Changeset 9507ce3

Oct 11, 2018, 2:48:48 PM (6 years ago)
Thierry Delisle <tdelisle@…>
ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, deferred_resn, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, no_list, persistent-indexer, pthread-emulation, qualifiedEnum
2a75572 (diff), 1f690b3 (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.

Merge branch 'master' into shared_library

7 added
25 edited


  • doc/bibliography/pl.bib

    r2a75572 r9507ce3  
    830830    month       = oct,
    831831    type        = {Diplomarbeit},
    832     note        = {{\small\textsf{ftp://\\-pub/\-theses/\}}},
     832    note        = {\href{}{https://\\-$\sim$usystem/\-theses/\-KrischerThesis.pdf}},
    925925    key         = {Cforall},
    926926    author      = {{\textsf{C}{$\mathbf{\forall}$} Features}},
    927     howpublished= {\href{}{https://\\-~cforall/\-features}},
     927    howpublished= {\href{}{https://\\-$\sim$cforall/\-features}},
    928928    optnote     = {Accessed: 2018-01-01},
    11011101    month       = oct,
    11021102    year        = 2001,
    1103     note        = {\href{}{http://\\-\char`\~cforall/\}},
     1103    note        = {\href{}{http://\\-$\sim$cforall/\}},
    15161516    month       = dec,
    15171517    year        = 2017,
    1518     note        = {\href{}{https://\\-~usystem/\-pub/\-uSystem/uC++.pdf}},
     1518    note        = {\href{}{https://\\-$\sim$usystem/\-pub/\-uSystem/uC++.pdf}},
    18091809    author      = {Glen Ditchfield},
    18101810    title       = {Conversions for \textsf{C}$\mathbf{\forall}$},
    1811     note        = {\href{}{http://\\-\textasciitilde cforall/\-Conversions/\-index.html}},
     1811    note        = {\href{}{http://\\-$\sim$cforall/\-Conversions/\-index.html}},
    18121812    month       = {Nov},
    18131813    year        = {2002},
    18771877    title       = {CS343},
    18781878    year        = 2018,
    1879     howpublished= {\href{}{https://\\-~cs343}},
     1879    howpublished= {\href{}{https://\\-$\sim$cs343}},
    41444144    month       = sep,
    41454145    year        = 2006,
    4146     note        = {\textsf{\-\char`\~Robin.Garner/\-mmtk-guide.pdf}},
     4146    note        = {\textsf{\-$\sim$Robin.Garner/\-mmtk-guide.pdf}},
    42484248    month       = sep,
    42494249    year        = 1994,
    4250     note        = {{\small\textsf{ftp://\\-pub/\-uSystem/\}}},
     4250    note        = {\href{}{https://\\-$\sim$usystem/\-pub/\-uSystem/\-uSystem.pdf}},
    47904790    year        = 1995,
    47914791    number      = 31,
    4792     note        = {{\small\textsf{http://\\-\char`\~schmidt/\-PDF/\-IPC\_SAP-92.pdf}}},
     4792    note        = {{\small\textsf{http://\\-$\sim$schmidt/\-PDF/\-IPC\_SAP-92.pdf}}},
    61326132    month       = apr,
    61336133    type        = {Diplomarbeit},
    6134     note        = {\href{}{ftp://\\-pub/\-theses/\}},
     6134    note        = {\href{}{https://\\-$\sim$usystem/\-theses/\-SchusterThesis.pdf}},
  • doc/papers/concurrency/Makefile

    r2a75572 r9507ce3  
    44Figures = figures
    55Macros = ../AMA/AMA-stix/ama
    6 TeXLIB = .:annex:../../LaTeXmacros:${Macros}:${Build}:../../bibliography:
     6TeXLIB = .:../../LaTeXmacros:${Macros}:${Build}:
    77LaTeX  = TEXINPUTS=${TeXLIB} && export TEXINPUTS && latex -halt-on-error -output-directory=${Build}
    8 BibTeX = BIBINPUTS=${TeXLIB} && export BIBINPUTS && bibtex
     8BibTeX = BIBINPUTS=annex:../../bibliography: && export BIBINPUTS && bibtex
    1010MAKEFLAGS = --no-print-directory # --silent
  • doc/papers/general/Makefile

    r2a75572 r9507ce3  
    44Figures = figures
    55Macros = ../AMA/AMA-stix/ama
    6 TeXLIB = .:${Macros}:${Build}:../../bibliography:
