


B(3p)            Perl Programmers Reference Guide           B(3p)


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 back-
       ends. 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" mod-
       ule is the methods for accessing fields of these struc-
       tures. Note that all access is read-only: you cannot mod-
       ify 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 under-
       lying C structures of similar names. The inheritance hier-
       archy mimics the underlying C "inheritance". Access meth-
       ods 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 abbre-
       viation would clash with the "superclass" method "REFCNT"
       (corresponding to the C function "SvREFCNT").

       B::SV METHODS


       REFCNT
       FLAGS






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B(3p)            Perl Programmers Reference Guide           B(3p)


       B::IV METHODS


       IV  Returns the value of the IV, interpreted as a signed
           integer. This will be misleading if "FLAGS & SVf_IVi-
           sUV". Perhaps you want the "int_value" method instead?

       IVX
       UVX
       int_value
           This method returns the value of the IV as an integer.
           It differs from "IV" in that it returns the correct
           value regardless of whether it's stored signed or
           unsigned.

       needs64bits
       packiv

       B::NV METHODS


       NV
       NVX

       B::RV METHODS


       RV

       B::PV METHODS

       PV  This method is the one you usually want. It constructs
           a string using the length and offset information in
           the struct: for ordinary scalars it will return the
           string that you'd see from Perl, even if it contains
           null characters.

       PVX This method is less often useful. It assumes that the
           string stored in the struct is null-terminated, and
           disregards the length information.

           It is the appropriate method to use if you need to get
           the name of a lexical variable from a padname array.
           Lexical variable names are always stored with a null
           terminator, and the length field (SvCUR) is overloaded
           for other purposes and can't be relied on here.

       B::PVMG METHODS


       MAGIC
       SvSTASH





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B(3p)            Perl Programmers Reference Guide           B(3p)


       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


       is_empty
           This method returns TRUE if the GP field of the GV is
           NULL.

       NAME
       SAFENAME
           This method returns the name of the glob, but if the
           first character of the name is a control character,
           then it converts it to ^X first, so that *^G would
           return "^G" rather than "\cG".

           It's useful if you want to print out the name of a
           variable.  If you restrict yourself to globs which
           exist at compile-time then the result ought to be
           unambiguous, because code like "${"^G"} = 1" is com-
           piled as two ops - a constant string and a dereference
           (rv2gv) - so that the glob is created at runtime.

           If you're working with globs at runtime, and need to
           disambiguate *^G from *{"^G"}, then you should use the
           raw NAME method.

       STASH





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B(3p)            Perl Programmers Reference Guide           B(3p)


       SV
       IO
       FORM
       AV
       HV
       EGV
       CV
       CVGEN
       LINE
       FILE
       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
       FILE
       DEPTH
       PADLIST
       OUTSIDE
       XSUB





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B(3p)            Perl Programmers Reference Guide           B(3p)


       XSUBANY
       CvFLAGS

       B::HV METHODS


       FILL
       MAX
       KEYS
       RITER
       NAME
       PMROOT
       ARRAY

       OP-RELATED CLASSES

       B::OP, B::UNOP, B::BINOP, B::LOGOP, B::LISTOP, B::PMOP,
       B::SVOP, B::PADOP, B::PVOP, B::CVOP, B::LOOP, B::COP.
       These classes correspond in the obvious way to the under-
       lying C structures of similar names. The inheritance hier-
       archy mimics the underlying C "inheritance". Access meth-
       ods correspond to the underlying C structre field names,
       with the leading "class indication" prefix removed (op_).

       B::OP METHODS


       next
       sibling
       name
           This returns the op name as a string (e.g. "add",
           "rv2av").

       ppaddr
           This returns the function name as a string (e.g.
           "PL_ppaddr[OP_ADD]", "PL_ppaddr[OP_RV2AV]").

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

       targ
       type
       seq
       flags
       private

       B::UNOP METHOD


       first






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B(3p)            Perl Programmers Reference Guide           B(3p)


       B::BINOP METHOD

       last

       B::LOGOP METHOD


       other

       B::LISTOP METHOD

       children

       B::PMOP METHODS


       pmreplroot
       pmreplstart
       pmnext
       pmregexp
       pmflags
       pmpermflags
       precomp

       B::SVOP METHOD


       sv
       gv

       B::PADOP METHOD


       padix

       B::PVOP METHOD

       pv

       B::LOOP METHODS


       redoop
       nextop
       lastop

       B::COP METHODS


       label
       stash
       file





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B(3p)            Perl Programmers Reference Guide           B(3p)


       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.

       init_av
           Returns the AV object (i.e. in class B::AV) represent-
           ing INIT blocks.

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

       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".

       amagic_generation
           Returns the SV object corresponding to the C variable
           "amagic_generation".

       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 vis-
           ited 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.



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B(3p)            Perl Programmers Reference Guide           B(3p)


       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 num-
           ber 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.

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





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