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/* Conditional constant propagation pass for the GNU compiler.
   Copyright (C) 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
   Adapted from original RTL SSA-CCP by Daniel Berlin <dberlin@dberlin.org>
   Adapted to GIMPLE trees 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 2, 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 COPYING.  If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

/* Conditional constant propagation.

   References:

     Constant propagation with conditional branches,
     Wegman and Zadeck, ACM TOPLAS 13(2):181-210.

     Building an Optimizing Compiler,
     Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.

     Advanced Compiler Design and Implementation,
     Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6  */

#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 "output.h"
#include "errors.h"
#include "expr.h"
#include "function.h"
#include "diagnostic.h"
#include "timevar.h"
#include "tree-dump.h"
#include "tree-flow.h"
#include "tree-pass.h"
#include "tree-ssa-propagate.h"
#include "langhooks.h"


/* Possible lattice values.  */
typedef enum
{
  UNINITIALIZED = 0,
  UNDEFINED,
  UNKNOWN_VAL,
  CONSTANT,
  VARYING
} latticevalue;

/* Main structure for CCP.  Contains the lattice value and, if it's a
    constant, the constant value.  */
typedef struct
{
  latticevalue lattice_val;
  tree const_val;
} value;

/* This is used to track the current value of each variable.  */
static value *value_vector;


/* Dump lattice value VAL to file OUTF prefixed by PREFIX.  */

static void
dump_lattice_value (FILE *outf, const char *prefix, value val)
{
  switch (val.lattice_val)
    {
    case UNDEFINED:
      fprintf (outf, "%sUNDEFINED", prefix);
      break;
    case VARYING:
      fprintf (outf, "%sVARYING", prefix);
      break;
    case UNKNOWN_VAL:
      fprintf (outf, "%sUNKNOWN_VAL", prefix);
      break;
    case CONSTANT:
      fprintf (outf, "%sCONSTANT ", prefix);
      print_generic_expr (outf, val.const_val, dump_flags);
      break;
    default:
      gcc_unreachable ();
    }
}


/* Return a default value for variable VAR using the following rules:

   1- Function arguments are considered VARYING.
   
   2- Global and static variables that are declared constant are
      considered CONSTANT.

   3- Any other virtually defined variable is considered UNKNOWN_VAL.

   4- Any other value is considered UNDEFINED.  This is useful when
      considering PHI nodes.  PHI arguments that are undefined do not
      change the constant value of the PHI node, which allows for more
      constants to be propagated.  */

static value
get_default_value (tree var)
{
  value val;
  tree sym;

  if (TREE_CODE (var) == SSA_NAME)
    sym = SSA_NAME_VAR (var);
  else
    {
      gcc_assert (DECL_P (var));
      sym = var;
    }

  val.lattice_val = UNDEFINED;
  val.const_val = NULL_TREE;

  if (TREE_CODE (var) == SSA_NAME
      && SSA_NAME_VALUE (var)
      && is_gimple_min_invariant (SSA_NAME_VALUE (var)))
    {
      val.lattice_val = CONSTANT;
      val.const_val = SSA_NAME_VALUE (var);
    }
  else if (TREE_CODE (sym) == PARM_DECL || TREE_THIS_VOLATILE (sym))
    {
      /* Function arguments and volatile variables are considered VARYING.  */
      val.lattice_val = VARYING;
    }
  else if (TREE_STATIC (sym))
    {
      /* Globals and static variables are considered UNKNOWN_VAL,
         unless they are declared 'const'.  */
      if (TREE_READONLY (sym)
	  && DECL_INITIAL (sym)
	  && is_gimple_min_invariant (DECL_INITIAL (sym)))
	{
	  val.lattice_val = CONSTANT;
	  val.const_val = DECL_INITIAL (sym);
	}
      else
        {
          val.const_val = NULL_TREE;
	  val.lattice_val = UNKNOWN_VAL;
	}
    }
  else if (!is_gimple_reg (sym))
    {
      val.const_val = NULL_TREE;
      val.lattice_val = UNKNOWN_VAL;
    }
  else
    {
      enum tree_code code;
      tree stmt = SSA_NAME_DEF_STMT (var);

      if (!IS_EMPTY_STMT (stmt))
        {
	  code = TREE_CODE (stmt);
	  if (code != MODIFY_EXPR && code != PHI_NODE)
	    val.lattice_val = VARYING;
	}
    }

  return val;
}

/* Get the constant value associated with variable VAR.  */

static value *
get_value (tree var)
{
  value *val;

  gcc_assert (TREE_CODE (var) == SSA_NAME);

  val = &value_vector[SSA_NAME_VERSION (var)];
  if (val->lattice_val == UNINITIALIZED)
    *val = get_default_value (var);

  return val;
}


/* Set the lattice value for variable VAR to VAL.  Return true if VAL
   is different from VAR's previous value.  */

static bool
set_lattice_value (tree var, value val)
{
  value *old = get_value (var);

  if (val.lattice_val == UNDEFINED)
    {
      /* CONSTANT->UNDEFINED is never a valid state transition.  */
      gcc_assert (old->lattice_val != CONSTANT);
	
      /* UNKNOWN_VAL->UNDEFINED is never a valid state transition.  */
      gcc_assert (old->lattice_val != UNKNOWN_VAL);

      /* VARYING->UNDEFINED is generally not a valid state transition,
	 except for values which are initialized to VARYING.  */
      gcc_assert (old->lattice_val != VARYING
		  || get_default_value (var).lattice_val == VARYING);
    }
  else if (val.lattice_val == CONSTANT)
    /* VARYING -> CONSTANT is an invalid state transition, except
	for objects which start off in a VARYING state.  */
    gcc_assert (old->lattice_val != VARYING
		|| get_default_value (var).lattice_val == VARYING);

  /* If the constant for VAR has changed, then this VAR is really varying.  */
  if (old->lattice_val == CONSTANT
      && val.lattice_val == CONSTANT
      && !simple_cst_equal (old->const_val, val.const_val))
    {
      val.lattice_val = VARYING;
      val.const_val = NULL_TREE;
    }

  if (old->lattice_val != val.lattice_val)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	{
	  dump_lattice_value (dump_file, "Lattice value changed to ", val);
	  fprintf (dump_file, ".  Adding definition to SSA edges.\n");
	}

      *old = val;
      return true;
    }

  return false;
}


/* Set the lattice value for the variable VAR to VARYING.  */

static void
def_to_varying (tree var)
{
  value val;
  val.lattice_val = VARYING;
  val.const_val = NULL_TREE;
  set_lattice_value (var, val);
}


/* Return the likely latticevalue for STMT.

