dist/gcc/tree-ssa-ifcombine.c

/* Combining of if-expressions on trees.
   Copyright (C) 2007-2019 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 "backend.h"
#include "rtl.h"
#include "tree.h"
#include "gimple.h"
#include "cfghooks.h"
#include "tree-pass.h"
#include "memmodel.h"
#include "tm_p.h"
#include "ssa.h"
#include "tree-pretty-print.h"
/* rtl is needed only because arm back-end requires it for
   BRANCH_COST.  */
#include "fold-const.h"
#include "cfganal.h"
#include "gimple-fold.h"
#include "gimple-iterator.h"
#include "gimplify-me.h"
#include "tree-cfg.h"
#include "tree-ssa.h"
#include "params.h"

#ifndef LOGICAL_OP_NON_SHORT_CIRCUIT
#define LOGICAL_OP_NON_SHORT_CIRCUIT \
  (BRANCH_COST (optimize_function_for_speed_p (cfun), \
                false) >= 2)
#endif

/* This pass combines COND_EXPRs to simplify control flow.  It
   currently recognizes bit tests and comparisons in chains that
   represent logical and or logical or of two COND_EXPRs.

   It does so by walking basic blocks in a approximate reverse
   post-dominator order and trying to match CFG patterns that
   represent logical and or logical or of two COND_EXPRs.
   Transformations are done if the COND_EXPR conditions match
   either

     1. two single bit tests X & (1 << Yn) (for logical and)

     2. two bit tests X & Yn (for logical or)

     3. two comparisons X OPn Y (for logical or)

   To simplify this pass, removing basic blocks and dead code
   is left to CFG cleanup and DCE.  */


/* Recognize a if-then-else CFG pattern starting to match with the
   COND_BB basic-block containing the COND_EXPR.  The recognized
   then end else blocks are stored to *THEN_BB and *ELSE_BB.  If
   *THEN_BB and/or *ELSE_BB are already set, they are required to
   match the then and else basic-blocks to make the pattern match.
   Returns true if the pattern matched, false otherwise.  */

static bool
recognize_if_then_else (basic_block cond_bb,
			basic_block *then_bb, basic_block *else_bb)
{
  edge t, e;

  if (EDGE_COUNT (cond_bb->succs) != 2)
    return false;

  /* Find the then/else edges.  */
  t = EDGE_SUCC (cond_bb, 0);
  e = EDGE_SUCC (cond_bb, 1);
  if (!(t->flags & EDGE_TRUE_VALUE))
    std::swap (t, e);
  if (!(t->flags & EDGE_TRUE_VALUE)
      || !(e->flags & EDGE_FALSE_VALUE))
    return false;

  /* Check if the edge destinations point to the required block.  */
  if (*then_bb
      && t->dest != *then_bb)
    return false;
  if (*else_bb
      && e->dest != *else_bb)
    return false;

  if (!*then_bb)
    *then_bb = t->dest;
  if (!*else_bb)
    *else_bb = e->dest;

  return true;
}

/* Verify if the basic block BB does not have side-effects.  Return
   true in this case, else false.  */

static bool
bb_no_side_effects_p (basic_block bb)
{
  gimple_stmt_iterator gsi;

  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
    {
      gimple *stmt = gsi_stmt (gsi);

      if (is_gimple_debug (stmt))
	continue;

      if (gimple_has_side_effects (stmt)
	  || gimple_uses_undefined_value_p (stmt)
	  || gimple_could_trap_p (stmt)
	  || gimple_vuse (stmt)
	  /* const calls don't match any of the above, yet they could
	     still have some side-effects - they could contain
	     gimple_could_trap_p statements, like floating point
	     exceptions or integer division by zero.  See PR70586.
	     FIXME: perhaps gimple_has_side_effects or gimple_could_trap_p
	     should handle this.  */
	  || is_gimple_call (stmt))
	return false;
    }

  return true;
}

/* Return true if BB is an empty forwarder block to TO_BB.  */

static bool
forwarder_block_to (basic_block bb, basic_block to_bb)
{
  return empty_block_p (bb)
	 && single_succ_p (bb)
	 && single_succ (bb) == to_bb;
}

