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/* Generic SSA value propagation engine.

   Copyright (C) 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.

   Contributed by Diego Novillo <dnovillo@redhat.com>

   This file is part of GCC.

   GCC is free software; you can redistribute it and/or modify it

   under the terms of the GNU General Public License as published by the

   Free Software Foundation; either version 3, or (at your option) any

   later version.

   GCC is distributed in the hope that it will be useful, but WITHOUT

   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

   FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

   for more details.

   You should have received a copy of the GNU General Public License

   along with GCC; see the file COPYING3.  If not see

   <http://www.gnu.org/licenses/>.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "tree.h"

#include "flags.h"

#include "rtl.h"

#include "tm_p.h"

#include "ggc.h"

#include "basic-block.h"

#include "output.h"

#include "expr.h"

#include "function.h"

#include "diagnostic.h"

#include "timevar.h"

#include "tree-dump.h"

#include "tree-flow.h"

#include "tree-pass.h"

#include "tree-ssa-propagate.h"

#include "langhooks.h"

#include "varray.h"

#include "vec.h"

#include "value-prof.h"

#include "gimple.h"

/* This file implements a generic value propagation engine based on

   the same propagation used by the SSA-CCP algorithm [1].

   Propagation is performed by simulating the execution of every

   statement that produces the value being propagated.  Simulation

   proceeds as follows:

   1- Initially, all edges of the CFG are marked not executable and

      the CFG worklist is seeded with all the statements in the entry

      basic block (block 0).

   2- Every statement S is simulated with a call to the call-back

      function SSA_PROP_VISIT_STMT.  This evaluation may produce 3

      results:

        SSA_PROP_NOT_INTERESTING: Statement S produces nothing of

            interest and does not affect any of the work lists.

        SSA_PROP_VARYING: The value produced by S cannot be determined

            at compile time.  Further simulation of S is not required.

            If S is a conditional jump, all the outgoing edges for the

            block are considered executable and added to the work

            list.

        SSA_PROP_INTERESTING: S produces a value that can be computed

            at compile time.  Its result can be propagated into the

            statements that feed from S.  Furthermore, if S is a

            conditional jump, only the edge known to be taken is added

            to the work list.  Edges that are known not to execute are

            never simulated.

   3- PHI nodes are simulated with a call to SSA_PROP_VISIT_PHI.  The

      return value from SSA_PROP_VISIT_PHI has the same semantics as

      described in #2.

   4- Three work lists are kept.  Statements are only added to these

      lists if they produce one of SSA_PROP_INTERESTING or

      SSA_PROP_VARYING.

        CFG_BLOCKS contains the list of blocks to be simulated.

            Blocks are added to this list if their incoming edges are

            found executable.

        VARYING_SSA_EDGES contains the list of statements that feed

            from statements that produce an SSA_PROP_VARYING result.

            These are simulated first to speed up processing.

        INTERESTING_SSA_EDGES contains the list of statements that

            feed from statements that produce an SSA_PROP_INTERESTING

            result.

   5- Simulation terminates when all three work lists are drained.

   Before calling ssa_propagate, it is important to clear

   prop_simulate_again_p for all the statements in the program that

   should be simulated.  This initialization allows an implementation

   to specify which statements should never be simulated.

   It is also important to compute def-use information before calling

   ssa_propagate.

   References:

     [1] Constant propagation with conditional branches,

         Wegman and Zadeck, ACM TOPLAS 13(2):181-210.

     [2] Building an Optimizing Compiler,

         Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.

     [3] Advanced Compiler Design and Implementation,

         Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6  */

/* Function pointers used to parameterize the propagation engine.  */

static ssa_prop_visit_stmt_fn ssa_prop_visit_stmt;

static ssa_prop_visit_phi_fn ssa_prop_visit_phi;

/* Keep track of statements that have been added to one of the SSA

   edges worklists.  This flag is used to avoid visiting statements

   unnecessarily when draining an SSA edge worklist.  If while

   simulating a basic block, we find a statement with

   STMT_IN_SSA_EDGE_WORKLIST set, we clear it to prevent SSA edge

   processing from visiting it again.

