// Copyright (C) 2020 Free Software Foundation, Inc.

// 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/>.

#ifndef RUST_BACKEND_H
#define RUST_BACKEND_H

#include <gmp.h>
#include <mpfr.h>
#include <mpc.h>

#include "operator.h"

extern bool
saw_errors (void);

// TODO: Will have to be significantly modified to work with Rust and current
// setup of gccrs

// Pointers to these types are created by the backend, passed to the
// frontend, and passed back to the backend.  The types must be
// defined by the backend using these names.

// The backend representation of a type.
class Btype;

// The backend represention of an expression.
class Bexpression;

// The backend representation of a statement.
class Bstatement;

// The backend representation of a function definition or declaration.
class Bfunction;

// The backend representation of a block.
class Bblock;

// The backend representation of a variable.
class Bvariable;

// The backend representation of a label.
class Blabel;

// The backend interface.  This is a pure abstract class that a
// specific backend will implement.

class Backend
{
public:
  virtual ~Backend () {}

  // Name/type/location.  Used for function parameters, struct fields,
  // interface methods.
  struct Btyped_identifier
  {
    std::string name;
    Btype *btype;
    Location location;

    Btyped_identifier ()
      : name (), btype (NULL), location (Linemap::unknown_location ())
    {}

    Btyped_identifier (const std::string &a_name, Btype *a_btype,
		       Location a_location)
      : name (a_name), btype (a_btype), location (a_location)
    {}
  };

  // Types.

  // Produce an error type.  Actually the backend could probably just
  // crash if this is called.
  virtual Btype *error_type () = 0;

  // Get a void type.  This is used in (at least) two ways: 1) as the
  // return type of a function with no result parameters; 2)
  // unsafe.Pointer is represented as *void.
  virtual Btype *void_type () = 0;

  // Get the unnamed boolean type.
  virtual Btype *bool_type () = 0;

  // Get an unnamed integer type with the given signedness and number
  // of bits.
  virtual Btype *integer_type (bool is_unsigned, int bits) = 0;

  // Get an unnamed floating point type with the given number of bits
  // (32 or 64).
  virtual Btype *float_type (int bits) = 0;

  // Get an unnamed complex type with the given number of bits (64 or 128).
  virtual Btype *complex_type (int bits) = 0;

  // Get a pointer type.
  virtual Btype *pointer_type (Btype *to_type) = 0;

  // Get a function type.  The receiver, parameter, and results are
  // generated from the types in the Function_type.  The Function_type
  // is provided so that the names are available.  This should return
  // not the type of a Go function (which is a pointer to a struct)
  // but the type of a C function pointer (which will be used as the
  // type of the first field of the struct).  If there is more than
  // one result, RESULT_STRUCT is a struct type to hold the results,
  // and RESULTS may be ignored; if there are zero or one results,
  // RESULT_STRUCT is NULL.
  virtual Btype *
  function_type (const Btyped_identifier &receiver,
		 const std::vector<Btyped_identifier> &parameters,
		 const std::vector<Btyped_identifier> &results,
		 Btype *result_struct, Location location)
    = 0;

  // Get a struct type.
  virtual Btype *struct_type (const std::vector<Btyped_identifier> &fields) = 0;

  // Get an array type.
  virtual Btype *array_type (Btype *element_type, Bexpression *length) = 0;

  // Create a placeholder pointer type.  This is used for a named
  // pointer type, since in Go a pointer type may refer to itself.
  // NAME is the name of the type, and the location is where the named
  // type is defined.  This function is also used for unnamed function
  // types with multiple results, in which case the type has no name
  // and NAME will be empty.  FOR_FUNCTION is true if this is for a C
  // pointer to function type.  A Go func type is represented as a
  // pointer to a struct, and the first field of the struct is a C
  // pointer to function.  The return value will later be passed as
  // the first parameter to set_placeholder_pointer_type or
  // set_placeholder_function_type.
  virtual Btype *placeholder_pointer_type (const std::string &name, Location,
					   bool for_function)
    = 0;

  // Fill in a placeholder pointer type as a pointer.  This takes a
  // type returned by placeholder_pointer_type and arranges for it to
  // point to the type that TO_TYPE points to (that is, PLACEHOLDER
  // becomes the same type as TO_TYPE).  Returns true on success,
  // false on failure.
  virtual bool set_placeholder_pointer_type (Btype *placeholder, Btype *to_type)
    = 0;

