--- /dev/null
+/* Dead store elimination
+ 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 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+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 COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "ggc.h"
+#include "tree.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "basic-block.h"
+#include "timevar.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "tree-pass.h"
+#include "tree-dump.h"
+#include "domwalk.h"
+#include "flags.h"
+#include "langhooks.h"
+
+/* This file implements dead store elimination.
+
+ A dead store is a store into a memory location which will later be
+ overwritten by another store without any intervening loads. In this
+ case the earlier store can be deleted.
+
+ In our SSA + virtual operand world we use immediate uses of virtual
+ operands to detect dead stores. If a store's virtual definition
+ is used precisely once by a later store to the same location which
+ post dominates the first store, then the first store is dead.
+
+ The single use of the store's virtual definition ensures that
+ there are no intervening aliased loads and the requirement that
+ the second load post dominate the first ensures that if the earlier
+ store executes, then the later stores will execute before the function
+ exits.
+
+ It may help to think of this as first moving the earlier store to
+ the point immediately before the later store. Again, the single
+ use of the virtual definition and the post-dominance relationship
+ ensure that such movement would be safe. Clearly if there are
+ back to back stores, then the second is redundant.
+
+ Reviewing section 10.7.2 in Morgan's "Building an Optimizing Compiler"
+ may also help in understanding this code since it discusses the
+ 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
+{
+ /* This is the global bitmap for store statements.
+
+ Each statement has a unique ID. When we encounter a store statement
+ that we want to record, set the bit corresponding to the statement's
+ unique ID in this bitmap. */
+ bitmap stores;
+};
+
+/* We allocate a bitmap-per-block for stores which are encountered
+ during the scan of that block. This allows us to restore the
+ global bitmap of stores when we finish processing a block. */
+struct dse_block_local_data
+{
+ 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 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,
+ gimple_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 record_voperand_set (bitmap, bitmap *, unsigned int);
+
+/* Returns uid of statement STMT. */
+
+static unsigned
+get_stmt_uid (gimple stmt)
+{
+ if (gimple_code (stmt) == GIMPLE_PHI)
+ return SSA_NAME_VERSION (gimple_phi_result (stmt))
+ + gimple_stmt_max_uid (cfun);
+
+ 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)
+{
+ /* Lazily allocate the bitmap. Note that we do not get a notification
+ when the block local data structures die, so we allocate the local
+ bitmap backed by the GC system. */
+ if (*local == NULL)
+ *local = BITMAP_GGC_ALLOC ();
+
+ /* Set the bit in the local and global bitmaps. */
+ bitmap_set_bit (*local, uid);
+ bitmap_set_bit (global, uid);
+}
+
+/* Initialize block local data structures. */
+
+static void
+dse_initialize_block_local_data (struct dom_walk_data *walk_data,
+ basic_block bb ATTRIBUTE_UNUSED,
+ bool recycled)
+{
+ struct dse_block_local_data *bd
+ = (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. */
+ if (recycled)
+ {
+ if (bd->stores)
+ bitmap_clear (bd->stores);
+ }
+}
+
+/* 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;
+ gimple 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 = gimple_bb (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 *expr_p;
+ }
+
+ 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 (gimple store1, gimple store2)
+{
+ struct address_walk_data walk_data;
+
+ walk_data.store1_bb = gimple_bb (store1);
+ walk_data.store2_bb = gimple_bb (store2);
+
+ return (walk_tree (gimple_assign_lhs_ptr (store1), 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 in between 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 (gimple stmt,
+ use_operand_p * first_use_p,
+ use_operand_p * use_p, gimple * use_stmt)
+{
+ tree lhs;
+
+ gcc_assert (is_gimple_assign (stmt));
+
+ lhs = gimple_assign_lhs (stmt);
+
+ /* 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;
+ 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 (!gimple_assign_single_p (stmt)
+ || (TREE_CODE (gimple_assign_rhs1 (stmt)) != SSA_NAME
+ && !is_gimple_min_invariant (gimple_assign_rhs1 (stmt))))
+ return false;
+
+ /* If the use stmts lhs matches the original lhs we have
+ found the kill, otherwise continue walking. */
+ use_lhs = gimple_assign_lhs (stmt);
+ if (operand_equal_p (use_lhs, lhs, 0))
+ {
+ *use_stmt = stmt;
+ return true;
+ }
+ }
+ while (1);
+}
+
+/* A helper of dse_optimize_stmt.
