/* Dead store elimination
- Copyright (C) 2004, 2005 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
+ 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"
#include "tree-dump.h"
#include "domwalk.h"
#include "flags.h"
+#include "langhooks.h"
/* This file implements dead store elimination.
relationship between dead store and redundant load elimination. In
fact, they are the same transformation applied to different views of
the CFG. */
-
+
struct dse_global_data
{
};
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);
-static void dse_optimize_stmt (struct dom_walk_data *,
- basic_block,
- 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 dse_enter_block (struct dom_walk_data *, basic_block);
+static void dse_leave_block (struct dom_walk_data *, basic_block);
static void record_voperand_set (bitmap, bitmap *, unsigned int);
-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. */
static unsigned
-get_stmt_uid (tree stmt)
+get_stmt_uid (gimple stmt)
{
- if (TREE_CODE (stmt) == PHI_NODE)
- return SSA_NAME_VERSION (PHI_RESULT (stmt)) + max_stmt_uid;
-
- return stmt_ann (stmt)->uid;
-}
+ if (gimple_code (stmt) == GIMPLE_PHI)
+ return SSA_NAME_VERSION (gimple_phi_result (stmt))
+ + gimple_stmt_max_uid (cfun);
-/* 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);
+ return gimple_uid (stmt);
}
-
/* 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);
+ = (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. */
}
}
+/* A helper of dse_optimize_stmt.
+ Given a GIMPLE_ASSIGN in STMT, find a candidate statement *USE_STMT that
+ may prove STMT to be dead.
+ Return TRUE if the above conditions are met, otherwise FALSE. */
+
+static bool
+dse_possible_dead_store_p (gimple stmt, gimple *use_stmt)
+{
+ gimple temp;
+ unsigned cnt = 0;
+
+ *use_stmt = NULL;
+
+ /* Find the first dominated statement that clobbers (part of) the
+ memory stmt stores to with no intermediate statement that may use
+ part of the memory stmt stores. That is, find a store that may
+ prove stmt to be a dead store. */
+ temp = stmt;
+ do
+ {
+ gimple prev, use_stmt;
+ imm_use_iterator ui;
+ bool fail = false;
+ tree defvar;
+
+ /* Limit stmt walking to be linear in the number of possibly
+ dead stores. */
+ if (++cnt > 256)
+ return false;
+
+ if (gimple_code (temp) == GIMPLE_PHI)
+ defvar = PHI_RESULT (temp);
+ else
+ defvar = gimple_vdef (temp);
+ prev = temp;
+ temp = NULL;
+ FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
+ {
+ cnt++;
+
+ /* In simple cases we can look through PHI nodes, but we
+ have to be careful with loops and with memory references
+ containing operands that are also operands of PHI nodes.
