stage3/constant_folding.cc
author mjsousa
Sat, 25 Oct 2014 11:21:40 +0100
changeset 940 61e2bdae5899
parent 890 499486ece119
child 945 477393b00f95
permissions -rw-r--r--
Filling of symbol->scope annotation moved from narrow to fill_candidate_datatypes_c (became possible because narrowing of struct, array and symbolic variables is now done directly in fill_candidate_datatypes_c)
/*
 *  matiec - a compiler for the programming languages defined in IEC 61131-3
 *
 *  Copyright (C) 2003-2011  Mario de Sousa (msousa@fe.up.pt)
 *  Copyright (C) 2012       Manuele Conti (conti.ma@alice.it)
 *
 *  This program 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 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * This code is made available on the understanding that it will not be
 * used in safety-critical situations without a full and competent review.
 */

/*
 * An IEC 61131-3 compiler.
 *
 * Based on the
 * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
 *
 */



/* TODO: 
 *         - Add support for comparison (= and !=) of enumeration literals!
 *              We will need to add another const_value entry to the symbol_c, containing the 
 *              possible enumeration value of the enum constant!
 *              Doing this will allow us to more easily implement a constant_propagation_c later on!
 *
 *         - Add support for comparison (= and !=) of the exact same variable
 *                (e.g. if (int_v = int_v) then ...)
 */



/* Do constant folding...
 *
 * I.e., Determine the value of all expressions in which only constant values (i.e. literals) are used.
 * The (constant) result of each operation is stored (annotated) in the respective operation symbol 
 * (e.g.: add_expression_c) in the abstract syntax tree,
 *
 * For example:
 *       2 + 3         -> the constant value '5'    is stored in the add_expression_c symbol.
 *       22.2 - 5.0    -> the constant value '17.2' is stored in the add_expression_c symbol.
 *       etc...
 *
 *
 * NOTE 1 
 *      Some operations and constants can have multiple data types. For example,
 *        1 AND 0
 *      may be either a BOOL, BYTE, WORD or LWORD.
 *
 *      The same happens with 
 *        1 + 2
 *      which may be signed (e.g. INT) or unsigned (UINT)
 *
 *      For the above reason, instead of storing a single constant value, we actually store 4:
 *        - bool
 *        - uint64
 *        -  int64
 *        - real64
 *
 *      Additionally, since the result of an operation may result in an overflow, we actually
 *      store the result inside a struct (defined in absyntax.hh)
 *
 *             ** During stage 3 (semantic analysis/checking) we will be doing constant folding.
 *              * That algorithm will anotate the abstract syntax tree with the result of operations
 *              * on literals (i.e. 44 + 55 will store the result 99).
 *              * Since the same source code (e.g. 1 + 0) may actually be a BOOL or an ANY_INT,
 *              * or an ANY_BIT, we need to handle all possibilities, and determine the result of the
 *              * operation assuming each type.
 *              * For this reason, we have one entry for each possible type, with some expressions
 *              * having more than one entry filled in!
 *              **
 *             typedef enum { cs_undefined,   // not defined --> const_value is not valid!
 *                            cs_const_value, // const value is valid
 *                            cs_overflow     // result produced overflow or underflow --> const_value is not valid!
 *                          } const_status_t;
 *    
 *             typedef struct {
 *                 const_status_t status;
 *                 real64_t       value; 
 *             } const_value_real64_t;
 *             const_value_real64_t *const_value_real64; // when NULL --> UNDEFINED
 *             
 *             typedef struct {
 *                 const_status_t status;
 *                 int64_t        value; 
 *             } const_value_int64_t;
 *             const_value_int64_t *const_value_int64; // when NULL --> UNDEFINED
 *             
 *             typedef struct {
 *                 const_status_t status;
 *                 uint64_t       value; 
 *             } const_value_uint64_t;
 *             const_value_uint64_t *const_value_uint64; // when NULL --> UNDEFINED
 *             
 *             typedef struct {
 *                 const_status_t status;
 *                 bool           value; 
 *             } const_value_bool_t;
 *             const_value_bool_t *const_value_bool; // when NULL --> UNDEFINED
 *
 *
 *
 * NOTE 2 
 *    This file does not print out any error messages!
 *    We cannot really print out error messages when we find an overflow. Since each operation
 *    (symbol in the abstract syntax tree for that operation) will have up to 4 constant results,
 *    it may happen that some of them overflow, while other do not.
 *    We must wait for data type checking to determine the exact data type of each expression
 *    before we can decide whether or not we should print out an overflow error message.
 *
 *    For this reason, this visitor merely annotates the abstract syntax tree, and leaves the
 *    actually printing of errors for the print_datatype_errors_c class!
 *
 * NOTE 3
 *    Constant Folding class is extended with a implementation constant propagation algorithm
 *    by Mario de Sousa.
 *    Main idea is not to implement a general constant propagation algorithm but to reinterpret it
 *    for visitor classes.
 *    We declared a hash map, it contains a variables list linked with current constant values.
 *    During expression evaluation we can retrieve a constant value to symbolic variables getting it from the map.
 *    Also at join source points we use a meet semilattice rules to merge current values between a block
 *    and adjacent block.
 *
 */

#include "constant_folding.hh"
#include <stdlib.h> /* required for malloc() */

#include <string.h>  /* required for strlen() */
// #include <stdlib.h>  /* required for atoi() */
#include <errno.h>   /* required for errno */

#include "../main.hh" // required for uint8_t, real_64_t, ..., and the macros NAN, INFINITY, INT8_MAX, REAL32_MAX, ... */






#define FIRST_(symbol1, symbol2) (((symbol1)->first_order < (symbol2)->first_order)   ? (symbol1) : (symbol2))
#define  LAST_(symbol1, symbol2) (((symbol1)->last_order  > (symbol2)->last_order)    ? (symbol1) : (symbol2))

#define STAGE3_ERROR(error_level, symbol1, symbol2, ...) {                                                                  \
  if (current_display_error_level >= error_level) {                                                                         \
    fprintf(stderr, "%s:%d-%d..%d-%d: error: ",                                                                             \
            FIRST_(symbol1,symbol2)->first_file, FIRST_(symbol1,symbol2)->first_line, FIRST_(symbol1,symbol2)->first_column,\
                                                 LAST_(symbol1,symbol2) ->last_line,  LAST_(symbol1,symbol2) ->last_column);\
    fprintf(stderr, __VA_ARGS__);                                                                                           \
    fprintf(stderr, "\n");                                                                                                  \
    error_count++;                                                                                                     \
  }                                                                                                                         \
}


#define STAGE3_WARNING(symbol1, symbol2, ...) {                                                                             \
    fprintf(stderr, "%s:%d-%d..%d-%d: warning: ",                                                                           \
            FIRST_(symbol1,symbol2)->first_file, FIRST_(symbol1,symbol2)->first_line, FIRST_(symbol1,symbol2)->first_column,\
                                                 LAST_(symbol1,symbol2) ->last_line,  LAST_(symbol1,symbol2) ->last_column);\
    fprintf(stderr, __VA_ARGS__);                                                                                           \
    fprintf(stderr, "\n");                                                                                                  \
    warning_found = true;                                                                                                   \
}












#define SET_CVALUE(dtype, symbol, new_value) {((symbol)->const_value._##dtype.value) = new_value; ((symbol)->const_value._##dtype.status) = symbol_c::cs_const_value;}
#define GET_CVALUE(dtype, symbol)             ((symbol)->const_value._##dtype.value)
#define SET_OVFLOW(dtype, symbol)             ((symbol)->const_value._##dtype.status) = symbol_c::cs_overflow
#define SET_NONCONST(dtype, symbol)           ((symbol)->const_value._##dtype.status) = symbol_c::cs_non_const

