My instances are methods suitable for interpretation by the virtual machine. This is the only class in the system whose instances have both indexable pointer fields and indexable 8-bit integer fields. The first part of a CompiledMethod is pointers, the second part is bytes. I'm a subclass of ByteArray to avoid duplicating some of ByteArray's methods, not because a CompiledMethod is-a ByteArray.
Class variables:
SmallFrame - the number of stack slots in a small frame Context
LargeFrame - the number of stack slots in a large frame Context
PrimaryBytecodeSetEncoderClass - the encoder class that defines the primary instruction set
SecondaryBytecodeSetEncoderClass - the encoder class that defines the secondary instruction set
The current format of a CompiledMethod is as follows:
header (4 or 8 bytes, SmallInteger)
literals (4 or 8 bytes each, Object)
bytecodes (variable, bytes)
trailer (variable, bytes)
The header is a 31-bit signed integer (a SmallInteger) with one of the two following formats, selected by the sign bit:
sign bit 0, header >= 0:
(index 0) 9 bits: main part of primitive number (#primitive)
(index 9) 8 bits: number of literals (#numLiterals)
(index 17) 1 bit: whether a large frame size is needed (#frameSize)
(index 18) 6 bits: number of temporary variables (#numTemps)
(index 24) 4 bits: number of arguments to the method (#numArgs)
(index 28) 1 bit: high-bit of primitive number (#primitive)
(index 29) 1 bit: flag bit, ignored by the VM (#flag)
(index 30/63) sign bit: 0 selects the Primary instruction set (#signFlag)
sign bit 1, header 0:
(index 0) 16 bits: number of literals (#numLiterals)
(index 16) 1 bit: has primitive
(index 17) 1 bit: whether a large frame size is needed (#frameSize)
(index 18) 6 bits: number of temporary variables (#numTemps)
(index 24) 4 bits: number of arguments to the method (#numArgs)
(index 28) 2 bits: reserved for an access modifier (00-unused, 01-private, 10-protected, 11-public)
(index 30/63) sign bit: 1 selects the Secondary instruction set (e.g. NewsqueakV4) (#signFlag)
i.e. the Secondary Bytecode Set expands the number of literals to 65535 by assuming a CallPrimitive bytecode.
The trailer is an encoding of an instance of CompiledMethodTrailer. It is typically used to encode the index into the source files array of the method's source, but may be used to encode other values, e.g. tempNames, source as a string, etc. See the class CompiledMethodTrailer.