   If STMT has no operands, then return CONSTANT.

   Else if any operands of STMT are undefined, then return UNDEFINED.

   Else if any operands of STMT are constants, then return CONSTANT.

   Else return VARYING.  */

static latticevalue
likely_value (tree stmt)
{
  vuse_optype vuses;
  int found_constant = 0;
  stmt_ann_t ann;
  tree use;
  ssa_op_iter iter;

  /* If the statement makes aliased loads or has volatile operands, it
     won't fold to a constant value.  */
  ann = stmt_ann (stmt);
  if (ann->makes_aliased_loads || ann->has_volatile_ops)
    return VARYING;

  /* A CALL_EXPR is assumed to be varying.  This may be overly conservative,
     in the presence of const and pure calls.  */
  if (get_call_expr_in (stmt) != NULL_TREE)
    return VARYING;

  get_stmt_operands (stmt);

  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
    {
      value *val = get_value (use);

      if (val->lattice_val == UNDEFINED)
	return UNDEFINED;

      if (val->lattice_val == CONSTANT)
	found_constant = 1;
    }
    
  vuses = VUSE_OPS (ann);
  
  if (NUM_VUSES (vuses))
    {
      tree vuse = VUSE_OP (vuses, 0);
      value *val = get_value (vuse);
      
      if (val->lattice_val == UNKNOWN_VAL)
        return UNKNOWN_VAL;
	
      /* There should be no VUSE operands that are UNDEFINED.  */
      gcc_assert (val->lattice_val != UNDEFINED);
	
      if (val->lattice_val == CONSTANT)
	found_constant = 1;
    }

  return ((found_constant || (!USE_OPS (ann) && !vuses)) ? CONSTANT : VARYING);
}


/* Function indicating whether we ought to include information for VAR
   when calculating immediate uses.  */

static bool
need_imm_uses_for (tree var)
{
  return get_value (var)->lattice_val != VARYING;
}


/* Initialize local data structures for CCP.  */

static void
ccp_initialize (void)
{
  basic_block bb;
  sbitmap is_may_def;

  value_vector = (value *) xmalloc (num_ssa_names * sizeof (value));
  memset (value_vector, 0, num_ssa_names * sizeof (value));

  /* Set of SSA_NAMEs that are defined by a V_MAY_DEF.  */
  is_may_def = sbitmap_alloc (num_ssa_names);
  sbitmap_zero (is_may_def);

  /* Initialize simulation flags for PHI nodes and statements.  */
  FOR_EACH_BB (bb)
    {
      block_stmt_iterator i;

      /* Mark all V_MAY_DEF operands VARYING.  */
      for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
        {
	  bool is_varying = false;
	  tree stmt = bsi_stmt (i);
	  ssa_op_iter iter;
	  tree def;

	  get_stmt_operands (stmt);

	  /* Get the default value for each DEF and V_MUST_DEF.  */
	  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, 
				     (SSA_OP_DEF | SSA_OP_VMUSTDEF))
	    {
	      if (get_value (def)->lattice_val == VARYING)
		is_varying = true;
	    }

	  /* Mark all V_MAY_DEF operands VARYING.  */
	  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_VMAYDEF)
	    {
	      get_value (def)->lattice_val = VARYING;
	      SET_BIT (is_may_def, SSA_NAME_VERSION (def));
	    }

	  /* Statements other than MODIFY_EXPR, COND_EXPR and
	     SWITCH_EXPR are not interesting for constant propagation.
	     Mark them VARYING.  */
	  if (TREE_CODE (stmt) != MODIFY_EXPR
	      && TREE_CODE (stmt) != COND_EXPR
	      && TREE_CODE (stmt) != SWITCH_EXPR)
	    is_varying = true;

	  DONT_SIMULATE_AGAIN (stmt) = is_varying;
	}
    }

  /* Now process PHI nodes.  */
  FOR_EACH_BB (bb)
    {
      tree phi, var;
      int x;

      for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
	{
	  value *val = get_value (PHI_RESULT (phi));

	  for (x = 0; x < PHI_NUM_ARGS (phi); x++)
	    {
	      var = PHI_ARG_DEF (phi, x);

	      /* If one argument has a V_MAY_DEF, the result is
		 VARYING.  */
	      if (TREE_CODE (var) == SSA_NAME)
		{
		  if (TEST_BIT (is_may_def, SSA_NAME_VERSION (var)))
		    {
		      val->lattice_val = VARYING;
		      SET_BIT (is_may_def, SSA_NAME_VERSION (PHI_RESULT (phi)));
		      break;
		    }
		}
	    }

	  DONT_SIMULATE_AGAIN (phi) = (val->lattice_val == VARYING);
	}
    }

  sbitmap_free (is_may_def);

  /* Compute immediate uses for variables we care about.  */
  compute_immediate_uses (TDFA_USE_OPS | TDFA_USE_VOPS, need_imm_uses_for);
}


/* Replace USE references in statement STMT with their immediate reaching
   definition.  Return true if at least one reference was replaced.  If
   REPLACED_ADDRESSES_P is given, it will be set to true if an address
   constant was replaced.  */

static bool
replace_uses_in (tree stmt, bool *replaced_addresses_p)
{
  bool replaced = false;
  use_operand_p use;
  ssa_op_iter iter;

  if (replaced_addresses_p)
    *replaced_addresses_p = false;

  get_stmt_operands (stmt);