     6TeXLIB = .:${Macros}:${Build}:
    77LaTeX  = TEXINPUTS=${TeXLIB} && export TEXINPUTS && latex -halt-on-error -output-directory=${Build}
    8 BibTeX = BIBINPUTS=${TeXLIB} && export BIBINPUTS && bibtex
     8BibTeX = BIBINPUTS=../../bibliography: && export BIBINPUTS && bibtex
    1010MAKEFLAGS = --no-print-directory # --silent
  • doc/theses/aaron_moss_PhD/phd/.gitignore

    r2a75572 r9507ce3  
  • doc/theses/aaron_moss_PhD/phd/Makefile

    r2a75572 r9507ce3  
    11BUILD = build
    22BIBDIR = ../../../bibliography
     3EVALDIR = evaluation
    34TEXLIB = .:${BUILD}:${BIBDIR}:
    5 LATEX = TEXINPUTS=${TEXLIB} && export TEXINPUTS && pdflatex -interaction= -output-directory=${BUILD}
     6# LATEX = TEXINPUTS=${TEXLIB} && export TEXINPUTS && pdflatex -interaction=nonstopmode -halt-on-error -output-directory=${BUILD}
     7LATEX = TEXINPUTS=${TEXLIB} && export TEXINPUTS && latex -halt-on-error -output-directory=${BUILD}
    68BIBTEX = BIBINPUTS=${TEXLIB} && export BIBINPUTS && bibtex
     10VPATH = ${EVALDIR}
    812BASE = thesis
    1721introduction \
    1822background \
     23generic-types \
    1924type-environment \
    2025resolution-heuristics \
    2126conclusion \
     29GRAPHS = ${addsuffix .tex, \
     30generic-timing \
    3241        wc ${SOURCES}
    34 ${DOCUMENT} : ${SOURCES} ${BUILD}
    35         ${LATEX} ${BASE}
    36         ${LATEX} ${BASE}
     43${DOCUMENT} : ${BASE}.ps
     44        ps2pdf ${BUILD}/$<
    38 rebuild-refs : ${SOURCES} ${BIBFILE} ${BUILD}
     46${BASE}.ps : ${BASE}.dvi
     47        dvips ${BUILD}/$< -o ${BUILD}/$@
     49${BASE}.dvi : Makefile ${SOURCES} ${GRAPHS} ${BIBFILE} ${BUILD}
    3950        ${LATEX} ${BASE}
    4051        ${BIBTEX} ${BUILD}/${BASE}
    4253        ${LATEX} ${BASE}
     55${GRAPHS} : generic-timing.dat ${BUILD}
     56        gnuplot -e BUILD="'${BUILD}/'" ${EVALDIR}/
    4559        mkdir -p ${BUILD}
  • doc/theses/aaron_moss_PhD/phd/cfa-macros.tex

    r2a75572 r9507ce3  
    4343tabsize=5,                                                                                              % N space tabbing
    4444xleftmargin=\parindentlnth,                                                             % indent code to paragraph indentation
    45 %mathescape=true,                                                                               % LaTeX math escape in CFA code $...$
    4645escapechar=\$,                                                                                  % LaTeX escape in CFA code
    4746keepspaces=true,                                                                                %
  • doc/theses/aaron_moss_PhD/phd/frontpgs.tex

    r2a75572 r9507ce3  
    160160% L I S T   O F   F I G U R E S
    161161% -----------------------------
    162 % \addcontentsline{toc}{chapter}{List of Figures}
    163 % \listoffigures
    164 % \cleardoublepage
    165 % \phantomsection               % allows hyperref to link to the correct page
     162\addcontentsline{toc}{chapter}{List of Figures}
     165\phantomsection         % allows hyperref to link to the correct page
    167167% GLOSSARIES (Lists of definitions, abbreviations, symbols, etc. provided by the glossaries-extra package)
  • doc/theses/aaron_moss_PhD/phd/generic-types.tex

    r2a75572 r9507ce3  
    4 Talk about generic types. Pull from Moss~\etal\cite{Moss18}.
    6 % TODO discuss layout function algorithm, application to separate compilation
    7 % TODO put a static const field in for _n_fields for each generic, describe utility for separate compilation
    9 % TODO mention impetus for zero_t design
    11 % TODO mention use in tuple-type implementation
    13 % TODO pull benchmarks from Moss et al.
