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[gcc.git] / gcc / tree-scalar-evolution.c

/* Scalar evolution detector.
   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009
   Free Software Foundation, Inc.
   Contributed by Sebastian Pop <s.pop@laposte.net>

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/>.  */

/* 
   Description: 
   
   This pass analyzes the evolution of scalar variables in loop
   structures.  The algorithm is based on the SSA representation,
   and on the loop hierarchy tree.  This algorithm is not based on
   the notion of versions of a variable, as it was the case for the
   previous implementations of the scalar evolution algorithm, but
   it assumes that each defined name is unique.

   The notation used in this file is called "chains of recurrences",
   and has been proposed by Eugene Zima, Robert Van Engelen, and
   others for describing induction variables in programs.  For example
   "b -> {0, +, 2}_1" means that the scalar variable "b" is equal to 0
   when entering in the loop_1 and has a step 2 in this loop, in other
   words "for (b = 0; b < N; b+=2);".  Note that the coefficients of
   this chain of recurrence (or chrec [shrek]) can contain the name of
   other variables, in which case they are called parametric chrecs.
   For example, "b -> {a, +, 2}_1" means that the initial value of "b"
   is the value of "a".  In most of the cases these parametric chrecs
   are fully instantiated before their use because symbolic names can
   hide some difficult cases such as self-references described later
   (see the Fibonacci example).
   
   A short sketch of the algorithm is:
     
   Given a scalar variable to be analyzed, follow the SSA edge to
   its definition:
     
   - When the definition is a GIMPLE_ASSIGN: if the right hand side
   (RHS) of the definition cannot be statically analyzed, the answer
   of the analyzer is: "don't know".  
   Otherwise, for all the variables that are not yet analyzed in the
   RHS, try to determine their evolution, and finally try to
   evaluate the operation of the RHS that gives the evolution
   function of the analyzed variable.

   - When the definition is a condition-phi-node: determine the
   evolution function for all the branches of the phi node, and
   finally merge these evolutions (see chrec_merge).

   - When the definition is a loop-phi-node: determine its initial
   condition, that is the SSA edge defined in an outer loop, and
   keep it symbolic.  Then determine the SSA edges that are defined
   in the body of the loop.  Follow the inner edges until ending on
   another loop-phi-node of the same analyzed loop.  If the reached
   loop-phi-node is not the starting loop-phi-node, then we keep
   this definition under a symbolic form.  If the reached
   loop-phi-node is the same as the starting one, then we compute a
   symbolic stride on the return path.  The result is then the
   symbolic chrec {initial_condition, +, symbolic_stride}_loop.

   Examples:
   
   Example 1: Illustration of the basic algorithm.
   
   | a = 3
   | loop_1
   |   b = phi (a, c)
   |   c = b + 1
   |   if (c > 10) exit_loop
   | endloop
   
   Suppose that we want to know the number of iterations of the
   loop_1.  The exit_loop is controlled by a COND_EXPR (c > 10).  We
   ask the scalar evolution analyzer two questions: what's the
   scalar evolution (scev) of "c", and what's the scev of "10".  For
   "10" the answer is "10" since it is a scalar constant.  For the
   scalar variable "c", it follows the SSA edge to its definition,
   "c = b + 1", and then asks again what's the scev of "b".
   Following the SSA edge, we end on a loop-phi-node "b = phi (a,
   c)", where the initial condition is "a", and the inner loop edge
   is "c".  The initial condition is kept under a symbolic form (it
   may be the case that the copy constant propagation has done its
   work and we end with the constant "3" as one of the edges of the
   loop-phi-node).  The update edge is followed to the end of the
   loop, and until reaching again the starting loop-phi-node: b -> c
   -> b.  At this point we have drawn a path from "b" to "b" from
   which we compute the stride in the loop: in this example it is
   "+1".  The resulting scev for "b" is "b -> {a, +, 1}_1".  Now
   that the scev for "b" is known, it is possible to compute the
   scev for "c", that is "c -> {a + 1, +, 1}_1".  In order to
   determine the number of iterations in the loop_1, we have to
   instantiate_parameters (loop_1, {a + 1, +, 1}_1), that gives after some
   more analysis the scev {4, +, 1}_1, or in other words, this is
   the function "f (x) = x + 4", where x is the iteration count of
   the loop_1.  Now we have to solve the inequality "x + 4 > 10",
   and take the smallest iteration number for which the loop is
   exited: x = 7.  This loop runs from x = 0 to x = 7, and in total
   there are 8 iterations.  In terms of loop normalization, we have
   created a variable that is implicitly defined, "x" or just "_1",
   and all the other analyzed scalars of the loop are defined in
   function of this variable:
   
   a -> 3
   b -> {3, +, 1}_1
   c -> {4, +, 1}_1
     
   or in terms of a C program: 
     
   | a = 3
   | for (x = 0; x <= 7; x++)
   |   {
   |     b = x + 3
   |     c = x + 4
   |   }
     
   Example 2a: Illustration of the algorithm on nested loops.
     
   | loop_1
   |   a = phi (1, b)
   |   c = a + 2
   |   loop_2  10 times
   |     b = phi (c, d)
   |     d = b + 3
   |   endloop
   | endloop
     
   For analyzing the scalar evolution of "a", the algorithm follows
   the SSA edge into the loop's body: "a -> b".  "b" is an inner
   loop-phi-node, and its analysis as in Example 1, gives: 
     
   b -> {c, +, 3}_2
   d -> {c + 3, +, 3}_2
     
   Following the SSA edge for the initial condition, we end on "c = a
   + 2", and then on the starting loop-phi-node "a".  From this point,
   the loop stride is computed: back on "c = a + 2" we get a "+2" in
   the loop_1, then on the loop-phi-node "b" we compute the overall
   effect of the inner loop that is "b = c + 30", and we get a "+30"
   in the loop_1.  That means that the overall stride in loop_1 is
   equal to "+32", and the result is: 
     
   a -> {1, +, 32}_1
   c -> {3, +, 32}_1

   Example 2b: Multivariate chains of recurrences.

   | loop_1
   |   k = phi (0, k + 1)
   |   loop_2  4 times
   |     j = phi (0, j + 1)
   |     loop_3 4 times
   |       i = phi (0, i + 1)
   |       A[j + k] = ...
   |     endloop
   |   endloop
   | endloop

   Analyzing the access function of array A with
   instantiate_parameters (loop_1, "j + k"), we obtain the
   instantiation and the analysis of the scalar variables "j" and "k"
   in loop_1.  This leads to the scalar evolution {4, +, 1}_1: the end
   value of loop_2 for "j" is 4, and the evolution of "k" in loop_1 is
   {0, +, 1}_1.  To obtain the evolution function in loop_3 and
   instantiate the scalar variables up to loop_1, one has to use:
   instantiate_scev (block_before_loop (loop_1), loop_3, "j + k").
   The result of this call is {{0, +, 1}_1, +, 1}_2.

   Example 3: Higher degree polynomials.
     
   | loop_1
   |   a = phi (2, b)
   |   c = phi (5, d)
   |   b = a + 1
   |   d = c + a
   | endloop
     
   a -> {2, +, 1}_1
   b -> {3, +, 1}_1
   c -> {5, +, a}_1
   d -> {5 + a, +, a}_1
     
   instantiate_parameters (loop_1, {5, +, a}_1) -> {5, +, 2, +, 1}_1
   instantiate_parameters (loop_1, {5 + a, +, a}_1) -> {7, +, 3, +, 1}_1
     
   Example 4: Lucas, Fibonacci, or mixers in general.
     
   | loop_1
   |   a = phi (1, b)
   |   c = phi (3, d)
   |   b = c
   |   d = c + a
   | endloop
     
   a -> (1, c)_1
   c -> {3, +, a}_1
     
   The syntax "(1, c)_1" stands for a PEELED_CHREC that has the
   following semantics: during the first iteration of the loop_1, the
   variable contains the value 1, and then it contains the value "c".
   Note that this syntax is close to the syntax of the loop-phi-node:
   "a -> (1, c)_1" vs. "a = phi (1, c)".
     
   The symbolic chrec representation contains all the semantics of the
   original code.  What is more difficult is to use this information.
     
   Example 5: Flip-flops, or exchangers.
     
   | loop_1
   |   a = phi (1, b)
   |   c = phi (3, d)
   |   b = c
   |   d = a
   | endloop
     
   a -> (1, c)_1
   c -> (3, a)_1
     
   Based on these symbolic chrecs, it is possible to refine this
   information into the more precise PERIODIC_CHRECs: 
     
   a -> |1, 3|_1
   c -> |3, 1|_1
     
   This transformation is not yet implemented.
     
   Further readings:
   
   You can find a more detailed description of the algorithm in:
   http://icps.u-strasbg.fr/~pop/DEA_03_Pop.pdf
   http://icps.u-strasbg.fr/~pop/DEA_03_Pop.ps.gz.  But note that
   this is a preliminary report and some of the details of the
   algorithm have changed.  I'm working on a research report that
   updates the description of the algorithms to reflect the design
   choices used in this implementation.
     
   A set of slides show a high level overview of the algorithm and run
   an example through the scalar evolution analyzer:
   http://cri.ensmp.fr/~pop/gcc/mar04/slides.pdf

   The slides that I have presented at the GCC Summit'04 are available
   at: http://cri.ensmp.fr/~pop/gcc/20040604/gccsummit-lno-spop.pdf
*/

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "ggc.h"
#include "tree.h"
#include "real.h"

/* These RTL headers are needed for basic-block.h.  */
#include "rtl.h"
#include "basic-block.h"
#include "diagnostic.h"
#include "tree-flow.h"
#include "tree-dump.h"
#include "timevar.h"
#include "cfgloop.h"
#include "tree-chrec.h"
#include "tree-scalar-evolution.h"
#include "tree-pass.h"
#include "flags.h"
#include "params.h"

static tree analyze_scalar_evolution_1 (struct loop *, tree, tree);

/* The cached information about an SSA name VAR, claiming that below
   basic block INSTANTIATED_BELOW, the value of VAR can be expressed
   as CHREC.  */

struct GTY(()) scev_info_str {
  basic_block instantiated_below;
  tree var;
  tree chrec;
};

/* Counters for the scev database.  */
static unsigned nb_set_scev = 0;
static unsigned nb_get_scev = 0;

/* The following trees are unique elements.  Thus the comparison of
   another element to these elements should be done on the pointer to
   these trees, and not on their value.  */

/* The SSA_NAMEs that are not yet analyzed are qualified with NULL_TREE.  */
tree chrec_not_analyzed_yet;

/* Reserved to the cases where the analyzer has detected an
   undecidable property at compile time.  */
tree chrec_dont_know;

/* When the analyzer has detected that a property will never
   happen, then it qualifies it with chrec_known.  */
tree chrec_known;

static GTY ((param_is (struct scev_info_str))) htab_t scalar_evolution_info;

\f
/* Constructs a new SCEV_INFO_STR structure for VAR and INSTANTIATED_BELOW.  */

static inline struct scev_info_str *
new_scev_info_str (basic_block instantiated_below, tree var)
{
  struct scev_info_str *res;
  
  res = GGC_NEW (struct scev_info_str);
  res->var = var;
  res->chrec = chrec_not_analyzed_yet;
  res->instantiated_below = instantiated_below;

  return res;
}

/* Computes a hash function for database element ELT.  */

static hashval_t
hash_scev_info (const void *elt)
{
  return SSA_NAME_VERSION (((const struct scev_info_str *) elt)->var);
}

/* Compares database elements E1 and E2.  */

static int
eq_scev_info (const void *e1, const void *e2)
{
  const struct scev_info_str *elt1 = (const struct scev_info_str *) e1;
  const struct scev_info_str *elt2 = (const struct scev_info_str *) e2;

  return (elt1->var == elt2->var
          && elt1->instantiated_below == elt2->instantiated_below);
}

