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317 terms

CS 375 Compilers Novak Vocabulary

STUDY
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absolute address
the numeric address of a location in memory.
cf. relative address.
absolute code
computer program code that is executable without
further processing: all addresses in the code are absolute.
cf. relocatable code.
abstract syntax tree (AST)
a tree representation of a program
that is abstracted from the details of a particular programming
language and its surface syntax.
accepting state
a state of a finite automaton in which the input string is accepted
as being a member of the language recognized by the automaton.
activation record
stack frame.
actual parameter
a parameter used in a call to a subprogram. cf. formal parameter.
address alignment
see storage alignment.
address space
1. the set of memory addresses that a program may reference.
2. the amount of memory allocated to a program or user.
3. the amount of memory addressable by the address size of a
machine instruction.
adjacency matrix
a method of representing a graph by a Boolean
matrix M , where M_{ij = 1 iff there is an arc from node i
to node j in the graph.
alias
an alternate name for a memory location. Whenever a given memory
location is denoted by more than one name, any of the names can be
considered to be an alias.
aliasing
the creation of an alternate name for data, either in the definition of
a program or during its operation.
alphabet
a set of symbols used in the definition of a language.
ambiguity
a case where more than one interpretation is possible.
ambiguous grammar
a grammar that allows some sentence or string to be generated
or parsed in more than one way (i.e., with distinct parse trees).
antisymmetric
a relation * is antisymmetric iff
forall a, b . a b and b a --> a = b .
Example <=
arity
the number of arguments of a function.
assembly language
a language for writing computer programs, in which
one assembly language instruction usually corresponds to one machine
instruction.
associativity
a specification of the order in which operations should be performed
when two operators of the same precedence are adjacent. Most operators
are left-associative, e.g. the expression A - B - C
should be interpreted as ((A - B) - C).
AST
abstract syntax tree.
augmented transition network (ATN)
a formalism for describing parsers, especially for natural language.
Similar to a finite automaton, but augmented in that arbitrary tests may be
attached to transition arcs, subgrammars may be called recursively, and
structure-building actions may be executed as an arc is traversed.
automatic programming
synthesis of a program that satisfies a
specification, where the specification is higher-level than ordinary
programming languages.
available
an expression is available if it has been computed previously in the
computation path preceding the current location and has not been killed.
backpatching
filling in the address of a label, which has just become defined, in
preceding parts of the program that made forward references to it.
base address
the address of the beginning of a data area. This address is added to
a relative address or offset to compute an absolute address.
basic block
a sequence of program statements such that if any of them is executed, all
of them are; a sequence of statements that has a label (if any) only at the
beginning and a branch (if any) only at the end.
basic type
a data type that is implemented in computer hardware
instructions, such as integer or real.
binding
the association of a name with a variable or value.
bison
a Free Software Foundation program similar to yacc.
bit vector
a sequence of Boolean values (0 or 1) represented as the
bits of one or more computer words. It is an efficient representation
for sets that are subsets of a fairly small finite set of possible elements.
block
short for basic block.
BNF
Backus-Naur Form, a syntax for writing context-free grammars
that describe computer languages.
Boolean matrix
a matrix whose elements are Boolean values, 0
or 1.
bottom-up parsing
a parsing method in which input words are matched against the right-hand
sides of grammar productions in an attempt to build a parse tree from the
bottom towards the top.
BSS
a pseudo-operation for some assemblers, used to specify the
reservation of a block of storage, perhaps initialized to some constant
value. (an abbreviation of Block Starting with Symbol.)
busy
describes a variable whose value will be needed later during
program execution. Also, live.
cache
a fast memory, smaller than the total main memory, used
by the CPU for faster access to data.
cache miss
a reference to a memory location that is not in the
cache, causing processing to be delayed until the operand can be fetched
from main memory.
cache prefetch
an instruction that causes the contents
of a specified memory address to be fetched from main memory into the cache
memory so that it will be available for fast access when needed.
call by name
a form of parameter transmission in which the effect of a textual
substitution of the actual parameter for the formal parameter is achieved.
call by reference
a form of parameter transmission in which the address of the actual
parameter is transmitted to the subprogram. Any changes to the parameter
made by the subprogram will change the argument as seen by the calling
program.
call by value
a form of parameter transmission in which the value of the actual
parameter is transmitted to the subprogram. Changes to the parameter
made by the subprogram will not be seen by the calling program.
canonical derivation
rightmost derivation.
canonical form
a standardized form of expressions or data. If all programs put their
expressions into a canonical form, the number of cases that will have
to be considered by other programs is reduced.
