/* Dead store elimination
- Copyright (C) 2004, 2005, 2006 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, 51 Franklin Street, Fifth Floor,
-Boston, MA 02110-1301, USA. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "tree-dump.h"
#include "domwalk.h"
#include "flags.h"
-#include "hashtab.h"
-#include "sbitmap.h"
/* This file implements dead store elimination.
the CFG. */
-/* Given an aggregate, this records the parts of it which have been
- stored into. */
-struct aggregate_vardecl_d
-{
- /* The aggregate. */
- tree decl;
-
- /* Some aggregates are too big for us to handle or never get stored
- to as a whole. If this field is TRUE, we don't care about this
- aggregate. */
- bool ignore;
-
- /* Number of parts in the whole. */
- unsigned nparts;
-
- /* A bitmap of parts of the aggregate that have been set. If part N
- of an aggregate has been stored to, bit N should be on. */
- sbitmap parts_set;
-};
-
struct dse_global_data
{
/* This is the global bitmap for store statements.
that we want to record, set the bit corresponding to the statement's
unique ID in this bitmap. */
bitmap stores;
-
- /* A hash table containing the parts of an aggregate which have been
- stored to. */
- htab_t aggregate_vardecl;
};
/* We allocate a bitmap-per-block for stores which are encountered
static void dse_record_phis (struct dom_walk_data *, basic_block);
static void dse_finalize_block (struct dom_walk_data *, basic_block);
static void record_voperand_set (bitmap, bitmap *, unsigned int);
-static void dse_record_partial_aggregate_store (tree, struct dse_global_data *);
static unsigned max_stmt_uid; /* Maximal uid of a statement. Uids to phi
nodes are assigned using the versions of
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. */
memory_ssa_name_same (tree *expr_p, int *walk_subtrees ATTRIBUTE_UNUSED,
void *data)
{
- struct address_walk_data *walk_data = data;
+ struct address_walk_data *walk_data = (struct address_walk_data *) data;
tree expr = *expr_p;
tree def_stmt;
basic_block def_bb;
== 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
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. */
}
else if (temp != *use_stmt)
{
- /* The immediate use and the previously found immediate use
- must be the same, except... if they're uses of different
- parts of the whole. */
- if (TREE_CODE (defvar) == SSA_NAME
- && TREE_CODE (SSA_NAME_VAR (defvar)) == STRUCT_FIELD_TAG
- && TREE_CODE (prev_defvar) == SSA_NAME
- && TREE_CODE (SSA_NAME_VAR (prev_defvar)) == STRUCT_FIELD_TAG
- && (SFT_PARENT_VAR (SSA_NAME_VAR (defvar))
- == SFT_PARENT_VAR (SSA_NAME_VAR (prev_defvar))))
- ;
- else
- {
- fail = true;
- break;
- }
+ fail = true;
+ break;
}
}
if (fail)
{
record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
- dse_record_partial_aggregate_store (stmt, dse_gd);
return false;
}
}
-/* Given a DECL, return its AGGREGATE_VARDECL_D entry. If no entry is
- found and INSERT is TRUE, add a new entry. */
-
-static struct aggregate_vardecl_d *
-get_aggregate_vardecl (tree decl, struct dse_global_data *dse_gd, bool insert)
-{
- struct aggregate_vardecl_d av, *av_p;
- void **slot;
-
- av.decl = decl;
- slot = htab_find_slot (dse_gd->aggregate_vardecl, &av, insert ? INSERT : NO_INSERT);
-
-
- /* Not found, and we don't want to insert. */
- if (slot == NULL)
- return NULL;
-
- /* Create new entry. */
- if (*slot == NULL)
- {
