CbC/CbC_gcc: gcc/tree-ssa-dom.c comparison

comparison gcc/tree-ssa-dom.c @ 0:a06113de4d67

first commit

author	kent <kent@cr.ie.u-ryukyu.ac.jp>
date	Fri, 17 Jul 2009 14:47:48 +0900
parents
children	3bfb6c00c1e0

comparison

equal deleted inserted replaced

--1:000000000000
+:a06113de4d67
+/* SSA Dominator optimizations for trees
+Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
+Free Software Foundation, Inc.
+Contributed by Diego Novillo <dnovillo@redhat.com>
+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 "tree.h"
+#include "flags.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "ggc.h"
+#include "basic-block.h"
+#include "cfgloop.h"
+#include "output.h"
+#include "expr.h"
+#include "function.h"
+#include "diagnostic.h"
+#include "timevar.h"
+#include "tree-dump.h"
+#include "tree-flow.h"
+#include "domwalk.h"
+#include "real.h"
+#include "tree-pass.h"
+#include "tree-ssa-propagate.h"
+#include "langhooks.h"
+#include "params.h"
+/* This file implements optimizations on the dominator tree.  */
+/* Representation of a "naked" right-hand-side expression, to be used
+in recording available expressions in the expression hash table.  */
+enum expr_kind
+{
+EXPR_SINGLE,
+EXPR_UNARY,
+EXPR_BINARY,
+EXPR_CALL
+};
+struct hashable_expr
+{
+tree type;
+enum expr_kind kind;
+union {
+struct { tree rhs; } single;
+struct { enum tree_code op;  tree opnd; } unary;
+struct { enum tree_code op;  tree opnd0; tree opnd1; } binary;
+struct { tree fn; bool pure; size_t nargs; tree *args; } call;
+} ops;
+};
+/* Structure for recording known values of a conditional expression
+at the exits from its block.  */
+struct cond_equivalence
+{
+struct hashable_expr cond;
+tree value;
+};
+/* Structure for recording edge equivalences as well as any pending
+edge redirections during the dominator optimizer.
+Computing and storing the edge equivalences instead of creating
+them on-demand can save significant amounts of time, particularly
+for pathological cases involving switch statements.
+These structures live for a single iteration of the dominator
+optimizer in the edge's AUX field.  At the end of an iteration we
+free each of these structures and update the AUX field to point
+to any requested redirection target (the code for updating the
+CFG and SSA graph for edge redirection expects redirection edge
+targets to be in the AUX field for each edge.  */
+struct edge_info
+{
+/* If this edge creates a simple equivalence, the LHS and RHS of
+the equivalence will be stored here.  */
+tree lhs;
+tree rhs;
+/* Traversing an edge may also indicate one or more particular conditions
+are true or false.  The number of recorded conditions can vary, but
+can be determined by the condition's code.  So we have an array
+and its maximum index rather than use a varray.  */
+struct cond_equivalence *cond_equivalences;
+unsigned int max_cond_equivalences;
+};
+/* Hash table with expressions made available during the renaming process.
+When an assignment of the form X_i = EXPR is found, the statement is
+stored in this table.  If the same expression EXPR is later found on the
+RHS of another statement, it is replaced with X_i (thus performing
+global redundancy elimination).  Similarly as we pass through conditionals
+we record the conditional itself as having either a true or false value
+in this table.  */
+static htab_t avail_exprs;
+/* Stack of available expressions in AVAIL_EXPRs.  Each block pushes any
+expressions it enters into the hash table along with a marker entry
+(null).  When we finish processing the block, we pop off entries and
+remove the expressions from the global hash table until we hit the
+marker.  */
+typedef struct expr_hash_elt * expr_hash_elt_t;
+DEF_VEC_P(expr_hash_elt_t);
+DEF_VEC_ALLOC_P(expr_hash_elt_t,heap);
+static VEC(expr_hash_elt_t,heap) *avail_exprs_stack;
+/* Stack of statements we need to rescan during finalization for newly
+exposed variables.
+Statement rescanning must occur after the current block's available
+expressions are removed from AVAIL_EXPRS.  Else we may change the
+hash code for an expression and be unable to find/remove it from
+AVAIL_EXPRS.  */
+typedef gimple *gimple_p;
+DEF_VEC_P(gimple_p);
+DEF_VEC_ALLOC_P(gimple_p,heap);
+static VEC(gimple_p,heap) *stmts_to_rescan;
+/* Structure for entries in the expression hash table.  */
+struct expr_hash_elt
+{
+/* The value (lhs) of this expression.  */
+tree lhs;
+/* The expression (rhs) we want to record.  */
+struct hashable_expr expr;
+/* The stmt pointer if this element corresponds to a statement.  */
+gimple stmt;
+/* The hash value for RHS.  */
+hashval_t hash;
+/* A unique stamp, typically the address of the hash
+element itself, used in removing entries from the table.  */
+struct expr_hash_elt *stamp;
+};
+/* Stack of dest,src pairs that need to be restored during finalization.
+A NULL entry is used to mark the end of pairs which need to be
+restored during finalization of this block.  */
+static VEC(tree,heap) *const_and_copies_stack;
+/* Track whether or not we have changed the control flow graph.  */
+static bool cfg_altered;
+/* Bitmap of blocks that have had EH statements cleaned.  We should
+remove their dead edges eventually.  */
+static bitmap need_eh_cleanup;
+/* Statistics for dominator optimizations.  */
+struct opt_stats_d
+{
+long num_stmts;
+long num_exprs_considered;
+long num_re;
+long num_const_prop;
+long num_copy_prop;
+};
+static struct opt_stats_d opt_stats;
+/* Local functions.  */
+static void optimize_stmt (struct dom_walk_data *,
+			   basic_block,
+			   gimple_stmt_iterator);
+static tree lookup_avail_expr (gimple, bool);
+static hashval_t avail_expr_hash (const void *);
+static hashval_t real_avail_expr_hash (const void *);
+static int avail_expr_eq (const void *, const void *);
+static void htab_statistics (FILE *, htab_t);
+static void record_cond (struct cond_equivalence *);
+static void record_const_or_copy (tree, tree);
+static void record_equality (tree, tree);
+static void record_equivalences_from_phis (basic_block);
+static void record_equivalences_from_incoming_edge (basic_block);
+static bool eliminate_redundant_computations (gimple_stmt_iterator *);
+static void record_equivalences_from_stmt (gimple, int);
+static void dom_thread_across_edge (struct dom_walk_data *, edge);
+static void dom_opt_finalize_block (struct dom_walk_data *, basic_block);
+static void dom_opt_initialize_block (struct dom_walk_data *, basic_block);
+static void propagate_to_outgoing_edges (struct dom_walk_data *, basic_block);
+static void remove_local_expressions_from_table (void);
+static void restore_vars_to_original_value (void);
+static edge single_incoming_edge_ignoring_loop_edges (basic_block);
+/* Given a statement STMT, initialize the hash table element pointed to
+by ELEMENT.  */
+static void
+initialize_hash_element (gimple stmt, tree lhs,
+struct expr_hash_elt *element)
+{
+enum gimple_code code = gimple_code (stmt);
+struct hashable_expr *expr = &element->expr;
+if (code == GIMPLE_ASSIGN)
+{
+enum tree_code subcode = gimple_assign_rhs_code (stmt);
+expr->type = NULL_TREE;
+switch (get_gimple_rhs_class (subcode))
+{
+case GIMPLE_SINGLE_RHS:
+expr->kind = EXPR_SINGLE;
+expr->ops.single.rhs = gimple_assign_rhs1 (stmt);
+break;
+case GIMPLE_UNARY_RHS:
+expr->kind = EXPR_UNARY;
+	  expr->type = TREE_TYPE (gimple_assign_lhs (stmt));
+expr->ops.unary.op = subcode;
+expr->ops.unary.opnd = gimple_assign_rhs1 (stmt);
+break;
+case GIMPLE_BINARY_RHS:
+expr->kind = EXPR_BINARY;
+	  expr->type = TREE_TYPE (gimple_assign_lhs (stmt));
+expr->ops.binary.op = subcode;
+expr->ops.binary.opnd0 = gimple_assign_rhs1 (stmt);
+expr->ops.binary.opnd1 = gimple_assign_rhs2 (stmt);
+break;
+default:
+gcc_unreachable ();
+}
+}
+else if (code == GIMPLE_COND)
+{
+expr->type = boolean_type_node;
+expr->kind = EXPR_BINARY;
+expr->ops.binary.op = gimple_cond_code (stmt);
+expr->ops.binary.opnd0 = gimple_cond_lhs (stmt);
+expr->ops.binary.opnd1 = gimple_cond_rhs (stmt);
+}
+else if (code == GIMPLE_CALL)
+{
+size_t nargs = gimple_call_num_args (stmt);
+size_t i;
+gcc_assert (gimple_call_lhs (stmt));
+expr->type = TREE_TYPE (gimple_call_lhs (stmt));
+expr->kind = EXPR_CALL;
+expr->ops.call.fn = gimple_call_fn (stmt);
+if (gimple_call_flags (stmt) & (ECF_CONST | ECF_PURE))
+expr->ops.call.pure = true;
+else
+expr->ops.call.pure = false;
+expr->ops.call.nargs = nargs;
+expr->ops.call.args = (tree *) xcalloc (nargs, sizeof (tree));
+for (i = 0; i < nargs; i++)
+expr->ops.call.args[i] = gimple_call_arg (stmt, i);
+}
+else if (code == GIMPLE_SWITCH)
+{
+expr->type = TREE_TYPE (gimple_switch_index (stmt));
+expr->kind = EXPR_SINGLE;
+expr->ops.single.rhs = gimple_switch_index (stmt);
+}
+else if (code == GIMPLE_GOTO)
+{
+expr->type = TREE_TYPE (gimple_goto_dest (stmt));
+expr->kind = EXPR_SINGLE;
+expr->ops.single.rhs = gimple_goto_dest (stmt);
+}
+else
+gcc_unreachable ();
+element->lhs = lhs;
+element->stmt = stmt;
+element->hash = avail_expr_hash (element);
+element->stamp = element;
+}
+/* Given a conditional expression COND as a tree, initialize
+a hashable_expr expression EXPR.  The conditional must be a
+comparison or logical negation.  A constant or a variable is
+not permitted.  */
+static void
+initialize_expr_from_cond (tree cond, struct hashable_expr *expr)
+{
+expr->type = boolean_type_node;
+if (COMPARISON_CLASS_P (cond))
+{
+expr->kind = EXPR_BINARY;
+expr->ops.binary.op = TREE_CODE (cond);
+expr->ops.binary.opnd0 = TREE_OPERAND (cond, 0);
+expr->ops.binary.opnd1 = TREE_OPERAND (cond, 1);
+}
+else if (TREE_CODE (cond) == TRUTH_NOT_EXPR)
+{
+expr->kind = EXPR_UNARY;
+expr->ops.unary.op = TRUTH_NOT_EXPR;
+expr->ops.unary.opnd = TREE_OPERAND (cond, 0);
+}
+else
+gcc_unreachable ();
+}
+/* Given a hashable_expr expression EXPR and an LHS,
+initialize the hash table element pointed to by ELEMENT.  */
+static void
+initialize_hash_element_from_expr (struct hashable_expr *expr,
+tree lhs,
+struct expr_hash_elt *element)
+{
+element->expr = *expr;
+element->lhs = lhs;
+element->stmt = NULL;
+element->hash = avail_expr_hash (element);
+element->stamp = element;
+}
+/* Compare two hashable_expr structures for equivalence.