   NOTE: users of the propagation engine are not allowed to use

   the GF_PLF_1 flag.  */

#define STMT_IN_SSA_EDGE_WORKLIST       GF_PLF_1

/* A bitmap to keep track of executable blocks in the CFG.  */

static sbitmap executable_blocks;

/* Array of control flow edges on the worklist.  */

static VEC(basic_block,heap) *cfg_blocks;

static unsigned int cfg_blocks_num = 0;

static int cfg_blocks_tail;

static int cfg_blocks_head;

static sbitmap bb_in_list;

/* Worklist of SSA edges which will need reexamination as their

   definition has changed.  SSA edges are def-use edges in the SSA

   web.  For each D-U edge, we store the target statement or PHI node

   U.  */

static GTY(()) VEC(gimple,gc) *interesting_ssa_edges;

/* Identical to INTERESTING_SSA_EDGES.  For performance reasons, the

   list of SSA edges is split into two.  One contains all SSA edges

   who need to be reexamined because their lattice value changed to

   varying (this worklist), and the other contains all other SSA edges

   to be reexamined (INTERESTING_SSA_EDGES).

   Since most values in the program are VARYING, the ideal situation

   is to move them to that lattice value as quickly as possible.

   Thus, it doesn't make sense to process any other type of lattice

   value until all VARYING values are propagated fully, which is one

   thing using the VARYING worklist achieves.  In addition, if we

   don't use a separate worklist for VARYING edges, we end up with

   situations where lattice values move from

   UNDEFINED->INTERESTING->VARYING instead of UNDEFINED->VARYING.  */

static GTY(()) VEC(gimple,gc) *varying_ssa_edges;

/* Return true if the block worklist empty.  */

static inline bool

cfg_blocks_empty_p (void)

{

  return (cfg_blocks_num == 0);

}

/* Add a basic block to the worklist.  The block must not be already

   in the worklist, and it must not be the ENTRY or EXIT block.  */

static void

cfg_blocks_add (basic_block bb)

{

  bool head = false;

  gcc_assert (bb != ENTRY_BLOCK_PTR && bb != EXIT_BLOCK_PTR);

  gcc_assert (!TEST_BIT (bb_in_list, bb->index));

  if (cfg_blocks_empty_p ())

    {

      cfg_blocks_tail = cfg_blocks_head = 0;

      cfg_blocks_num = 1;

    }

  else

    {

      cfg_blocks_num++;

      if (cfg_blocks_num > VEC_length (basic_block, cfg_blocks))

        {

          /* We have to grow the array now.  Adjust to queue to occupy

             the full space of the original array.  We do not need to

             initialize the newly allocated portion of the array

             because we keep track of CFG_BLOCKS_HEAD and

             CFG_BLOCKS_HEAD.  */

          cfg_blocks_tail = VEC_length (basic_block, cfg_blocks);

          cfg_blocks_head = 0;

          VEC_safe_grow (basic_block, heap, cfg_blocks, 2 * cfg_blocks_tail);

        }

      /* Minor optimization: we prefer to see blocks with more

         predecessors later, because there is more of a chance that

         the incoming edges will be executable.  */

      else if (EDGE_COUNT (bb->preds)

               >= EDGE_COUNT (VEC_index (basic_block, cfg_blocks,

                                         cfg_blocks_head)->preds))

        cfg_blocks_tail = ((cfg_blocks_tail + 1)

                           % VEC_length (basic_block, cfg_blocks));

      else

        {

          if (cfg_blocks_head == 0)

            cfg_blocks_head = VEC_length (basic_block, cfg_blocks);

          --cfg_blocks_head;

          head = true;

        }

    }

  VEC_replace (basic_block, cfg_blocks,

               head ? cfg_blocks_head : cfg_blocks_tail,

               bb);

  SET_BIT (bb_in_list, bb->index);

}

/* Remove a block from the worklist.  */

static basic_block

cfg_blocks_get (void)