Cartesian product
if A and B are sets, the Cartesian product
A X B is the set of ordered pairs (a, b) where
a in A and b in B .
cascading errors
a situation, e.g. in compiling a program, where one error causes many
reported errors. For example, failure to declare a variable may cause
an error every time that variable is referenced.
cast
to coerce a given value to be of a specified type.
Chomsky hierarchy
the hierarchy of formal language types: regular, context free, context
sensitive, and recursively enumerable languages, each of which is a proper
subset of the following class.
CISC
complex instruction set computer.
class
in object-oriented programming, a description of a set of similar objects.
For example, Fido, an object or instance, might be a member of the class Dogs.
class variable
in an object-oriented language, a variable associated with a class of
objects, e.g. the number of members of the class.
closed procecdure
a procedure whose code is separate from that of calling programs; the
procedure is entered by a subroutine call, and it returns to the calling
program when it is finished.
code generation
the phase of a compiler in which executable output code is generated
from intermediate code.
code motion
the movement of code by a compiler to a place other than where it appears
in the source program. For example, an expensive but unchanging
computation might be moved outside a loop.
coerce
see type coercion.
collision
in a hash table, a case in which a symbol has the same
hash function value as another symbol.
column-major order
a method of storing arrays in which values in a column of the array
are in adjacent memory locations. cf. row-major order.
common subexpression
an expression that appears more than once
in a program.
compiler
a program that translates a source language into an
object language that is executable on a computer.
compiler-compiler
a program that produces a compiler for a language from a specification
of the syntax and semantics of the language, e.g. yacc.
compile-time
describes a task that is or can be done by the compiler,
without running the program. cf. static.
complex instruction set computer
a CPU design featuring a large number of relatively complex instructions.
Abbreviated CISC. cf. RISC.
computed
of a subexpression, having its value computed within a given block of code.
concatenation
making a sequence that consists of the elements of a first sequence
followed by those of a second sequence.
concatenation of languages
a language consisting of the set of sentences formed by concatenating a
sentence from the first language and a sentence from the second language.
condition code register
A CPU register that describes the result of the last arithmetic operation
or comparison. It typically contains bits for <0, =0,
>0, carry, and overflow.
constant folding
performing at compile time an operation whose
operands are constant, giving a new constant result.
context-free grammar
a grammar in which the left-hand side of each production consists of a
single nonterminal symbol.
control flow analysis
analysis of the possible paths that control flow
may take in a program during execution.
current status variable
in a hand-written parser, a variable that
denotes the construct last seen, e.g., start of expression,
operator, or operand.
DAG
directed acyclic graph,
a graph consisting of a set of nodes and directed arcs (arrows) between
nodes, such that no circular paths (cycles) exist.
dangling reference
in execution of a program, a reference, usually by means of a pointer,
to storage that has been deallocated. For example, in a recursive
language, a pointer to storage that is allocated on the execution stack
could be retained after the routine associated with that stack frame has
exited, resulting in errors.
data area
a contiguous area of memory, specified by its base address and size.
Data within the area are referenced by the base address of the area and
the offset, or relative address, of the data within the area.
data flow analysis
analysis of places in the programs where data
receive values and the places where those data values can subsequently be used.
dead code
parts of a program that cannot be reached during execution and therefore
can never be executed.
declaration
a statement in a programming language that provides
information to the compiler, such as the structure of a data record,
but does not specify executable code.
defined
of a variable, having received a value prior to a given point in a program.
definition-use chain
the portion of a program flow graph across which a
variable is both defined and live (busy), beginning at the point where
the variable receives a value and ending at the last place that value is used.
Also, du-chain.
dereference
to convert from a pointer (address) to the data that is pointed to.
derivation
a list of steps that shows how a sentence
in a language is derived from a grammar by application of grammar rules.
descendant
a node in a tree that is a child of another node or a descendant of one
of its children.
deterministic finite automaton
a finite automaton that has at most one transition from a state for each
input symbol and no empty transitions. Abbreviated DFA.
