The parse tree

From Free Pascal wiki

English (en) français (fr)

back to contents FPC internals

The parse tree


(last updated for fpc version 1.0.x)

The tree is the basis of the compiler. When the compiler parses statements and blocks of code, they are converted to a tree representation. This tree representation is actually a doubly linked list. From this tree the code generation can easily be implemented.

Assuming that you have the following pascal syntax:

x := x * y + (6 shl x);

The tree structure will be built in memory, where each circle represents an element (a node) in the tree:

Node types

(last updated for fpc version 2.1.1, 2005-06-11)

The following tree nodes are possible (of type TNodeTyp):

Tree type definition Description
emptynode No node (returns nil when loading from ppu)
addn Represents the + operator
muln Represents the * operator
subn Represents the - operator
divn Represents the div operator
symdifn Represents the >< operator
modn Represents the mod operator
assignn Represents the := operator (assignment)
loadn Represents the use of a variabele
rangen Represents a range (i.e. 0..9)
ltn Represents the < operator
lten Represents the <= operator
gtn Represents the > operator
gten Represents the >= operator
equaln Represents the = operator
unequaln Represents the <> operator
inn Represents the in operator
orn Represents the or operator
xorn Represents the xor operator
shrn Represents the shr operator
shln Represents the shl operator
slashn Represents the / operator
andn Represents the and operator
subscriptn Represents a field in an object or record
derefn Represents a pointer reference (such as the ^ operator)
addrn Represents the @ operator
ordconstn Represents an ordinal constant
typeconvn Represents a typecast / type conversion
calln Represents a routine call
callparan Represents a parameter passed to a routine
realconstn Represents a floating point constant
unaryminusn Represents a sign change (e.g : -)
asmn Represents an assembler statement node
vecn Represents array indexing
pointerconstn Represents a pointer constant
stringconstn Represents a string constant
notn Represents the not operator
inlinen Represents one of the internal routines (writeln,ord,etc.)
niln Represents the nil pointer
errorn Represents error in parsing this node (used for error detection and correction)
typen Represents a type name (i.e typeof(obj))
setelementn Represents set elements (i.e : [a..b], [a,b,c]) (nonconstant)
setconstn Represents set element constants i.e : [1..9], [1,2,3])
blockn Represents a block of statements
statementn One statement in a block of nodes
ifn Represents an if statement
breakn Represents a break statement
continuen Represents a continue statement
whilerepeatn Represents a while or repeat statement
forn Represents a for statement
exitn Represents an exit statement
withn Represents a with statement
casen Represents a case statement
labeln Represents a label statement
goton Represents a goto statement
tryexceptn Represents a try..except statement
raisen Represents a raise statement
tryfinallyn Represents a try..finally statement
onn Represents an statement (in exception code)
isn Represents the is operator
asn Represents the as typecast operator
caretn Represents the ^ operator
starstarn Represents the ** operator (exponentiation)
arrayconstructorn Represents a construction node for [...] parsing
arrayconstructorrangen Range element to allow sets in array construction tree
tempcreaten for temps in the result/firstpass
temprefn references to temps
tempdeleten for temps in the result/firstpass
addoptn added for optimizations where we cannot suppress
nothingn NOP, Do nothing
loadvmtaddrn Load the address of the VMT of a class/object
guidconstn A GUID COM Interface constant
rttin Rtti information so they can be accessed in result/firstpass
loadparentfpn Load the framepointer of the parent for nested procedures

Node structure fields (node.pas)

(last updated for fpc version 2.1.1, 2005-06-11)

  TNode = class
    NodeType: TNodeType;            // type of this node
    BlockType: TBlock_Type;         // type of the current code block, general/const/type
    ExpectLoc: TCGLoc;              // expected location of the result of this node (pass1)
    Location: TLocation;            // the location of the result of this node (pass2)
    Parent: TNode;                  // the parent node of this is node
                                    // this field is set by concattolist  
    Flags: TNodeFlags;              // there are some properties about the node stored
    PpuIdx: Longint;
    RegistersInt,                   // the number of registers needed to evalute the node
    RegistersMm: Longint;           // must be longint !!!! 
    {$ifdef SUPPORT_MMX}
    RegistersMmx: Longint;
    {$endif SUPPORT_MMX}
    ResultType: TType;
    FileInfo: TFilePosInfo;
    LocalSwitches: TLocalSwitches;
    {$ifdef extdebug}
    FirstPassCount: Longint;
    {$endif extdebug}