/* Deletes database element E.  */

static void
del_scev_info (void *e)
{
  ggc_free (e);
}

/* Get the scalar evolution of VAR for INSTANTIATED_BELOW basic block.
   A first query on VAR returns chrec_not_analyzed_yet.  */

static tree *
find_var_scev_info (basic_block instantiated_below, tree var)
{
  struct scev_info_str *res;
  struct scev_info_str tmp;
  PTR *slot;

  tmp.var = var;
  tmp.instantiated_below = instantiated_below;
  slot = htab_find_slot (scalar_evolution_info, &tmp, INSERT);

  if (!*slot)
    *slot = new_scev_info_str (instantiated_below, var);
  res = (struct scev_info_str *) *slot;

  return &res->chrec;
}

/* Return true when CHREC contains symbolic names defined in
   LOOP_NB.  */

bool 
chrec_contains_symbols_defined_in_loop (const_tree chrec, unsigned loop_nb)
{
  int i, n;

  if (chrec == NULL_TREE)
    return false;

  if (is_gimple_min_invariant (chrec))
    return false;

  if (TREE_CODE (chrec) == VAR_DECL
      || TREE_CODE (chrec) == PARM_DECL
      || TREE_CODE (chrec) == FUNCTION_DECL
      || TREE_CODE (chrec) == LABEL_DECL
      || TREE_CODE (chrec) == RESULT_DECL
      || TREE_CODE (chrec) == FIELD_DECL)
    return true;

  if (TREE_CODE (chrec) == SSA_NAME)
    {
      gimple def = SSA_NAME_DEF_STMT (chrec);
      struct loop *def_loop = loop_containing_stmt (def);
      struct loop *loop = get_loop (loop_nb);

      if (def_loop == NULL)
        return false;

      if (loop == def_loop || flow_loop_nested_p (loop, def_loop))
        return true;

      return false;
    }

  n = TREE_OPERAND_LENGTH (chrec);
  for (i = 0; i < n; i++)
    if (chrec_contains_symbols_defined_in_loop (TREE_OPERAND (chrec, i), 
                                                loop_nb))
      return true;
  return false;
}

/* Return true when PHI is a loop-phi-node.  */

static bool
loop_phi_node_p (gimple phi)
{
  /* The implementation of this function is based on the following
     property: "all the loop-phi-nodes of a loop are contained in the
     loop's header basic block".  */

  return loop_containing_stmt (phi)->header == gimple_bb (phi);
}

/* Compute the scalar evolution for EVOLUTION_FN after crossing LOOP.
   In general, in the case of multivariate evolutions we want to get
   the evolution in different loops.  LOOP specifies the level for
   which to get the evolution.
   
   Example:
   
   | for (j = 0; j < 100; j++)
   |   {
   |     for (k = 0; k < 100; k++)
   |       {
   |         i = k + j;   - Here the value of i is a function of j, k. 
   |       }
   |      ... = i         - Here the value of i is a function of j. 
   |   }
   | ... = i              - Here the value of i is a scalar.  
   
   Example:  
   
   | i_0 = ...
   | loop_1 10 times
   |   i_1 = phi (i_0, i_2)
   |   i_2 = i_1 + 2
   | endloop
    
   This loop has the same effect as:
   LOOP_1 has the same effect as:
    
   | i_1 = i_0 + 20
   
   The overall effect of the loop, "i_0 + 20" in the previous example, 
   is obtained by passing in the parameters: LOOP = 1, 
   EVOLUTION_FN = {i_0, +, 2}_1.
*/
 
static tree 
compute_overall_effect_of_inner_loop (struct loop *loop, tree evolution_fn)
{
  bool val = false;

  if (evolution_fn == chrec_dont_know)
    return chrec_dont_know;

  else if (TREE_CODE (evolution_fn) == POLYNOMIAL_CHREC)
    {
      struct loop *inner_loop = get_chrec_loop (evolution_fn);

      if (inner_loop == loop
          || flow_loop_nested_p (loop, inner_loop))
        {
          tree nb_iter = number_of_latch_executions (inner_loop);

          if (nb_iter == chrec_dont_know)
            return chrec_dont_know;
          else
            {
              tree res;

              /* evolution_fn is the evolution function in LOOP.  Get
                 its value in the nb_iter-th iteration.  */
              res = chrec_apply (inner_loop->num, evolution_fn, nb_iter);
              
              /* Continue the computation until ending on a parent of LOOP.  */
              return compute_overall_effect_of_inner_loop (loop, res);
            }
        }
      else
        return evolution_fn;
     }
  
  /* If the evolution function is an invariant, there is nothing to do.  */
  else if (no_evolution_in_loop_p (evolution_fn, loop->num, &val) && val)
    return evolution_fn;
  
  else
    return chrec_dont_know;
}

/* Determine whether the CHREC is always positive/negative.  If the expression
   cannot be statically analyzed, return false, otherwise set the answer into
   VALUE.  */

bool
chrec_is_positive (tree chrec, bool *value)
{
  bool value0, value1, value2;
  tree end_value, nb_iter;
  
  switch (TREE_CODE (chrec))
    {
    case POLYNOMIAL_CHREC:
      if (!chrec_is_positive (CHREC_LEFT (chrec), &value0)
          || !chrec_is_positive (CHREC_RIGHT (chrec), &value1))
        return false;
     
      /* FIXME -- overflows.  */
      if (value0 == value1)
        {
          *value = value0;
          return true;
        }

      /* Otherwise the chrec is under the form: "{-197, +, 2}_1",
         and the proof consists in showing that the sign never
         changes during the execution of the loop, from 0 to
         loop->nb_iterations.  */
      if (!evolution_function_is_affine_p (chrec))
        return false;

      nb_iter = number_of_latch_executions (get_chrec_loop (chrec));
      if (chrec_contains_undetermined (nb_iter))
        return false;

#if 0
      /* TODO -- If the test is after the exit, we may decrease the number of
         iterations by one.  */
      if (after_exit)
        nb_iter = chrec_fold_minus (type, nb_iter, build_int_cst (type, 1));
#endif

      end_value = chrec_apply (CHREC_VARIABLE (chrec), chrec, nb_iter);
              
      if (!chrec_is_positive (end_value, &value2))
        return false;
        
      *value = value0;
      return value0 == value1;
      
    case INTEGER_CST:
      *value = (tree_int_cst_sgn (chrec) == 1);
      return true;
      
    default:
      return false;
    }
}

/* Associate CHREC to SCALAR.  */

static void
set_scalar_evolution (basic_block instantiated_below, tree scalar, tree chrec)
{
  tree *scalar_info;
 
  if (TREE_CODE (scalar) != SSA_NAME)
    return;

  scalar_info = find_var_scev_info (instantiated_below, scalar);
  
  if (dump_file)
    {
      if (dump_flags & TDF_DETAILS)
        {
          fprintf (dump_file, "(set_scalar_evolution \n");
          fprintf (dump_file, "  instantiated_below = %d \n",
                   instantiated_below->index);
          fprintf (dump_file, "  (scalar = ");
          print_generic_expr (dump_file, scalar, 0);
          fprintf (dump_file, ")\n  (scalar_evolution = ");
          print_generic_expr (dump_file, chrec, 0);
          fprintf (dump_file, "))\n");
        }
      if (dump_flags & TDF_STATS)
        nb_set_scev++;
    }
  
  *scalar_info = chrec;
}

/* Retrieve the chrec associated to SCALAR instantiated below
   INSTANTIATED_BELOW block.  */

static tree
get_scalar_evolution (basic_block instantiated_below, tree scalar)
{
  tree res;
  
  if (dump_file)
    {
      if (dump_flags & TDF_DETAILS)
        {
          fprintf (dump_file, "(get_scalar_evolution \n");
          fprintf (dump_file, "  (scalar = ");
          print_generic_expr (dump_file, scalar, 0);
          fprintf (dump_file, ")\n");
        }
      if (dump_flags & TDF_STATS)
        nb_get_scev++;
    }
  
  switch (TREE_CODE (scalar))
    {
    case SSA_NAME:
      res = *find_var_scev_info (instantiated_below, scalar);
      break;

    case REAL_CST:
    case FIXED_CST:
    case INTEGER_CST:
      res = scalar;
      break;

    default:
      res = chrec_not_analyzed_yet;
      break;
    }
  
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "  (scalar_evolution = ");
      print_generic_expr (dump_file, res, 0);
      fprintf (dump_file, "))\n");
    }
  
  return res;
}

/* Helper function for add_to_evolution.  Returns the evolution
   function for an assignment of the form "a = b + c", where "a" and
   "b" are on the strongly connected component.  CHREC_BEFORE is the
   information that we already have collected up to this point.
   TO_ADD is the evolution of "c".  
   
   When CHREC_BEFORE has an evolution part in LOOP_NB, add to this
   evolution the expression TO_ADD, otherwise construct an evolution
   part for this loop.  */

static tree
add_to_evolution_1 (unsigned loop_nb, tree chrec_before, tree to_add,
                    gimple at_stmt)
{
  tree type, left, right;
  struct loop *loop = get_loop (loop_nb), *chloop;

  switch (TREE_CODE (chrec_before))
    {
    case POLYNOMIAL_CHREC:
      chloop = get_chrec_loop (chrec_before);
      if (chloop == loop
          || flow_loop_nested_p (chloop, loop))
        {
          unsigned var;

          type = chrec_type (chrec_before);
          
          /* When there is no evolution part in this loop, build it.  */
          if (chloop != loop)
            {
              var = loop_nb;
              left = chrec_before;
              right = SCALAR_FLOAT_TYPE_P (type)
                ? build_real (type, dconst0)
                : build_int_cst (type, 0);
            }
          else
            {
              var = CHREC_VARIABLE (chrec_before);
              left = CHREC_LEFT (chrec_before);
              right = CHREC_RIGHT (chrec_before);
            }

          to_add = chrec_convert (type, to_add, at_stmt);
          right = chrec_convert_rhs (type, right, at_stmt);
          right = chrec_fold_plus (chrec_type (right), right, to_add);
          return build_polynomial_chrec (var, left, right);
        }
      else
        {
          gcc_assert (flow_loop_nested_p (loop, chloop));

          /* Search the evolution in LOOP_NB.  */
          left = add_to_evolution_1 (loop_nb, CHREC_LEFT (chrec_before),
                                     to_add, at_stmt);
          right = CHREC_RIGHT (chrec_before);
          right = chrec_convert_rhs (chrec_type (left), right, at_stmt);
          return build_polynomial_chrec (CHREC_VARIABLE (chrec_before),
                                         left, right);
        }
      
    default:
      /* These nodes do not depend on a loop.  */
      if (chrec_before == chrec_dont_know)
        return chrec_dont_know;

      left = chrec_before;
      right = chrec_convert_rhs (chrec_type (left), to_add, at_stmt);
      return build_polynomial_chrec (loop_nb, left, right);
    }
}

/* Add TO_ADD to the evolution part of CHREC_BEFORE in the dimension
   of LOOP_NB.  
   
   Description (provided for completeness, for those who read code in
   a plane, and for my poor 62 bytes brain that would have forgotten
   all this in the next two or three months):
   
   The algorithm of translation of programs from the SSA representation
   into the chrecs syntax is based on a pattern matching.  After having
   reconstructed the overall tree expression for a loop, there are only
   two cases that can arise:
   
   1. a = loop-phi (init, a + expr)
   2. a = loop-phi (init, expr)
   
   where EXPR is either a scalar constant with respect to the analyzed
   loop (this is a degree 0 polynomial), or an expression containing
   other loop-phi definitions (these are higher degree polynomials).
   
   Examples:
   
   1. 
   | init = ...
   | loop_1
   |   a = phi (init, a + 5)
   | endloop
   
   2. 
   | inita = ...
   | initb = ...
   | loop_1
   |   a = phi (inita, 2 * b + 3)
   |   b = phi (initb, b + 1)
   | endloop
   
   For the first case, the semantics of the SSA representation is: 
   
   | a (x) = init + \sum_{j = 0}^{x - 1} expr (j)
   
   that is, there is a loop index "x" that determines the scalar value
   of the variable during the loop execution.  During the first
   iteration, the value is that of the initial condition INIT, while
   during the subsequent iterations, it is the sum of the initial
   condition with the sum of all the values of EXPR from the initial
   iteration to the before last considered iteration.  
   
   For the second case, the semantics of the SSA program is:
   
   | a (x) = init, if x = 0;
   |         expr (x - 1), otherwise.
   
