gcc/tree-ssa-phiprop.c - gcc - Git at Google

 /* Backward propagation of indirect loads through PHIs.
    Copyright (C) 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
    Contributed by Richard Guenther <rguenther@suse.de>

 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 "tm_p.h"
 #include "basic-block.h"
 #include "timevar.h"
 #include "tree-pretty-print.h"
 #include "gimple-pretty-print.h"
 #include "tree-flow.h"
 #include "tree-pass.h"
 #include "tree-dump.h"
 #include "langhooks.h"
 #include "flags.h"

 /* This pass propagates indirect loads through the PHI node for its
    address to make the load source possibly non-addressable and to
    allow for PHI optimization to trigger.

    For example the pass changes

      # addr_1 = PHI <&a, &b>
      tmp_1 = *addr_1;

    to

      # tmp_1 = PHI <a, b>

    but also handles more complex scenarios like

      D.2077_2 = &this_1(D)->a1;
      ...

      # b_12 = PHI <&c(2), D.2077_2(3)>
      D.2114_13 = *b_12;
      ...

      # b_15 = PHI <b_12(4), &b(5)>
      D.2080_5 = &this_1(D)->a0;
      ...

      # b_18 = PHI <D.2080_5(6), &c(7)>
      ...

      # b_21 = PHI <b_15(8), b_18(9)>
      D.2076_8 = *b_21;

    where the addresses loaded are defined by PHIs itself.
    The above happens for

      std::max(std::min(a0, c), std::min(std::max(a1, c), b))

    where this pass transforms it to a form later PHI optimization
    recognizes and transforms it to the simple

      D.2109_10 = this_1(D)->a1;
      D.2110_11 = c;
      D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
      D.2115_14 = b;
      D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
      D.2119_16 = this_1(D)->a0;
      D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
      D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;

    The pass does a dominator walk processing loads using a basic-block
    local analysis and stores the result for use by transformations on
    dominated basic-blocks.  */


 /* Structure to keep track of the value of a dereferenced PHI result
    and the virtual operand used for that dereference.  */

 struct phiprop_d
 {
   tree value;
   tree vuse;
 };

 /* Verify if the value recorded for NAME in PHIVN is still valid at
    the start of basic block BB.  */

 static bool
 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
 {
   tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
   gimple use_stmt;
   imm_use_iterator ui2;
   bool ok = true;

   /* The def stmts of the virtual uses need to be dominated by bb.  */
   gcc_assert (vuse != NULL_TREE);

   FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
     {
       /* If BB does not dominate a VDEF, the value is invalid.  */
       if ((gimple_vdef (use_stmt) != NULL_TREE
 	   || gimple_code (use_stmt) == GIMPLE_PHI)
 	  && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
 	{
 	  ok = false;
 	  BREAK_FROM_IMM_USE_STMT (ui2);
 	}
     }

   return ok;
 }

 /* Insert a new phi node for the dereference of PHI at basic_block
    BB with the virtual operands from USE_STMT.  */

 static tree
 phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,
 		    struct phiprop_d *phivn, size_t n)
 {
   tree res;
   gimple new_phi;
   edge_iterator ei;
   edge e;

   gcc_assert (is_gimple_assign (use_stmt)
 	      && gimple_assign_rhs_code (use_stmt) == MEM_REF);

   /* Build a new PHI node to replace the definition of
      the indirect reference lhs.  */
   res = gimple_assign_lhs (use_stmt);
   SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb);

   if (dump_file && (dump_flags & TDF_DETAILS))
     {
       fprintf (dump_file, "Inserting PHI for result of load ");
       print_gimple_stmt (dump_file, use_stmt, 0, 0);
     }

