go/expressions.cc

// expressions.cc -- Go frontend expression handling.

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "go-system.h"

#include <algorithm>

#include "go-c.h"
#include "gogo.h"
#include "go-diagnostics.h"
#include "go-encode-id.h"
#include "types.h"
#include "export.h"
#include "import.h"
#include "statements.h"
#include "lex.h"
#include "runtime.h"
#include "backend.h"
#include "expressions.h"
#include "ast-dump.h"

// Class Expression.

Expression::Expression(Expression_classification classification,
		       Location location)
  : classification_(classification), location_(location)
{
}

Expression::~Expression()
{
}

// Traverse the expressions.

int
Expression::traverse(Expression** pexpr, Traverse* traverse)
{
  Expression* expr = *pexpr;
  if ((traverse->traverse_mask() & Traverse::traverse_expressions) != 0)
    {
      int t = traverse->expression(pexpr);
      if (t == TRAVERSE_EXIT)
	return TRAVERSE_EXIT;
      else if (t == TRAVERSE_SKIP_COMPONENTS)
	return TRAVERSE_CONTINUE;
    }
  return expr->do_traverse(traverse);
}

// Traverse subexpressions of this expression.

int
Expression::traverse_subexpressions(Traverse* traverse)
{
  return this->do_traverse(traverse);
}

// A traversal used to set the location of subexpressions.

class Set_location : public Traverse
{
 public:
  Set_location(Location loc)
    : Traverse(traverse_expressions),
      loc_(loc)
  { }

  int
  expression(Expression** pexpr);

 private:
  Location loc_;
};

// Set the location of an expression.

int
Set_location::expression(Expression** pexpr)
{
  // Some expressions are shared or don't have an independent
  // location, so we shouldn't change their location.  This is the set
  // of expressions for which do_copy is just "return this" or
  // otherwise does not pass down the location.
  switch ((*pexpr)->classification())
    {
    case Expression::EXPRESSION_ERROR:
    case Expression::EXPRESSION_VAR_REFERENCE:
    case Expression::EXPRESSION_ENCLOSED_VAR_REFERENCE:
    case Expression::EXPRESSION_STRING:
    case Expression::EXPRESSION_FUNC_DESCRIPTOR:
    case Expression::EXPRESSION_TYPE:
    case Expression::EXPRESSION_BOOLEAN:
    case Expression::EXPRESSION_CONST_REFERENCE:
    case Expression::EXPRESSION_NIL:
    case Expression::EXPRESSION_TYPE_DESCRIPTOR:
    case Expression::EXPRESSION_GC_SYMBOL:
    case Expression::EXPRESSION_PTRMASK_SYMBOL:
    case Expression::EXPRESSION_TYPE_INFO:
    case Expression::EXPRESSION_STRUCT_FIELD_OFFSET:
      return TRAVERSE_CONTINUE;
    default:
      break;
    }

  (*pexpr)->location_ = this->loc_;
  return TRAVERSE_CONTINUE;
}

// Set the location of an expression and its subexpressions.

void
Expression::set_location(Location loc)
{
  this->location_ = loc;
  Set_location sl(loc);
  this->traverse_subexpressions(&sl);
}

// Default implementation for do_traverse for child classes.

int
Expression::do_traverse(Traverse*)
{
  return TRAVERSE_CONTINUE;
}

// This virtual function is called by the parser if the value of this
// expression is being discarded.  By default, we give an error.
// Expressions with side effects override.

bool
Expression::do_discarding_value()
{
  this->unused_value_error();
  return false;
}

// This virtual function is called to export expressions.  This will
// only be used by expressions which may be constant.

void
Expression::do_export(Export_function_body*) const
{
  go_unreachable();
}

// Write a name to the export data.

void
Expression::export_name(Export_function_body* efb, const Named_object* no)
{
  if (no->package() != NULL)
    {
      char buf[50];
      snprintf(buf, sizeof buf, "<p%d>", efb->package_index(no->package()));
      efb->write_c_string(buf);
    }

  if (!Gogo::is_hidden_name(no->name()))
    efb->write_string(no->name());
  else
    {
      efb->write_c_string(".");
      efb->write_string(Gogo::unpack_hidden_name(no->name()));
    }
}

// Give an error saying that the value of the expression is not used.

void
Expression::unused_value_error()
{
  if (this->type()->is_error())
    {
      go_assert(saw_errors());
      this->set_is_error();
    }
  else
    this->report_error(_("value computed is not used"));
}

// Note that this expression is an error.  This is called by children
// when they discover an error.

void
Expression::set_is_error()
{
  this->classification_ = EXPRESSION_ERROR;
}

// For children to call to report an error conveniently.

void
Expression::report_error(const char* msg)
{
  go_error_at(this->location_, "%s", msg);
  this->set_is_error();
}

// A convenience function for handling a type in do_is_untyped.  If
// TYPE is not abstract, return false.  Otherwise set *PTYPE to TYPE
// and return true.

bool
Expression::is_untyped_type(Type* type, Type** ptype)
{
  if (!type->is_abstract())
    return false;
  *ptype = type;
  return true;
}

// Report whether this is a type expression.

bool
Expression::is_type_expression() const
{
  if (this->classification_ == EXPRESSION_TYPE)
    return true;
  if (this->unknown_expression() != NULL)
    {
      Named_object* no = this->unknown_expression()->named_object();
      if (no->is_unknown())
	{
	  no = no->unknown_value()->real_named_object();
	  if (no == NULL)
	    return false;
	}
      return no->is_type();
    }
  if (this->unary_expression() != NULL
      && this->unary_expression()->op() == OPERATOR_MULT
      && this->unary_expression()->operand()->is_type_expression())
    return true;
  return false;
}

// Set types of variables and constants.  This is implemented by the
// child class.

void
Expression::determine_type(Gogo* gogo, const Type_context* context)
{
  this->do_determine_type(gogo, context);
}

// Set types when there is no context.

void
Expression::determine_type_no_context(Gogo* gogo)
{
  Type_context context;
  this->do_determine_type(gogo, &context);
}

// Return true if two expressions refer to the same variable or struct
// field.  This can only be true when there are no side effects.

bool
Expression::is_same_variable(Expression* a, Expression* b)
{
  if (a->classification() != b->classification())
    return false;

  Var_expression* av = a->var_expression();
  if (av != NULL)
    return av->named_object() == b->var_expression()->named_object();

  Field_reference_expression* af = a->field_reference_expression();
  if (af != NULL)
    {
      Field_reference_expression* bf = b->field_reference_expression();
      return (af->field_index() == bf->field_index()
	      && Expression::is_same_variable(af->expr(), bf->expr()));
    }

  Unary_expression* au = a->unary_expression();
  if (au != NULL)
    {
      Unary_expression* bu = b->unary_expression();
      return (au->op() == OPERATOR_MULT
	      && bu->op() == OPERATOR_MULT
	      && Expression::is_same_variable(au->operand(),
					      bu->operand()));
    }

  Array_index_expression* aie = a->array_index_expression();
  if (aie != NULL)
    {
      Array_index_expression* bie = b->array_index_expression();
      return (aie->end() == NULL
	      && bie->end() == NULL
	      && Expression::is_same_variable(aie->array(), bie->array())
	      && Expression::is_same_variable(aie->start(), bie->start()));
    }

  Numeric_constant aval;
  if (a->numeric_constant_value(&aval))
    {
      Numeric_constant bval;
      if (b->numeric_constant_value(&bval))
	return aval.equals(bval);
    }

  return false;
}

// Return an expression handling any conversions which must be done during
// assignment.

Expression*
Expression::convert_for_assignment(Gogo* gogo, Type* lhs_type,
				   Expression* rhs, Location location)
{
  Type* rhs_type = rhs->type();
  if (lhs_type->is_error()
      || rhs_type->is_error()
      || rhs->is_error_expression())
    return Expression::make_error(location);

  bool are_identical = Type::are_identical(lhs_type, rhs_type,
					   (Type::COMPARE_ERRORS
					    | Type::COMPARE_TAGS),
					   NULL);
  Expression* ret;
  if (!are_identical && lhs_type->interface_type() != NULL)
    {
      // Type to interface conversions have been made explicit early.
      go_assert(rhs_type->interface_type() != NULL);
      ret = Expression::convert_interface_to_interface(gogo, lhs_type, rhs,
						       false, location);
    }
  else if (!are_identical && rhs_type->interface_type() != NULL)
    ret = Expression::convert_interface_to_type(gogo, lhs_type, rhs, location);
  else if (lhs_type->is_slice_type() && rhs_type->is_nil_type())
    {
      // Assigning nil to a slice.
      Expression* nil = Expression::make_nil(location);
      Expression* zero = Expression::make_integer_ul(0, NULL, location);
      ret = Expression::make_slice_value(lhs_type, nil, zero, zero, location);
    }
  else if (rhs_type->is_nil_type())
    ret = Expression::make_nil(location);
  else if (are_identical)
    {
      if (lhs_type->forwarded() != rhs_type->forwarded())
	{
	  // Different but identical types require an explicit
	  // conversion.  This happens with type aliases.
	  return Expression::make_cast(lhs_type, rhs, location);
	}

      // No conversion is needed.
      return rhs;
    }
  else if (lhs_type->points_to() != NULL)
    ret = Expression::make_unsafe_cast(lhs_type, rhs, location);
  else if (lhs_type->is_numeric_type())
    ret = Expression::make_cast(lhs_type, rhs, location);
  else if ((lhs_type->struct_type() != NULL
            && rhs_type->struct_type() != NULL)
           || (lhs_type->array_type() != NULL
               && rhs_type->array_type() != NULL))
    {
      // This conversion must be permitted by Go, or we wouldn't have
      // gotten here.
      ret = Expression::make_unsafe_cast(lhs_type, rhs, location);
    }
  else
    return rhs;

  Type_context context(lhs_type, false);
  ret->determine_type(gogo, &context);
  return ret;
}

// Return an expression for a conversion from a non-interface type to an
// interface type.  If ON_STACK is true, it can allocate the storage on
// stack.

Expression*
Expression::convert_type_to_interface(Type* lhs_type, Expression* rhs,
                                      bool on_stack, Location location)
{
  Interface_type* lhs_interface_type = lhs_type->interface_type();
  bool lhs_is_empty = lhs_interface_type->is_empty();

  // Since RHS_TYPE is a static type, we can create the interface
  // method table at compile time.