+They are considered equivalent when the the expressions
+they denote must necessarily be equal.  The logic is intended
+to follow that of operand_equal_p in fold-const.c  */
+static bool
+hashable_expr_equal_p (const struct hashable_expr *expr0,
+const struct hashable_expr *expr1)
+{
+tree type0 = expr0->type;
+tree type1 = expr1->type;
+/* If either type is NULL, there is nothing to check.  */
+if ((type0 == NULL_TREE) ^ (type1 == NULL_TREE))
+return false;
+/* If both types don't have the same signedness, precision, and mode,
+then we can't consider  them equal.  */
+if (type0 != type1
+&& (TREE_CODE (type0) == ERROR_MARK
+	  || TREE_CODE (type1) == ERROR_MARK
+	  || TYPE_UNSIGNED (type0) != TYPE_UNSIGNED (type1)
+	  || TYPE_PRECISION (type0) != TYPE_PRECISION (type1)
+	  || TYPE_MODE (type0) != TYPE_MODE (type1)))
+return false;
+if (expr0->kind != expr1->kind)
+return false;
+switch (expr0->kind)
+{
+case EXPR_SINGLE:
+return operand_equal_p (expr0->ops.single.rhs,
+expr1->ops.single.rhs, 0);
+case EXPR_UNARY:
+if (expr0->ops.unary.op != expr1->ops.unary.op)
+return false;
+if ((CONVERT_EXPR_CODE_P (expr0->ops.unary.op)
+|| expr0->ops.unary.op == NON_LVALUE_EXPR)
+&& TYPE_UNSIGNED (expr0->type) != TYPE_UNSIGNED (expr1->type))
+return false;
+return operand_equal_p (expr0->ops.unary.opnd,
+expr1->ops.unary.opnd, 0);
+case EXPR_BINARY:
+{
+if (expr0->ops.binary.op != expr1->ops.binary.op)
+return false;
+if (operand_equal_p (expr0->ops.binary.opnd0,
+expr1->ops.binary.opnd0, 0)
+&& operand_equal_p (expr0->ops.binary.opnd1,
+expr1->ops.binary.opnd1, 0))
+return true;
+/* For commutative ops, allow the other order.  */
+return (commutative_tree_code (expr0->ops.binary.op)
+&& operand_equal_p (expr0->ops.binary.opnd0,
+expr1->ops.binary.opnd1, 0)
+&& operand_equal_p (expr0->ops.binary.opnd1,
+expr1->ops.binary.opnd0, 0));
+}
+case EXPR_CALL:
+{
+size_t i;
+/* If the calls are to different functions, then they
+clearly cannot be equal.  */
+if (! operand_equal_p (expr0->ops.call.fn,
+expr1->ops.call.fn, 0))
+return false;
+if (! expr0->ops.call.pure)
+return false;
+if (expr0->ops.call.nargs !=  expr1->ops.call.nargs)
+return false;
+for (i = 0; i < expr0->ops.call.nargs; i++)
+if (! operand_equal_p (expr0->ops.call.args[i],
+expr1->ops.call.args[i], 0))
+return false;
+return true;
+}
+default:
+gcc_unreachable ();
+}
+}
+/* Compute a hash value for a hashable_expr value EXPR and a
+previously accumulated hash value VAL.  If two hashable_expr
+values compare equal with hashable_expr_equal_p, they must
+hash to the same value, given an identical value of VAL.
+The logic is intended to follow iterative_hash_expr in tree.c.  */
+static hashval_t
+iterative_hash_hashable_expr (const struct hashable_expr *expr, hashval_t val)
+{
+switch (expr->kind)
+{
+case EXPR_SINGLE:
+val = iterative_hash_expr (expr->ops.single.rhs, val);
+break;
+case EXPR_UNARY:
+val = iterative_hash_object (expr->ops.unary.op, val);
+/* Make sure to include signedness in the hash computation.
+Don't hash the type, that can lead to having nodes which
+compare equal according to operand_equal_p, but which
+have different hash codes.  */
+if (CONVERT_EXPR_CODE_P (expr->ops.unary.op)
+|| expr->ops.unary.op == NON_LVALUE_EXPR)
+val += TYPE_UNSIGNED (expr->type);
+val = iterative_hash_expr (expr->ops.unary.opnd, val);
+break;
+case EXPR_BINARY:
+val = iterative_hash_object (expr->ops.binary.op, val);
+if (commutative_tree_code (expr->ops.binary.op))
+val = iterative_hash_exprs_commutative (expr->ops.binary.opnd0,
+expr->ops.binary.opnd1, val);
+else
+{
+val = iterative_hash_expr (expr->ops.binary.opnd0, val);
+val = iterative_hash_expr (expr->ops.binary.opnd1, val);
+}
+break;
+case EXPR_CALL:
+{
+size_t i;
+enum tree_code code = CALL_EXPR;
+val = iterative_hash_object (code, val);
+val = iterative_hash_expr (expr->ops.call.fn, val);
+for (i = 0; i < expr->ops.call.nargs; i++)
+val = iterative_hash_expr (expr->ops.call.args[i], val);
+}
+break;
+default:
+gcc_unreachable ();
+}
+return val;
+}
+/* Print a diagnostic dump of an expression hash table entry.  */
+static void
+print_expr_hash_elt (FILE * stream, const struct expr_hash_elt *element)
+{
+if (element->stmt)
+fprintf (stream, "STMT ");
+else
+fprintf (stream, "COND ");
+if (element->lhs)
+{
+print_generic_expr (stream, element->lhs, 0);
+fprintf (stream, " = ");
+}
+switch (element->expr.kind)
+{
+case EXPR_SINGLE:
+print_generic_expr (stream, element->expr.ops.single.rhs, 0);
+break;
+case EXPR_UNARY:
+fprintf (stream, "%s ", tree_code_name[element->expr.ops.unary.op]);
+print_generic_expr (stream, element->expr.ops.unary.opnd, 0);
+break;
+case EXPR_BINARY:
+print_generic_expr (stream, element->expr.ops.binary.opnd0, 0);
+fprintf (stream, " %s ", tree_code_name[element->expr.ops.binary.op]);
+print_generic_expr (stream, element->expr.ops.binary.opnd1, 0);
+break;
+case EXPR_CALL:
+{
+size_t i;
+size_t nargs = element->expr.ops.call.nargs;
+print_generic_expr (stream, element->expr.ops.call.fn, 0);
+fprintf (stream, " (");
+for (i = 0; i < nargs; i++)
+{
+print_generic_expr (stream, element->expr.ops.call.args[i], 0);
+if (i + 1 < nargs)
+fprintf (stream, ", ");
+}
+fprintf (stream, ")");
+}
+break;
+}
+fprintf (stream, "\n");
+if (element->stmt)
+{
+fprintf (stream, "          ");
+print_gimple_stmt (stream, element->stmt, 0, 0);
+}
+}
+/* Delete an expr_hash_elt and reclaim its storage.  */
+static void
+free_expr_hash_elt (void *elt)
+{
+struct expr_hash_elt *element = ((struct expr_hash_elt *)elt);
+if (element->expr.kind == EXPR_CALL)
+free (element->expr.ops.call.args);
+free (element);
+}
+/* Allocate an EDGE_INFO for edge E and attach it to E.
+Return the new EDGE_INFO structure.  */
+static struct edge_info *
+allocate_edge_info (edge e)
+{
+struct edge_info *edge_info;
+edge_info = XCNEW (struct edge_info);
+e->aux = edge_info;
+return edge_info;
+}
+/* Free all EDGE_INFO structures associated with edges in the CFG.
+If a particular edge can be threaded, copy the redirection
+target from the EDGE_INFO structure into the edge's AUX field
+as required by code to update the CFG and SSA graph for
+jump threading.  */
+static void
+free_all_edge_infos (void)
+{
+basic_block bb;
+edge_iterator ei;
+edge e;
+FOR_EACH_BB (bb)
+{
+FOR_EACH_EDGE (e, ei, bb->preds)
+{
+	 struct edge_info *edge_info = (struct edge_info *) e->aux;
+	  if (edge_info)
+	    {
+	      if (edge_info->cond_equivalences)
+		free (edge_info->cond_equivalences);
+	      free (edge_info);
+	      e->aux = NULL;
+	    }
+	}
+}
+}
+/* Jump threading, redundancy elimination and const/copy propagation.
+This pass may expose new symbols that need to be renamed into SSA.  For
+every new symbol exposed, its corresponding bit will be set in
+VARS_TO_RENAME.  */
+static unsigned int
+tree_ssa_dominator_optimize (void)
+{
+struct dom_walk_data walk_data;
+unsigned int i;
+memset (&opt_stats, 0, sizeof (opt_stats));
+/* Create our hash tables.  */
+avail_exprs = htab_create (1024, real_avail_expr_hash, avail_expr_eq, free_expr_hash_elt);
+avail_exprs_stack = VEC_alloc (expr_hash_elt_t, heap, 20);
+const_and_copies_stack = VEC_alloc (tree, heap, 20);
+stmts_to_rescan = VEC_alloc (gimple_p, heap, 20);
+need_eh_cleanup = BITMAP_ALLOC (NULL);
+/* Setup callbacks for the generic dominator tree walker.  */
+walk_data.walk_stmts_backward = false;
+walk_data.dom_direction = CDI_DOMINATORS;
+walk_data.initialize_block_local_data = NULL;
+walk_data.before_dom_children_before_stmts = dom_opt_initialize_block;
+walk_data.before_dom_children_walk_stmts = optimize_stmt;
+walk_data.before_dom_children_after_stmts = propagate_to_outgoing_edges;
+walk_data.after_dom_children_before_stmts = NULL;
+walk_data.after_dom_children_walk_stmts = NULL;
+walk_data.after_dom_children_after_stmts = dom_opt_finalize_block;
+/* Right now we only attach a dummy COND_EXPR to the global data pointer.
+When we attach more stuff we'll need to fill this out with a real
+structure.  */
+walk_data.global_data = NULL;
+walk_data.block_local_data_size = 0;
+walk_data.interesting_blocks = NULL;
+/* Now initialize the dominator walker.  */
+init_walk_dominator_tree (&walk_data);
+calculate_dominance_info (CDI_DOMINATORS);
+cfg_altered = false;
+/* We need to know loop structures in order to avoid destroying them
+in jump threading.  Note that we still can e.g. thread through loop
+headers to an exit edge, or through loop header to the loop body, assuming
+that we update the loop info.  */
+loop_optimizer_init (LOOPS_HAVE_SIMPLE_LATCHES);
+/* We need accurate information regarding back edges in the CFG
+for jump threading; this may include back edges that are not part of
+a single loop.  */
+mark_dfs_back_edges ();
+/* Recursively walk the dominator tree optimizing statements.  */
+walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR);
+{
+gimple_stmt_iterator gsi;
+basic_block bb;
+FOR_EACH_BB (bb)
+{for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+	  update_stmt_if_modified (gsi_stmt (gsi));
+}
+}
+/* If we exposed any new variables, go ahead and put them into
+SSA form now, before we handle jump threading.  This simplifies
+interactions between rewriting of _DECL nodes into SSA form
+and rewriting SSA_NAME nodes into SSA form after block
+duplication and CFG manipulation.  */
+update_ssa (TODO_update_ssa);
+free_all_edge_infos ();
+/* Thread jumps, creating duplicate blocks as needed.  */
+cfg_altered |= thread_through_all_blocks (first_pass_instance);
+if (cfg_altered)
+free_dominance_info (CDI_DOMINATORS);
+/* Removal of statements may make some EH edges dead.  Purge
+such edges from the CFG as needed.  */
+if (!bitmap_empty_p (need_eh_cleanup))
+{
+unsigned i;
+bitmap_iterator bi;
+/* Jump threading may have created forwarder blocks from blocks
+	 needing EH cleanup; the new successor of these blocks, which
+	 has inherited from the original block, needs the cleanup.  */
+EXECUTE_IF_SET_IN_BITMAP (need_eh_cleanup, 0, i, bi)
+	{
+	  basic_block bb = BASIC_BLOCK (i);
+	  if (single_succ_p (bb) == 1
+	      && (single_succ_edge (bb)->flags & EDGE_EH) == 0)
+	    {
+	      bitmap_clear_bit (need_eh_cleanup, i);
+	      bitmap_set_bit (need_eh_cleanup, single_succ (bb)->index);
+	    }
+	}
+gimple_purge_all_dead_eh_edges (need_eh_cleanup);
+bitmap_zero (need_eh_cleanup);
+}
+/* Finally, remove everything except invariants in SSA_NAME_VALUE.