+ See gcc.c-torture/execute/20051110-*.c. */
+ if (gimple_code (use_stmt) == GIMPLE_PHI)
+ {
+ if (temp
+ /* We can look through PHIs to post-dominated regions
+ without worrying if the use not also dominates prev
+ (in which case it would be a loop PHI with the use
+ in a latch block). */
+ || gimple_bb (prev) == gimple_bb (use_stmt)
+ || !dominated_by_p (CDI_POST_DOMINATORS,
+ gimple_bb (prev), gimple_bb (use_stmt))
+ || dominated_by_p (CDI_DOMINATORS,
+ gimple_bb (prev), gimple_bb (use_stmt)))
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ temp = use_stmt;
+ }
+ /* If the statement is a use the store is not dead. */
+ else if (ref_maybe_used_by_stmt_p (use_stmt,
+ gimple_assign_lhs (stmt)))
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ /* If this is a store, remember it or bail out if we have
+ multiple ones (the will be in different CFG parts then). */
+ else if (gimple_vdef (use_stmt))
+ {
+ if (temp)
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ temp = use_stmt;
+ }
+ }
+
+ if (fail)
+ return false;
+
+ /* If we didn't find any definition this means the store is dead
+ if it isn't a store to global reachable memory. In this case
+ just pretend the stmt makes itself dead. Otherwise fail. */
+ if (!temp)
+ {
+ if (is_hidden_global_store (stmt))
+ return false;
+
+ temp = stmt;
+ break;
+ }
+ }
+ /* We deliberately stop on clobbering statements and not only on
+ killing ones to make walking cheaper. Otherwise we can just
+ continue walking until both stores have equal reference trees. */
+ while (!stmt_may_clobber_ref_p (temp, gimple_assign_lhs (stmt)));
+
+ if (!is_gimple_assign (temp))
+ return false;
+
+ *use_stmt = temp;
+
+ 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
post dominates the first store, then the first store is dead. */
static void
-dse_optimize_stmt (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED,
- block_stmt_iterator bsi)
+dse_optimize_stmt (struct dse_global_data *dse_gd,
+ struct dse_block_local_data *bd,
+ gimple_stmt_iterator gsi)
{
- struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (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;
-
- v_may_defs = V_MAY_DEF_OPS (ann);
+ gimple stmt = gsi_stmt (gsi);
/* If this statement has no virtual defs, then there is nothing
to do. */
- if (NUM_V_MAY_DEFS (v_may_defs) == 0)
+ if (!gimple_vdef (stmt))
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))
+ /* We know we have virtual definitions. If this is a GIMPLE_ASSIGN
+ that's not also a function call, then record it into our table. */
+ if (is_gimple_call (stmt) && gimple_call_fndecl (stmt))
return;
- if (ann->has_volatile_ops)
+ if (gimple_has_volatile_ops (stmt))
return;
- if (TREE_CODE (stmt) == MODIFY_EXPR)
+ if (is_gimple_assign (stmt))
{
- unsigned int num_uses = 0, count = 0;
- use_operand_p first_use_p = NULL_USE_OPERAND_P;
- use_operand_p use_p;
- tree use, use_stmt;
- tree defvar = NULL_TREE, usevar = NULL_TREE;
- use_operand_p var2;
- def_operand_p var1;
- ssa_op_iter op_iter;
-
- FOR_EACH_SSA_MAYDEF_OPERAND (var1, var2, stmt, op_iter)
- {
- defvar = DEF_FROM_PTR (var1);
- usevar = USE_FROM_PTR (var2);
- num_uses += num_imm_uses (defvar);
- count++;
- if (num_uses > 1 || count > 1)
- break;
- }
+ gimple use_stmt;
- if (count == 1 && num_uses == 1)
- {
- single_imm_use (defvar, &use_p, &use_stmt);
- gcc_assert (use_p != NULL_USE_OPERAND_P);
- first_use_p = use_p;
- use = USE_FROM_PTR (use_p);
- }
- else
- {
- 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.
+ record_voperand_set (dse_gd->stores, &bd->stores, gimple_uid (stmt));
- 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
- 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, &use_stmt))
+ return;
- /* If we have precisely one immediate use at this point, 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))
+ /* 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 (bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
+ && operand_equal_p (gimple_assign_lhs (stmt),
+ gimple_assign_lhs (use_stmt), 0))
{
- 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);
+ /* If use_stmt is or might be a nop assignment, e.g. for
+ struct { ... } S a, b, *p; ...