DFA
deterministic finite automaton.
disambiguating rules
rules that allow an ambiguous situation to be resolved to a single
outcome, e.g. rules of operator precedence.
display
in an activation record, an array of pointers to the activation records
of surrounding blocks, used to access variables defined in those blocks.
dominator
a basic block of a program is a dominator of a second block if every
path from the entry of the program to the second block passes through it.
dynamic
refers to things that happen or can only be determined
during actual execution of a program. cf. static.
dynamic memory
memory that is assigned during execution of a program, especially heap
memory.
dynamic scoping
a convention in a language, such as Lisp, that a variable can be referenced
by any procedure that is executed after it has become bound and before
it becomes unbound; thus, the scope of the variable can depend on the
execution sequence.
dynamic type checking
testing of the types of the values of variables at runtime, as is done
in Lisp and object-oriented languages. cf. static type checking.
effective address
the address of a data element, taking into account
offsets due to array indexing and record accesses.
encapsulation
a method of making a software system modular by creating
well-defined interface routines that deal with a particular kind of data
and allowing other programs to access the data only through those routines;
the interface routines encapsulate the data. cf. information hiding.
enumerate
to generate all of the members of a set.
enumerated type
a scalar type consisting of a finite set of
enumerated values, e.g. type boolean = (false, true);.
epilogue
a section of code that is executed just before leaving a subprogram
to restore register values, transfer the result of the subprogram to
the calling program, and branch to the return address.
equivalence relation
a relation that is reflexive, symmetric, and transitive.
equivalent grammars
grammars that denote the same language.
error production
a grammar production, as in a Yacc grammar,
that is executed if no other production matches the input.
execution stack
a stack of activation records or stack frames that is maintained
during execution of programs in a block-structured or recursive language.
FA
finite automaton.
FAR
finite automaton recognizable.
field
a component part of a data record.
finite automaton
an abstract computer consisting of an alphabet of symbols, a finite
set of states, a starting state, a subset of accepting states, and
transition rules that specify transitions from one state to another
depending on the input symbol. The machine begins in the starting
state; for each input symbol, it makes a transition as specifies by the
transition rules. If the automaton is in an accepting state at the end
of the input, the input is recognized. Also, finite state machine.
Abbreviated FA.
finite automaton recognizable
a language that is regular. Abbreviated FAR.
finite state machine
see finite automaton.
flex
a Free Software Foundation program similar to lex.
formal grammar
see grammar.
formal parameter
a parameter specified in the argument list of a procedure definition.
cf. actual parameter.
forward reference
reference to a label in a program that has not yet appeared in the program
text.
fragmentation
the breaking up of memory into blocks that are too small to be of use.
cf. internal fragmentation, external fragmentation.
garbage
storage that can no longer be accessed because no pointer to it exists.
garbage collection
the identification of unused storage and collection of it so that it can
be placed back on the heap for reuse.
GC
1. garbage collection.
2. the occurrence of a garbage collection during execution.
3. to perform garbage collection.
generator
a procedure that produces the elements of a sequence, returning the next
element each time it is called; e.g., a pseudo-random number generator.
global analysis
analysis of the properties of an entire program or
procedure.
global optimization
optimization based on analysis of the entire
program or procedure.
grammar
a formal specification of a language, consisting of a set of nonterminal
symbols, a set of terminal symbols or words, and production rules that specify
transformations of strings containing nonterminals into other strings.
graph
a (directed) graph is a pair ( S, Gamma ) where S is a set of
nodes and Gamma subset S X S is a set of transitions between
nodes.
graph coloring
an algorithm for assigning a minimal number of ``colors'' to nodes of
a graph such that no two nodes that are connected have the same color.