/* Verify if all PHI node arguments in DEST for edges from BB1 or
   BB2 to DEST are the same.  This makes the CFG merge point
   free from side-effects.  Return true in this case, else false.  */

static bool
same_phi_args_p (basic_block bb1, basic_block bb2, basic_block dest)
{
  edge e1 = find_edge (bb1, dest);
  edge e2 = find_edge (bb2, dest);
  gphi_iterator gsi;
  gphi *phi;

  for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
    {
      phi = gsi.phi ();
      if (!operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi, e1),
			    PHI_ARG_DEF_FROM_EDGE (phi, e2), 0))
        return false;
    }

  return true;
}

/* Return the best representative SSA name for CANDIDATE which is used
   in a bit test.  */

static tree
get_name_for_bit_test (tree candidate)
{
  /* Skip single-use names in favor of using the name from a
     non-widening conversion definition.  */
  if (TREE_CODE (candidate) == SSA_NAME
      && has_single_use (candidate))
    {
      gimple *def_stmt = SSA_NAME_DEF_STMT (candidate);
      if (is_gimple_assign (def_stmt)
	  && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt)))
	{
	  if (TYPE_PRECISION (TREE_TYPE (candidate))
	      <= TYPE_PRECISION (TREE_TYPE (gimple_assign_rhs1 (def_stmt))))
	    return gimple_assign_rhs1 (def_stmt);
	}
    }

  return candidate;
}

/* Recognize a single bit test pattern in GIMPLE_COND and its defining
   statements.  Store the name being tested in *NAME and the bit
   in *BIT.  The GIMPLE_COND computes *NAME & (1 << *BIT).
   Returns true if the pattern matched, false otherwise.  */

static bool
recognize_single_bit_test (gcond *cond, tree *name, tree *bit, bool inv)
{
  gimple *stmt;

  /* Get at the definition of the result of the bit test.  */
  if (gimple_cond_code (cond) != (inv ? EQ_EXPR : NE_EXPR)
      || TREE_CODE (gimple_cond_lhs (cond)) != SSA_NAME
      || !integer_zerop (gimple_cond_rhs (cond)))
    return false;
  stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond));
  if (!is_gimple_assign (stmt))
    return false;

  /* Look at which bit is tested.  One form to recognize is
     D.1985_5 = state_3(D) >> control1_4(D);
     D.1986_6 = (int) D.1985_5;
     D.1987_7 = op0 & 1;
     if (D.1987_7 != 0)  */
  if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
      && integer_onep (gimple_assign_rhs2 (stmt))
      && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME)
    {
      tree orig_name = gimple_assign_rhs1 (stmt);

      /* Look through copies and conversions to eventually
	 find the stmt that computes the shift.  */
      stmt = SSA_NAME_DEF_STMT (orig_name);

      while (is_gimple_assign (stmt)
	     && ((CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (stmt))
		  && (TYPE_PRECISION (TREE_TYPE (gimple_assign_lhs (stmt)))
		      <= TYPE_PRECISION (TREE_TYPE (gimple_assign_rhs1 (stmt))))
		  && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME)
		 || gimple_assign_ssa_name_copy_p (stmt)))
	stmt = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmt));

      /* If we found such, decompose it.  */
      if (is_gimple_assign (stmt)
	  && gimple_assign_rhs_code (stmt) == RSHIFT_EXPR)
	{
	  /* op0 & (1 << op1) */
	  *bit = gimple_assign_rhs2 (stmt);
	  *name = gimple_assign_rhs1 (stmt);
	}
      else
	{
	  /* t & 1 */
	  *bit = integer_zero_node;
	  *name = get_name_for_bit_test (orig_name);
	}

      return true;
    }

  /* Another form is
     D.1987_7 = op0 & (1 << CST)
     if (D.1987_7 != 0)  */
  if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
      && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
      && integer_pow2p (gimple_assign_rhs2 (stmt)))
    {
      *name = gimple_assign_rhs1 (stmt);
      *bit = build_int_cst (integer_type_node,
			    tree_log2 (gimple_assign_rhs2 (stmt)));
      return true;
    }

  /* Another form is
     D.1986_6 = 1 << control1_4(D)
     D.1987_7 = op0 & D.1986_6
     if (D.1987_7 != 0)  */
  if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
      && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
      && TREE_CODE (gimple_assign_rhs2 (stmt)) == SSA_NAME)
    {
      gimple *tmp;