     4A significant shortcoming in standard C is the lack of reusable type-safe abstractions for generic data structures and algorithms.
     5Broadly speaking, there are three approaches to implement abstract data structures in C.
     6One approach is to write bespoke data structures for each context in which they are needed.
     7While this approach is flexible and supports integration with the C type checker and tooling, it is also tedious and error prone, especially for more complex data structures.
     8A second approach is to use !void*!-based polymorphism, \eg{} the C standard library functions !bsearch! and !qsort!, which allow for the reuse of common functionality.
     9However, basing all polymorphism on !void*! eliminates the type checker's ability to ensure that argument types are properly matched, often requiring a number of extra function parameters, pointer indirection, and dynamic allocation that is otherwise not needed.
     10A third approach to generic code is to use preprocessor macros, which does allow the generated code to be both generic and type checked, but errors in such code may be difficult to locate and debug.
     11Furthermore, writing and using preprocessor macros is unnatural and inflexible.
     12Figure~\ref{bespoke-generic-fig} demonstrates the bespoke approach for a simple linked list with !insert! and !head! operations, while Figure~\ref{void-generic-fig} and Figure~\ref{macro-generic-fig} show the same example using !void*!- and !#define!-based polymorphism, respectively.
     15        \begin{cfa}
     16                struct int_list { int value; struct int_list* next; };
     18                void int_list_insert( struct int_list** ls, int x ) {
     19                        struct int_list* node = malloc(sizeof(struct int_list));
     20                        node->value = x; node->next = *ls;
     21                        *ls = node;
     22                }
     24                int int_list_head( const struct int_list* ls ) { return ls->value; }
     26                $\C[\textwidth]{// all code must be duplicated for every generic instantiation}$
     28                struct string_list { const char* value; struct string_list* next; };
     30                void string_list_insert( struct string_list** ls, const char* x ) {
     31                        struct string_list* node = malloc(sizeof(struct string_list));
     32                        node->value = x; node->next = *ls;
     33                        *ls = node;
     34                }
     36                const char* string_list_head( const struct string_list* ls )
     37                        { return ls->value; }
     39                $\C[\textwidth]{// use is efficient and idiomatic}$
     41                int main() {
     42                        struct int_list* il = NULL;
     43                        int_list_insert( &il, 42 );
     44                        printf("%d\n", int_list_head(il));
     46                        struct string_list* sl = NULL;
     47                        string_list_insert( &sl, "hello" );
     48                        printf("%s\n", string_list_head(sl));
     49                }
     50        \end{cfa}
     52        \caption{Bespoke code for linked list implementation.} \label{bespoke-generic-fig}
     56        \begin{cfa}
     57                // single code implementation
     59                struct list { void* value; struct list* next; };
     61                $\C[\textwidth]{// internal memory management requires helper functions}$
     63                void list_insert( struct list** ls, void* x, void* (*copy)(void*) ) {
     64                        struct list* node = malloc(sizeof(struct list));
     65                        node->value = copy(x); node->next = *ls;
     66                        *ls = node;
     67                }
     69                void* list_head( const struct list* ls ) { return ls->value; }
     71                $\C[\textwidth]{// helpers duplicated per type}$
     73                void* int_copy(void* x) {
     74                        int* n = malloc(sizeof(int));
     75                        *n = *(int*)x;
     76                        return n;
     77                }
     79                void* string_copy(void* x) { return strdup((const char*)x); }
     81                int main() {
     82                        struct list* il = NULL;
     83                        int i = 42;
     84                        list_insert( &il, &i, int_copy );
     85                        printf("%d\n", *(int*)list_head(il));  $\C[2in]{// unsafe type cast}$
     87                        struct list* sl = NULL;
     88                        list_insert( &sl, "hello", string_copy );
     89                        printf("%s\n", (char*)list_head(sl));  $\C[2in]{// unsafe type cast}$
     90                }
     91        \end{cfa}
     93        \caption{\lstinline{void*}-polymorphic code for linked list implementation.} \label{void-generic-fig}
     97        \begin{cfa}
     98                $\C[\textwidth]{// code is nested in macros}$
     100                #define list(N) N ## _list
     102                #define list_insert(N) N ## _list_insert