#define VALID_CVALUE(dtype, symbol)           (symbol_c::cs_const_value == (symbol)->const_value._##dtype.status)
#define IS_OVFLOW(dtype, symbol)              (symbol_c::cs_overflow    == (symbol)->const_value._##dtype.status)
#define IS_NONCONST(dtype, symbol)            (symbol_c::cs_non_const   == (symbol)->const_value._##dtype.status)
#define ISZERO_CVALUE(dtype, symbol)          ((VALID_CVALUE(dtype, symbol)) && (GET_CVALUE(dtype, symbol) == 0))

#define ISEQUAL_CVALUE(dtype, symbol1, symbol2) \
	(VALID_CVALUE(dtype, symbol1) && VALID_CVALUE(dtype, symbol2) && (GET_CVALUE(dtype, symbol1) == GET_CVALUE(dtype, symbol2))) 

#define DO_BINARY_OPER(oper_type, operation, res_type, operand1, operand2) {                                              \
	if      (VALID_CVALUE(oper_type, operand1) && VALID_CVALUE(oper_type, operand2))                                  \
		{SET_CVALUE(res_type, symbol, GET_CVALUE(oper_type, operand1) operation GET_CVALUE(oper_type, operand2));}\
	else if (IS_OVFLOW   (oper_type, operand1) || IS_OVFLOW   (oper_type, operand2))                                  \
		{SET_OVFLOW(res_type, symbol);}  /* does it really make sense to set OVFLOW when restype is boolean??  */ \
	else if (IS_NONCONST (oper_type, operand1) || IS_NONCONST (oper_type, operand2))                                  \
		{SET_NONCONST(res_type, symbol);}                                                                         \
}

#define DO_UNARY_OPER(dtype, operation, operand) {                                                                        \
	if      (VALID_CVALUE(dtype, operand))                                                                            \
		{SET_CVALUE(dtype, symbol, operation GET_CVALUE(dtype, operand));}                                        \
	else if (IS_OVFLOW   (dtype, operand))                                                                            \
		{SET_OVFLOW(dtype, symbol);}                                                                              \
	else if (IS_NONCONST (dtype, operand))                                                                            \
		{SET_NONCONST(dtype, symbol);}                                                                            \
}

/* Constant Propagation: Rules for Meet from "Cooper K., Torczon L. - Engineering a Compiler, Second Edition - 2011"
 * at 9.3 Static Single-Assignment Form  page 517
 * - any * undefined = any
 * - any * non_const = non_const
 * - constant * constant = constant  (if equal)
 * - constant * constant = non_const (if not equal)
 */
#define COMPUTE_MEET_SEMILATTICE(dtype, c1, c2, resValue) {\
		if (( c1._##dtype.value  != c2._##dtype.value && c2._##dtype.status == symbol_c::cs_const_value &&\
              c1._##dtype.status == symbol_c::cs_const_value) ||\
		    ( c1._##dtype.status == symbol_c::cs_non_const && c2._##dtype.status == symbol_c::cs_const_value ) ||\
		    ( c2._##dtype.status == symbol_c::cs_non_const && c1._##dtype.status == symbol_c::cs_const_value  )) {\
			resValue._##dtype.status = symbol_c::cs_non_const;\
		} else {\
			resValue._##dtype.status = symbol_c::cs_const_value;\
			resValue._##dtype.value  = c1._##dtype.value;\
		}\
}

typedef std::map <std::string, symbol_c::const_value_t> map_values_t;

static map_values_t values;



/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***            convert string to numerical value                    ***/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/



  /* To allow the compiler to be portable, we cannot assume that int64_t is mapped onto long long int,
   * so we cannot call strtoll() and strtoull() in extract_int64() and extract_uint64().
   *
   * So, we create our own strtouint64() and strtoint64() functions.
   * (We actually call them matiec_strtoint64() so they will not clash with any function
   *  that may be added to the standard library in the future).
   * We actually create several of each, and let the compiler choose which is the correct one,
   * by having it resolve the call to the overloaded function. For the C++ compiler to be able
   * to resolve this ambiguity, we need to add a dummy parameter to each function!
   *
   * TODO: support platforms (where the compiler will run) in which int64_t is mapped onto int !!
   *       Is this really needed?
   *       Currently, when trying to compile matiec on sych a platform, the C++ compiler will not
   *       find any apropriate matiec_strtoint64() to call, so matiec will not be able to be compiled.
   *       If you need this, you are welcome to fix it yourself...
   */
static  int64_t matiec_strtoint64 (         long      int *dummy, const char *nptr, char **endptr, int base) {return strtol  (nptr, endptr, base);}
static  int64_t matiec_strtoint64 (         long long int *dummy, const char *nptr, char **endptr, int base) {return strtoll (nptr, endptr, base);}
  
static uint64_t matiec_strtouint64(unsigned long      int *dummy, const char *nptr, char **endptr, int base) {return strtoul (nptr, endptr, base);}
static uint64_t matiec_strtouint64(unsigned long long int *dummy, const char *nptr, char **endptr, int base) {return strtoull(nptr, endptr, base);}


/* extract the value of an integer from an integer_c object !! */
/* NOTE: it must ignore underscores! */
/* NOTE: To follow the basic structure used throughout the compiler's code, we should really be
 * writing this as a visitor_c (and do away with the dynamic casts!), but since we only have 3 distinct 
 * symbol class types to handle, it is probably easier to read if we write it as a standard function... 
 */
int64_t extract_int64_value(symbol_c *sym, bool *overflow) {
  int64_t      ret;
  std::string  str = "";
  char        *endptr;
  const char  *value = NULL;
  int          base;
  integer_c         *integer;
  hex_integer_c     *hex_integer;
  octal_integer_c   *octal_integer;
  binary_integer_c  *binary_integer;

   if       ((integer        = dynamic_cast<integer_c *>(sym))        != NULL) {value = integer       ->value + 0; base = 10;}
   else  if ((hex_integer    = dynamic_cast<hex_integer_c *>(sym))    != NULL) {value = hex_integer   ->value + 3; base = 16;}
   else  if ((octal_integer  = dynamic_cast<octal_integer_c *>(sym))  != NULL) {value = octal_integer ->value + 2; base =  8;}
   else  if ((binary_integer = dynamic_cast<binary_integer_c *>(sym)) != NULL) {value = binary_integer->value + 2; base =  2;}
   else  ERROR;

  for(unsigned int i = 0; i < strlen(value); i++)
    if (value[i] != '_')  str += value[i];

  errno = 0; // since strtoXX() may legally return 0, we must set errno to 0 to detect errors correctly!
  ret = matiec_strtoint64((int64_t *)NULL, str.c_str(), &endptr, base);
  if (overflow != NULL)
    *overflow = (errno == ERANGE);
  if (((errno != 0) && (errno != ERANGE)) || (*endptr != '\0'))
    ERROR;

  return ret;
}



uint64_t extract_uint64_value(symbol_c *sym, bool *overflow) {
  uint64_t     ret;
  std::string  str = "";
  char        *endptr;
  const char  *value = NULL;
  int          base;
  integer_c         *integer;
  hex_integer_c     *hex_integer;
  octal_integer_c   *octal_integer;
  binary_integer_c  *binary_integer;

   if       ((integer        = dynamic_cast<integer_c *>(sym))        != NULL) {value = integer       ->value + 0; base = 10;}
   else  if ((hex_integer    = dynamic_cast<hex_integer_c *>(sym))    != NULL) {value = hex_integer   ->value + 3; base = 16;}
   else  if ((octal_integer  = dynamic_cast<octal_integer_c *>(sym))  != NULL) {value = octal_integer ->value + 2; base =  8;}
   else  if ((binary_integer = dynamic_cast<binary_integer_c *>(sym)) != NULL) {value = binary_integer->value + 2; base =  2;}
   else  ERROR;

  for(unsigned int i = 0; i < strlen(value); i++)
    if (value[i] != '_')  str += value[i];

  errno = 0; // since strtoXX() may legally return 0, we must set errno to 0 to detect errors correctly!
  ret = matiec_strtouint64((uint64_t *)NULL, str.c_str(), &endptr, base);
  if (overflow != NULL)
    *overflow = (errno == ERANGE);
  if (((errno != 0) && (errno != ERANGE)) || (*endptr != '\0'))
    ERROR;