  // When setting an interface to nil, we just set both fields to
  // NULL.
  Type* rhs_type = rhs->type();
  if (rhs_type->is_nil_type())
    {
      Expression* nil = Expression::make_nil(location);
      return Expression::make_interface_value(lhs_type, nil, nil, location);
    }

  // This should have been checked already.
  if (!lhs_interface_type->implements_interface(rhs_type, NULL))
    {
      go_assert(saw_errors());
      return Expression::make_error(location);
    }

  // An interface is a tuple.  If LHS_TYPE is an empty interface type,
  // then the first field is the type descriptor for RHS_TYPE.
  // Otherwise it is the interface method table for RHS_TYPE.
  Expression* first_field;
  if (lhs_is_empty)
    first_field = Expression::make_type_descriptor(rhs_type, location);
  else
    {
      // Build the interface method table for this interface and this
      // object type: a list of function pointers for each interface
      // method.
      Named_type* rhs_named_type = rhs_type->named_type();
      Struct_type* rhs_struct_type = rhs_type->struct_type();
      bool is_pointer = false;
      if (rhs_named_type == NULL && rhs_struct_type == NULL)
	{
	  rhs_named_type = rhs_type->deref()->named_type();
	  rhs_struct_type = rhs_type->deref()->struct_type();
	  is_pointer = true;
	}
      if (rhs_named_type != NULL)
	first_field =
	  rhs_named_type->interface_method_table(lhs_interface_type,
                                                 is_pointer);
      else if (rhs_struct_type != NULL)
	first_field =
	  rhs_struct_type->interface_method_table(lhs_interface_type,
                                                  is_pointer);
      else
	first_field = Expression::make_nil(location);
    }

  Expression* obj;
  if (rhs_type->is_direct_iface_type())
    {
      // We are assigning a pointer to the interface; the interface
      // holds the pointer itself.
      obj = unpack_direct_iface(rhs, location);
    }
  else
    {
      // We are assigning a non-pointer value to the interface; the
      // interface gets a copy of the value in the heap if it escapes.

      // An exception is &global if global is notinheap, which is a
      // pointer value but not a direct-iface type and we can't simply
      // take its address.
      bool is_address = (rhs->unary_expression() != NULL
                         && rhs->unary_expression()->op() == OPERATOR_AND);

      if (rhs->is_constant() && !is_address)
        obj = Expression::make_unary(OPERATOR_AND, rhs, location);
      else
        {
          obj = Expression::make_heap_expression(rhs, location);
          if (on_stack)
            obj->heap_expression()->set_allocate_on_stack();
        }
    }

  return Expression::make_interface_value(lhs_type, first_field, obj, location);
}

// Return an expression for the pointer-typed value of a direct interface
// type.  Specifically, for single field struct or array, get the single
// field, and do this recursively.  The reason for this is that we don't
// want to assign a struct or an array to a pointer-typed field.  The
// backend may not like that.

Expression*
Expression::unpack_direct_iface(Expression* rhs, Location loc)
{
  Struct_type* st = rhs->type()->struct_type();
  if (st != NULL)
    {
      go_assert(st->field_count() == 1);
      Expression* field = Expression::make_field_reference(rhs, 0, loc);
      return unpack_direct_iface(field, loc);
    }
  Array_type* at = rhs->type()->array_type();
  if (at != NULL)
    {
      int64_t len;
      bool ok = at->int_length(&len);
      go_assert(ok && len == 1);
      Type* int_type = Type::lookup_integer_type("int");
      Expression* index = Expression::make_integer_ul(0, int_type, loc);
      Expression* elem = Expression::make_array_index(rhs, index, NULL, NULL, loc);
      return unpack_direct_iface(elem, loc);
    }
  return rhs;
}

// The opposite of unpack_direct_iface.

Expression*
Expression::pack_direct_iface(Type* t, Expression* rhs, Location loc)
{
  if (rhs->type() == t)
    return rhs;
  Struct_type* st = t->struct_type();
  if (st != NULL)
    {
      Expression_list* vals = new Expression_list();
      vals->push_back(pack_direct_iface(st->field(0)->type(), rhs, loc));
      return Expression::make_struct_composite_literal(t, vals, loc);
    }
  Array_type* at = t->array_type();
  if (at != NULL)
    {
      Expression_list* vals = new Expression_list();
      vals->push_back(pack_direct_iface(at->element_type(), rhs, loc));
      return Expression::make_array_composite_literal(t, vals, loc);
    }
  return Expression::make_unsafe_cast(t, rhs, loc);
}

// Return an expression for the type descriptor of RHS.

Expression*
Expression::get_interface_type_descriptor(Expression* rhs)
{
  go_assert(rhs->type()->interface_type() != NULL);
  Location location = rhs->location();

  // The type descriptor is the first field of an empty interface.
  if (rhs->type()->interface_type()->is_empty())
    return Expression::make_interface_info(rhs, INTERFACE_INFO_TYPE_DESCRIPTOR,
                                           location);

  Expression* mtable =
      Expression::make_interface_info(rhs, INTERFACE_INFO_METHODS, location);

  Expression* descriptor =
      Expression::make_dereference(mtable, NIL_CHECK_NOT_NEEDED, location);
  descriptor = Expression::make_field_reference(descriptor, 0, location);
  Expression* nil = Expression::make_nil(location);

  Expression* eq =
      Expression::make_binary(OPERATOR_EQEQ, mtable, nil, location);
  return Expression::make_conditional(eq, nil, descriptor, location);
}

// Return an expression for the conversion of an interface type to an
// interface type.

Expression*
Expression::convert_interface_to_interface(Gogo* gogo, Type *lhs_type,
					   Expression* rhs,
                                           bool for_type_guard,
                                           Location location)
{
  if (Type::are_identical(lhs_type, rhs->type(),
			  Type::COMPARE_ERRORS | Type::COMPARE_TAGS,
			  NULL))
    return rhs;

  Interface_type* lhs_interface_type = lhs_type->interface_type();
  bool lhs_is_empty = lhs_interface_type->is_empty();

  // In the general case this requires runtime examination of the type
  // method table to match it up with the interface methods.

  // FIXME: If all of the methods in the right hand side interface
  // also appear in the left hand side interface, then we don't need
  // to do a runtime check, although we still need to build a new
  // method table.

  // We are going to evaluate RHS multiple times.
  go_assert(rhs->is_multi_eval_safe());

  // Get the type descriptor for the right hand side.  This will be
  // NULL for a nil interface.
  Expression* rhs_type_expr = Expression::get_interface_type_descriptor(rhs);
  Expression* lhs_type_expr =
      Expression::make_type_descriptor(lhs_type, location);

  Expression* first_field;
  if (for_type_guard)
    {
      // A type assertion fails when converting a nil interface.
      first_field = Runtime::make_call(gogo, Runtime::ASSERTITAB, location, 2,
				       lhs_type_expr, rhs_type_expr);
    }
  else if (lhs_is_empty)
    {
      // A conversion to an empty interface always succeeds, and the
      // first field is just the type descriptor of the object.
      first_field = rhs_type_expr;
    }
  else
    {
      // A conversion to a non-empty interface may fail, but unlike a
      // type assertion converting nil will always succeed.
      first_field = Runtime::make_call(gogo, Runtime::REQUIREITAB, location, 2,
				       lhs_type_expr, rhs_type_expr);
    }

  // The second field is simply the object pointer.
  Expression* obj =
      Expression::make_interface_info(rhs, INTERFACE_INFO_OBJECT, location);
  Expression* ret = Expression::make_interface_value(lhs_type, first_field,
						     obj, location);
  Type_context context(lhs_type, false);
  ret->determine_type(gogo, &context);
  return ret;
}

// Return an expression for the conversion of an interface type to a
// non-interface type.

Expression*
Expression::convert_interface_to_type(Gogo* gogo, Type *lhs_type, Expression* rhs,
                                      Location location)
{
  // We are going to evaluate RHS multiple times.
  go_assert(rhs->is_multi_eval_safe());

  // Build an expression to check that the type is valid.  It will
  // panic with an appropriate runtime type error if the type is not
  // valid.
  // (lhs_type == rhs_type ? nil /*dummy*/ :
  //    panicdottype(lhs_type, rhs_type, inter_type))
  // For some Oses, we need to call runtime.eqtype instead of
  // lhs_type == rhs_type, as we may have unmerged type descriptors
  // from shared libraries.
  Expression* lhs_type_expr = Expression::make_type_descriptor(lhs_type,
                                                                location);
  Expression* rhs_descriptor =
      Expression::get_interface_type_descriptor(rhs);

  Type* rhs_type = rhs->type();
  Expression* rhs_inter_expr = Expression::make_type_descriptor(rhs_type,
                                                                location);

  Expression* cond;
  if (gogo->need_eqtype()) {
    cond = Runtime::make_call(gogo, Runtime::EQTYPE, location,
                              2, lhs_type_expr,
                              rhs_descriptor);
  } else {
    cond = Expression::make_binary(OPERATOR_EQEQ, lhs_type_expr,
                                   rhs_descriptor, location);
  }

  rhs_descriptor = Expression::get_interface_type_descriptor(rhs);
  Expression* panic = Runtime::make_call(gogo, Runtime::PANICDOTTYPE, location,
                                         3, lhs_type_expr->copy(),
                                         rhs_descriptor,
                                         rhs_inter_expr);
  Expression* nil = Expression::make_nil(location);
  Expression* check = Expression::make_conditional(cond, nil, panic,
                                                   location);

  // If the conversion succeeds, pull out the value.
  Expression* obj = Expression::make_interface_info(rhs, INTERFACE_INFO_OBJECT,
                                                    location);

  // If the value is a direct interface, then it is the value we want.
  // Otherwise it points to the value.
  if (lhs_type->is_direct_iface_type())
    obj = Expression::pack_direct_iface(lhs_type, obj, location);
  else
    {
      obj = Expression::make_unsafe_cast(Type::make_pointer_type(lhs_type), obj,
                                         location);
      obj = Expression::make_dereference(obj, NIL_CHECK_NOT_NEEDED,
                                         location);
    }
  return Expression::make_compound(check, obj, location);
}

// Convert an expression to its backend representation.  This is implemented by
// the child class.  Not that it is not in general safe to call this multiple
// times for a single expression, but that we don't catch such errors.

