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/* Backward propagation of indirect loads through PHIs.

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

   Contributed by Richard Guenther <rguenther@suse.de>

This file is part of GCC.

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

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

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

any later version.

GCC is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

GNU General Public License for more details.

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

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

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

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "ggc.h"

#include "tree.h"

#include "rtl.h"

#include "tm_p.h"

#include "basic-block.h"

#include "timevar.h"

#include "diagnostic.h"

#include "tree-flow.h"

#include "tree-pass.h"

#include "tree-dump.h"

#include "langhooks.h"

#include "flags.h"

/* This pass propagates indirect loads through the PHI node for its

   address to make the load source possibly non-addressable and to

   allow for PHI optimization to trigger.

   For example the pass changes

     # addr_1 = PHI <&a, &b>

     tmp_1 = *addr_1;

   to

     # tmp_1 = PHI <a, b>

   but also handles more complex scenarios like

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

     ...

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

     D.2114_13 = *b_12;

     ...

     # b_15 = PHI <b_12(4), &b(5)>

     D.2080_5 = &this_1(D)->a0;

     ...

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

     ...

     # b_21 = PHI <b_15(8), b_18(9)>

     D.2076_8 = *b_21;

   where the addresses loaded are defined by PHIs itself.

   The above happens for

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

   where this pass transforms it to a form later PHI optimization

   recognizes and transforms it to the simple

     D.2109_10 = this_1(D)->a1;

     D.2110_11 = c;

     D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;

     D.2115_14 = b;

     D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;

     D.2119_16 = this_1(D)->a0;

     D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;

     D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;

   The pass does a dominator walk processing loads using a basic-block

   local analysis and stores the result for use by transformations on

   dominated basic-blocks.  */

/* Structure to keep track of the value of a dereferenced PHI result

   and the virtual operand used for that dereference.  */

struct phiprop_d

{

  tree value;

  tree vuse;

};

/* Verify if the value recorded for NAME in PHIVN is still valid at

   the start of basic block BB.  */

static bool

phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)

{

  tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;

  gimple use_stmt;

  imm_use_iterator ui2;

  bool ok = true;

  /* The def stmts of the virtual uses need to be dominated by bb.  */

  gcc_assert (vuse != NULL_TREE);

  FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)

    {

      /* If BB does not dominate a VDEF, the value is invalid.  */

      if ((gimple_vdef (use_stmt) != NULL_TREE

           || gimple_code (use_stmt) == GIMPLE_PHI)

          && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))

        {

          ok = false;

          BREAK_FROM_IMM_USE_STMT (ui2);

        }

    }

  return ok;

}

/* Insert a new phi node for the dereference of PHI at basic_block

   BB with the virtual operands from USE_STMT.  */

static tree

phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,

                    struct phiprop_d *phivn, size_t n)

{

  tree res;

  gimple new_phi;

  edge_iterator ei;

  edge e;

  gcc_assert (is_gimple_assign (use_stmt)

              && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF);

  /* Build a new PHI node to replace the definition of

     the indirect reference lhs.  */

  res = gimple_assign_lhs (use_stmt);

  SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb);

  if (dump_file && (dump_flags & TDF_DETAILS))

    {

      fprintf (dump_file, "Inserting PHI for result of load ");

      print_gimple_stmt (dump_file, use_stmt, 0, 0);

    }

  /* Add PHI arguments for each edge inserting loads of the

     addressable operands.  */

  FOR_EACH_EDGE (e, ei, bb->preds)

    {

      tree old_arg, new_var;

      gimple tmp;

      source_location locus;

      old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);

      locus = gimple_phi_arg_location_from_edge (phi, e);

      while (TREE_CODE (old_arg) == SSA_NAME

             && (SSA_NAME_VERSION (old_arg) >= n

                 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))

        {

          gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);

          old_arg = gimple_assign_rhs1 (def_stmt);

          locus = gimple_location (def_stmt);