  // Fill in a placeholder pointer type as a function.  This takes a
  // type returned by placeholder_pointer_type and arranges for it to
  // become a real Go function type (which corresponds to a C/C++
  // pointer to function type).  FT will be something returned by the
  // function_type method.  Returns true on success, false on failure.
  virtual bool set_placeholder_function_type (Btype *placeholder, Btype *ft)
    = 0;

  // Create a placeholder struct type.  This is used for a named
  // struct type, as with placeholder_pointer_type.  It is also used
  // for interface types, in which case NAME will be the empty string.
  virtual Btype *placeholder_struct_type (const std::string &name, Location)
    = 0;

  // Fill in a placeholder struct type.  This takes a type returned by
  // placeholder_struct_type and arranges for it to become a real
  // struct type.  The parameter is as for struct_type.  Returns true
  // on success, false on failure.
  virtual bool
  set_placeholder_struct_type (Btype *placeholder,
			       const std::vector<Btyped_identifier> &fields)
    = 0;

  // Create a placeholder array type.  This is used for a named array
  // type, as with placeholder_pointer_type, to handle cases like
  // type A []*A.
  virtual Btype *placeholder_array_type (const std::string &name, Location) = 0;

  // Fill in a placeholder array type.  This takes a type returned by
  // placeholder_array_type and arranges for it to become a real array
  // type.  The parameters are as for array_type.  Returns true on
  // success, false on failure.
  virtual bool set_placeholder_array_type (Btype *placeholder,
					   Btype *element_type,
					   Bexpression *length)
    = 0;

  // Return a named version of a type.  The location is the location
  // of the type definition.  This will not be called for a type
  // created via placeholder_pointer_type, placeholder_struct_type, or
  // placeholder_array_type..  (It may be called for a pointer,
  // struct, or array type in a case like "type P *byte; type Q P".)
  virtual Btype *named_type (const std::string &name, Btype *, Location) = 0;

  // Create a marker for a circular pointer type.  Go pointer and
  // function types can refer to themselves in ways that are not
  // permitted in C/C++.  When a circular type is found, this function
  // is called for the circular reference.  This permits the backend
  // to decide how to handle such a type.  PLACEHOLDER is the
  // placeholder type which has already been created; if the backend
  // is prepared to handle a circular pointer type, it may simply
  // return PLACEHOLDER.  FOR_FUNCTION is true if this is for a
  // function type.
  //
  // For "type P *P" the sequence of calls will be
  //   bt1 = placeholder_pointer_type();
  //   bt2 = circular_pointer_type(bt1, false);
  //   set_placeholder_pointer_type(bt1, bt2);
  virtual Btype *circular_pointer_type (Btype *placeholder, bool for_function)
    = 0;

  // Return whether the argument could be a special type created by
  // circular_pointer_type.  This is used to introduce explicit type
  // conversions where needed.  If circular_pointer_type returns its
  // PLACEHOLDER parameter, this may safely always return false.
  virtual bool is_circular_pointer_type (Btype *) = 0;

  // Return the size of a type.
  virtual int64_t type_size (Btype *) = 0;

  // Return the alignment of a type.
  virtual int64_t type_alignment (Btype *) = 0;

  // Return the alignment of a struct field of this type.  This is
  // normally the same as type_alignment, but not always.
  virtual int64_t type_field_alignment (Btype *) = 0;

  // Return the offset of field INDEX in a struct type.  INDEX is the
  // entry in the FIELDS std::vector parameter of struct_type or
  // set_placeholder_struct_type.
  virtual int64_t type_field_offset (Btype *, size_t index) = 0;

  // Expressions.