  FOR_EACH_SSA_USE_OPERAND (use, stmt, iter, SSA_OP_USE)
    {
      tree tuse = USE_FROM_PTR (use);
      value *val = get_value (tuse);

      if (val->lattice_val != CONSTANT)
	continue;

      if (TREE_CODE (stmt) == ASM_EXPR
	  && !may_propagate_copy_into_asm (tuse))
	continue;

      SET_USE (use, val->const_val);

      replaced = true;
      if (POINTER_TYPE_P (TREE_TYPE (tuse)) && replaced_addresses_p)
	*replaced_addresses_p = true;
    }

  return replaced;
}


/* Replace the VUSE references in statement STMT with its immediate reaching
   definition.  Return true if the reference was replaced.  If
   REPLACED_ADDRESSES_P is given, it will be set to true if an address
   constant was replaced.  */

static bool
replace_vuse_in (tree stmt, bool *replaced_addresses_p)
{
  bool replaced = false;
  vuse_optype vuses;
  use_operand_p vuse;
  value *val;

  if (replaced_addresses_p)
    *replaced_addresses_p = false;

  get_stmt_operands (stmt);

  vuses = STMT_VUSE_OPS (stmt);

  if (NUM_VUSES (vuses) != 1)
    return false;

  vuse = VUSE_OP_PTR (vuses, 0);
  val = get_value (USE_FROM_PTR (vuse));

  if (val->lattice_val == CONSTANT
      && TREE_CODE (stmt) == MODIFY_EXPR
      && DECL_P (TREE_OPERAND (stmt, 1))
      && TREE_OPERAND (stmt, 1) == SSA_NAME_VAR (USE_FROM_PTR (vuse)))
    {
      TREE_OPERAND (stmt, 1) = val->const_val;
      replaced = true;
      if (POINTER_TYPE_P (TREE_TYPE (USE_FROM_PTR (vuse))) 
          && replaced_addresses_p)
        *replaced_addresses_p = true;
    }

  return replaced;
}


/* Perform final substitution and folding.  After this pass the program
   should still be in SSA form.  */

static void
substitute_and_fold (void)
{
  basic_block bb;
  unsigned int i;

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file,
	     "\nSubstituing constants and folding statements\n\n");

  /* Substitute constants in every statement of every basic block.  */
  FOR_EACH_BB (bb)
    {
      block_stmt_iterator i;
      tree phi;

      /* Propagate our known constants into PHI nodes.  */
      for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
	{
	  int i;

	  for (i = 0; i < PHI_NUM_ARGS (phi); i++)
	    {
	      value *new_val;
	      use_operand_p orig_p = PHI_ARG_DEF_PTR (phi, i);
	      tree orig = USE_FROM_PTR (orig_p);

	      if (! SSA_VAR_P (orig))
		break;

	      new_val = get_value (orig);
	      if (new_val->lattice_val == CONSTANT
		  && may_propagate_copy (orig, new_val->const_val))
		SET_USE (orig_p, new_val->const_val);
	    }
	}

      for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
	{
          bool replaced_address;
	  tree stmt = bsi_stmt (i);

	  /* Skip statements that have been folded already.  */
	  if (stmt_modified_p (stmt) || !is_exec_stmt (stmt))
	    continue;

	  /* Replace the statement with its folded version and mark it
	     folded.  */
	  if (dump_file && (dump_flags & TDF_DETAILS))
	    {
	      fprintf (dump_file, "Line %d: replaced ", get_lineno (stmt));
	      print_generic_stmt (dump_file, stmt, TDF_SLIM);
	    }

	  if (replace_uses_in (stmt, &replaced_address)
	      || replace_vuse_in (stmt, &replaced_address))
	    {
	      bool changed = fold_stmt (bsi_stmt_ptr (i));
	      stmt = bsi_stmt(i);
	      /* If we folded a builtin function, we'll likely
		 need to rename VDEFs.  */
	      if (replaced_address || changed)
		{
		  mark_new_vars_to_rename (stmt, vars_to_rename);
		  if (maybe_clean_eh_stmt (stmt))
		    tree_purge_dead_eh_edges (bb);
		}
	      else
		modify_stmt (stmt);
	    }

	  if (dump_file && (dump_flags & TDF_DETAILS))
	    {
	      fprintf (dump_file, " with ");
	      print_generic_stmt (dump_file, stmt, TDF_SLIM);
	      fprintf (dump_file, "\n");
	    }
	}
    }

  /* And transfer what we learned from VALUE_VECTOR into the
     SSA_NAMEs themselves.  This probably isn't terribly important
     since we probably constant propagated the values to their
     use sites above.  */
  for (i = 0; i < num_ssa_names; i++)
    {
      tree name = ssa_name (i);
      value *value;

      if (!name)
	continue;

      value = get_value (name);
      if (value->lattice_val == CONSTANT
          && is_gimple_reg (name)
	  && is_gimple_min_invariant (value->const_val))
	SSA_NAME_VALUE (name) = value->const_val;
    }
}


/* Free allocated storage.  */

static void
ccp_finalize (void)
{
  /* Perform substitutions based on the known constant values.  */
  substitute_and_fold ();

  /* Now cleanup any unreachable code.  */
  cleanup_tree_cfg ();

  free (value_vector);
}



/* Compute the meet operator between VAL1 and VAL2:

   		any  M UNDEFINED     = any
		any  M VARYING       = VARYING
		any  M UNKNOWN_VAL   = UNKNOWN_VAL
		Ci   M Cj	     = Ci	if (i == j)
		Ci   M Cj	     = VARYING	if (i != j)  */
static value
ccp_lattice_meet (value val1, value val2)
{
  value result;