     104                #define list_head(N) N ## _list_head
     106                #define define_list(N, T) $\C[0.25in]{ \textbackslash }$
     107                        struct list(N) { T value; struct list(N)* next; }; $\C[0.25in]{ \textbackslash }$
     108                        $\C[0.25in]{ \textbackslash }$
     109                        void list_insert(N)( struct list(N)** ls, T x ) { $\C[0.25in]{ \textbackslash }$
     110                                struct list(N)* node = malloc(sizeof(struct list(N))); $\C[0.25in]{ \textbackslash }$
     111                                node->value = x; node->next = *ls; $\C[0.25in]{ \textbackslash }$
     112                                *ls = node; $\C[0.25in]{ \textbackslash }$
     113                        } $\C[0.25in]{ \textbackslash }$
     114                        $\C[0.25in]{ \textbackslash }$
     115                        T list_head(N)( const struct list(N)* ls ) { return ls->value; }
     117                define_list(int, int); $\C[3in]{// defines int\_list}$
     118                define_list(string, const char*); $\C[3in]{// defines string\_list}$
     120                $\C[\textwidth]{// use is efficient, but syntactically idiosyncratic}$
     122                int main() {
     123                        struct list(int)* il = NULL; $\C[3in]{// does not match compiler-visible name}$
     124                        list_insert(int)( &il, 42 );
     125                        printf("%d\n", list_head(int)(il));
     127                        struct list(string)* sl = NULL;
     128                        list_insert(string)( &sl, "hello" );
     129                        printf("%s\n", list_head(string)(sl));
     130                }
     131        \end{cfa}
     133        \caption{Macros for generic linked list implementation.} \label{macro-generic-fig}
     136\CC{}, Java, and other languages use \emph{generic types} to produce type-safe abstract data types.
     137Design and implementation of generic types for \CFA{} is the first major contribution of this thesis, a summary of which is published in \cite{Moss18} and from which this chapter is closely based.
     138\CFA{} generic types integrate efficiently and naturally with the existing polymorphic functions in \CFA{}, while retaining backward compatibility with C in layout and support for separate compilation.
     139A generic type can be declared in \CFA{} by placing a !forall! specifier on a !struct! or !union! declaration, and instantiated using a parenthesized list of types after the generic name.
     140An example comparable to the C polymorphism examples in Figures~\ref{bespoke-generic-fig}, \ref{void-generic-fig}, and \ref{macro-generic-fig} can be seen in Figure~\ref{cfa-generic-fig} \TODO{test this code}.
     143        \begin{cfa}
     144                forall(otype T) struct list { T value; list(T)* next; };
     146                $\C[\textwidth]{// single polymorphic implementation of each function}$
     147                $\C[\textwidth]{// overloading reduces need for namespace prefixes}$
     149                forall(otype T) void insert( list(T)** ls, T x ) {
     150                        list(T)* node = alloc();  $\C{// type-inferring alloc}$
     151                        (*node){ x, *ls };  $\C{// concise constructor syntax}$
     152                        *ls = node;
     153                }
     155                forall(otype T) T head( const list(T)* ls ) { return ls->value; }
     157                $\C[\textwidth]{// use is clear and efficient}$
     159                int main() {
     160                        list(int)* il = 0;
     161                        insert( &il, 42 );  $\C{// inferred polymorphic T}$
     162                        printf("%d\n", head(il));
     164                        list(const char*)* sl = 0;
     165                        insert( &sl, "hello" );
     166                        printf("%s\n", head(sl));
     167                }
     168        \end{cfa}
     170        \caption{\CFA{} generic linked list implementation.} \label{cfa-generic-fig}
     175Though a number of languages have some implementation of generic types, backward compatibility with both C and existing \CFA{} polymorphism presented some unique design constraints for this project.
     176The guiding principle was to maintain an unsurprising language model for C programmers without compromising runtime efficiency.
     177A key insight for this design was that C already possesses a handful of built-in generic types (\emph{compound types} in the language of the standard\cit{}), notably pointer (!T*!) and array (!T[]!), and that user-definable generics should act similarly.
     179\subsection{Related Work}
     181One approach to the design of generic types is that taken by \CC{} templates\cite{C++}.
     182The template approach is closely related to the macro-expansion approach to C polymorphism demonstrated in Figure~\ref{macro-generic-fig}, but where the macro-expansion syntax has been given first-class language support.
     183Template expansion has the benefit of generating code with near-optimal runtime efficiency, as distinct optimizations can be applied for each instantiation of the template.