+Long term we will be able to let everything in SSA_NAME_VALUE
+persist.  However, for now, we know this is the safe thing to do.  */
+for (i = 0; i < num_ssa_names; i++)
+{
+tree name = ssa_name (i);
+tree value;
+if (!name)
+continue;
+value = SSA_NAME_VALUE (name);
+if (value && !is_gimple_min_invariant (value))
+	SSA_NAME_VALUE (name) = NULL;
+}
+statistics_counter_event (cfun, "Redundant expressions eliminated",
+			    opt_stats.num_re);
+statistics_counter_event (cfun, "Constants propagated",
+			    opt_stats.num_const_prop);
+statistics_counter_event (cfun, "Copies propagated",
+			    opt_stats.num_copy_prop);
+/* Debugging dumps.  */
+if (dump_file && (dump_flags & TDF_STATS))
+dump_dominator_optimization_stats (dump_file);
+loop_optimizer_finalize ();
+/* Delete our main hashtable.  */
+htab_delete (avail_exprs);
+/* And finalize the dominator walker.  */
+fini_walk_dominator_tree (&walk_data);
+/* Free asserted bitmaps and stacks.  */
+BITMAP_FREE (need_eh_cleanup);
+VEC_free (expr_hash_elt_t, heap, avail_exprs_stack);
+VEC_free (tree, heap, const_and_copies_stack);
+VEC_free (gimple_p, heap, stmts_to_rescan);
+return 0;
+}
+static bool
+gate_dominator (void)
+{
+return flag_tree_dom != 0;
+}
+struct gimple_opt_pass pass_dominator =
+{
+{
+GIMPLE_PASS,
+"dom",				/* name */
+gate_dominator,			/* gate */
+tree_ssa_dominator_optimize,		/* execute */
+NULL,					/* sub */
+NULL,					/* next */
+0,					/* static_pass_number */
+TV_TREE_SSA_DOMINATOR_OPTS,		/* tv_id */
+PROP_cfg | PROP_ssa | PROP_alias,	/* properties_required */
+0,					/* properties_provided */
+0,					/* properties_destroyed */
+0,					/* todo_flags_start */
+TODO_dump_func
+| TODO_update_ssa
+| TODO_cleanup_cfg
+| TODO_verify_ssa			/* todo_flags_finish */
+}
+};
+/* Given a conditional statement CONDSTMT, convert the
+condition to a canonical form.  */
+static void
+canonicalize_comparison (gimple condstmt)
+{
+tree op0;
+tree op1;
+enum tree_code code;
+gcc_assert (gimple_code (condstmt) == GIMPLE_COND);
+op0 = gimple_cond_lhs (condstmt);
+op1 = gimple_cond_rhs (condstmt);
+code = gimple_cond_code (condstmt);
+/* If it would be profitable to swap the operands, then do so to
+canonicalize the statement, enabling better optimization.
+By placing canonicalization of such expressions here we
+transparently keep statements in canonical form, even
+when the statement is modified.  */
+if (tree_swap_operands_p (op0, op1, false))
+{
+/* For relationals we need to swap the operands
+	 and change the code.  */
+if (code == LT_EXPR
+	  || code == GT_EXPR
+	  || code == LE_EXPR
+	  || code == GE_EXPR)
+	{
+code = swap_tree_comparison (code);
+gimple_cond_set_code (condstmt, code);
+gimple_cond_set_lhs (condstmt, op1);
+gimple_cond_set_rhs (condstmt, op0);
+update_stmt (condstmt);
+	}
+}
+}
+/* Initialize local stacks for this optimizer and record equivalences
+upon entry to BB.  Equivalences can come from the edge traversed to
+reach BB or they may come from PHI nodes at the start of BB.  */
+static void
+dom_opt_initialize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			  basic_block bb)
+{
+if (dump_file && (dump_flags & TDF_DETAILS))
+fprintf (dump_file, "\n\nOptimizing block #%d\n\n", bb->index);
+/* Push a marker on the stacks of local information so that we know how
+far to unwind when we finalize this block.  */
+VEC_safe_push (expr_hash_elt_t, heap, avail_exprs_stack, NULL);
+VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE);
+record_equivalences_from_incoming_edge (bb);
+/* PHI nodes can create equivalences too.  */
+record_equivalences_from_phis (bb);
+}
+/* Remove all the expressions in LOCALS from TABLE, stopping when there are
+LIMIT entries left in LOCALs.  */
+static void
+remove_local_expressions_from_table (void)
+{
+/* Remove all the expressions made available in this block.  */
+while (VEC_length (expr_hash_elt_t, avail_exprs_stack) > 0)
+{
+struct expr_hash_elt element;
+expr_hash_elt_t victim = VEC_pop (expr_hash_elt_t, avail_exprs_stack);
+if (victim == NULL)
+	break;
+element = *victim;
+/* This must precede the actual removal from the hash table,
+as ELEMENT and the table entry may share a call argument
+vector which will be freed during removal.  */
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "<<<< ");
+print_expr_hash_elt (dump_file, &element);
+}
+htab_remove_elt_with_hash (avail_exprs, &element, element.hash);
+}
+}
+/* Use the source/dest pairs in CONST_AND_COPIES_STACK to restore
+CONST_AND_COPIES to its original state, stopping when we hit a
+NULL marker.  */
+static void
+restore_vars_to_original_value (void)
+{
+while (VEC_length (tree, const_and_copies_stack) > 0)
+{
+tree prev_value, dest;
+dest = VEC_pop (tree, const_and_copies_stack);
+if (dest == NULL)
+	break;
+if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "<<<< COPY ");
+	  print_generic_expr (dump_file, dest, 0);
+	  fprintf (dump_file, " = ");
+	  print_generic_expr (dump_file, SSA_NAME_VALUE (dest), 0);
+	  fprintf (dump_file, "\n");
+	}
+prev_value = VEC_pop (tree, const_and_copies_stack);
+SSA_NAME_VALUE (dest) =  prev_value;
+}
+}
+/* A trivial wrapper so that we can present the generic jump
+threading code with a simple API for simplifying statements.  */
+static tree
+simplify_stmt_for_jump_threading (gimple stmt,
+				  gimple within_stmt ATTRIBUTE_UNUSED)
+{
+return lookup_avail_expr (stmt, false);
+}
+/* Wrapper for common code to attempt to thread an edge.  For example,
+it handles lazily building the dummy condition and the bookkeeping
+when jump threading is successful.  */
+static void
+dom_thread_across_edge (struct dom_walk_data *walk_data, edge e)
+{
+if (! walk_data->global_data)
+{
+gimple dummy_cond =
+gimple_build_cond (NE_EXPR,
+integer_zero_node, integer_zero_node,
+NULL, NULL);
+walk_data->global_data = dummy_cond;
+}
+thread_across_edge ((gimple) walk_data->global_data, e, false,
+		      &const_and_copies_stack,
+		      simplify_stmt_for_jump_threading);
+}
+/* We have finished processing the dominator children of BB, perform
+any finalization actions in preparation for leaving this node in
+the dominator tree.  */
+static void
+dom_opt_finalize_block (struct dom_walk_data *walk_data, basic_block bb)
+{
+gimple last;
+/* If we have an outgoing edge to a block with multiple incoming and
+outgoing edges, then we may be able to thread the edge, i.e., we
+may be able to statically determine which of the outgoing edges
+will be traversed when the incoming edge from BB is traversed.  */
+if (single_succ_p (bb)
+&& (single_succ_edge (bb)->flags & EDGE_ABNORMAL) == 0
+&& potentially_threadable_block (single_succ (bb)))
+{
+dom_thread_across_edge (walk_data, single_succ_edge (bb));
+}
+else if ((last = last_stmt (bb))
+	   && gimple_code (last) == GIMPLE_COND
+	   && EDGE_COUNT (bb->succs) == 2
+	   && (EDGE_SUCC (bb, 0)->flags & EDGE_ABNORMAL) == 0
+	   && (EDGE_SUCC (bb, 1)->flags & EDGE_ABNORMAL) == 0)
+{
+edge true_edge, false_edge;
+extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
+/* Only try to thread the edge if it reaches a target block with
+	 more than one predecessor and more than one successor.  */
+if (potentially_threadable_block (true_edge->dest))
+	{
+	  struct edge_info *edge_info;
+	  unsigned int i;
+	  /* Push a marker onto the available expression stack so that we
+	     unwind any expressions related to the TRUE arm before processing
+	     the false arm below.  */
+VEC_safe_push (expr_hash_elt_t, heap, avail_exprs_stack, NULL);
+	  VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE);
+	  edge_info = (struct edge_info *) true_edge->aux;
+	  /* If we have info associated with this edge, record it into
+	     our equivalence tables.  */
+	  if (edge_info)
+	    {
+	      struct cond_equivalence *cond_equivalences = edge_info->cond_equivalences;
+	      tree lhs = edge_info->lhs;
+	      tree rhs = edge_info->rhs;
+	      /* If we have a simple NAME = VALUE equivalence, record it.  */
+	      if (lhs && TREE_CODE (lhs) == SSA_NAME)
+		record_const_or_copy (lhs, rhs);
+	      /* If we have 0 = COND or 1 = COND equivalences, record them
+		 into our expression hash tables.  */
+	      if (cond_equivalences)
+		for (i = 0; i < edge_info->max_cond_equivalences; i++)
+record_cond (&cond_equivalences[i]);
+	    }
+	  dom_thread_across_edge (walk_data, true_edge);
+	  /* And restore the various tables to their state before
+	     we threaded this edge.  */
+	  remove_local_expressions_from_table ();
+	}
+/* Similarly for the ELSE arm.  */
+if (potentially_threadable_block (false_edge->dest))
+	{
+	  struct edge_info *edge_info;
+	  unsigned int i;
+	  VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE);
+	  edge_info = (struct edge_info *) false_edge->aux;
+	  /* If we have info associated with this edge, record it into
+	     our equivalence tables.  */
+	  if (edge_info)
+	    {
+	      struct cond_equivalence *cond_equivalences = edge_info->cond_equivalences;
+	      tree lhs = edge_info->lhs;
+	      tree rhs = edge_info->rhs;
+	      /* If we have a simple NAME = VALUE equivalence, record it.  */
+	      if (lhs && TREE_CODE (lhs) == SSA_NAME)
+		record_const_or_copy (lhs, rhs);
+	      /* If we have 0 = COND or 1 = COND equivalences, record them
+		 into our expression hash tables.  */
+	      if (cond_equivalences)
+		for (i = 0; i < edge_info->max_cond_equivalences; i++)
+record_cond (&cond_equivalences[i]);
+	    }
+	  /* Now thread the edge.  */
+	  dom_thread_across_edge (walk_data, false_edge);
+	  /* No need to remove local expressions from our tables
+	     or restore vars to their original value as that will
+	     be done immediately below.  */
+	}
+}
+remove_local_expressions_from_table ();
+restore_vars_to_original_value ();
+/* If we queued any statements to rescan in this block, then
+go ahead and rescan them now.  */
+while (VEC_length (gimple_p, stmts_to_rescan) > 0)
+{
+gimple *stmt_p = VEC_last (gimple_p, stmts_to_rescan);
+gimple stmt = *stmt_p;
+basic_block stmt_bb = gimple_bb (stmt);
+if (stmt_bb != bb)
+	break;
+VEC_pop (gimple_p, stmts_to_rescan);
+pop_stmt_changes (stmt_p);
+}
+}
+/* PHI nodes can create equivalences too.