Used in compilers as a method of register assignment: colors correspond
to registers, nodes to variables or def-use chains, and connections to
variables that are simultaneously live.
hash function
a deterministic function that converts converts a
symbol or other input to a ``randomized'' integer value.
hash table
a table that associates key values with data by use of
a hash function.
heap
an area of contiguous memory and/or a set of unused storage records that
can be allocated to the running program as dynamic memory upon request;
the address of the record is returned and assigned to a pointer variable.
new in Pascal, malloc in C, and cons in Lisp allocate
heap memory.
identifier
a symbol that is used as the name of a variable, type,
constant, procedure, etc.
infix
an expression written with an operator between its operand,
e.g. a + b . cf. prefix, postfix.
implicit parameter
a parameter that is passed to a subprogram without being specified directly
by the programmer, e.g., the return address.
induction variable
a variable that is incremented during a loop and used to perform a similar
action on multiple data; also, loop index.
information hiding
a method of making programs modular by allowing programs to see only
a set of well-defined interfaces to a data type, but not the internal
implementation of the data. cf. encapsulation.
inherit
to use a method defined in a superclass.
inheritance
the availability of procedures or data by virtue of membership in a class,
as in an object-oriented system.
inherited attribute
an attribute of a node in a parse tree that is derived from the context
in which the node appears. cf. synthesized attribute.
inlining
inserting code of a subprogram directly into the code compiled for the
calling program, rather than compiling a subroutine call to an external
procedure.
inorder
an order of visiting binary trees, in which the left subtree of a node
is examined, followed by the node itself, followed by the right subtree.
instance
in object-oriented programming, an individual data object
that is an instance of a class of similar objects. Also, object.
instance variable
a data field in an instance.
intermediate code
see intermediate language.
intermediate language
an internal language used as the representation of a program during
compilation, such as trees or quadruples. The source language is
translated to intermediate language, then to the object language.
internal fragmentation
wasted storage within a block, either because the block is of fixed size
and is not all used, or because of padding.
interpreted code
a form of program that is read and executed by an interpreter program.
The interpreter reads an instruction, determines its meaning, and executes it.
interval
a set of basic blocks of a program that comprise a sequence of statements or
simple loop.
invariant code
code whose value does not change during a certain
period of program execution.
keyword
a special word that is used to indicate the structure of a language,
such as the reserved words of computer languages.
killed
of a subexpression, having any previously computed value invalidated
by redefinition of a component of the subexpression. Note that the term
``killed'' cannot properly be applied to a program variable.
Kleene closure
zero or more occurrences of a grammar item;
indicated by a superscript *.
language denoted by a grammar
L(G), the set of strings that can
be derived from a grammar, beginning with the start symbol.
left-associative operator
an operator in an arithmetic expression such that if there are two adjacent
occurrences of the operator, the left one should be done first.
left factoring
a method of modifying a grammar to eliminate left recursion.
left recursion
in top-down parsing, a grammar rule whose right-hand side begins with the
nonterminal symbol on the left-hand side will cause an infinite recursion,
called left recursion. Also, describes such a production.
leftmost derivation
a derivation in which the leftmost nonterminal of the string is replaced
at each step.
lex
a popular software tool for constructing a lexical analyzer from a regular
grammar and actions associated with the grammar productions.
lexeme
a basic symbol in a language; e.g., a variable name would be a lexeme for
a grammar of a programming language.
lexical
1. refers to information associated with words or symbols in a dictionary
or symbol table.
2. refers to information that can be determined by static examination
of a program, i.e., at compile time, without running the program.
lexical analysis
parsing and conversion to internal form of the simplest elements of a
language, usually specified by a regular grammar, such as variable
names, numbers, etc.
lexical analyzer
a program that performs lexical analysis and outputs the internal form
of lexemes.
lexical scoping
a convention in a block-structured programming language that a variable
can only be referenced within the block in which it is defined and
blocks contained within that block; thus, the scope of a variable is
completely determined at compile time. cf. dynamic scoping.
link editor
a program that combines relocatable code modules to form an executable
absolute code file. The link editor assigns memory locations for each
relocatable module, relocates relative addresses to form absolute
addresses, finds library modules whose names are referenced as external
symbols and includes those modules in the loading process, and fills in
absolute addresses for external references between modules.
live variable
a variable whose value will be used at a later point during execution.
load time
1. refers to something that happens during link editing or loading
of a program into memory for execution, e.g., a load-time error.
cf. compile-time, run-time.
2. the amount of time required to link-edit and/or load a program.
loader
a program in the operating system that executes an absolute program by
allocating storage for it in main memory, reading the program into memory,
and jumping to its entry point. Sometimes link-editing is performed prior
to loading.
local ambiguity
a case in which a language construct might be parsed
in more than one way; the correct parsing is determined by examining the
wider context of the construct. Example: 3.14 vs. 3..14
local optimization
optimization that can be done correctly taking
into account only a small part of the program.
location counter
1. a counter that denotes the next location in memory for code or
data during assembly or compilation of a program.