   The second case corresponds to the PEELED_CHREC, whose syntax is
   close to the syntax of a loop-phi-node: 
   
   | phi (init, expr)  vs.  (init, expr)_x
   
   The proof of the translation algorithm for the first case is a
   proof by structural induction based on the degree of EXPR.  
   
   Degree 0:
   When EXPR is a constant with respect to the analyzed loop, or in
   other words when EXPR is a polynomial of degree 0, the evolution of
   the variable A in the loop is an affine function with an initial
   condition INIT, and a step EXPR.  In order to show this, we start
   from the semantics of the SSA representation:
   
   f (x) = init + \sum_{j = 0}^{x - 1} expr (j)
   
   and since "expr (j)" is a constant with respect to "j",
   
   f (x) = init + x * expr 
   
   Finally, based on the semantics of the pure sum chrecs, by
   identification we get the corresponding chrecs syntax:
   
   f (x) = init * \binom{x}{0} + expr * \binom{x}{1} 
   f (x) -> {init, +, expr}_x
   
   Higher degree:
   Suppose that EXPR is a polynomial of degree N with respect to the
   analyzed loop_x for which we have already determined that it is
   written under the chrecs syntax:
   
   | expr (x)  ->  {b_0, +, b_1, +, ..., +, b_{n-1}} (x)
   
   We start from the semantics of the SSA program:
   
   | f (x) = init + \sum_{j = 0}^{x - 1} expr (j)
   |
   | f (x) = init + \sum_{j = 0}^{x - 1} 
   |                (b_0 * \binom{j}{0} + ... + b_{n-1} * \binom{j}{n-1})
   |
   | f (x) = init + \sum_{j = 0}^{x - 1} 
   |                \sum_{k = 0}^{n - 1} (b_k * \binom{j}{k}) 
   |
   | f (x) = init + \sum_{k = 0}^{n - 1} 
   |                (b_k * \sum_{j = 0}^{x - 1} \binom{j}{k}) 
   |
   | f (x) = init + \sum_{k = 0}^{n - 1} 
   |                (b_k * \binom{x}{k + 1}) 
   |
   | f (x) = init + b_0 * \binom{x}{1} + ... 
   |              + b_{n-1} * \binom{x}{n} 
   |
   | f (x) = init * \binom{x}{0} + b_0 * \binom{x}{1} + ... 
   |                             + b_{n-1} * \binom{x}{n} 
   |
   
   And finally from the definition of the chrecs syntax, we identify:
   | f (x)  ->  {init, +, b_0, +, ..., +, b_{n-1}}_x 
   
   This shows the mechanism that stands behind the add_to_evolution
   function.  An important point is that the use of symbolic
   parameters avoids the need of an analysis schedule.
   
   Example:
   
   | inita = ...
   | initb = ...
   | loop_1 
   |   a = phi (inita, a + 2 + b)
   |   b = phi (initb, b + 1)
   | endloop
   
   When analyzing "a", the algorithm keeps "b" symbolically:
   
   | a  ->  {inita, +, 2 + b}_1
   
   Then, after instantiation, the analyzer ends on the evolution:
   
   | a  ->  {inita, +, 2 + initb, +, 1}_1

*/

static tree 
add_to_evolution (unsigned loop_nb, tree chrec_before, enum tree_code code,
                  tree to_add, gimple at_stmt)
{
  tree type = chrec_type (to_add);
  tree res = NULL_TREE;
  
  if (to_add == NULL_TREE)
    return chrec_before;
  
  /* TO_ADD is either a scalar, or a parameter.  TO_ADD is not
     instantiated at this point.  */
  if (TREE_CODE (to_add) == POLYNOMIAL_CHREC)
    /* This should not happen.  */
    return chrec_dont_know;
  
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "(add_to_evolution \n");
      fprintf (dump_file, "  (loop_nb = %d)\n", loop_nb);
      fprintf (dump_file, "  (chrec_before = ");
      print_generic_expr (dump_file, chrec_before, 0);
      fprintf (dump_file, ")\n  (to_add = ");
      print_generic_expr (dump_file, to_add, 0);
      fprintf (dump_file, ")\n");
    }

  if (code == MINUS_EXPR)
    to_add = chrec_fold_multiply (type, to_add, SCALAR_FLOAT_TYPE_P (type)
                                  ? build_real (type, dconstm1)
                                  : build_int_cst_type (type, -1));

  res = add_to_evolution_1 (loop_nb, chrec_before, to_add, at_stmt);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "  (res = ");
      print_generic_expr (dump_file, res, 0);
      fprintf (dump_file, "))\n");
    }

  return res;
}

/* Helper function.  */

static inline tree
set_nb_iterations_in_loop (struct loop *loop, 
                           tree res)
{
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "  (set_nb_iterations_in_loop = ");
      print_generic_expr (dump_file, res, 0);
      fprintf (dump_file, "))\n");
    }
  
  loop->nb_iterations = res;
  return res;
}

\f

/* This section selects the loops that will be good candidates for the
   scalar evolution analysis.  For the moment, greedily select all the
   loop nests we could analyze.  */

/* For a loop with a single exit edge, return the COND_EXPR that
   guards the exit edge.  If the expression is too difficult to
   analyze, then give up.  */

gimple 
get_loop_exit_condition (const struct loop *loop)
{
  gimple res = NULL;
  edge exit_edge = single_exit (loop);
  
  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "(get_loop_exit_condition \n  ");
  
  if (exit_edge)
    {
      gimple stmt;
      
      stmt = last_stmt (exit_edge->src);
      if (gimple_code (stmt) == GIMPLE_COND)
        res = stmt;
    }
  
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      print_gimple_stmt (dump_file, res, 0, 0);
      fprintf (dump_file, ")\n");
    }
  
  return res;
}

/* Recursively determine and enqueue the exit conditions for a loop.  */

static void 
get_exit_conditions_rec (struct loop *loop, 
                         VEC(gimple,heap) **exit_conditions)
{
  if (!loop)
    return;
  
  /* Recurse on the inner loops, then on the next (sibling) loops.  */
  get_exit_conditions_rec (loop->inner, exit_conditions);
  get_exit_conditions_rec (loop->next, exit_conditions);
  
  if (single_exit (loop))
    {
      gimple loop_condition = get_loop_exit_condition (loop);
      
      if (loop_condition)
        VEC_safe_push (gimple, heap, *exit_conditions, loop_condition);
    }
}

/* Select the candidate loop nests for the analysis.  This function
   initializes the EXIT_CONDITIONS array.  */

static void
select_loops_exit_conditions (VEC(gimple,heap) **exit_conditions)
{
  struct loop *function_body = current_loops->tree_root;
  
  get_exit_conditions_rec (function_body->inner, exit_conditions);
}

\f
/* Depth first search algorithm.  */

typedef enum t_bool {
  t_false,
  t_true,
  t_dont_know
} t_bool;


static t_bool follow_ssa_edge (struct loop *loop, gimple, gimple, tree *, int);

/* Follow the ssa edge into the binary expression RHS0 CODE RHS1.
   Return true if the strongly connected component has been found.  */

static t_bool
follow_ssa_edge_binary (struct loop *loop, gimple at_stmt,
                        tree type, tree rhs0, enum tree_code code, tree rhs1,
                        gimple halting_phi, tree *evolution_of_loop, int limit)
{
  t_bool res = t_false;
  tree evol;

  switch (code)
    {
    case POINTER_PLUS_EXPR:
    case PLUS_EXPR:
      if (TREE_CODE (rhs0) == SSA_NAME)
        {
          if (TREE_CODE (rhs1) == SSA_NAME)
            {
              /* Match an assignment under the form: 
                 "a = b + c".  */
      
              /* We want only assignments of form "name + name" contribute to
                 LIMIT, as the other cases do not necessarily contribute to
                 the complexity of the expression.  */
              limit++;

              evol = *evolution_of_loop;
              res = follow_ssa_edge 
                (loop, SSA_NAME_DEF_STMT (rhs0), halting_phi, &evol, limit);
              
              if (res == t_true)
                *evolution_of_loop = add_to_evolution 
                  (loop->num, 
                   chrec_convert (type, evol, at_stmt), 
                   code, rhs1, at_stmt);
              
              else if (res == t_false)
                {
                  res = follow_ssa_edge 
                    (loop, SSA_NAME_DEF_STMT (rhs1), halting_phi, 
                     evolution_of_loop, limit);
                  
                  if (res == t_true)
                    *evolution_of_loop = add_to_evolution 
                      (loop->num, 
                       chrec_convert (type, *evolution_of_loop, at_stmt), 
                       code, rhs0, at_stmt);

                  else if (res == t_dont_know)
                    *evolution_of_loop = chrec_dont_know;
                }

              else if (res == t_dont_know)
                *evolution_of_loop = chrec_dont_know;
            }
          
          else
            {
              /* Match an assignment under the form: 
                 "a = b + ...".  */
              res = follow_ssa_edge 
                (loop, SSA_NAME_DEF_STMT (rhs0), halting_phi, 
                 evolution_of_loop, limit);
              if (res == t_true)
                *evolution_of_loop = add_to_evolution 
                  (loop->num, chrec_convert (type, *evolution_of_loop,
                                             at_stmt),
                   code, rhs1, at_stmt);

              else if (res == t_dont_know)
                *evolution_of_loop = chrec_dont_know;
            }
        }
      
      else if (TREE_CODE (rhs1) == SSA_NAME)
        {
          /* Match an assignment under the form: 
             "a = ... + c".  */
          res = follow_ssa_edge 
            (loop, SSA_NAME_DEF_STMT (rhs1), halting_phi, 
             evolution_of_loop, limit);
          if (res == t_true)
            *evolution_of_loop = add_to_evolution 
              (loop->num, chrec_convert (type, *evolution_of_loop,
                                         at_stmt),
               code, rhs0, at_stmt);

          else if (res == t_dont_know)
            *evolution_of_loop = chrec_dont_know;
        }

      else
        /* Otherwise, match an assignment under the form: 
           "a = ... + ...".  */
        /* And there is nothing to do.  */
        res = t_false;
      break;
      
    case MINUS_EXPR:
      /* This case is under the form "opnd0 = rhs0 - rhs1".  */
      if (TREE_CODE (rhs0) == SSA_NAME)
        {
          /* Match an assignment under the form: 
             "a = b - ...".  */

          /* We want only assignments of form "name - name" contribute to
             LIMIT, as the other cases do not necessarily contribute to
             the complexity of the expression.  */
          if (TREE_CODE (rhs1) == SSA_NAME)
            limit++;

          res = follow_ssa_edge (loop, SSA_NAME_DEF_STMT (rhs0), halting_phi, 
                                 evolution_of_loop, limit);
          if (res == t_true)
            *evolution_of_loop = add_to_evolution 
              (loop->num, chrec_convert (type, *evolution_of_loop, at_stmt),
               MINUS_EXPR, rhs1, at_stmt);

          else if (res == t_dont_know)
            *evolution_of_loop = chrec_dont_know;
        }
      else
        /* Otherwise, match an assignment under the form: 
           "a = ... - ...".  */
        /* And there is nothing to do.  */
        res = t_false;
      break;

    default:
      res = t_false;
    }

  return res;
}
    
/* Follow the ssa edge into the expression EXPR.
   Return true if the strongly connected component has been found.  */

static t_bool
follow_ssa_edge_expr (struct loop *loop, gimple at_stmt, tree expr, 
                      gimple halting_phi, tree *evolution_of_loop, int limit)
{
  t_bool res = t_false;
  tree rhs0, rhs1;
  tree type = TREE_TYPE (expr);
  enum tree_code code;
  