+Ignoring any alternatives which are the same as the result, if
+all the alternatives are equal, then the PHI node creates an
+equivalence.  */
+static void
+record_equivalences_from_phis (basic_block bb)
+{
+gimple_stmt_iterator gsi;
+for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+{
+gimple phi = gsi_stmt (gsi);
+tree lhs = gimple_phi_result (phi);
+tree rhs = NULL;
+size_t i;
+for (i = 0; i < gimple_phi_num_args (phi); i++)
+	{
+	  tree t = gimple_phi_arg_def (phi, i);
+	  /* Ignore alternatives which are the same as our LHS.  Since
+	     LHS is a PHI_RESULT, it is known to be a SSA_NAME, so we
+	     can simply compare pointers.  */
+	  if (lhs == t)
+	    continue;
+	  /* If we have not processed an alternative yet, then set
+	     RHS to this alternative.  */
+	  if (rhs == NULL)
+	    rhs = t;
+	  /* If we have processed an alternative (stored in RHS), then
+	     see if it is equal to this one.  If it isn't, then stop
+	     the search.  */
+	  else if (! operand_equal_for_phi_arg_p (rhs, t))
+	    break;
+	}
+/* If we had no interesting alternatives, then all the RHS alternatives
+	 must have been the same as LHS.  */
+if (!rhs)
+	rhs = lhs;
+/* If we managed to iterate through each PHI alternative without
+	 breaking out of the loop, then we have a PHI which may create
+	 a useful equivalence.  We do not need to record unwind data for
+	 this, since this is a true assignment and not an equivalence
+	 inferred from a comparison.  All uses of this ssa name are dominated
+	 by this assignment, so unwinding just costs time and space.  */
+if (i == gimple_phi_num_args (phi) && may_propagate_copy (lhs, rhs))
+	SSA_NAME_VALUE (lhs) = rhs;
+}
+}
+/* Ignoring loop backedges, if BB has precisely one incoming edge then
+return that edge.  Otherwise return NULL.  */
+static edge
+single_incoming_edge_ignoring_loop_edges (basic_block bb)
+{
+edge retval = NULL;
+edge e;
+edge_iterator ei;
+FOR_EACH_EDGE (e, ei, bb->preds)
+{
+/* A loop back edge can be identified by the destination of
+	 the edge dominating the source of the edge.  */
+if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest))
+	continue;
+/* If we have already seen a non-loop edge, then we must have
+	 multiple incoming non-loop edges and thus we return NULL.  */
+if (retval)
+	return NULL;
+/* This is the first non-loop incoming edge we have found.  Record
+	 it.  */
+retval = e;
+}
+return retval;
+}
+/* Record any equivalences created by the incoming edge to BB.  If BB
+has more than one incoming edge, then no equivalence is created.  */
+static void
+record_equivalences_from_incoming_edge (basic_block bb)
+{
+edge e;
+basic_block parent;
+struct edge_info *edge_info;
+/* If our parent block ended with a control statement, then we may be
+able to record some equivalences based on which outgoing edge from
+the parent was followed.  */
+parent = get_immediate_dominator (CDI_DOMINATORS, bb);
+e = single_incoming_edge_ignoring_loop_edges (bb);
+/* If we had a single incoming edge from our parent block, then enter
+any data associated with the edge into our tables.  */
+if (e && e->src == parent)
+{
+unsigned int i;
+edge_info = (struct edge_info *) e->aux;
+if (edge_info)
+	{
+	  tree lhs = edge_info->lhs;
+	  tree rhs = edge_info->rhs;
+	  struct cond_equivalence *cond_equivalences = edge_info->cond_equivalences;
+	  if (lhs)
+	    record_equality (lhs, rhs);
+	  if (cond_equivalences)
+for (i = 0; i < edge_info->max_cond_equivalences; i++)
+record_cond (&cond_equivalences[i]);
+	}
+}
+}
+/* Dump SSA statistics on FILE.  */
+void
+dump_dominator_optimization_stats (FILE *file)
+{
+fprintf (file, "Total number of statements:                   %6ld\n\n",
+	   opt_stats.num_stmts);
+fprintf (file, "Exprs considered for dominator optimizations: %6ld\n",
+opt_stats.num_exprs_considered);
+fprintf (file, "\nHash table statistics:\n");
+fprintf (file, "    avail_exprs: ");
+htab_statistics (file, avail_exprs);
+}
+/* Dump SSA statistics on stderr.  */
+void
+debug_dominator_optimization_stats (void)
+{
+dump_dominator_optimization_stats (stderr);
+}
+/* Dump statistics for the hash table HTAB.  */
+static void
+htab_statistics (FILE *file, htab_t htab)
+{
+fprintf (file, "size %ld, %ld elements, %f collision/search ratio\n",
+	   (long) htab_size (htab),
+	   (long) htab_elements (htab),
+	   htab_collisions (htab));
+}
+/* Enter condition equivalence into the expression hash table.
+This indicates that a conditional expression has a known
+boolean value.  */
+static void
+record_cond (struct cond_equivalence *p)
+{
+struct expr_hash_elt *element = XCNEW (struct expr_hash_elt);
+void **slot;
+initialize_hash_element_from_expr (&p->cond, p->value, element);
+slot = htab_find_slot_with_hash (avail_exprs, (void *)element,
+				   element->hash, INSERT);
+if (*slot == NULL)
+{
+*slot = (void *) element;
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "1>>> ");
+print_expr_hash_elt (dump_file, element);
+}
+VEC_safe_push (expr_hash_elt_t, heap, avail_exprs_stack, element);
+}
+else
+free (element);
+}
+/* Build a cond_equivalence record indicating that the comparison
+CODE holds between operands OP0 and OP1.  */
+static void
+build_and_record_new_cond (enum tree_code code,
+tree op0, tree op1,
+struct cond_equivalence *p)
+{
+struct hashable_expr *cond = &p->cond;
+gcc_assert (TREE_CODE_CLASS (code) == tcc_comparison);
+cond->type = boolean_type_node;
+cond->kind = EXPR_BINARY;
+cond->ops.binary.op = code;
+cond->ops.binary.opnd0 = op0;
+cond->ops.binary.opnd1 = op1;
+p->value = boolean_true_node;
+}
+/* Record that COND is true and INVERTED is false into the edge information
+structure.  Also record that any conditions dominated by COND are true
+as well.
+For example, if a < b is true, then a <= b must also be true.  */
+static void
+record_conditions (struct edge_info *edge_info, tree cond, tree inverted)
+{
+tree op0, op1;
+if (!COMPARISON_CLASS_P (cond))
+return;
+op0 = TREE_OPERAND (cond, 0);
+op1 = TREE_OPERAND (cond, 1);
+switch (TREE_CODE (cond))
+{
+case LT_EXPR:
+case GT_EXPR:
+if (FLOAT_TYPE_P (TREE_TYPE (op0)))
+	{
+	  edge_info->max_cond_equivalences = 6;
+	  edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 6);
+	  build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[4]);
+	  build_and_record_new_cond (LTGT_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[5]);
+	}
+else
+{
+edge_info->max_cond_equivalences = 4;
+	  edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 4);
+	}
+build_and_record_new_cond ((TREE_CODE (cond) == LT_EXPR
+				  ? LE_EXPR : GE_EXPR),
+				 op0, op1, &edge_info->cond_equivalences[2]);
+build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[3]);
+break;
+case GE_EXPR:
+case LE_EXPR:
+if (FLOAT_TYPE_P (TREE_TYPE (op0)))
+	{
+	  edge_info->max_cond_equivalences = 3;
+	  edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 3);
+	  build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[2]);
+	}
+else
+	{
+	  edge_info->max_cond_equivalences = 2;
+	  edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 2);
+	}
+break;
+case EQ_EXPR:
+if (FLOAT_TYPE_P (TREE_TYPE (op0)))
+	{
+	  edge_info->max_cond_equivalences = 5;
+	  edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 5);
+	  build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[4]);
+	}
+else
+	{
+	  edge_info->max_cond_equivalences = 4;
+	  edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 4);
+	}
+build_and_record_new_cond (LE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[2]);
+build_and_record_new_cond (GE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[3]);
+break;
+case UNORDERED_EXPR:
+edge_info->max_cond_equivalences = 8;
+edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 8);
+build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[2]);
+build_and_record_new_cond (UNLE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[3]);
+build_and_record_new_cond (UNGE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[4]);
+build_and_record_new_cond (UNEQ_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[5]);
+build_and_record_new_cond (UNLT_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[6]);
+build_and_record_new_cond (UNGT_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[7]);
+break;
+case UNLT_EXPR:
+case UNGT_EXPR:
+edge_info->max_cond_equivalences = 4;
+edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 4);
+build_and_record_new_cond ((TREE_CODE (cond) == UNLT_EXPR
+				  ? UNLE_EXPR : UNGE_EXPR),
+				 op0, op1, &edge_info->cond_equivalences[2]);
+build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[3]);
+break;
+case UNEQ_EXPR:
+edge_info->max_cond_equivalences = 4;
+edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 4);
+build_and_record_new_cond (UNLE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[2]);
+build_and_record_new_cond (UNGE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[3]);
+break;
+case LTGT_EXPR:
+edge_info->max_cond_equivalences = 4;
+edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 4);
+build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[2]);
+build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[3]);
+break;
+default:
+edge_info->max_cond_equivalences = 2;
+edge_info->cond_equivalences = XNEWVEC (struct cond_equivalence, 2);
+break;
+}
+/* Now store the original true and false conditions into the first
+two slots.  */
+initialize_expr_from_cond (cond, &edge_info->cond_equivalences[0].cond);
+edge_info->cond_equivalences[0].value = boolean_true_node;
+/* It is possible for INVERTED to be the negation of a comparison,
+and not a valid RHS or GIMPLE_COND condition.  This happens because
+invert_truthvalue may return such an expression when asked to invert
+a floating-point comparison.  These comparisons are not assumed to
+obey the trichotomy law.  */
+initialize_expr_from_cond (inverted, &edge_info->cond_equivalences[1].cond);
+edge_info->cond_equivalences[1].value = boolean_false_node;
+}
+/* A helper function for record_const_or_copy and record_equality.
+Do the work of recording the value and undo info.  */
+static void
+record_const_or_copy_1 (tree x, tree y, tree prev_x)
+{
+SSA_NAME_VALUE (x) = y;
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "0>>> COPY ");
+print_generic_expr (dump_file, x, 0);
+fprintf (dump_file, " = ");
+print_generic_expr (dump_file, y, 0);
+fprintf (dump_file, "\n");
+}
+VEC_reserve (tree, heap, const_and_copies_stack, 2);
+VEC_quick_push (tree, const_and_copies_stack, prev_x);
+VEC_quick_push (tree, const_and_copies_stack, x);
+}
+/* Return the loop depth of the basic block of the defining statement of X.
+This number should not be treated as absolutely correct because the loop
+information may not be completely up-to-date when dom runs.  However, it
+will be relatively correct, and as more passes are taught to keep loop info
+up to date, the result will become more and more accurate.  */
+int
+loop_depth_of_name (tree x)
+{
+gimple defstmt;
+basic_block defbb;
+/* If it's not an SSA_NAME, we have no clue where the definition is.  */
+if (TREE_CODE (x) != SSA_NAME)
+return 0;
+/* Otherwise return the loop depth of the defining statement's bb.
+Note that there may not actually be a bb for this statement, if the
+ssa_name is live on entry.  */
+defstmt = SSA_NAME_DEF_STMT (x);
+defbb = gimple_bb (defstmt);
+if (!defbb)
+return 0;
+return defbb->loop_depth;
+}
+/* Record that X is equal to Y in const_and_copies.  Record undo
+information in the block-local vector.  */
+static void
+record_const_or_copy (tree x, tree y)
+{
+tree prev_x = SSA_NAME_VALUE (x);
+gcc_assert (TREE_CODE (x) == SSA_NAME);
+if (TREE_CODE (y) == SSA_NAME)
+{
+tree tmp = SSA_NAME_VALUE (y);
+if (tmp)
+	y = tmp;
+}
+record_const_or_copy_1 (x, y, prev_x);
+}
+/* Similarly, but assume that X and Y are the two operands of an EQ_EXPR.
+This constrains the cases in which we may treat this as assignment.  */
+static void
+record_equality (tree x, tree y)
+{
+tree prev_x = NULL, prev_y = NULL;
+if (TREE_CODE (x) == SSA_NAME)
+prev_x = SSA_NAME_VALUE (x);
+if (TREE_CODE (y) == SSA_NAME)
+prev_y = SSA_NAME_VALUE (y);
+/* If one of the previous values is invariant, or invariant in more loops
+(by depth), then use that.