  /* any M UNDEFINED = any.  */
  if (val1.lattice_val == UNDEFINED)
    return val2;
  else if (val2.lattice_val == UNDEFINED)
    return val1;

  /* any M VARYING = VARYING.  */
  if (val1.lattice_val == VARYING || val2.lattice_val == VARYING)
    {
      result.lattice_val = VARYING;
      result.const_val = NULL_TREE;
      return result;
    }

  /* any M UNKNOWN_VAL = UNKNOWN_VAL.  */
  if (val1.lattice_val == UNKNOWN_VAL 
      || val2.lattice_val == UNKNOWN_VAL)
    {
      result.lattice_val = UNKNOWN_VAL;
      result.const_val = NULL_TREE;
      return result;
    }

  /* Ci M Cj = Ci	if (i == j)
     Ci M Cj = VARYING	if (i != j)  */
  if (simple_cst_equal (val1.const_val, val2.const_val) == 1)
    {
      result.lattice_val = CONSTANT;
      result.const_val = val1.const_val;
    }
  else
    {
      result.lattice_val = VARYING;
      result.const_val = NULL_TREE;
    }

  return result;
}


/* Loop through the PHI_NODE's parameters for BLOCK and compare their
   lattice values to determine PHI_NODE's lattice value.  The value of a
   PHI node is determined calling ccp_lattice_meet() with all the arguments
   of the PHI node that are incoming via executable edges.  */

static enum ssa_prop_result
ccp_visit_phi_node (tree phi)
{
  value new_val, *old_val;
  int i;

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "\nVisiting PHI node: ");
      print_generic_expr (dump_file, phi, dump_flags);
    }

  old_val = get_value (PHI_RESULT (phi));
  switch (old_val->lattice_val)
    {
    case VARYING:
      return SSA_PROP_NOT_INTERESTING;

    case CONSTANT:
      new_val = *old_val;
      break;

    case UNKNOWN_VAL:
      /* To avoid the default value of UNKNOWN_VAL overriding
         that of its possible constant arguments, temporarily
	 set the PHI node's default lattice value to be 
	 UNDEFINED.  If the PHI node's old value was UNKNOWN_VAL and
	 the new value is UNDEFINED, then we prevent the invalid
	 transition by not calling set_lattice_value.  */
      new_val.lattice_val = UNDEFINED;
      new_val.const_val = NULL_TREE;
      break;

    case UNDEFINED:
    case UNINITIALIZED:
      new_val.lattice_val = UNDEFINED;
      new_val.const_val = NULL_TREE;
      break;

    default:
      gcc_unreachable ();
    }

  for (i = 0; i < PHI_NUM_ARGS (phi); i++)
    {
      /* Compute the meet operator over all the PHI arguments.  */
      edge e = PHI_ARG_EDGE (phi, i);

      if (dump_file && (dump_flags & TDF_DETAILS))
	{
	  fprintf (dump_file,
	      "\n    Argument #%d (%d -> %d %sexecutable)\n",
	      i, e->src->index, e->dest->index,
	      (e->flags & EDGE_EXECUTABLE) ? "" : "not ");
	}

      /* If the incoming edge is executable, Compute the meet operator for
	 the existing value of the PHI node and the current PHI argument.  */
      if (e->flags & EDGE_EXECUTABLE)
	{
	  tree rdef = PHI_ARG_DEF (phi, i);
	  value *rdef_val, val;

	  if (is_gimple_min_invariant (rdef))
	    {
	      val.lattice_val = CONSTANT;
	      val.const_val = rdef;
	      rdef_val = &val;
	    }
	  else
	    rdef_val = get_value (rdef);

	  new_val = ccp_lattice_meet (new_val, *rdef_val);

	  if (dump_file && (dump_flags & TDF_DETAILS))
	    {
	      fprintf (dump_file, "\t");
	      print_generic_expr (dump_file, rdef, dump_flags);
	      dump_lattice_value (dump_file, "\tValue: ", *rdef_val);
	      fprintf (dump_file, "\n");
	    }

	  if (new_val.lattice_val == VARYING)
	    break;
	}
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      dump_lattice_value (dump_file, "\n    PHI node value: ", new_val);
      fprintf (dump_file, "\n\n");
    }

  /* Check for an invalid change from UNKNOWN_VAL to UNDEFINED.  */
  if (old_val->lattice_val == UNKNOWN_VAL
      && new_val.lattice_val == UNDEFINED)
    return SSA_PROP_NOT_INTERESTING;

  /* Otherwise, make the transition to the new value.  */
  if (set_lattice_value (PHI_RESULT (phi), new_val))
    {
      if (new_val.lattice_val == VARYING)
	return SSA_PROP_VARYING;
      else
	return SSA_PROP_INTERESTING;
    }
  else
    return SSA_PROP_NOT_INTERESTING;
}


/* CCP specific front-end to the non-destructive constant folding
   routines.

   Attempt to simplify the RHS of STMT knowing that one or more
   operands are constants.

   If simplification is possible, return the simplified RHS,
   otherwise return the original RHS.  */

static tree
ccp_fold (tree stmt)
{
  tree rhs = get_rhs (stmt);
  enum tree_code code = TREE_CODE (rhs);
  enum tree_code_class kind = TREE_CODE_CLASS (code);
  tree retval = NULL_TREE;
  vuse_optype vuses;
  
  vuses = STMT_VUSE_OPS (stmt);

  /* If the RHS is just a variable, then that variable must now have
     a constant value that we can return directly.  */
  if (TREE_CODE (rhs) == SSA_NAME)
    return get_value (rhs)->const_val;
  else if (DECL_P (rhs) 
           && NUM_VUSES (vuses) == 1
           && rhs == SSA_NAME_VAR (VUSE_OP (vuses, 0)))
    return get_value (VUSE_OP (vuses, 0))->const_val;