+ b = a; b = b;
+ or
+ b = a; b = *p; where p might be &b,
+ or
+ *p = a; *p = b; where p might be &b,
+ or
+ *p = *u; *p = *v; where p might be v, then USE_STMT
+ acts as a use as well as definition, so store in STMT
+ is not dead. */
+ if (stmt != use_stmt
+ && !is_gimple_reg (gimple_assign_rhs1 (use_stmt))
+ && !is_gimple_min_invariant (gimple_assign_rhs1 (use_stmt))
+ /* ??? Should {} be invariant? */
+ && gimple_assign_rhs_code (use_stmt) != CONSTRUCTOR
+ && refs_may_alias_p (gimple_assign_lhs (use_stmt),
+ gimple_assign_rhs1 (use_stmt)))
+ return;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, " Deleted dead store '");
- print_generic_expr (dump_file, bsi_stmt (bsi), dump_flags);
+ print_gimple_stmt (dump_file, gsi_stmt (gsi), dump_flags, 0);
fprintf (dump_file, "'\n");
}
- /* Remove the dead store. */
- bsi_remove (&bsi);
+ /* Then we need to fix the operand of the consuming stmt. */
+ unlink_stmt_vdef (stmt);
- /* 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));
+ /* Remove the dead store. */
+ gsi_remove (&gsi, true);
/* 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);
}
}
/* Record that we have seen the PHIs at the start of BB which correspond
to virtual operands. */
static void
-dse_record_phis (struct dom_walk_data *walk_data, basic_block bb)
+dse_record_phi (struct dse_global_data *dse_gd,
+ struct dse_block_local_data *bd,
+ gimple phi)
+{
+ if (!is_gimple_reg (gimple_phi_result (phi)))
+ record_voperand_set (dse_gd->stores, &bd->stores, get_stmt_uid (phi));
+}
+
+static void
+dse_enter_block (struct dom_walk_data *walk_data, basic_block bb)
{
struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (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)))
- record_voperand_set (dse_gd->stores,
- &bd->stores,
- get_stmt_uid (phi));
+ = (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;
+ gimple_stmt_iterator gsi;
+
+ for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); gsi_prev (&gsi))
+ dse_optimize_stmt (dse_gd, bd, gsi);
+ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+ dse_record_phi (dse_gd, bd, gsi_stmt (gsi));
}
static void
-dse_finalize_block (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED)
+dse_leave_block (struct dom_walk_data *walk_data,
+ basic_block bb ATTRIBUTE_UNUSED)
{
struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (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;
struct dse_global_data dse_gd;
- 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;
-
- for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- stmt_ann (bsi_stmt (bsi))->uid = max_stmt_uid++;
- }
+ renumber_gimple_stmt_uids ();
/* We might consider making this a property of each pass so that it
can be [re]computed on an as-needed basis. Particularly since
this pass could be seen as an extension of DCE which needs post
dominators. */
calculate_dominance_info (CDI_POST_DOMINATORS);
+ calculate_dominance_info (CDI_DOMINATORS);
/* 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.dom_direction = CDI_POST_DOMINATORS;
walk_data.initialize_block_local_data = dse_initialize_block_local_data;
- walk_data.before_dom_children_before_stmts = NULL;
- walk_data.before_dom_children_walk_stmts = dse_optimize_stmt;
- walk_data.before_dom_children_after_stmts = dse_record_phis;
- 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.before_dom_children = dse_enter_block;
+ walk_data.after_dom_children = dse_leave_block;
walk_data.block_local_data_size = sizeof (struct dse_block_local_data);
/* For now, just wipe the post-dominator information. */
free_dominance_info (CDI_POST_DOMINATORS);
+ return 0;
}
static bool
return flag_tree_dse != 0;
}
-struct tree_opt_pass pass_dse = {
+struct gimple_opt_pass pass_dse =
+{
+ {
+ GIMPLE_PASS,
"dse", /* name */
gate_dse, /* gate */
tree_ssa_dse, /* execute */
NULL, /* next */
0, /* static_pass_number */
TV_TREE_DSE, /* tv_id */
- PROP_cfg
- | PROP_ssa
- | PROP_alias, /* properties_required */
+ PROP_cfg | PROP_ssa, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_dump_func
| TODO_ggc_collect
- | TODO_update_ssa
- | TODO_verify_ssa, /* todo_flags_finish */
- 0 /* letter */
+ | TODO_verify_ssa /* todo_flags_finish */
+ }
};
+
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