decl.c

#include "defs.h"
#include "data.h"
#include "decl.h"

// Parsing of declarations
// Copyright (c) 2019 Warren Toomey, GPL3

static struct symtable *struct_declaration(void);


// Parse the current token and return
// a primitive type enum value and a pointer
// to any composite type.
// Also scan in the next token
int parse_type(struct symtable **ctype) {
  int type;
  switch (Token.token) {
    case T_VOID:
      type = P_VOID;
      scan(&Token);
      break;
    case T_CHAR:
      type = P_CHAR;
      scan(&Token);
      break;
    case T_INT:
      type = P_INT;
      scan(&Token);
      break;
    case T_LONG:
      type = P_LONG;
      scan(&Token);
      break;
    case T_STRUCT:
      type = P_STRUCT;
      *ctype = struct_declaration();
      break;
    default:
      fatald("Illegal type, token", Token.token);
  }

  // Scan in one or more further '*' tokens 
  // and determine the correct pointer type
  while (1) {
    if (Token.token != T_STAR)
      break;
    type = pointer_to(type);
    scan(&Token);
  }

  // We leave with the next token already scanned
  return (type);
}

// variable_declaration: type identifier ';'
//        | type identifier '[' INTLIT ']' ';'
//        ;
//
// Parse the declaration of a scalar variable or an array
// with a given size.
// The identifier has been scanned & we have the type.
// class is the variable's class
// Return the pointer to variable's entry in the symbol table
struct symtable *var_declaration(int type, struct symtable *ctype, int class) {
  struct symtable *sym = NULL;

  // See if this has already been declared
  switch (class) {
    case C_GLOBAL:
      if (findglob(Text) != NULL)
	fatals("Duplicate global variable declaration", Text);
    case C_LOCAL:
    case C_PARAM:
      if (findlocl(Text) != NULL)
	fatals("Duplicate local variable declaration", Text);
    case C_MEMBER:
      if (findmember(Text) != NULL)
	fatals("Duplicate struct/union member declaration", Text);
  }

  // Text now has the identifier's name.
  // If the next token is a '['
  if (Token.token == T_LBRACKET) {
    // Skip past the '['
    scan(&Token);

    // Check we have an array size
    if (Token.token == T_INTLIT) {
      // Add this as a known array and generate its space in assembly.
      // We treat the array as a pointer to its elements' type
      switch (class) {
	case C_GLOBAL:
	  sym =
	    addglob(Text, pointer_to(type), ctype, S_ARRAY, Token.intvalue);
	  break;
	case C_LOCAL:
	case C_PARAM:
	case C_MEMBER:
	  fatal
	    ("For now, declaration of non-global arrays is not implemented");
      }
    }
    // Ensure we have a following ']'
    scan(&Token);
    match(T_RBRACKET, "]");
  } else {
    // Add this as a known scalar
    // and generate its space in assembly
    switch (class) {
      case C_GLOBAL:
	sym = addglob(Text, type, ctype, S_VARIABLE, 1);
	break;
      case C_LOCAL:
	sym = addlocl(Text, type, ctype, S_VARIABLE, 1);
	break;
      case C_PARAM:
	sym = addparm(Text, type, ctype, S_VARIABLE, 1);
	break;
      case C_MEMBER:
	sym = addmemb(Text, type, ctype, S_VARIABLE, 1);
	break;
    }
  }
  return (sym);
}

// var_declaration_list: <null>
//           | variable_declaration
//           | variable_declaration separate_token var_declaration_list ;
//
// When called to parse function parameters, separate_token is ','.
// When called to parse members of a struct/union, separate_token is ';'.
//
// Parse a list of variables.
// Add them as symbols to one of the symbol table lists, and return the
// number of variables. If funcsym is not NULL, there is an existing function
// prototype, so compare each variable's type against this prototype.
static int var_declaration_list(struct symtable *funcsym, int class,
				int separate_token, int end_token) {
  int type;
  int paramcnt = 0;
  struct symtable *protoptr = NULL;
  struct symtable *ctype;

  // If there is a prototype, get the pointer
  // to the first prototype parameter
  if (funcsym != NULL)
    protoptr = funcsym->member;

  // Loop until the final end token
  while (Token.token != end_token) {
    // Get the type and identifier
    type = parse_type(&ctype);
    ident();

    // Check that this type matches the prototype if there is one
    if (protoptr != NULL) {
      if (type != protoptr->type)
	fatald("Type doesn't match prototype for parameter", paramcnt + 1);
      protoptr = protoptr->next;
    } else {
      // Add a new parameter to the right symbol table list, based on the class
      var_declaration(type, ctype, class);
    }
    paramcnt++;

    // Must have a separate_token or ')' at this point
    if ((Token.token != separate_token) && (Token.token != end_token))
      fatald("Unexpected token in parameter list", Token.token);
    if (Token.token == separate_token)
      scan(&Token);
  }

  // Check that the number of parameters in this list matches
  // any existing prototype
  if ((funcsym != NULL) && (paramcnt != funcsym->nelems))
    fatals("Parameter count mismatch for function", funcsym->name);

  // Return the count of parameters
  return (paramcnt);
}

//
// function_declaration: type identifier '(' parameter_list ')' ;
//      | type identifier '(' parameter_list ')' compound_statement   ;
//
// Parse the declaration of function.
// The identifier has been scanned & we have the type.
struct ASTnode *function_declaration(int type) {
  struct ASTnode *tree, *finalstmt;
  struct symtable *oldfuncsym, *newfuncsym = NULL;
  int endlabel, paramcnt;