Bexpression*
Expression::get_backend(Translate_context* context)
{
  // The child may have marked this expression as having an error.
  if (this->classification_ == EXPRESSION_ERROR)
    {
      go_assert(saw_errors());
      return context->backend()->error_expression();
    }

  return this->do_get_backend(context);
}

// Return a backend expression for VAL.
Bexpression*
Expression::backend_numeric_constant_expression(Translate_context* context,
                                                Numeric_constant* val)
{
  Gogo* gogo = context->gogo();
  Type* type = val->type();
  if (type == NULL)
    return gogo->backend()->error_expression();

  Btype* btype = type->get_backend(gogo);
  Bexpression* ret;
  if (type->integer_type() != NULL)
    {
      mpz_t ival;
      if (!val->to_int(&ival))
        {
          go_assert(saw_errors());
          return gogo->backend()->error_expression();
        }
      ret = gogo->backend()->integer_constant_expression(btype, ival);
      mpz_clear(ival);
    }
  else if (type->float_type() != NULL)
    {
      mpfr_t fval;
      if (!val->to_float(&fval))
        {
          go_assert(saw_errors());
          return gogo->backend()->error_expression();
        }
      ret = gogo->backend()->float_constant_expression(btype, fval);
      mpfr_clear(fval);
    }
  else if (type->complex_type() != NULL)
    {
      mpc_t cval;
      if (!val->to_complex(&cval))
        {
          go_assert(saw_errors());
          return gogo->backend()->error_expression();
        }
      ret = gogo->backend()->complex_constant_expression(btype, cval);
      mpc_clear(cval);
    }
  else
    go_unreachable();

  return ret;
}

// Insert bounds checks for an index expression.  Check that that VAL
// >= 0 and that it fits in an int.  Then check that VAL OP BOUND is
// true.  If any condition is false, call one of the CODE runtime
// functions, which will panic.

void
Expression::check_bounds(Gogo* gogo, Expression* val, Operator op,
			 Expression* bound,
			 Runtime::Function code,
			 Runtime::Function code_u,
			 Runtime::Function code_extend,
			 Runtime::Function code_extend_u,
			 Statement_inserter* inserter,
			 Location loc)
{
  go_assert(val->is_multi_eval_safe());
  go_assert(bound->is_multi_eval_safe());

  Type* int_type = Type::lookup_integer_type("int");
  int int_type_size = int_type->integer_type()->bits();

  Type* val_type = val->type();
  if (val_type->integer_type() == NULL)
    {
      go_assert(saw_errors());
      return;
    }
  int val_type_size = val_type->integer_type()->bits();
  bool val_is_unsigned = val_type->integer_type()->is_unsigned();

  // Check that VAL >= 0.
  Expression* check = NULL;
  if (!val_is_unsigned)
    {
      Expression* zero = Expression::make_integer_ul(0, val_type, loc);
      check = Expression::make_binary(OPERATOR_GE, val->copy(), zero, loc);
    }

  // If VAL's type is larger than int, check that VAL fits in an int.
  if (val_type_size > int_type_size
      || (val_type_size == int_type_size
	  && val_is_unsigned))
    {
      mpz_t one;
      mpz_init_set_ui(one, 1UL);

      // maxval = 2^(int_type_size - 1) - 1
      mpz_t maxval;
      mpz_init(maxval);
      mpz_mul_2exp(maxval, one, int_type_size - 1);
      mpz_sub_ui(maxval, maxval, 1);
      Expression* max = Expression::make_integer_z(&maxval, val_type, loc);
      mpz_clear(one);
      mpz_clear(maxval);

      Expression* cmp = Expression::make_binary(OPERATOR_LE, val->copy(),
						max, loc);
      if (check == NULL)
	check = cmp;
      else
	check = Expression::make_binary(OPERATOR_ANDAND, check, cmp, loc);
    }

  // For the final check we can assume that VAL fits in an int.
  Expression* ival;
  if (val_type == int_type)
    ival = val->copy();
  else
    ival = Expression::make_cast(int_type, val->copy(), loc);

  // BOUND is assumed to fit in an int.  Either it comes from len or
  // cap, or it was checked by an earlier call.
  Expression* ibound;
  if (bound->type() == int_type)
    ibound = bound->copy();
  else
    ibound = Expression::make_cast(int_type, bound->copy(), loc);

  Expression* cmp = Expression::make_binary(op, ival, ibound, loc);
  if (check == NULL)
    check = cmp;
  else
    check = Expression::make_binary(OPERATOR_ANDAND, check, cmp, loc);

  Runtime::Function c;
  if (val_type_size > int_type_size)
    {
      if (val_is_unsigned)
	c = code_extend_u;
      else
	c = code_extend;
    }
  else
    {
      if (val_is_unsigned)
	c = code_u;
      else
	c = code;
    }

  Expression* ignore = Expression::make_boolean(true, loc);
  Expression* crash = Runtime::make_call(gogo, c, loc, 2,
					 val->copy(), bound->copy());
  Expression* cond = Expression::make_conditional(check, ignore, crash, loc);
  Statement* s = Statement::make_statement(cond, true);
  s->determine_types(gogo);
  inserter->insert(s);
}

void
Expression::dump_expression(Ast_dump_context* ast_dump_context) const
{
  this->do_dump_expression(ast_dump_context);
}

// Error expressions.  This are used to avoid cascading errors.

class Error_expression : public Expression
{
 public:
  Error_expression(Location location)
    : Expression(EXPRESSION_ERROR, location)
  { }

 protected:
  bool
  do_is_constant() const
  { return true; }

  bool
  do_is_untyped(Type**) const
  { return false; }

  bool
  do_numeric_constant_value(Numeric_constant*)
  { return false; }

  bool
  do_discarding_value()
  { return true; }

  Type*
  do_type()
  { return Type::make_error_type(); }

  void
  do_determine_type(Gogo*, const Type_context*)
  { }

  Expression*
  do_copy()
  { return this; }

  bool
  do_is_addressable() const
  { return true; }

  Bexpression*
  do_get_backend(Translate_context* context)
  { return context->backend()->error_expression(); }

  void
  do_dump_expression(Ast_dump_context*) const;
};

// Dump the ast representation for an error expression to a dump context.

void
Error_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->ostream() << "_Error_" ;
}

Expression*
Expression::make_error(Location location)
{
  return new Error_expression(location);
}

// An expression which is really a type.  This is used during parsing.
// It is an error if these survive after lowering.

class Type_expression : public Expression
{
 public:
  Type_expression(Type* type, Location location)
    : Expression(EXPRESSION_TYPE, location),
      type_(type)
  { }

 protected:
  int
  do_traverse(Traverse* traverse)
  { return Type::traverse(this->type_, traverse); }

  Type*
  do_type()
  { return this->type_; }

  void
  do_determine_type(Gogo*, const Type_context*)
  { }

  void
  do_check_types(Gogo*);

  Expression*
  do_copy()
  { return this; }

  Bexpression*
  do_get_backend(Translate_context*);

  void do_dump_expression(Ast_dump_context*) const;

 private:
  // The type which we are representing as an expression.
  Type* type_;
};

void
Type_expression::do_check_types(Gogo*)
{
  if (this->type_->is_error())
    {
      go_assert(saw_errors());
      this->set_is_error();
    }
}

Bexpression*
Type_expression::do_get_backend(Translate_context* context)
{
  if (!this->is_error_expression())
    this->report_error("invalid use of type");
  return context->backend()->error_expression();
}

void
Type_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->dump_type(this->type_);
}

Expression*
Expression::make_type(Type* type, Location location)
{
  return new Type_expression(type, location);
}

// Class Var_expression.

// Lower a variable expression.  Here we just make sure that the
// initialization expression of the variable has been lowered.  This
// ensures that we will be able to determine the type of the variable
// if necessary.

Expression*
Var_expression::do_lower(Gogo* gogo, Named_object* function,
			 Statement_inserter* inserter)
{
  if (this->variable_->is_variable())
    {
      Variable* var = this->variable_->var_value();
      // This is either a local variable or a global variable.  A
      // reference to a variable which is local to an enclosing
      // function will be a reference to a field in a closure.
      if (var->is_global())
	{
	  function = NULL;
	  inserter = NULL;
	}
      var->lower_init_expression(gogo, function, inserter);
    }
  return this;
}

// Return the type of a reference to a variable.

Type*
Var_expression::do_type()
{
  if (this->variable_->is_variable())
    return this->variable_->var_value()->type();
  else if (this->variable_->is_result_variable())
    return this->variable_->result_var_value()->type();
  else
    go_unreachable();
}

// Determine the type of a reference to a variable.

void
Var_expression::do_determine_type(Gogo* gogo, const Type_context*)
{
  if (this->variable_->is_variable())
    this->variable_->var_value()->determine_type(gogo);
}

// Something takes the address of this variable.  This means that we
// may want to move the variable onto the heap.

void
Var_expression::do_address_taken(bool escapes)
{
  if (!escapes)
    {
      if (this->variable_->is_variable())
	this->variable_->var_value()->set_non_escaping_address_taken();
      else if (this->variable_->is_result_variable())
	this->variable_->result_var_value()->set_non_escaping_address_taken();
      else
	go_unreachable();
    }
  else
    {
      if (this->variable_->is_variable())
	this->variable_->var_value()->set_address_taken();
      else if (this->variable_->is_result_variable())
	this->variable_->result_var_value()->set_address_taken();
      else
	go_unreachable();
    }

  if (this->variable_->is_variable()
      && this->variable_->var_value()->is_in_heap())
    {
      Node::make_node(this)->set_encoding(Node::ESCAPE_HEAP);
      Node::make_node(this->variable_)->set_encoding(Node::ESCAPE_HEAP);
    }
}

// Export a reference to a variable.

void
Var_expression::do_export(Export_function_body* efb) const
{
  Named_object* no = this->variable_;
  if (no->is_result_variable() || !no->var_value()->is_global())
    efb->write_string(Gogo::unpack_hidden_name(no->name()));
  else
    Expression::export_name(efb, no);
}

// Get the backend representation for a reference to a variable.