      /* Both arguments of the BIT_AND_EXPR can be the single-bit
	 specifying expression.  */
      tmp = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmt));
      if (is_gimple_assign (tmp)
	  && gimple_assign_rhs_code (tmp) == LSHIFT_EXPR
	  && integer_onep (gimple_assign_rhs1 (tmp)))
	{
	  *name = gimple_assign_rhs2 (stmt);
	  *bit = gimple_assign_rhs2 (tmp);
	  return true;
	}

      tmp = SSA_NAME_DEF_STMT (gimple_assign_rhs2 (stmt));
      if (is_gimple_assign (tmp)
	  && gimple_assign_rhs_code (tmp) == LSHIFT_EXPR
	  && integer_onep (gimple_assign_rhs1 (tmp)))
	{
	  *name = gimple_assign_rhs1 (stmt);
	  *bit = gimple_assign_rhs2 (tmp);
	  return true;
	}
    }

  return false;
}

/* Recognize a bit test pattern in a GIMPLE_COND and its defining
   statements.  Store the name being tested in *NAME and the bits
   in *BITS.  The COND_EXPR computes *NAME & *BITS.
   Returns true if the pattern matched, false otherwise.  */

static bool
recognize_bits_test (gcond *cond, tree *name, tree *bits, bool inv)
{
  gimple *stmt;

  /* Get at the definition of the result of the bit test.  */
  if (gimple_cond_code (cond) != (inv ? EQ_EXPR : NE_EXPR)
      || TREE_CODE (gimple_cond_lhs (cond)) != SSA_NAME
      || !integer_zerop (gimple_cond_rhs (cond)))
    return false;
  stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond));
  if (!is_gimple_assign (stmt)
      || gimple_assign_rhs_code (stmt) != BIT_AND_EXPR)
    return false;

  *name = get_name_for_bit_test (gimple_assign_rhs1 (stmt));
  *bits = gimple_assign_rhs2 (stmt);

  return true;
}


/* Update profile after code in outer_cond_bb was adjusted so
   outer_cond_bb has no condition.  */

static void
update_profile_after_ifcombine (basic_block inner_cond_bb,
			        basic_block outer_cond_bb)
{
  edge outer_to_inner = find_edge (outer_cond_bb, inner_cond_bb);
  edge outer2 = (EDGE_SUCC (outer_cond_bb, 0) == outer_to_inner
		 ? EDGE_SUCC (outer_cond_bb, 1)
		 : EDGE_SUCC (outer_cond_bb, 0));
  edge inner_taken = EDGE_SUCC (inner_cond_bb, 0);
  edge inner_not_taken = EDGE_SUCC (inner_cond_bb, 1);

  if (inner_taken->dest != outer2->dest)
    std::swap (inner_taken, inner_not_taken);
  gcc_assert (inner_taken->dest == outer2->dest);

  /* In the following we assume that inner_cond_bb has single predecessor.  */
  gcc_assert (single_pred_p (inner_cond_bb));

  /* Path outer_cond_bb->(outer2) needs to be merged into path
     outer_cond_bb->(outer_to_inner)->inner_cond_bb->(inner_taken)
     and probability of inner_not_taken updated.  */

  inner_cond_bb->count = outer_cond_bb->count;

  /* Handle special case where inner_taken probability is always. In this case
     we know that the overall outcome will be always as well, but combining
     probabilities will be conservative because it does not know that
     outer2->probability is inverse of outer_to_inner->probability.  */
  if (inner_taken->probability == profile_probability::always ())
    ;
  else
    inner_taken->probability = outer2->probability + outer_to_inner->probability
			       * inner_taken->probability;
  inner_not_taken->probability = profile_probability::always ()
				 - inner_taken->probability;

  outer_to_inner->probability = profile_probability::always ();
  outer2->probability = profile_probability::never ();
}