2. a numeric value that denotes the location of the beginning of a data
area, which is added to addresses during relocation.
logic
1. mathematical logic, i.e., propositional or predicate calculus.
2. the algorithm or decision procedures used by a program.
loop index
a variable that is incremented during a loop and used to perform a similar
action on successive data; also, loop variable, induction variable.
machine language
the language executed by computer hardware.
macro
a statement in a programming language that is expanded into
one or more statements in the same language, by substitution of
arguments into a language pattern or by construction of the statements
by a program.
mark-and-sweep
a method of garbage collection in which all storage that is in use is
marked, then all storage that is not marked is swept up for reuse.
materialize
to store in memory as a discrete data value; to make a copy in memory of
otherwise transient data, such as a value in a register.
memoization
remembering the result of a function for given
argument value(s); if the function is called again with the same
arguments, the result can be returned from memory. Also, memorization.
memory hierarchy
a hierarchy of different kinds of computer memory, in which there is a
small amount of costly fast memory (such as registers or cache) and
increasing amounts of slower kinds of memory.
memory leak
failure to return dynamic memory that is no longer in use; eventually
causes the program to run out of memory.
message
in object-oriented programming, an indirect function call.
A message is sent to an object; the selector of the message
(an abstract procedure name) is looked up in the class to which the
object belongs to determine the method that is the actual function
that is called.
metaclass
in an object-oriented system, a class that describes the structure of classes.
method
in an object-oriented system, a procedure associated with a class that performs
the action associated with a message.
multiple inheritance
in an object-oriented system, the ability of a
class to have multiple superclasses and to inherit methods from all of them.
name equivalence
type equivalence testing in which two types are considered equal only if
they have the same name. cf. structural equivalence.
nondeterministic
describes a process that can do one of multiple things; which one it will
do is not predetermined.
nondeterministic finite automaton
a finite automaton that has multiple state transitions from a single state
for a given input symbol, or that has a null transition, not requiring an
input symbol. Abbreviated NFA.
nonterminal symbol
a symbol that names a phrase in a grammar.
nonvolatile register
a register whose value must be preserved across a procedure call.
object
in an object-oriented programming system, a data structure containing
instance variables and a pointer to the class to which the object belongs.
object language
the output language of a compiler.
object-oriented programming
a style of programming based on the use of
objects and messages, as opposed to data structures and procedure
calls.
offset
the location of data relative to the start of a data area.
operand
a data value upon which an operation is performed.
operator
a symbol that denotes an operation to be performed on data in an expression.
optimization
transformation of a program to produce a program whose input-output
behavior is equivalent to that of the original program, but that has lower cost,
e.g. faster execution time.
out-of-order execution
the ability of some CPU's to execute instructions in an order different
from that specified in the program, allowing idle CPU functional units to
be used and improving performance.
overloading
the assignment of multiple meanings to an operator, depending on the type
of data to which it is applied; e.g., the symbol + could represent
integer addition, floating-point addition, or matrix addition.
padding
insertion of an area of unused storage in order to achieve storage alignment.
parametric polymorphism
polymorphism in which type expressions
are parameterized, e.g. list of T where T is a type parameter.
parser
a program that determines how a given statement in a language could be
derived from the grammar of the language, producing a parse tree or other
information about the statement as output.
parser generator
a program that constructs a parser from a specification of the grammar
of a language and actions that are to be taken when phrases of the language
are recognized.
parse tree
a data structure that shows how a statement in a language is derived from
the context-free grammar of the language; it may be annotated with additional
information, e.g. for compilation purposes.
parsing
the process of reading a source language, determining its structure,
and producing intermediate code for it.
partial evaluation
optimization of a program by evaluating parts of the program that are
constant at compile time. This may include unrolling loops and algebraic
optimization of operations involving constant data; the resulting program
may be larger, but faster and more suitable for parallel execution.
partial order
a relation that is reflexive, antisymmetric, and transitive. Example: <=
partition
a division of a set into disjoint subsets whose union
is the set. A partition corresponds to an equivalence relation.
pass
a phase of a compiler or assembler in which the entire source program
(in its original form or some later representation) is processed.
