


Diff of /doc/cmucl/internals/glossary.tex [000000] .. [a530bb] Maximize Restore

  Switch to side-by-side view

--- a
+++ b/doc/cmucl/internals/glossary.tex
@@ -0,0 +1,411 @@
+\chapter{Glossary}% -*- Dictionary: int:design -*-
+% Note: in an entry, any word that is also defined should be \it
+% should entries have page references as well?
+\item[assert (a type)]
+In Python, all type checking is done via a general type assertion
+mechanism.  Explicit declarations and implicit assertions (e.g. the arg to
++ is a number) are recorded in the front-end (implicit continuation)
+representation.  Type assertions (and thus type-checking) are "unbundled"
+from the operations that are affected by the assertion.  This has two major
+\item Code that implements operations need not concern itself with checking
+operand types.
+\item Run-time type checks can be eliminated when the compiler can prove that
+the assertion will always be satisfied.
+See also {\it restrict}.
+\item[back end] The back end is the part of the compiler that operates on the
+{\it virtual machine} intermediate representation.  Also included are the
+compiler phases involved in the conversion from the {\it front end}
+representation (or {\it ICR}).
+\item[bind node] This is a node type the that marks the start of a {\it lambda}
+body in {\it ICR}.  This serves as a placeholder for environment manipulation
+\item[IR1] The first intermediate representation, also known as {\it ICR}, or
+the Implicit Continuation Represenation.
+\item[IR2] The second intermediate representation, also known as {\it VMR}, or
+the Virtual Machine Representation.
+\item[basic block] A basic block (or simply "block") has the pretty much the
+usual meaning of representing a straight-line sequence of code.  However, the
+code sequence ultimately generated for a block might contain internal branches
+that were hidden inside the implementation of a particular operation.  The type
+of a block is actually {\tt cblock}.  The {\tt block-info} slot holds an 
+{\tt VMR-block} containing backend information.
+\item[block compilation] Block compilation is a term commonly used to describe
+the compile-time resolution of function names.  This enables many
+\item[call graph]
+Each node in the call graph is a function (represented by a {\it flow graph}.)
+The arcs in the call graph represent a possible call from one function to
+another.  See also {\it tail set}.
+A cleanup is the part of the implicit continuation representation that
+retains information scoping relationships.  For indefinite extent bindings
+(variables and functions), we can abandon scoping information after ICR
+conversion, recovering the lifetime information using flow analysis.  But
+dynamic bindings (special values, catch, unwind protect, etc.) must be
+removed at a precise time (whenever the scope is exited.)  Cleanup
+structures form a hierarchy that represents the static nesting of dynamic
+binding structures.  When the compiler does a control transfer, it can use
+the cleanup information to determine what cleanup code needs to be emitted.
+\item[closure variable]
+A closure variable is any lexical variable that has references outside of
+its {\it home environment}.  See also {\it indirect value cell}.
+\item[closed continuation] A closed continuation represents a {\tt tagbody} tag
+or {\tt block} name that is closed over.  These two cases are mostly
+indistinguishable in {\it ICR}.
+\item[home] Home is a term used to describe various back-pointers.  A lambda
+variable's "home" is the lambda that the variable belongs to.  A lambda's "home
+environment" is the environment in which that lambda's variables are allocated.
+\item[indirect value cell]
+Any closure variable that has assignments ({\tt setq}s) will be allocated in an
+indirect value cell.  This is necessary to ensure that all references to
+the variable will see assigned values, since the compiler normally freely
+copies values when creating a closure.
+\item[set variable] Any variable that is assigned to is called a "set
+variable".  Several optimizations must special-case set variables, and set
+closure variables must have an {\it indirect value cell}.
+\item[code generator] The code generator for a {\it VOP} is a potentially
+arbitrary list code fragment which is responsible for emitting assembly code to
+implement that VOP.
+\item[constant pool] The part of a compiled code object that holds pointers to
+non-immediate constants.
+\item[constant TN]
+A constant TN is the {\it VMR} of a compile-time constant value.  A
+constant may be immediate, or may be allocated in the {\it constant pool}.
+\item[constant leaf]
+A constant {\it leaf} is the {\it ICR} of a compile-time constant value.
+A combination {\it node} is the {\it ICR} of any fixed-argument function
+call (not {\tt apply} or {\tt multiple-value-call}.)  
+\item[top-level component]
+A top-level component is any component whose only entry points are top-level
+\item[top-level lambda]
+A top-level lambda represents the execution of the outermost form on which
+the compiler was invoked.  In the case of {\tt compile-file}, this is often a
+truly top-level form in the source file, but the compiler can recursively
+descend into some forms ({\tt eval-when}, etc.) breaking them into separate
+\item[component] A component is basically a sequence of blocks.  Each component
+is compiled into a separate code object.  With {\it block compilation} or {\it
+local functions}, a component will contain the code for more than one function.