  /* The EXPR is one of the following cases:
     - an SSA_NAME, 
     - an INTEGER_CST,
     - a PLUS_EXPR, 
     - a POINTER_PLUS_EXPR, 
     - a MINUS_EXPR,
     - an ASSERT_EXPR,
     - other cases are not yet handled.  */
  code = TREE_CODE (expr);
  switch (code)
    {
    case NOP_EXPR:
      /* This assignment is under the form "a_1 = (cast) rhs.  */
      res = follow_ssa_edge_expr (loop, at_stmt, TREE_OPERAND (expr, 0),
                                  halting_phi, evolution_of_loop, limit);
      *evolution_of_loop = chrec_convert (type, *evolution_of_loop, at_stmt);
      break;

    case INTEGER_CST:
      /* This assignment is under the form "a_1 = 7".  */
      res = t_false;
      break;
      
    case SSA_NAME:
      /* This assignment is under the form: "a_1 = b_2".  */
      res = follow_ssa_edge 
        (loop, SSA_NAME_DEF_STMT (expr), halting_phi, evolution_of_loop, limit);
      break;
      
    case POINTER_PLUS_EXPR:
    case PLUS_EXPR:
    case MINUS_EXPR:
      /* This case is under the form "rhs0 +- rhs1".  */
      rhs0 = TREE_OPERAND (expr, 0);
      rhs1 = TREE_OPERAND (expr, 1);
      STRIP_TYPE_NOPS (rhs0);
      STRIP_TYPE_NOPS (rhs1);
      return follow_ssa_edge_binary (loop, at_stmt, type, rhs0, code, rhs1,
                                     halting_phi, evolution_of_loop, limit);

    case ASSERT_EXPR:
      {
        /* This assignment is of the form: "a_1 = ASSERT_EXPR <a_2, ...>"
           It must be handled as a copy assignment of the form a_1 = a_2.  */
        tree op0 = ASSERT_EXPR_VAR (expr);
        if (TREE_CODE (op0) == SSA_NAME)
          res = follow_ssa_edge (loop, SSA_NAME_DEF_STMT (op0),
                                 halting_phi, evolution_of_loop, limit);
        else
          res = t_false;
        break;
      }


    default:
      res = t_false;
      break;
    }
  
  return res;
}

/* Follow the ssa edge into the right hand side of an assignment STMT.
   Return true if the strongly connected component has been found.  */

static t_bool
follow_ssa_edge_in_rhs (struct loop *loop, gimple stmt,
                        gimple halting_phi, tree *evolution_of_loop, int limit)
{
  tree type = TREE_TYPE (gimple_assign_lhs (stmt));
  enum tree_code code = gimple_assign_rhs_code (stmt);

  switch (get_gimple_rhs_class (code))
    {
    case GIMPLE_BINARY_RHS:
      return follow_ssa_edge_binary (loop, stmt, type,
                                     gimple_assign_rhs1 (stmt), code,
                                     gimple_assign_rhs2 (stmt),
                                     halting_phi, evolution_of_loop, limit);
    case GIMPLE_SINGLE_RHS:
      return follow_ssa_edge_expr (loop, stmt, gimple_assign_rhs1 (stmt),
                                   halting_phi, evolution_of_loop, limit);
    case GIMPLE_UNARY_RHS:
      if (code == NOP_EXPR)
        {
          /* This assignment is under the form "a_1 = (cast) rhs.  */
          t_bool res
            = follow_ssa_edge_expr (loop, stmt, gimple_assign_rhs1 (stmt),
                                    halting_phi, evolution_of_loop, limit);
          *evolution_of_loop = chrec_convert (type, *evolution_of_loop, stmt);
          return res;
        }
      /* FALLTHRU */

    default:
      return t_false;
    }
}

/* Checks whether the I-th argument of a PHI comes from a backedge.  */

static bool
backedge_phi_arg_p (gimple phi, int i)
{
  const_edge e = gimple_phi_arg_edge (phi, i);

  /* We would in fact like to test EDGE_DFS_BACK here, but we do not care
     about updating it anywhere, and this should work as well most of the
     time.  */
  if (e->flags & EDGE_IRREDUCIBLE_LOOP)
    return true;

  return false;
}

/* Helper function for one branch of the condition-phi-node.  Return
   true if the strongly connected component has been found following
   this path.  */

static inline t_bool
follow_ssa_edge_in_condition_phi_branch (int i,
                                         struct loop *loop, 
                                         gimple condition_phi, 
                                         gimple halting_phi,
                                         tree *evolution_of_branch,
                                         tree init_cond, int limit)
{
  tree branch = PHI_ARG_DEF (condition_phi, i);
  *evolution_of_branch = chrec_dont_know;

  /* Do not follow back edges (they must belong to an irreducible loop, which
     we really do not want to worry about).  */
  if (backedge_phi_arg_p (condition_phi, i))
    return t_false;

  if (TREE_CODE (branch) == SSA_NAME)
    {
      *evolution_of_branch = init_cond;
      return follow_ssa_edge (loop, SSA_NAME_DEF_STMT (branch), halting_phi, 
                              evolution_of_branch, limit);
    }

  /* This case occurs when one of the condition branches sets 
     the variable to a constant: i.e. a phi-node like
     "a_2 = PHI <a_7(5), 2(6)>;".  
         
     FIXME:  This case have to be refined correctly: 
     in some cases it is possible to say something better than
     chrec_dont_know, for example using a wrap-around notation.  */
  return t_false;
}

/* This function merges the branches of a condition-phi-node in a
   loop.  */

static t_bool
follow_ssa_edge_in_condition_phi (struct loop *loop,
                                  gimple condition_phi, 
                                  gimple halting_phi, 
                                  tree *evolution_of_loop, int limit)
{
  int i, n;
  tree init = *evolution_of_loop;
  tree evolution_of_branch;
  t_bool res = follow_ssa_edge_in_condition_phi_branch (0, loop, condition_phi,
                                                        halting_phi,
                                                        &evolution_of_branch,
                                                        init, limit);
  if (res == t_false || res == t_dont_know)
    return res;

  *evolution_of_loop = evolution_of_branch;

  n = gimple_phi_num_args (condition_phi);
  for (i = 1; i < n; i++)
    {
      /* Quickly give up when the evolution of one of the branches is
         not known.  */
      if (*evolution_of_loop == chrec_dont_know)
        return t_true;

      /* Increase the limit by the PHI argument number to avoid exponential
         time and memory complexity.  */
      res = follow_ssa_edge_in_condition_phi_branch (i, loop, condition_phi,
                                                     halting_phi,
                                                     &evolution_of_branch,
                                                     init, limit + i);
      if (res == t_false || res == t_dont_know)
        return res;

      *evolution_of_loop = chrec_merge (*evolution_of_loop,
                                        evolution_of_branch);
    }
  
  return t_true;
}

/* Follow an SSA edge in an inner loop.  It computes the overall
   effect of the loop, and following the symbolic initial conditions,
   it follows the edges in the parent loop.  The inner loop is
   considered as a single statement.  */

static t_bool
follow_ssa_edge_inner_loop_phi (struct loop *outer_loop,
                                gimple loop_phi_node, 
                                gimple halting_phi,
                                tree *evolution_of_loop, int limit)
{
  struct loop *loop = loop_containing_stmt (loop_phi_node);
  tree ev = analyze_scalar_evolution (loop, PHI_RESULT (loop_phi_node));

  /* Sometimes, the inner loop is too difficult to analyze, and the
     result of the analysis is a symbolic parameter.  */
  if (ev == PHI_RESULT (loop_phi_node))
    {
      t_bool res = t_false;
      int i, n = gimple_phi_num_args (loop_phi_node);

      for (i = 0; i < n; i++)
        {
          tree arg = PHI_ARG_DEF (loop_phi_node, i);
          basic_block bb;

          /* Follow the edges that exit the inner loop.  */
          bb = gimple_phi_arg_edge (loop_phi_node, i)->src;
          if (!flow_bb_inside_loop_p (loop, bb))
            res = follow_ssa_edge_expr (outer_loop, loop_phi_node,
                                        arg, halting_phi,
                                        evolution_of_loop, limit);
          if (res == t_true)
            break;
        }

      /* If the path crosses this loop-phi, give up.  */
      if (res == t_true)
        *evolution_of_loop = chrec_dont_know;

      return res;
    }

  /* Otherwise, compute the overall effect of the inner loop.  */
  ev = compute_overall_effect_of_inner_loop (loop, ev);
  return follow_ssa_edge_expr (outer_loop, loop_phi_node, ev, halting_phi,
                               evolution_of_loop, limit);
}

/* Follow an SSA edge from a loop-phi-node to itself, constructing a
   path that is analyzed on the return walk.  */

static t_bool
follow_ssa_edge (struct loop *loop, gimple def, gimple halting_phi,
                 tree *evolution_of_loop, int limit)
{
  struct loop *def_loop;
  
  if (gimple_nop_p (def))
    return t_false;
  
  /* Give up if the path is longer than the MAX that we allow.  */
  if (limit > PARAM_VALUE (PARAM_SCEV_MAX_EXPR_SIZE))
    return t_dont_know;
  
  def_loop = loop_containing_stmt (def);
  
  switch (gimple_code (def))
    {
    case GIMPLE_PHI:
      if (!loop_phi_node_p (def))
        /* DEF is a condition-phi-node.  Follow the branches, and
           record their evolutions.  Finally, merge the collected
           information and set the approximation to the main
           variable.  */
        return follow_ssa_edge_in_condition_phi 
          (loop, def, halting_phi, evolution_of_loop, limit);

      /* When the analyzed phi is the halting_phi, the
         depth-first search is over: we have found a path from
         the halting_phi to itself in the loop.  */
      if (def == halting_phi)
        return t_true;
          
      /* Otherwise, the evolution of the HALTING_PHI depends
         on the evolution of another loop-phi-node, i.e. the
         evolution function is a higher degree polynomial.  */
      if (def_loop == loop)
        return t_false;
          
      /* Inner loop.  */
      if (flow_loop_nested_p (loop, def_loop))
        return follow_ssa_edge_inner_loop_phi 
          (loop, def, halting_phi, evolution_of_loop, limit + 1);

      /* Outer loop.  */
      return t_false;

    case GIMPLE_ASSIGN:
      return follow_ssa_edge_in_rhs (loop, def, halting_phi, 
                                     evolution_of_loop, limit);
      
    default:
      /* At this level of abstraction, the program is just a set
         of GIMPLE_ASSIGNs and PHI_NODEs.  In principle there is no
         other node to be handled.  */
      return t_false;
    }
}

\f

/* Given a LOOP_PHI_NODE, this function determines the evolution
   function from LOOP_PHI_NODE to LOOP_PHI_NODE in the loop.  */

static tree
analyze_evolution_in_loop (gimple loop_phi_node, 
                           tree init_cond)
{
  int i, n = gimple_phi_num_args (loop_phi_node);
  tree evolution_function = chrec_not_analyzed_yet;
  struct loop *loop = loop_containing_stmt (loop_phi_node);
  basic_block bb;
  
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "(analyze_evolution_in_loop \n");
      fprintf (dump_file, "  (loop_phi_node = ");
      print_gimple_stmt (dump_file, loop_phi_node, 0, 0);
      fprintf (dump_file, ")\n");
    }
  
  for (i = 0; i < n; i++)
    {
      tree arg = PHI_ARG_DEF (loop_phi_node, i);
      gimple ssa_chain;
      tree ev_fn;
      t_bool res;

      /* Select the edges that enter the loop body.  */
      bb = gimple_phi_arg_edge (loop_phi_node, i)->src;
      if (!flow_bb_inside_loop_p (loop, bb))
        continue;
      
      if (TREE_CODE (arg) == SSA_NAME)
        {
          ssa_chain = SSA_NAME_DEF_STMT (arg);

          /* Pass in the initial condition to the follow edge function.  */
          ev_fn = init_cond;
          res = follow_ssa_edge (loop, ssa_chain, loop_phi_node, &ev_fn, 0);
        }
      else
        res = t_false;
              
      /* When it is impossible to go back on the same
         loop_phi_node by following the ssa edges, the
         evolution is represented by a peeled chrec, i.e. the
         first iteration, EV_FN has the value INIT_COND, then
         all the other iterations it has the value of ARG.  
         For the moment, PEELED_CHREC nodes are not built.  */
      if (res != t_true)
        ev_fn = chrec_dont_know;
      
      /* When there are multiple back edges of the loop (which in fact never
         happens currently, but nevertheless), merge their evolutions.  */
      evolution_function = chrec_merge (evolution_function, ev_fn);
    }
  
