+ VEC_last (void_p, walk_data->block_data_stack);
+ struct dse_global_data *dse_gd
+ = (struct dse_global_data *) walk_data->global_data;
tree phi;
for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
basic_block bb ATTRIBUTE_UNUSED)
{
struct dse_block_local_data *bd
- = VEC_last (void_p, walk_data->block_data_stack);
- struct dse_global_data *dse_gd = walk_data->global_data;
+ = (struct dse_block_local_data *)
+ VEC_last (void_p, walk_data->block_data_stack);
+ struct dse_global_data *dse_gd
+ = (struct dse_global_data *) walk_data->global_data;
bitmap stores = dse_gd->stores;
unsigned int i;
bitmap_iterator bi;
}
}
-static void
+/* Main entry point. */
+
+static unsigned int
tree_ssa_dse (void)
{
struct dom_walk_data walk_data;
/* For now, just wipe the post-dominator information. */
free_dominance_info (CDI_POST_DOMINATORS);
+ return 0;
}
static bool
0, /* todo_flags_start */
TODO_dump_func
| TODO_ggc_collect
- | TODO_update_ssa
| TODO_verify_ssa, /* todo_flags_finish */
0 /* letter */
};
+
+/* A very simple dead store pass eliminating write only local variables.
+ The pass does not require alias information and thus can be run before
+ inlining to quickly eliminate artifacts of some common C++ constructs. */
+
+static unsigned int
+execute_simple_dse (void)
+{
+ block_stmt_iterator bsi;
+ basic_block bb;
+ bitmap variables_loaded = BITMAP_ALLOC (NULL);
+ unsigned int todo = 0;
+
+ /* Collect into VARIABLES LOADED all variables that are read in function
+ body. */
+ FOR_EACH_BB (bb)
+ for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
+ if (LOADED_SYMS (bsi_stmt (bsi)))
+ bitmap_ior_into (variables_loaded,
+ LOADED_SYMS (bsi_stmt (bsi)));
+
+ /* Look for statements writing into the write only variables.
+ And try to remove them. */
+
+ FOR_EACH_BB (bb)
+ for (bsi = bsi_start (bb); !bsi_end_p (bsi);)
+ {
+ tree stmt = bsi_stmt (bsi), op;
+ bool removed = false;
+ ssa_op_iter iter;
+
+ if (STORED_SYMS (stmt) && TREE_CODE (stmt) == GIMPLE_MODIFY_STMT
+ && TREE_CODE (stmt) != RETURN_EXPR
+ && !bitmap_intersect_p (STORED_SYMS (stmt), variables_loaded))
+ {
+ unsigned int i;
+ bitmap_iterator bi;
+ bool dead = true;
+
+
+
+ /* See if STMT only stores to write-only variables and
+ verify that there are no volatile operands. tree-ssa-operands
+ sets has_volatile_ops flag for all statements involving
+ reads and writes when aliases are not built to prevent passes
+ from removing them as dead. The flag thus has no use for us
+ and we need to look into all operands. */
+
+ EXECUTE_IF_SET_IN_BITMAP (STORED_SYMS (stmt), 0, i, bi)
+ {
+ tree var = referenced_var_lookup (i);
+ if (TREE_ADDRESSABLE (var)
+ || is_global_var (var)
+ || TREE_THIS_VOLATILE (var))
+ dead = false;
+ }
+
+ if (dead && LOADED_SYMS (stmt))
+ EXECUTE_IF_SET_IN_BITMAP (LOADED_SYMS (stmt), 0, i, bi)
+ if (TREE_THIS_VOLATILE (referenced_var_lookup (i)))
+ dead = false;
+
+ if (dead)
+ FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_ALL_OPERANDS)
+ if (TREE_THIS_VOLATILE (op))
+ dead = false;
+
+ /* Look for possible occurence var = indirect_ref (...) where
+ indirect_ref itself is volatile. */
+
+ if (dead && TREE_THIS_VOLATILE (GIMPLE_STMT_OPERAND (stmt, 1)))
+ dead = false;
+
+ if (dead)
+ {
+ tree call = get_call_expr_in (stmt);
+
+ /* When LHS of var = call (); is dead, simplify it into
+ call (); saving one operand. */
+ if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT
+ && call
+ && TREE_SIDE_EFFECTS (call))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Deleted LHS of call: ");
+ print_generic_stmt (dump_file, stmt, TDF_SLIM);
+ fprintf (dump_file, "\n");
+ }
+ push_stmt_changes (bsi_stmt_ptr (bsi));
+ TREE_BLOCK (call) = TREE_BLOCK (stmt);
+ bsi_replace (&bsi, call, false);
+ maybe_clean_or_replace_eh_stmt (stmt, call);
+ mark_symbols_for_renaming (call);
+ pop_stmt_changes (bsi_stmt_ptr (bsi));
+ }
+ else
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, " Deleted dead store '");
+ print_generic_expr (dump_file, stmt, dump_flags);
+ fprintf (dump_file, "'\n");
+ }
+ removed = true;
+ bsi_remove (&bsi, true);
+ todo |= TODO_cleanup_cfg;
+ }
+ todo |= TODO_remove_unused_locals | TODO_ggc_collect;
+ }
+ }
+ if (!removed)
+ bsi_next (&bsi);
+ }
+ BITMAP_FREE (variables_loaded);
+ return todo;
+}
+
+struct tree_opt_pass pass_simple_dse =
+{
+ "sdse", /* name */
+ NULL, /* gate */
+ execute_simple_dse, /* execute */
+ NULL, /* sub */
+ NULL, /* next */
+ 0, /* static_pass_number */
+ 0, /* tv_id */
+ PROP_ssa, /* properties_required */
+ 0, /* properties_provided */
+ 0, /* properties_destroyed */
+ 0, /* todo_flags_start */
+ TODO_dump_func, /* todo_flags_finish */
+ 0 /* letter */
+};
OSDN Git Service