Bexpression*
Var_expression::do_get_backend(Translate_context* context)
{
  Bvariable* bvar = this->variable_->get_backend_variable(context->gogo(),
							  context->function());
  bool is_in_heap;
  Location loc = this->location();
  Btype* btype;
  Gogo* gogo = context->gogo();
  if (this->variable_->is_variable())
    {
      is_in_heap = this->variable_->var_value()->is_in_heap();
      btype = this->variable_->var_value()->type()->get_backend(gogo);
    }
  else if (this->variable_->is_result_variable())
    {
      is_in_heap = this->variable_->result_var_value()->is_in_heap();
      btype = this->variable_->result_var_value()->type()->get_backend(gogo);
    }
  else
    go_unreachable();

  Bexpression* ret =
      context->backend()->var_expression(bvar, loc);
  if (is_in_heap)
    ret = context->backend()->indirect_expression(btype, ret, true, loc);
  return ret;
}

// Ast dump for variable expression.

void
Var_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->ostream() << this->variable_->message_name() ;
}

// Make a reference to a variable in an expression.

Expression*
Expression::make_var_reference(Named_object* var, Location location)
{
  if (var->is_sink())
    return Expression::make_sink(location);
  if (var->is_redefinition())
    return Expression::make_error(location);

  // FIXME: Creating a new object for each reference to a variable is
  // wasteful.
  return new Var_expression(var, location);
}

// Class Enclosed_var_expression.

int
Enclosed_var_expression::do_traverse(Traverse*)
{
  return TRAVERSE_CONTINUE;
}

// Lower the reference to the enclosed variable.

Expression*
Enclosed_var_expression::do_lower(Gogo* gogo, Named_object* function,
				  Statement_inserter* inserter)
{
  gogo->lower_expression(function, inserter, &this->reference_);
  return this;
}

// Flatten the reference to the enclosed variable.

Expression*
Enclosed_var_expression::do_flatten(Gogo* gogo, Named_object* function,
				    Statement_inserter* inserter)
{
  gogo->flatten_expression(function, inserter, &this->reference_);
  return this;
}

void
Enclosed_var_expression::do_address_taken(bool escapes)
{
  if (!escapes)
    {
      if (this->variable_->is_variable())
	this->variable_->var_value()->set_non_escaping_address_taken();
      else if (this->variable_->is_result_variable())
	this->variable_->result_var_value()->set_non_escaping_address_taken();
      else
	go_unreachable();
    }
  else
    {
      if (this->variable_->is_variable())
	this->variable_->var_value()->set_address_taken();
      else if (this->variable_->is_result_variable())
	this->variable_->result_var_value()->set_address_taken();
      else
	go_unreachable();
    }

  if (this->variable_->is_variable()
      && this->variable_->var_value()->is_in_heap())
    Node::make_node(this->variable_)->set_encoding(Node::ESCAPE_HEAP);
}

// Ast dump for enclosed variable expression.

void
Enclosed_var_expression::do_dump_expression(Ast_dump_context* adc) const
{
  adc->ostream() << this->variable_->message_name();
}

// Make a reference to a variable within an enclosing function.

Expression*
Expression::make_enclosing_var_reference(Expression* reference,
					 Named_object* var, Location location)
{
  return new Enclosed_var_expression(reference, var, location);
}

// Class Temporary_reference_expression.

// The type.

Type*
Temporary_reference_expression::do_type()
{
  return this->statement_->type();
}

// Called if something takes the address of this temporary variable.
// We never have to move temporary variables to the heap, but we do
// need to know that they must live in the stack rather than in a
// register.

void
Temporary_reference_expression::do_address_taken(bool)
{
  this->statement_->set_is_address_taken();
}

// Export a reference to a temporary.

void
Temporary_reference_expression::do_export(Export_function_body* efb) const
{
  unsigned int idx = efb->temporary_index(this->statement_);
  char buf[50];
  snprintf(buf, sizeof buf, "$t%u", idx);
  efb->write_c_string(buf);
}

// Import a reference to a temporary.

Expression*
Temporary_reference_expression::do_import(Import_function_body* ifb,
					  Location loc)
{
  std::string id = ifb->read_identifier();
  go_assert(id[0] == '$' && id[1] == 't');
  const char *p = id.c_str();
  char *end;
  long idx = strtol(p + 2, &end, 10);
  if (*end != '\0' || idx > 0x7fffffff)
    {
      if (!ifb->saw_error())
	go_error_at(loc,
		    ("invalid export data for %qs: "
		     "invalid temporary reference index at %lu"),
		    ifb->name().c_str(),
		    static_cast<unsigned long>(ifb->off()));
      ifb->set_saw_error();
      return Expression::make_error(loc);
    }

  Temporary_statement* temp =
    ifb->temporary_statement(static_cast<unsigned int>(idx));
  if (temp == NULL)
    {
      if (!ifb->saw_error())
	go_error_at(loc,
		    ("invalid export data for %qs: "
		     "undefined temporary reference index at %lu"),
		    ifb->name().c_str(),
		    static_cast<unsigned long>(ifb->off()));
      ifb->set_saw_error();
      return Expression::make_error(loc);
    }

  return Expression::make_temporary_reference(temp, loc);
}

// Get a backend expression referring to the variable.

Bexpression*
Temporary_reference_expression::do_get_backend(Translate_context* context)
{
  Gogo* gogo = context->gogo();
  Bvariable* bvar = this->statement_->get_backend_variable(context);
  Bexpression* ret = gogo->backend()->var_expression(bvar, this->location());

  // The backend can't always represent the same set of recursive types
  // that the Go frontend can.  In some cases this means that a
  // temporary variable won't have the right backend type.  Correct
  // that here by adding a type cast.  We need to use base() to push
  // the circularity down one level.
  Type* stype = this->statement_->type();
  if (!this->is_lvalue_
      && stype->points_to() != NULL
      && stype->points_to()->is_void_type())
    {
      Btype* btype = this->type()->base()->get_backend(gogo);
      ret = gogo->backend()->convert_expression(btype, ret, this->location());
    }
  return ret;
}

// Ast dump for temporary reference.

void
Temporary_reference_expression::do_dump_expression(
                                Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->dump_temp_variable_name(this->statement_);
}

// Make a reference to a temporary variable.

Temporary_reference_expression*
Expression::make_temporary_reference(Temporary_statement* statement,
				     Location location)
{
  statement->add_use();
  return new Temporary_reference_expression(statement, location);
}

// Class Set_and_use_temporary_expression.

// Return the type.

Type*
Set_and_use_temporary_expression::do_type()
{
  return this->statement_->type();
}

// Determine the type of the expression.

void
Set_and_use_temporary_expression::do_determine_type(
    Gogo* gogo,
    const Type_context* context)
{
  this->expr_->determine_type(gogo, context);
}

// Take the address.

void
Set_and_use_temporary_expression::do_address_taken(bool)
{
  this->statement_->set_is_address_taken();
}

// Return the backend representation.

Bexpression*
Set_and_use_temporary_expression::do_get_backend(Translate_context* context)
{
  Location loc = this->location();
  Gogo* gogo = context->gogo();
  Bvariable* bvar = this->statement_->get_backend_variable(context);
  Bexpression* lvar_ref = gogo->backend()->var_expression(bvar, loc);

  Named_object* fn = context->function();
  go_assert(fn != NULL);
  Bfunction* bfn = fn->func_value()->get_or_make_decl(gogo, fn);
  Bexpression* bexpr = this->expr_->get_backend(context);
  Bstatement* set = gogo->backend()->assignment_statement(bfn, lvar_ref,
                                                          bexpr, loc);
  Bexpression* var_ref = gogo->backend()->var_expression(bvar, loc);
  Bexpression* ret = gogo->backend()->compound_expression(set, var_ref, loc);
  return ret;
}

// Dump.

void
Set_and_use_temporary_expression::do_dump_expression(
    Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->ostream() << '(';
  ast_dump_context->dump_temp_variable_name(this->statement_);
  ast_dump_context->ostream() << " = ";
  this->expr_->dump_expression(ast_dump_context);
  ast_dump_context->ostream() << ')';
}

// Make a set-and-use temporary.

Set_and_use_temporary_expression*
Expression::make_set_and_use_temporary(Temporary_statement* statement,
				       Expression* expr, Location location)
{
  return new Set_and_use_temporary_expression(statement, expr, location);
}

// A sink expression--a use of the blank identifier _.

class Sink_expression : public Expression
{
 public:
  Sink_expression(Location location)
    : Expression(EXPRESSION_SINK, location),
      type_(NULL), bvar_(NULL)
  { }

 protected:
  bool
  do_discarding_value()
  { return true; }

  Type*
  do_type();

  void
  do_determine_type(Gogo*, const Type_context*);

  Expression*
  do_copy()
  { return new Sink_expression(this->location()); }

  Bexpression*
  do_get_backend(Translate_context*);

  void
  do_dump_expression(Ast_dump_context*) const;

 private:
  // The type of this sink variable.
  Type* type_;
  // The temporary variable we generate.
  Bvariable* bvar_;
};

// Return the type of a sink expression.

Type*
Sink_expression::do_type()
{
  if (this->type_ == NULL)
    return Type::make_sink_type();
  return this->type_;
}

// Determine the type of a sink expression.

void
Sink_expression::do_determine_type(Gogo*, const Type_context* context)
{
  if (context->type != NULL)
    this->type_ = context->type;
}

// Return a temporary variable for a sink expression.  This will
// presumably be a write-only variable which the middle-end will drop.

Bexpression*
Sink_expression::do_get_backend(Translate_context* context)
{
  Location loc = this->location();
  Gogo* gogo = context->gogo();
  if (this->bvar_ == NULL)
    {
      if (this->type_ == NULL || this->type_->is_sink_type())
	{
	  go_assert(saw_errors());
	  return gogo->backend()->error_expression();
	}

      Named_object* fn = context->function();
      go_assert(fn != NULL);
      Bfunction* fn_ctx = fn->func_value()->get_or_make_decl(gogo, fn);
      Btype* bt = this->type_->get_backend(context->gogo());
      Bstatement* decl;
      this->bvar_ =
	gogo->backend()->temporary_variable(fn_ctx, context->bblock(), bt, NULL,
					    0, loc, &decl);
      Bexpression* var_ref =
          gogo->backend()->var_expression(this->bvar_, loc);
      var_ref = gogo->backend()->compound_expression(decl, var_ref, loc);
      return var_ref;
    }
  return gogo->backend()->var_expression(this->bvar_, loc);
}

// Ast dump for sink expression.

void
Sink_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->ostream() << "_" ;
}

// Make a sink expression.

Expression*
Expression::make_sink(Location location)
{
  return new Sink_expression(location);
}

// Class Func_expression.