/* If-convert on a and pattern with a common else block.  The inner
   if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB.
   inner_inv, outer_inv and result_inv indicate whether the conditions
   are inverted.
   Returns true if the edges to the common else basic-block were merged.  */

static bool
ifcombine_ifandif (basic_block inner_cond_bb, bool inner_inv,
		   basic_block outer_cond_bb, bool outer_inv, bool result_inv)
{
  gimple_stmt_iterator gsi;
  gimple *inner_stmt, *outer_stmt;
  gcond *inner_cond, *outer_cond;
  tree name1, name2, bit1, bit2, bits1, bits2;

  inner_stmt = last_stmt (inner_cond_bb);
  if (!inner_stmt
      || gimple_code (inner_stmt) != GIMPLE_COND)
    return false;
  inner_cond = as_a <gcond *> (inner_stmt);

  outer_stmt = last_stmt (outer_cond_bb);
  if (!outer_stmt
      || gimple_code (outer_stmt) != GIMPLE_COND)
    return false;
  outer_cond = as_a <gcond *> (outer_stmt);

  /* See if we test a single bit of the same name in both tests.  In
     that case remove the outer test, merging both else edges,
     and change the inner one to test for
     name & (bit1 | bit2) == (bit1 | bit2).  */
  if (recognize_single_bit_test (inner_cond, &name1, &bit1, inner_inv)
      && recognize_single_bit_test (outer_cond, &name2, &bit2, outer_inv)
      && name1 == name2)
    {
      tree t, t2;

      /* Do it.  */
      gsi = gsi_for_stmt (inner_cond);
      t = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
		       build_int_cst (TREE_TYPE (name1), 1), bit1);
      t2 = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
		        build_int_cst (TREE_TYPE (name1), 1), bit2);
      t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), t, t2);
      t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
				    true, GSI_SAME_STMT);
      t2 = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
      t2 = force_gimple_operand_gsi (&gsi, t2, true, NULL_TREE,
				     true, GSI_SAME_STMT);
      t = fold_build2 (result_inv ? NE_EXPR : EQ_EXPR,
		       boolean_type_node, t2, t);
      t = canonicalize_cond_expr_cond (t);
      if (!t)
	return false;
      gimple_cond_set_condition_from_tree (inner_cond, t);
      update_stmt (inner_cond);

      /* Leave CFG optimization to cfg_cleanup.  */
      gimple_cond_set_condition_from_tree (outer_cond,
	outer_inv ? boolean_false_node : boolean_true_node);
      update_stmt (outer_cond);

      update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);

      if (dump_file)
	{
	  fprintf (dump_file, "optimizing double bit test to ");
	  print_generic_expr (dump_file, name1);
	  fprintf (dump_file, " & T == T\nwith temporary T = (1 << ");
	  print_generic_expr (dump_file, bit1);
	  fprintf (dump_file, ") | (1 << ");
	  print_generic_expr (dump_file, bit2);
	  fprintf (dump_file, ")\n");
	}

      return true;
    }

  /* See if we have two bit tests of the same name in both tests.
     In that case remove the outer test and change the inner one to
     test for name & (bits1 | bits2) != 0.  */
  else if (recognize_bits_test (inner_cond, &name1, &bits1, !inner_inv)
      && recognize_bits_test (outer_cond, &name2, &bits2, !outer_inv))
    {
      gimple_stmt_iterator gsi;
      tree t;

      /* Find the common name which is bit-tested.  */
      if (name1 == name2)
	;
      else if (bits1 == bits2)
	{
	  std::swap (name2, bits2);
	  std::swap (name1, bits1);
	}
      else if (name1 == bits2)
	std::swap (name2, bits2);
      else if (bits1 == name2)
	std::swap (name1, bits1);
      else
	return false;

      /* As we strip non-widening conversions in finding a common
         name that is tested make sure to end up with an integral
	 type for building the bit operations.  */
      if (TYPE_PRECISION (TREE_TYPE (bits1))
	  >= TYPE_PRECISION (TREE_TYPE (bits2)))
	{
	  bits1 = fold_convert (unsigned_type_for (TREE_TYPE (bits1)), bits1);
	  name1 = fold_convert (TREE_TYPE (bits1), name1);
	  bits2 = fold_convert (unsigned_type_for (TREE_TYPE (bits2)), bits2);
	  bits2 = fold_convert (TREE_TYPE (bits1), bits2);
	}
      else
	{
	  bits2 = fold_convert (unsigned_type_for (TREE_TYPE (bits2)), bits2);
	  name1 = fold_convert (TREE_TYPE (bits2), name1);
	  bits1 = fold_convert (unsigned_type_for (TREE_TYPE (bits1)), bits1);
	  bits1 = fold_convert (TREE_TYPE (bits2), bits1);
	}