     184On the other hand, template expansion can also lead to significant code bloat, exponential in the worst case\cit{}, and the costs of increased instruction cache pressure at runtime and wasted developer time when compiling cannot be discounted.
     185The most significant restriction of the \CC{} template model is that it breaks separate compilation and C's translation-unit-based encapsulation mechanisms.
     186Because a \CC{} template is not actually code, but rather a sort of ``recipe'' to generate code, template code must be visible at its call site to be used.
     187Furthermore, \CC{} template code cannot be type-checked without instantiating it, a time consuming process with no hope of improvement until \CC{} concepts\cite{C++Concepts} are standardized in \CCtwenty{}.
     188C code, by contrast, only needs a !struct! or function declaration to call that function or use (by-pointer) values of that type, a desirable property to maintain for \CFA{}.
     190Java\cite{Java8} has another prominent implementation for generic types, introduced in Java~5 and based on a significantly different approach than \CC{}.
     191The Java approach has much more in common with the !void*!-polymorphism shown in Figure~\ref{void-generic-fig}; since in Java nearly all data is stored by reference, the Java approach to polymorphic data is to store pointers to arbitrary data and insert type-checked implicit casts at compile-time.
     192This process of \emph{type erasure} has the benefit of allowing a single instantiation of polymorphic code, but relies heavily on Java's object model and garbage collector.
     193To use this model, a more C-like language such as \CFA{} would be required to dynamically allocate internal storage for variables, track their lifetime, and properly clean them up afterward.
     195Cyclone\cite{Grossman06} is another language extending C, and also provides capabilities for polymorphic functions and existential types, similar to \CFA{}'s !forall! functions and generic types.
     196Cyclone existential types can include function pointers in a construct similar to a virtual function table, but these pointers must be explicitly initialized at some point in the code, which is tedious and error-prone compared to \CFA{}'s implicit assertion satisfaction.
     197Furthermore, Cyclone's polymorphic functions and types are restricted to abstraction over types with the same layout and calling convention as !void*!, \ie{} only pointer types and !int!.
     198In the \CFA{} terminology discussed in Section~\ref{generic-impl-sec}, all Cyclone polymorphism must be dtype-static.
     199While the Cyclone polymorphism design provides the efficiency benefits discussed in Section~\ref{dtype-static-sec} for dtype-static polymorphism, it is more restrictive than the more general model of \CFA{}.
     201Many other languages include some form of generic types.
     202As a brief survey, ML\cite{ML} was the first language to support parameteric polymorphism, but unlike \CFA{} does not support the use of assertions and traits to constrain type arguments.
     203Haskell\cite{Haskell10} combines ML-style polymorphism with the notion of type classes, similar to \CFA{} traits, but requiring an explicit association with their implementing types, unlike \CFA{}.
     204Objective-C\cite{obj-c-book} is an extension to C which has had some industrial success; however, it did not support type-checked generics until recently\cite{xcode7}, and it's garbage-collected, message-passing object-oriented model is a radical departure from C.
     205Go\cite{Go}, and Rust\cite{Rust} are modern compiled languages with abstraction features similar to \CFA{} traits, \emph{interfaces} in Go and \emph{traits} in Rust.
     206Go has implicit interface implementation and uses a ``fat pointer'' construct to pass polymorphic objects to functions, similar in principle to \CFA{}'s implicit forall paramters.
     207Go does not, however, allow user code to define generic types, restricting Go programmers to the small set of generic types defined by the compiler.
     208Rust has powerful abstractions for generic programming, including explicit implemenation of traits and options for both separately-compiled virtual dispatch and template-instantiated static dispatch in functions.
     209On the other hand, the safety guarantees of Rust's \emph{lifetime} abstraction and borrow checker impose a distinctly idiosyncratic programming style and steep learning curve; \CFA{}, with its more modest safety features, allows direct ports of C code while maintaining the idiomatic style of the original source.
     211\subsection{\CFA{} Generics}
     213The generic types design in \CFA{} draws inspiration from both \CC{} and Java generics, capturing the better aspects of each.
     214Like \CC{} template types, generic !struct!s and !union!s in \CFA{} have macro-expanded storage layouts, but, like Java generics, \CFA{} generic types can be used with separately-compiled polymorphic functions without requiring either the type or function definition to be visible to the other.