// FIXME: Can a function expression appear in a constant expression?
// The value is unchanging.  Initializing a constant to the address of
// a function seems like it could work, though there might be little
// point to it.

// Traversal.

int
Func_expression::do_traverse(Traverse* traverse)
{
  return (this->closure_ == NULL
	  ? TRAVERSE_CONTINUE
	  : Expression::traverse(&this->closure_, traverse));
}

// Return the type of a function expression.

Type*
Func_expression::do_type()
{
  if (this->function_->is_function())
    return this->function_->func_value()->type();
  else if (this->function_->is_function_declaration())
    return this->function_->func_declaration_value()->type();
  else
    go_unreachable();
}

// Get the backend representation for the code of a function expression.

Bexpression*
Func_expression::get_code_pointer(Gogo* gogo, Named_object* no, Location loc)
{
  Function_type* fntype;
  if (no->is_function())
    fntype = no->func_value()->type();
  else if (no->is_function_declaration())
    fntype = no->func_declaration_value()->type();
  else
    go_unreachable();

  // Builtin functions are handled specially by Call_expression.  We
  // can't take their address.
  if (fntype->is_builtin())
    {
      go_error_at(loc,
		  ("invalid use of special built-in function %qs; "
		   "must be called"),
		  no->message_name().c_str());
      return gogo->backend()->error_expression();
    }

  Bfunction* fndecl;
  if (no->is_function())
    fndecl = no->func_value()->get_or_make_decl(gogo, no);
  else if (no->is_function_declaration())
    fndecl = no->func_declaration_value()->get_or_make_decl(gogo, no);
  else
    go_unreachable();

  return gogo->backend()->function_code_expression(fndecl, loc);
}

// Get the backend representation for a function expression.  This is used when
// we take the address of a function rather than simply calling it.  A func
// value is represented as a pointer to a block of memory.  The first
// word of that memory is a pointer to the function code.  The
// remaining parts of that memory are the addresses of variables that
// the function closes over.

Bexpression*
Func_expression::do_get_backend(Translate_context* context)
{
  // If there is no closure, just use the function descriptor.
  if (this->closure_ == NULL)
    {
      Gogo* gogo = context->gogo();
      Named_object* no = this->function_;
      Expression* descriptor;
      if (no->is_function())
	descriptor = no->func_value()->descriptor(gogo, no);
      else if (no->is_function_declaration())
	{
	  if (no->func_declaration_value()->type()->is_builtin())
	    {
	      go_error_at(this->location(),
			  ("invalid use of special built-in function %qs; "
			   "must be called"),
			  no->message_name().c_str());
	      return gogo->backend()->error_expression();
	    }
	  descriptor = no->func_declaration_value()->descriptor(gogo, no);
	}
      else
	go_unreachable();

      Bexpression* bdesc = descriptor->get_backend(context);
      return gogo->backend()->address_expression(bdesc, this->location());
    }

  go_assert(this->function_->func_value()->enclosing() != NULL);

  // If there is a closure, then the closure is itself the function
  // expression.  It is a pointer to a struct whose first field points
  // to the function code and whose remaining fields are the addresses
  // of the closed-over variables.
  Bexpression *bexpr = this->closure_->get_backend(context);

  // Introduce a backend type conversion, to account for any differences
  // between the argument type (function descriptor, struct with a
  // single field) and the closure (struct with multiple fields).
  Gogo* gogo = context->gogo();
  Btype *btype = this->type()->get_backend(gogo);
  return gogo->backend()->convert_expression(btype, bexpr, this->location());
}

// The cost of inlining a function reference.

int
Func_expression::do_inlining_cost() const
{
  // FIXME: We don't inline references to nested functions.
  if (this->closure_ != NULL)
    return 0x100000;
  if (this->function_->is_function()
      && this->function_->func_value()->enclosing() != NULL)
    return 0x100000;

  return 1;
}

// Export a reference to a function.

void
Func_expression::do_export(Export_function_body* efb) const
{
  Expression::export_name(efb, this->function_);
}

// Ast dump for function.

void
Func_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->ostream() << this->function_->name();
  if (this->closure_ != NULL)
    {
      ast_dump_context->ostream() << " {closure =  ";
      this->closure_->dump_expression(ast_dump_context);
      ast_dump_context->ostream() << "}";
    }
}

// Make a reference to a function in an expression.

Expression*
Expression::make_func_reference(Named_object* function, Expression* closure,
				Location location)
{
  Func_expression* fe = new Func_expression(function, closure, location);

  // Detect references to builtin functions and set the runtime code if
  // appropriate.
  if (function->is_function_declaration())
    fe->set_runtime_code(Runtime::name_to_code(function->name()));
  return fe;
}

// Class Func_descriptor_expression.

// Constructor.

Func_descriptor_expression::Func_descriptor_expression(Named_object* fn)
  : Expression(EXPRESSION_FUNC_DESCRIPTOR, fn->location()),
    fn_(fn), dvar_(NULL)
{
  go_assert(!fn->is_function() || !fn->func_value()->needs_closure());
}

// Traversal.

int
Func_descriptor_expression::do_traverse(Traverse*)
{
  return TRAVERSE_CONTINUE;
}

// All function descriptors have the same type.

Type* Func_descriptor_expression::descriptor_type;

void
Func_descriptor_expression::make_func_descriptor_type()
{
  if (Func_descriptor_expression::descriptor_type != NULL)
    return;
  Type* uintptr_type = Type::lookup_integer_type("uintptr");
  Type* struct_type = Type::make_builtin_struct_type(1, "fn", uintptr_type);
  Func_descriptor_expression::descriptor_type =
    Type::make_builtin_named_type("functionDescriptor", struct_type);
}

Type*
Func_descriptor_expression::do_type()
{
  Func_descriptor_expression::make_func_descriptor_type();
  return Func_descriptor_expression::descriptor_type;
}

// The backend representation for a function descriptor.

Bexpression*
Func_descriptor_expression::do_get_backend(Translate_context* context)
{
  Named_object* no = this->fn_;
  Location loc = no->location();
  if (this->dvar_ != NULL)
    return context->backend()->var_expression(this->dvar_, loc);

  Gogo* gogo = context->gogo();
  Backend_name bname;
  gogo->function_descriptor_backend_name(no, &bname);
  bool is_descriptor = false;
  if (no->is_function_declaration()
      && !no->func_declaration_value()->asm_name().empty()
      && Linemap::is_predeclared_location(no->location()))
    is_descriptor = true;

  // The runtime package implements some functions defined in the
  // syscall package.  Let the syscall package define the descriptor
  // in this case.
  if (gogo->compiling_runtime()
      && gogo->package_name() == "runtime"
      && no->is_function()
      && !no->func_value()->asm_name().empty()
      && no->func_value()->asm_name().compare(0, 8, "syscall.") == 0)
    is_descriptor = true;

  Btype* btype = this->type()->get_backend(gogo);

  Bvariable* bvar;
  if (no->package() != NULL || is_descriptor)
    bvar =
      context->backend()->immutable_struct_reference(bname.name(),
						     bname.optional_asm_name(),
						     btype, loc);
  else
    {
      Location bloc = Linemap::predeclared_location();

      // The runtime package has hash/equality functions that are
      // referenced by type descriptors outside of the runtime, so the
      // function descriptors must be visible even though they are not
      // exported.
      bool is_exported_runtime = false;
      if (gogo->compiling_runtime()
	  && gogo->package_name() == "runtime"
	  && (no->name().find("hash") != std::string::npos
	      || no->name().find("equal") != std::string::npos))
	is_exported_runtime = true;

      bool is_hidden = ((no->is_function()
			 && no->func_value()->enclosing() != NULL)
			|| (Gogo::is_hidden_name(no->name())
			    && !is_exported_runtime)
			|| Gogo::is_thunk(no));

      if (no->is_function() && no->func_value()->is_referenced_by_inline())
	is_hidden = false;

      unsigned int flags = 0;
      if (is_hidden)
	flags |= Backend::variable_is_hidden;
      bvar = context->backend()->immutable_struct(bname.name(),
						  bname.optional_asm_name(),
						  flags, btype, bloc);
      Expression_list* vals = new Expression_list();
      vals->push_back(Expression::make_func_code_reference(this->fn_, bloc));
      Expression* init =
	Expression::make_struct_composite_literal(this->type(), vals, bloc);
      Translate_context bcontext(gogo, NULL, NULL, NULL);
      bcontext.set_is_const();
      Bexpression* binit = init->get_backend(&bcontext);
      context->backend()->immutable_struct_set_init(bvar, bname.name(),
						    flags, btype, bloc, binit);
    }

  this->dvar_ = bvar;
  return gogo->backend()->var_expression(bvar, loc);
}

// Print a function descriptor expression.

void
Func_descriptor_expression::do_dump_expression(Ast_dump_context* context) const
{
  context->ostream() << "[descriptor " << this->fn_->name() << "]";
}

// Make a function descriptor expression.

Func_descriptor_expression*
Expression::make_func_descriptor(Named_object* fn)
{
  return new Func_descriptor_expression(fn);
}

// Make the function descriptor type, so that it can be converted.

void
Expression::make_func_descriptor_type()
{
  Func_descriptor_expression::make_func_descriptor_type();
}

// A reference to just the code of a function.

class Func_code_reference_expression : public Expression
{
 public:
  Func_code_reference_expression(Named_object* function, Location location)
    : Expression(EXPRESSION_FUNC_CODE_REFERENCE, location),
      function_(function)
  { }

 protected:
  int
  do_traverse(Traverse*)
  { return TRAVERSE_CONTINUE; }

  bool
  do_is_static_initializer() const
  { return true; }

  Type*
  do_type()
  { return Type::make_pointer_type(Type::make_void_type()); }

  void
  do_determine_type(Gogo*, const Type_context*)
  { }

  Expression*
  do_copy()
  {
    return Expression::make_func_code_reference(this->function_,
						this->location());
  }

  Bexpression*
  do_get_backend(Translate_context*);

  void
  do_dump_expression(Ast_dump_context* context) const
  { context->ostream() << "[raw " << this->function_->name() << "]" ; }

 private:
  // The function.
  Named_object* function_;
};

// Get the backend representation for a reference to function code.

Bexpression*
Func_code_reference_expression::do_get_backend(Translate_context* context)
{
  return Func_expression::get_code_pointer(context->gogo(), this->function_,
					   this->location());
}

// Make a reference to the code of a function.