+Otherwise it doesn't matter which value we choose, just so
+long as we canonicalize on one value.  */
+if (is_gimple_min_invariant (y))
+;
+else if (is_gimple_min_invariant (x)
+	   || (loop_depth_of_name (x) <= loop_depth_of_name (y)))
+prev_x = x, x = y, y = prev_x, prev_x = prev_y;
+else if (prev_x && is_gimple_min_invariant (prev_x))
+x = y, y = prev_x, prev_x = prev_y;
+else if (prev_y)
+y = prev_y;
+/* After the swapping, we must have one SSA_NAME.  */
+if (TREE_CODE (x) != SSA_NAME)
+return;
+/* For IEEE, -0.0 == 0.0, so we don't necessarily know the sign of a
+variable compared against zero.  If we're honoring signed zeros,
+then we cannot record this value unless we know that the value is
+nonzero.  */
+if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (x)))
+&& (TREE_CODE (y) != REAL_CST
+	  || REAL_VALUES_EQUAL (dconst0, TREE_REAL_CST (y))))
+return;
+record_const_or_copy_1 (x, y, prev_x);
+}
+/* Returns true when STMT is a simple iv increment.  It detects the
+following situation:
+i_1 = phi (..., i_2)
+i_2 = i_1 +/- ...  */
+static bool
+simple_iv_increment_p (gimple stmt)
+{
+tree lhs, preinc;
+gimple phi;
+size_t i;
+if (gimple_code (stmt) != GIMPLE_ASSIGN)
+return false;
+lhs = gimple_assign_lhs (stmt);
+if (TREE_CODE (lhs) != SSA_NAME)
+return false;
+if (gimple_assign_rhs_code (stmt) != PLUS_EXPR
+&& gimple_assign_rhs_code (stmt) != MINUS_EXPR)
+return false;
+preinc = gimple_assign_rhs1 (stmt);
+if (TREE_CODE (preinc) != SSA_NAME)
+return false;
+phi = SSA_NAME_DEF_STMT (preinc);
+if (gimple_code (phi) != GIMPLE_PHI)
+return false;
+for (i = 0; i < gimple_phi_num_args (phi); i++)
+if (gimple_phi_arg_def (phi, i) == lhs)
+return true;
+return false;
+}
+/* CONST_AND_COPIES is a table which maps an SSA_NAME to the current
+known value for that SSA_NAME (or NULL if no value is known).
+Propagate values from CONST_AND_COPIES into the PHI nodes of the
+successors of BB.  */
+static void
+cprop_into_successor_phis (basic_block bb)
+{
+edge e;
+edge_iterator ei;
+FOR_EACH_EDGE (e, ei, bb->succs)
+{
+int indx;
+gimple_stmt_iterator gsi;
+/* If this is an abnormal edge, then we do not want to copy propagate
+	 into the PHI alternative associated with this edge.  */
+if (e->flags & EDGE_ABNORMAL)
+	continue;
+gsi = gsi_start_phis (e->dest);
+if (gsi_end_p (gsi))
+	continue;
+indx = e->dest_idx;
+for ( ; !gsi_end_p (gsi); gsi_next (&gsi))
+	{
+	  tree new_val;
+	  use_operand_p orig_p;
+	  tree orig_val;
+gimple phi = gsi_stmt (gsi);
+	  /* The alternative may be associated with a constant, so verify
+	     it is an SSA_NAME before doing anything with it.  */
+	  orig_p = gimple_phi_arg_imm_use_ptr (phi, indx);
+	  orig_val = get_use_from_ptr (orig_p);
+	  if (TREE_CODE (orig_val) != SSA_NAME)
+	    continue;
+	  /* If we have *ORIG_P in our constant/copy table, then replace
+	     ORIG_P with its value in our constant/copy table.  */
+	  new_val = SSA_NAME_VALUE (orig_val);
+	  if (new_val
+	      && new_val != orig_val
+	      && (TREE_CODE (new_val) == SSA_NAME
+		  || is_gimple_min_invariant (new_val))
+	      && may_propagate_copy (orig_val, new_val))
+	    propagate_value (orig_p, new_val);
+	}
+}
+}
+/* We have finished optimizing BB, record any information implied by
+taking a specific outgoing edge from BB.  */
+static void
+record_edge_info (basic_block bb)
+{
+gimple_stmt_iterator gsi = gsi_last_bb (bb);
+struct edge_info *edge_info;
+if (! gsi_end_p (gsi))
+{
+gimple stmt = gsi_stmt (gsi);
+if (gimple_code (stmt) == GIMPLE_SWITCH)
+	{
+	  tree index = gimple_switch_index (stmt);
+	  if (TREE_CODE (index) == SSA_NAME)
+	    {
+	      int i;
+int n_labels = gimple_switch_num_labels (stmt);
+	      tree *info = XCNEWVEC (tree, last_basic_block);
+	      edge e;
+	      edge_iterator ei;
+	      for (i = 0; i < n_labels; i++)
+		{
+		  tree label = gimple_switch_label (stmt, i);
+		  basic_block target_bb = label_to_block (CASE_LABEL (label));
+		  if (CASE_HIGH (label)
+		      || !CASE_LOW (label)
+		      || info[target_bb->index])
+		    info[target_bb->index] = error_mark_node;
+		  else
+		    info[target_bb->index] = label;
+		}
+	      FOR_EACH_EDGE (e, ei, bb->succs)
+		{
+		  basic_block target_bb = e->dest;
+		  tree label = info[target_bb->index];
+		  if (label != NULL && label != error_mark_node)
+		    {
+		      tree x = fold_convert (TREE_TYPE (index), CASE_LOW (label));
+		      edge_info = allocate_edge_info (e);
+		      edge_info->lhs = index;
+		      edge_info->rhs = x;
+		    }
+		}
+	      free (info);
+	    }
+	}
+/* A COND_EXPR may create equivalences too.  */
+if (gimple_code (stmt) == GIMPLE_COND)
+	{
+	  edge true_edge;
+	  edge false_edge;
+tree op0 = gimple_cond_lhs (stmt);
+tree op1 = gimple_cond_rhs (stmt);
+enum tree_code code = gimple_cond_code (stmt);
+	  extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
+/* Special case comparing booleans against a constant as we
+know the value of OP0 on both arms of the branch.  i.e., we
+can record an equivalence for OP0 rather than COND.  */
+if ((code == EQ_EXPR || code == NE_EXPR)
+&& TREE_CODE (op0) == SSA_NAME
+&& TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE
+&& is_gimple_min_invariant (op1))
+{
+if (code == EQ_EXPR)
+{
+edge_info = allocate_edge_info (true_edge);
+edge_info->lhs = op0;
+edge_info->rhs = (integer_zerop (op1)
+? boolean_false_node
+: boolean_true_node);
+edge_info = allocate_edge_info (false_edge);
+edge_info->lhs = op0;
+edge_info->rhs = (integer_zerop (op1)
+? boolean_true_node
+: boolean_false_node);
+}
+else
+{
+edge_info = allocate_edge_info (true_edge);
+edge_info->lhs = op0;
+edge_info->rhs = (integer_zerop (op1)
+? boolean_true_node
+: boolean_false_node);
+edge_info = allocate_edge_info (false_edge);
+edge_info->lhs = op0;
+edge_info->rhs = (integer_zerop (op1)
+? boolean_false_node
+: boolean_true_node);
+}
+}
+else if (is_gimple_min_invariant (op0)
+&& (TREE_CODE (op1) == SSA_NAME
+|| is_gimple_min_invariant (op1)))
+{
+tree cond = build2 (code, boolean_type_node, op0, op1);
+tree inverted = invert_truthvalue (cond);
+struct edge_info *edge_info;
+edge_info = allocate_edge_info (true_edge);
+record_conditions (edge_info, cond, inverted);
+if (code == EQ_EXPR)
+{
+edge_info->lhs = op1;
+edge_info->rhs = op0;
+}
+edge_info = allocate_edge_info (false_edge);
+record_conditions (edge_info, inverted, cond);
+if (code == NE_EXPR)
+{
+edge_info->lhs = op1;
+edge_info->rhs = op0;
+}
+}
+else if (TREE_CODE (op0) == SSA_NAME
+&& (is_gimple_min_invariant (op1)
+|| TREE_CODE (op1) == SSA_NAME))
+{
+tree cond = build2 (code, boolean_type_node, op0, op1);
+tree inverted = invert_truthvalue (cond);
+struct edge_info *edge_info;
+edge_info = allocate_edge_info (true_edge);
+record_conditions (edge_info, cond, inverted);
+if (code == EQ_EXPR)
+{
+edge_info->lhs = op0;
+edge_info->rhs = op1;
+}
+edge_info = allocate_edge_info (false_edge);
+record_conditions (edge_info, inverted, cond);
+if (TREE_CODE (cond) == NE_EXPR)
+{
+edge_info->lhs = op0;
+edge_info->rhs = op1;
+}
+}
+}
+/* ??? TRUTH_NOT_EXPR can create an equivalence too.  */
+}
+}
+/* Propagate information from BB to its outgoing edges.
+This can include equivalence information implied by control statements
+at the end of BB and const/copy propagation into PHIs in BB's
+successor blocks.  */
+static void
+propagate_to_outgoing_edges (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			     basic_block bb)
+{
+record_edge_info (bb);
+cprop_into_successor_phis (bb);
+}
+/* Search for redundant computations in STMT.  If any are found, then
+replace them with the variable holding the result of the computation.
+If safe, record this expression into the available expression hash
+table.  */
+static bool
+eliminate_redundant_computations (gimple_stmt_iterator* gsi)
+{
+tree expr_type;
+tree cached_lhs;
+bool insert = true;
+bool retval = false;
+bool assigns_var_p = false;
+gimple stmt = gsi_stmt (*gsi);
+tree def = gimple_get_lhs (stmt);
+/* Certain expressions on the RHS can be optimized away, but can not
+themselves be entered into the hash tables.  */
+if (! def
+|| TREE_CODE (def) != SSA_NAME
+|| SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def)
+|| !ZERO_SSA_OPERANDS (stmt, SSA_OP_VDEF)
+/* Do not record equivalences for increments of ivs.  This would create
+	 overlapping live ranges for a very questionable gain.  */
+|| simple_iv_increment_p (stmt))
+insert = false;
+/* Check if the expression has been computed before.  */
+cached_lhs = lookup_avail_expr (stmt, insert);
+opt_stats.num_exprs_considered++;
+/* Get the type of the expression we are trying to optimize.  */
+if (is_gimple_assign (stmt))
+{
+expr_type = TREE_TYPE (gimple_assign_lhs (stmt));
+assigns_var_p = true;
+}
+else if (gimple_code (stmt) == GIMPLE_COND)
+expr_type = boolean_type_node;
+else if (is_gimple_call (stmt))
+{
+gcc_assert (gimple_call_lhs (stmt));
+expr_type = TREE_TYPE (gimple_call_lhs (stmt));
+assigns_var_p = true;
+}
+else if (gimple_code (stmt) == GIMPLE_SWITCH)
+expr_type = TREE_TYPE (gimple_switch_index (stmt));
+else
+gcc_unreachable ();
+if (!cached_lhs)
+return false;
+/* It is safe to ignore types here since we have already done
+type checking in the hashing and equality routines.  In fact
+type checking here merely gets in the way of constant
+propagation.  Also, make sure that it is safe to propagate
+CACHED_LHS into the expression in STMT.  */
+if ((TREE_CODE (cached_lhs) != SSA_NAME
+&& (assigns_var_p
+|| useless_type_conversion_p (expr_type, TREE_TYPE (cached_lhs))))
+|| may_propagate_copy_into_stmt (stmt, cached_lhs))
+{
+#if defined ENABLE_CHECKING
+gcc_assert (TREE_CODE (cached_lhs) == SSA_NAME
+		  || is_gimple_min_invariant (cached_lhs));
+#endif
+if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  Replaced redundant expr '");
+	  print_gimple_expr (dump_file, stmt, 0, dump_flags);
+	  fprintf (dump_file, "' with '");
+	  print_generic_expr (dump_file, cached_lhs, dump_flags);
+fprintf (dump_file, "'\n");
+	}
+opt_stats.num_re++;
+if (TREE_CODE (cached_lhs) == ADDR_EXPR
+	  || (POINTER_TYPE_P (expr_type)
+	      && is_gimple_min_invariant (cached_lhs)))
+	retval = true;
+if (assigns_var_p
+	  && !useless_type_conversion_p (expr_type, TREE_TYPE (cached_lhs)))
+	cached_lhs = fold_convert (expr_type, cached_lhs);
+propagate_tree_value_into_stmt (gsi, cached_lhs);
+/* Since it is always necessary to mark the result as modified,
+perhaps we should move this into propagate_tree_value_into_stmt
+itself.  */
+gimple_set_modified (gsi_stmt (*gsi), true);
+}
+return retval;
+}
+/* Return true if statement GS is an assignment that peforms a useless
+type conversion.  It is is intended to be a tuples analog of function
+tree_ssa_useless_type_conversion.  */
+static bool
+gimple_assign_unary_useless_conversion_p (gimple gs)
+{
+if (is_gimple_assign (gs)
+&& (CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (gs))
+|| gimple_assign_rhs_code (gs) == VIEW_CONVERT_EXPR
+|| gimple_assign_rhs_code (gs) == NON_LVALUE_EXPR))
+{
+tree lhs_type = TREE_TYPE (gimple_assign_lhs (gs));
+tree rhs_type = TREE_TYPE (gimple_assign_rhs1 (gs));
+return useless_type_conversion_p (lhs_type, rhs_type);
+}
+return false;
+}
+/* STMT, a GIMPLE_ASSIGN, may create certain equivalences, in either
+the available expressions table or the const_and_copies table.