{

  basic_block bb;

  bb = VEC_index (basic_block, cfg_blocks, cfg_blocks_head);

  gcc_assert (!cfg_blocks_empty_p ());

  gcc_assert (bb);

  cfg_blocks_head = ((cfg_blocks_head + 1)

                     % VEC_length (basic_block, cfg_blocks));

  --cfg_blocks_num;

  RESET_BIT (bb_in_list, bb->index);

  return bb;

}

/* We have just defined a new value for VAR.  If IS_VARYING is true,

   add all immediate uses of VAR to VARYING_SSA_EDGES, otherwise add

   them to INTERESTING_SSA_EDGES.  */

static void

add_ssa_edge (tree var, bool is_varying)

{

  imm_use_iterator iter;

  use_operand_p use_p;

  FOR_EACH_IMM_USE_FAST (use_p, iter, var)

    {

      gimple use_stmt = USE_STMT (use_p);

      if (prop_simulate_again_p (use_stmt)

          && !gimple_plf (use_stmt, STMT_IN_SSA_EDGE_WORKLIST))

        {

          gimple_set_plf (use_stmt, STMT_IN_SSA_EDGE_WORKLIST, true);

          if (is_varying)

            VEC_safe_push (gimple, gc, varying_ssa_edges, use_stmt);

          else

            VEC_safe_push (gimple, gc, interesting_ssa_edges, use_stmt);

        }

    }

}

/* Add edge E to the control flow worklist.  */

static void

add_control_edge (edge e)

{

  basic_block bb = e->dest;

  if (bb == EXIT_BLOCK_PTR)

    return;

  /* If the edge had already been executed, skip it.  */

  if (e->flags & EDGE_EXECUTABLE)

    return;

  e->flags |= EDGE_EXECUTABLE;

  /* If the block is already in the list, we're done.  */

  if (TEST_BIT (bb_in_list, bb->index))

    return;

  cfg_blocks_add (bb);

  if (dump_file && (dump_flags & TDF_DETAILS))

    fprintf (dump_file, "Adding Destination of edge (%d -> %d) to worklist\n\n",

        e->src->index, e->dest->index);

}

/* Simulate the execution of STMT and update the work lists accordingly.  */

static void

simulate_stmt (gimple stmt)

{

  enum ssa_prop_result val = SSA_PROP_NOT_INTERESTING;

  edge taken_edge = NULL;

  tree output_name = NULL_TREE;

  /* Don't bother visiting statements that are already

     considered varying by the propagator.  */

  if (!prop_simulate_again_p (stmt))

    return;

  if (gimple_code (stmt) == GIMPLE_PHI)

    {

      val = ssa_prop_visit_phi (stmt);

      output_name = gimple_phi_result (stmt);

    }

  else

    val = ssa_prop_visit_stmt (stmt, &taken_edge, &output_name);

  if (val == SSA_PROP_VARYING)

    {

      prop_set_simulate_again (stmt, false);

      /* If the statement produced a new varying value, add the SSA

         edges coming out of OUTPUT_NAME.  */

      if (output_name)

        add_ssa_edge (output_name, true);

      /* If STMT transfers control out of its basic block, add

         all outgoing edges to the work list.  */

      if (stmt_ends_bb_p (stmt))

        {

          edge e;

          edge_iterator ei;

          basic_block bb = gimple_bb (stmt);

          FOR_EACH_EDGE (e, ei, bb->succs)

            add_control_edge (e);

        }

    }

  else if (val == SSA_PROP_INTERESTING)

    {

      /* If the statement produced new value, add the SSA edges coming

         out of OUTPUT_NAME.  */

      if (output_name)

        add_ssa_edge (output_name, false);

      /* If we know which edge is going to be taken out of this block,

         add it to the CFG work list.  */

      if (taken_edge)

        add_control_edge (taken_edge);

    }

}

/* Process an SSA edge worklist.  WORKLIST is the SSA edge worklist to

   drain.  This pops statements off the given WORKLIST and processes

   them until there are no more statements on WORKLIST.