Expression*
Expression::make_func_code_reference(Named_object* function, Location location)
{
  return new Func_code_reference_expression(function, location);
}

// Class Unknown_expression.

// Return the name of an unknown expression.

const std::string&
Unknown_expression::name() const
{
  return this->named_object_->name();
}

// Set the iota value if this could be a reference to iota.

void
Unknown_expression::set_iota_value(int iota_value)
{
  this->iota_value_ = iota_value;
  this->is_iota_ = true;
}

// Traversal.

int
Unknown_expression::do_traverse(Traverse* traverse)
{
  if (this->lowered_ != NULL)
    {
      if (Expression::traverse(&this->lowered_, traverse) == TRAVERSE_EXIT)
	return TRAVERSE_EXIT;
    }
  return TRAVERSE_CONTINUE;
}

// Determine the type of a reference to an unknown name.  At this
// point we have to figure out what the name refers to.

void
Unknown_expression::do_determine_type(Gogo* gogo, const Type_context* context)
{
  if (this->is_error_expression())
    return;

  if (this->lowered_ != NULL)
    {
      this->lowered_->determine_type(gogo, context);
      return;
    }

  Location loc = this->location();

  Named_object* no = this->named_object_;
  if (no->is_unknown())
    {
      Named_object* real = no->unknown_value()->real_named_object();
      if (real == NULL)
	{
	  if (!this->no_error_message_)
	    go_error_at(loc, "reference to undefined name %qs",
			no->message_name().c_str());
	  this->set_is_error();
	  return;
	}
      no = real;
      this->named_object_ = real;
    }

  switch (no->classification())
    {
    case Named_object::NAMED_OBJECT_TYPE:
      this->lowered_ = Expression::make_type(no->type_value(), loc);
      break;
    case Named_object::NAMED_OBJECT_FUNC:
    case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
      this->lowered_ = Expression::make_func_reference(no, NULL, loc);
      break;
    case Named_object::NAMED_OBJECT_CONST:
      this->lowered_ = Expression::make_const_reference(no, loc);
      this->lowered_->determine_type(gogo, context);
      if (this->is_iota_)
	this->lowered_->const_expression()->set_iota_value(this->iota_value_);
      break;
    case Named_object::NAMED_OBJECT_VAR:
      this->lowered_ = Expression::make_var_reference(no, loc);
      no->var_value()->set_is_used();
      this->lowered_->determine_type(gogo, context);
      break;
    case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
      if (!this->no_error_message_)
	go_error_at(this->location(), "reference to undefined type %qs",
		    no->message_name().c_str());
      this->set_is_error();
      break;
    case Named_object::NAMED_OBJECT_PACKAGE:
      if (!this->no_error_message_)
	this->report_error(_("unexpected reference to package"));
      this->set_is_error();
      break;
    default:
      go_unreachable();
    }
}

Type*
Unknown_expression::do_type()
{
  if (this->is_error_expression())
    return Type::make_error_type();
  go_assert(this->lowered_ != NULL);
  return this->lowered_->type();
}

bool
Unknown_expression::do_is_constant() const
{
  if (this->is_error_expression())
    return true;
  if (this->lowered_ != NULL)
    return this->lowered_->is_constant();

  // This can be called before do_determine_types by
  // Binary_expression::do_determine_type, which needs to know which
  // values are constant before it works out the appropriate
  // Type_context to pass down.
  Named_object* no = this->named_object_;
  if (no->is_unknown())
    {
      no = no->unknown_value()->real_named_object();
      if (no == NULL)
	return true;
    }
  return no->is_const();
}

bool
Unknown_expression::do_is_untyped(Type** ptype) const
{
  if (this->is_error_expression())
    return false;
  if (this->lowered_ != NULL)
    return this->lowered_->is_untyped(ptype);

  Named_object* no = this->named_object_;
  if (no->is_unknown())
    {
      no = no->unknown_value()->real_named_object();
      if (no == NULL)
	return false;
    }

  if (!no->is_const())
    return false;
  Type* t = no->const_value()->type();
  if (t != NULL)
    return Expression::is_untyped_type(t, ptype);
  return no->const_value()->expr()->is_untyped(ptype);
}

bool
Unknown_expression::do_numeric_constant_value(Numeric_constant* nc)
{
  if (this->is_error_expression())
    return false;
  if (this->lowered_ != NULL)
    return this->lowered_->numeric_constant_value(nc);

  // This can be called before the determine_types pass.
  Named_object* no = this->named_object_;
  if (no->is_unknown())
    {
      no = no->unknown_value()->real_named_object();
      if (no == NULL)
	return false;
    }
  if (!no->is_const())
    return false;
  return no->const_value()->expr()->numeric_constant_value(nc);
}

bool
Unknown_expression::do_string_constant_value(std::string* val)
{
  if (this->is_error_expression())
    return false;
  go_assert(this->lowered_ != NULL);
  return this->lowered_->string_constant_value(val);
}

bool
Unknown_expression::do_boolean_constant_value(bool* val)
{
  if (this->is_error_expression())
    return false;
  go_assert(this->lowered_ != NULL);
  return this->lowered_->boolean_constant_value(val);
}

bool
Unknown_expression::do_is_addressable() const
{
  if (this->is_error_expression())
    return true;
  go_assert(this->lowered_ != NULL);
  return this->lowered_->is_addressable();
}

// Lower a reference to an unknown name.

Expression*
Unknown_expression::do_lower(Gogo*, Named_object*, Statement_inserter*)
{
  if (this->is_error_expression())
    return Expression::make_error(this->location());
  go_assert(this->lowered_ != NULL);
  return this->lowered_;
}

// Dump the ast representation for an unknown expression to a dump context.

void
Unknown_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  if (this->lowered_ != NULL)
    this->lowered_->dump_expression(ast_dump_context);
  else
    ast_dump_context->ostream() << "_Unknown_(" << this->named_object_->name()
				<< ")";
}

// Make a reference to an unknown name.

Unknown_expression*
Expression::make_unknown_reference(Named_object* no, Location location)
{
  return new Unknown_expression(no, location);
}

// Start exporting a type conversion for a constant, if needed.  This
// returns whether we need to export a closing parenthesis.

bool
Expression::export_constant_type(Export_function_body* efb, Type* type)
{
  if (type == NULL
      || type->is_abstract()
      || type == efb->type_context())
    return false;
  efb->write_c_string("$convert(");
  efb->write_type(type);
  efb->write_c_string(", ");
  return true;
}

// Finish a type conversion for a constant.

void
Expression::finish_export_constant_type(Export_function_body* efb, bool needed)
{
  if (needed)
    efb->write_c_string(")");
}

// A boolean expression.

class Boolean_expression : public Expression
{
 public:
  Boolean_expression(bool val, Location location)
    : Expression(EXPRESSION_BOOLEAN, location),
      val_(val), type_(NULL)
  { }

  static Expression*
  do_import(Import_expression*, Location);

 protected:
  int
  do_traverse(Traverse*);

  bool
  do_is_constant() const
  { return true; }

  bool
  do_is_untyped(Type**) const;

  bool
  do_is_zero_value() const
  { return this->val_ == false; }

  bool
  do_boolean_constant_value(bool* val)
  {
    *val = this->val_;
    return true;
  }

  bool
  do_is_static_initializer() const
  { return true; }

  Type*
  do_type();

  void
  do_determine_type(Gogo*, const Type_context*);

  Expression*
  do_copy()
  { return this; }

  Bexpression*
  do_get_backend(Translate_context* context)
  { return context->backend()->boolean_constant_expression(this->val_); }

  int
  do_inlining_cost() const
  { return 1; }

  void
  do_export(Export_function_body* efb) const;

  void
  do_dump_expression(Ast_dump_context* ast_dump_context) const
  { ast_dump_context->ostream() << (this->val_ ? "true" : "false"); }

 private:
  // The constant.
  bool val_;
  // The type as determined by context.
  Type* type_;
};

// Traverse a boolean expression.  We just need to traverse the type
// if there is one.

int
Boolean_expression::do_traverse(Traverse* traverse)
{
  if (this->type_ != NULL)
    return Type::traverse(this->type_, traverse);
  return TRAVERSE_CONTINUE;
}

bool
Boolean_expression::do_is_untyped(Type** ptype) const
{
  if (this->type_ != NULL)
    return Expression::is_untyped_type(this->type_, ptype);
  *ptype = Type::make_boolean_type();
  return true;
}

// Get the type.

Type*
Boolean_expression::do_type()
{
  if (this->type_ == NULL)
    this->type_ = Type::make_boolean_type();
  return this->type_;
}

// Set the type from the context.

void
Boolean_expression::do_determine_type(Gogo*, const Type_context* context)
{
  if (this->type_ != NULL && !this->type_->is_abstract())
    ;
  else if (context->type != NULL && context->type->is_boolean_type())
    this->type_ = context->type;
  else if (!context->may_be_abstract)
    this->type_ = Type::lookup_bool_type();
}

// Export a boolean constant.

void
Boolean_expression::do_export(Export_function_body* efb) const
{
  bool exported_type = Expression::export_constant_type(efb, this->type_);
  efb->write_c_string(this->val_ ? "$true" : "$false");
  Expression::finish_export_constant_type(efb, exported_type);
}

// Import a boolean constant.

Expression*
Boolean_expression::do_import(Import_expression* imp, Location loc)
{
  if (imp->version() >= EXPORT_FORMAT_V3)
    imp->require_c_string("$");
  if (imp->peek_char() == 't')
    {
      imp->require_c_string("true");
      return Expression::make_boolean(true, loc);
    }
  else
    {
      imp->require_c_string("false");
      return Expression::make_boolean(false, loc);
    }
}

// Make a boolean expression.

Expression*
Expression::make_boolean(bool val, Location location)
{
  return new Boolean_expression(val, location);
}

// Class String_expression.

// Traverse a string expression.  We just need to traverse the type
// if there is one.

int
String_expression::do_traverse(Traverse* traverse)
{
  if (this->type_ != NULL)
    return Type::traverse(this->type_, traverse);
  return TRAVERSE_CONTINUE;
}

bool
String_expression::do_is_untyped(Type** ptype) const
{
  if (this->type_ != NULL)
    return Expression::is_untyped_type(this->type_, ptype);
  *ptype = Type::make_string_type();
  return true;
}

// Get the type.

