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:
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 on..do 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)
pascal
type
TNode =classpublic
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
RegistersFpu,
RegistersMm: Longint;// must be longint !!!! {$ifdef SUPPORT_MMX}
RegistersMmx: Longint;{$endif SUPPORT_MMX}
ResultType: TType;
FileInfo: TFilePosInfo;
LocalSwitches: TLocalSwitches;{$ifdef extdebug}
MaxFirstPassCount,
FirstPassCount: Longint;{$endif extdebug}end;
TNodeFlag
(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
TLocalSwitches
(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
MMX
TLocalSwitches
Switch
Param
Description
cs_mmx
{$MMX+}
Code generator can use MMX commands
cs_mmx_saturation
{$SATURATION+}
Code generator can use saturated operations (MMX)
Parser
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.
AddN
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.
CallParaN
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;
AssignN
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)
LoadN
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)
CallN
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
addrn
Field
Description
ProcVarLoad: Boolean;
Set to TRUE if this is a procedural variable call
OrdConstN
Field
Description
Value: LongInt;
The numeric value of this constant node
RealConstN
Field
Description
Value_Real: Best_Real;
The numeric value of this constant node
Lab_Real: PAsmLabel;
The assembler label reference to this constant
FixConstN
Field
Description
Value_Fix: LongInt;
The numeric value of this constant node
FuncRetN
Field
Description
FuncRetProcInfo: Pointer; (PProcInfo)
Pointer to procedure information
RetType: TType;
Indicates the return type of the function
Is_First_FuncRet: Boolean;
SubscriptN
Field
Description
vs: pVarSym;
Symbol table entry for this variable (a field of object/class/record)
RaiseN
Field
Description
FrameTree: PTree;
Exception frame tree (code in Raise statement)
VecN
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;
StringConstN
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)
TypeConvN
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)
TypeN
Field
Description
TypeNodeType: PDef;
The type definition for this node
TypeNodeSym: PTypeSym;
The type symbol information
InlineN
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
ProcInlineN
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
SetConstN
Field
Description
Value_Set: PConstSet;
The numeric value of this constant node
Lab_Set: PAsmLabel;
The assembler label reference to this constant
LoopN
Field
Description
AsmN
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.
CaseN
Field
Description
Nodes: PCaseRecord;
Tree for each of the possible case in the case statement
From the Free Pascal wiki, page "The parse tree", as it stood on 2020-12-19 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.