  // Return an expression for a zero value of the given type.  This is
  // used for cases such as local variable initialization and
  // converting nil to other types.
  virtual Bexpression *zero_expression (Btype *) = 0;

  // Create an error expression. This is used for cases which should
  // not occur in a correct program, in order to keep the compilation
  // going without crashing.
  virtual Bexpression *error_expression () = 0;

  // Create a nil pointer expression.
  virtual Bexpression *nil_pointer_expression () = 0;

  // Create a reference to a variable.
  virtual Bexpression *var_expression (Bvariable *var, Location) = 0;

  // Create an expression that indirects through the pointer expression EXPR
  // (i.e., return the expression for *EXPR). KNOWN_VALID is true if the pointer
  // is known to point to a valid memory location.  BTYPE is the expected type
  // of the indirected EXPR.
  virtual Bexpression *indirect_expression (Btype *btype, Bexpression *expr,
					    bool known_valid, Location)
    = 0;

  // Return an expression that declares a constant named NAME with the
  // constant value VAL in BTYPE.
  virtual Bexpression *named_constant_expression (Btype *btype,
						  const std::string &name,
						  Bexpression *val, Location)
    = 0;

  // Return an expression for the multi-precision integer VAL in BTYPE.
  virtual Bexpression *integer_constant_expression (Btype *btype, mpz_t val)
    = 0;

  // Return an expression for the floating point value VAL in BTYPE.
  virtual Bexpression *float_constant_expression (Btype *btype, mpfr_t val) = 0;

  // Return an expression for the complex value VAL in BTYPE.
  virtual Bexpression *complex_constant_expression (Btype *btype, mpc_t val)
    = 0;

  // Return an expression for the string value VAL.
  virtual Bexpression *string_constant_expression (const std::string &val) = 0;

  // Return an expression for the boolean value VAL.
  virtual Bexpression *boolean_constant_expression (bool val) = 0;

  // Return an expression for the real part of BCOMPLEX.
  virtual Bexpression *real_part_expression (Bexpression *bcomplex, Location)
    = 0;

  // Return an expression for the imaginary part of BCOMPLEX.
  virtual Bexpression *imag_part_expression (Bexpression *bcomplex, Location)
    = 0;

  // Return an expression for the complex number (BREAL, BIMAG).
  virtual Bexpression *complex_expression (Bexpression *breal,
					   Bexpression *bimag, Location)
    = 0;

  // Return an expression that converts EXPR to TYPE.
  virtual Bexpression *convert_expression (Btype *type, Bexpression *expr,
					   Location)
    = 0;

  // Create an expression for the address of a function.  This is used to
  // get the address of the code for a function.
  virtual Bexpression *function_code_expression (Bfunction *, Location) = 0;

  // Create an expression that takes the address of an expression.
  virtual Bexpression *address_expression (Bexpression *, Location) = 0;

  // Return an expression for the field at INDEX in BSTRUCT.
  virtual Bexpression *struct_field_expression (Bexpression *bstruct,
						size_t index, Location)
    = 0;

  // Create an expression that executes BSTAT before BEXPR.
  virtual Bexpression *compound_expression (Bstatement *bstat,
					    Bexpression *bexpr, Location)
    = 0;

  // Return an expression that executes THEN_EXPR if CONDITION is true, or
  // ELSE_EXPR otherwise and returns the result as type BTYPE, within the
  // specified function FUNCTION.  ELSE_EXPR may be NULL.  BTYPE may be NULL.
  virtual Bexpression *
  conditional_expression (Bfunction *function, Btype *btype,
			  Bexpression *condition, Bexpression *then_expr,
			  Bexpression *else_expr, Location)
    = 0;

  // Return an expression for the unary operation OP EXPR.
  // Supported values of OP are (from operators.h):
  //    MINUS, NOT, XOR.
  virtual Bexpression *unary_expression (Operator op, Bexpression *expr,
					 Location)
    = 0;

  // Return an expression for the binary operation LEFT OP RIGHT.
  // Supported values of OP are (from operators.h):
  //    EQEQ, NOTEQ, LT, LE, GT, GE, PLUS, MINUS, OR, XOR, MULT, DIV, MOD,
  //    LSHIFT, RSHIFT, AND, NOT.
  virtual Bexpression *binary_expression (Operator op, Bexpression *left,
					  Bexpression *right, Location)
    = 0;

  // Return an expression that constructs BTYPE with VALS.  BTYPE must be the
  // backend representation a of struct.  VALS must be in the same order as the
  // corresponding fields in BTYPE.
  virtual Bexpression *
  constructor_expression (Btype *btype, const std::vector<Bexpression *> &vals,
			  Location)
    = 0;

  // Return an expression that constructs an array of BTYPE with INDEXES and
  // VALS.  INDEXES and VALS must have the same amount of elements. Each index
  // in INDEXES must be in the same order as the corresponding value in VALS.
  virtual Bexpression *array_constructor_expression (
    Btype *btype, const std::vector<unsigned long> &indexes,
    const std::vector<Bexpression *> &vals, Location)
    = 0;