   /* Add PHI arguments for each edge inserting loads of the
      addressable operands.  */
   FOR_EACH_EDGE (e, ei, bb->preds)
     {
       tree old_arg, new_var;
       gimple tmp;
       source_location locus;

       old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
       locus = gimple_phi_arg_location_from_edge (phi, e);
       while (TREE_CODE (old_arg) == SSA_NAME
 	     && (SSA_NAME_VERSION (old_arg) >= n
 	         || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
 	{
 	  gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
 	  old_arg = gimple_assign_rhs1 (def_stmt);
 	  locus = gimple_location (def_stmt);
 	}

       if (TREE_CODE (old_arg) == SSA_NAME)
 	{
 	  if (dump_file && (dump_flags & TDF_DETAILS))
 	    {
 	      fprintf (dump_file, "  for edge defining ");
 	      print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
 	      fprintf (dump_file, " reusing PHI result ");
 	      print_generic_expr (dump_file,
 				  phivn[SSA_NAME_VERSION (old_arg)].value, 0);
 	      fprintf (dump_file, "\n");
 	    }
 	  /* Reuse a formerly created dereference.  */
 	  new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
 	}
       else
 	{
 	  tree rhs = gimple_assign_rhs1 (use_stmt);
 	  gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
 	  new_var = create_tmp_reg (TREE_TYPE (rhs), NULL);
 	  if (!is_gimple_min_invariant (old_arg))
 	    old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
 	  else
 	    old_arg = unshare_expr (old_arg);
 	  tmp = gimple_build_assign (new_var,
 				     fold_build2 (MEM_REF, TREE_TYPE (rhs),
 						  old_arg,
 						  TREE_OPERAND (rhs, 1)));
 	  gcc_assert (is_gimple_reg (new_var));
 	  add_referenced_var (new_var);
 	  new_var = make_ssa_name (new_var, tmp);
 	  gimple_assign_set_lhs (tmp, new_var);
 	  gimple_set_location (tmp, locus);

 	  gsi_insert_on_edge (e, tmp);
 	  update_stmt (tmp);

 	  if (dump_file && (dump_flags & TDF_DETAILS))
 	    {
 	      fprintf (dump_file, "  for edge defining ");
 	      print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
 	      fprintf (dump_file, " inserting load ");
 	      print_gimple_stmt (dump_file, tmp, 0, 0);
 	    }
 	}

       add_phi_arg (new_phi, new_var, e, locus);
     }

   update_stmt (new_phi);

   if (dump_file && (dump_flags & TDF_DETAILS))
     print_gimple_stmt (dump_file, new_phi, 0, 0);

   return res;
 }

 /* Propagate between the phi node arguments of PHI in BB and phi result
    users.  For now this matches
         # p_2 = PHI <&x, &y>
       <Lx>:;
 	p_3 = p_2;
 	z_2 = *p_3;
    and converts it to
 	# z_2 = PHI <x, y>
       <Lx>:;
    Returns true if a transformation was done and edge insertions
    need to be committed.  Global data PHIVN and N is used to track
    past transformation results.  We need to be especially careful here
    with aliasing issues as we are moving memory reads.  */

 static bool
 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
 		    size_t n)
 {
   tree ptr = PHI_RESULT (phi);
   gimple use_stmt;
   tree res = NULL_TREE;
   gimple_stmt_iterator gsi;
   imm_use_iterator ui;
   use_operand_p arg_p, use;
   ssa_op_iter i;
   bool phi_inserted;
   tree type = NULL_TREE;
   bool one_invariant = false;

   if (!POINTER_TYPE_P (TREE_TYPE (ptr))
       || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
     return false;

   /* Check if we can "cheaply" dereference all phi arguments.  */
   FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
     {
       tree arg = USE_FROM_PTR (arg_p);
       /* Walk the ssa chain until we reach a ssa name we already
 	 created a value for or we reach a definition of the form
 	 ssa_name_n = &var;  */
       while (TREE_CODE (arg) == SSA_NAME
 	     && !SSA_NAME_IS_DEFAULT_DEF (arg)
 	     && (SSA_NAME_VERSION (arg) >= n
 	         || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
 	{
 	  gimple def_stmt = SSA_NAME_DEF_STMT (arg);
 	  if (!gimple_assign_single_p (def_stmt))
 	    return false;
 	  arg = gimple_assign_rhs1 (def_stmt);
 	}
       if (TREE_CODE (arg) != ADDR_EXPR
 	  && !(TREE_CODE (arg) == SSA_NAME
 	       && SSA_NAME_VERSION (arg) < n
 	       && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
 	       && (!type
 		   || types_compatible_p
 		       (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
 	       && phivn_valid_p (phivn, arg, bb)))
 	return false;
       if (!type
 	  && TREE_CODE (arg) == SSA_NAME)
 	type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
       if (TREE_CODE (arg) == ADDR_EXPR
 	  && is_gimple_min_invariant (arg))
 	one_invariant = true;
     }