  return ret;
}



/* extract the value of a real from an real_c object !! */
/* NOTE: it must ignore underscores! */
/* From iec_bison.yy
 *  real:
 *   real_token		{$$ = new real_c($1, locloc(@$));}
 * | fixed_point_token	{$$ = new real_c($1, locloc(@$));}
 *
 * From iec_flex.ll
 * {real}			{yylval.ID=strdup(yytext); return real_token;}
 * {fixed_point}		{yylval.ID=strdup(yytext); return fixed_point_token;}
 *
 * real		{integer}\.{integer}{exponent}
 * fixed_point		{integer}\.{integer}
 * exponent        [Ee]([+-]?){integer}
 * integer         {digit}((_?{digit})*)
 */
real64_t extract_real_value(symbol_c *sym, bool *overflow) {
  std::string str = "";
  real_c *real_sym;
  fixed_point_c *fixed_point_sym;
  char   *endptr;
  real64_t ret;

  if ((real_sym = dynamic_cast<real_c *>(sym)) != NULL) {
	for(unsigned int i = 0; i < strlen(real_sym->value); i++)
      if (real_sym->value[i] != '_') str += real_sym->value[i];
  }
  else if ((fixed_point_sym = dynamic_cast<fixed_point_c *>(sym)) != NULL) {
    for(unsigned int i = 0; i < strlen(fixed_point_sym->value); i++)
      if (fixed_point_sym->value[i] != '_') str += fixed_point_sym->value[i];
  }
  else ERROR;
    
  errno = 0; // since strtoXX() may legally return 0, we must set errno to 0 to detect errors correctly!
  #if    (real64_tX  == float)
    ret = strtof(str.c_str(),  &endptr);
  #elif  (real64_tX  == double)
    ret = strtod(str.c_str(),  &endptr);
  #elif  (real64_tX  == long_double)
    ret = strtold(str.c_str(), &endptr);
  #else 
    #error Could not determine which data type is being used for real64_t (defined in main.hh). Aborting!
  #endif
  if (overflow != NULL)
    *overflow = (errno == ERANGE);
  if (((errno != 0) && (errno != ERANGE)) || (*endptr != '\0'))
    ERROR;

  return ret;
}





/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***        Functions to check for overflow situation                ***/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/


/* NOTE:
 *   Most of the conditions to detect overflows on signed and unsigned integer operations were adapted from
 *   https://www.securecoding.cert.org/confluence/display/seccode/INT32-C.+Ensure+that+operations+on+signed+integers+do+not+result+in+overflow?showComments=false
 *   https://www.securecoding.cert.org/confluence/display/seccode/INT30-C.+Ensure+that+unsigned+integer+operations+do+not+wrap
 */

/* NOTE: If at all possible, all overflow tests are done by pre-condition tests, i.e. tests that 
 *       can be run _before_ the operation is executed, and therefore without accessing the result!
 *
 *       The exception is for real/floating point values, that simply test if the result is NaN (not a number).
 */

/* res = a + b */
static void CHECK_OVERFLOW_uint64_SUM(symbol_c *res, symbol_c *a, symbol_c *b) {
	if (!VALID_CVALUE(uint64, res))
		return;
	/* Test by post-condition: If sum is smaller than either operand => overflow! */
	// if (GET_CVALUE(uint64, res) < GET_CVALUE(uint64, a))
	/* Test by pre-condition: If (UINT64_MAX - a) < b => overflow! */
	if ((UINT64_MAX - GET_CVALUE(uint64, a)) < GET_CVALUE(uint64, b))
		SET_OVFLOW(uint64, res);
}


/* res = a - b */
static void CHECK_OVERFLOW_uint64_SUB(symbol_c *res, symbol_c *a, symbol_c *b) {
	if (!VALID_CVALUE(uint64, res))
		return;
	/* Test by post-condition: If diference is larger than a => overflow! */
	// if (GET_CVALUE(uint64, res) > GET_CVALUE(uint64, a))
	/* Test by pre-condition: if b > a => overflow! */
	if (GET_CVALUE(uint64, b) > GET_CVALUE(uint64, a))
		SET_OVFLOW(uint64, res);
}


/* res = a * b */
static void CHECK_OVERFLOW_uint64_MUL(symbol_c *res, symbol_c *a, symbol_c *b) {
	if (!VALID_CVALUE(uint64, res))
		return;
	/* Test by pre-condition: If (UINT64_MAX / a) < b => overflow! */
	if (0 == GET_CVALUE(uint64, a))
		return; // multiplying by 0 will always result in 0, a valid result!	  
	if ((UINT64_MAX / GET_CVALUE(uint64, a)) < GET_CVALUE(uint64, b))
		SET_OVFLOW(uint64, res);
}


/* res = a / b */
static void CHECK_OVERFLOW_uint64_DIV(symbol_c *res, symbol_c *a, symbol_c *b) {
	if (!VALID_CVALUE(uint64, res))
		return;
	if (GET_CVALUE(uint64, b) == 0) /* division by zero! */
		SET_OVFLOW(uint64, res);
}


/* res = a MOD b */
static void CHECK_OVERFLOW_uint64_MOD(symbol_c *res, symbol_c *a, symbol_c *b) {
	if (!VALID_CVALUE(uint64, res))
		return;
	/* no overflow condition exists, including division by zero, which IEC 61131-3 considers legal for MOD operation! */
	if (false) 
		SET_OVFLOW(uint64, res);
}


/* res = - a */
static void CHECK_OVERFLOW_uint64_NEG(symbol_c *res, symbol_c *a) {
	/* The only legal operation is res = -0, everything else is an overflow! */
	if (VALID_CVALUE(uint64, a) && (GET_CVALUE(uint64, a) != 0))
		SET_OVFLOW(uint64, res);
}






/* res = a + b */
static void CHECK_OVERFLOW_int64_SUM(symbol_c *res, symbol_c *a_ptr, symbol_c *b_ptr) {
	if (!VALID_CVALUE(int64, res))
		return;
	int64_t a = GET_CVALUE(int64, a_ptr);
	int64_t b = GET_CVALUE(int64, b_ptr);
	/* The following test is valid no matter what representation is being used (e.g. two's complement, etc...) */
	if (((b > 0) && (a > (INT64_MAX - b)))
	 || ((b < 0) && (a < (INT64_MIN - b))))
		SET_OVFLOW(int64, res);
}


/* res = a - b */
static void CHECK_OVERFLOW_int64_SUB(symbol_c *res, symbol_c *a_ptr, symbol_c *b_ptr) {
	if (!VALID_CVALUE(int64, res))
		return;
	int64_t a = GET_CVALUE(int64, a_ptr);
	int64_t b = GET_CVALUE(int64, b_ptr);
	/* The following test is valid no matter what representation is being used (e.g. two's complement, etc...) */
	if (((b > 0) && (a < (INT64_MIN + b)))
	 || ((b < 0) && (a > (INT64_MAX + b))))
		SET_OVFLOW(int64, res);
}


/* res = a * b */
static void CHECK_OVERFLOW_int64_MUL(symbol_c *res, symbol_c *a_ptr, symbol_c *b_ptr) {
	if (!VALID_CVALUE(int64, res))
		return;
	int64_t a = GET_CVALUE(int64, a_ptr);
	int64_t b = GET_CVALUE(int64, b_ptr);
	if (   ( (a > 0) &&  (b > 0) &&             (a > (INT64_MAX / b))) 
	    || ( (a > 0) && !(b > 0) &&             (b < (INT64_MIN / a))) 
	    || (!(a > 0) &&  (b > 0) &&             (a < (INT64_MIN / b))) 
	    || (!(a > 0) && !(b > 0) && (a != 0) && (b < (INT64_MAX / a))))
		SET_OVFLOW(int64, res);
}