   We take a pointer to WORKLIST because it may be reallocated when an

   SSA edge is added to it in simulate_stmt.  */

static void

process_ssa_edge_worklist (VEC(gimple,gc) **worklist)

{

  /* Drain the entire worklist.  */

  while (VEC_length (gimple, *worklist) > 0)

    {

      basic_block bb;

      /* Pull the statement to simulate off the worklist.  */

      gimple stmt = VEC_pop (gimple, *worklist);

      /* If this statement was already visited by simulate_block, then

         we don't need to visit it again here.  */

      if (!gimple_plf (stmt, STMT_IN_SSA_EDGE_WORKLIST))

        continue;

      /* STMT is no longer in a worklist.  */

      gimple_set_plf (stmt, STMT_IN_SSA_EDGE_WORKLIST, false);

      if (dump_file && (dump_flags & TDF_DETAILS))

        {

          fprintf (dump_file, "\nSimulating statement (from ssa_edges): ");

          print_gimple_stmt (dump_file, stmt, 0, dump_flags);

        }

      bb = gimple_bb (stmt);

      /* PHI nodes are always visited, regardless of whether or not

         the destination block is executable.  Otherwise, visit the

         statement only if its block is marked executable.  */

      if (gimple_code (stmt) == GIMPLE_PHI

          || TEST_BIT (executable_blocks, bb->index))

        simulate_stmt (stmt);

    }

}

/* Simulate the execution of BLOCK.  Evaluate the statement associated

   with each variable reference inside the block.  */

static void

simulate_block (basic_block block)

{

  gimple_stmt_iterator gsi;

  /* There is nothing to do for the exit block.  */

  if (block == EXIT_BLOCK_PTR)

    return;

  if (dump_file && (dump_flags & TDF_DETAILS))

    fprintf (dump_file, "\nSimulating block %d\n", block->index);

  /* Always simulate PHI nodes, even if we have simulated this block

     before.  */

  for (gsi = gsi_start_phis (block); !gsi_end_p (gsi); gsi_next (&gsi))

    simulate_stmt (gsi_stmt (gsi));

  /* If this is the first time we've simulated this block, then we

     must simulate each of its statements.  */

  if (!TEST_BIT (executable_blocks, block->index))

    {

      gimple_stmt_iterator j;

      unsigned int normal_edge_count;

      edge e, normal_edge;

      edge_iterator ei;

      /* Note that we have simulated this block.  */

      SET_BIT (executable_blocks, block->index);

      for (j = gsi_start_bb (block); !gsi_end_p (j); gsi_next (&j))

        {

          gimple stmt = gsi_stmt (j);

          /* If this statement is already in the worklist then

             "cancel" it.  The reevaluation implied by the worklist

             entry will produce the same value we generate here and

             thus reevaluating it again from the worklist is

             pointless.  */

          if (gimple_plf (stmt, STMT_IN_SSA_EDGE_WORKLIST))

            gimple_set_plf (stmt, STMT_IN_SSA_EDGE_WORKLIST, false);

          simulate_stmt (stmt);

        }

      /* We can not predict when abnormal and EH edges will be executed, so

         once a block is considered executable, we consider any

         outgoing abnormal edges as executable.

         TODO: This is not exactly true.  Simplifying statement might

         prove it non-throwing and also computed goto can be handled

         when destination is known.

         At the same time, if this block has only one successor that is

         reached by non-abnormal edges, then add that successor to the

         worklist.  */

      normal_edge_count = 0;

      normal_edge = NULL;

      FOR_EACH_EDGE (e, ei, block->succs)

        {

          if (e->flags & (EDGE_ABNORMAL | EDGE_EH))

            add_control_edge (e);

          else

            {

              normal_edge_count++;

              normal_edge = e;

            }

        }

      if (normal_edge_count == 1)

        add_control_edge (normal_edge);

    }

}

/* Initialize local data structures and work lists.  */

static void

ssa_prop_init (void)

{

  edge e;

  edge_iterator ei;

  basic_block bb;