+This is called a component because it represents a connected portion of the
+call graph.  Normally the blocks are in depth-first order ({\it DFO}).
+\item[component, initial] During ICR conversion, blocks are temporarily
+assigned to initial components.  The "flow graph canonicalization" phase
+determines the true component structure.
+\item[component, head and tail]
+The head and tail of a component are dummy blocks that mark the start and
+end of the {\it DFO} sequence.  The component head and tail double as the root
+and finish node of the component's flow graph.
+\item[local function (call)]
+A local function call is a call to a function known at compile time to be
+in the same {\it component}.  Local call allows compile time resolution of the
+target address and calling conventions.  See {\it block compilation}.
+\item[conflict (of TNs, set)]
+Register allocation terminology.  Two TNs conflict if they could ever be
+live simultaneously.  The conflict set of a TN is all TNs that it conflicts
+The ICR data structure which represents both:
+\item The receiving of a value (or multiple values), and
+\item A control location in the flow graph.
+In the Implicit Continuation Representation, the environment is implicit in the
+continuation's BLOCK (hence the name.)  The ICR continuation is very similar to
+a CPS continuation in its use, but its representation doesn't much resemble (is
+not interchangeable with) a lambda.
+\item[cont] A slot in the {\it node} holding the {\it continuation} which
+receives the node's value(s).  Unless the node ends a {\it block}, this also
+implicitly indicates which node should be evaluated next.
+\item[cost] Approximations of the run-time costs of operations are widely used
+in the back end.  By convention, the unit is generally machine cycles, but the
+values are only used for comparison between alternatives.  For example, the
+VOP cost is used to determine the preferred order in which to try possible
+\item[CSP, CFP] See {\it control stack pointer} and {\it control frame
+\item[Control stack] The main call stack, which holds function stack frames.
+All words on the control stack are tagged {\it descriptors}.  In all ports done
+so far, the control stack grows from low memory to high memory.  The most
+recent call frames are considered to be ``on top'' of earlier call frames.
+\item[Control stack pointer] The allocation pointer for the {\it control
+stack}.  Generally this points to the first free word at the top of the stack.
+\item[Control frame pointer] The pointer to the base of the {\it control stack}
+frame for a particular function invocation.  The CFP for the running function
+must be in a register.
+\item[Number stack] The auxiliary stack used to hold any {\it non-descriptor}
+(untagged) objects.  This is generally the same as the C call stack, and thus
+typically grows down.
+\item[Number stack pointer] The allocation pointer for the {\it number stack}.
+This is typically the C stack pointer, and is thus kept in a register.
+\item[NSP, NFP] See {\it number stack pointer}, {\it number frame pointer}.
+\item[Number frame pointer] The pointer to the base of the {\it number stack}
+frame for a particular function invocation.  Functions that don't use the
+number stack won't have an NFP, but if an NFP is allocated, it is always
+allocated in a particular register.  If there is no variable-size data on the
+number stack, then the NFP will generally be identical to the NSP.
+\item[Lisp return address] The name of the {\it descriptor} encoding the
+"return pc" for a function call.
+\item[LRA] See {\it lisp return address}.  Also, the name of the register where
+the LRA is passed.
+\item[Code pointer] A pointer to the header of a code object.  The code pointer
+for the currently running function is stored in the {\tt code} register.
+\item[Interior pointer] A pointer into the inside of some heap-allocated
+object.  Interior pointers confuse the garbage collector, so their use is
+highly constrained.  Typically there is a single register dedicated to holding
+interior pointers.
+A slot in the {\it continuation} which points the the node that receives this
+value.  Null if this value is not received by anyone.
+\item[DFN, DFO] See {\it Depth First Number}, {\it Depth First Order}.
+\item[Depth first number] Blocks are numbered according to their appearance in
+the depth-first ordering (the {\tt block-number} slot.)  The numbering actually
+increases from the component tail, so earlier blocks have larger numbers.
+\item[Depth first order] This is a linearization of the flow graph, obtained by
+a depth-first walk.  Iterative flow analysis algorithms work better when blocks
+are processed in DFO (or reverse DFO.)
+\item[Object] In low-level design discussions, an object is one of the
+\item a single word containing immediate data (characters, fixnums, etc)
+\item a single word pointing to an object (structures, conses, etc.)
+These are tagged with three low-tag bits as described in the section
+\ref{tagging} This is synonymous with {\it descriptor}.
+In other parts of the documentation, may be used more loosely to refer to a
+{\it lisp object}.
+\item[Lisp object]
+A Lisp object is a high-level object discussed as a data type in the Common
+Lisp definition.