  /* Unary operators.  Note that we know the single operand must
     be a constant.  So this should almost always return a
     simplified RHS.  */
  if (kind == tcc_unary)
    {
      /* Handle unary operators which can appear in GIMPLE form.  */
      tree op0 = TREE_OPERAND (rhs, 0);

      /* Simplify the operand down to a constant.  */
      if (TREE_CODE (op0) == SSA_NAME)
	{
	  value *val = get_value (op0);
	  if (val->lattice_val == CONSTANT)
	    op0 = get_value (op0)->const_val;
	}

      retval = nondestructive_fold_unary_to_constant (code,
		     				      TREE_TYPE (rhs),
						      op0);

      /* If we folded, but did not create an invariant, then we can not
	 use this expression.  */
      if (retval && ! is_gimple_min_invariant (retval))
	return NULL;

      /* If we could not fold the expression, but the arguments are all
         constants and gimple values, then build and return the new
	 expression. 

	 In some cases the new expression is still something we can
	 use as a replacement for an argument.  This happens with
	 NOP conversions of types for example.

	 In other cases the new expression can not be used as a
	 replacement for an argument (as it would create non-gimple
	 code).  But the new expression can still be used to derive
	 other constants.  */
      if (! retval && is_gimple_min_invariant (op0))
	return build1 (code, TREE_TYPE (rhs), op0);
    }

  /* Binary and comparison operators.  We know one or both of the
     operands are constants.  */
  else if (kind == tcc_binary
           || kind == tcc_comparison
           || code == TRUTH_AND_EXPR
           || code == TRUTH_OR_EXPR
           || code == TRUTH_XOR_EXPR)
    {
      /* Handle binary and comparison operators that can appear in
         GIMPLE form.  */
      tree op0 = TREE_OPERAND (rhs, 0);
      tree op1 = TREE_OPERAND (rhs, 1);

      /* Simplify the operands down to constants when appropriate.  */
      if (TREE_CODE (op0) == SSA_NAME)
	{
	  value *val = get_value (op0);
	  if (val->lattice_val == CONSTANT)
	    op0 = val->const_val;
	}

      if (TREE_CODE (op1) == SSA_NAME)
	{
	  value *val = get_value (op1);
	  if (val->lattice_val == CONSTANT)
	    op1 = val->const_val;
	}

      retval = nondestructive_fold_binary_to_constant (code,
		     				       TREE_TYPE (rhs),
						       op0, op1);

      /* If we folded, but did not create an invariant, then we can not
	 use this expression.  */
      if (retval && ! is_gimple_min_invariant (retval))
	return NULL;
      
      /* If we could not fold the expression, but the arguments are all
         constants and gimple values, then build and return the new
	 expression. 

	 In some cases the new expression is still something we can
	 use as a replacement for an argument.  This happens with
	 NOP conversions of types for example.

	 In other cases the new expression can not be used as a
	 replacement for an argument (as it would create non-gimple
	 code).  But the new expression can still be used to derive
	 other constants.  */
      if (! retval
	  && is_gimple_min_invariant (op0)
	  && is_gimple_min_invariant (op1))
	return build (code, TREE_TYPE (rhs), op0, op1);
    }

  /* We may be able to fold away calls to builtin functions if their
     arguments are constants.  */
  else if (code == CALL_EXPR
	   && TREE_CODE (TREE_OPERAND (rhs, 0)) == ADDR_EXPR
	   && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0))
	       == FUNCTION_DECL)
	   && DECL_BUILT_IN (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0)))
    {
      use_optype uses = STMT_USE_OPS (stmt);
      if (NUM_USES (uses) != 0)
	{
	  tree *orig;
	  size_t i;

	  /* Preserve the original values of every operand.  */
	  orig = xmalloc (sizeof (tree) * NUM_USES (uses));
	  for (i = 0; i < NUM_USES (uses); i++)
	    orig[i] = USE_OP (uses, i);

	  /* Substitute operands with their values and try to fold.  */
	  replace_uses_in (stmt, NULL);
	  retval = fold_builtin (rhs, false);

	  /* Restore operands to their original form.  */
	  for (i = 0; i < NUM_USES (uses); i++)
	    SET_USE_OP (uses, i, orig[i]);
	  free (orig);
	}
    }
  else
    return rhs;

  /* If we got a simplified form, see if we need to convert its type.  */
  if (retval)
    return fold_convert (TREE_TYPE (rhs), retval);

  /* No simplification was possible.  */
  return rhs;
}


/* Evaluate statement STMT.  */

static value
evaluate_stmt (tree stmt)
{
  value val;
  tree simplified;
  latticevalue likelyvalue = likely_value (stmt);

  /* If the statement is likely to have a CONSTANT result, then try
     to fold the statement to determine the constant value.  */
  if (likelyvalue == CONSTANT)
    simplified = ccp_fold (stmt);
  /* If the statement is likely to have a VARYING result, then do not
     bother folding the statement.  */
  else if (likelyvalue == VARYING)
    simplified = get_rhs (stmt);
  /* Otherwise the statement is likely to have an UNDEFINED value and
     there will be nothing to do.  */
  else
    simplified = NULL_TREE;

  if (simplified && is_gimple_min_invariant (simplified))
    {
      /* The statement produced a constant value.  */
      val.lattice_val = CONSTANT;
      val.const_val = simplified;
    }
  else
    {
      /* The statement produced a nonconstant value.  If the statement
         had undefined or virtual operands, then the result of the 
	 statement should be undefined or virtual respectively.  
	 Else the result of the statement is VARYING.  */
      val.lattice_val = (likelyvalue == UNDEFINED ? UNDEFINED : VARYING);
      val.lattice_val = (likelyvalue == UNKNOWN_VAL 
                           ? UNKNOWN_VAL : val.lattice_val);
      val.const_val = NULL_TREE;
    }

  return val;
}


/* Visit the assignment statement STMT.  Set the value of its LHS to the
   value computed by the RHS and store LHS in *OUTPUT_P.  */

static enum ssa_prop_result
visit_assignment (tree stmt, tree *output_p)
{
  value val;
  tree lhs, rhs;
  vuse_optype vuses;
  v_must_def_optype v_must_defs;

  lhs = TREE_OPERAND (stmt, 0);
  rhs = TREE_OPERAND (stmt, 1);
  vuses = STMT_VUSE_OPS (stmt);
  v_must_defs = STMT_V_MUST_DEF_OPS (stmt);

  gcc_assert (NUM_V_MAY_DEFS (STMT_V_MAY_DEF_OPS (stmt)) == 0);
  gcc_assert (NUM_V_MUST_DEFS (v_must_defs) == 1
	      || TREE_CODE (lhs) == SSA_NAME);