peephole optimization
a kind of optimization, performed on generated code by a compiler,
in which a linear pass is made over the code examining a small region
of code to see if it can be improved; e.g., a jump instruction to the
next sequential location can be eliminated.
phase of compiler
a major section of the compilation process, generally involving examination
of the entire program, e.g., syntax analysis, optimization, or code
generation.
phrase structure grammar
see grammar.
pointer
a variable that denotes another variable. A pointer typically
is implemented as an integer variable containing the memory address of the
other variable.
polymorphic function
a function that can operate on data of more than one type.
polymorphic type
an abstract data type, such as linked list, that could be implemented
in different ways or could take multiple forms, such as a linked list of
integers or a linked list of reals using a similar record format.
postamble
see epilogue.
postfix
a way of writing expressions in which an operator appears
after its operands: ab+.
postincrement
a CPU feature in which the value of an index register is automatically
incremented by a fixed amount after its use, thus pointing to the next data
in an array.
postorder
an order of visiting trees, in which the children of a node are examined
first, in left-to-right order, followed by examination of the node itself.
preamble
see prologue.
precedence
an ordering of operators that specifies that certain operators should
be performed before others when no ordering is otherwise specified.
precedence relations
a specification of the relative precedence of a set of operators,
i.e., that one operator is less, equal, or greater in precedence
than another.
predecrement
a CPU feature in which the value of an index register is automatically
decremented by a fixed amount before its use, thus pointing to the next data
to be processed.
predictive parsing
a form of parsing in which the grammar rule to be used for later input
is predicted, e.g., on the basis of a keyword that begins a statement.
prefix
1. a contiguous set of symbols at the beginning of a
string. 2. a way of writing expressions in which an operator appears
before its operands: +ab.
preorder
an order of visiting trees, in which a node is examined first, followed
by recursive examination of its children, in left-to-right order, in
the same fashion.
processor stall
a situation in which the CPU must temporarily
suspend execution until some event occurs, e.g. delivery of requested
memory or availability of an operand.
production
a rule of a context-free grammar, specifying that a nonterminal symbol
can be replaced by another string of symbols.
prologue
a section of code that is executed immediately upon entry to a subprogram
to save register values, save the return address, and transfer parameters
to the subprogram.
quadruple
a form of intermediate program code used in compilers, equivalent to
a small ``assignment statement'' of the form ``R = X op Y'' where R
is the result, X and Y are operands, and op is the operation.
RE
recursively enumerable.
recognizer
a program or abstract device that can read a string of symbols and decide
whether the string is a member of a particular language.
record
a data area consisting of contiguous component fields,
which may be of different types.
recursive descent
a method of writing a parser in which a grammar rule is written as a
procedure that recognizes that phrase, calling subroutines as needed for
sub-phrases and producing a parse tree or other data structure as output.
recursively enumerable language
a language whose sentences can be enumerated by a recursive program,
i.e., any language described by a formal grammar. Abbreviated RE.
reduce-reduce conflict
in a grammar for a shift-reduce parser,
a case in which an input might be reduced by more than one production.
reduction in strength
an optimization in which an operator is changed to a less-expensive
operator; e.g., x * 2 becomes x + x .
reduction step
in shift-reduce parsing, the reduction of items at the top of the stack
to a phrase that encompasses those items.
reference
to read the value of a variable.
referenced
of a variable, having its value read within a sequence of
code.
reflexive transitive closure
in a graph, the mapping from each node to the set of nodes that can be
reached from it in 0 or more steps.
register assignment
the assignment of registers to hold intermediate
results during parts of the computation, and in some cases to hold the
values of variables.
regular expression
an algebraic expression that denotes a regular language.
regular grammar
a grammar that denotes a regular language; its productions can only have
on the right-hand side either a terminal string or a terminal string
followed by a single nonterminal.
regular language
a language described by a regular grammar, or recognizable by a finite
automaton, e.g. a simple item such as a variable name or a number in a
programming language.
relation
a subset of the Cartesian product of two sets.
relative address
an address specified by an offset relative to some other address.
relocatable code
program code that can be relocated to run in different locations in
computer memory. Addresses within the program are specified relative to
location counters; external addresses are specified by symbolic names.
relocation
the process performed by a link editor to convert relocatable code
into absolute code that can be executed, by adding the absolute starting
address of a data area to relative addresses of data within that data area.