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "  (evolution_function = ");
      print_generic_expr (dump_file, evolution_function, 0);
      fprintf (dump_file, "))\n");
    }
  
  return evolution_function;
}

/* Given a loop-phi-node, return the initial conditions of the
   variable on entry of the loop.  When the CCP has propagated
   constants into the loop-phi-node, the initial condition is
   instantiated, otherwise the initial condition is kept symbolic.
   This analyzer does not analyze the evolution outside the current
   loop, and leaves this task to the on-demand tree reconstructor.  */

static tree 
analyze_initial_condition (gimple loop_phi_node)
{
  int i, n;
  tree init_cond = chrec_not_analyzed_yet;
  struct loop *loop = loop_containing_stmt (loop_phi_node);
  
  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "(analyze_initial_condition \n");
      fprintf (dump_file, "  (loop_phi_node = \n");
      print_gimple_stmt (dump_file, loop_phi_node, 0, 0);
      fprintf (dump_file, ")\n");
    }
  
  n = gimple_phi_num_args (loop_phi_node);
  for (i = 0; i < n; i++)
    {
      tree branch = PHI_ARG_DEF (loop_phi_node, i);
      basic_block bb = gimple_phi_arg_edge (loop_phi_node, i)->src;
      
      /* When the branch is oriented to the loop's body, it does
         not contribute to the initial condition.  */
      if (flow_bb_inside_loop_p (loop, bb))
        continue;

      if (init_cond == chrec_not_analyzed_yet)
        {
          init_cond = branch;
          continue;
        }

      if (TREE_CODE (branch) == SSA_NAME)
        {
          init_cond = chrec_dont_know;
          break;
        }

      init_cond = chrec_merge (init_cond, branch);
    }

  /* Ooops -- a loop without an entry???  */
  if (init_cond == chrec_not_analyzed_yet)
    init_cond = chrec_dont_know;

  /* During early loop unrolling we do not have fully constant propagated IL.
     Handle degenerate PHIs here to not miss important unrollings.  */
  if (TREE_CODE (init_cond) == SSA_NAME)
    {
      gimple def = SSA_NAME_DEF_STMT (init_cond);
      tree res;
      if (gimple_code (def) == GIMPLE_PHI
          && (res = degenerate_phi_result (def)) != NULL_TREE
          /* Only allow invariants here, otherwise we may break
             loop-closed SSA form.  */
          && is_gimple_min_invariant (res))
        init_cond = res;
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "  (init_cond = ");
      print_generic_expr (dump_file, init_cond, 0);
      fprintf (dump_file, "))\n");
    }
  
  return init_cond;
}

/* Analyze the scalar evolution for LOOP_PHI_NODE.  */

static tree 
interpret_loop_phi (struct loop *loop, gimple loop_phi_node)
{
  tree res;
  struct loop *phi_loop = loop_containing_stmt (loop_phi_node);
  tree init_cond;
  
  if (phi_loop != loop)
    {
      struct loop *subloop;
      tree evolution_fn = analyze_scalar_evolution
        (phi_loop, PHI_RESULT (loop_phi_node));

      /* Dive one level deeper.  */
      subloop = superloop_at_depth (phi_loop, loop_depth (loop) + 1);

      /* Interpret the subloop.  */
      res = compute_overall_effect_of_inner_loop (subloop, evolution_fn);
      return res;
    }

  /* Otherwise really interpret the loop phi.  */
  init_cond = analyze_initial_condition (loop_phi_node);
  res = analyze_evolution_in_loop (loop_phi_node, init_cond);

  return res;
}

/* This function merges the branches of a condition-phi-node,
   contained in the outermost loop, and whose arguments are already
   analyzed.  */

static tree
interpret_condition_phi (struct loop *loop, gimple condition_phi)
{
  int i, n = gimple_phi_num_args (condition_phi);
  tree res = chrec_not_analyzed_yet;
  
  for (i = 0; i < n; i++)
    {
      tree branch_chrec;
      
      if (backedge_phi_arg_p (condition_phi, i))
        {
          res = chrec_dont_know;
          break;
        }

      branch_chrec = analyze_scalar_evolution
        (loop, PHI_ARG_DEF (condition_phi, i));
      
      res = chrec_merge (res, branch_chrec);
    }

  return res;
}

/* Interpret the operation RHS1 OP RHS2.  If we didn't
   analyze this node before, follow the definitions until ending
   either on an analyzed GIMPLE_ASSIGN, or on a loop-phi-node.  On the
   return path, this function propagates evolutions (ala constant copy
   propagation).  OPND1 is not a GIMPLE expression because we could
   analyze the effect of an inner loop: see interpret_loop_phi.  */

static tree
interpret_rhs_expr (struct loop *loop, gimple at_stmt,
                    tree type, tree rhs1, enum tree_code code, tree rhs2)
{
  tree res, chrec1, chrec2;

  if (get_gimple_rhs_class (code) == GIMPLE_SINGLE_RHS)
    {
      if (is_gimple_min_invariant (rhs1))
        return chrec_convert (type, rhs1, at_stmt);

      if (code == SSA_NAME)
        return chrec_convert (type, analyze_scalar_evolution (loop, rhs1),
                              at_stmt);

      if (code == ASSERT_EXPR)
        {
          rhs1 = ASSERT_EXPR_VAR (rhs1);
          return chrec_convert (type, analyze_scalar_evolution (loop, rhs1),
                                at_stmt);
        }

      return chrec_dont_know;
    }

  switch (code)
    {
    case POINTER_PLUS_EXPR:
      chrec1 = analyze_scalar_evolution (loop, rhs1);
      chrec2 = analyze_scalar_evolution (loop, rhs2);
      chrec1 = chrec_convert (type, chrec1, at_stmt);
      chrec2 = chrec_convert (sizetype, chrec2, at_stmt);
      res = chrec_fold_plus (type, chrec1, chrec2);
      break;

    case PLUS_EXPR:
      chrec1 = analyze_scalar_evolution (loop, rhs1);
      chrec2 = analyze_scalar_evolution (loop, rhs2);
      chrec1 = chrec_convert (type, chrec1, at_stmt);
      chrec2 = chrec_convert (type, chrec2, at_stmt);
      res = chrec_fold_plus (type, chrec1, chrec2);
      break;
      
    case MINUS_EXPR:
      chrec1 = analyze_scalar_evolution (loop, rhs1);
      chrec2 = analyze_scalar_evolution (loop, rhs2);
      chrec1 = chrec_convert (type, chrec1, at_stmt);
      chrec2 = chrec_convert (type, chrec2, at_stmt);
      res = chrec_fold_minus (type, chrec1, chrec2);
      break;

    case NEGATE_EXPR:
      chrec1 = analyze_scalar_evolution (loop, rhs1);
      chrec1 = chrec_convert (type, chrec1, at_stmt);
      /* TYPE may be integer, real or complex, so use fold_convert.  */
      res = chrec_fold_multiply (type, chrec1,
                                 fold_convert (type, integer_minus_one_node));
      break;

    case BIT_NOT_EXPR:
      /* Handle ~X as -1 - X.  */
      chrec1 = analyze_scalar_evolution (loop, rhs1);
      chrec1 = chrec_convert (type, chrec1, at_stmt);
      res = chrec_fold_minus (type,
                              fold_convert (type, integer_minus_one_node),
                              chrec1);
      break;

    case MULT_EXPR:
      chrec1 = analyze_scalar_evolution (loop, rhs1);
      chrec2 = analyze_scalar_evolution (loop, rhs2);
      chrec1 = chrec_convert (type, chrec1, at_stmt);
      chrec2 = chrec_convert (type, chrec2, at_stmt);
      res = chrec_fold_multiply (type, chrec1, chrec2);
      break;
      
    CASE_CONVERT:
      chrec1 = analyze_scalar_evolution (loop, rhs1);
      res = chrec_convert (type, chrec1, at_stmt);
      break;
      
    default:
      res = chrec_dont_know;
      break;
    }
  
  return res;
}

/* Interpret the expression EXPR.  */

static tree
interpret_expr (struct loop *loop, gimple at_stmt, tree expr)
{
  enum tree_code code;
  tree type = TREE_TYPE (expr), op0, op1;

  if (automatically_generated_chrec_p (expr))
    return expr;

  if (TREE_CODE (expr) == POLYNOMIAL_CHREC)
    return chrec_dont_know;

  extract_ops_from_tree (expr, &code, &op0, &op1);

  return interpret_rhs_expr (loop, at_stmt, type,
                             op0, code, op1);
}

/* Interpret the rhs of the assignment STMT.  */

static tree
interpret_gimple_assign (struct loop *loop, gimple stmt)
{
  tree type = TREE_TYPE (gimple_assign_lhs (stmt));
  enum tree_code code = gimple_assign_rhs_code (stmt);

  return interpret_rhs_expr (loop, stmt, type,
                             gimple_assign_rhs1 (stmt), code,
                             gimple_assign_rhs2 (stmt));
}

\f

/* This section contains all the entry points: 
   - number_of_iterations_in_loop,
   - analyze_scalar_evolution,
   - instantiate_parameters.
*/

/* Compute and return the evolution function in WRTO_LOOP, the nearest
   common ancestor of DEF_LOOP and USE_LOOP.  */

static tree 
compute_scalar_evolution_in_loop (struct loop *wrto_loop, 
                                  struct loop *def_loop, 
                                  tree ev)
{
  tree res;
  if (def_loop == wrto_loop)
    return ev;

  def_loop = superloop_at_depth (def_loop, loop_depth (wrto_loop) + 1);
  res = compute_overall_effect_of_inner_loop (def_loop, ev);

  return analyze_scalar_evolution_1 (wrto_loop, res, chrec_not_analyzed_yet);
}

/* Helper recursive function.  */

static tree
analyze_scalar_evolution_1 (struct loop *loop, tree var, tree res)
{
  tree type = TREE_TYPE (var);
  gimple def;
  basic_block bb;
  struct loop *def_loop;

  if (loop == NULL || TREE_CODE (type) == VECTOR_TYPE)
    return chrec_dont_know;

  if (TREE_CODE (var) != SSA_NAME)
    return interpret_expr (loop, NULL, var);

  def = SSA_NAME_DEF_STMT (var);
  bb = gimple_bb (def);
  def_loop = bb ? bb->loop_father : NULL;

  if (bb == NULL
      || !flow_bb_inside_loop_p (loop, bb))
    {
      /* Keep the symbolic form.  */
      res = var;
      goto set_and_end;
    }

  if (res != chrec_not_analyzed_yet)
    {
      if (loop != bb->loop_father)
        res = compute_scalar_evolution_in_loop 
            (find_common_loop (loop, bb->loop_father), bb->loop_father, res);

      goto set_and_end;
    }

  if (loop != def_loop)
    {
      res = analyze_scalar_evolution_1 (def_loop, var, chrec_not_analyzed_yet);
      res = compute_scalar_evolution_in_loop (loop, def_loop, res);

      goto set_and_end;
    }

  switch (gimple_code (def))
    {
    case GIMPLE_ASSIGN:
      res = interpret_gimple_assign (loop, def);
      break;

    case GIMPLE_PHI:
      if (loop_phi_node_p (def))
        res = interpret_loop_phi (loop, def);
      else
        res = interpret_condition_phi (loop, def);
      break;

    default:
      res = chrec_dont_know;
      break;
    }

 set_and_end:

  /* Keep the symbolic form.  */
  if (res == chrec_dont_know)
    res = var;

  if (loop == def_loop)
    set_scalar_evolution (block_before_loop (loop), var, res);

  return res;
}

/* Entry point for the scalar evolution analyzer.
   Analyzes and returns the scalar evolution of the ssa_name VAR.
   LOOP_NB is the identifier number of the loop in which the variable
   is used.
   
