gcc/gimple-range-stmt.cc

/* Code for GIMPLE range related routines.
   Copyright (C) 2019-2020 Free Software Foundation, Inc.
   Contributed by Andrew MacLeod <amacleod@redhat.com>
   and Aldy Hernandez <aldyh@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 "backend.h"
#include "insn-codes.h"
#include "rtl.h"
#include "tree.h"
#include "gimple.h"
#include "ssa.h"
#include "gimple-iterator.h"
#include "tree-cfg.h"
#include "gimple-range-stmt.h"

// Adjust the range for a pointer difference where the operands came
// from a memchr.
//
// This notices the following sequence:
//
//	def = __builtin_memchr (arg, 0, sz)
//	n = def - arg
//
// The range for N can be narrowed to [0, PTRDIFF_MAX - 1].

static void
adjust_pointer_diff_expr (irange &res, const gimple *diff_stmt)
{
  tree op0 = gimple_assign_rhs1 (diff_stmt);
  tree op1 = gimple_assign_rhs2 (diff_stmt);
  tree op0_ptype = TREE_TYPE (TREE_TYPE (op0));
  tree op1_ptype = TREE_TYPE (TREE_TYPE (op1));
  gimple *call;

  if (TREE_CODE (op0) == SSA_NAME
      && TREE_CODE (op1) == SSA_NAME
      && (call = SSA_NAME_DEF_STMT (op0))
      && is_gimple_call (call)
      && gimple_call_builtin_p (call, BUILT_IN_MEMCHR)
      && TYPE_MODE (op0_ptype) == TYPE_MODE (char_type_node)
      && TYPE_PRECISION (op0_ptype) == TYPE_PRECISION (char_type_node)
      && TYPE_MODE (op1_ptype) == TYPE_MODE (char_type_node)
      && TYPE_PRECISION (op1_ptype) == TYPE_PRECISION (char_type_node)
      && gimple_call_builtin_p (call, BUILT_IN_MEMCHR)
      && vrp_operand_equal_p (op1, gimple_call_arg (call, 0))
      && integer_zerop (gimple_call_arg (call, 1)))
    {
      tree max = vrp_val_max (ptrdiff_type_node);
      wide_int wmax = wi::to_wide (max, TYPE_PRECISION (TREE_TYPE (max)));
      tree expr_type = gimple_expr_type (diff_stmt);
      tree range_min = build_zero_cst (expr_type);
      tree range_max = wide_int_to_tree (expr_type, wmax - 1);
      int_range<1> r (range_min, range_max);
      res.intersect (r);
    }
}

// This function looks for situations when walking the use/def chains
// may provide additonal contextual range information not exposed on
// this statement.  Like knowing the IMAGPART return value from a
// builtin function is a boolean result.

// We should rework how we're called, as we have an op_unknown entry
// for IMAGPART_EXPR and POINTER_DIFF_EXPR in range-ops just so this
// function gets called.

static void
gimple_range_adjustment (irange &res, const gimple *stmt)
{
  switch (gimple_expr_code (stmt))
    {
    case POINTER_DIFF_EXPR:
      adjust_pointer_diff_expr (res, stmt);
      return;

    case IMAGPART_EXPR:
      {
	tree name = TREE_OPERAND (gimple_assign_rhs1 (stmt), 0);
	if (TREE_CODE (name) == SSA_NAME)
	  {
	    gimple *def_stmt = SSA_NAME_DEF_STMT (name);
	    if (def_stmt && is_gimple_call (def_stmt)
		&& gimple_call_internal_p (def_stmt))
	      {
		switch (gimple_call_internal_fn (def_stmt))
		  {
		  case IFN_ADD_OVERFLOW:
		  case IFN_SUB_OVERFLOW:
		  case IFN_MUL_OVERFLOW:
		  case IFN_ATOMIC_COMPARE_EXCHANGE:
		    {
		      int_range<1> r;
		      r.set_varying (boolean_type_node);
		      tree type = TREE_TYPE (gimple_assign_lhs (stmt));
		      range_cast (r, type);
		      res.intersect (r);
		    }
		  default:
		    break;
		  }
	      }
	  }
	break;
      }

    default:
      break;
    }
}

// ------------------------------------------------------------------------

// This function will calculate the "constant" range on edge E from
// switch SW returning it in R, and return the switch statement
// itself.  This is currently not very efficent as the way we
// represent switches in GIMPLE does not map well to this calculation.

static gimple *
calc_range_for_switch_on_edge (irange &r, gswitch *sw, edge e)
{
  unsigned x, lim;
  lim = gimple_switch_num_labels (sw);
  tree type = TREE_TYPE (gimple_switch_index (sw));