reserved word
a word in a programming language that is reserved for
use as part of the language and may not be used as an identifier.
restore registers
to load nonvolatile registers with the saved values that the registers
had upon entry to a subprogram.
return address
the address immediately following a call to a subprogram; the subprogram
returns when finished by branching to this address.
return statement
a statement in a high-level language to cause execution of a subprogram
to terminate and to return a value to the calling program. A return
statement is implemented by loading the returned value into a register
and branching to the epilogue of the subprogram.
reverse Polish
an unambiguous, parenthesis-free notation for expressing an arithmetic
expression. Operators appear after their operands.
right-associative operator
an operator in an arithmetic expression such that if there are two adjacent
occurrences of the operator, the right one should be done first.
rightmost derivation
a derivation in which the rightmost nonterminal in the string is replaced
at each step. Also, canonical derivation.
RISC
reduced instruction set computer. A CPU in which only a basic set
of instructions is provided and in which extra responsibilities may be
placed upon the compiler, e.g. not using the result of an instruction
until after a certain amount of time has passed.
row-major order
a method of storing a multi-dimensional array, such that elements of a row
of the array are adjacent in memory. cf. column-major order.
run-time
of or referring to something
that happens during execution of a program. Also, runtime.
cf. compile-time, load-time.
save registers
to save the values of nonvolatile registers upon entry to a subprogram
so that the values can be restored before the subprogram exits.
scalar type
a data type that occupies a fixed amount of storage.
scanner
lexical analyzer.
selector
in object-oriented programming, an abstract procedure name or
name of a message action. The class describes the association between the
selector and the corresponding method that performs that action for objects
in the class.
semantics
the meaning of a statement in a language. cf. syntax.
send
1. a statement in an object-oriented language that specifies the
sending of a message.
2. the action of sending a message to an object.
sentence symbol
a distinguished nonterminal symbol in a formal grammar that represents a
complete statement (sentence) in the language.
sentential form
a string of terminal and/or nonterminal symbols that is produced during
the derivation of a sentence according to a grammar.
shift-reduce conflict
in a grammar for a shift-reduce parser,
a case in which an input might either be shifted onto the stack or reduced.
shift-reduce parser
a parser that operates by alternately shifting input elements onto the
top of a stack or reducing a group of elements from the top of the stack to
a larger element representing a phrase.
side-effect
any effect of an operation or function call other than returning a value,
e.g. changing a value in memory, I/O.
sound
describes a theorem-proving technique or method of reasoning that is
guaranteed to derive only valid conclusions.
sound type system
a type system of a programming language in which it is guaranteed that
the value of a variable at runtime can only be of the type that was
determined for that variable at compile time; i.e., there can be no
runtime type errors.
source language
the original language in which a program is written, such as a high-level
programming language.
speculative execution
the ability of some CPU's to execute instructions ahead of the current
location and beyond a conditional branch. The results of these
instructions will be usable only if the CPU guessed the branch direction
correctly.
spill code
code to store the values of some registers into main memory so that the
registers can be used for other purposes.
stack frame
a collection of the local variables of a procedure, as well as return
address, saved register values, etc. that are put on the execution
stack for each invocation of a procedure. Also, activation record.
stack pointer
a CPU register that points to the start of the current stack frame and
is used as an index register to access data within the stack frame.
start symbol
the initial, or ``sentence'' nonterminal symbol S of a grammar.
static
refers to things that can be determined or performed
prior to execution of a program, e.g., at compile time.
cf. dynamic.
static analysis
analysis of a program by examining it, but without running it.
static data
data whose address in memory is constant during execution of a program
static type checking
checking or determination of the types of variables in a language at
compile time. This eliminates the need for dynamic type checking, but
requires that a variable have only a single type.
storage alignment
1. the requirement of some CPU's that certain data have addresses
that fall at even memory word boundaries, so that the data will be
contained in whole memory words.