  // Return an expression for the address of BASE[INDEX].
  // BASE has a pointer type.  This is used for slice indexing.
  virtual Bexpression *pointer_offset_expression (Bexpression *base,
						  Bexpression *index, Location)
    = 0;

  // Return an expression for ARRAY[INDEX] as an l-value.  ARRAY is a valid
  // fixed-length array, not a slice.
  virtual Bexpression *array_index_expression (Bexpression *array,
					       Bexpression *index, Location)
    = 0;

  // Create an expression for a call to FN with ARGS, taking place within
  // caller CALLER.
  virtual Bexpression *call_expression (Bfunction *caller, Bexpression *fn,
					const std::vector<Bexpression *> &args,
					Bexpression *static_chain, Location)
    = 0;

  // Statements.

  // Create an error statement.  This is used for cases which should
  // not occur in a correct program, in order to keep the compilation
  // going without crashing.
  virtual Bstatement *error_statement () = 0;

  // Create an expression statement within the specified function.
  virtual Bstatement *expression_statement (Bfunction *, Bexpression *) = 0;

  // Create a variable initialization statement in the specified
  // function.  This initializes a local variable at the point in the
  // program flow where it is declared.
  virtual Bstatement *init_statement (Bfunction *, Bvariable *var,
				      Bexpression *init)
    = 0;

  // Create an assignment statement within the specified function.
  virtual Bstatement *assignment_statement (Bfunction *, Bexpression *lhs,
					    Bexpression *rhs, Location)
    = 0;

  // Create a return statement, passing the representation of the
  // function and the list of values to return.
  virtual Bstatement *
  return_statement (Bfunction *, const std::vector<Bexpression *> &, Location)
    = 0;

  // Create an if statement within a function.  ELSE_BLOCK may be NULL.
  virtual Bstatement *if_statement (Bfunction *, Bexpression *condition,
				    Bblock *then_block, Bblock *else_block,
				    Location)
    = 0;

  // Create a switch statement where the case values are constants.
  // CASES and STATEMENTS must have the same number of entries.  If
  // VALUE matches any of the list in CASES[i], which will all be
  // integers, then STATEMENTS[i] is executed.  STATEMENTS[i] will
  // either end with a goto statement or will fall through into
  // STATEMENTS[i + 1].  CASES[i] is empty for the default clause,
  // which need not be last.  FUNCTION is the current function.
  virtual Bstatement *
  switch_statement (Bfunction *function, Bexpression *value,
		    const std::vector<std::vector<Bexpression *> > &cases,
		    const std::vector<Bstatement *> &statements, Location)
    = 0;

  // Create a single statement from two statements.
  virtual Bstatement *compound_statement (Bstatement *, Bstatement *) = 0;

  // Create a single statement from a list of statements.
  virtual Bstatement *statement_list (const std::vector<Bstatement *> &) = 0;

  // Create a statement that attempts to execute BSTAT and calls EXCEPT_STMT if
  // an exception occurs. EXCEPT_STMT may be NULL.  FINALLY_STMT may be NULL and
  // if not NULL, it will always be executed.  This is used for handling defers
  // in Go functions.  In C++, the resulting code is of this form:
  //   try { BSTAT; } catch { EXCEPT_STMT; } finally { FINALLY_STMT; }
  virtual Bstatement *
  exception_handler_statement (Bstatement *bstat, Bstatement *except_stmt,
			       Bstatement *finally_stmt, Location)
    = 0;

  // Blocks.

  // Create a block.  The frontend will call this function when it
  // starts converting a block within a function.  FUNCTION is the
  // current function.  ENCLOSING is the enclosing block; it will be
  // NULL for the top-level block in a function.  VARS is the list of
  // local variables defined within this block; each entry will be
  // created by the local_variable function.  START_LOCATION is the
  // location of the start of the block, more or less the location of
  // the initial curly brace.  END_LOCATION is the location of the end
  // of the block, more or less the location of the final curly brace.
  // The statements will be added after the block is created.
  virtual Bblock *block (Bfunction *function, Bblock *enclosing,
			 const std::vector<Bvariable *> &vars,
			 Location start_location, Location end_location)
    = 0;

  // Add the statements to a block.  The block is created first.  Then
  // the statements are created.  Then the statements are added to the
  // block.  This will called exactly once per block.  The vector may
  // be empty if there are no statements.
  virtual void block_add_statements (Bblock *,
				     const std::vector<Bstatement *> &)
    = 0;

  // Return the block as a statement.  This is used to include a block
  // in a list of statements.
  virtual Bstatement *block_statement (Bblock *) = 0;

  // Variables.