     215The fact that the storage layout of any instantiation of a \CFA{} generic type is identical to that of the monomorphic type produced by simple macro replacement of the generic type parameters is important to provide consistent and predictable runtime performance, and to not impose any undue abstraction penalty on generic code.
     216As an example, consider the following generic type and function \TODO{test this}:
     219forall( otype R, otype S ) struct pair { R first; S second; };
     221pair(const char*, int) with_len( const char* s ) {
     222        return (pair(const char*), int){ s, strlen(s) };
     226In this example, !with_len! is defined at the same scope as !pair!, but it could be called from any context that can see the definition of !pair! and a declaration of !with_len!.
     227If its return type was !pair(const char*, int)*!, callers of !with_len! would only need the declaration !forall(otype R, otype S) struct pair! to call it, in accordance with the usual C rules for opaque types.
     229!with_len! is itself a monomorphic function, returning a type that is structurally identical to !struct { const char* first; int second; }!, and as such could be called from C given an appropriate redeclaration and demangling flags.
     230However, the definition of !with_len! depends on a polymorphic function call to the !pair! constructor, which only needs to be written once (in this case, implicitly by the compiler according to the usual \CFA{} constructor generation\cite{Moss18}) and can be re-used for a wide variety of !pair! instantiations.
     231Since the parameters to this polymorphic constructor call are all statically known, compiler inlining can eliminate any runtime overhead of this polymorphic call.
     233\CFA{} deliberately does not support \CC{}-style partial specializations of generic types.
     234A particularly infamous example in the \CC{} standard library is !vector<bool>!, which is represented as a bitstring rather than the array representation of the other !vector! instantiations.
     235Complications from this inconsistency (chiefly the fact that a single bit is not addressable, unlike an array element) make the \CC{} !vector! unpleasant to use in generic contexts due to the break in its public interface.
     236Rather than attempting to plug leaks in the template specialization abstraction with a detailed method interface, \CFA{} takes the more principled position that two types with an unrelated data layout are in fact unrelated types, and should be handled with different code.
     237Of course, to the degree that distinct types are similar enough to share an interface, the \CFA{} !trait! system allows one to be defined, and objects of types implementing that !trait! to be operated on in the same polymorphic functions.
     239Since \CFA{} polymorphic functions can operate over polymorphic generic types, functions over such types can be partially or completely specialized using the usual overload selection rules.
     240As an example, the !with_len! function above could be an optimization of the following more general function:
     243forall(otype T, otype I | { I len(T); })
     244pair(T, I) with_len( T s ) {
     245        return (pair(T,I)){ s, len(s) };
     249\CFA{} generic types also support the type constraints from !forall! functions.
     250For example, the following declaration of a sorted set type ensures that the set key implements equality and relational comparison:
     253forall(otype Key | { int ?==?(Key, Key); int ?<?(Key, Key); }) struct sorted_set;
     256These constraints are implemented by applying equivalent constraints to the compiler-generated constructors for this type.
     258\section{Implementation} \label{generic-impl-sec}
     260The ability to use generic types in polymorphic contexts means that the \CFA{} implementation in \CFACC{} must support a mechanism for accessing fields of generic types dynamically at runtime.
     261While \CFACC{} could in principle use this same mechanism for accessing fields of all generic types, such an approach would throw away compiler knowledge of static types and impose an unnecessary runtime cost, limiting the utility of the generic type design.
     262Instead, my design for generic type support in \CFACC{} distinguishes between \emph{concrete} generic types that have a fixed memory layout regardless of type parameters and \emph{dynamic} generic types that may vary in memory layout depending on their type parameters.
     263A \emph{dtype-static} type has polymorphic parameters but is still concrete.
     264Polymorphic pointers are an example of dtype-static types; given some type variable !T!, T is a polymorphic type, but !T*! has a fixed size and can therefore be represented by a !void*! in code generation.
     265In particular, generic types where all parameters are un-!sized! (\ie{} they do not conform to the built-in !sized! trait because the compiler does not know their size and alignment) are always concrete, as there is no possibility for their layout to vary based on type parameters of unknown size and alignment.
     266More precisely, a type is concrete if and only if all of its !sized! type parameters are concrete, and a concrete type is dtype-static if any of its type parameters are (possibly recursively) polymorphic.