+ Given a GIMPLE_ASSIGN 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 (gimple stmt,
+ use_operand_p *first_use_p,
+ use_operand_p *use_p,
+ gimple *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;
+ tree prev_defvar = NULL_TREE;
+ gimple temp;
+
+ /* 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;
+
+ /* ??? If we hit a GIMPLE_PHI we could skip to the PHI_RESULT uses.
+ Don't bother to do that for now. */
+ if (gimple_code (temp) == GIMPLE_PHI)
+ {
+ fail = true;
+ break;
+ }
+
+ /* 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 (is_gimple_assign (temp))
+ {
+ tree base1 = get_base_address (gimple_assign_lhs (stmt));
+ tree base2 = get_base_address (gimple_assign_lhs (temp));
+
+ 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, gimple_uid (stmt));
+ return false;
+ }
+
+ 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
+ overwritten by another store without any intervening loads. In this
+ case the earlier store can be deleted.
+
+ In our SSA + virtual operand world we use immediate uses of virtual
+ operands to detect dead stores. If a store's virtual definition
+ is used precisely once by a later store to the same location which
+ 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,
+ gimple_stmt_iterator gsi)
+{
+ struct dse_block_local_data *bd
+ = (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 = gsi_stmt (gsi);
+
+ /* If this statement has no virtual defs, then there is nothing
+ to do. */
+ if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VDEF))
+ return;
+
+ /* 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 (gimple_has_volatile_ops (stmt))
+ return;
+
+ if (is_gimple_assign (stmt))
+ {
+ use_operand_p first_use_p = NULL_USE_OPERAND_P;
+ use_operand_p use_p = NULL;
+ gimple use_stmt;
+
+ 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. 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_assign_lhs (stmt),
+ gimple_assign_lhs (use_stmt), 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,
+ gimple_uid (stmt));
+ 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_assign_lhs (stmt),
+ gimple_assign_lhs (use_stmt), 0)
+ && memory_address_same (stmt, use_stmt))
+ {
+ ssa_op_iter op_iter;
+ def_operand_p var1;
+ vuse_vec_p vv;
+ tree stmt_lhs;
+
+ /* 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 (gimple_loaded_syms (use_stmt)
+ && bitmap_intersect_p (gimple_loaded_syms (use_stmt),
+ gimple_stored_syms (use_stmt)))
+ {
+ record_voperand_set (dse_gd->stores, &bd->stores,
+ gimple_uid (stmt));
+ return;
+ }
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, " Deleted dead store '");
+ print_gimple_stmt (dump_file, gsi_stmt (gsi), dump_flags, 0);
+ fprintf (dump_file, "'\n");
+ }
+
+ /* 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;
+ gimple temp;
+
+ 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. */
+ 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, gimple_uid (stmt));
+ }
+}
+
+/* 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)
+{
+ struct dse_block_local_data *bd
+ = (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 phi;
+ gimple_stmt_iterator gsi;
+
+ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+ {
+ phi = gsi_stmt (gsi);
+ if (!is_gimple_reg (gimple_phi_result (phi)))
+ record_voperand_set (dse_gd->stores, &bd->stores, get_stmt_uid (phi));
+ }
+}
+
+static void
+dse_finalize_block (struct dom_walk_data *walk_data,
+ basic_block bb ATTRIBUTE_UNUSED)
+{
+ struct dse_block_local_data *bd
+ = (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;
+
+ /* Unwind the stores noted in this basic block. */
+ if (bd->stores)
+ EXECUTE_IF_SET_IN_BITMAP (bd->stores, 0, i, bi)
+ {
+ bitmap_clear_bit (stores, i);
+ }
+}
+
+/* Main entry point. */
+
+static unsigned int
+tree_ssa_dse (void)
+{
+ struct dom_walk_data walk_data;