Type*
String_expression::do_type()
{
  if (this->type_ == NULL)
    this->type_ = Type::make_string_type();
  return this->type_;
}

// Set the type from the context.

void
String_expression::do_determine_type(Gogo*, const Type_context* context)
{
  if (this->type_ != NULL && !this->type_->is_abstract())
    ;
  else if (context->type != NULL && context->type->is_string_type())
    this->type_ = context->type;
  else if (!context->may_be_abstract)
    this->type_ = Type::lookup_string_type();
}

// Build a string constant.

Bexpression*
String_expression::do_get_backend(Translate_context* context)
{
  Gogo* gogo = context->gogo();
  Btype* btype = Type::make_string_type()->get_backend(gogo);

  Location loc = this->location();
  std::vector<Bexpression*> init(2);

  if (this->val_.size() == 0)
    init[0] = gogo->backend()->nil_pointer_expression();
  else
    {
      Bexpression* str_cst =
	gogo->backend()->string_constant_expression(this->val_);
      init[0] = gogo->backend()->address_expression(str_cst, loc);
    }

  Btype* int_btype = Type::lookup_integer_type("int")->get_backend(gogo);
  mpz_t lenval;
  mpz_init_set_ui(lenval, this->val_.length());
  init[1] = gogo->backend()->integer_constant_expression(int_btype, lenval);
  mpz_clear(lenval);

  return gogo->backend()->constructor_expression(btype, init, loc);
}

 // Write string literal to string dump.

void
String_expression::export_string(String_dump* exp,
				 const String_expression* str)
{
  std::string s;
  s.reserve(str->val_.length() * 4 + 2);
  s += '"';
  for (std::string::const_iterator p = str->val_.begin();
       p != str->val_.end();
       ++p)
    {
      if (*p == '\\' || *p == '"')
	{
	  s += '\\';
	  s += *p;
	}
      else if (*p >= 0x20 && *p < 0x7f)
	s += *p;
      else if (*p == '\n')
	s += "\\n";
      else if (*p == '\t')
	s += "\\t";
      else
	{
	  s += "\\x";
	  unsigned char c = *p;
	  unsigned int dig = c >> 4;
	  s += dig < 10 ? '0' + dig : 'A' + dig - 10;
	  dig = c & 0xf;
	  s += dig < 10 ? '0' + dig : 'A' + dig - 10;
	}
    }
  s += '"';
  exp->write_string(s);
}

// Export a string expression.

void
String_expression::do_export(Export_function_body* efb) const
{
  bool exported_type = Expression::export_constant_type(efb, this->type_);
  String_expression::export_string(efb, this);
  Expression::finish_export_constant_type(efb, exported_type);
}

// Import a string expression.

Expression*
String_expression::do_import(Import_expression* imp, Location loc)
{
  imp->require_c_string("\"");
  std::string val;
  while (true)
    {
      int c = imp->get_char();
      if (c == '"' || c == -1)
	break;
      if (c != '\\')
	val += static_cast<char>(c);
      else
	{
	  c = imp->get_char();
	  if (c == '\\' || c == '"')
	    val += static_cast<char>(c);
	  else if (c == 'n')
	    val += '\n';
	  else if (c == 't')
	    val += '\t';
	  else if (c == 'x')
	    {
	      c = imp->get_char();
	      unsigned int vh = c >= '0' && c <= '9' ? c - '0' : c - 'A' + 10;
	      c = imp->get_char();
	      unsigned int vl = c >= '0' && c <= '9' ? c - '0' : c - 'A' + 10;
	      char v = (vh << 4) | vl;
	      val += v;
	    }
	  else
	    {
	      go_error_at(imp->location(), "bad string constant");
	      return Expression::make_error(loc);
	    }
	}
    }
  return Expression::make_string(val, loc);
}

// Ast dump for string expression.

void
String_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  String_expression::export_string(ast_dump_context, this);
}

// Make a string expression with abstract string type (common case).

Expression*
Expression::make_string(const std::string& val, Location location)
{
  return new String_expression(val, NULL, location);
}

// Make a string expression with a specific string type.

Expression*
Expression::make_string_typed(const std::string& val, Type* type, Location location)
{
  return new String_expression(val, type, location);
}

// An expression that evaluates to some characteristic of a string.
// This is used when indexing, bound-checking, or nil checking a string.

class String_info_expression : public Expression
{
 public:
  String_info_expression(Expression* string, String_info string_info,
                        Location location)
    : Expression(EXPRESSION_STRING_INFO, location),
      string_(string), string_info_(string_info)
  { }

 protected:
  Type*
  do_type();

  void
  do_determine_type(Gogo*, const Type_context*)
  { }

  Expression*
  do_copy()
  {
    return new String_info_expression(this->string_->copy(), this->string_info_,
				      this->location());
  }

  Bexpression*
  do_get_backend(Translate_context* context);

  void
  do_dump_expression(Ast_dump_context*) const;

  void
  do_issue_nil_check()
  { this->string_->issue_nil_check(); }

 private:
  // The string for which we are getting information.
  Expression* string_;
  // What information we want.
  String_info string_info_;
};

// Return the type of the string info.

Type*
String_info_expression::do_type()
{
  switch (this->string_info_)
    {
    case STRING_INFO_DATA:
      {
	Type* byte_type = Type::lookup_integer_type("uint8");
	return Type::make_pointer_type(byte_type);
      }
    case STRING_INFO_LENGTH:
        return Type::lookup_integer_type("int");
    default:
      go_unreachable();
    }
}

// Return string information in GENERIC.

Bexpression*
String_info_expression::do_get_backend(Translate_context* context)
{
  Gogo* gogo = context->gogo();

  Bexpression* bstring = this->string_->get_backend(context);
  switch (this->string_info_)
    {
    case STRING_INFO_DATA:
    case STRING_INFO_LENGTH:
      return gogo->backend()->struct_field_expression(bstring,
						      this->string_info_,
						      this->location());
      break;
    default:
      go_unreachable();
    }
}

// Dump ast representation for a type info expression.

void
String_info_expression::do_dump_expression(
    Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->ostream() << "stringinfo(";
  this->string_->dump_expression(ast_dump_context);
  ast_dump_context->ostream() << ",";
  ast_dump_context->ostream() <<
      (this->string_info_ == STRING_INFO_DATA ? "data"
    : this->string_info_ == STRING_INFO_LENGTH ? "length"
    : "unknown");
  ast_dump_context->ostream() << ")";
}

// Make a string info expression.

Expression*
Expression::make_string_info(Expression* string, String_info string_info,
                            Location location)
{
  return new String_info_expression(string, string_info, location);
}

// An expression that represents an string value: a struct with value pointer
// and length fields.

class String_value_expression : public Expression
{
 public:
  String_value_expression(Expression* valptr, Expression* len, Location location)
      : Expression(EXPRESSION_STRING_VALUE, location),
        valptr_(valptr), len_(len)
  { }

 protected:
  int
  do_traverse(Traverse*);

  Type*
  do_type()
  { return Type::make_string_type(); }

  void
  do_determine_type(Gogo*, const Type_context*)
  { go_unreachable(); }

  Expression*
  do_copy()
  {
    return new String_value_expression(this->valptr_->copy(),
                                       this->len_->copy(),
                                       this->location());
  }

  Bexpression*
  do_get_backend(Translate_context* context);

  void
  do_dump_expression(Ast_dump_context*) const;

 private:
  // The value pointer.
  Expression* valptr_;
  // The length.
  Expression* len_;
};

int
String_value_expression::do_traverse(Traverse* traverse)
{
  if (Expression::traverse(&this->valptr_, traverse) == TRAVERSE_EXIT
      || Expression::traverse(&this->len_, traverse) == TRAVERSE_EXIT)
    return TRAVERSE_EXIT;
  return TRAVERSE_CONTINUE;
}

Bexpression*
String_value_expression::do_get_backend(Translate_context* context)
{
  std::vector<Bexpression*> vals(2);
  vals[0] = this->valptr_->get_backend(context);
  vals[1] = this->len_->get_backend(context);

  Gogo* gogo = context->gogo();
  Btype* btype = Type::make_string_type()->get_backend(gogo);
  return gogo->backend()->constructor_expression(btype, vals, this->location());
}

void
String_value_expression::do_dump_expression(
    Ast_dump_context* ast_dump_context) const
{
  ast_dump_context->ostream() << "stringvalue(";
  ast_dump_context->ostream() << "value: ";
  this->valptr_->dump_expression(ast_dump_context);
  ast_dump_context->ostream() << ", length: ";
  this->len_->dump_expression(ast_dump_context);
  ast_dump_context->ostream() << ")";
}

Expression*
Expression::make_string_value(Expression* valptr, Expression* len,
                              Location location)
{
  return new String_value_expression(valptr, len, location);
}

// Make an integer expression.

class Integer_expression : public Expression
{
 public:
  Integer_expression(const mpz_t* val, Type* type, bool is_character_constant,
		     Location location)
    : Expression(EXPRESSION_INTEGER, location),
      type_(type), is_character_constant_(is_character_constant)
  { mpz_init_set(this->val_, *val); }

  static Expression*
  do_import(Import_expression*, Location);

  // Write VAL to string dump.
  static void
  export_integer(String_dump* exp, const mpz_t val);

  // Write VAL to dump context.
  static void
  dump_integer(Ast_dump_context* ast_dump_context, const mpz_t val);

 protected:
  int
  do_traverse(Traverse*);

  bool
  do_is_constant() const
  { return true; }

  bool
  do_is_untyped(Type**) const;

  bool
  do_is_zero_value() const
  { return mpz_sgn(this->val_) == 0; }

  bool
  do_is_static_initializer() const
  { return true; }

  bool
  do_numeric_constant_value(Numeric_constant* nc);

  Type*
  do_type();

  void
  do_determine_type(Gogo*, const Type_context* context);

  void
  do_check_types(Gogo*);

  Bexpression*
  do_get_backend(Translate_context*);

  Expression*
  do_copy()
  {
    if (this->is_character_constant_)
      return Expression::make_character(&this->val_,
					(this->type_ == NULL
					 ? NULL
					 : this->type_->copy_expressions()),
					this->location());
    else
      return Expression::make_integer_z(&this->val_,
					(this->type_ == NULL
					 ? NULL
					 : this->type_->copy_expressions()),
					this->location());
  }

  int
  do_inlining_cost() const
  { return 1; }

  void
  do_export(Export_function_body*) const;

  void
  do_dump_expression(Ast_dump_context*) const;

 private:
  // The integer value.
  mpz_t val_;
  // The type so far.
  Type* type_;
  // Whether this is a character constant.
  bool is_character_constant_;
};

// Traverse an integer expression.  We just need to traverse the type
// if there is one.

int
Integer_expression::do_traverse(Traverse* traverse)
{
  if (this->type_ != NULL)
    return Type::traverse(this->type_, traverse);
  return TRAVERSE_CONTINUE;
}

// Return a numeric constant for this expression.  We have to mark
// this as a character when appropriate.

bool
Integer_expression::do_numeric_constant_value(Numeric_constant* nc)
{
  if (this->is_character_constant_)
    nc->set_rune(this->type_, this->val_);
  else
    nc->set_int(this->type_, this->val_);
  return true;
}

bool
Integer_expression::do_is_untyped(Type** ptype) const
{
  if (this->type_ != NULL)
    return Expression::is_untyped_type(this->type_, ptype);
  if (this->is_character_constant_)
    *ptype = Type::make_abstract_character_type();
  else
    *ptype = Type::make_abstract_integer_type();
  return true;
}

// Return the current type.  If we haven't set the type yet, we return
// an abstract integer type.