   Example of use: having a pointer VAR to a SSA_NAME node, STMT a
   pointer to the statement that uses this variable, in order to
   determine the evolution function of the variable, use the following
   calls:
   
   unsigned loop_nb = loop_containing_stmt (stmt)->num;
   tree chrec_with_symbols = analyze_scalar_evolution (loop_nb, var);
   tree chrec_instantiated = instantiate_parameters (loop, chrec_with_symbols);
*/

tree 
analyze_scalar_evolution (struct loop *loop, tree var)
{
  tree res;

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "(analyze_scalar_evolution \n");
      fprintf (dump_file, "  (loop_nb = %d)\n", loop->num);
      fprintf (dump_file, "  (scalar = ");
      print_generic_expr (dump_file, var, 0);
      fprintf (dump_file, ")\n");
    }

  res = get_scalar_evolution (block_before_loop (loop), var);
  res = analyze_scalar_evolution_1 (loop, var, res);

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, ")\n");

  return res;
}

/* Analyze scalar evolution of use of VERSION in USE_LOOP with respect to
   WRTO_LOOP (which should be a superloop of USE_LOOP)

   FOLDED_CASTS is set to true if resolve_mixers used
   chrec_convert_aggressive (TODO -- not really, we are way too conservative
   at the moment in order to keep things simple). 
   
   To illustrate the meaning of USE_LOOP and WRTO_LOOP, consider the following
   example:

   for (i = 0; i < 100; i++)                    -- loop 1
     {
       for (j = 0; j < 100; j++)                -- loop 2
         {
           k1 = i;
           k2 = j;

           use2 (k1, k2);

           for (t = 0; t < 100; t++)            -- loop 3
             use3 (k1, k2);

         }
       use1 (k1, k2);
     }

   Both k1 and k2 are invariants in loop3, thus
     analyze_scalar_evolution_in_loop (loop3, loop3, k1) = k1
     analyze_scalar_evolution_in_loop (loop3, loop3, k2) = k2

   As they are invariant, it does not matter whether we consider their
   usage in loop 3 or loop 2, hence
     analyze_scalar_evolution_in_loop (loop2, loop3, k1) =
       analyze_scalar_evolution_in_loop (loop2, loop2, k1) = i
     analyze_scalar_evolution_in_loop (loop2, loop3, k2) =
       analyze_scalar_evolution_in_loop (loop2, loop2, k2) = [0,+,1]_2

   Similarly for their evolutions with respect to loop 1.  The values of K2
   in the use in loop 2 vary independently on loop 1, thus we cannot express
   the evolution with respect to loop 1:
     analyze_scalar_evolution_in_loop (loop1, loop3, k1) =
       analyze_scalar_evolution_in_loop (loop1, loop2, k1) = [0,+,1]_1
     analyze_scalar_evolution_in_loop (loop1, loop3, k2) =
       analyze_scalar_evolution_in_loop (loop1, loop2, k2) = dont_know

   The value of k2 in the use in loop 1 is known, though:
     analyze_scalar_evolution_in_loop (loop1, loop1, k1) = [0,+,1]_1
     analyze_scalar_evolution_in_loop (loop1, loop1, k2) = 100
   */

static tree
analyze_scalar_evolution_in_loop (struct loop *wrto_loop, struct loop *use_loop,
                                  tree version, bool *folded_casts)
{
  bool val = false;
  tree ev = version, tmp;

  /* We cannot just do 

     tmp = analyze_scalar_evolution (use_loop, version);
     ev = resolve_mixers (wrto_loop, tmp);

     as resolve_mixers would query the scalar evolution with respect to
     wrto_loop.  For example, in the situation described in the function
     comment, suppose that wrto_loop = loop1, use_loop = loop3 and
     version = k2.  Then

     analyze_scalar_evolution (use_loop, version) = k2

     and resolve_mixers (loop1, k2) finds that the value of k2 in loop 1
     is 100, which is a wrong result, since we are interested in the
     value in loop 3.

     Instead, we need to proceed from use_loop to wrto_loop loop by loop,
     each time checking that there is no evolution in the inner loop.  */

  if (folded_casts)
    *folded_casts = false;
  while (1)
    {
      tmp = analyze_scalar_evolution (use_loop, ev);
      ev = resolve_mixers (use_loop, tmp);

      if (folded_casts && tmp != ev)
        *folded_casts = true;

      if (use_loop == wrto_loop)
        return ev;

      /* If the value of the use changes in the inner loop, we cannot express
         its value in the outer loop (we might try to return interval chrec,
         but we do not have a user for it anyway)  */
      if (!no_evolution_in_loop_p (ev, use_loop->num, &val)
          || !val)
        return chrec_dont_know;

      use_loop = loop_outer (use_loop);
    }
}

/* Returns from CACHE the value for VERSION instantiated below
   INSTANTIATED_BELOW block.  */

static tree
get_instantiated_value (htab_t cache, basic_block instantiated_below,
                        tree version)
{
  struct scev_info_str *info, pattern;
  
  pattern.var = version;
  pattern.instantiated_below = instantiated_below;
  info = (struct scev_info_str *) htab_find (cache, &pattern);

  if (info)
    return info->chrec;
  else
    return NULL_TREE;
}

/* Sets in CACHE the value of VERSION instantiated below basic block
   INSTANTIATED_BELOW to VAL.  */

static void
set_instantiated_value (htab_t cache, basic_block instantiated_below,
                        tree version, tree val)
{
  struct scev_info_str *info, pattern;
  PTR *slot;
  
  pattern.var = version;
  pattern.instantiated_below = instantiated_below;
  slot = htab_find_slot (cache, &pattern, INSERT);

  if (!*slot)
    *slot = new_scev_info_str (instantiated_below, version);
  info = (struct scev_info_str *) *slot;
  info->chrec = val;
}

/* Return the closed_loop_phi node for VAR.  If there is none, return
   NULL_TREE.  */

static tree
loop_closed_phi_def (tree var)
{
  struct loop *loop;
  edge exit;
  gimple phi;
  gimple_stmt_iterator psi;

  if (var == NULL_TREE
      || TREE_CODE (var) != SSA_NAME)
    return NULL_TREE;

  loop = loop_containing_stmt (SSA_NAME_DEF_STMT (var));
  exit = single_exit (loop);
  if (!exit)
    return NULL_TREE;

  for (psi = gsi_start_phis (exit->dest); !gsi_end_p (psi); gsi_next (&psi))
    {
      phi = gsi_stmt (psi);
      if (PHI_ARG_DEF_FROM_EDGE (phi, exit) == var)
        return PHI_RESULT (phi);
    }

  return NULL_TREE;
}

/* Analyze all the parameters of the chrec, between INSTANTIATE_BELOW
   and EVOLUTION_LOOP, that were left under a symbolic form.  

   CHREC is the scalar evolution to instantiate.

   CACHE is the cache of already instantiated values.

   FOLD_CONVERSIONS should be set to true when the conversions that
   may wrap in signed/pointer type are folded, as long as the value of
   the chrec is preserved.

   SIZE_EXPR is used for computing the size of the expression to be
   instantiated, and to stop if it exceeds some limit.  */
  
static tree
instantiate_scev_1 (basic_block instantiate_below,
                    struct loop *evolution_loop, tree chrec,
                    bool fold_conversions, htab_t cache, int size_expr)
{
  tree res, op0, op1, op2;
  basic_block def_bb;
  struct loop *def_loop;
  tree type = chrec_type (chrec);

  /* Give up if the expression is larger than the MAX that we allow.  */
  if (size_expr++ > PARAM_VALUE (PARAM_SCEV_MAX_EXPR_SIZE))
    return chrec_dont_know;

  if (automatically_generated_chrec_p (chrec)
      || is_gimple_min_invariant (chrec))
    return chrec;

  switch (TREE_CODE (chrec))
    {
    case SSA_NAME:
      def_bb = gimple_bb (SSA_NAME_DEF_STMT (chrec));

      /* A parameter (or loop invariant and we do not want to include
         evolutions in outer loops), nothing to do.  */
      if (!def_bb
          || loop_depth (def_bb->loop_father) == 0
          || dominated_by_p (CDI_DOMINATORS, instantiate_below, def_bb))
        return chrec;

      /* We cache the value of instantiated variable to avoid exponential
         time complexity due to reevaluations.  We also store the convenient
         value in the cache in order to prevent infinite recursion -- we do
         not want to instantiate the SSA_NAME if it is in a mixer
         structure.  This is used for avoiding the instantiation of
         recursively defined functions, such as: 

         | a_2 -> {0, +, 1, +, a_2}_1  */

      res = get_instantiated_value (cache, instantiate_below, chrec);
      if (res)
        return res;

      res = chrec_dont_know;
      set_instantiated_value (cache, instantiate_below, chrec, res);

      def_loop = find_common_loop (evolution_loop, def_bb->loop_father);

      /* If the analysis yields a parametric chrec, instantiate the
         result again.  */
      res = analyze_scalar_evolution (def_loop, chrec);

      /* Don't instantiate loop-closed-ssa phi nodes.  */
      if (TREE_CODE (res) == SSA_NAME
          && (loop_containing_stmt (SSA_NAME_DEF_STMT (res)) == NULL
              || (loop_depth (loop_containing_stmt (SSA_NAME_DEF_STMT (res)))
                  > loop_depth (def_loop))))
        {
          if (res == chrec)
            res = loop_closed_phi_def (chrec);
          else
            res = chrec;

          if (res == NULL_TREE)
            res = chrec_dont_know;
        }

      else if (res != chrec_dont_know)
        res = instantiate_scev_1 (instantiate_below, evolution_loop, res,
                                  fold_conversions, cache, size_expr);

      /* Store the correct value to the cache.  */
      set_instantiated_value (cache, instantiate_below, chrec, res);
      return res;

    case POLYNOMIAL_CHREC:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                CHREC_LEFT (chrec), fold_conversions, cache,
                                size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      op1 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                CHREC_RIGHT (chrec), fold_conversions, cache,
                                size_expr);
      if (op1 == chrec_dont_know)
        return chrec_dont_know;

      if (CHREC_LEFT (chrec) != op0
          || CHREC_RIGHT (chrec) != op1)
        {
          op1 = chrec_convert_rhs (chrec_type (op0), op1, NULL);
          chrec = build_polynomial_chrec (CHREC_VARIABLE (chrec), op0, op1);
        }
      return chrec;

    case POINTER_PLUS_EXPR:
    case PLUS_EXPR:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0), fold_conversions, cache,
                                size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      op1 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 1), fold_conversions, cache,
                                size_expr);
      if (op1 == chrec_dont_know)
        return chrec_dont_know;

      if (TREE_OPERAND (chrec, 0) != op0
          || TREE_OPERAND (chrec, 1) != op1)
        {
          op0 = chrec_convert (type, op0, NULL);
          op1 = chrec_convert_rhs (type, op1, NULL);
          chrec = chrec_fold_plus (type, op0, op1);
        }
      return chrec;

    case MINUS_EXPR:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0), fold_conversions, cache,
                                size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      op1 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 1),
                                fold_conversions, cache, size_expr);
      if (op1 == chrec_dont_know)
        return chrec_dont_know;

      if (TREE_OPERAND (chrec, 0) != op0
          || TREE_OPERAND (chrec, 1) != op1)
        {
          op0 = chrec_convert (type, op0, NULL);
          op1 = chrec_convert (type, op1, NULL);
          chrec = chrec_fold_minus (type, op0, op1);
        }
      return chrec;

    case MULT_EXPR:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0),
                                fold_conversions, cache, size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      op1 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 1),
                                fold_conversions, cache, size_expr);
      if (op1 == chrec_dont_know)
        return chrec_dont_know;

      if (TREE_OPERAND (chrec, 0) != op0
          || TREE_OPERAND (chrec, 1) != op1)
        {
          op0 = chrec_convert (type, op0, NULL);
          op1 = chrec_convert (type, op1, NULL);
          chrec = chrec_fold_multiply (type, op0, op1);
        }
      return chrec;

    CASE_CONVERT:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0),
                                fold_conversions, cache, size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      if (fold_conversions)
        {
          tree tmp = chrec_convert_aggressive (TREE_TYPE (chrec), op0);
          if (tmp)
            return tmp;
        }

      if (op0 == TREE_OPERAND (chrec, 0))
        return chrec;