/* res = a / b */
static void CHECK_OVERFLOW_int64_DIV(symbol_c *res, symbol_c *a_ptr, symbol_c *b_ptr) {
	if (!VALID_CVALUE(int64, res))
		return;
	int64_t a = GET_CVALUE(int64, a_ptr);
	int64_t b = GET_CVALUE(int64, b_ptr);
	if ((b == 0) || ((a == INT64_MIN) && (b == -1)))
		SET_OVFLOW(int64, res);
}


/* res = a MOD b */
static void CHECK_OVERFLOW_int64_MOD(symbol_c *res, symbol_c *a_ptr, symbol_c *b_ptr) {
	if (!VALID_CVALUE(int64, res))
		return;
	int64_t a = GET_CVALUE(int64, a_ptr);
	int64_t b = GET_CVALUE(int64, b_ptr);
	/* IEC 61131-3 standard says IN1 MOD IN2 must be equivalent to
	 *  IF (IN2 = 0) THEN OUT:=0 ; ELSE OUT:=IN1 - (IN1/IN2)*IN2 ; END_IF
	 *
	 * Note that, when IN1 = INT64_MIN, and IN2 = -1, an overflow occurs in the division,
	 * so although the MOD operation should be OK, acording to the above definition, we actually have an overflow!!
	 *
	 * On the other hand, division by 0 is OK!!
	 */
	if ((a == INT64_MIN) && (b == -1))
		SET_OVFLOW(int64, res);
}


/* res = - a */
static void CHECK_OVERFLOW_int64_NEG(symbol_c *res, symbol_c *a) {
	if (!VALID_CVALUE(int64, res))
		return;
	if (GET_CVALUE(int64, a) == INT64_MIN)
		SET_OVFLOW(int64, res);
}




static void CHECK_OVERFLOW_real64(symbol_c *res_ptr) {
	if (!VALID_CVALUE(real64, res_ptr))
		return;
	real64_t res = GET_CVALUE(real64, res_ptr);
	/* NaN => underflow, overflow, number is a higher precision format, is a complex number (IEEE standard) */
	/* The IEC 61131-3 clearly states in section '2.5.1.5.2 Numerical functions':
	 * "It is an error if the result of evaluation of one of these [numerical] functions exceeds the range of values
	 *  specified for the data type of the function output, or if division by zero is attempted."
	 * For this reason, any operation that has as a result a positive or negative inifinity, is also an error!
	 */
	if ((isnan(res)) || (res == INFINITY) || (res == -INFINITY))
		SET_OVFLOW(real64, res_ptr);
}




/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***        Functions to execute operations on the const values      ***/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/

/* static void *handle_cmp(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2, OPERATION) */
#define handle_cmp(symbol, oper1, oper2, operation) {               \
	if ((NULL == oper1) || (NULL == oper2)) return NULL;        \
	DO_BINARY_OPER(  bool, operation, bool, oper1, oper2);     \
	DO_BINARY_OPER(uint64, operation, bool, oper1, oper2);     \
	DO_BINARY_OPER( int64, operation, bool, oper1, oper2);     \
	DO_BINARY_OPER(real64, operation, bool, oper1, oper2);     \
	return NULL;                                                \
}


/* NOTE: the MOVE standard function is equivalent to the ':=' in ST syntax */
static void *handle_move(symbol_c *to, symbol_c *from) {
	if (NULL == from) return NULL;
	to->const_value = from->const_value;
	return NULL;
}


/* unary negation (multiply by -1) */
static void *handle_neg(symbol_c *symbol, symbol_c *oper) {
	if (NULL == oper) return NULL;
	/* NOTE: The oper may never be an integer/real literal, '-1' and '-2.2' are stored as an neg_integer_c/neg_real_c instead.
	 *       Because of this, we MUST NOT handle the INT_MIN special situation that is handled in neg_integer_c visitor!
	 *
	 *       VAR v1, v2, v3 : UINT; END_VAR;
	 *       v1 =  9223372036854775808 ; (* |INT64_MIN| == -INT64_MIN *)   <------ LEGAL
	 *       v2 =  -(-v1);                                                 <------ ILLEGAL (since it -v1 is overflow!)
	 *       v2 =  -(-9223372036854775808 );                               <------ MUST also be ILLEGAL 
	 */
	DO_UNARY_OPER(uint64, -, oper);	CHECK_OVERFLOW_uint64_NEG(symbol, oper);  /* handle the uint_v := -0 situation! */
	DO_UNARY_OPER( int64, -, oper);	CHECK_OVERFLOW_int64_NEG (symbol, oper);
	DO_UNARY_OPER(real64, -, oper);	CHECK_OVERFLOW_real64(symbol);
	return NULL;
}


/* unary boolean negation (NOT) */
static void *handle_not(symbol_c *symbol, symbol_c *oper) {
	if (NULL == oper) return NULL;
	DO_UNARY_OPER(  bool, !, oper);
	DO_UNARY_OPER(uint64, ~, oper);
	return NULL;
}


static void *handle_or (symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	DO_BINARY_OPER(  bool, ||, bool  , oper1, oper2);
	DO_BINARY_OPER(uint64, | , uint64, oper1, oper2);
	return NULL;
}


static void *handle_xor(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	DO_BINARY_OPER(  bool, ^, bool  , oper1, oper2);
	DO_BINARY_OPER(uint64, ^, uint64, oper1, oper2);
	return NULL;
}


static void *handle_and(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	DO_BINARY_OPER(  bool, &&, bool, oper1, oper2);
	DO_BINARY_OPER(uint64, & , uint64, oper1, oper2);
	return NULL;
}


static void *handle_add(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	DO_BINARY_OPER(uint64, +, uint64, oper1, oper2);   CHECK_OVERFLOW_uint64_SUM(symbol, oper1, oper2);
	DO_BINARY_OPER( int64, +,  int64, oper1, oper2);   CHECK_OVERFLOW_int64_SUM (symbol, oper1, oper2);
	DO_BINARY_OPER(real64, +, real64, oper1, oper2);   CHECK_OVERFLOW_real64    (symbol);
	return NULL;
}


static void *handle_sub(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	DO_BINARY_OPER(uint64, -, uint64, oper1, oper2);   CHECK_OVERFLOW_uint64_SUB(symbol, oper1, oper2);
	DO_BINARY_OPER( int64, -,  int64, oper1, oper2);   CHECK_OVERFLOW_int64_SUB (symbol, oper1, oper2);
	DO_BINARY_OPER(real64, -, real64, oper1, oper2);   CHECK_OVERFLOW_real64    (symbol);
	return NULL;
}


static void *handle_mul(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	DO_BINARY_OPER(uint64, *, uint64, oper1, oper2);   CHECK_OVERFLOW_uint64_MUL(symbol, oper1, oper2);
	DO_BINARY_OPER( int64, *,  int64, oper1, oper2);   CHECK_OVERFLOW_int64_MUL (symbol, oper1, oper2);
	DO_BINARY_OPER(real64, *, real64, oper1, oper2);   CHECK_OVERFLOW_real64    (symbol);
	return NULL;
}


static void *handle_div(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	if (ISZERO_CVALUE(uint64, oper2))  {SET_OVFLOW(uint64, symbol);} else {DO_BINARY_OPER(uint64, /, uint64, oper1, oper2); CHECK_OVERFLOW_uint64_DIV(symbol, oper1, oper2);};
	if (ISZERO_CVALUE( int64, oper2))  {SET_OVFLOW( int64, symbol);} else {DO_BINARY_OPER( int64, /,  int64, oper1, oper2); CHECK_OVERFLOW_int64_DIV (symbol, oper1, oper2);};
	if (ISZERO_CVALUE(real64, oper2))  {SET_OVFLOW(real64, symbol);} else {DO_BINARY_OPER(real64, /, real64, oper1, oper2); CHECK_OVERFLOW_real64(symbol);};
	return NULL;
}