        }

      if (TREE_CODE (old_arg) == SSA_NAME)

        {

          if (dump_file && (dump_flags & TDF_DETAILS))

            {

              fprintf (dump_file, "  for edge defining ");

              print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);

              fprintf (dump_file, " reusing PHI result ");

              print_generic_expr (dump_file,

                                  phivn[SSA_NAME_VERSION (old_arg)].value, 0);

              fprintf (dump_file, "\n");

            }

          /* Reuse a formerly created dereference.  */

          new_var = phivn[SSA_NAME_VERSION (old_arg)].value;

        }

      else

        {

          gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);

          old_arg = TREE_OPERAND (old_arg, 0);

          new_var = create_tmp_var (TREE_TYPE (old_arg), NULL);

          tmp = gimple_build_assign (new_var, unshare_expr (old_arg));

          if (TREE_CODE (TREE_TYPE (old_arg)) == COMPLEX_TYPE

              || TREE_CODE (TREE_TYPE (old_arg)) == VECTOR_TYPE)

            DECL_GIMPLE_REG_P (new_var) = 1;

          gcc_assert (is_gimple_reg (new_var));

          add_referenced_var (new_var);

          new_var = make_ssa_name (new_var, tmp);

          gimple_assign_set_lhs (tmp, new_var);

          gimple_set_location (tmp, locus);

          gsi_insert_on_edge (e, tmp);

          update_stmt (tmp);

          if (dump_file && (dump_flags & TDF_DETAILS))

            {

              fprintf (dump_file, "  for edge defining ");

              print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);

              fprintf (dump_file, " inserting load ");

              print_gimple_stmt (dump_file, tmp, 0, 0);

            }

        }

      add_phi_arg (new_phi, new_var, e, locus);

    }

  update_stmt (new_phi);

  if (dump_file && (dump_flags & TDF_DETAILS))

    print_gimple_stmt (dump_file, new_phi, 0, 0);

  return res;

}

/* Propagate between the phi node arguments of PHI in BB and phi result

   users.  For now this matches

        # p_2 = PHI <&x, &y>

      <Lx>:;

        p_3 = p_2;

        z_2 = *p_3;

   and converts it to

        # z_2 = PHI <x, y>

      <Lx>:;

   Returns true if a transformation was done and edge insertions

   need to be committed.  Global data PHIVN and N is used to track

   past transformation results.  We need to be especially careful here

   with aliasing issues as we are moving memory reads.  */

static bool

propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,

                    size_t n)

{

  tree ptr = PHI_RESULT (phi);

  gimple use_stmt;

  tree res = NULL_TREE;

  gimple_stmt_iterator gsi;

  imm_use_iterator ui;

  use_operand_p arg_p, use;

  ssa_op_iter i;

  bool phi_inserted;

  if (!POINTER_TYPE_P (TREE_TYPE (ptr))

      || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))

    return false;

  /* Check if we can "cheaply" dereference all phi arguments.  */

  FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)

    {

      tree arg = USE_FROM_PTR (arg_p);

      /* Walk the ssa chain until we reach a ssa name we already

         created a value for or we reach a definition of the form

         ssa_name_n = &var;  */

      while (TREE_CODE (arg) == SSA_NAME

             && !SSA_NAME_IS_DEFAULT_DEF (arg)

             && (SSA_NAME_VERSION (arg) >= n

                 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))

        {

          gimple def_stmt = SSA_NAME_DEF_STMT (arg);

          if (!gimple_assign_single_p (def_stmt))

            return false;

          arg = gimple_assign_rhs1 (def_stmt);

        }

      if ((TREE_CODE (arg) != ADDR_EXPR

           /* Avoid to have to decay *&a to a[0] later.  */

           || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg, 0))))

          && !(TREE_CODE (arg) == SSA_NAME

               && SSA_NAME_VERSION (arg) < n

               && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE

               && phivn_valid_p (phivn, arg, bb)))

        return false;