     267To illustrate, the following code using the !pair! type from above \TODO{test this} has each use of !pair! commented with its class:
     270//dynamic, layout varies based on T
     271forall(otype T) T value( pair(const char*, T) p ) { return p.second; }
     273// dtype-static, F* and T* are concrete but recursively polymorphic
     274forall(dtype F, otype T) T value( pair(F*, T*) ) { return *p.second; }
     276pair(const char*, int) p = {"magic", 42}; $\C[2.5in]{// concrete}$
     277int i = value(p);
     278pair(void*, int*) q = {0, &p.second}; $\C[2.5in]{// concrete}$
     279i = value(q);
     280double d = 1.0;
     281pair(double*, double*) r = {&d, &d}; $\C[2.5in]{// concrete}$
     282d = value(r);
     285\subsection{Concrete Generic Types}
     287The \CFACC{} translator template expands concrete generic types into new structure types, affording maximal inlining.
     288To enable interoperation among equivalent instantiations of a generic type, \CFACC{} saves the set of instantiations currently in scope and reuses the generated structure declarations where appropriate.
     289In particular, tuple types are implemented as a single compiler-generated generic type definition per tuple arity, and can be instantiated and reused according to the usual rules for generic types.
     290A function declaration that accepts or returns a concrete generic type produces a declaration for the instantiated structure in the same scope, which all callers may reuse.
     291As an example, the concrete instantiation for !pair(const char*, int)! is\footnote{This omits the field name mangling performed by \CFACC{} for overloading purposes.\label{mangle-foot}}
     294struct _pair_conc0 { const char * first; int second; };
     297A concrete generic type with dtype-static parameters is also expanded to a structure type, but this type is used for all matching instantiations.
     298In the example above, the !pair(F*, T*)! parameter to !value! is such a type; its expansion is below\footref{mangle-foot}, and it is used as the type of the variables !q! and !r! as well, with casts for member access where appropriate.
     301struct _pair_conc1 { void* first; void* second; };
     304\subsection{Dynamic Generic Types}
     306In addition to this efficient implementation of concrete generic types, \CFA{} also offers flexibility with powerful support for dynamic generic types.
     307In the pre-existing compiler design, !otype! (and all !sized!) type parameters come with implicit size and alignment parameters provided by the caller.
     308The design for generic types presented here adds an \emph{offset array} containing structure-member offsets for dynamic generic !struct! types.
     309A dynamic generic !union! needs no such offset array, as all members are at offset 0, but size and alignment are still necessary.
     310Access to members of a dynamic structure is provided at runtime via base displacement addressing the structure pointer and the member offset (similar to the !offsetof! macro), moving a compile-time offset calculation to runtime.
     312the offset arrays are statically generated where possible.
     313If a dynamic generic type is passed or returned by value from a polymorphic function, \CFACC{} can safely assume that the generic type is complete (\ie{} has a known layout) at any call site, and the offset array is passed from the caller; if the generic type is concrete at the call site, the elements of this offset array can even be statically generated using the C !offsetof! macro.
     314As an example, the body of the second !value! function above is implemented as
     317_assign_T( _retval, p + _offsetof_pair[1] ); $\C[2in]{// return *p.second}$
     320Here, !_assign_T! is passed in as an implicit parameter from !otype T! and takes two !T*! (!void*! in the generated code), a destination and a source, and !_retval! is the pointer to a caller-allocated buffer for the return value, the usual \CFA{} method to handle dynamically-sized return types.
     321!_offsetof_pair! is the offset array passed into !value!; this array is generated at the call site as
     324size_t _offsetof_pair[] = {offsetof(_pair_conc0, first),  offsetof(_pair_conc0, second)};
     327\subsubsection{Layout Functions}
     329In some cases, the offset arrays cannot be statically generated.
     330For instance, modularity is generally provided in C by including an opaque forward declaration of a structure and associated accessor and mutator functions in a header file, with the actual implementations in a separately-compiled \texttt{.c} file.
     331\CFA{} supports this pattern for generic types, implying that the caller of a polymorphic function may not know the actual layout or size of a dynamic generic type and only holds it by pointer.
     332\CFACC{} automatically generates \emph{layout functions} for cases where the size, alignment, and offset array of a generic struct cannot be passed into a function from that functions's caller.
     333These layout functions take as arguments pointers to size and alignment variables and a caller-allocated array of member offsets, as well as the size and alignment of all !sized! parameters to the generic structure.
     334Un!sized! parameters not passed because they are forbidden from being used in a context that affects layout by C's usual rules about incomplete types.