static void *handle_mod(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	if ((NULL == oper1) || (NULL == oper2)) return NULL;
	/* IEC 61131-3 standard says IN1 MOD IN2 must be equivalent to
	 *  IF (IN2 = 0) THEN OUT:=0 ; ELSE OUT:=IN1 - (IN1/IN2)*IN2 ; END_IF
	 *
	 * Note that, when IN1 = INT64_MIN, and IN2 = -1, an overflow occurs in the division,
	 * so although the MOD operation should be OK, acording to the above definition, we actually have an overflow!!
	 */
	if (ISZERO_CVALUE(uint64, oper2))  {SET_CVALUE(uint64, symbol, 0);} else {DO_BINARY_OPER(uint64, %, uint64, oper1, oper2); CHECK_OVERFLOW_uint64_MOD(symbol, oper1, oper2);};
	if (ISZERO_CVALUE( int64, oper2))  {SET_CVALUE( int64, symbol, 0);} else {DO_BINARY_OPER( int64, %,  int64, oper1, oper2); CHECK_OVERFLOW_int64_MOD (symbol, oper1, oper2);};
	return NULL;
}


static void *handle_pow(symbol_c *symbol, symbol_c *oper1, symbol_c *oper2) {
	/* NOTE: If the const_value in symbol->r_exp is within the limits of both int64 and uint64, then we do both operations.
	 *       That is OK, as the result should be identicial (we do create an unnecessary CVALUE variable, but who cares?).
	 *       If only one is valid, then that is the oper we will do!
	 */
	if (VALID_CVALUE(real64, oper1) && VALID_CVALUE( int64, oper2))
		SET_CVALUE(real64, symbol, pow(GET_CVALUE(real64, oper1), GET_CVALUE( int64, oper2)));
	if (VALID_CVALUE(real64, oper1) && VALID_CVALUE(uint64, oper2))
		SET_CVALUE(real64, symbol, pow(GET_CVALUE(real64, oper1), GET_CVALUE(uint64, oper2)));
	CHECK_OVERFLOW_real64(symbol);
	return NULL;
}

static map_values_t inner_left_join_values(map_values_t m1, map_values_t m2) {
	map_values_t::const_iterator itr;
	map_values_t ret;

	itr = m1.begin();
	for ( ; itr != m1.end(); ++itr) {
		std::string name = itr->first;
		symbol_c::const_value_t value;

		if (m2.count(name) > 0) {
			symbol_c::const_value_t c1 = itr->second;
			symbol_c::const_value_t c2 = m2[name];
			COMPUTE_MEET_SEMILATTICE (real64, c1, c2, value);
			COMPUTE_MEET_SEMILATTICE (uint64, c1, c2, value);
			COMPUTE_MEET_SEMILATTICE ( int64, c1, c2, value);
			COMPUTE_MEET_SEMILATTICE (  bool, c1, c2, value);
		} else
			value = m1[name];
		ret[name] = value;
	}

	return ret;
}

/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***        Helper functions for handling IL instruction lists.      ***/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/


/* If the cvalues of all the prev_il_intructions have the same VALID value, then set the local cvalue to that value, otherwise, set it to NONCONST! */
#define intersect_prev_CVALUE_(dtype, symbol) {                                                                   \
	symbol->const_value._##dtype = symbol->prev_il_instruction[0]->const_value._##dtype;                      \
	for (unsigned int i = 1; i < symbol->prev_il_instruction.size(); i++) {                                   \
		if (!ISEQUAL_CVALUE(dtype, symbol, symbol->prev_il_instruction[i]))                               \
			{SET_NONCONST(dtype, symbol); break;}                                                     \
	}                                                                                                         \
}

static void intersect_prev_cvalues(il_instruction_c *symbol) {
	if (symbol->prev_il_instruction.empty())
		return;
	intersect_prev_CVALUE_(real64, symbol);
	intersect_prev_CVALUE_(uint64, symbol);
	intersect_prev_CVALUE_( int64, symbol);
	intersect_prev_CVALUE_(  bool, symbol);
}



/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***        The constant_folding_c                                   ***/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/






constant_folding_c::constant_folding_c(symbol_c *symbol) {
    error_count = 0;
    warning_found = false;
    current_display_error_level = 0;
    il_operand = NULL;
    search_varfb_instance_type = NULL;
    prev_il_instruction = NULL;
    
    /* check whether the platform on which the compiler is being run implements IEC 559 floating point data types. */
    symbol_c null_symbol;
    if (! (std::numeric_limits<real64_t>::is_iec559) )
        STAGE3_WARNING(&null_symbol, &null_symbol, "The platform running the compiler does not implement IEC 60559 floating point numbers. "
                                                   "Any error and/or warning messages related to overflow/underflow of the result of operations on REAL/LREAL literals "
                                                   "(i.e. constant folding) may themselves be erroneous, although are most probably correct."
                                                   "However, more likely is the possible existance of overflow/underflow errors that are not detected.");
}


constant_folding_c::~constant_folding_c(void) {
}


int constant_folding_c::get_error_count() {
	return error_count;
}


/*********************/
/* B 1.2 - Constants */
/*********************/
/******************************/
/* B 1.2.1 - Numeric Literals */
/******************************/
void *constant_folding_c::visit(real_c *symbol) {
	bool overflow;
	SET_CVALUE(real64, symbol, extract_real_value(symbol, &overflow));
	if (overflow) SET_OVFLOW(real64, symbol);
	return NULL;
}


void *constant_folding_c::visit(integer_c *symbol) {
	bool overflow;
	SET_CVALUE( int64, symbol, extract_int64_value (symbol, &overflow));
	if (overflow) SET_OVFLOW(int64, symbol);
	SET_CVALUE(uint64, symbol, extract_uint64_value(symbol, &overflow));
	if (overflow) SET_OVFLOW(uint64, symbol);
	return NULL;
}


void *constant_folding_c::visit(neg_real_c *symbol) {
	symbol->exp->accept(*this);
	DO_UNARY_OPER(real64, -, symbol->exp); CHECK_OVERFLOW_real64(symbol);
	if (IS_OVFLOW(real64, symbol->exp)) SET_OVFLOW(real64, symbol);
	return NULL;
}



/* | '-' integer	{$$ = new neg_integer_c($2, locloc(@$));} */
void *constant_folding_c::visit(neg_integer_c *symbol) {
	symbol->exp->accept(*this);
	/* Note that due to syntax restrictions, the value of symbol->exp will always be positive. 
	 * However, the following code does not depend on that restriction.
	 */
	/* The remainder of the code (for example, data type checking) considers the neg_integer_c as a leaf of the
	 * abstract syntax tree, and therefore simply ignores the values of neg_integer_c->exp.
	 * For this reason only, and in only this situation, we must guarantee that any 'overflow' situation in 
	 * the cvalue of neg_integer_c->exp is also reflected back to this neg_integer_c symbol.
	 * For the rest of the code we do NOT do this, as it would gurantee that a single overflow deep inside
	 * an expression would imply that the expression itself would also be set to 'overflow' condition.
	 * This in turn would then have the compiler produce a whole load of error messages where they are not wanted!
	 */
	DO_UNARY_OPER(uint64, -, symbol->exp); CHECK_OVERFLOW_uint64_NEG(symbol, symbol->exp);  /* handle the uintv := -0 situation */
	if (IS_OVFLOW(uint64, symbol->exp)) SET_OVFLOW(uint64, symbol);
	DO_UNARY_OPER( int64, -, symbol->exp); CHECK_OVERFLOW_int64_NEG (symbol, symbol->exp);
	if (IS_OVFLOW( int64, symbol->exp)) SET_OVFLOW( int64, symbol);
	/* NOTE 1: INT64_MIN = -(INT64_MAX + 1)   ---> assuming two's complement representation!!!
	 * NOTE 2: if the user happens to want INT_MIN, that value will first be parsed as a positive integer, before being negated here.
	 * However, the positive value cannot be stored inside an int64! So, in this case, we will get the value from the uint64 cvalue.
	 *
	 * This same situation is usually considered an overflow (check handle_neg() function). However, here we have a special
	 * situation. If we do not allow this, then the user would never the able to use the following code:
	 *  VAR v : LINT; END_VAR
	 *    v := -9223372036854775809 ; (* - |INT64_MIN| == INT64_MIN *)
	 */
	// if (INT64_MIN == -INT64_MAX - 1) // We do not really need to check that the platform uses two's complement
	if (VALID_CVALUE(uint64, symbol->exp) && (GET_CVALUE(uint64, symbol->exp) == (uint64_t)INT64_MAX+1)) {
		SET_CVALUE(int64, symbol, INT64_MIN);
	}
	return NULL;
}