   /* If we neither have an address of a decl nor can reuse a previously
      inserted load, do not hoist anything.  */
   if (!one_invariant
       && !type)
     return false;

   /* Find a dereferencing use.  First follow (single use) ssa
      copy chains for ptr.  */
   while (single_imm_use (ptr, &use, &use_stmt)
 	 && gimple_assign_ssa_name_copy_p (use_stmt))
     ptr = gimple_assign_lhs (use_stmt);

   /* Replace the first dereference of *ptr if there is one and if we
      can move the loads to the place of the ptr phi node.  */
   phi_inserted = false;
   FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
     {
       gimple def_stmt;
       tree vuse;

       /* Check whether this is a load of *ptr.  */
       if (!(is_gimple_assign (use_stmt)
 	    && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
 	    && gimple_assign_rhs_code (use_stmt) == MEM_REF
 	    && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
 	    && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
 	    && (!type
 		|| types_compatible_p
 		     (TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
 	    /* We cannot replace a load that may throw or is volatile.  */
 	    && !stmt_can_throw_internal (use_stmt)))
 	continue;

       /* Check if we can move the loads.  The def stmt of the virtual use
 	 needs to be in a different basic block dominating bb.  */
       vuse = gimple_vuse (use_stmt);
       def_stmt = SSA_NAME_DEF_STMT (vuse);
       if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
 	  && (gimple_bb (def_stmt) == bb
 	      || !dominated_by_p (CDI_DOMINATORS,
 				  bb, gimple_bb (def_stmt))))
 	goto next;

       /* Found a proper dereference.  Insert a phi node if this
 	 is the first load transformation.  */
       if (!phi_inserted)
 	{
 	  res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
 	  type = TREE_TYPE (res);

 	  /* Remember the value we created for *ptr.  */
 	  phivn[SSA_NAME_VERSION (ptr)].value = res;
 	  phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;

 	  /* Remove old stmt.  The phi is taken care of by DCE, if we
 	     want to delete it here we also have to delete all intermediate
 	     copies.  */
 	  gsi = gsi_for_stmt (use_stmt);
 	  gsi_remove (&gsi, true);

 	  phi_inserted = true;
 	}
       else
 	{
 	  /* Further replacements are easy, just make a copy out of the
 	     load.  */
 	  gimple_assign_set_rhs1 (use_stmt, res);
 	  update_stmt (use_stmt);
 	}

 next:;
       /* Continue searching for a proper dereference.  */
     }

   return phi_inserted;
 }

 /* Main entry for phiprop pass.  */

 static unsigned int
 tree_ssa_phiprop (void)
 {
   VEC(basic_block, heap) *bbs;
   struct phiprop_d *phivn;
   bool did_something = false;
   basic_block bb;
   gimple_stmt_iterator gsi;
   unsigned i;
   size_t n;

   calculate_dominance_info (CDI_DOMINATORS);

   n = num_ssa_names;
   phivn = XCNEWVEC (struct phiprop_d, n);

   /* Walk the dominator tree in preorder.  */
   bbs = get_all_dominated_blocks (CDI_DOMINATORS,
 				  single_succ (ENTRY_BLOCK_PTR));
   FOR_EACH_VEC_ELT (basic_block, bbs, i, bb)
     for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
       did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);

   if (did_something)
     gsi_commit_edge_inserts ();

   VEC_free (basic_block, heap, bbs);
   free (phivn);

   return 0;
 }

 static bool
 gate_phiprop (void)
 {
   return flag_tree_phiprop;
 }

 struct gimple_opt_pass pass_phiprop =
 {
  {
   GIMPLE_PASS,
   "phiprop",			/* name */
   gate_phiprop,			/* gate */
   tree_ssa_phiprop,		/* execute */
   NULL,				/* sub */
   NULL,				/* next */
   0,				/* static_pass_number */
   TV_TREE_PHIPROP,		/* tv_id */
   PROP_cfg | PROP_ssa,		/* properties_required */
   0,				/* properties_provided */
   0,				/* properties_destroyed */
   0,				/* todo_flags_start */
   TODO_dump_func
   | TODO_ggc_collect
   | TODO_update_ssa
   | TODO_verify_ssa		/* todo_flags_finish */
  }
 };
	/* Backward propagation of indirect loads through PHIs.
	Copyright (C) 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
	Contributed by Richard Guenther <rguenther@suse.de>