+Detect and record those equivalences.  */
+/* We handle only very simple copy equivalences here.  The heavy
+lifing is done by eliminate_redundant_computations.  */
+static void
+record_equivalences_from_stmt (gimple stmt, int may_optimize_p)
+{
+tree lhs;
+enum tree_code lhs_code;
+gcc_assert (is_gimple_assign (stmt));
+lhs = gimple_assign_lhs (stmt);
+lhs_code = TREE_CODE (lhs);
+if (lhs_code == SSA_NAME
+&& (gimple_assign_single_p (stmt)
+|| gimple_assign_unary_useless_conversion_p (stmt)))
+{
+tree rhs = gimple_assign_rhs1 (stmt);
+/* Strip away any useless type conversions.  */
+STRIP_USELESS_TYPE_CONVERSION (rhs);
+/* If the RHS of the assignment is a constant or another variable that
+	 may be propagated, register it in the CONST_AND_COPIES table.  We
+	 do not need to record unwind data for this, since this is a true
+	 assignment and not an equivalence inferred from a comparison.  All
+	 uses of this ssa name are dominated by this assignment, so unwinding
+	 just costs time and space.  */
+if (may_optimize_p
+	  && (TREE_CODE (rhs) == SSA_NAME
+	      || is_gimple_min_invariant (rhs)))
+{
+	if (dump_file && (dump_flags & TDF_DETAILS))
+	  {
+	    fprintf (dump_file, "==== ASGN ");
+	    print_generic_expr (dump_file, lhs, 0);
+	    fprintf (dump_file, " = ");
+	    print_generic_expr (dump_file, rhs, 0);
+	    fprintf (dump_file, "\n");
+	  }
+	SSA_NAME_VALUE (lhs) = rhs;
+}
+}
+/* A memory store, even an aliased store, creates a useful
+equivalence.  By exchanging the LHS and RHS, creating suitable
+vops and recording the result in the available expression table,
+we may be able to expose more redundant loads.  */
+if (!gimple_has_volatile_ops (stmt)
+&& gimple_references_memory_p (stmt)
+&& gimple_assign_single_p (stmt)
+&& (TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
+	  || is_gimple_min_invariant (gimple_assign_rhs1 (stmt)))
+&& !is_gimple_reg (lhs))
+{
+tree rhs = gimple_assign_rhs1 (stmt);
+gimple new_stmt;
+/* Build a new statement with the RHS and LHS exchanged.  */
+if (TREE_CODE (rhs) == SSA_NAME)
+{
+/* NOTE tuples.  The call to gimple_build_assign below replaced
+a call to build_gimple_modify_stmt, which did not set the
+SSA_NAME_DEF_STMT on the LHS of the assignment.  Doing so
+may cause an SSA validation failure, as the LHS may be a
+default-initialized name and should have no definition.  I'm
+a bit dubious of this, as the artificial statement that we
+generate here may in fact be ill-formed, but it is simply
+used as an internal device in this pass, and never becomes
+part of the CFG.  */
+gimple defstmt = SSA_NAME_DEF_STMT (rhs);
+new_stmt = gimple_build_assign (rhs, lhs);
+SSA_NAME_DEF_STMT (rhs) = defstmt;
+}
+else
+new_stmt = gimple_build_assign (rhs, lhs);
+create_ssa_artificial_load_stmt (new_stmt, stmt, true);
+/* Finally enter the statement into the available expression
+	 table.  */
+lookup_avail_expr (new_stmt, true);
+}
+}
+/* Replace *OP_P in STMT with any known equivalent value for *OP_P from
+CONST_AND_COPIES.  */
+static bool
+cprop_operand (gimple stmt, use_operand_p op_p)
+{
+bool may_have_exposed_new_symbols = false;
+tree val;
+tree op = USE_FROM_PTR (op_p);
+/* If the operand has a known constant value or it is known to be a
+copy of some other variable, use the value or copy stored in
+CONST_AND_COPIES.  */
+val = SSA_NAME_VALUE (op);
+if (val && val != op)
+{
+/* Do not change the base variable in the virtual operand
+	 tables.  That would make it impossible to reconstruct
+	 the renamed virtual operand if we later modify this
+	 statement.  Also only allow the new value to be an SSA_NAME
+	 for propagation into virtual operands.  */
+if (!is_gimple_reg (op)
+	  && (TREE_CODE (val) != SSA_NAME
+	      || is_gimple_reg (val)
+	      || get_virtual_var (val) != get_virtual_var (op)))
+	return false;
+/* Do not replace hard register operands in asm statements.  */
+if (gimple_code (stmt) == GIMPLE_ASM
+	  && !may_propagate_copy_into_asm (op))
+	return false;
+/* Certain operands are not allowed to be copy propagated due
+	 to their interaction with exception handling and some GCC
+	 extensions.  */
+if (!may_propagate_copy (op, val))
+	return false;
+/* Do not propagate addresses that point to volatiles into memory
+	 stmts without volatile operands.  */
+if (POINTER_TYPE_P (TREE_TYPE (val))
+	  && TYPE_VOLATILE (TREE_TYPE (TREE_TYPE (val)))
+	  && gimple_has_mem_ops (stmt)
+	  && !gimple_has_volatile_ops (stmt))
+	return false;
+/* Do not propagate copies if the propagated value is at a deeper loop
+	 depth than the propagatee.  Otherwise, this may move loop variant
+	 variables outside of their loops and prevent coalescing
+	 opportunities.  If the value was loop invariant, it will be hoisted
+	 by LICM and exposed for copy propagation.  */
+if (loop_depth_of_name (val) > loop_depth_of_name (op))
+	return false;
+/* Dump details.  */
+if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  Replaced '");
+	  print_generic_expr (dump_file, op, dump_flags);
+	  fprintf (dump_file, "' with %s '",
+		   (TREE_CODE (val) != SSA_NAME ? "constant" : "variable"));
+	  print_generic_expr (dump_file, val, dump_flags);
+	  fprintf (dump_file, "'\n");
+	}
+/* If VAL is an ADDR_EXPR or a constant of pointer type, note
+	 that we may have exposed a new symbol for SSA renaming.  */
+if (TREE_CODE (val) == ADDR_EXPR
+	  || (POINTER_TYPE_P (TREE_TYPE (op))
+	      && is_gimple_min_invariant (val)))
+	may_have_exposed_new_symbols = true;
+if (TREE_CODE (val) != SSA_NAME)
+	opt_stats.num_const_prop++;
+else
+	opt_stats.num_copy_prop++;
+propagate_value (op_p, val);
+/* And note that we modified this statement.  This is now
+	 safe, even if we changed virtual operands since we will
+	 rescan the statement and rewrite its operands again.  */
+gimple_set_modified (stmt, true);
+}
+return may_have_exposed_new_symbols;
+}
+/* CONST_AND_COPIES is a table which maps an SSA_NAME to the current
+known value for that SSA_NAME (or NULL if no value is known).
+Propagate values from CONST_AND_COPIES into the uses, vuses and
+vdef_ops of STMT.  */
+static bool
+cprop_into_stmt (gimple stmt)
+{
+bool may_have_exposed_new_symbols = false;
+use_operand_p op_p;
+ssa_op_iter iter;
+FOR_EACH_SSA_USE_OPERAND (op_p, stmt, iter, SSA_OP_ALL_USES)
+{
+if (TREE_CODE (USE_FROM_PTR (op_p)) == SSA_NAME)
+	may_have_exposed_new_symbols |= cprop_operand (stmt, op_p);
+}
+return may_have_exposed_new_symbols;
+}
+/* Optimize the statement pointed to by iterator SI.
+We try to perform some simplistic global redundancy elimination and
+constant propagation:
+1- To detect global redundancy, we keep track of expressions that have
+been computed in this block and its dominators.  If we find that the
+same expression is computed more than once, we eliminate repeated
+computations by using the target of the first one.
+2- Constant values and copy assignments.  This is used to do very
+simplistic constant and copy propagation.  When a constant or copy
+assignment is found, we map the value on the RHS of the assignment to
+the variable in the LHS in the CONST_AND_COPIES table.  */
+static void
+optimize_stmt (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+	       basic_block bb, gimple_stmt_iterator si)
+{
+gimple stmt, old_stmt;
+bool may_optimize_p;
+bool may_have_exposed_new_symbols;
+bool modified_p = false;
+old_stmt = stmt = gsi_stmt (si);
+if (gimple_code (stmt) == GIMPLE_COND)
+canonicalize_comparison (stmt);
+update_stmt_if_modified (stmt);
+opt_stats.num_stmts++;
+push_stmt_changes (gsi_stmt_ptr (&si));
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "Optimizing statement ");
+print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+}
+/* Const/copy propagate into USES, VUSES and the RHS of VDEFs.  */
+may_have_exposed_new_symbols = cprop_into_stmt (stmt);
+/* If the statement has been modified with constant replacements,
+fold its RHS before checking for redundant computations.  */
+if (gimple_modified_p (stmt))
+{
+tree rhs = NULL;
+/* Try to fold the statement making sure that STMT is kept
+	 up to date.  */
+if (fold_stmt (&si))
+	{
+	  stmt = gsi_stmt (si);
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "  Folded to: ");
+	      print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+	    }
+	}
+/* We only need to consider cases that can yield a gimple operand.  */
+if (gimple_assign_single_p (stmt))
+rhs = gimple_assign_rhs1 (stmt);
+else if (gimple_code (stmt) == GIMPLE_GOTO)
+rhs = gimple_goto_dest (stmt);
+else if (gimple_code (stmt) == GIMPLE_SWITCH)
+/* This should never be an ADDR_EXPR.  */
+rhs = gimple_switch_index (stmt);
+if (rhs && TREE_CODE (rhs) == ADDR_EXPR)
+recompute_tree_invariant_for_addr_expr (rhs);
+/* Constant/copy propagation above may change the set of
+	 virtual operands associated with this statement.  Folding
+	 may remove the need for some virtual operands.
+	 Indicate we will need to rescan and rewrite the statement.  */
+may_have_exposed_new_symbols = true;
+/* Indicate that maybe_clean_or_replace_eh_stmt needs to be called,
+	 even if fold_stmt updated the stmt already and thus cleared
+	 gimple_modified_p flag on it.  */
+modified_p = true;
+}
+/* Check for redundant computations.  Do this optimization only
+for assignments that have no volatile ops and conditionals.  */
+may_optimize_p = (!gimple_has_volatile_ops (stmt)
+&& ((is_gimple_assign (stmt)
+&& !gimple_rhs_has_side_effects (stmt))
+|| (is_gimple_call (stmt)
+&& gimple_call_lhs (stmt) != NULL_TREE
+&& !gimple_rhs_has_side_effects (stmt))
+|| gimple_code (stmt) == GIMPLE_COND
+|| gimple_code (stmt) == GIMPLE_SWITCH));
+if (may_optimize_p)
+{
+may_have_exposed_new_symbols |= eliminate_redundant_computations (&si);
+stmt = gsi_stmt (si);
+}
+/* Record any additional equivalences created by this statement.  */
+if (is_gimple_assign (stmt))
+record_equivalences_from_stmt (stmt, may_optimize_p);
+/* If STMT is a COND_EXPR and it was modified, then we may know
+where it goes.  If that is the case, then mark the CFG as altered.
+This will cause us to later call remove_unreachable_blocks and
+cleanup_tree_cfg when it is safe to do so.  It is not safe to
+clean things up here since removal of edges and such can trigger
+the removal of PHI nodes, which in turn can release SSA_NAMEs to
+the manager.