void *constant_folding_c::visit(binary_integer_c *symbol) {
	bool overflow;
	SET_CVALUE( int64, symbol, extract_int64_value (symbol, &overflow));
	if (overflow) SET_OVFLOW(int64, symbol);
	SET_CVALUE(uint64, symbol, extract_uint64_value(symbol, &overflow));
	if (overflow) SET_OVFLOW(uint64, symbol);
	return NULL;
}


void *constant_folding_c::visit(octal_integer_c *symbol) {
	bool overflow;
	SET_CVALUE( int64, symbol, extract_int64_value (symbol, &overflow));
	if (overflow) SET_OVFLOW(int64, symbol);
	SET_CVALUE(uint64, symbol, extract_uint64_value(symbol, &overflow));
	if (overflow) SET_OVFLOW(uint64, symbol);
	return NULL;
}


void *constant_folding_c::visit(hex_integer_c *symbol) {
	bool overflow;
	SET_CVALUE( int64, symbol, extract_int64_value (symbol, &overflow));
	if (overflow) SET_OVFLOW(int64, symbol);
	SET_CVALUE(uint64, symbol, extract_uint64_value(symbol, &overflow));
	if (overflow) SET_OVFLOW(uint64, symbol);
	return NULL;
}


/*
integer_literal:
  integer_type_name '#' signed_integer	{$$ = new integer_literal_c($1, $3, locloc(@$));}
| integer_type_name '#' binary_integer	{$$ = new integer_literal_c($1, $3, locloc(@$));}
| integer_type_name '#' octal_integer	{$$ = new integer_literal_c($1, $3, locloc(@$));}
| integer_type_name '#' hex_integer	{$$ = new integer_literal_c($1, $3, locloc(@$));}
*/
// SYM_REF2(integer_literal_c, type, value)
void *constant_folding_c::visit(integer_literal_c *symbol) {
	symbol->value->accept(*this);
	DO_UNARY_OPER( int64, /* none */, symbol->value);
	DO_UNARY_OPER(uint64, /* none */, symbol->value);
	return NULL;
}


void *constant_folding_c::visit(real_literal_c *symbol) {
	symbol->value->accept(*this);
	DO_UNARY_OPER(real64, /* none */, symbol->value);
	return NULL;
}


void *constant_folding_c::visit(bit_string_literal_c *symbol) {
	return NULL;
}


void *constant_folding_c::visit(boolean_literal_c *symbol) {
	symbol->value->accept(*this);
	DO_UNARY_OPER(bool, /* none */, symbol->value);
	return NULL;
}


void *constant_folding_c::visit(boolean_true_c *symbol) {
	SET_CVALUE(bool, symbol, true);
	return NULL;
}


void *constant_folding_c::visit(boolean_false_c *symbol) {
	SET_CVALUE(bool, symbol, false);
	return NULL;
}

/************************/
/* B 1.2.3.1 - Duration */
/********* **************/
void *constant_folding_c::visit(fixed_point_c *symbol) {
	bool overflow;
	SET_CVALUE(real64, symbol, extract_real_value(symbol, &overflow));
	if (overflow) SET_OVFLOW(real64, symbol);
	return NULL;
}

/*********************/
/* B 1.4 - Variables */
/*********************/
#if DO_CONSTANT_PROPAGATION__
void *constant_folding_c::visit(symbolic_variable_c *symbol) {
	std::string varName;

	varName = get_var_name_c::get_name(symbol->var_name)->value;
	if (values.count(varName) > 0) {
		symbol->const_value = values[varName];
	}
	return NULL;
}
#endif  // DO_CONSTANT_PROPAGATION__


/**********************/
/* B 1.5.3 - Programs */
/**********************/
#if DO_CONSTANT_PROPAGATION__
void *constant_folding_c::visit(program_declaration_c *symbol) {
	symbol_c *var_name;

	symbol->var_declarations->accept(*this);
	values.clear(); /* Clear global map */
	search_var_instance_decl_c search_var_instance_decl(symbol);
	function_param_iterator_c fpi(symbol);
	while((var_name = fpi.next()) != NULL) {
		std::string varName = get_var_name_c::get_name(var_name)->value;
		symbol_c   *varDecl = search_var_instance_decl.get_decl(var_name);
		values[varName] = varDecl->const_value;
	}
	/* Add all variables declared into Values map and put them to initial value */
	symbol->function_block_body->accept(*this);
	return NULL;
}
#endif  // DO_CONSTANT_PROPAGATION__


/****************************************/
/* B.2 - Language IL (Instruction List) */
/****************************************/
/***********************************/
/* B 2.1 Instructions and Operands */
/***********************************/
/* Not needed, since we inherit from iterator_visitor_c */
/*| instruction_list il_instruction */
// SYM_LIST(instruction_list_c)
// void *constant_folding_c::visit(instruction_list_c *symbol) {}

/* | label ':' [il_incomplete_instruction] eol_list */
// SYM_REF2(il_instruction_c, label, il_instruction)
// void *visit(instruction_list_c *symbol);
void *constant_folding_c::visit(il_instruction_c *symbol) {
	if (NULL == symbol->il_instruction) {
		/* This empty/null il_instruction does not change the value of the current/default IL variable.
		 * So it inherits the candidate_datatypes from it's previous IL instructions!
		 */
		intersect_prev_cvalues(symbol);
	} else {
		il_instruction_c fake_prev_il_instruction = *symbol;
		intersect_prev_cvalues(&fake_prev_il_instruction);

		if (symbol->prev_il_instruction.size() == 0)  prev_il_instruction = NULL;
		else                                          prev_il_instruction = &fake_prev_il_instruction;
		symbol->il_instruction->accept(*this);
		prev_il_instruction = NULL;

		/* This object has (inherits) the same cvalues as the il_instruction */
		symbol->const_value = symbol->il_instruction->const_value;
	}

	return NULL;
}


void *constant_folding_c::visit(il_simple_operation_c *symbol) {
	/* determine the cvalue of the operand */
	if (NULL != symbol->il_operand) {
		symbol->il_operand->accept(*this);
	}
	/* determine the cvalue resulting from executing the il_operator... */
	il_operand = symbol->il_operand;
	symbol->il_simple_operator->accept(*this);
	il_operand = NULL;
	/* This object has (inherits) the same cvalues as the il_instruction */
	symbol->const_value = symbol->il_simple_operator->const_value;
	return NULL;
}


/* TODO: handle function invocations... */
/* | function_name [il_operand_list] */
/* NOTE: The parameters 'called_function_declaration' and 'extensible_param_count' are used to pass data between the stage 3 and stage 4. */
// SYM_REF2(il_function_call_c, function_name, il_operand_list, symbol_c *called_function_declaration; int extensible_param_count;)
// void *constant_folding_c::visit(il_function_call_c *symbol) {}


/* | il_expr_operator '(' [il_operand] eol_list [simple_instr_list] ')' */
// SYM_REF3(il_expression_c, il_expr_operator, il_operand, simple_instr_list);
void *constant_folding_c::visit(il_expression_c *symbol) {
  symbol_c *prev_il_instruction_backup = prev_il_instruction;
  