- av_p = XNEW (struct aggregate_vardecl_d);
- av_p->decl = decl;
-
- /* Record how many parts the whole has. */
- if (TREE_CODE (TREE_TYPE (decl)) == COMPLEX_TYPE)
- av_p->nparts = 2;
- else if (TREE_CODE (TREE_TYPE (decl)) == RECORD_TYPE)
- {
- tree fields;
-
- /* Count the number of fields. */
- fields = TYPE_FIELDS (TREE_TYPE (decl));
- av_p->nparts = 0;
- while (fields)
- {
- av_p->nparts++;
- fields = TREE_CHAIN (fields);
- }
- }
- else
- abort ();
-
- av_p->ignore = true;
- av_p->parts_set = sbitmap_alloc (HOST_BITS_PER_LONG);
- sbitmap_zero (av_p->parts_set);
- *slot = av_p;
- }
- else
- av_p = (struct aggregate_vardecl_d *) *slot;
-
- return av_p;
-}
-
-
-/* If STMT is a partial store into an aggregate, record which part got set. */
-
-static void
-dse_record_partial_aggregate_store (tree stmt, struct dse_global_data *dse_gd)
-{
- tree lhs, decl;
- enum tree_code code;
- struct aggregate_vardecl_d *av_p;
- int part;
-
- gcc_assert (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT);
-
- lhs = GIMPLE_STMT_OPERAND (stmt, 0);
- code = TREE_CODE (lhs);
- if (code != IMAGPART_EXPR
- && code != REALPART_EXPR
- && code != COMPONENT_REF)
- return;
- decl = TREE_OPERAND (lhs, 0);
- /* Early bail on things like nested COMPONENT_REFs. */
- if (TREE_CODE (decl) != VAR_DECL)
- return;
- /* Early bail on unions. */
- if (code == COMPONENT_REF
- && TREE_CODE (TREE_TYPE (TREE_OPERAND (lhs, 0))) != RECORD_TYPE)
- return;
-
- av_p = get_aggregate_vardecl (decl, dse_gd, /*insert=*/false);
- /* Run away, this isn't an aggregate we care about. */
- if (!av_p || av_p->ignore)
- return;
-
- switch (code)
- {
- case IMAGPART_EXPR:
- part = 0;
- break;
- case REALPART_EXPR:
- part = 1;
- break;
- case COMPONENT_REF:
- {
- tree orig_field, fields;
- tree record_type = TREE_TYPE (TREE_OPERAND (lhs, 0));
-
- /* Get FIELD_DECL. */
- orig_field = TREE_OPERAND (lhs, 1);
-
- /* FIXME: Eeech, do this more efficiently. Perhaps
- calculate bit/byte offsets. */
- part = -1;
- fields = TYPE_FIELDS (record_type);
- while (fields)
- {
- ++part;
- if (fields == orig_field)
- break;
- fields = TREE_CHAIN (fields);
- }
- gcc_assert (part >= 0);
- }
- break;
- default:
- return;
- }
-
- /* Record which part was set. */
- SET_BIT (av_p->parts_set, part);
-}
-
-
-/* Return TRUE if all parts in an AGGREGATE_VARDECL have been set. */
-
-static inline bool
-dse_whole_aggregate_clobbered_p (struct aggregate_vardecl_d *av_p)
-{
- unsigned int i;
- sbitmap_iterator sbi;
- int nbits_set = 0;
-
- /* Count the number of partial stores (bits set). */
- EXECUTE_IF_SET_IN_SBITMAP (av_p->parts_set, 0, i, sbi)
- nbits_set++;
- return ((unsigned) nbits_set == av_p->nparts);
-}
-
-
-/* Return TRUE if STMT is a store into a whole aggregate whose parts we
- have already seen and recorded. */
-
-static bool
-dse_partial_kill_p (tree stmt, struct dse_global_data *dse_gd)
-{
- tree decl;
- struct aggregate_vardecl_d *av_p;
-
- /* Make sure this is a store into the whole. */
- if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT)
- {
- enum tree_code code;
-
- decl = GIMPLE_STMT_OPERAND (stmt, 0);
- code = TREE_CODE (TREE_TYPE (decl));
-
- if (code != COMPLEX_TYPE && code != RECORD_TYPE)
- return false;
-
- if (TREE_CODE (decl) != VAR_DECL)
- return false;
- }
- else
- return false;
-
- av_p = get_aggregate_vardecl (decl, dse_gd, /*insert=*/false);
- gcc_assert (av_p != NULL);