+ struct dse_global_data dse_gd;
+
+ 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);
+
+ /* 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.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_ALLOC (NULL);
+ walk_data.global_data = &dse_gd;
+
+ /* Initialize the dominator walker. */
+ init_walk_dominator_tree (&walk_data);
+
+ /* Recursively walk the dominator tree. */
+ walk_dominator_tree (&walk_data, EXIT_BLOCK_PTR);
+
+ /* Finalize the dominator walker. */
+ fini_walk_dominator_tree (&walk_data);
+
+ /* Release the main bitmap. */
+ BITMAP_FREE (dse_gd.stores);
+
+ /* For now, just wipe the post-dominator information. */
+ free_dominance_info (CDI_POST_DOMINATORS);
+ return 0;
+}
+
+static bool
+gate_dse (void)
+{
+ return flag_tree_dse != 0;
+}
+
+struct gimple_opt_pass pass_dse =
+{
+ {
+ GIMPLE_PASS,
+ "dse", /* name */
+ gate_dse, /* gate */
+ tree_ssa_dse, /* execute */
+ NULL, /* sub */
+ NULL, /* next */
+ 0, /* static_pass_number */
+ TV_TREE_DSE, /* tv_id */
+ 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_verify_ssa /* todo_flags_finish */
+ }
+};
+
+/* 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)
+{
+ gimple_stmt_iterator gsi;
+ 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 (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+
+ if (gimple_loaded_syms (gsi_stmt (gsi)))
+ bitmap_ior_into (variables_loaded,
+ gimple_loaded_syms (gsi_stmt (gsi)));
+
+ /* Look for statements writing into the write only variables.
+ And try to remove them. */
+
+ FOR_EACH_BB (bb)
+ for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi);)
+ {
+ gimple stmt = gsi_stmt (gsi);
+ tree op;
+ bool removed = false;
+ ssa_op_iter iter;
+ tree size;
+
+ if (is_gimple_assign (stmt)
+ && AGGREGATE_TYPE_P (TREE_TYPE (gimple_assign_lhs (stmt)))
+ && (size = lang_hooks.expr_size (gimple_assign_lhs (stmt)))
+ && integer_zerop (size))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, " Deleted zero-sized store '");
+ print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+ fprintf (dump_file, "'\n");
+ }
+ removed = true;
+ gsi_remove (&gsi, true);
+ todo |= TODO_cleanup_cfg;
+ }
+ else if (gimple_stored_syms (stmt)
+ && !bitmap_empty_p (gimple_stored_syms (stmt))
+ && (is_gimple_assign (stmt)
+ || (is_gimple_call (stmt)
+ && gimple_call_lhs (stmt)))
+ && !bitmap_intersect_p (gimple_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 (gimple_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 && gimple_loaded_syms (stmt))
+ EXECUTE_IF_SET_IN_BITMAP (gimple_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 occurrence var = indirect_ref (...) where
+ indirect_ref itself is volatile. */
+
+ if (dead && is_gimple_assign (stmt)
+ && TREE_THIS_VOLATILE (gimple_assign_rhs1 (stmt)))
+ dead = false;
+
+ if (dead)
+ {
+ /* When LHS of var = call (); is dead, simplify it into
+ call (); saving one operand. */
+ if (is_gimple_call (stmt)
+ && gimple_has_side_effects (stmt))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Deleted LHS of call: ");
+ print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+ fprintf (dump_file, "\n");
+ }
+ push_stmt_changes (gsi_stmt_ptr (&gsi));
+ gimple_call_set_lhs (stmt, NULL);
+ pop_stmt_changes (gsi_stmt_ptr (&gsi));
+ }
+ else
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, " Deleted dead store '");
+ print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+ fprintf (dump_file, "'\n");
+ }
+ removed = true;
+ gsi_remove (&gsi, true);
+ todo |= TODO_cleanup_cfg;
+ }
+ todo |= TODO_remove_unused_locals | TODO_ggc_collect;
+ }
+ }
+ if (!removed)
+ gsi_next (&gsi);
+ }
+ BITMAP_FREE (variables_loaded);
+ return todo;
+}
+
+struct gimple_opt_pass pass_simple_dse =
+{
+ {
+ GIMPLE_PASS,
+ "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 */
+ }
+};
projects / msp430-gcc.git / blobdiff