      /* Do it.  */
      gsi = gsi_for_stmt (inner_cond);
      t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), bits1, bits2);
      t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
				    true, GSI_SAME_STMT);
      t = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
      t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
				    true, GSI_SAME_STMT);
      t = fold_build2 (result_inv ? NE_EXPR : EQ_EXPR, boolean_type_node, t,
		       build_int_cst (TREE_TYPE (t), 0));
      t = canonicalize_cond_expr_cond (t);
      if (!t)
	return false;
      gimple_cond_set_condition_from_tree (inner_cond, t);
      update_stmt (inner_cond);

      /* Leave CFG optimization to cfg_cleanup.  */
      gimple_cond_set_condition_from_tree (outer_cond,
	outer_inv ? boolean_false_node : boolean_true_node);
      update_stmt (outer_cond);
      update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);

      if (dump_file)
	{
	  fprintf (dump_file, "optimizing bits or bits test to ");
	  print_generic_expr (dump_file, name1);
	  fprintf (dump_file, " & T != 0\nwith temporary T = ");
	  print_generic_expr (dump_file, bits1);
	  fprintf (dump_file, " | ");
	  print_generic_expr (dump_file, bits2);
	  fprintf (dump_file, "\n");
	}

      return true;
    }

  /* See if we have two comparisons that we can merge into one.  */
  else if (TREE_CODE_CLASS (gimple_cond_code (inner_cond)) == tcc_comparison
	   && TREE_CODE_CLASS (gimple_cond_code (outer_cond)) == tcc_comparison)
    {
      tree t;
      enum tree_code inner_cond_code = gimple_cond_code (inner_cond);
      enum tree_code outer_cond_code = gimple_cond_code (outer_cond);

      /* Invert comparisons if necessary (and possible).  */
      if (inner_inv)
	inner_cond_code = invert_tree_comparison (inner_cond_code,
	  HONOR_NANS (gimple_cond_lhs (inner_cond)));
      if (inner_cond_code == ERROR_MARK)
	return false;
      if (outer_inv)
	outer_cond_code = invert_tree_comparison (outer_cond_code,
	  HONOR_NANS (gimple_cond_lhs (outer_cond)));
      if (outer_cond_code == ERROR_MARK)
	return false;
      /* Don't return false so fast, try maybe_fold_or_comparisons?  */

      if (!(t = maybe_fold_and_comparisons (inner_cond_code,
					    gimple_cond_lhs (inner_cond),
					    gimple_cond_rhs (inner_cond),
					    outer_cond_code,
					    gimple_cond_lhs (outer_cond),
					    gimple_cond_rhs (outer_cond))))
	{
	  tree t1, t2;
	  gimple_stmt_iterator gsi;
	  bool logical_op_non_short_circuit = LOGICAL_OP_NON_SHORT_CIRCUIT;
	  if (PARAM_VALUE (PARAM_LOGICAL_OP_NON_SHORT_CIRCUIT) != -1)
	    logical_op_non_short_circuit
	      = PARAM_VALUE (PARAM_LOGICAL_OP_NON_SHORT_CIRCUIT);
	  if (!logical_op_non_short_circuit || flag_sanitize_coverage)
	    return false;
	  /* Only do this optimization if the inner bb contains only the conditional. */
	  if (!gsi_one_before_end_p (gsi_start_nondebug_after_labels_bb (inner_cond_bb)))
	    return false;
	  t1 = fold_build2_loc (gimple_location (inner_cond),
				inner_cond_code,
				boolean_type_node,
				gimple_cond_lhs (inner_cond),
				gimple_cond_rhs (inner_cond));
	  t2 = fold_build2_loc (gimple_location (outer_cond),
				outer_cond_code,
				boolean_type_node,
				gimple_cond_lhs (outer_cond),
				gimple_cond_rhs (outer_cond));
	  t = fold_build2_loc (gimple_location (inner_cond),
			       TRUTH_AND_EXPR, boolean_type_node, t1, t2);
	  if (result_inv)
	    {
	      t = fold_build1 (TRUTH_NOT_EXPR, TREE_TYPE (t), t);
	      result_inv = false;
	    }
	  gsi = gsi_for_stmt (inner_cond);
	  t = force_gimple_operand_gsi_1 (&gsi, t, is_gimple_condexpr, NULL, true,
					  GSI_SAME_STMT);
        }
      if (result_inv)
	t = fold_build1 (TRUTH_NOT_EXPR, TREE_TYPE (t), t);
      t = canonicalize_cond_expr_cond (t);
      if (!t)
	return false;
      gimple_cond_set_condition_from_tree (inner_cond, t);
      update_stmt (inner_cond);