  /* Stage2 will insert an artificial (and equivalent) LD <il_operand> to the simple_instr_list if necessary. We can therefore ignore the 'il_operand' entry! */
  // if (NULL != symbol->il_operand)
  //   symbol->il_operand->accept(*this);

  if(symbol->simple_instr_list != NULL)
    symbol->simple_instr_list->accept(*this);

  /* Now do the operation,  */
  il_operand = symbol->simple_instr_list;
  prev_il_instruction = prev_il_instruction_backup;
  symbol->il_expr_operator->accept(*this);
  il_operand = NULL;
  
  /* This object has (inherits) the same cvalues as the il_instruction */
  symbol->const_value = symbol->il_expr_operator->const_value;
  
  /* Since stage2 will insert an artificial (and equivalent) LD <il_operand> to the simple_instr_list when an 'il_operand' exists, we know
   * that if (symbol->il_operand != NULL), then the first IL instruction in the simple_instr_list will be the equivalent and artificial
   * 'LD <il_operand>' IL instruction.
   * Just to be cosistent, we will copy the constant info back into the il_operand, even though this should not be necessary!
   */
  if ((NULL != symbol->il_operand) && ((NULL == symbol->simple_instr_list) || (0 == ((list_c *)symbol->simple_instr_list)->n))) ERROR; // stage2 is not behaving as we expect it to!
  if  (NULL != symbol->il_operand)
    symbol->il_operand->const_value = ((list_c *)symbol->simple_instr_list)->elements[0]->const_value;

  return NULL;
}



void *constant_folding_c::visit(il_jump_operation_c *symbol) {
  /* recursive call to fill const values... */
  il_operand = NULL;
  symbol->il_jump_operator->accept(*this);
  il_operand = NULL;
  /* This object has (inherits) the same cvalues as the il_jump_operator */
  symbol->const_value = symbol->il_jump_operator->const_value;
  return NULL;
}



/* FB calls leave the value in the accumulator unchanged */
/*   il_call_operator prev_declared_fb_name
 * | il_call_operator prev_declared_fb_name '(' ')'
 * | il_call_operator prev_declared_fb_name '(' eol_list ')'
 * | il_call_operator prev_declared_fb_name '(' il_operand_list ')'
 * | il_call_operator prev_declared_fb_name '(' eol_list il_param_list ')'
 */
/* NOTE: The parameter 'called_fb_declaration'is used to pass data between stage 3 and stage4 (although currently it is not used in stage 4 */
// SYM_REF4(il_fb_call_c, il_call_operator, fb_name, il_operand_list, il_param_list, symbol_c *called_fb_declaration)
void *constant_folding_c::visit(il_fb_call_c *symbol) {return handle_move(symbol, prev_il_instruction);}


/* TODO: handle function invocations... */
/* | function_name '(' eol_list [il_param_list] ')' */
/* NOTE: The parameter 'called_function_declaration' is used to pass data between the stage 3 and stage 4. */
// SYM_REF2(il_formal_funct_call_c, function_name, il_param_list, symbol_c *called_function_declaration; int extensible_param_count;)
// void *constant_folding_c::visit(il_formal_funct_call_c *symbol) {return NULL;}



/* Not needed, since we inherit from iterator_visitor_c */
//  void *constant_folding_c::visit(il_operand_list_c *symbol);



/* | simple_instr_list il_simple_instruction */
/* This object is referenced by il_expression_c objects */
void *constant_folding_c::visit(simple_instr_list_c *symbol) {
  if (symbol->n <= 0)
    return NULL;  /* List is empty! Nothing to do. */
    
  for(int i = 0; i < symbol->n; i++)
    symbol->elements[i]->accept(*this);

  /* This object has (inherits) the same cvalues as the il_jump_operator */
  symbol->const_value = symbol->elements[symbol->n-1]->const_value;
  return NULL;
}



// SYM_REF1(il_simple_instruction_c, il_simple_instruction, symbol_c *prev_il_instruction;)
void *constant_folding_c::visit(il_simple_instruction_c *symbol) {
  if (symbol->prev_il_instruction.size() > 1) ERROR; /* There should be no labeled insructions inside an IL expression! */
  if (symbol->prev_il_instruction.size() == 0)  prev_il_instruction = NULL;
  else                                          prev_il_instruction = symbol->prev_il_instruction[0];
  symbol->il_simple_instruction->accept(*this);
  prev_il_instruction = NULL;

  /* This object has (inherits) the same cvalues as the il_jump_operator */
  symbol->const_value = symbol->il_simple_instruction->const_value;
  return NULL;
}


/*
    void *visit(il_param_list_c *symbol);
    void *visit(il_param_assignment_c *symbol);
    void *visit(il_param_out_assignment_c *symbol);
*/


/*******************/
/* B 2.2 Operators */
/*******************/
void *constant_folding_c::visit(   LD_operator_c *symbol) {return handle_move(symbol, il_operand);}
void *constant_folding_c::visit(  LDN_operator_c *symbol) {return handle_not (symbol, il_operand);}

/* NOTE: we are implementing a constant folding algorithm, not a constant propagation algorithm.
 *       For the constant propagation algorithm, the correct implementation of ST(N)_operator_c would be...
 */
//void *constant_folding_c::visit(   ST_operator_c *symbol) {return handle_move(il_operand, symbol);}
//void *constant_folding_c::visit(  STN_operator_c *symbol) {return handle_not (il_operand, symbol);}
void *constant_folding_c::visit(   ST_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(  STN_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}

/* NOTE: the standard allows syntax in which the NOT operator is followed by an optional <il_operand>
 *              NOT [<il_operand>]
 *       However, it does not define the semantic of the NOT operation when the <il_operand> is specified.
 *       We therefore consider it an error if an il_operand is specified! This error will be caught elsewhere!
 */
void *constant_folding_c::visit(  NOT_operator_c *symbol) {return handle_not(symbol, prev_il_instruction);}

/* NOTE: Since we are only implementing a constant folding algorithm, and not a constant propagation algorithm,
 *       the following IL instructions do not change/set the value of the il_operand!
 */
void *constant_folding_c::visit(    S_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(    R_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}

/* FB calls leave the value in the accumulator unchanged */
void *constant_folding_c::visit(   S1_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(   R1_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(  CLK_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(   CU_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(   CD_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(   PV_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(   IN_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(   PT_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}

void *constant_folding_c::visit(  AND_operator_c *symbol) {return handle_and (symbol, prev_il_instruction, il_operand);}
void *constant_folding_c::visit(   OR_operator_c *symbol) {return handle_or  (symbol, prev_il_instruction, il_operand);}
void *constant_folding_c::visit(  XOR_operator_c *symbol) {return handle_xor (symbol, prev_il_instruction, il_operand);}
void *constant_folding_c::visit( ANDN_operator_c *symbol) {       handle_and (symbol, prev_il_instruction, il_operand); return handle_not(symbol, symbol);}
void *constant_folding_c::visit(  ORN_operator_c *symbol) {       handle_or  (symbol, prev_il_instruction, il_operand); return handle_not(symbol, symbol);}
void *constant_folding_c::visit( XORN_operator_c *symbol) {       handle_xor (symbol, prev_il_instruction, il_operand); return handle_not(symbol, symbol);}

void *constant_folding_c::visit(  ADD_operator_c *symbol) {return handle_add (symbol, prev_il_instruction, il_operand);}
void *constant_folding_c::visit(  SUB_operator_c *symbol) {return handle_sub (symbol, prev_il_instruction, il_operand);}
void *constant_folding_c::visit(  MUL_operator_c *symbol) {return handle_mul (symbol, prev_il_instruction, il_operand);}
void *constant_folding_c::visit(  DIV_operator_c *symbol) {return handle_div (symbol, prev_il_instruction, il_operand);}
void *constant_folding_c::visit(  MOD_operator_c *symbol) {return handle_mod (symbol, prev_il_instruction, il_operand);}

void *constant_folding_c::visit(   GT_operator_c *symbol) {       handle_cmp (symbol, prev_il_instruction, il_operand, > );}
void *constant_folding_c::visit(   GE_operator_c *symbol) {       handle_cmp (symbol, prev_il_instruction, il_operand, >=);}
void *constant_folding_c::visit(   EQ_operator_c *symbol) {       handle_cmp (symbol, prev_il_instruction, il_operand, ==);}
void *constant_folding_c::visit(   LT_operator_c *symbol) {       handle_cmp (symbol, prev_il_instruction, il_operand, < );}
void *constant_folding_c::visit(   LE_operator_c *symbol) {       handle_cmp (symbol, prev_il_instruction, il_operand, <=);}
void *constant_folding_c::visit(   NE_operator_c *symbol) {       handle_cmp (symbol, prev_il_instruction, il_operand, !=);}

void *constant_folding_c::visit(  CAL_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(  RET_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(  JMP_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit( CALC_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(CALCN_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit( RETC_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(RETCN_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit( JMPC_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}
void *constant_folding_c::visit(JMPCN_operator_c *symbol) {return handle_move(symbol, prev_il_instruction);}