  // Create an error variable.  This is used for cases which should
  // not occur in a correct program, in order to keep the compilation
  // going without crashing.
  virtual Bvariable *error_variable () = 0;

  // Create a global variable. NAME is the package-qualified name of
  // the variable.  ASM_NAME is the encoded identifier for the
  // variable, incorporating the package, and made safe for the
  // assembler.  BTYPE is the type of the variable.  IS_EXTERNAL is
  // true if the variable is defined in some other package.  IS_HIDDEN
  // is true if the variable is not exported (name begins with a lower
  // case letter).  IN_UNIQUE_SECTION is true if the variable should
  // be put into a unique section if possible; this is intended to
  // permit the linker to garbage collect the variable if it is not
  // referenced.  LOCATION is where the variable was defined.
  virtual Bvariable *global_variable (const std::string &name,
				      const std::string &asm_name, Btype *btype,
				      bool is_external, bool is_hidden,
				      bool in_unique_section, Location location)
    = 0;

  // A global variable will 1) be initialized to zero, or 2) be
  // initialized to a constant value, or 3) be initialized in the init
  // function.  In case 2, the frontend will call
  // global_variable_set_init to set the initial value.  If this is
  // not called, the backend should initialize a global variable to 0.
  // The init function may then assign a value to it.
  virtual void global_variable_set_init (Bvariable *, Bexpression *) = 0;

  // Create a local variable.  The frontend will create the local
  // variables first, and then create the block which contains them.
  // FUNCTION is the function in which the variable is defined.  NAME
  // is the name of the variable.  TYPE is the type.  DECL_VAR, if not
  // null, gives the location at which the value of this variable may
  // be found, typically used to create an inner-scope reference to an
  // outer-scope variable, to extend the lifetime of the variable beyond
  // the inner scope.  IS_ADDRESS_TAKEN is true if the address of this
  // variable is taken (this implies that the address does not escape
  // the function, as otherwise the variable would be on the heap).
  // LOCATION is where the variable is defined.  For each local variable
  // the frontend will call init_statement to set the initial value.
  virtual Bvariable *
  local_variable (Bfunction *function, const std::string &name, Btype *type,
		  Bvariable *decl_var, bool is_address_taken, Location location)
    = 0;

  // Create a function parameter.  This is an incoming parameter, not
  // a result parameter (result parameters are treated as local
  // variables).  The arguments are as for local_variable.
  virtual Bvariable *
  parameter_variable (Bfunction *function, const std::string &name, Btype *type,
		      bool is_address_taken, Location location)
    = 0;

  // Create a static chain parameter.  This is the closure parameter.
  virtual Bvariable *static_chain_variable (Bfunction *function,
					    const std::string &name,
					    Btype *type, Location location)
    = 0;

  // Create a temporary variable.  A temporary variable has no name,
  // just a type.  We pass in FUNCTION and BLOCK in case they are
  // needed.  If INIT is not NULL, the variable should be initialized
  // to that value.  Otherwise the initial value is irrelevant--the
  // backend does not have to explicitly initialize it to zero.
  // ADDRESS_IS_TAKEN is true if the programs needs to take the
  // address of this temporary variable.  LOCATION is the location of
  // the statement or expression which requires creating the temporary
  // variable, and may not be very useful.  This function should
  // return a variable which can be referenced later and should set
  // *PSTATEMENT to a statement which initializes the variable.
  virtual Bvariable *
  temporary_variable (Bfunction *, Bblock *, Btype *, Bexpression *init,
		      bool address_is_taken, Location location,
		      Bstatement **pstatement)
    = 0;