	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 "tm_p.h"
	#include "basic-block.h"
	#include "timevar.h"
	#include "tree-pretty-print.h"
	#include "gimple-pretty-print.h"
	#include "tree-flow.h"
	#include "tree-pass.h"
	#include "tree-dump.h"
	#include "langhooks.h"
	#include "flags.h"

	/* This pass propagates indirect loads through the PHI node for its
	address to make the load source possibly non-addressable and to
	allow for PHI optimization to trigger.

	For example the pass changes

	# addr_1 = PHI <&a, &b>
	tmp_1 = *addr_1;

	to

	# tmp_1 = PHI <a, b>

	but also handles more complex scenarios like

	D.2077_2 = &this_1(D)->a1;
	...

	# b_12 = PHI <&c(2), D.2077_2(3)>
	D.2114_13 = *b_12;
	...

	# b_15 = PHI <b_12(4), &b(5)>
	D.2080_5 = &this_1(D)->a0;
	...

	# b_18 = PHI <D.2080_5(6), &c(7)>
	...

	# b_21 = PHI <b_15(8), b_18(9)>
	D.2076_8 = *b_21;

	where the addresses loaded are defined by PHIs itself.
	The above happens for

	std::max(std::min(a0, c), std::min(std::max(a1, c), b))

	where this pass transforms it to a form later PHI optimization
	recognizes and transforms it to the simple

	D.2109_10 = this_1(D)->a1;
	D.2110_11 = c;
	D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
	D.2115_14 = b;
	D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
	D.2119_16 = this_1(D)->a0;
	D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
	D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;

	The pass does a dominator walk processing loads using a basic-block
	local analysis and stores the result for use by transformations on
	dominated basic-blocks. */


	/* Structure to keep track of the value of a dereferenced PHI result
	and the virtual operand used for that dereference. */

	struct phiprop_d
	{
	tree value;
	tree vuse;
	};

	/* Verify if the value recorded for NAME in PHIVN is still valid at
	the start of basic block BB. */

	static bool
	phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
	{
	tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
	gimple use_stmt;
	imm_use_iterator ui2;
	bool ok = true;

	/* The def stmts of the virtual uses need to be dominated by bb. */
	gcc_assert (vuse != NULL_TREE);

	FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
	{
	/* If BB does not dominate a VDEF, the value is invalid. */
	if ((gimple_vdef (use_stmt) != NULL_TREE
	\|\| gimple_code (use_stmt) == GIMPLE_PHI)
	&& !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
	{
	ok = false;
	BREAK_FROM_IMM_USE_STMT (ui2);
	}
	}

	return ok;
	}

	/* Insert a new phi node for the dereference of PHI at basic_block
	BB with the virtual operands from USE_STMT. */

	static tree
	phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,
	struct phiprop_d *phivn, size_t n)
	{
	tree res;
	gimple new_phi;
	edge_iterator ei;
	edge e;

	gcc_assert (is_gimple_assign (use_stmt)
	&& gimple_assign_rhs_code (use_stmt) == MEM_REF);

	/* Build a new PHI node to replace the definition of
	the indirect reference lhs. */
	res = gimple_assign_lhs (use_stmt);
	SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb);

	if (dump_file && (dump_flags & TDF_DETAILS))
	{
	fprintf (dump_file, "Inserting PHI for result of load ");
	print_gimple_stmt (dump_file, use_stmt, 0, 0);
	}