  // Text has the identifier's name. If this exists and is a
  // function, get the id. Otherwise, set oldfuncsym to NULL.
  if ((oldfuncsym = findsymbol(Text)) != NULL)
    if (oldfuncsym->stype != S_FUNCTION)
      oldfuncsym = NULL;

  // If this is a new function declaration, get a
  // label-id for the end label, and add the function
  // to the symbol table,
  if (oldfuncsym == NULL) {
    endlabel = genlabel();
    // Assumtion: functions only return scalar types, so NULL below
    newfuncsym = addglob(Text, type, NULL, S_FUNCTION, endlabel);
  }
  // Scan in the '(', any parameters and the ')'.
  // Pass in any existing function prototype pointer
  lparen();
  paramcnt = var_declaration_list(oldfuncsym, C_PARAM, T_COMMA, T_RPAREN);
  rparen();

  // If this is a new function declaration, update the
  // function symbol entry with the number of parameters.
  // Also copy the parameter list into the function's node.
  if (newfuncsym) {
    newfuncsym->nelems = paramcnt;
    newfuncsym->member = Parmhead;
    oldfuncsym = newfuncsym;
  }
  // Clear out the parameter list
  Parmhead = Parmtail = NULL;

  // Declaration ends in a semicolon, only a prototype.
  if (Token.token == T_SEMI) {
    scan(&Token);
    return (NULL);
  }
  // This is not just a prototype.
  // Set the Functionid global to the function's symbol pointer
  Functionid = oldfuncsym;

  // Get the AST tree for the compound statement
  tree = compound_statement();

  // If the function type isn't P_VOID ..
  if (type != P_VOID) {

    // Error if no statements in the function
    if (tree == NULL)
      fatal("No statements in function with non-void type");

    // Check that the last AST operation in the
    // compound statement was a return statement
    finalstmt = (tree->op == A_GLUE) ? tree->right : tree;
    if (finalstmt == NULL || finalstmt->op != A_RETURN)
      fatal("No return for function with non-void type");
  }
  // Return an A_FUNCTION node which has the function's symbol pointer
  // and the compound statement sub-tree
  return (mkuastunary(A_FUNCTION, type, tree, oldfuncsym, endlabel));
}

// Parse struct declarations. Either find an existing
// struct declaration, or build a struct symbol table
// entry and return its pointer.
static struct symtable *struct_declaration(void) {
  struct symtable *ctype = NULL;
  struct symtable *m;
  int offset;

  // Skip the struct keyword
  scan(&Token);

  // See if there is a following struct name
  if (Token.token == T_IDENT) {
    // Find any matching composite type
    ctype = findstruct(Text);
    scan(&Token);
  }
  // If the next token isn't an LBRACE , this is
  // the usage of an existing struct type.
  // Return the pointer to the type.
  if (Token.token != T_LBRACE) {
    if (ctype == NULL)
      fatals("unknown struct type", Text);
    return (ctype);
  }
  // Ensure this struct type hasn't been
  // previously defined
  if (ctype)
    fatals("previously defined struct", Text);

  // Build the struct node and skip the left brace
  ctype = addstruct(Text, P_STRUCT, NULL, 0, 0);
  scan(&Token);

  // Scan in the list of members and attach
  // to the struct type's node
  var_declaration_list(NULL, C_MEMBER, T_SEMI, T_RBRACE);
  rbrace();
  ctype->member = Membhead;
  Membhead = Membtail = NULL;

  // Set the offset of the initial member
  // and find the first free byte after it
  m = ctype->member;
  m->posn = 0;
  offset = typesize(m->type, m->ctype);

  // Set the position of each successive member in the struct
  for (m = m->next; m != NULL; m = m->next) {
    // Set the offset for this member
    m->posn = genalign(m->type, offset, 1);

    // Get the offset of the next free byte after this member
    offset += typesize(m->type, m->ctype);
  }

  // Set the overall size of the struct
  ctype->size = offset;
  return (ctype);
}

// Parse one or more global declarations, either
// variables, functions or structs
void global_declarations(void) {
  struct ASTnode *tree;
  struct symtable *ctype;
  int type;

  while (1) {
    // Stop when we have reached EOF
    if (Token.token == T_EOF)
      break;

    // Get the type
    type = parse_type(&ctype);

    // We might have just parsed a struct declaration
    // with no associated variable. The next token
    // might be a ';'. Loop back if it is. XXX. I'm
    // not happy with this as it allows "struct fred;"
    // as an accepted statement
    if (type == P_STRUCT && Token.token == T_SEMI) {
      scan(&Token);
      continue;
    }
    // We have to read past the identifier
    // to see either a '(' for a function declaration
    // or a ',' or ';' for a variable declaration.
    // Text is filled in by the ident() call.
    ident();
    if (Token.token == T_LPAREN) {

      // Parse the function declaration
      tree = function_declaration(type);

      // Only a function prototype, no code
      if (tree == NULL)
	continue;

      // A real function, generate the assembly code for it
      if (O_dumpAST) {
	dumpAST(tree, NOLABEL, 0);
	fprintf(stdout, "\n\n");
      }
      genAST(tree, NOLABEL, 0);

      // Now free the symbols associated
      // with this function
      freeloclsyms();
    } else {

      // Parse the global variable declaration
      // and skip past the trailing semicolon
      var_declaration(type, ctype, C_GLOBAL);
      semi();
    }
  }
}