Type*
Integer_expression::do_type()
{
  if (this->type_ == NULL)
    {
      if (this->is_character_constant_)
	this->type_ = Type::make_abstract_character_type();
      else
	this->type_ = Type::make_abstract_integer_type();
    }
  return this->type_;
}

// Set the type of the integer value.  Here we may switch from an
// abstract type to a real type.

void
Integer_expression::do_determine_type(Gogo*, const Type_context* context)
{
  if (this->type_ != NULL && !this->type_->is_abstract())
    ;
  else if (context->type != NULL && context->type->is_numeric_type())
    this->type_ = context->type;
  else if (!context->may_be_abstract)
    {
      if (this->is_character_constant_)
	this->type_ = Type::lookup_integer_type("int32");
      else
	this->type_ = Type::lookup_integer_type("int");
    }
}

// Check the type of an integer constant.

void
Integer_expression::do_check_types(Gogo*)
{
  Type* type = this->type_;
  if (type == NULL)
    return;
  Numeric_constant nc;
  if (this->is_character_constant_)
    nc.set_rune(NULL, this->val_);
  else
    nc.set_int(NULL, this->val_);
  if (!nc.set_type(type, true, this->location()))
    this->set_is_error();
}

// Get the backend representation for an integer constant.

Bexpression*
Integer_expression::do_get_backend(Translate_context* context)
{
  if (this->is_error_expression()
      || (this->type_ != NULL && this->type_->is_error_type()))
    {
      go_assert(saw_errors());
      return context->gogo()->backend()->error_expression();
    }

  Type* resolved_type = NULL;
  if (this->type_ != NULL && !this->type_->is_abstract())
    resolved_type = this->type_;
  else if (this->type_ != NULL && this->type_->float_type() != NULL)
    {
      // We are converting to an abstract floating point type.
      resolved_type = Type::lookup_float_type("float64");
    }
  else if (this->type_ != NULL && this->type_->complex_type() != NULL)
    {
      // We are converting to an abstract complex type.
      resolved_type = Type::lookup_complex_type("complex128");
    }
  else
    {
      // If we still have an abstract type here, then this is being
      // used in a constant expression which didn't get reduced for
      // some reason.  Use a type which will fit the value.  We use <,
      // not <=, because we need an extra bit for the sign bit.
      int bits = mpz_sizeinbase(this->val_, 2);
      Type* int_type = Type::lookup_integer_type("int");
      if (bits < int_type->integer_type()->bits())
	resolved_type = int_type;
      else if (bits < 64)
        resolved_type = Type::lookup_integer_type("int64");
      else
        {
          if (!saw_errors())
            go_error_at(this->location(), "integer constant overflow");
          return context->gogo()->backend()->error_expression();
        }
    }
  Numeric_constant nc;
  nc.set_int(resolved_type, this->val_);
  return Expression::backend_numeric_constant_expression(context, &nc);
}

// Write VAL to export data.

void
Integer_expression::export_integer(String_dump* exp, const mpz_t val)
{
  char* s = mpz_get_str(NULL, 10, val);
  exp->write_c_string(s);
  free(s);
}

// Export an integer in a constant expression.

void
Integer_expression::do_export(Export_function_body* efb) const
{
  bool exported_type = Expression::export_constant_type(efb, this->type_);

  Integer_expression::export_integer(efb, this->val_);
  if (this->is_character_constant_)
    efb->write_c_string("'");
  // A trailing space lets us reliably identify the end of the number.
  efb->write_c_string(" ");

  Expression::finish_export_constant_type(efb, exported_type);
}

// Import an integer, floating point, or complex value.  This handles
// all these types because they all start with digits.

Expression*
Integer_expression::do_import(Import_expression* imp, Location loc)
{
  std::string num = imp->read_identifier();
  imp->require_c_string(" ");
  if (!num.empty() && num[num.length() - 1] == 'i')
    {
      mpfr_t real;
      size_t plus_pos = num.find('+', 1);
      size_t minus_pos = num.find('-', 1);
      size_t pos;
      if (plus_pos == std::string::npos)
	pos = minus_pos;
      else if (minus_pos == std::string::npos)
	pos = plus_pos;
      else
	{
	  go_error_at(imp->location(), "bad number in import data: %qs",
		      num.c_str());
	  return Expression::make_error(loc);
	}
      if (pos == std::string::npos)
	mpfr_init_set_ui(real, 0, MPFR_RNDN);
      else
	{
	  std::string real_str = num.substr(0, pos);
	  if (mpfr_init_set_str(real, real_str.c_str(), 10, MPFR_RNDN) != 0)
	    {
	      go_error_at(imp->location(), "bad number in import data: %qs",
			  real_str.c_str());
	      return Expression::make_error(loc);
	    }
	}

      std::string imag_str;
      if (pos == std::string::npos)
	imag_str = num;
      else
	imag_str = num.substr(pos);
      imag_str = imag_str.substr(0, imag_str.size() - 1);
      mpfr_t imag;
      if (mpfr_init_set_str(imag, imag_str.c_str(), 10, MPFR_RNDN) != 0)
	{
	  go_error_at(imp->location(), "bad number in import data: %qs",
		      imag_str.c_str());
	  return Expression::make_error(loc);
	}
      mpc_t cval;
      mpc_init2(cval, mpc_precision);
      mpc_set_fr_fr(cval, real, imag, MPC_RNDNN);
      mpfr_clear(real);
      mpfr_clear(imag);
      Expression* ret = Expression::make_complex(&cval, NULL, loc);
      mpc_clear(cval);
      return ret;
    }
  else if (num.find('.') == std::string::npos
	   && num.find('E') == std::string::npos)
    {
      bool is_character_constant = (!num.empty()
				    && num[num.length() - 1] == '\'');
      if (is_character_constant)
	num = num.substr(0, num.length() - 1);
      mpz_t val;
      if (mpz_init_set_str(val, num.c_str(), 10) != 0)
	{
	  go_error_at(imp->location(), "bad number in import data: %qs",
		      num.c_str());
	  return Expression::make_error(loc);
	}
      Expression* ret;
      if (is_character_constant)
	ret = Expression::make_character(&val, NULL, loc);
      else
	ret = Expression::make_integer_z(&val, NULL, loc);
      mpz_clear(val);
      return ret;
    }
  else
    {
      mpfr_t val;
      if (mpfr_init_set_str(val, num.c_str(), 10, MPFR_RNDN) != 0)
	{
	  go_error_at(imp->location(), "bad number in import data: %qs",
		      num.c_str());
	  return Expression::make_error(loc);
	}
      Expression* ret = Expression::make_float(&val, NULL, loc);
      mpfr_clear(val);
      return ret;
    }
}
// Ast dump for integer expression.

void
Integer_expression::do_dump_expression(Ast_dump_context* ast_dump_context) const
{
  if (this->is_character_constant_)
    ast_dump_context->ostream() << '\'';
  Integer_expression::export_integer(ast_dump_context, this->val_);
  if (this->is_character_constant_)
    ast_dump_context->ostream() << '\'';
}

// Build a new integer value from a multi-precision integer.

Expression*
Expression::make_integer_z(const mpz_t* val, Type* type, Location location)
{
  return new Integer_expression(val, type, false, location);
}

// Build a new integer value from an unsigned long.

Expression*
Expression::make_integer_ul(unsigned long val, Type *type, Location location)
{
  mpz_t zval;
  mpz_init_set_ui(zval, val);
  Expression* ret = Expression::make_integer_z(&zval, type, location);
  mpz_clear(zval);
  return ret;
}

// Build a new integer value from a signed long.

Expression*
Expression::make_integer_sl(long val, Type *type, Location location)
{
  mpz_t zval;
  mpz_init_set_si(zval, val);
  Expression* ret = Expression::make_integer_z(&zval, type, location);
  mpz_clear(zval);
  return ret;
}

// Store an int64_t in an uninitialized mpz_t.

static void
set_mpz_from_int64(mpz_t* zval, int64_t val)
{
  if (val >= 0)
    {
      unsigned long ul = static_cast<unsigned long>(val);
      if (static_cast<int64_t>(ul) == val)
	{
	  mpz_init_set_ui(*zval, ul);
	  return;
	}
    }
  uint64_t uv;
  if (val >= 0)
    uv = static_cast<uint64_t>(val);
  else
    uv = static_cast<uint64_t>(- val);
  unsigned long ul = uv & 0xffffffffUL;
  mpz_init_set_ui(*zval, ul);
  mpz_t hval;
  mpz_init_set_ui(hval, static_cast<unsigned long>(uv >> 32));
  mpz_mul_2exp(hval, hval, 32);
  mpz_add(*zval, *zval, hval);
  mpz_clear(hval);
  if (val < 0)
    mpz_neg(*zval, *zval);
}

// Build a new integer value from an int64_t.

Expression*
Expression::make_integer_int64(int64_t val, Type* type, Location location)
{
  mpz_t zval;
  set_mpz_from_int64(&zval, val);
  Expression* ret = Expression::make_integer_z(&zval, type, location);
  mpz_clear(zval);
  return ret;
}