  /* We require the SSA version number of the lhs for the value_vector.
     Make sure we have it.  */
  if (TREE_CODE (lhs) != SSA_NAME)
    {
      /* If we make it here, then stmt only has one definition:
         a V_MUST_DEF.  */
      lhs = V_MUST_DEF_RESULT (v_must_defs, 0);
    }

  if (TREE_CODE (rhs) == SSA_NAME)
    {
      /* For a simple copy operation, we copy the lattice values.  */
      value *nval = get_value (rhs);
      val = *nval;
    }
  else if (DECL_P (rhs) 
           && NUM_VUSES (vuses) == 1
           && rhs == SSA_NAME_VAR (VUSE_OP (vuses, 0)))
    {
      /* Same as above, but the rhs is not a gimple register and yet
        has a known VUSE.  */
      value *nval = get_value (VUSE_OP (vuses, 0));
      val = *nval;
    }
  else
    {
      /* Evaluate the statement.  */
      val = evaluate_stmt (stmt);
    }

  /* FIXME: Hack.  If this was a definition of a bitfield, we need to widen
     the constant value into the type of the destination variable.  This
     should not be necessary if GCC represented bitfields properly.  */
  {
    tree lhs = TREE_OPERAND (stmt, 0);
    if (val.lattice_val == CONSTANT
	&& TREE_CODE (lhs) == COMPONENT_REF
	&& DECL_BIT_FIELD (TREE_OPERAND (lhs, 1)))
      {
	tree w = widen_bitfield (val.const_val, TREE_OPERAND (lhs, 1), lhs);

	if (w && is_gimple_min_invariant (w))
	  val.const_val = w;
	else
	  {
	    val.lattice_val = VARYING;
	    val.const_val = NULL;
	  }
      }
  }

  /* If LHS is not a gimple register, then it cannot take on an
     UNDEFINED value.  */
  if (!is_gimple_reg (SSA_NAME_VAR (lhs)) 
      && val.lattice_val == UNDEFINED)
    val.lattice_val = UNKNOWN_VAL;      

  /* Set the lattice value of the statement's output.  */
  if (set_lattice_value (lhs, val))
    {
      *output_p = lhs;
      if (val.lattice_val == VARYING)
	return SSA_PROP_VARYING;
      else
	return SSA_PROP_INTERESTING;
    }
  else
    return SSA_PROP_NOT_INTERESTING;
}


/* Visit the conditional statement STMT.  Return SSA_PROP_INTERESTING
   if it can determine which edge will be taken.  Otherwise, return
   SSA_PROP_VARYING.  */

static enum ssa_prop_result
visit_cond_stmt (tree stmt, edge *taken_edge_p)
{
  value val;
  basic_block block;

  block = bb_for_stmt (stmt);
  val = evaluate_stmt (stmt);

  /* Find which edge out of the conditional block will be taken and add it
     to the worklist.  If no single edge can be determined statically,
     return SSA_PROP_VARYING to feed all the outgoing edges to the
     propagation engine.  */
  *taken_edge_p = find_taken_edge (block, val.const_val);
  if (*taken_edge_p)
    return SSA_PROP_INTERESTING;
  else
    return SSA_PROP_VARYING;
}


/* Evaluate statement STMT.  If the statement produces an output value and
   its evaluation changes the lattice value of its output, return
   SSA_PROP_INTERESTING and set *OUTPUT_P to the SSA_NAME holding the
   output value.
   
   If STMT is a conditional branch and we can determine its truth
   value, set *TAKEN_EDGE_P accordingly.  If STMT produces a varying
   value, return SSA_PROP_VARYING.  */

static enum ssa_prop_result
ccp_visit_stmt (tree stmt, edge *taken_edge_p, tree *output_p)
{
  stmt_ann_t ann;
  v_may_def_optype v_may_defs;
  v_must_def_optype v_must_defs;
  tree def;
  ssa_op_iter iter;

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "\nVisiting statement: ");
      print_generic_stmt (dump_file, stmt, TDF_SLIM);
      fprintf (dump_file, "\n");
    }

  ann = stmt_ann (stmt);

  v_must_defs = V_MUST_DEF_OPS (ann);
  v_may_defs = V_MAY_DEF_OPS (ann);
  if (TREE_CODE (stmt) == MODIFY_EXPR
      && NUM_V_MAY_DEFS (v_may_defs) == 0
      && (NUM_V_MUST_DEFS (v_must_defs) == 1
          || TREE_CODE (TREE_OPERAND (stmt, 0)) == SSA_NAME))
    {
      /* If the statement is an assignment that produces a single
	 output value, evaluate its RHS to see if the lattice value of
	 its output has changed.  */
      return visit_assignment (stmt, output_p);
    }
  else if (TREE_CODE (stmt) == COND_EXPR || TREE_CODE (stmt) == SWITCH_EXPR)
    {
      /* If STMT is a conditional branch, see if we can determine
	 which branch will be taken.  */
      return visit_cond_stmt (stmt, taken_edge_p);
    }

  /* Any other kind of statement is not interesting for constant
     propagation and, therefore, not worth simulating.  */
  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "No interesting values produced.  Marked VARYING.\n");

  /* Definitions made by statements other than assignments to
     SSA_NAMEs represent unknown modifications to their outputs.
     Mark them VARYING.  */
  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
    def_to_varying (def);

  /* Mark all V_MAY_DEF operands VARYING.  */
  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_VMAYDEF)
    def_to_varying (def);

  return SSA_PROP_VARYING;
}


/* Main entry point for SSA Conditional Constant Propagation.