      /* Leave CFG optimization to cfg_cleanup.  */
      gimple_cond_set_condition_from_tree (outer_cond,
	outer_inv ? boolean_false_node : boolean_true_node);
      update_stmt (outer_cond);
      update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);

      if (dump_file)
	{
	  fprintf (dump_file, "optimizing two comparisons to ");
	  print_generic_expr (dump_file, t);
	  fprintf (dump_file, "\n");
	}

      return true;
    }

  return false;
}

/* Helper function for tree_ssa_ifcombine_bb.  Recognize a CFG pattern and
   dispatch to the appropriate if-conversion helper for a particular
   set of INNER_COND_BB, OUTER_COND_BB, THEN_BB and ELSE_BB.
   PHI_PRED_BB should be one of INNER_COND_BB, THEN_BB or ELSE_BB.  */

static bool
tree_ssa_ifcombine_bb_1 (basic_block inner_cond_bb, basic_block outer_cond_bb,
			 basic_block then_bb, basic_block else_bb,
			 basic_block phi_pred_bb)
{
  /* The && form is characterized by a common else_bb with
     the two edges leading to it mergable.  The latter is
     guaranteed by matching PHI arguments in the else_bb and
     the inner cond_bb having no side-effects.  */
  if (phi_pred_bb != else_bb
      && recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &else_bb)
      && same_phi_args_p (outer_cond_bb, phi_pred_bb, else_bb))
    {
      /* We have
	   <outer_cond_bb>
	     if (q) goto inner_cond_bb; else goto else_bb;
	   <inner_cond_bb>
	     if (p) goto ...; else goto else_bb;
	     ...
	   <else_bb>
	     ...
       */
      return ifcombine_ifandif (inner_cond_bb, false, outer_cond_bb, false,
				false);
    }

  /* And a version where the outer condition is negated.  */
  if (phi_pred_bb != else_bb
      && recognize_if_then_else (outer_cond_bb, &else_bb, &inner_cond_bb)
      && same_phi_args_p (outer_cond_bb, phi_pred_bb, else_bb))
    {
      /* We have
	   <outer_cond_bb>
	     if (q) goto else_bb; else goto inner_cond_bb;
	   <inner_cond_bb>
	     if (p) goto ...; else goto else_bb;
	     ...
	   <else_bb>
	     ...
       */
      return ifcombine_ifandif (inner_cond_bb, false, outer_cond_bb, true,
				false);
    }

  /* The || form is characterized by a common then_bb with the
     two edges leading to it mergable.  The latter is guaranteed
     by matching PHI arguments in the then_bb and the inner cond_bb
     having no side-effects.  */
  if (phi_pred_bb != then_bb
      && recognize_if_then_else (outer_cond_bb, &then_bb, &inner_cond_bb)
      && same_phi_args_p (outer_cond_bb, phi_pred_bb, then_bb))
    {
      /* We have
	   <outer_cond_bb>
	     if (q) goto then_bb; else goto inner_cond_bb;
	   <inner_cond_bb>
	     if (q) goto then_bb; else goto ...;
	   <then_bb>
	     ...
       */
      return ifcombine_ifandif (inner_cond_bb, true, outer_cond_bb, true,
				true);
    }

  /* And a version where the outer condition is negated.  */
  if (phi_pred_bb != then_bb
      && recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &then_bb)
      && same_phi_args_p (outer_cond_bb, phi_pred_bb, then_bb))
    {
      /* We have
	   <outer_cond_bb>
	     if (q) goto inner_cond_bb; else goto then_bb;
	   <inner_cond_bb>
	     if (q) goto then_bb; else goto ...;
	   <then_bb>
	     ...
       */
      return ifcombine_ifandif (inner_cond_bb, true, outer_cond_bb, false,
				true);
    }

  return false;
}

/* Recognize a CFG pattern and dispatch to the appropriate
   if-conversion helper.  We start with BB as the innermost
   worker basic-block.  Returns true if a transformation was done.  */

static bool
tree_ssa_ifcombine_bb (basic_block inner_cond_bb)
{
  basic_block then_bb = NULL, else_bb = NULL;

  if (!recognize_if_then_else (inner_cond_bb, &then_bb, &else_bb))
    return false;