-
- return dse_whole_aggregate_clobbered_p (av_p);
-}
-
-
/* 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);
dse_gd, bd))
return;
- /* If this is a partial store into an aggregate, record it. */
- dse_record_partial_aggregate_store (stmt, dse_gd);
-
/* If we have precisely one immediate use at this point, then we may
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 (GIMPLE_STMT_OPERAND (stmt, 0),
- GIMPLE_STMT_OPERAND (use_stmt, 0), 0)
- || dse_partial_kill_p (stmt, dse_gd))
+ && operand_equal_p (GIMPLE_STMT_OPERAND (stmt, 0),
+ GIMPLE_STMT_OPERAND (use_stmt, 0), 0)
&& memory_address_same (stmt, use_stmt))
{
ssa_op_iter op_iter;
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;
}
}
-
-/* Hashing and equality functions for AGGREGATE_VARDECL. */
-
-static hashval_t
-aggregate_vardecl_hash (const void *p)
-{
- return htab_hash_pointer
- ((const void *)((const struct aggregate_vardecl_d *)p)->decl);
-}
-
-static int
-aggregate_vardecl_eq (const void *p1, const void *p2)
-{
- return ((const struct aggregate_vardecl_d *)p1)->decl
- == ((const struct aggregate_vardecl_d *)p2)->decl;
-}
-
-
-/* Free memory allocated by one entry in AGGREGATE_VARDECL. */
-
-static void
-aggregate_vardecl_free (void *p)
-{
- struct aggregate_vardecl_d *entry = (struct aggregate_vardecl_d *) p;
- sbitmap_free (entry->parts_set);
- free (entry);
-}
-
-
-/* Return true if STMT is a store into an entire aggregate. */
-
-static bool
-aggregate_whole_store_p (tree stmt)
-{
- if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT)
- {
- tree lhs = GIMPLE_STMT_OPERAND (stmt, 0);
- enum tree_code code = TREE_CODE (TREE_TYPE (lhs));
-
- if (code == COMPLEX_TYPE || code == RECORD_TYPE)
- return true;
- }
- return false;
-}
-
-
/* Main entry point. */
static unsigned int
struct dse_global_data dse_gd;
basic_block bb;
- dse_gd.aggregate_vardecl =
- htab_create (37, aggregate_vardecl_hash,
- aggregate_vardecl_eq, aggregate_vardecl_free);
-
+ /* 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))
- {
- tree stmt = bsi_stmt (bsi);
-
- /* Record aggregates which have been stored into as a whole. */
- if (aggregate_whole_store_p (stmt))
- {
- tree lhs = GIMPLE_STMT_OPERAND (stmt, 0);
- if (TREE_CODE (lhs) == VAR_DECL)
- {
- struct aggregate_vardecl_d *av_p;
-
- av_p = get_aggregate_vardecl (lhs, &dse_gd, /*insert=*/true);
- av_p->ignore = false;
-
- /* Ignore aggregates with too many parts. */
- if (av_p->nparts > HOST_BITS_PER_LONG)
- av_p->ignore = true;
- }
- }
-
- /* Create a UID for each statement in the function.
- Ordering of the UIDs is not important for this pass. */
- stmt_ann (stmt)->uid = max_stmt_uid++;
- }
+ stmt_ann (bsi_stmt (bsi))->uid = max_stmt_uid++;
}
/* We might consider making this a property of each pass so that it
/* This is the main hash table for the dead store elimination pass. */
dse_gd.stores = BITMAP_ALLOC (NULL);
-
walk_data.global_data = &dse_gd;
/* Initialize the dominator walker. */
/* Finalize the dominator walker. */
fini_walk_dominator_tree (&walk_data);
- /* Release unneeded data. */
+ /* Release the main bitmap. */
BITMAP_FREE (dse_gd.stores);
- htab_delete (dse_gd.aggregate_vardecl);
/* For now, just wipe the post-dominator information. */
free_dominance_info (CDI_POST_DOMINATORS);
| 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 */
+};
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