   [ DESCRIBE MAIN ALGORITHM HERE ]  */

static void
execute_ssa_ccp (void)
{
  ccp_initialize ();
  ssa_propagate (ccp_visit_stmt, ccp_visit_phi_node);
  ccp_finalize ();
}


static bool
gate_ccp (void)
{
  return flag_tree_ccp != 0;
}


struct tree_opt_pass pass_ccp = 
{
  "ccp",				/* name */
  gate_ccp,				/* gate */
  execute_ssa_ccp,			/* execute */
  NULL,					/* sub */
  NULL,					/* next */
  0,					/* static_pass_number */
  TV_TREE_CCP,				/* tv_id */
  PROP_cfg | PROP_ssa | PROP_alias,	/* properties_required */
  0,					/* properties_provided */
  0,					/* properties_destroyed */
  0,					/* todo_flags_start */
  TODO_dump_func | TODO_rename_vars
    | TODO_ggc_collect | TODO_verify_ssa
    | TODO_verify_stmts,		/* todo_flags_finish */
  0					/* letter */
};


/* Given a constant value VAL for bitfield FIELD, and a destination
   variable VAR, return VAL appropriately widened to fit into VAR.  If
   FIELD is wider than HOST_WIDE_INT, NULL is returned.  */

tree
widen_bitfield (tree val, tree field, tree var)
{
  unsigned HOST_WIDE_INT var_size, field_size;
  tree wide_val;
  unsigned HOST_WIDE_INT mask;
  unsigned int i;

  /* We can only do this if the size of the type and field and VAL are
     all constants representable in HOST_WIDE_INT.  */
  if (!host_integerp (TYPE_SIZE (TREE_TYPE (var)), 1)
      || !host_integerp (DECL_SIZE (field), 1)
      || !host_integerp (val, 0))
    return NULL_TREE;

  var_size = tree_low_cst (TYPE_SIZE (TREE_TYPE (var)), 1);
  field_size = tree_low_cst (DECL_SIZE (field), 1);

  /* Give up if either the bitfield or the variable are too wide.  */
  if (field_size > HOST_BITS_PER_WIDE_INT || var_size > HOST_BITS_PER_WIDE_INT)
    return NULL_TREE;

  gcc_assert (var_size >= field_size);

  /* If the sign bit of the value is not set or the field's type is unsigned,
     just mask off the high order bits of the value.  */
  if (DECL_UNSIGNED (field)
      || !(tree_low_cst (val, 0) & (((HOST_WIDE_INT)1) << (field_size - 1))))
    {
      /* Zero extension.  Build a mask with the lower 'field_size' bits
	 set and a BIT_AND_EXPR node to clear the high order bits of
	 the value.  */
      for (i = 0, mask = 0; i < field_size; i++)
	mask |= ((HOST_WIDE_INT) 1) << i;

      wide_val = build (BIT_AND_EXPR, TREE_TYPE (var), val, 
			fold_convert (TREE_TYPE (var),
				      build_int_cst (NULL_TREE, mask)));
    }
  else
    {
      /* Sign extension.  Create a mask with the upper 'field_size'
	 bits set and a BIT_IOR_EXPR to set the high order bits of the
	 value.  */
      for (i = 0, mask = 0; i < (var_size - field_size); i++)
	mask |= ((HOST_WIDE_INT) 1) << (var_size - i - 1);

      wide_val = build (BIT_IOR_EXPR, TREE_TYPE (var), val,
			fold_convert (TREE_TYPE (var),
				      build_int_cst (NULL_TREE, mask)));
    }

  return fold (wide_val);
}


/* A subroutine of fold_stmt_r.  Attempts to fold *(A+O) to A[X].
   BASE is an array type.  OFFSET is a byte displacement.  ORIG_TYPE
   is the desired result type.  */

static tree
maybe_fold_offset_to_array_ref (tree base, tree offset, tree orig_type)
{
  tree min_idx, idx, elt_offset = integer_zero_node;
  tree array_type, elt_type, elt_size;

  /* If BASE is an ARRAY_REF, we can pick up another offset (this time
     measured in units of the size of elements type) from that ARRAY_REF).
     We can't do anything if either is variable.

     The case we handle here is *(&A[N]+O).  */
  if (TREE_CODE (base) == ARRAY_REF)
    {
      tree low_bound = array_ref_low_bound (base);

      elt_offset = TREE_OPERAND (base, 1);
      if (TREE_CODE (low_bound) != INTEGER_CST
	  || TREE_CODE (elt_offset) != INTEGER_CST)
	return NULL_TREE;

      elt_offset = int_const_binop (MINUS_EXPR, elt_offset, low_bound, 0);
      base = TREE_OPERAND (base, 0);
    }

  /* Ignore stupid user tricks of indexing non-array variables.  */
  array_type = TREE_TYPE (base);
  if (TREE_CODE (array_type) != ARRAY_TYPE)
    return NULL_TREE;
  elt_type = TREE_TYPE (array_type);
  if (!lang_hooks.types_compatible_p (orig_type, elt_type))
    return NULL_TREE;
	