2. in a compiler or assembler, the adjustment of memory addresses
so that data will be properly aligned.
storage allocation
the assignment of memory locations to data
and program code.
string
a sequence of symbols or characters.
strip mining
A compiler technique of decomposing loops over matrices into ``strips''
whose processing and memory are assigned to different processors in a
multi-processor machine.
strong typing
a system of static type checking in which the types of all variables must
be declared and correct use of types is enforced by the compiler.
straight-line code
a sequence of computer instructions that does not contain any branches
and is executed in sequence.
structural equivalence
a form of type checking in which two types are considered to be equivalent
if they have the same basic data type, or if they have the same
kind of structure whose components are structurally equivalent.
cf. name equivalence.
subrange
a contiguous subsequence of a sequence, e.g. 1..10
is a subrange of integer.
substring
a sequence of symbols that matches a contiguous subsequence of another string.
suffix
a sequence of symbols at the end of a string.
subclass
in object-oriented programming, a class that is a subset of
another class and can inherit messages from it. Dog might be a subclass
of Mammal.
superclass
in object-oriented programming, a superset of other
classes. A superclass can provide methods that are inherited by its
subclasses. Mammal might be a superclass of Dog.
superscalar
a type of CPU design in which, although there is only a single instruction
stream, certain operations that are nearby in that stream can be
executed concurrently using independent functional units in the CPU.
symbol table
a data structure that associates a name (symbol) with
information about the named object.
syntax
the rules by which legitimate statements can be constructed.
cf. semantics.
syntax analysis
1.the analysis of the form of a statement, such as a programming
language statement or command, to determine its component parts; parsing.
2. the syntax analysis phase of a compiler.
syntax directed translation
in parsing a programming language, building the translation of a statement
or construct in a mechanical way from the translations of its syntactic
components.
syntax directed translator
a program, such as a compiler, that performs translation from a language
into another form in a syntax-directed manner.
synthesized attribute
an attribute of a structure, e.g. a phrase in a programming language
statement, that is derived from the attributes of its components. For
example, the sum of two floating-point quantities will also be
floating-point.
synthesized translation
a method of translating statements, e.g. in a programming language,
such that the translation of a phrase is built up from the translations
of its components.
terminal symbol
a symbol in a phrase structure grammar that is a part of the language
described by the grammar, such as a word or character of the language.
cf. nonterminal symbol.
three-address code
see quadruple.
three-address machine
a CPU in which an instruction specifies two source
addresses and one destination address for the result.
token
a word, name, or sequence of characters having a meaning as a unit
in a language.
top-down parsing
a predictive form of parsing, such as recursive descent, in which the
parse tree of a statement is constructed starting at the root (sentence
symbol).
transitive closure
a relation formed from another relation by making it transitive.
Beginning with the original relation, if a b and b c ,
then a * c is added.
In a graph, the mapping from each node to the set of nodes that can be
reached from it in one or more steps.
triad
a form of intermediate code used in a compiler, consisting of an operator
and two operands. Also called two-address code.
triple
see triad.
two-address code
see triad.
two-address machine
a CPU in which an instruction specifies two source
addresses and the result of the operation replaces the contents of
one source.
type
a description of a kind of variables, including a set of
possible values and a set of operations.
type coercion
the automatic conversion of data from its existing type into the type
required for an operation.
type constructor
an operator that makes a type from other types,
e.g. array or record.
type hierarchy
1. in an object-oriented system, the hierarchy of data types formed
by the class-superclass relationships.
2. in general, a lattice of data types formed by containment
by higher types, e.g., integers are a subset of reals, which are
a subset of complex numbers.
type signature
a specification of the argument types and result type of a function or
procedure, e.g. push: item X stack --> stack
unary operator
an operator that takes only a single argument, such as NOT or
MINUS.
union of languages
a language whose sentences are members of any of its component languages.
union type
a type formed by the union of other types, i.e. a member of the
union type can have the type of any one of its component types.
unreachable code
program code that cannot be executed because it is
impossible to get to it.
unrolling
a method of program optimization in which a loop is expanded at compile
time by duplicating the contents of the loop for each value taken by the
loop index and compiling the result as straight-line code. The result
may take more memory but run faster. Also, unscrolling.
value
a possible state of data.
variable
an element of computer memory that can hold a value.
variable name
a symbol that denotes a variable.
variant record
a record whose component parts can vary, perhaps
depending on the value of a tag.
vocabulary
the union of the terminal and nonterminal symbols of a
grammar.
volatile register
a register whose value may be destroyed during a subroutine call.
yacc
(pronounced ``yack'')
a widely used context-free parser generator program for producing
syntax-directed translators such as compilers. (an abbreviation for Yet
Another Compiler-Compiler.)