      /* If we used chrec_convert_aggressive, we can no longer assume that
         signed chrecs do not overflow, as chrec_convert does, so avoid
         calling it in that case.  */
      if (fold_conversions)
        return fold_convert (TREE_TYPE (chrec), op0);

      return chrec_convert (TREE_TYPE (chrec), op0, NULL);

    case BIT_NOT_EXPR:
      /* Handle ~X as -1 - X.  */
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0),
                                fold_conversions, cache, size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      if (TREE_OPERAND (chrec, 0) != op0)
        {
          op0 = chrec_convert (type, op0, NULL);
          chrec = chrec_fold_minus (type,
                                    fold_convert (type,
                                                  integer_minus_one_node),
                                    op0);
        }
      return chrec;

    case SCEV_NOT_KNOWN:
      return chrec_dont_know;

    case SCEV_KNOWN:
      return chrec_known;
                                     
    default:
      break;
    }

  if (VL_EXP_CLASS_P (chrec))
    return chrec_dont_know;

  switch (TREE_CODE_LENGTH (TREE_CODE (chrec)))
    {
    case 3:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0),
                                fold_conversions, cache, size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      op1 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 1),
                                fold_conversions, cache, size_expr);
      if (op1 == chrec_dont_know)
        return chrec_dont_know;

      op2 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 2),
                                fold_conversions, cache, size_expr);
      if (op2 == chrec_dont_know)
        return chrec_dont_know;

      if (op0 == TREE_OPERAND (chrec, 0)
          && op1 == TREE_OPERAND (chrec, 1)
          && op2 == TREE_OPERAND (chrec, 2))
        return chrec;

      return fold_build3 (TREE_CODE (chrec),
                          TREE_TYPE (chrec), op0, op1, op2);

    case 2:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0),
                                fold_conversions, cache, size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;

      op1 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 1),
                                fold_conversions, cache, size_expr);
      if (op1 == chrec_dont_know)
        return chrec_dont_know;

      if (op0 == TREE_OPERAND (chrec, 0)
          && op1 == TREE_OPERAND (chrec, 1))
        return chrec;
      return fold_build2 (TREE_CODE (chrec), TREE_TYPE (chrec), op0, op1);
            
    case 1:
      op0 = instantiate_scev_1 (instantiate_below, evolution_loop,
                                TREE_OPERAND (chrec, 0),
                                fold_conversions, cache, size_expr);
      if (op0 == chrec_dont_know)
        return chrec_dont_know;
      if (op0 == TREE_OPERAND (chrec, 0))
        return chrec;
      return fold_build1 (TREE_CODE (chrec), TREE_TYPE (chrec), op0);

    case 0:
      return chrec;

    default:
      break;
    }

  /* Too complicated to handle.  */
  return chrec_dont_know;
}

/* Analyze all the parameters of the chrec that were left under a
   symbolic form.  INSTANTIATE_BELOW is the basic block that stops the
   recursive instantiation of parameters: a parameter is a variable
   that is defined in a basic block that dominates INSTANTIATE_BELOW or
   a function parameter.  */

tree
instantiate_scev (basic_block instantiate_below, struct loop *evolution_loop,
                  tree chrec)
{
  tree res;
  htab_t cache = htab_create (10, hash_scev_info, eq_scev_info, del_scev_info);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "(instantiate_scev \n");
      fprintf (dump_file, "  (instantiate_below = %d)\n", instantiate_below->index);
      fprintf (dump_file, "  (evolution_loop = %d)\n", evolution_loop->num);
      fprintf (dump_file, "  (chrec = ");
      print_generic_expr (dump_file, chrec, 0);
      fprintf (dump_file, ")\n");
    }
 
  res = instantiate_scev_1 (instantiate_below, evolution_loop, chrec, false,
                            cache, 0);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "  (res = ");
      print_generic_expr (dump_file, res, 0);
      fprintf (dump_file, "))\n");
    }

  htab_delete (cache);
  
  return res;
}

/* Similar to instantiate_parameters, but does not introduce the
   evolutions in outer loops for LOOP invariants in CHREC, and does not
   care about causing overflows, as long as they do not affect value
   of an expression.  */

tree
resolve_mixers (struct loop *loop, tree chrec)
{
  htab_t cache = htab_create (10, hash_scev_info, eq_scev_info, del_scev_info);
  tree ret = instantiate_scev_1 (block_before_loop (loop), loop, chrec, true,
                                 cache, 0);
  htab_delete (cache);
  return ret;
}

/* Entry point for the analysis of the number of iterations pass.  
   This function tries to safely approximate the number of iterations
   the loop will run.  When this property is not decidable at compile
   time, the result is chrec_dont_know.  Otherwise the result is
   a scalar or a symbolic parameter.
   
   Example of analysis: suppose that the loop has an exit condition:
   
   "if (b > 49) goto end_loop;"
   
   and that in a previous analysis we have determined that the
   variable 'b' has an evolution function:
   
   "EF = {23, +, 5}_2".  
   
   When we evaluate the function at the point 5, i.e. the value of the
   variable 'b' after 5 iterations in the loop, we have EF (5) = 48,
   and EF (6) = 53.  In this case the value of 'b' on exit is '53' and
   the loop body has been executed 6 times.  */

tree 
number_of_latch_executions (struct loop *loop)
{
  tree res, type;
  edge exit;
  struct tree_niter_desc niter_desc;

  /* Determine whether the number_of_iterations_in_loop has already
     been computed.  */
  res = loop->nb_iterations;
  if (res)
    return res;
  res = chrec_dont_know;

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "(number_of_iterations_in_loop\n");
  
  exit = single_exit (loop);
  if (!exit)
    goto end;

  if (!number_of_iterations_exit (loop, exit, &niter_desc, false))
    goto end;

  type = TREE_TYPE (niter_desc.niter);
  if (integer_nonzerop (niter_desc.may_be_zero))
    res = build_int_cst (type, 0);
  else if (integer_zerop (niter_desc.may_be_zero))
    res = niter_desc.niter;
  else
    res = chrec_dont_know;

end:
  return set_nb_iterations_in_loop (loop, res);
}

/* Returns the number of executions of the exit condition of LOOP,
   i.e., the number by one higher than number_of_latch_executions.
   Note that unlike number_of_latch_executions, this number does
   not necessarily fit in the unsigned variant of the type of
   the control variable -- if the number of iterations is a constant,
   we return chrec_dont_know if adding one to number_of_latch_executions
   overflows; however, in case the number of iterations is symbolic
   expression, the caller is responsible for dealing with this
   the possible overflow.  */

tree 
number_of_exit_cond_executions (struct loop *loop)
{
  tree ret = number_of_latch_executions (loop);
  tree type = chrec_type (ret);

  if (chrec_contains_undetermined (ret))
    return ret;

  ret = chrec_fold_plus (type, ret, build_int_cst (type, 1));
  if (TREE_CODE (ret) == INTEGER_CST
      && TREE_OVERFLOW (ret))
    return chrec_dont_know;

  return ret;
}

/* One of the drivers for testing the scalar evolutions analysis.
   This function computes the number of iterations for all the loops
   from the EXIT_CONDITIONS array.  */

static void 
number_of_iterations_for_all_loops (VEC(gimple,heap) **exit_conditions)
{
  unsigned int i;
  unsigned nb_chrec_dont_know_loops = 0;
  unsigned nb_static_loops = 0;
  gimple cond;
  
  for (i = 0; VEC_iterate (gimple, *exit_conditions, i, cond); i++)
    {
      tree res = number_of_latch_executions (loop_containing_stmt (cond));
      if (chrec_contains_undetermined (res))
        nb_chrec_dont_know_loops++;
      else
        nb_static_loops++;
    }
  
  if (dump_file)
    {
      fprintf (dump_file, "\n(\n");
      fprintf (dump_file, "-----------------------------------------\n");
      fprintf (dump_file, "%d\tnb_chrec_dont_know_loops\n", nb_chrec_dont_know_loops);
      fprintf (dump_file, "%d\tnb_static_loops\n", nb_static_loops);
      fprintf (dump_file, "%d\tnb_total_loops\n", number_of_loops ());
      fprintf (dump_file, "-----------------------------------------\n");
      fprintf (dump_file, ")\n\n");
      
      print_loops (dump_file, 3);
    }
}

\f

/* Counters for the stats.  */

struct chrec_stats 
{
  unsigned nb_chrecs;
  unsigned nb_affine;
  unsigned nb_affine_multivar;
  unsigned nb_higher_poly;
  unsigned nb_chrec_dont_know;
  unsigned nb_undetermined;
};

/* Reset the counters.  */

static inline void
reset_chrecs_counters (struct chrec_stats *stats)
{
  stats->nb_chrecs = 0;
  stats->nb_affine = 0;
  stats->nb_affine_multivar = 0;
  stats->nb_higher_poly = 0;
  stats->nb_chrec_dont_know = 0;
  stats->nb_undetermined = 0;
}

/* Dump the contents of a CHREC_STATS structure.  */

static void
dump_chrecs_stats (FILE *file, struct chrec_stats *stats)
{
  fprintf (file, "\n(\n");
  fprintf (file, "-----------------------------------------\n");
  fprintf (file, "%d\taffine univariate chrecs\n", stats->nb_affine);
  fprintf (file, "%d\taffine multivariate chrecs\n", stats->nb_affine_multivar);
  fprintf (file, "%d\tdegree greater than 2 polynomials\n", 
           stats->nb_higher_poly);
  fprintf (file, "%d\tchrec_dont_know chrecs\n", stats->nb_chrec_dont_know);
  fprintf (file, "-----------------------------------------\n");
  fprintf (file, "%d\ttotal chrecs\n", stats->nb_chrecs);
  fprintf (file, "%d\twith undetermined coefficients\n", 
           stats->nb_undetermined);
  fprintf (file, "-----------------------------------------\n");
  fprintf (file, "%d\tchrecs in the scev database\n", 
           (int) htab_elements (scalar_evolution_info));
  fprintf (file, "%d\tsets in the scev database\n", nb_set_scev);
  fprintf (file, "%d\tgets in the scev database\n", nb_get_scev);
  fprintf (file, "-----------------------------------------\n");
  fprintf (file, ")\n\n");
}

/* Gather statistics about CHREC.  */

static void
gather_chrec_stats (tree chrec, struct chrec_stats *stats)
{
  if (dump_file && (dump_flags & TDF_STATS))
    {
      fprintf (dump_file, "(classify_chrec ");
      print_generic_expr (dump_file, chrec, 0);
      fprintf (dump_file, "\n");
    }
  
  stats->nb_chrecs++;
  
  if (chrec == NULL_TREE)
    {
      stats->nb_undetermined++;
      return;
    }
  
  switch (TREE_CODE (chrec))
    {
    case POLYNOMIAL_CHREC:
      if (evolution_function_is_affine_p (chrec))
        {
          if (dump_file && (dump_flags & TDF_STATS))
            fprintf (dump_file, "  affine_univariate\n");
          stats->nb_affine++;
        }
      else if (evolution_function_is_affine_multivariate_p (chrec, 0))
        {
          if (dump_file && (dump_flags & TDF_STATS))
            fprintf (dump_file, "  affine_multivariate\n");
          stats->nb_affine_multivar++;
        }
      else
        {
          if (dump_file && (dump_flags & TDF_STATS))
            fprintf (dump_file, "  higher_degree_polynomial\n");
          stats->nb_higher_poly++;
        }
      
      break;

    default:
      break;
    }
  
  if (chrec_contains_undetermined (chrec))
    {
      if (dump_file && (dump_flags & TDF_STATS))
        fprintf (dump_file, "  undetermined\n");
      stats->nb_undetermined++;
    }
  
  if (dump_file && (dump_flags & TDF_STATS))
    fprintf (dump_file, ")\n");
}

/* One of the drivers for testing the scalar evolutions analysis.
   This function analyzes the scalar evolution of all the scalars
   defined as loop phi nodes in one of the loops from the
   EXIT_CONDITIONS array.  
   