/***************************************/
/* B.3 - Language ST (Structured Text) */
/***************************************/
/***********************/
/* B 3.1 - Expressions */
/***********************/
void *constant_folding_c::visit(    or_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_or (symbol, symbol->l_exp, symbol->r_exp);}
void *constant_folding_c::visit(   xor_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_xor(symbol, symbol->l_exp, symbol->r_exp);}
void *constant_folding_c::visit(   and_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_and(symbol, symbol->l_exp, symbol->r_exp);}

void *constant_folding_c::visit(   equ_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this);        handle_cmp (symbol, symbol->l_exp, symbol->r_exp, ==);}
void *constant_folding_c::visit(notequ_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this);        handle_cmp (symbol, symbol->l_exp, symbol->r_exp, !=);}
void *constant_folding_c::visit(    lt_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this);        handle_cmp (symbol, symbol->l_exp, symbol->r_exp, < );}
void *constant_folding_c::visit(    gt_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this);        handle_cmp (symbol, symbol->l_exp, symbol->r_exp, > );}
void *constant_folding_c::visit(    le_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this);        handle_cmp (symbol, symbol->l_exp, symbol->r_exp, <=);}
void *constant_folding_c::visit(    ge_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this);        handle_cmp (symbol, symbol->l_exp, symbol->r_exp, >=);}

void *constant_folding_c::visit(   add_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_add(symbol, symbol->l_exp, symbol->r_exp);}
void *constant_folding_c::visit(   sub_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_sub(symbol, symbol->l_exp, symbol->r_exp);}
void *constant_folding_c::visit(   mul_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_mul(symbol, symbol->l_exp, symbol->r_exp);}
void *constant_folding_c::visit(   div_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_div(symbol, symbol->l_exp, symbol->r_exp);}
void *constant_folding_c::visit(   mod_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_mod(symbol, symbol->l_exp, symbol->r_exp);}
void *constant_folding_c::visit( power_expression_c *symbol) {symbol->l_exp->accept(*this); symbol->r_exp->accept(*this); return handle_pow(symbol, symbol->l_exp, symbol->r_exp);}

void *constant_folding_c::visit(   neg_expression_c *symbol) {symbol->  exp->accept(*this); return handle_neg(symbol, symbol->exp);}
void *constant_folding_c::visit(   not_expression_c *symbol) {symbol->  exp->accept(*this); return handle_not(symbol, symbol->exp);}

/* TODO: handle function invocations... */
// void *fill_candidate_datatypes_c::visit(function_invocation_c *symbol) {}



#if DO_CONSTANT_PROPAGATION__
/*********************************/
/* B 3.2.1 Assignment Statements */
/*********************************/
void *constant_folding_c::visit(assignment_statement_c *symbol) {
	std::string varName;

	symbol->r_exp->accept(*this);
	symbol->l_exp->const_value = symbol->r_exp->const_value;
	varName = get_var_name_c::get_name(symbol->l_exp)->value;
	values[varName] = symbol->l_exp->const_value;

	return NULL;
}

/********************************/
/* B 3.2.3 Selection Statements */
/********************************/
void *constant_folding_c::visit(if_statement_c *symbol) {
	map_values_t values_incoming;
	map_values_t values_statement_result;
	map_values_t values_elsestatement_result;
	map_values_t::iterator itr;

	/* Optimize dead code */
	symbol->expression->accept(*this);
	if (VALID_CVALUE(bool, symbol->expression) && GET_CVALUE(bool, symbol->expression) == false)
		return NULL;

	values_incoming = values; /* save incoming status */
	symbol->statement_list->accept(*this);
	values_statement_result = values;
	if (NULL != symbol->else_statement_list) {
		values = values_incoming;
		symbol->else_statement_list->accept(*this);
		values_elsestatement_result = values;
	} else
		values_elsestatement_result = values_incoming;
	values = inner_left_join_values(values_statement_result, values_elsestatement_result);

	return NULL;
}

/********************************/
/* B 3.2.4 Iteration Statements */
/********************************/
void *constant_folding_c::visit(for_statement_c *symbol) {
	map_values_t values_incoming;
	map_values_t values_statement_result;
	std::string varName;

	values_incoming = values; /* save incoming status */
	symbol->beg_expression->accept(*this);
	symbol->end_expression->accept(*this);
	varName =  get_var_name_c::get_name(symbol->control_variable)->value;
	values[varName]._int64.status = symbol_c::cs_non_const;

	/* Optimize dead code */
	if (NULL != symbol->by_expression) {
		symbol->by_expression->accept(*this);
		if (VALID_CVALUE(int64, symbol->by_expression ) &&   GET_CVALUE(int64, symbol->by_expression ) > 0 &&
			VALID_CVALUE(int64, symbol->beg_expression) && VALID_CVALUE(int64, symbol->end_expression)     &&
			  GET_CVALUE(int64, symbol->beg_expression) >    GET_CVALUE(int64, symbol->end_expression))
			return NULL;

		if (VALID_CVALUE(int64, symbol->by_expression ) &&   GET_CVALUE(int64, symbol->by_expression ) < 0 &&
			VALID_CVALUE(int64, symbol->beg_expression) && VALID_CVALUE(int64, symbol->end_expression)    &&
			  GET_CVALUE(int64, symbol->beg_expression) <    GET_CVALUE(int64, symbol->end_expression))
			return NULL;

	} else {
		if (VALID_CVALUE(int64, symbol->beg_expression) && VALID_CVALUE(int64, symbol->end_expression)     &&
			  GET_CVALUE(int64, symbol->beg_expression) >    GET_CVALUE(int64, symbol->end_expression))
			return NULL;

	}


	symbol->statement_list->accept(*this);
	values_statement_result = values;
	values = inner_left_join_values(values_statement_result, values_incoming);

	return NULL;
}

void *constant_folding_c::visit(while_statement_c *symbol) {
	map_values_t values_incoming;
	map_values_t values_statement_result;

	/* Optimize dead code */
	symbol->expression->accept(*this);
	if (VALID_CVALUE(bool, symbol->expression) && GET_CVALUE(bool, symbol->expression) == false)
		return NULL;

	values_incoming = values; /* save incoming status */
	symbol->statement_list->accept(*this);
	values_statement_result = values;
	values = inner_left_join_values(values_statement_result, values_incoming);

	return NULL;
}

void *constant_folding_c::visit(repeat_statement_c *symbol) {
	map_values_t values_incoming;
	map_values_t values_statement_result;

	values_incoming = values; /* save incoming status */
	symbol->statement_list->accept(*this);

	/* Optimize dead code */
	symbol->expression->accept(*this);
	if (VALID_CVALUE(bool, symbol->expression) && GET_CVALUE(bool, symbol->expression) == true)
		return NULL;

	values_statement_result = values;
	values = inner_left_join_values(values_statement_result, values_incoming);

	return NULL;
}

#endif  // DO_CONSTANT_PROPAGATION__