  // Create an implicit variable that is compiler-defined.  This is
  // used when generating GC data and roots, when storing the values
  // of a slice constructor, and for the zero value of types.  This returns a
  // Bvariable because it corresponds to an initialized variable in C.
  //
  // NAME is the name to use for the initialized variable this will create.
  //
  // ASM_NAME is encoded assembler-friendly version of the name, or the
  // empty string if no encoding is needed.
  //
  // TYPE is the type of the implicit variable.
  //
  // IS_HIDDEN will be true if the descriptor should only be visible
  // within the current object.
  //
  // IS_CONSTANT is true if the implicit variable should be treated like it is
  // immutable.  For slice initializers, if the values must be copied to the
  // heap, the variable IS_CONSTANT.
  //
  // IS_COMMON is true if the implicit variable should
  // be treated as a common variable (multiple definitions with
  // different sizes permitted in different object files, all merged
  // into the largest definition at link time); this will be true for
  // the zero value.  IS_HIDDEN and IS_COMMON will never both be true.
  //
  // If ALIGNMENT is not zero, it is the desired alignment of the variable.
  virtual Bvariable *
  implicit_variable (const std::string &name, const std::string &asm_name,
		     Btype *type, bool is_hidden, bool is_constant,
		     bool is_common, int64_t alignment)
    = 0;

  // Set the initial value of a variable created by implicit_variable.
  // This must be called even if there is no initializer, i.e., INIT is NULL.
  // The NAME, TYPE, IS_HIDDEN, IS_CONSTANT, and IS_COMMON parameters are
  // the same ones passed to implicit_variable.  INIT will be a composite
  // literal of type TYPE.  It will not contain any function calls or anything
  // else that can not be put into a read-only data section.
  // It may contain the address of variables created by implicit_variable.
  //
  // If IS_COMMON is true, INIT will be NULL, and the
  // variable should be initialized to all zeros.
  virtual void implicit_variable_set_init (Bvariable *, const std::string &name,
					   Btype *type, bool is_hidden,
					   bool is_constant, bool is_common,
					   Bexpression *init)
    = 0;

  // Create a reference to a named implicit variable defined in some
  // other package.  This will be a variable created by a call to
  // implicit_variable with the same NAME, ASM_NAME and TYPE and with
  // IS_COMMON passed as false.  This corresponds to an extern global
  // variable in C.
  virtual Bvariable *implicit_variable_reference (const std::string &name,
						  const std::string &asm_name,
						  Btype *type)
    = 0;

  // Create a named immutable initialized data structure.  This is
  // used for type descriptors, map descriptors, and function
  // descriptors.  This returns a Bvariable because it corresponds to
  // an initialized const variable in C.
  //
  // NAME is the name to use for the initialized global variable which
  // this call will create.
  //
  // ASM_NAME is the encoded, assembler-friendly version of NAME, or
  // the empty string if no encoding is needed.
  //
  // IS_HIDDEN will be true if the descriptor should only be visible
  // within the current object.
  //
  // IS_COMMON is true if NAME may be defined by several packages, and
  // the linker should merge all such definitions.  If IS_COMMON is
  // false, NAME should be defined in only one file.  In general
  // IS_COMMON will be true for the type descriptor of an unnamed type
  // or a builtin type.  IS_HIDDEN and IS_COMMON will never both be
  // true.
  //
  // TYPE will be a struct type; the type of the returned expression
  // must be a pointer to this struct type.
  //
  // We must create the named structure before we know its
  // initializer, because the initializer may refer to its own
  // address.  After calling this the frontend will call
  // immutable_struct_set_init.
  virtual Bvariable *
  immutable_struct (const std::string &name, const std::string &asm_name,
		    bool is_hidden, bool is_common, Btype *type, Location)
    = 0;

  // Set the initial value of a variable created by immutable_struct.
  // The NAME, IS_HIDDEN, IS_COMMON, TYPE, and location parameters are
  // the same ones passed to immutable_struct.  INITIALIZER will be a
  // composite literal of type TYPE.  It will not contain any function
  // calls or anything else that can not be put into a read-only data
  // section.  It may contain the address of variables created by
  // immutable_struct.
  virtual void immutable_struct_set_init (Bvariable *, const std::string &name,
					  bool is_hidden, bool is_common,
					  Btype *type, Location,
					  Bexpression *initializer)
    = 0;

  // Create a reference to a named immutable initialized data
  // structure defined in some other package.  This will be a
  // structure created by a call to immutable_struct with the same
  // NAME, ASM_NAME and TYPE and with IS_COMMON passed as false.  This
  // corresponds to an extern const global variable in C.
  virtual Bvariable *immutable_struct_reference (const std::string &name,
						 const std::string &asm_name,
						 Btype *type, Location)
    = 0;

  // Labels.

