The main data structure used through the whole compiler is the NODE. The parse trees are built out of NODEs and it is the underlying data structure when generating code.

The NODE structure contains lots of fields in unions to keep the size down of the struct. Different NODE types uses different elements in the structure. The NODE struct is declared like this:

typedef struct node {
    int     n_op;
    int     n_rall;
    TWORD   n_type;
    TWORD   n_qual;
    int     n_su;
    union {
            char *  _name;
            int     _stsize;
            union   dimfun *_df;
    } n_5;
    union {
            int     _label;
            int     _stalign;
    struct attr *_ap;
    } n_6;
    union {
            struct {
                    union {
                            struct node *_left;
                            CONSZ _lval;
#ifdef SPECIAL_INTEGERS
                            SPECLVAL _slval;
#endif
                    } n_l;
                    union {
                            struct node *_right;
                            int _rval;
                            struct symtab *_sp;
                    } n_r;
            } n_u;
            long double     _dcon;
    } n_f;
} NODE;

#define n_name  n_5._name
#define n_stsize n_5._stsize
#define n_df    n_5._df

#define n_label n_6._label
#define n_stalign n_6._stalign
#define n_ap    n_6._ap

#define n_left  n_f.n_u.n_l._left
#define n_lval  n_f.n_u.n_l._lval
#define n_slval n_f.n_u.n_l._slval
#define n_right n_f.n_u.n_r._right
#define n_rval  n_f.n_u.n_r._rval
#define n_sp    n_f.n_u.n_r._sp
#define n_dcon  n_f._dcon

NODE fields

All Nodes

The fields that are valid in all nodes are:

• n_op

  Tells which op the node is.

• n_type/n_qual

  Keeps the encoded type of the node.

• n_rall/n_su

  Used in pass2 to generate code.

Leaf Nodes

• NAME

  n_lval has offset to the NAME (in bits). In pass1, n_sp is a pointer to this node symtab entry, in pass2 the name string is stored in n_name.

• ICON

  Holds an integer constant in n_lval. If it is a memory referenced constant, n_sp is a pointer to this node symtab entry in pass1 and n_name points to its name in pass2.

• FCON

  Holds a floating point constant in n_dcon.

• REG

  Reference to a register. The register number is held in n_rval.

• OREG

  An indirect reference to memory via an offset to a register. The register number is held in n_rval, the offset in n_lval.

Unary Nodes

The node leg is always the left leg.

• COMPL

  Complements the left node.

• UMUL

  Type indirection operator; does PTR int -> int.

• UMINUS

  Negates the left node.

• FLD

  The left leg is a bitfield reference. n_rval holds the bit offsets in packed format.

• SCONV

  Type converts any type to an integer or float type.

• PCONV

  The same as SCONV but the result is a pointer.

• PMCONV/PVCONV

  Used to do struct offset calculations. Mostly they can be replaced in pass1.

• UCALL/UFORTCALL/USTCALL

  Call to a function without arguments. UFORTCALL is to call a fortran function, USTCALL for functions returning structures or unions.

• FORCE

  Forces the return value from a function to end up in the return register.

• GOTO

  Just goto the left-node label.

• RETURN

  Return from a function.

• FUNARG

  Make the tree result an argument for a function to call.

• ADDROF

  The inverse of UMUL, get the address of an object.