   TODO Optimization: A loop is in canonical form if it contains only
   a single scalar loop phi node.  All the other scalars that have an
   evolution in the loop are rewritten in function of this single
   index.  This allows the parallelization of the loop.  */

static void 
analyze_scalar_evolution_for_all_loop_phi_nodes (VEC(gimple,heap) **exit_conditions)
{
  unsigned int i;
  struct chrec_stats stats;
  gimple cond, phi;
  gimple_stmt_iterator psi;
  
  reset_chrecs_counters (&stats);
  
  for (i = 0; VEC_iterate (gimple, *exit_conditions, i, cond); i++)
    {
      struct loop *loop;
      basic_block bb;
      tree chrec;
      
      loop = loop_containing_stmt (cond);
      bb = loop->header;
      
      for (psi = gsi_start_phis (bb); !gsi_end_p (psi); gsi_next (&psi))
        {
          phi = gsi_stmt (psi);
          if (is_gimple_reg (PHI_RESULT (phi)))
            {
              chrec = instantiate_parameters 
                        (loop, 
                         analyze_scalar_evolution (loop, PHI_RESULT (phi)));
            
              if (dump_file && (dump_flags & TDF_STATS))
                gather_chrec_stats (chrec, &stats);
            }
        }
    }
  
  if (dump_file && (dump_flags & TDF_STATS))
    dump_chrecs_stats (dump_file, &stats);
}

/* Callback for htab_traverse, gathers information on chrecs in the
   hashtable.  */

static int
gather_stats_on_scev_database_1 (void **slot, void *stats)
{
  struct scev_info_str *entry = (struct scev_info_str *) *slot;

  gather_chrec_stats (entry->chrec, (struct chrec_stats *) stats);

  return 1;
}

/* Classify the chrecs of the whole database.  */

void 
gather_stats_on_scev_database (void)
{
  struct chrec_stats stats;
  
  if (!dump_file)
    return;
  
  reset_chrecs_counters (&stats);
 
  htab_traverse (scalar_evolution_info, gather_stats_on_scev_database_1,
                 &stats);

  dump_chrecs_stats (dump_file, &stats);
}

\f

/* Initializer.  */

static void
initialize_scalar_evolutions_analyzer (void)
{
  /* The elements below are unique.  */
  if (chrec_dont_know == NULL_TREE)
    {
      chrec_not_analyzed_yet = NULL_TREE;
      chrec_dont_know = make_node (SCEV_NOT_KNOWN);
      chrec_known = make_node (SCEV_KNOWN);
      TREE_TYPE (chrec_dont_know) = void_type_node;
      TREE_TYPE (chrec_known) = void_type_node;
    }
}

/* Initialize the analysis of scalar evolutions for LOOPS.  */

void
scev_initialize (void)
{
  loop_iterator li;
  struct loop *loop;

  scalar_evolution_info = htab_create_alloc (100,
                                             hash_scev_info,
                                             eq_scev_info,
                                             del_scev_info,
                                             ggc_calloc,
                                             ggc_free);
  
  initialize_scalar_evolutions_analyzer ();

  FOR_EACH_LOOP (li, loop, 0)
    {
      loop->nb_iterations = NULL_TREE;
    }
}

/* Cleans up the information cached by the scalar evolutions analysis.  */

void
scev_reset (void)
{
  loop_iterator li;
  struct loop *loop;

  if (!scalar_evolution_info || !current_loops)
    return;

  htab_empty (scalar_evolution_info);
  FOR_EACH_LOOP (li, loop, 0)
    {
      loop->nb_iterations = NULL_TREE;
    }
}

/* Checks whether use of OP in USE_LOOP behaves as a simple affine iv with
   respect to WRTO_LOOP and returns its base and step in IV if possible
   (see analyze_scalar_evolution_in_loop for more details on USE_LOOP
   and WRTO_LOOP).  If ALLOW_NONCONSTANT_STEP is true, we want step to be
   invariant in LOOP.  Otherwise we require it to be an integer constant.
   
   IV->no_overflow is set to true if we are sure the iv cannot overflow (e.g.
   because it is computed in signed arithmetics).  Consequently, adding an
   induction variable
   
   for (i = IV->base; ; i += IV->step)

   is only safe if IV->no_overflow is false, or TYPE_OVERFLOW_UNDEFINED is
   false for the type of the induction variable, or you can prove that i does
   not wrap by some other argument.  Otherwise, this might introduce undefined
   behavior, and
   
   for (i = iv->base; ; i = (type) ((unsigned type) i + (unsigned type) iv->step))

   must be used instead.  */

bool
simple_iv (struct loop *wrto_loop, struct loop *use_loop, tree op,
           affine_iv *iv, bool allow_nonconstant_step)
{
  tree type, ev;
  bool folded_casts;

  iv->base = NULL_TREE;
  iv->step = NULL_TREE;
  iv->no_overflow = false;

  type = TREE_TYPE (op);
  if (TREE_CODE (type) != INTEGER_TYPE
      && TREE_CODE (type) != POINTER_TYPE)
    return false;

  ev = analyze_scalar_evolution_in_loop (wrto_loop, use_loop, op,
                                         &folded_casts);
  if (chrec_contains_undetermined (ev)
      || chrec_contains_symbols_defined_in_loop (ev, wrto_loop->num))
    return false;

  if (tree_does_not_contain_chrecs (ev))
    {
      iv->base = ev;
      iv->step = build_int_cst (TREE_TYPE (ev), 0);
      iv->no_overflow = true;
      return true;
    }

  if (TREE_CODE (ev) != POLYNOMIAL_CHREC
      || CHREC_VARIABLE (ev) != (unsigned) wrto_loop->num)
    return false;

  iv->step = CHREC_RIGHT (ev);
  if ((!allow_nonconstant_step && TREE_CODE (iv->step) != INTEGER_CST)
      || tree_contains_chrecs (iv->step, NULL))
    return false;

  iv->base = CHREC_LEFT (ev);
  if (tree_contains_chrecs (iv->base, NULL))
    return false;

  iv->no_overflow = !folded_casts && TYPE_OVERFLOW_UNDEFINED (type);

  return true;
}

/* Runs the analysis of scalar evolutions.  */

void
scev_analysis (void)
{
  VEC(gimple,heap) *exit_conditions;
  
  exit_conditions = VEC_alloc (gimple, heap, 37);
  select_loops_exit_conditions (&exit_conditions);

  if (dump_file && (dump_flags & TDF_STATS))
    analyze_scalar_evolution_for_all_loop_phi_nodes (&exit_conditions);
  
  number_of_iterations_for_all_loops (&exit_conditions);
  VEC_free (gimple, heap, exit_conditions);
}

/* Finalize the scalar evolution analysis.  */

void
scev_finalize (void)
{
  if (!scalar_evolution_info)
    return;
  htab_delete (scalar_evolution_info);
  scalar_evolution_info = NULL;
}

/* Returns true if the expression EXPR is considered to be too expensive
   for scev_const_prop.  */

bool
expression_expensive_p (tree expr)
{
  enum tree_code code;

  if (is_gimple_val (expr))
    return false;

  code = TREE_CODE (expr);
  if (code == TRUNC_DIV_EXPR
      || code == CEIL_DIV_EXPR
      || code == FLOOR_DIV_EXPR
      || code == ROUND_DIV_EXPR
      || code == TRUNC_MOD_EXPR
      || code == CEIL_MOD_EXPR
      || code == FLOOR_MOD_EXPR
      || code == ROUND_MOD_EXPR
      || code == EXACT_DIV_EXPR)
    {
      /* Division by power of two is usually cheap, so we allow it.
         Forbid anything else.  */
      if (!integer_pow2p (TREE_OPERAND (expr, 1)))
        return true;
    }

  switch (TREE_CODE_CLASS (code))
    {
    case tcc_binary:
    case tcc_comparison:
      if (expression_expensive_p (TREE_OPERAND (expr, 1)))
        return true;

      /* Fallthru.  */
    case tcc_unary:
      return expression_expensive_p (TREE_OPERAND (expr, 0));

    default:
      return true;
    }
}

/* Replace ssa names for that scev can prove they are constant by the
   appropriate constants.  Also perform final value replacement in loops,
   in case the replacement expressions are cheap.
   
   We only consider SSA names defined by phi nodes; rest is left to the
   ordinary constant propagation pass.  */

unsigned int
scev_const_prop (void)
{
  basic_block bb;
  tree name, type, ev;
  gimple phi, ass;
  struct loop *loop, *ex_loop;
  bitmap ssa_names_to_remove = NULL;
  unsigned i;
  loop_iterator li;
  gimple_stmt_iterator psi;

  if (number_of_loops () <= 1)
    return 0;

  FOR_EACH_BB (bb)
    {
      loop = bb->loop_father;

      for (psi = gsi_start_phis (bb); !gsi_end_p (psi); gsi_next (&psi))
        {
          phi = gsi_stmt (psi);
          name = PHI_RESULT (phi);

          if (!is_gimple_reg (name))
            continue;

          type = TREE_TYPE (name);

          if (!POINTER_TYPE_P (type)
              && !INTEGRAL_TYPE_P (type))
            continue;

          ev = resolve_mixers (loop, analyze_scalar_evolution (loop, name));
          if (!is_gimple_min_invariant (ev)
              || !may_propagate_copy (name, ev))
            continue;

          /* Replace the uses of the name.  */
          if (name != ev)
            replace_uses_by (name, ev);

          if (!ssa_names_to_remove)
            ssa_names_to_remove = BITMAP_ALLOC (NULL);
          bitmap_set_bit (ssa_names_to_remove, SSA_NAME_VERSION (name));
        }
    }

  /* Remove the ssa names that were replaced by constants.  We do not
     remove them directly in the previous cycle, since this
     invalidates scev cache.  */
  if (ssa_names_to_remove)
    {
      bitmap_iterator bi;

      EXECUTE_IF_SET_IN_BITMAP (ssa_names_to_remove, 0, i, bi)
        {
          gimple_stmt_iterator psi;
          name = ssa_name (i);
          phi = SSA_NAME_DEF_STMT (name);

          gcc_assert (gimple_code (phi) == GIMPLE_PHI);
          psi = gsi_for_stmt (phi);
          remove_phi_node (&psi, true);
        }

      BITMAP_FREE (ssa_names_to_remove);
      scev_reset ();
    }

  /* Now the regular final value replacement.  */
  FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
    {
      edge exit;
      tree def, rslt, niter;
      gimple_stmt_iterator bsi;

      /* If we do not know exact number of iterations of the loop, we cannot
         replace the final value.  */
      exit = single_exit (loop);
      if (!exit)
        continue;

      niter = number_of_latch_executions (loop);
      if (niter == chrec_dont_know)
        continue;

      /* Ensure that it is possible to insert new statements somewhere.  */
      if (!single_pred_p (exit->dest))
        split_loop_exit_edge (exit);
      bsi = gsi_after_labels (exit->dest);

      ex_loop = superloop_at_depth (loop,
                                    loop_depth (exit->dest->loop_father) + 1);

      for (psi = gsi_start_phis (exit->dest); !gsi_end_p (psi); )
        {
          phi = gsi_stmt (psi);
          rslt = PHI_RESULT (phi);
          def = PHI_ARG_DEF_FROM_EDGE (phi, exit);
          if (!is_gimple_reg (def))
            {
              gsi_next (&psi);
              continue;
            }

          if (!POINTER_TYPE_P (TREE_TYPE (def))
              && !INTEGRAL_TYPE_P (TREE_TYPE (def)))
            {
              gsi_next (&psi);
              continue;
            }

          def = analyze_scalar_evolution_in_loop (ex_loop, loop, def, NULL);
          def = compute_overall_effect_of_inner_loop (ex_loop, def);
          if (!tree_does_not_contain_chrecs (def)
              || chrec_contains_symbols_defined_in_loop (def, ex_loop->num)
              /* Moving the computation from the loop may prolong life range
                 of some ssa names, which may cause problems if they appear
                 on abnormal edges.  */
              || contains_abnormal_ssa_name_p (def)
              /* Do not emit expensive expressions.  The rationale is that
                 when someone writes a code like

                 while (n > 45) n -= 45;

                 he probably knows that n is not large, and does not want it
                 to be turned into n %= 45.  */
              || expression_expensive_p (def))
            {
              gsi_next (&psi);
              continue;
            }

          /* Eliminate the PHI node and replace it by a computation outside
             the loop.  */
          def = unshare_expr (def);
          remove_phi_node (&psi, false);

          def = force_gimple_operand_gsi (&bsi, def, false, NULL_TREE,
                                          true, GSI_SAME_STMT);
          ass = gimple_build_assign (rslt, def);
          gsi_insert_before (&bsi, ass, GSI_SAME_STMT);
        }
    }
  return 0;
}

#include "gt-tree-scalar-evolution.h"