B(3)

NAME
B - The Perl Compiler

SYNOPSIS

        use B;

DESCRIPTION
The B module supplies classes which allow a Perl program to delve into its own innards. It is the module used to implement the "backends" of the Perl compiler. Usage of the compiler does not require knowledge of this module: see the O module for the user-visible part. The B module is of use to those who want to write new compiler backends. This documentation assumes that the reader knows a fair amount about perl's internals including such things as SVs, OPs and the internal symbol table and syntax tree of a program.

OVERVIEW OF CLASSES
The C structures used by Perl's internals to hold SV and OP information (PVIV, AV, HV, ..., OP, SVOP, UNOP, ...) are modelled on a class hierarchy and the B module gives access to them via a true object hierarchy. Structure fields which point to other objects (whether types of SV or types of OP) are represented by the B module as Perl objects of the appropriate class. The bulk of the B module is the methods for accessing fields of these structures. Note that all access is read-only: you cannot modify the internals by using this module.

  SV-RELATED CLASSES
B::IV, B::NV, B::RV, B::PV, B::PVIV, B::PVNV, B::PVMG, B::BM, B::PVLV, B::AV, B::HV, B::CV, B::GV, B::FM, B::IO. These classes correspond in the obvious way to the underlying C structures of similar names. The inheritance hierarchy mimics the underlying C "inheritance". Access methods correspond to the underlying C macros for field access, usually with the leading "class indication" prefix removed (Sv, Av, Hv, ...). The leading prefix is only left in cases where its removal would cause a clash in method name. For example, GvREFCNT stays as-is since its abbreviation would clash with the "superclass" method REFCNT (corresponding to the C function SvREFCNT).

  B::SV METHODS

REFCNT

FLAGS

  B::IV METHODS

IV

IVX

needs64bits

packiv

  B::NV METHODS

NV

NVX

  B::RV METHODS

RV

  B::PV METHODS

PV

  B::PVMG METHODS

MAGIC

SvSTASH

  B::MAGIC METHODS

MOREMAGIC

PRIVATE

TYPE

FLAGS

OBJ

PTR

  B::PVLV METHODS

TARGOFF

TARGLEN

TYPE

TARG

  B::BM METHODS

USEFUL

PREVIOUS

RARE

TABLE

  B::GV METHODS

NAME

STASH

SV

IO

FORM

AV

HV

EGV

CV

CVGEN

LINE

FILEGV

GvREFCNT

FLAGS

  B::IO METHODS

LINES

PAGE

PAGE_LEN

LINES_LEFT

TOP_NAME

TOP_GV

FMT_NAME

FMT_GV

BOTTOM_NAME

BOTTOM_GV

SUBPROCESS

IoTYPE

IoFLAGS

  B::AV METHODS

FILL

MAX

OFF

ARRAY

AvFLAGS

  B::CV METHODS

STASH

START

ROOT

GV

FILEGV

DEPTH

PADLIST

OUTSIDE

XSUB

XSUBANY

  B::HV METHODS

FILL

MAX

KEYS

RITER

NAME

PMROOT

ARRAY

  OP-RELATED CLASSES
B::OP, B::UNOP, B::BINOP, B::LOGOP, B::CONDOP, B::LISTOP, B::PMOP, B::SVOP, B::GVOP, B::PVOP, B::CVOP, B::LOOP, B::COP. These classes correspond in the obvious way to the underlying C structures of similar names. The inheritance hierarchy mimics the underlying C "inheritance". Access methods correspond to the underlying C structre field names, with the leading "class indication" prefix removed (op_).

  B::OP METHODS

next

sibling

ppaddr
    This returns the function name as a string (e.g. pp_add, pp_rv2av).

desc
    This returns the op description from the global C op_desc array (e.g. "addition" "array deref").

targ

type

seq

flags

private

  B::UNOP METHOD

first

  B::BINOP METHOD

last

  B::LOGOP METHOD

other

  B::CONDOP METHODS

true

false

  B::LISTOP METHOD

children

  B::PMOP METHODS

pmreplroot

pmreplstart

pmnext

pmregexp

pmflags

pmpermflags

precomp

  B::SVOP METHOD

sv

  B::GVOP METHOD

gv

  B::PVOP METHOD

pv

  B::LOOP METHODS

redoop

nextop

lastop

  B::COP METHODS

label

stash

filegv

cop_seq

arybase

line

FUNCTIONS EXPORTED BY B
The B module exports a variety of functions: some are simple utility functions, others provide a Perl program with a way to get an initial "handle" on an internal object.

main_cv
    Return the (faked) CV corresponding to the main part of the Perl program.

main_root
    Returns the root op (i.e. an object in the appropriate B::OP-derived class) of the main part of the Perl program.

main_start
    Returns the starting op of the main part of the Perl program.

comppadlist
    Returns the AV object (i.e. in class B::AV) of the global comppadlist.

sv_undef
    Returns the SV object corresponding to the C variable sv_undef.

sv_yes
    Returns the SV object corresponding to the C variable sv_yes.

sv_no
    Returns the SV object corresponding to the C variable sv_no.

walkoptree(OP, METHOD)
    Does a tree-walk of the syntax tree based at OP and calls METHOD on each op it visits. Each node is visited before its children. If walkoptree_debug (q.v.) has been called to turn debugging on then the method walkoptree_debug is called on each op before METHOD is called.

walkoptree_debug(DEBUG)
    Returns the current debugging flag for walkoptree. If the optional DEBUG argument is non-zero, it sets the debugging flag to that. See the description of walkoptree above for what the debugging flag does.

walksymtable(SYMREF, METHOD, RECURSE)
    Walk the symbol table starting at SYMREF and call METHOD on each symbol visited. When the walk reached package symbols "Foo::" it invokes RECURSE and only recurses into the package if that sub returns true.

svref_2object(SV)
    Takes any Perl variable and turns it into an object in the appropriate B::OP-derived or B::SV-derived class. Apart from functions such as main_root, this is the primary way to get an initial "handle" on a internal perl data structure which can then be followed with the other access methods.

ppname(OPNUM)
    Return the PP function name (e.g. "pp_add") of op number OPNUM.

hash(STR)
    Returns a string in the form "0x..." representing the value of the internal hash function used by perl on string STR.

cast_I32(I)
    Casts I to the internal I32 type used by that perl.

minus_c
    Does the equivalent of the -c command-line option. Obviously, this is only useful in a BEGIN block or else the flag is set too late.

cstring(STR)
    Returns a double-quote-surrounded escaped version of STR which can be used as a string in C source code.

class(OBJ)
    Returns the class of an object without the part of the classname preceding the first "::". This is used to turn "B::UNOP" into "UNOP" for example.

threadsv_names
    In a perl compiled for threads, this returns a list of the special per-thread threadsv variables.

byteload_fh(FILEHANDLE)
    Load the contents of FILEHANDLE as bytecode. See documentation for the Bytecode module in B::Backend for how to generate bytecode.

AUTHOR
Malcolm Beattie, mbeattie@sable.ox.ac.uk