  // ADA and FORTRAN currently have cases where the index is 64 bits
  // and the case arguments are 32 bit, causing a trap when we create
  // a case_range.  Until this is resolved
  // (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87798) punt on
  // these switches.  Furthermore, cfamily fails during a bootstrap
  // due to a signed index and unsigned cases.  So punting unless
  // types_compatible_p () for now.
  tree case_type = TREE_TYPE (CASE_LOW (gimple_switch_label (sw, 1)));
  if (lim > 1 && !types_compatible_p (type, case_type))
    return NULL;

  edge default_edge = gimple_switch_default_edge (cfun, sw);
  if (e != default_edge)
    {
      r.set_undefined ();
      // Union all the ranges for each switch edge, ignoring the
      // default edge.
      for (x = 1; x < lim; x++)
	{
	  if (gimple_switch_edge (cfun, sw, x) != e)
	    continue;
	  tree low = CASE_LOW (gimple_switch_label (sw, x));
	  tree high = CASE_HIGH (gimple_switch_label (sw, x));
	  if (!high)
	    high = low;
	  int_range<1> case_range (low, high);
	  r.union_ (case_range);
	}
    }
  else
    {
      r.set_varying (type);
      // Loop through all the switches edges, ignoring the default
      // edge, while intersecting the ranges not covered by the case.
      for (x = 1; x < lim; x++)
	{
	  // Some other edge could still point to the default edge
	  // destination.  Ignore it.
	  if (gimple_switch_edge (cfun, sw, x) == default_edge)
	    continue;
	  tree low = CASE_LOW (gimple_switch_label (sw, x));
	  tree high = CASE_HIGH (gimple_switch_label (sw, x));
	  if (!high)
	    high = low;
	  int_range<1> case_range (low, high, VR_ANTI_RANGE);
	  r.intersect (case_range);
	}
    }
  return sw;
}


// If there is a range control statment at the end of block BB, return it.

gimple_stmt_iterator
gsi_outgoing_range_stmt (basic_block bb)
{
  gimple_stmt_iterator gsi = gsi_last_nondebug_bb (bb);
  if (!gsi_end_p (gsi))
    {
      gimple *s = gsi_stmt (gsi);
      if (is_a<gcond *> (s) || is_a<gswitch *> (s))
	return gsi;
    }
  return gsi_none ();
}


// If there is a range control statment at the end of block BB, return it.

gimple *
gimple_outgoing_range_stmt_p (basic_block bb)
{
  // This will return NULL if there is not a branch statement.
  return gsi_stmt (gsi_outgoing_range_stmt (bb));
}


// Calculate the range forced on on edge E by control flow, return it
// in R.  Return the statment which defines the range, otherwise
// return NULL

gimple *
gimple_outgoing_edge_range_p (irange &r, edge e)
{
  // Determine if there is an outgoing edge.
  gimple *s = gimple_outgoing_range_stmt_p (e->src);
  if (!s)
    return NULL;

  if (is_a<gcond *> (s))
    {
      if (e->flags & EDGE_TRUE_VALUE)
	r = int_range<1> (boolean_true_node, boolean_true_node);
      else if (e->flags & EDGE_FALSE_VALUE)
	r = int_range<1> (boolean_false_node, boolean_false_node);
      else
	gcc_unreachable ();
      return s;
    }

  gcc_checking_assert (is_a<gswitch *> (s));
  gswitch *sw = as_a<gswitch *> (s);
  tree type = TREE_TYPE (gimple_switch_index (sw));

  if (!irange::supports_type_p (type))
    return NULL;

  return calc_range_for_switch_on_edge (r, sw, e);
}



// Fold this unary statement using R1 as operand1's range, returning
// the result in RES.  Return false if the operation fails.

bool
gimple_range_fold (const gimple *stmt, irange &res, const irange &r1)
{
  gcc_checking_assert (gimple_range_handler (stmt));

  tree type = gimple_expr_type (stmt);
  // Unary SSA operations require the LHS type as the second range.
  int_range<1> r2 (type);

  return gimple_range_fold (stmt, res, r1, r2);
}


// Fold this binary statement using R1 and R2 as the operands ranges,
// returning the result in RES.  Return false if the operation fails.

bool
gimple_range_fold (const gimple *stmt, irange &res,
		   const irange &r1, const irange &r2)
{
  gcc_checking_assert (gimple_range_handler (stmt));

  gimple_range_handler (stmt)->fold_range (res, gimple_expr_type (stmt),
					   r1, r2);