  // Create a new label.  NAME will be empty if this is a label
  // created by the frontend for a loop construct.  The location is
  // where the label is defined.
  virtual Blabel *label (Bfunction *, const std::string &name, Location) = 0;

  // Create a statement which defines a label.  This statement will be
  // put into the codestream at the point where the label should be
  // defined.
  virtual Bstatement *label_definition_statement (Blabel *) = 0;

  // Create a goto statement to a label.
  virtual Bstatement *goto_statement (Blabel *, Location) = 0;

  // Create an expression for the address of a label.  This is used to
  // get the return address of a deferred function which may call
  // recover.
  virtual Bexpression *label_address (Blabel *, Location) = 0;

  // Functions.

  // Create an error function.  This is used for cases which should
  // not occur in a correct program, in order to keep the compilation
  // going without crashing.
  virtual Bfunction *error_function () = 0;

  // Bit flags to pass to the function method.

  // Set if the function should be visible outside of the current
  // compilation unit.
  static const unsigned int function_is_visible = 1 << 0;

  // Set if this is a function declaration rather than a definition;
  // the definition will be in another compilation unit.
  static const unsigned int function_is_declaration = 1 << 1;

  // Set if the function can be inlined.  This is normally set, but is
  // false for functions that may not be inlined because they call
  // recover and must be visible for correct panic recovery.
  static const unsigned int function_is_inlinable = 1 << 2;

  // Set if the function may not split the stack.  This is set for the
  // implementation of recover itself, among other things.
  static const unsigned int function_no_split_stack = 1 << 3;

  // Set if the function does not return.  This is set for the
  // implementation of panic.
  static const unsigned int function_does_not_return = 1 << 4;

  // Set if the function should be put in a unique section if
  // possible.  This is used for field tracking.
  static const unsigned int function_in_unique_section = 1 << 5;

  // Set if the function should be available for inlining in the
  // backend, but should not be emitted as a standalone function.  Any
  // call to the function that is not inlined should be treated as a
  // call to a function defined in a different compilation unit.  This
  // is like a C99 function marked inline but not extern.
  static const unsigned int function_only_inline = 1 << 6;

  // Declare or define a function of FNTYPE.
  // NAME is the Go name of the function.  ASM_NAME, if not the empty
  // string, is the name that should be used in the symbol table; this
  // will be non-empty if a magic extern comment is used.  FLAGS is
  // bit flags described above.
  virtual Bfunction *function (Btype *fntype, const std::string &name,
			       const std::string &asm_name, unsigned int flags,
			       Location)
    = 0;

  // Create a statement that runs all deferred calls for FUNCTION.  This should
  // be a statement that looks like this in C++:
  //   finish:
  //     try { DEFER_RETURN; } catch { CHECK_DEFER; goto finish; }
  virtual Bstatement *
  function_defer_statement (Bfunction *function, Bexpression *undefer,
			    Bexpression *check_defer, Location)
    = 0;

  // Record PARAM_VARS as the variables to use for the parameters of FUNCTION.
  // This will only be called for a function definition.  Returns true on
  // success, false on failure.
  virtual bool
  function_set_parameters (Bfunction *function,
			   const std::vector<Bvariable *> &param_vars)
    = 0;

  // Set the function body for FUNCTION using the code in CODE_STMT.  Returns
  // true on success, false on failure.
  virtual bool function_set_body (Bfunction *function, Bstatement *code_stmt)
    = 0;

  // Look up a named built-in function in the current backend implementation.
  // Returns NULL if no built-in function by that name exists.
  virtual Bfunction *lookup_builtin (const std::string &) = 0;

  // Utility.

  // Write the definitions for all TYPE_DECLS, CONSTANT_DECLS,
  // FUNCTION_DECLS, and VARIABLE_DECLS declared globally.
  virtual void
  write_global_definitions (const std::vector<Btype *> &type_decls,
			    const std::vector<Bexpression *> &constant_decls,
			    const std::vector<Bfunction *> &function_decls,
			    const std::vector<Bvariable *> &variable_decls)
    = 0;

  // Write SIZE bytes of export data from BYTES to the proper
  // section in the output object file.
  virtual void write_export_data (const char *bytes, unsigned int size) = 0;
};

#endif // RUST_BACKEND_H