(last updated for fpc version 2.1.1, 2005-06-11)

TNodeType   Description
nf_swapable TBinOp operands can be swapped
nf_swaped TBinOp operands are swapped
nf_error   Set to TRUE if there was an error parsing this node
nf_pass1_done general  
nf_write general Node is written to
nf_isproperty general TRUE if this is a property
nf_typedaddr TAddrNode  
nf_no_checkpointer TDerefNode  
nf_memindex TVecNode  
nf_memseg TVecNode  
nf_callunique TVecNode  
nf_absolute TLoadNode  
nf_is_self TLoadNode  
nf_load_self_pointer TLoadNode  
nf_is_currency TAddNode  
nf_has_pointerdiv TAddNode  
nf_concat_string TAssignmentNode  
nf_use_strconcat TAssignmentNode  
nf_forcevaria TArrayConstructNode  
nf_novariaallowed TArrayConstructNode  
nf_explicit TTypeConvNode  
nf_internal TTypeConvNode no warnings/hints generated
nf_load_procvar TTypeConvNode  
nf_inlineconst TInlineNode  
nf_get_asm_position TAsmNode  
nf_block_with_exit TBlockNode  


(last updated for fpc version 2.1.1, 2005-06-11)

Gébnération de code

TLocalSwitches Commutateur Paramètre Description
cs_check_overflow {$Q+} -Co Le générateur de code devrait émettre du code de contrôle de dépassement
cs_check_range {$R+} -Cr, -CR Code generator should emit range checking code
cs_check_object   -CR Code generator should emit code to verify object method call validity
cs_check_io {$I+} -Ci Code generator should emit I/O checking code
cs_check_stack {$S+} -Ct Code generator should emit stack checking code
cs_checkpointer   -gc Code generator should emit pointer checking code
cs_omitstackframe N/A   Code generator should not emit frame_pointer setup code in entry code (don't used in the compiler)
cs_do_assertion {$C+} -Sa Code generator supports using the assert inline routine
cs_generate_rtti {$M+}   Code generator should emit runtime type information
cs_full_boolean_eval {$B+}   Boolean evalution mode
cs_typed_const_writable {$J+}   todo
cs_allow_enum_calc     todo


TLocalSwitches Switch Param Description
cs_mmx {$MMX+}   Code generator can use MMX commands
cs_mmx_saturation {$SATURATION+}   Code generator can use saturated operations (MMX)


TLocalSwitches Switch Param Description
cs_typed_addresses {$T+}   Parser emits typed pointer using the @ operator
cs_strict_var_strings {$V+}   String types must be identical (same length) to be compatible
cs_ansistrings {$H+} -Sh Parser creates an ansistring when an unspecified String type is declared instead of the default ShortString

MACPAS specific

TLocalSwitches Switch Param Description
cs_external_var {$J+}   todo
cs_externally_visible {$Z+}   todo

Additional fields

(last updated for fpc version 1.0.x)

Depending on the tree type, some additional fields may be present in the tree node. This section describes these additional fields. Before accessing these additional fields, a check on the treetype should always be done to verify if not reading invalid memory ranges.


Field Description
Use_StrConcat: Boolean; Currently unused (use for optimizations in future versions)
String_Typ: TStringType; In the case where the + operator is applied on a string, this field indicates the string type.


Field Description
Is_Colon_Para : Boolean; Used for internal routines which can use optional format parameters (using colons). Is set to TRUE if this parameter was preceded by a colon (i.e : :1)
Exact_Match_Found : Boolean; Set to TRUE if the parameter type is exactly the same as the one expected by the routine.
ConvLevel1Found : Boolean; Set to TRUE if the parameter type requires a level 1 type conversion to conform to the parameter expected by the routine.
ConvLevel2Found : Boolean; Set to TRUE if the parameter type requires a level 2 type conversion to conform to the parameter expected by the routine.
HighTree : pTree;  


Field Description
AssignTyp: TAssignTyp; Currently unused (Used to be used for C-like assigns)
Concat_String: Boolean; Currently unused (use for optimizations in future versions)