  /* Worklists of SSA edges.  */

  interesting_ssa_edges = VEC_alloc (gimple, gc, 20);

  varying_ssa_edges = VEC_alloc (gimple, gc, 20);

  executable_blocks = sbitmap_alloc (last_basic_block);

  sbitmap_zero (executable_blocks);

  bb_in_list = sbitmap_alloc (last_basic_block);

  sbitmap_zero (bb_in_list);

  if (dump_file && (dump_flags & TDF_DETAILS))

    dump_immediate_uses (dump_file);

  cfg_blocks = VEC_alloc (basic_block, heap, 20);

  VEC_safe_grow (basic_block, heap, cfg_blocks, 20);

  /* Initially assume that every edge in the CFG is not executable.

     (including the edges coming out of ENTRY_BLOCK_PTR).  */

  FOR_ALL_BB (bb)

    {

      gimple_stmt_iterator si;

      for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si))

        gimple_set_plf (gsi_stmt (si), STMT_IN_SSA_EDGE_WORKLIST, false);

      for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si))

        gimple_set_plf (gsi_stmt (si), STMT_IN_SSA_EDGE_WORKLIST, false);

      FOR_EACH_EDGE (e, ei, bb->succs)

        e->flags &= ~EDGE_EXECUTABLE;

    }

  /* Seed the algorithm by adding the successors of the entry block to the

     edge worklist.  */

  FOR_EACH_EDGE (e, ei, ENTRY_BLOCK_PTR->succs)

    add_control_edge (e);

}

/* Free allocated storage.  */

static void

ssa_prop_fini (void)

{

  VEC_free (gimple, gc, interesting_ssa_edges);

  VEC_free (gimple, gc, varying_ssa_edges);

  VEC_free (basic_block, heap, cfg_blocks);

  cfg_blocks = NULL;

  sbitmap_free (bb_in_list);

  sbitmap_free (executable_blocks);

}

/* Return true if EXPR is an acceptable right-hand-side for a

   GIMPLE assignment.  We validate the entire tree, not just

   the root node, thus catching expressions that embed complex

   operands that are not permitted in GIMPLE.  This function

   is needed because the folding routines in fold-const.c

   may return such expressions in some cases, e.g., an array

   access with an embedded index addition.  It may make more

   sense to have folding routines that are sensitive to the

   constraints on GIMPLE operands, rather than abandoning any

   any attempt to fold if the usual folding turns out to be too

   aggressive.  */

bool

valid_gimple_rhs_p (tree expr)

{

  enum tree_code code = TREE_CODE (expr);

  switch (TREE_CODE_CLASS (code))

    {

    case tcc_declaration:

      if (!is_gimple_variable (expr))

        return false;

      break;

    case tcc_constant:

      /* All constants are ok.  */

      break;

    case tcc_binary:

    case tcc_comparison:

      if (!is_gimple_val (TREE_OPERAND (expr, 0))

          || !is_gimple_val (TREE_OPERAND (expr, 1)))

        return false;

      break;

    case tcc_unary:

      if (!is_gimple_val (TREE_OPERAND (expr, 0)))

        return false;

      break;

    case tcc_expression:

      switch (code)

        {

        case ADDR_EXPR:

          {

            tree t;

            if (is_gimple_min_invariant (expr))

              return true;

            t = TREE_OPERAND (expr, 0);

            while (handled_component_p (t))

              {

                /* ??? More checks needed, see the GIMPLE verifier.  */

                if ((TREE_CODE (t) == ARRAY_REF

                     || TREE_CODE (t) == ARRAY_RANGE_REF)

                    && !is_gimple_val (TREE_OPERAND (t, 1)))

                  return false;

                t = TREE_OPERAND (t, 0);

              }

            if (!is_gimple_id (t))

              return false;

          }

          break;

        case TRUTH_NOT_EXPR:

          if (!is_gimple_val (TREE_OPERAND (expr, 0)))

            return false;

          break;

        case TRUTH_AND_EXPR:

        case TRUTH_XOR_EXPR:

        case TRUTH_OR_EXPR:

          if (!is_gimple_val (TREE_OPERAND (expr, 0))

              || !is_gimple_val (TREE_OPERAND (expr, 1)))

            return false;

          break;

        default:

          return false;