+That's all fine and good, except that once SSA_NAMEs are released
+to the manager, we must not call create_ssa_name until all references
+to released SSA_NAMEs have been eliminated.
+All references to the deleted SSA_NAMEs can not be eliminated until
+we remove unreachable blocks.
+We can not remove unreachable blocks until after we have completed
+any queued jump threading.
+We can not complete any queued jump threads until we have taken
+appropriate variables out of SSA form.  Taking variables out of
+SSA form can call create_ssa_name and thus we lose.
+Ultimately I suspect we're going to need to change the interface
+into the SSA_NAME manager.  */
+if (gimple_modified_p (stmt) || modified_p)
+{
+tree val = NULL;
+if (gimple_code (stmt) == GIMPLE_COND)
+val = fold_binary (gimple_cond_code (stmt), boolean_type_node,
+gimple_cond_lhs (stmt),  gimple_cond_rhs (stmt));
+else if (gimple_code (stmt) == GIMPLE_SWITCH)
+	val = gimple_switch_index (stmt);
+if (val && TREE_CODE (val) == INTEGER_CST && find_taken_edge (bb, val))
+	cfg_altered = true;
+/* If we simplified a statement in such a way as to be shown that it
+	 cannot trap, update the eh information and the cfg to match.  */
+if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
+	{
+	  bitmap_set_bit (need_eh_cleanup, bb->index);
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    fprintf (dump_file, "  Flagged to clear EH edges.\n");
+	}
+}
+if (may_have_exposed_new_symbols)
+{
+/* Queue the statement to be re-scanned after all the
+	 AVAIL_EXPRS have been processed.  The change buffer stack for
+	 all the pushed statements will be processed when this queue
+	 is emptied.  */
+VEC_safe_push (gimple_p, heap, stmts_to_rescan, gsi_stmt_ptr (&si));
+}
+else
+{
+/* Otherwise, just discard the recently pushed change buffer.  If
+	 not, the STMTS_TO_RESCAN queue will get out of synch with the
+	 change buffer stack.  */
+discard_stmt_changes (gsi_stmt_ptr (&si));
+}
+}
+/* Search for an existing instance of STMT in the AVAIL_EXPRS table.
+If found, return its LHS. Otherwise insert STMT in the table and
+return NULL_TREE.
+Also, when an expression is first inserted in the  table, it is also
+is also added to AVAIL_EXPRS_STACK, so that it can be removed when
+we finish processing this block and its children.  */
+static tree
+lookup_avail_expr (gimple stmt, bool insert)
+{
+void **slot;
+tree lhs;
+tree temp;
+struct expr_hash_elt *element = XNEW (struct expr_hash_elt);
+/* Get LHS of assignment or call, else NULL_TREE.  */
+lhs = gimple_get_lhs (stmt);
+initialize_hash_element (stmt, lhs, element);
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "LKUP ");
+print_expr_hash_elt (dump_file, element);
+}
+/* Don't bother remembering constant assignments and copy operations.
+Constants and copy operations are handled by the constant/copy propagator
+in optimize_stmt.  */
+if (element->expr.kind == EXPR_SINGLE
+&& (TREE_CODE (element->expr.ops.single.rhs) == SSA_NAME
+|| is_gimple_min_invariant (element->expr.ops.single.rhs)))
+{
+free (element);
+return NULL_TREE;
+}
+/* Finally try to find the expression in the main expression hash table.  */
+slot = htab_find_slot_with_hash (avail_exprs, element, element->hash,
+				   (insert ? INSERT : NO_INSERT));
+if (slot == NULL)
+{
+free (element);
+return NULL_TREE;
+}
+if (*slot == NULL)
+{
+*slot = (void *) element;
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "2>>> ");
+print_expr_hash_elt (dump_file, element);
+}
+VEC_safe_push (expr_hash_elt_t, heap, avail_exprs_stack, element);
+return NULL_TREE;
+}
+/* Extract the LHS of the assignment so that it can be used as the current
+definition of another variable.  */
+lhs = ((struct expr_hash_elt *)*slot)->lhs;
+/* See if the LHS appears in the CONST_AND_COPIES table.  If it does, then
+use the value from the const_and_copies table.  */
+if (TREE_CODE (lhs) == SSA_NAME)
+{
+temp = SSA_NAME_VALUE (lhs);
+if (temp)
+	lhs = temp;
+}
+free (element);
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "FIND: ");
+print_generic_expr (dump_file, lhs, 0);
+fprintf (dump_file, "\n");
+}
+return lhs;
+}
+/* Hashing and equality functions for AVAIL_EXPRS.  We compute a value number
+for expressions using the code of the expression and the SSA numbers of
+its operands.  */
+static hashval_t
+avail_expr_hash (const void *p)
+{
+gimple stmt = ((const struct expr_hash_elt *)p)->stmt;
+const struct hashable_expr *expr = &((const struct expr_hash_elt *)p)->expr;
+tree vuse;
+ssa_op_iter iter;
+hashval_t val = 0;
+val = iterative_hash_hashable_expr (expr, val);
+/* If the hash table entry is not associated with a statement, then we
+can just hash the expression and not worry about virtual operands
+and such.  */
+if (!stmt)
+return val;
+/* Add the SSA version numbers of every vuse operand.  This is important
+because compound variables like arrays are not renamed in the
+operands.  Rather, the rename is done on the virtual variable
+representing all the elements of the array.  */
+FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, iter, SSA_OP_VUSE)
+val = iterative_hash_expr (vuse, val);
+return val;
+}
+static hashval_t
+real_avail_expr_hash (const void *p)
+{
+return ((const struct expr_hash_elt *)p)->hash;
+}
+static int
+avail_expr_eq (const void *p1, const void *p2)
+{
+gimple stmt1 = ((const struct expr_hash_elt *)p1)->stmt;
+const struct hashable_expr *expr1 = &((const struct expr_hash_elt *)p1)->expr;
+const struct expr_hash_elt *stamp1 = ((const struct expr_hash_elt *)p1)->stamp;
+gimple stmt2 = ((const struct expr_hash_elt *)p2)->stmt;
+const struct hashable_expr *expr2 = &((const struct expr_hash_elt *)p2)->expr;
+const struct expr_hash_elt *stamp2 = ((const struct expr_hash_elt *)p2)->stamp;
+/* This case should apply only when removing entries from the table.  */
+if (stamp1 == stamp2)
+return true;
+/* FIXME tuples:
+We add stmts to a hash table and them modify them. To detect the case
+that we modify a stmt and then search for it, we assume that the hash
+is always modified by that change.
+We have to fully check why this doesn't happen on trunk or rewrite
+this in a more  reliable (and easier to understand) way. */
+if (((const struct expr_hash_elt *)p1)->hash
+!= ((const struct expr_hash_elt *)p2)->hash)
+return false;
+/* In case of a collision, both RHS have to be identical and have the
+same VUSE operands.  */
+if (hashable_expr_equal_p (expr1, expr2)
+&& types_compatible_p (expr1->type, expr2->type))
+{
+/* Note that STMT1 and/or STMT2 may be NULL.  */
+bool ret = compare_ssa_operands_equal (stmt1, stmt2, SSA_OP_VUSE);
+return ret;
+}
+return false;
+}
+/* PHI-ONLY copy and constant propagation.  This pass is meant to clean
+up degenerate PHIs created by or exposed by jump threading.  */
+/* Given PHI, return its RHS if the PHI is a degenerate, otherwise return
+NULL.  */
+static tree
+degenerate_phi_result (gimple phi)
+{
+tree lhs = gimple_phi_result (phi);
+tree val = NULL;
+size_t i;
+/* Ignoring arguments which are the same as LHS, if all the remaining
+arguments are the same, then the PHI is a degenerate and has the
+value of that common argument.  */
+for (i = 0; i < gimple_phi_num_args (phi); i++)
+{
+tree arg = gimple_phi_arg_def (phi, i);
+if (arg == lhs)
+	continue;
+else if (!val)
+	val = arg;
+else if (!operand_equal_p (arg, val, 0))
+	break;
+}
+return (i == gimple_phi_num_args (phi) ? val : NULL);
+}
+/* Given a statement STMT, which is either a PHI node or an assignment,
+remove it from the IL.  */
+static void
+remove_stmt_or_phi (gimple stmt)
+{
+gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
+if (gimple_code (stmt) == GIMPLE_PHI)
+remove_phi_node (&gsi, true);
+else
+{
+gsi_remove (&gsi, true);
+release_defs (stmt);
+}
+}
+/* Given a statement STMT, which is either a PHI node or an assignment,
+return the "rhs" of the node, in the case of a non-degenerate
+phi, NULL is returned.  */
+static tree
+get_rhs_or_phi_arg (gimple stmt)
+{
+if (gimple_code (stmt) == GIMPLE_PHI)
+return degenerate_phi_result (stmt);
+else if (gimple_assign_single_p (stmt))
+return gimple_assign_rhs1 (stmt);
+else
+gcc_unreachable ();
+}
+/* Given a statement STMT, which is either a PHI node or an assignment,
+return the "lhs" of the node.  */
+static tree
+get_lhs_or_phi_result (gimple stmt)
+{
+if (gimple_code (stmt) == GIMPLE_PHI)
+return gimple_phi_result (stmt);
+else if (is_gimple_assign (stmt))
+return gimple_assign_lhs (stmt);
+else
+gcc_unreachable ();
+}
+/* Propagate RHS into all uses of LHS (when possible).
+RHS and LHS are derived from STMT, which is passed in solely so
+that we can remove it if propagation is successful.
+When propagating into a PHI node or into a statement which turns
+into a trivial copy or constant initialization, set the
+appropriate bit in INTERESTING_NAMEs so that we will visit those
+nodes as well in an effort to pick up secondary optimization
+opportunities.  */
+static void
+propagate_rhs_into_lhs (gimple stmt, tree lhs, tree rhs, bitmap interesting_names)
+{
+/* First verify that propagation is valid and isn't going to move a
+loop variant variable outside its loop.  */
+if (! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs)
+&& (TREE_CODE (rhs) != SSA_NAME
+	  || ! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs))
+&& may_propagate_copy (lhs, rhs)
+&& loop_depth_of_name (lhs) >= loop_depth_of_name (rhs))
+{
+use_operand_p use_p;
+imm_use_iterator iter;
+gimple use_stmt;
+bool all = true;
+/* Dump details.  */
+if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  Replacing '");
+	  print_generic_expr (dump_file, lhs, dump_flags);
+	  fprintf (dump_file, "' with %s '",
+	           (TREE_CODE (rhs) != SSA_NAME ? "constant" : "variable"));
+		   print_generic_expr (dump_file, rhs, dump_flags);
+	  fprintf (dump_file, "'\n");
+	}
+/* Walk over every use of LHS and try to replace the use with RHS.
+	 At this point the only reason why such a propagation would not
+	 be successful would be if the use occurs in an ASM_EXPR.  */
+FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
+	{
+	  /* It's not always safe to propagate into an ASM_EXPR.  */
+	  if (gimple_code (use_stmt) == GIMPLE_ASM
+&& ! may_propagate_copy_into_asm (lhs))
+	    {
+	      all = false;
+	      continue;
+	    }
+	  /* Dump details.  */
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "    Original statement:");
+	      print_gimple_stmt (dump_file, use_stmt, 0, dump_flags);
+	    }
+	  push_stmt_changes (&use_stmt);
+	  /* Propagate the RHS into this use of the LHS.  */
+	  FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+	    propagate_value (use_p, rhs);
+	  /* Special cases to avoid useless calls into the folding
+	     routines, operand scanning, etc.
+	     First, propagation into a PHI may cause the PHI to become
+	     a degenerate, so mark the PHI as interesting.  No other
+	     actions are necessary.