Field Description
SymTableEntry: PSym; Symbol table entry for this symbol
SymTable: PSymTable; Symbol table in which this symbol is stored
Is_Absolute: Boolean; set to TRUE if this variable is absolute
Is_First: Boolean; set to TRUE if this is the first occurrence of the load for this variable (used with the varstate variable for optimizations)


Field Description
SymTableProcEntry: PProcSym; Symbol table entry for this routine
SymTableProc: PSymTable; Symbol table associated with a call (object symbol table or routine symbol table)
ProcDefinition: pAbstractProcDef; Type definition for this routine
MethodPointer: pTree; ?????????
No_Check: Boolean; Currently unused
Unit_Specific: Boolean; set to TRUE if the routine is imported in a unit specific way (for example: system.writeln())
Return_Value_Used : Boolean set to TRUE if the routine is a function and that the return value is not used (in extended syntax parsing - $X+)
Static_Call: Boolean; unused


Field Description
ProcVarLoad: Boolean; Set to TRUE if this is a procedural variable call


Field Description
Value: LongInt; The numeric value of this constant node


Field Description
Value_Real: Best_Real; The numeric value of this constant node
Lab_Real: PAsmLabel; The assembler label reference to this constant


Field Description
Value_Fix: LongInt; The numeric value of this constant node


Field Description
FuncRetProcInfo: Pointer; (PProcInfo) Pointer to procedure information
RetType: TType; Indicates the return type of the function
Is_First_FuncRet: Boolean;  


Field Description
vs: pVarSym; Symbol table entry for this variable (a field of object/class/record)


Field Description
FrameTree: PTree; Exception frame tree (code in Raise statement)


Field Description
MemIndex: Boolean; Set to TRUE if Mem[Seg:Ofs] directive is parsed
MemSeg: Boolean; Set to TRUE if Mem[Seg:Ofs] directive is parsed
CallUnique: Boolean;  


Field Description
Value_Str: PChar; The constant value of the string
Length: LongInt; Length of the string in bytes (or in characters???)
Lab_Str: PAsmLabel; The assembler label reference to this constant
StringType: TStringType; The string type (short, long, ansi, wide)


Field Description
ConvType: TConvertType; Indicates the conversion type to do
Explizit: Boolean; set to TRUE if this was an explicit conversion (with explicit typecast, or calling one of the internal conversion routines)


Field Description
TypeNodeType: PDef; The type definition for this node
TypeNodeSym: PTypeSym; The type symbol information


Field Description
InlineNumber: Byte; Indicates the internal routine called (Cf. code generator)
InlineConst: Boolean; One or more of the parameters to this inline routine call contains constant values


Inline nodes are created when a routine is declared as being inline. The routine is actually inlined when the following conditions are satisfied:

It is called within the same module

The appropriate compiler switch to support inline is activated

It is a non-method routine (a standard procedure or function)

Otherwise a normal call is made, ignoring the inline directive. In the case where a routine is inlined, all parameters, return values and local variables of the inlined routine are actually allocated in the stack space of the routine which called the inline routine.

Field Description
InlineTree: PTree; The complete tree for this inline procedure
InlineProcsym: PProcSym; Symbol table entry for this procedure
RetOffset: LongInt; Return offset in parent routine stack space
Para_Offset: LongInt; Parameter start offset in parent routine stack space
Para_Size: LongInt; Parameter size in the parent routine stack space


Field Description
Value_Set: PConstSet; The numeric value of this constant node
Lab_Set: PAsmLabel; The assembler label reference to this constant


Field Description


Field Description
p_Asm: PAasmOutput; The instruction tree created by the assembler parser
Object_Preserved: Boolean; set to FALSE if the Self_Register was modified in the asm statement.


Field Description
Nodes: PCaseRecord; Tree for each of the possible case in the case statement
ElseBlock: PTree; Else statement block tree

LabelN, GotoN

Field Description
LabelNr: PAsmLabel; Assembler label associated with this statement
ExceptionBlock: PTree; ?
LabSym: PLabelSym; Symbol table entry for this label


Field Description
WithSymTables: PWithSymTable;  
TableCount: LongInt;  
WithReference: PReference;  
IsLocal: Boolean;  


Field Description
ExceptSymTable: PSymTable;  
ExceptType: PObjectDef;  


Field Description
CArgs: Boolean;  
CArgSwap: Boolean;  
ForceVaria: Boolean;  
NoVariaAllowed: Boolean;  
ConstructorDef: PDef;  

Next chapter: Symbol tables