  // If there are any gimple lookups, do those now.
  gimple_range_adjustment (res, stmt);
  return true;
}

// Return the base of the RHS of an assignment.

tree
gimple_range_base_of_assignment (const gimple *stmt)
{
  gcc_checking_assert (gimple_code (stmt) == GIMPLE_ASSIGN);
  tree op1 = gimple_assign_rhs1 (stmt);
  if (gimple_assign_rhs_code (stmt) == ADDR_EXPR)
    return get_base_address (TREE_OPERAND (op1, 0));
  return op1;
}

// Return the first operand of this statement if it is a valid operand
// supported by ranges, otherwise return NULL_TREE.  Special case is
// &(SSA_NAME expr), return the SSA_NAME instead of the ADDR expr.

tree
gimple_range_operand1 (const gimple *stmt)
{
  gcc_checking_assert (gimple_range_handler (stmt));

  switch (gimple_code (stmt))
    {
      case GIMPLE_COND:
	return gimple_cond_lhs (stmt);
      case GIMPLE_ASSIGN:
	{
	  tree base = gimple_range_base_of_assignment (stmt);
	  if (base && TREE_CODE (base) == MEM_REF)
	    {
	      // If the base address is an SSA_NAME, we return it
	      // here.  This allows processing of the range of that
	      // name, while the rest of the expression is simply
	      // ignored.  The code in range_ops will see the
	      // ADDR_EXPR and do the right thing.
	      tree ssa = TREE_OPERAND (base, 0);
	      if (TREE_CODE (ssa) == SSA_NAME)
		return ssa;
	    }
	  return base;
	}
      default:
	break;
    }
  return NULL;
}


// Return the second operand of statement STMT, otherwise return NULL_TREE.

tree
gimple_range_operand2 (const gimple *stmt)
{
  gcc_checking_assert (gimple_range_handler (stmt));

  switch (gimple_code (stmt))
    {
    case GIMPLE_COND:
      return gimple_cond_rhs (stmt);
    case GIMPLE_ASSIGN:
      if (gimple_num_ops (stmt) >= 3)
	return gimple_assign_rhs2 (stmt);
    default:
      break;
    }
  return NULL_TREE;
}



// Calculate what we can determine of the range of this unary
// statement's operand if the lhs of the expression has the range
// LHS_RANGE.  Return false if nothing can be determined.

bool
gimple_range_calc_op1 (const gimple *stmt, irange &r, const irange &lhs_range)
{
  gcc_checking_assert (gimple_num_ops (stmt) < 3);
  // An empty range is viral, so return an empty range.

  tree type = TREE_TYPE (gimple_range_operand1 (stmt));
  if (lhs_range.undefined_p ())
    {
      r.set_undefined ();
      return true;
    }
  // Unary operations require the type of the first operand in the
  // second range position.
  int_range<1> type_range (type);
  return gimple_range_handler (stmt)->op1_range (r, type, lhs_range,
						 type_range);
}


// Calculate what we can determine of the range of this statement's
// first operand if the lhs of the expression has the range LHS_RANGE
// and the second operand has the range OP2_RANGE.  Return false if
// nothing can be determined.

bool
gimple_range_calc_op1 (const gimple *stmt, irange &r,
		       const irange &lhs_range, const irange &op2_range)
{
  // Unary operation are allowed to pass a range in for second operand
  // as there are often additional restrictions beyond the type which
  // can be imposed.  See operator_cast::op1_range.()
  tree type = TREE_TYPE (gimple_range_operand1 (stmt));
  // An empty range is viral, so return an empty range.
  if (op2_range.undefined_p () || lhs_range.undefined_p ())
    {
      r.set_undefined ();
      return true;
    }
  return gimple_range_handler (stmt)->op1_range (r, type, lhs_range,
						 op2_range);
}


// Calculate what we can determine of the range of this statement's
// second operand if the lhs of the expression has the range LHS_RANGE
// and the first operand has the range OP1_RANGE.  Return false if
// nothing can be determined.

bool
gimple_range_calc_op2 (const gimple *stmt, irange &r,
		       const irange &lhs_range, const irange &op1_range)
{
  tree type = TREE_TYPE (gimple_range_operand2 (stmt));
  // An empty range is viral, so return an empty range.
  if (op1_range.undefined_p () || lhs_range.undefined_p ())
    {
      r.set_undefined ();
      return true;
    }
  return gimple_range_handler (stmt)->op2_range (r, type, lhs_range,
						 op1_range);
}