+	     Second, if we're propagating a virtual operand and the
+	     propagation does not change the underlying _DECL node for
+	     the virtual operand, then no further actions are necessary.  */
+	  if (gimple_code (use_stmt) == GIMPLE_PHI
+	      || (! is_gimple_reg (lhs)
+		  && TREE_CODE (rhs) == SSA_NAME
+		  && SSA_NAME_VAR (lhs) == SSA_NAME_VAR (rhs)))
+	    {
+	      /* Dump details.  */
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		{
+		  fprintf (dump_file, "    Updated statement:");
+		  print_gimple_stmt (dump_file, use_stmt, 0, dump_flags);
+		}
+	      /* Propagation into a PHI may expose new degenerate PHIs,
+		 so mark the result of the PHI as interesting.  */
+	      if (gimple_code (use_stmt) == GIMPLE_PHI)
+		{
+		  tree result = get_lhs_or_phi_result (use_stmt);
+		  bitmap_set_bit (interesting_names, SSA_NAME_VERSION (result));
+		}
+	      discard_stmt_changes (&use_stmt);
+	      continue;
+	    }
+	  /* From this point onward we are propagating into a
+	     real statement.  Folding may (or may not) be possible,
+	     we may expose new operands, expose dead EH edges,
+	     etc.  */
+/* NOTE tuples. In the tuples world, fold_stmt_inplace
+cannot fold a call that simplifies to a constant,
+because the GIMPLE_CALL must be replaced by a
+GIMPLE_ASSIGN, and there is no way to effect such a
+transformation in-place.  We might want to consider
+using the more general fold_stmt here.  */
+	  fold_stmt_inplace (use_stmt);
+	  /* Sometimes propagation can expose new operands to the
+	     renamer.  Note this will call update_stmt at the
+	     appropriate time.  */
+	  pop_stmt_changes (&use_stmt);
+	  /* Dump details.  */
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "    Updated statement:");
+	      print_gimple_stmt (dump_file, use_stmt, 0, dump_flags);
+	    }
+	  /* If we replaced a variable index with a constant, then
+	     we would need to update the invariant flag for ADDR_EXPRs.  */
+if (gimple_assign_single_p (use_stmt)
+&& TREE_CODE (gimple_assign_rhs1 (use_stmt)) == ADDR_EXPR)
+	    recompute_tree_invariant_for_addr_expr
+(gimple_assign_rhs1 (use_stmt));
+	  /* If we cleaned up EH information from the statement,
+	     mark its containing block as needing EH cleanups.  */
+	  if (maybe_clean_or_replace_eh_stmt (use_stmt, use_stmt))
+	    {
+	      bitmap_set_bit (need_eh_cleanup, gimple_bb (use_stmt)->index);
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		fprintf (dump_file, "  Flagged to clear EH edges.\n");
+	    }
+	  /* Propagation may expose new trivial copy/constant propagation
+	     opportunities.  */
+if (gimple_assign_single_p (use_stmt)
+&& TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
+&& (TREE_CODE (gimple_assign_rhs1 (use_stmt)) == SSA_NAME
+|| is_gimple_min_invariant (gimple_assign_rhs1 (use_stmt))))
+{
+	      tree result = get_lhs_or_phi_result (use_stmt);
+	      bitmap_set_bit (interesting_names, SSA_NAME_VERSION (result));
+	    }
+	  /* Propagation into these nodes may make certain edges in
+	     the CFG unexecutable.  We want to identify them as PHI nodes
+	     at the destination of those unexecutable edges may become
+	     degenerates.  */
+	  else if (gimple_code (use_stmt) == GIMPLE_COND
+		   || gimple_code (use_stmt) == GIMPLE_SWITCH
+		   || gimple_code (use_stmt) == GIMPLE_GOTO)
+{
+	      tree val;
+	      if (gimple_code (use_stmt) == GIMPLE_COND)
+val = fold_binary (gimple_cond_code (use_stmt),
+boolean_type_node,
+gimple_cond_lhs (use_stmt),
+gimple_cond_rhs (use_stmt));
+else if (gimple_code (use_stmt) == GIMPLE_SWITCH)
+		val = gimple_switch_index (use_stmt);
+	      else
+		val = gimple_goto_dest  (use_stmt);
+	      if (val && is_gimple_min_invariant (val))
+		{
+		  basic_block bb = gimple_bb (use_stmt);
+		  edge te = find_taken_edge (bb, val);
+		  edge_iterator ei;
+		  edge e;
+		  gimple_stmt_iterator gsi, psi;
+		  /* Remove all outgoing edges except TE.  */
+		  for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei));)
+		    {
+		      if (e != te)
+			{
+			  /* Mark all the PHI nodes at the destination of
+			     the unexecutable edge as interesting.  */
+for (psi = gsi_start_phis (e->dest);
+!gsi_end_p (psi);
+gsi_next (&psi))
+{
+gimple phi = gsi_stmt (psi);
+			      tree result = gimple_phi_result (phi);
+			      int version = SSA_NAME_VERSION (result);
+			      bitmap_set_bit (interesting_names, version);
+			    }
+			  te->probability += e->probability;
+			  te->count += e->count;
+			  remove_edge (e);
+			  cfg_altered = true;
+			}
+		      else
+			ei_next (&ei);
+		    }
+		  gsi = gsi_last_bb (gimple_bb (use_stmt));
+		  gsi_remove (&gsi, true);
+		  /* And fixup the flags on the single remaining edge.  */
+		  te->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
+		  te->flags &= ~EDGE_ABNORMAL;
+		  te->flags |= EDGE_FALLTHRU;
+		  if (te->probability > REG_BR_PROB_BASE)
+		    te->probability = REG_BR_PROB_BASE;
+	        }
+	    }
+	}
+/* Ensure there is nothing else to do. */
+gcc_assert (!all || has_zero_uses (lhs));
+/* If we were able to propagate away all uses of LHS, then
+	 we can remove STMT.  */
+if (all)
+	remove_stmt_or_phi (stmt);
+}
+}
+/* STMT is either a PHI node (potentially a degenerate PHI node) or
+a statement that is a trivial copy or constant initialization.
+Attempt to eliminate T by propagating its RHS into all uses of
+its LHS.  This may in turn set new bits in INTERESTING_NAMES
+for nodes we want to revisit later.
+All exit paths should clear INTERESTING_NAMES for the result
+of STMT.  */
+static void
+eliminate_const_or_copy (gimple stmt, bitmap interesting_names)
+{
+tree lhs = get_lhs_or_phi_result (stmt);
+tree rhs;
+int version = SSA_NAME_VERSION (lhs);
+/* If the LHS of this statement or PHI has no uses, then we can
+just eliminate it.  This can occur if, for example, the PHI
+was created by block duplication due to threading and its only
+use was in the conditional at the end of the block which was
+deleted.  */
+if (has_zero_uses (lhs))
+{
+bitmap_clear_bit (interesting_names, version);
+remove_stmt_or_phi (stmt);
+return;
+}
+/* Get the RHS of the assignment or PHI node if the PHI is a
+degenerate.  */
+rhs = get_rhs_or_phi_arg (stmt);
+if (!rhs)
+{
+bitmap_clear_bit (interesting_names, version);
+return;
+}
+propagate_rhs_into_lhs (stmt, lhs, rhs, interesting_names);
+/* Note that STMT may well have been deleted by now, so do
+not access it, instead use the saved version # to clear
+T's entry in the worklist.  */
+bitmap_clear_bit (interesting_names, version);
+}
+/* The first phase in degenerate PHI elimination.
+Eliminate the degenerate PHIs in BB, then recurse on the
+dominator children of BB.  */
+static void
+eliminate_degenerate_phis_1 (basic_block bb, bitmap interesting_names)
+{
+gimple_stmt_iterator gsi;
+basic_block son;
+for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+{
+gimple phi = gsi_stmt (gsi);
+eliminate_const_or_copy (phi, interesting_names);
+}
+/* Recurse into the dominator children of BB.  */
+for (son = first_dom_son (CDI_DOMINATORS, bb);
+son;
+son = next_dom_son (CDI_DOMINATORS, son))
+eliminate_degenerate_phis_1 (son, interesting_names);
+}
+/* A very simple pass to eliminate degenerate PHI nodes from the
+IL.  This is meant to be fast enough to be able to be run several
+times in the optimization pipeline.
+Certain optimizations, particularly those which duplicate blocks
+or remove edges from the CFG can create or expose PHIs which are
+trivial copies or constant initializations.
+While we could pick up these optimizations in DOM or with the
+combination of copy-prop and CCP, those solutions are far too
+heavy-weight for our needs.
+This implementation has two phases so that we can efficiently
+eliminate the first order degenerate PHIs and second order
+degenerate PHIs.
+The first phase performs a dominator walk to identify and eliminate
+the vast majority of the degenerate PHIs.  When a degenerate PHI
+is identified and eliminated any affected statements or PHIs
+are put on a worklist.
+The second phase eliminates degenerate PHIs and trivial copies
+or constant initializations using the worklist.  This is how we
+pick up the secondary optimization opportunities with minimal
+cost.  */
+static unsigned int
+eliminate_degenerate_phis (void)
+{
+bitmap interesting_names;
+bitmap interesting_names1;
+/* Bitmap of blocks which need EH information updated.  We can not
+update it on-the-fly as doing so invalidates the dominator tree.  */
+need_eh_cleanup = BITMAP_ALLOC (NULL);
+/* INTERESTING_NAMES is effectively our worklist, indexed by
+SSA_NAME_VERSION.
+A set bit indicates that the statement or PHI node which
+defines the SSA_NAME should be (re)examined to determine if
+it has become a degenerate PHI or trivial const/copy propagation
+opportunity.
+Experiments have show we generally get better compilation
+time behavior with bitmaps rather than sbitmaps.  */
+interesting_names = BITMAP_ALLOC (NULL);
+interesting_names1 = BITMAP_ALLOC (NULL);
+calculate_dominance_info (CDI_DOMINATORS);
+cfg_altered = false;
+/* First phase.  Eliminate degenerate PHIs via a dominator
+walk of the CFG.
+Experiments have indicated that we generally get better
+compile-time behavior by visiting blocks in the first
+phase in dominator order.  Presumably this is because walking
+in dominator order leaves fewer PHIs for later examination
+by the worklist phase.  */
+eliminate_degenerate_phis_1 (ENTRY_BLOCK_PTR, interesting_names);
+/* Second phase.  Eliminate second order degenerate PHIs as well
+as trivial copies or constant initializations identified by
+the first phase or this phase.  Basically we keep iterating
+until our set of INTERESTING_NAMEs is empty.   */
+while (!bitmap_empty_p (interesting_names))
+{
+unsigned int i;
+bitmap_iterator bi;
+/* EXECUTE_IF_SET_IN_BITMAP does not like its bitmap
+	 changed during the loop.  Copy it to another bitmap and
+	 use that.  */
+bitmap_copy (interesting_names1, interesting_names);
+EXECUTE_IF_SET_IN_BITMAP (interesting_names1, 0, i, bi)
+	{
+	  tree name = ssa_name (i);
+	  /* Ignore SSA_NAMEs that have been released because
+	     their defining statement was deleted (unreachable).  */
+	  if (name)
+	    eliminate_const_or_copy (SSA_NAME_DEF_STMT (ssa_name (i)),
+				     interesting_names);
+	}
+}
+if (cfg_altered)
+free_dominance_info (CDI_DOMINATORS);
+/* Propagation of const and copies may make some EH edges dead.  Purge
+such edges from the CFG as needed.  */
+if (!bitmap_empty_p (need_eh_cleanup))
+{
+gimple_purge_all_dead_eh_edges (need_eh_cleanup);
+BITMAP_FREE (need_eh_cleanup);
+}
+BITMAP_FREE (interesting_names);
+BITMAP_FREE (interesting_names1);
+return 0;
+}
+struct gimple_opt_pass pass_phi_only_cprop =
+{
+{
+GIMPLE_PASS,
+"phicprop",                           /* name */
+gate_dominator,                       /* gate */
+eliminate_degenerate_phis,            /* execute */
+NULL,                                 /* sub */
+NULL,                                 /* next */
+0,                                    /* static_pass_number */
+TV_TREE_PHI_CPROP,                    /* tv_id */
+PROP_cfg | PROP_ssa | PROP_alias,     /* properties_required */
+0,                                    /* properties_provided */
+0,		                        /* properties_destroyed */
+0,                                    /* todo_flags_start */
+TODO_cleanup_cfg
+| TODO_dump_func
+| TODO_ggc_collect
+| TODO_verify_ssa
+| TODO_verify_stmts
+| TODO_update_ssa			/* todo_flags_finish */
+}
+};

Mercurial > hg > CbC > CbC_gcc

comparison gcc/tree-ssa-dom.c @ 0:a06113de4d67