	/* Add PHI arguments for each edge inserting loads of the
	addressable operands. */
	FOR_EACH_EDGE (e, ei, bb->preds)
	{
	tree old_arg, new_var;
	gimple tmp;
	source_location locus;

	old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
	locus = gimple_phi_arg_location_from_edge (phi, e);
	while (TREE_CODE (old_arg) == SSA_NAME
	&& (SSA_NAME_VERSION (old_arg) >= n
	\|\| phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
	{
	gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
	old_arg = gimple_assign_rhs1 (def_stmt);
	locus = gimple_location (def_stmt);
	}

	if (TREE_CODE (old_arg) == SSA_NAME)
	{
	if (dump_file && (dump_flags & TDF_DETAILS))
	{
	fprintf (dump_file, " for edge defining ");
	print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
	fprintf (dump_file, " reusing PHI result ");
	print_generic_expr (dump_file,
	phivn[SSA_NAME_VERSION (old_arg)].value, 0);
	fprintf (dump_file, "\n");
	}
	/* Reuse a formerly created dereference. */
	new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
	}
	else
	{
	tree rhs = gimple_assign_rhs1 (use_stmt);
	gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
	new_var = create_tmp_reg (TREE_TYPE (rhs), NULL);
	if (!is_gimple_min_invariant (old_arg))
	old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
	else
	old_arg = unshare_expr (old_arg);
	tmp = gimple_build_assign (new_var,
	fold_build2 (MEM_REF, TREE_TYPE (rhs),
	old_arg,
	TREE_OPERAND (rhs, 1)));
	gcc_assert (is_gimple_reg (new_var));
	add_referenced_var (new_var);
	new_var = make_ssa_name (new_var, tmp);
	gimple_assign_set_lhs (tmp, new_var);
	gimple_set_location (tmp, locus);

	gsi_insert_on_edge (e, tmp);
	update_stmt (tmp);

	if (dump_file && (dump_flags & TDF_DETAILS))
	{
	fprintf (dump_file, " for edge defining ");
	print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
	fprintf (dump_file, " inserting load ");
	print_gimple_stmt (dump_file, tmp, 0, 0);
	}
	}

	add_phi_arg (new_phi, new_var, e, locus);
	}

	update_stmt (new_phi);

	if (dump_file && (dump_flags & TDF_DETAILS))
	print_gimple_stmt (dump_file, new_phi, 0, 0);

	return res;
	}

	/* Propagate between the phi node arguments of PHI in BB and phi result
	users. For now this matches
	# p_2 = PHI <&x, &y>
	<Lx>:;
	p_3 = p_2;
	z_2 = *p_3;
	and converts it to
	# z_2 = PHI <x, y>
	<Lx>:;
	Returns true if a transformation was done and edge insertions
	need to be committed. Global data PHIVN and N is used to track
	past transformation results. We need to be especially careful here
	with aliasing issues as we are moving memory reads. */

	static bool
	propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
	size_t n)
	{
	tree ptr = PHI_RESULT (phi);
	gimple use_stmt;
	tree res = NULL_TREE;
	gimple_stmt_iterator gsi;
	imm_use_iterator ui;
	use_operand_p arg_p, use;
	ssa_op_iter i;
	bool phi_inserted;
	tree type = NULL_TREE;
	bool one_invariant = false;

	if (!POINTER_TYPE_P (TREE_TYPE (ptr))
	\|\| !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
	return false;

	/* Check if we can "cheaply" dereference all phi arguments. */
	FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
	{
	tree arg = USE_FROM_PTR (arg_p);
	/* Walk the ssa chain until we reach a ssa name we already
	created a value for or we reach a definition of the form
	ssa_name_n = &var; */
	while (TREE_CODE (arg) == SSA_NAME
	&& !SSA_NAME_IS_DEFAULT_DEF (arg)
	&& (SSA_NAME_VERSION (arg) >= n
	\|\| phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
	{
	gimple def_stmt = SSA_NAME_DEF_STMT (arg);
	if (!gimple_assign_single_p (def_stmt))
	return false;
	arg = gimple_assign_rhs1 (def_stmt);
	}
	if (TREE_CODE (arg) != ADDR_EXPR
	&& !(TREE_CODE (arg) == SSA_NAME
	&& SSA_NAME_VERSION (arg) < n
	&& phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
	&& (!type
	\|\| types_compatible_p
	(type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
	&& phivn_valid_p (phivn, arg, bb)))
	return false;
	if (!type
	&& TREE_CODE (arg) == SSA_NAME)
	type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
	if (TREE_CODE (arg) == ADDR_EXPR
	&& is_gimple_min_invariant (arg))
	one_invariant = true;
	}