  /* If OFFSET and ELT_OFFSET are zero, we don't care about the size of the
     element type (so we can use the alignment if it's not constant).
     Otherwise, compute the offset as an index by using a division.  If the
     division isn't exact, then don't do anything.  */
  elt_size = TYPE_SIZE_UNIT (elt_type);
  if (integer_zerop (offset))
    {
      if (TREE_CODE (elt_size) != INTEGER_CST)
	elt_size = size_int (TYPE_ALIGN (elt_type));

      idx = integer_zero_node;
    }
  else
    {
      unsigned HOST_WIDE_INT lquo, lrem;
      HOST_WIDE_INT hquo, hrem;

      if (TREE_CODE (elt_size) != INTEGER_CST
	  || div_and_round_double (TRUNC_DIV_EXPR, 1,
				   TREE_INT_CST_LOW (offset),
				   TREE_INT_CST_HIGH (offset),
				   TREE_INT_CST_LOW (elt_size),
				   TREE_INT_CST_HIGH (elt_size),
				   &lquo, &hquo, &lrem, &hrem)
	  || lrem || hrem)
	return NULL_TREE;

      idx = build_int_cst_wide (NULL_TREE, lquo, hquo);
    }

  /* Assume the low bound is zero.  If there is a domain type, get the
     low bound, if any, convert the index into that type, and add the
     low bound.  */
  min_idx = integer_zero_node;
  if (TYPE_DOMAIN (array_type))
    {
      if (TYPE_MIN_VALUE (TYPE_DOMAIN (array_type)))
	min_idx = TYPE_MIN_VALUE (TYPE_DOMAIN (array_type));
      else
	min_idx = fold_convert (TYPE_DOMAIN (array_type), min_idx);

      if (TREE_CODE (min_idx) != INTEGER_CST)
	return NULL_TREE;

      idx = fold_convert (TYPE_DOMAIN (array_type), idx);
      elt_offset = fold_convert (TYPE_DOMAIN (array_type), elt_offset);
    }

  if (!integer_zerop (min_idx))
    idx = int_const_binop (PLUS_EXPR, idx, min_idx, 0);
  if (!integer_zerop (elt_offset))
    idx = int_const_binop (PLUS_EXPR, idx, elt_offset, 0);

  return build (ARRAY_REF, orig_type, base, idx, min_idx,
		size_int (tree_low_cst (elt_size, 1)
			  / (TYPE_ALIGN_UNIT (elt_type))));
}


/* A subroutine of fold_stmt_r.  Attempts to fold *(S+O) to S.X.
   BASE is a record type.  OFFSET is a byte displacement.  ORIG_TYPE
   is the desired result type.  */
/* ??? This doesn't handle class inheritance.  */

static tree
maybe_fold_offset_to_component_ref (tree record_type, tree base, tree offset,
				    tree orig_type, bool base_is_ptr)
{
  tree f, t, field_type, tail_array_field, field_offset;

  if (TREE_CODE (record_type) != RECORD_TYPE
      && TREE_CODE (record_type) != UNION_TYPE
      && TREE_CODE (record_type) != QUAL_UNION_TYPE)
    return NULL_TREE;

  /* Short-circuit silly cases.  */
  if (lang_hooks.types_compatible_p (record_type, orig_type))
    return NULL_TREE;

  tail_array_field = NULL_TREE;
  for (f = TYPE_FIELDS (record_type); f ; f = TREE_CHAIN (f))
    {
      int cmp;

      if (TREE_CODE (f) != FIELD_DECL)
	continue;
      if (DECL_BIT_FIELD (f))
	continue;

      field_offset = byte_position (f);
      if (TREE_CODE (field_offset) != INTEGER_CST)
	continue;

      /* ??? Java creates "interesting" fields for representing base classes.
	 They have no name, and have no context.  With no context, we get into
	 trouble with nonoverlapping_component_refs_p.  Skip them.  */
      if (!DECL_FIELD_CONTEXT (f))
	continue;

      /* The previous array field isn't at the end.  */
      tail_array_field = NULL_TREE;

      /* Check to see if this offset overlaps with the field.  */
      cmp = tree_int_cst_compare (field_offset, offset);
      if (cmp > 0)
	continue;

      field_type = TREE_TYPE (f);
      if (cmp < 0)
	{
	  /* Don't care about offsets into the middle of scalars.  */
	  if (!AGGREGATE_TYPE_P (field_type))
	    continue;

	  /* Check for array at the end of the struct.  This is often
	     used as for flexible array members.  We should be able to
	     turn this into an array access anyway.  */
	  if (TREE_CODE (field_type) == ARRAY_TYPE)
	    tail_array_field = f;

	  /* Check the end of the field against the offset.  */
	  if (!DECL_SIZE_UNIT (f)
	      || TREE_CODE (DECL_SIZE_UNIT (f)) != INTEGER_CST)
	    continue;
	  t = int_const_binop (MINUS_EXPR, offset, DECL_FIELD_OFFSET (f), 1);
	  if (!tree_int_cst_lt (t, DECL_SIZE_UNIT (f)))
	    continue;

	  /* If we matched, then set offset to the displacement into
	     this field.  */
	  offset = t;
	}

      /* Here we exactly match the offset being checked.  If the types match,
	 then we can return that field.  */
      else if (lang_hooks.types_compatible_p (orig_type, field_type))
	{
	  if (base_is_ptr)
	    base = build1 (INDIRECT_REF, record_type, base);
	  t = build (COMPONENT_REF, field_type, base, f, NULL_TREE);
	  return t;
	}

      /* Don't care about type-punning of scalars.  */
      else if (!AGGREGATE_TYPE_P (field_type))
	return NULL_TREE;

      goto found;
    }

  if (!tail_array_field)
    return NULL_TREE;

  f = tail_array_field;
  field_type = TREE_TYPE (f);

 found:
  /* If we get here, we've got an aggregate field, and a possibly 
     nonzero offset into them.  Recurse and hope for a valid match.  */
  if (base_is_ptr)
    base = build1 (INDIRECT_REF, record_type, base);
  base = build (COMPONENT_REF, field_type, base, f, NULL_TREE);

  t = maybe_fold_offset_to_array_ref (base, offset, orig_type);
  if (t)
    return t;