    }

  /* Find a dereferencing use.  First follow (single use) ssa

     copy chains for ptr.  */

  while (single_imm_use (ptr, &use, &use_stmt)

         && gimple_assign_ssa_name_copy_p (use_stmt))

    ptr = gimple_assign_lhs (use_stmt);

  /* Replace the first dereference of *ptr if there is one and if we

     can move the loads to the place of the ptr phi node.  */

  phi_inserted = false;

  FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)

    {

      gimple def_stmt;

      tree vuse;

      /* Check whether this is a load of *ptr.  */

      if (!(is_gimple_assign (use_stmt)

            && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME

            && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF

            && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr

            /* We cannot replace a load that may throw or is volatile.  */

            && !stmt_can_throw_internal (use_stmt)))

        continue;

      /* Check if we can move the loads.  The def stmt of the virtual use

         needs to be in a different basic block dominating bb.  */

      vuse = gimple_vuse (use_stmt);

      def_stmt = SSA_NAME_DEF_STMT (vuse);

      if (!SSA_NAME_IS_DEFAULT_DEF (vuse)

          && (gimple_bb (def_stmt) == bb

              || !dominated_by_p (CDI_DOMINATORS,

                                  bb, gimple_bb (def_stmt))))

        goto next;

      /* Found a proper dereference.  Insert a phi node if this

         is the first load transformation.  */

      if (!phi_inserted)

        {

          res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);

          /* Remember the value we created for *ptr.  */

          phivn[SSA_NAME_VERSION (ptr)].value = res;

          phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;

          /* Remove old stmt.  The phi is taken care of by DCE, if we

             want to delete it here we also have to delete all intermediate

             copies.  */

          gsi = gsi_for_stmt (use_stmt);

          gsi_remove (&gsi, false);

          phi_inserted = true;

        }

      else

        {

          /* Further replacements are easy, just make a copy out of the

             load.  */

          gimple_assign_set_rhs1 (use_stmt, res);

          update_stmt (use_stmt);

        }

next:;

      /* Continue searching for a proper dereference.  */

    }

  return phi_inserted;

}

/* Main entry for phiprop pass.  */

static unsigned int

tree_ssa_phiprop (void)

{

  VEC(basic_block, heap) *bbs;

  struct phiprop_d *phivn;

  bool did_something = false;

  basic_block bb;

  gimple_stmt_iterator gsi;

  unsigned i;

  size_t n;

  calculate_dominance_info (CDI_DOMINATORS);

  n = num_ssa_names;

  phivn = XCNEWVEC (struct phiprop_d, n);

  /* Walk the dominator tree in preorder.  */

  bbs = get_all_dominated_blocks (CDI_DOMINATORS,

                                  single_succ (ENTRY_BLOCK_PTR));

  for (i = 0; VEC_iterate (basic_block, bbs, i, bb); ++i)

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

      did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);

  if (did_something)

    gsi_commit_edge_inserts ();

  VEC_free (basic_block, heap, bbs);

  free (phivn);

  return 0;

}

static bool

gate_phiprop (void)

{

  return flag_tree_phiprop;

}

struct gimple_opt_pass pass_phiprop =

{

 {

  GIMPLE_PASS,

  "phiprop",                    /* name */

  gate_phiprop,                 /* gate */

  tree_ssa_phiprop,             /* execute */

  NULL,                         /* sub */

  NULL,                         /* next */

  0,                             /* static_pass_number */

  TV_TREE_PHIPROP,              /* tv_id */

  PROP_cfg | PROP_ssa,          /* properties_required */

  0,                             /* properties_provided */

  0,                             /* properties_destroyed */

  0,                             /* todo_flags_start */

  TODO_dump_func

  | TODO_ggc_collect

  | TODO_update_ssa

  | TODO_verify_ssa             /* todo_flags_finish */

 }

};