+A data-block is a dual-word aligned block of memory that either manifests a
+Lisp object (vectors, code, symbols, etc.) or helps manage a Lisp object on
+the heap (array header, function header, etc.).
+A descriptor is a tagged, single-word object.  It either contains immediate
+data or a pointer to data.  This is synonymous with {\it object}.  Storage
+locations that must contain descriptors are referred to as descriptor
+\item[Pointer descriptor]
+A descriptor that points to a {\it data block} in memory (i.e. not an immediate
+\item[Immediate descriptor]
+A descriptor that encodes the object value in the descriptor itself; used for
+characters, fixnums, etc.
+A word is a 32-bit quantity.
+Any chunk of bits that isn't a valid tagged descriptor.  For example, a
+double-float on the number stack.  Storage locations that are not scanned by
+the garbage collector (and thus cannot contain {\it pointer descriptors}) are
+called non-descriptor locations.  {\it Immediate descriptors} can be stored in
+non-descriptor locations.
+\item[Entry point] An entry point is a function that may be subject to
+``unpredictable'' control transfers.  All entry points are linked to the root
+of the flow graph (the component head.)  The only functions that aren't entry
+points are {\it let} functions.  When complex lambda-list syntax is used,
+multiple entry points may be created for a single lisp-level function.
+See {\it external entry point}.
+\item[External entry point] A function that serves as a ``trampoline'' to
+intercept function calls coming in from outside of the component.  The XEP does
+argument syntax and type checking, and may also translate the arguments and
+return values for a locally specialized calling calling convention.
+\item[XEP] An {\it external entry point}.
+\item[lexical environment] A lexical environment is a structure that is used
+during VMR conversion to represent all lexically scoped bindings (variables,
+functions, declarations, etc.)  Each {\tt node} is annotated with its lexical
+environment, primarily for use by the debugger and other user interfaces.  This
+structure is also the environment object passed to {\tt macroexpand}.
+\item[environment] The environment is part of the ICR, created during
+environment analysis.  Environment analysis apportions code to disjoint
+environments, with all code in the same environment sharing the same stack
+frame.  Each environment has a ``{\it real}'' function that allocates it, and
+some collection {\tt let} functions.   Although environment analysis is the
+last ICR phase, in earlier phases, code is sometimes said to be ``in the
+same/different environment(s)''.  This means that the code will definitely be
+in the same environment (because it is in the same real function), or that is
+might not be in the same environment, because it is not in the same function.
+\item[fixup]  Some sort of back-patching annotation.  The main sort encountered
+are load-time {\it assembler fixups}, which are a linkage annotation mechanism.
+\item[flow graph] A flow graph is a directed graph of basic blocks, where each
+arc represents a possible control transfer.  The flow graph is the basic data
+structure used to represent code, and provides direct support for data flow
+analysis.  See component and ICR.
+\item[foldable] An attribute of {\it known functions}.  A function is foldable
+if calls may be constant folded whenever the arguments are compile-time
+constant.  Generally this means that it is a pure function with no side
+full call
+function attribute
+	"real" (allocates environment)
+	meaning function-entry
+	more vague (any lambda?)
+funny function
+GEN (kill and...)
+global TN, conflicts, preference
+GTN (number)
+IR ICR VMR  ICR conversion, VMR conversion (translation)
+inline expansion, call
+kill (to make dead)
+known function
+let call
+lifetime analysis, live (tn, variable)
+load tn
+LOCS (passing, return locations)
+local call
+local TN, conflicts, (or just used in one block)
+location (selection)
+LTN (number)
+main entry
+mess-up (for cleanup)
+more arg (entry)
+non-local exit
+non-packed SC, TN
+non-set variable
+operand (to vop)
+optimizer (in icr optimize)
+pack, packing, packed
+pass (in a transform)
+	locations (value)
+	conventions (known, unknown)
+policy (safe, fast, small, ...)
+predecessor block
+reaching definition
+	selection
+	for value
+result continuation (for function)
+result type assertion (for template) (or is it restriction)
+	a TN to finite SBs
+	a template operand to a primitive type (boxed...)
+	a tn-ref to particular SCs
+return (node, vops)
+safe, safety
+saving (of registers, costs)
+SC (restriction)
+	in ICR
+	in VMR
+sparse set
+splitting (of VMR blocks)
+successor block
+tail recursion
+	tail recursive
+	tail recursive loop
+	user tail recursion
+transform (source, ICR)
+	assertion
+	inference
+		top-down, bottom-up
+	assertion propagation
+        derived, asserted
+	descriptor, specifier, intersection, union, member type
+        check
+type-check (in continuation)
+UNBOXED (boxed) descriptor
+unknown values continuation
+unset variable
+unwind-block, unwinding
+used value (dest)
+value passing