/* Dead store elimination
- Copyright (C) 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010
+ Free Software Foundation, Inc.
This file is part of GCC.
#include "tree-dump.h"
#include "domwalk.h"
#include "flags.h"
+#include "langhooks.h"
/* This file implements dead store elimination.
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.
+ 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
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
+ 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"
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
{
};
/* We allocate a bitmap-per-block for stores which are encountered
- during the scan of that block. This allows us to restore the
+ 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,
- 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;
+ if (gimple_code (stmt) == GIMPLE_PHI)
+ return SSA_NAME_VERSION (gimple_phi_result (stmt))
+ + gimple_stmt_max_uid (cfun);
- return stmt_ann (stmt)->uid;
+ return gimple_uid (stmt);
}
/* Set bit UID in bitmaps GLOBAL and *LOCAL, creating *LOCAL as needed. */
}
}
-/* 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. */
+/* 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
-get_kill_of_stmt_lhs (tree stmt,
- use_operand_p * first_use_p,
- use_operand_p * use_p, tree * use_stmt)
+dse_possible_dead_store_p (gimple stmt, gimple *use_stmt)
{
- tree lhs;
-
- gcc_assert (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT);
+ gimple temp;
+ unsigned cnt = 0;
- lhs = GIMPLE_STMT_OPERAND (stmt, 0);
+ *use_stmt = NULL;
- /* 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. */
+ /* 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
{
- 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))
+ gimple 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;
- 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))
+ if (gimple_code (temp) == GIMPLE_PHI)
+ defvar = PHI_RESULT (temp);
+ else
+ defvar = gimple_vdef (temp);
+ temp = NULL;
+ FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
{
- *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);
+ cnt++;
- if (base1 != base2)
+ /* If we ever reach our DSE candidate stmt again fail. We
+ cannot handle dead stores in loops. */
+ if (use_stmt == stmt)
{
fail = true;
- break;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ /* 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. */
+ else if (gimple_code (use_stmt) == GIMPLE_PHI)
+ {
+ if (temp
+ /* Make sure we are not in a loop latch block. */
+ || gimple_bb (stmt) == gimple_bb (use_stmt)
+ || dominated_by_p (CDI_DOMINATORS,
+ gimple_bb (stmt), gimple_bb (use_stmt))
+ /* We can look through PHIs to regions post-dominating
+ the DSE candidate stmt. */
+ || !dominated_by_p (CDI_POST_DOMINATORS,
+ gimple_bb (stmt), 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 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)
+ 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)
{
- fail = true;
+ 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 (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.
+ if (!is_gimple_assign (temp))
+ return false;
- 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);
- }
+ *use_stmt = temp;
return true;
}
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
- = (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);
+ 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))
+ if (!gimple_vdef (stmt))
return;
- /* We know we have virtual definitions. If this is a GIMPLE_MODIFY_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 (get_call_expr_in (stmt))
+ 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) == GIMPLE_MODIFY_STMT)
+ if (is_gimple_assign (stmt))
{
- use_operand_p first_use_p = NULL_USE_OPERAND_P;
- use_operand_p use_p = NULL;
- tree use_stmt;
+ gimple use_stmt;
- if (!dse_possible_dead_store_p (stmt, &first_use_p, &use_p, &use_stmt,
- dse_gd, bd))
- return;
+ record_voperand_set (dse_gd->stores, &bd->stores, gimple_uid (stmt));
- /* 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 (!dse_possible_dead_store_p (stmt, &use_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_STMT_OPERAND (stmt, 0),
- GIMPLE_STMT_OPERAND (use_stmt, 0), 0)
- && memory_address_same (stmt, use_stmt))
+ 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))
{
- 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 (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");
}
/* 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;
-
- 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;
- }
+ unlink_stmt_vdef (stmt);
/* Remove the dead store. */
- bsi_remove (&bsi, true);
+ 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
= (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;
+ gimple_stmt_iterator gsi;
- for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
- if (!is_gimple_reg (PHI_RESULT (phi)))
- record_voperand_set (dse_gd->stores,
- &bd->stores,
- get_stmt_uid (phi));
+ 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
= (struct dse_block_local_data *)
{
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);
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_verify_ssa, /* todo_flags_finish */
- 0 /* letter */
+ | 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)
-{
- 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 writting 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