        }

      break;

    case tcc_vl_exp:

      return false;

    case tcc_exceptional:

      if (code != SSA_NAME)

        return false;

      break;

    default:

      return false;

    }

  return true;

}

/* Return true if EXPR is a CALL_EXPR suitable for representation

   as a single GIMPLE_CALL statement.  If the arguments require

   further gimplification, return false.  */

bool

valid_gimple_call_p (tree expr)

{

  unsigned i, nargs;

  if (TREE_CODE (expr) != CALL_EXPR)

    return false;

  nargs = call_expr_nargs (expr);

  for (i = 0; i < nargs; i++)

    if (! is_gimple_operand (CALL_EXPR_ARG (expr, i)))

      return false;

  return true;

}

/* Make SSA names defined by OLD_STMT point to NEW_STMT

   as their defining statement.  */

void

move_ssa_defining_stmt_for_defs (gimple new_stmt, gimple old_stmt)

{

  tree var;

  ssa_op_iter iter;

  if (gimple_in_ssa_p (cfun))

    {

      /* Make defined SSA_NAMEs point to the new

         statement as their definition.  */

      FOR_EACH_SSA_TREE_OPERAND (var, old_stmt, iter, SSA_OP_ALL_DEFS)

        {

          if (TREE_CODE (var) == SSA_NAME)

            SSA_NAME_DEF_STMT (var) = new_stmt;

        }

    }

}

/* Update a GIMPLE_CALL statement at iterator *SI_P to reflect the

   value of EXPR, which is expected to be the result of folding the

   call.  This can only be done if EXPR is a CALL_EXPR with valid

   GIMPLE operands as arguments, or if it is a suitable RHS expression

   for a GIMPLE_ASSIGN.  More complex expressions will require

   gimplification, which will introduce addtional statements.  In this

   event, no update is performed, and the function returns false.

   Note that we cannot mutate a GIMPLE_CALL in-place, so we always

   replace the statement at *SI_P with an entirely new statement.

   The new statement need not be a call, e.g., if the original call

   folded to a constant.  */

bool

update_call_from_tree (gimple_stmt_iterator *si_p, tree expr)

{

  tree lhs;

  gimple stmt = gsi_stmt (*si_p);

  gcc_assert (is_gimple_call (stmt));

  lhs = gimple_call_lhs (stmt);

  if (valid_gimple_call_p (expr))

    {

      /* The call has simplified to another call.  */

      tree fn = CALL_EXPR_FN (expr);

      unsigned i;

      unsigned nargs = call_expr_nargs (expr);

      VEC(tree, heap) *args = NULL;

      gimple new_stmt;

      if (nargs > 0)

        {

          args = VEC_alloc (tree, heap, nargs);

          VEC_safe_grow (tree, heap, args, nargs);

          for (i = 0; i < nargs; i++)

            VEC_replace (tree, args, i, CALL_EXPR_ARG (expr, i));

        }

      new_stmt = gimple_build_call_vec (fn, args);

      gimple_call_set_lhs (new_stmt, lhs);

      move_ssa_defining_stmt_for_defs (new_stmt, stmt);

      gimple_set_vuse (new_stmt, gimple_vuse (stmt));

      gimple_set_vdef (new_stmt, gimple_vdef (stmt));

      gimple_set_location (new_stmt, gimple_location (stmt));

      gsi_replace (si_p, new_stmt, false);

      VEC_free (tree, heap, args);

      return true;

    }

  else if (valid_gimple_rhs_p (expr))

    {

      gimple new_stmt;

      /* The call has simplified to an expression

         that cannot be represented as a GIMPLE_CALL. */

      if (lhs)

        {

          /* A value is expected.

             Introduce a new GIMPLE_ASSIGN statement.  */

          STRIP_USELESS_TYPE_CONVERSION (expr);

          new_stmt = gimple_build_assign (lhs, expr);