  /* Recognize && and || of two conditions with a common
     then/else block which entry edges we can merge.  That is:
       if (a || b)
	 ;
     and
       if (a && b)
	 ;
     This requires a single predecessor of the inner cond_bb.  */
  if (single_pred_p (inner_cond_bb)
      && bb_no_side_effects_p (inner_cond_bb))
    {
      basic_block outer_cond_bb = single_pred (inner_cond_bb);

      if (tree_ssa_ifcombine_bb_1 (inner_cond_bb, outer_cond_bb,
				   then_bb, else_bb, inner_cond_bb))
	return true;

      if (forwarder_block_to (else_bb, then_bb))
	{
	  /* Other possibilities for the && form, if else_bb is
	     empty forwarder block to then_bb.  Compared to the above simpler
	     forms this can be treated as if then_bb and else_bb were swapped,
	     and the corresponding inner_cond_bb not inverted because of that.
	     For same_phi_args_p we look at equality of arguments between
	     edge from outer_cond_bb and the forwarder block.  */
	  if (tree_ssa_ifcombine_bb_1 (inner_cond_bb, outer_cond_bb, else_bb,
				       then_bb, else_bb))
	    return true;
	}
      else if (forwarder_block_to (then_bb, else_bb))
	{
	  /* Other possibilities for the || form, if then_bb is
	     empty forwarder block to else_bb.  Compared to the above simpler
	     forms this can be treated as if then_bb and else_bb were swapped,
	     and the corresponding inner_cond_bb not inverted because of that.
	     For same_phi_args_p we look at equality of arguments between
	     edge from outer_cond_bb and the forwarder block.  */
	  if (tree_ssa_ifcombine_bb_1 (inner_cond_bb, outer_cond_bb, else_bb,
				       then_bb, then_bb))
	    return true;
	}
    }

  return false;
}

/* Main entry for the tree if-conversion pass.  */

namespace {

const pass_data pass_data_tree_ifcombine =
{
  GIMPLE_PASS, /* type */
  "ifcombine", /* name */
  OPTGROUP_NONE, /* optinfo_flags */
  TV_TREE_IFCOMBINE, /* tv_id */
  ( PROP_cfg | PROP_ssa ), /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  TODO_update_ssa, /* todo_flags_finish */
};

class pass_tree_ifcombine : public gimple_opt_pass
{
public:
  pass_tree_ifcombine (gcc::context *ctxt)
    : gimple_opt_pass (pass_data_tree_ifcombine, ctxt)
  {}

  /* opt_pass methods: */
  virtual unsigned int execute (function *);

}; // class pass_tree_ifcombine

unsigned int
pass_tree_ifcombine::execute (function *fun)
{
  basic_block *bbs;
  bool cfg_changed = false;
  int i;

  bbs = single_pred_before_succ_order ();
  calculate_dominance_info (CDI_DOMINATORS);

  /* Search every basic block for COND_EXPR we may be able to optimize.

     We walk the blocks in order that guarantees that a block with
     a single predecessor is processed after the predecessor.
     This ensures that we collapse outter ifs before visiting the
     inner ones, and also that we do not try to visit a removed
     block.  This is opposite of PHI-OPT, because we cascade the
     combining rather than cascading PHIs. */
  for (i = n_basic_blocks_for_fn (fun) - NUM_FIXED_BLOCKS - 1; i >= 0; i--)
    {
      basic_block bb = bbs[i];
      gimple *stmt = last_stmt (bb);

      if (stmt
	  && gimple_code (stmt) == GIMPLE_COND)
	if (tree_ssa_ifcombine_bb (bb))
	  {
	    /* Clear range info from all stmts in BB which is now executed
	       conditional on a always true/false condition.  */
	    reset_flow_sensitive_info_in_bb (bb);
	    cfg_changed |= true;
	  }
    }

  free (bbs);

  return cfg_changed ? TODO_cleanup_cfg : 0;
}

} // anon namespace

gimple_opt_pass *
make_pass_tree_ifcombine (gcc::context *ctxt)
{
  return new pass_tree_ifcombine (ctxt);
}