	/* If we neither have an address of a decl nor can reuse a previously
	inserted load, do not hoist anything. */
	if (!one_invariant
	&& !type)
	return false;

	/* Find a dereferencing use. First follow (single use) ssa
	copy chains for ptr. */
	while (single_imm_use (ptr, &use, &use_stmt)
	&& gimple_assign_ssa_name_copy_p (use_stmt))
	ptr = gimple_assign_lhs (use_stmt);

	/* Replace the first dereference of *ptr if there is one and if we
	can move the loads to the place of the ptr phi node. */
	phi_inserted = false;
	FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
	{
	gimple def_stmt;
	tree vuse;

	/* Check whether this is a load of ptr. /
	if (!(is_gimple_assign (use_stmt)
	&& TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
	&& gimple_assign_rhs_code (use_stmt) == MEM_REF
	&& TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
	&& integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
	&& (!type
	\|\| types_compatible_p
	(TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
	/* We cannot replace a load that may throw or is volatile. */
	&& !stmt_can_throw_internal (use_stmt)))
	continue;

	/* Check if we can move the loads. The def stmt of the virtual use
	needs to be in a different basic block dominating bb. */
	vuse = gimple_vuse (use_stmt);
	def_stmt = SSA_NAME_DEF_STMT (vuse);
	if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
	&& (gimple_bb (def_stmt) == bb
	\|\| !dominated_by_p (CDI_DOMINATORS,
	bb, gimple_bb (def_stmt))))
	goto next;

	/* Found a proper dereference. Insert a phi node if this
	is the first load transformation. */
	if (!phi_inserted)
	{
	res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
	type = TREE_TYPE (res);

	/* Remember the value we created for ptr. /
	phivn[SSA_NAME_VERSION (ptr)].value = res;
	phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;

	/* Remove old stmt. The phi is taken care of by DCE, if we
	want to delete it here we also have to delete all intermediate
	copies. */
	gsi = gsi_for_stmt (use_stmt);
	gsi_remove (&gsi, true);

	phi_inserted = true;
	}
	else
	{
	/* Further replacements are easy, just make a copy out of the
	load. */
	gimple_assign_set_rhs1 (use_stmt, res);
	update_stmt (use_stmt);
	}

	next:;
	/* Continue searching for a proper dereference. */
	}

	return phi_inserted;
	}

	/* Main entry for phiprop pass. */

	static unsigned int
	tree_ssa_phiprop (void)
	{
	VEC(basic_block, heap) *bbs;
	struct phiprop_d *phivn;
	bool did_something = false;
	basic_block bb;
	gimple_stmt_iterator gsi;
	unsigned i;
	size_t n;

	calculate_dominance_info (CDI_DOMINATORS);

	n = num_ssa_names;
	phivn = XCNEWVEC (struct phiprop_d, n);

	/* Walk the dominator tree in preorder. */
	bbs = get_all_dominated_blocks (CDI_DOMINATORS,
	single_succ (ENTRY_BLOCK_PTR));
	FOR_EACH_VEC_ELT (basic_block, bbs, i, bb)
	for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
	did_something \|= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);

	if (did_something)
	gsi_commit_edge_inserts ();

	VEC_free (basic_block, heap, bbs);
	free (phivn);

	return 0;
	}

	static bool
	gate_phiprop (void)
	{
	return flag_tree_phiprop;
	}

	struct gimple_opt_pass pass_phiprop =
	{
	{
	GIMPLE_PASS,
	"phiprop", /* name */
	gate_phiprop, /* gate */
	tree_ssa_phiprop, /* execute */
	NULL, /* sub */
	NULL, /* next */
	0, /* static_pass_number */
	TV_TREE_PHIPROP, /* tv_id */
	PROP_cfg \| PROP_ssa, /* properties_required */
	0, /* properties_provided */
	0, /* properties_destroyed */
	0, /* todo_flags_start */
	TODO_dump_func
	\| TODO_ggc_collect
	\| TODO_update_ssa
	\| TODO_verify_ssa /* todo_flags_finish */
	}
	};