     335Similarly, the layout function can only safely be called from a context where the generic type definition is visible, because otherwise the caller will not know how large to allocate the array of member offsets.
     337The C standard does not specify a memory layout for structs, but the POSIX ABI for x86\cit{} does; this memory layout is common for C implementations, but is a platform-specific issue for porting \CFA{}.
     338This algorithm, sketched below in pseudo-\CFA{}, is a straightforward mapping of consecutive fields into the first properly-aligned offset in the !struct! layout; layout functions for !union! types omit the offset array and simply calculate the maximum size and alignment over all union variants.
     339Since \CFACC{} generates a distinct layout function for each type, constant-folding and loop unrolling are applied.
     342forall(dtype T1, dtype T2, ... | sized(T1) | sized(T2) | ...)
     343void layout(size_t* size, size_t* align, size_t* offsets) {
     344        // initialize values
     345        *size = 0; *align = 1;
     346        // set up members
     347        for ( int i = 0; i < n_fields; ++i ) {
     348                // pad to alignment
     349                size_t off_align = *size % alignof(field[i]);
     350                if ( off_align != 0 ) { *size += alignof(field[i]) - off_align; }
     351                // mark member, increase size, and fix alignment
     352                offsets[i] = *size;
     353                *size += sizeof(field[i]);
     354                if ( *align < alignof(field[i]) ) { *align = alignof(field[i]); }
     355        }
     356        // final padding to alignment
     357        size_t off_align = *size % *align;
     358        if ( off_align != 0 ) { *size += *align - off_align; }
     362Results of layout function calls are cached so that they are only computed once per type per function.
     363Layout functions also allow generic types to be used in a function definition without reflecting them in the function signature, an important implemenation-hiding constraint of the design.
     364For instance, a function that strips duplicate values from an unsorted !list(T)! likely has a reference to the list as its only explicit parameter, but uses some sort of !set(T)! internally to test for duplicate values.
     365This function could acquire the layout for !set(T)! by calling its layout function, providing as an argument the layout of !T! implicitly passed into that function.
     367Whether a type is concrete, dtype-static, or dynamic is decided solely on the basis of the type arguments and !forall! clause type paramters.
     368This design allows opaque forward declarations of generic types, \eg{} !forall(otype T) struct Box;! like in C, all uses of $Box(T)$ can be separately compiled, and callers from other translation units know the proper calling conventions to use.
     369In an alternate design where the definition of a structure type is included in deciding whether a generic type is dynamic or concrete, some further types may be recognized as dtype-static --- \eg{} !Box! could be defined with a body !{ T* p; }!, and would thus not depend on !T! for its layout.
     370However, the existence of an !otype! parameter !T! means that !Box! \emph{could} depend on !T! for its layout if this definition is not visible, and we judged preserving separate compilation (and the associated C compatibility) in the implemented design to be an acceptable trade-off.
     372\subsection{Applications of Dtype-static Types} \label{dtype-static-sec}
     374The reuse of dtype-static structure instantiations enables useful programming patterns at zero runtime cost.
     375The most important such pattern is using !forall(dtype T) T*! as a type-checked replacement for !void*!, \eg{} creating a lexicographic comparison function for pairs of pointers.
     378forall(dtype T)
     379int lexcmp( pair(T*, T*)* a, pair(T*, T*)* b, int (*cmp)(T*, T*) ) {
     380        int c = cmp( a->first, b->first );
     381        return c ? c : cmp( a->second, b->second );
     385Since !pair(T*, T*)! is a concrete type, there are no implicit parameters passed to !lexcmp!; hence, the generated code is identical to a function written in standard C using !void*!, yet the \CFA{} version is type-checked to ensure members of both pairs and arguments to the comparison function match in type.
     387Another useful pattern enabled by reused dtype-static type instantiations is zero-cost \emph{tag structures}.
     388Sometimes, information is only used for type checking and can be omitted at runtime.
     389In the example below, !scalar! is a dtype-static type; hence, all uses have a single structure definition containing !unsigned long! and can share the same implementations of common functions like !?+?!.
     390These implementations may even be separately compiled, unlike \CC{} template functions.
     391However, the \CFA{} type checker ensures matching types are used by all calls to !?+?!, preventing nonsensical computations like adding a length to a volume.
     394forall(dtype Unit) struct scalar { unsigned long value; };
     395struct metres {};
     396struct litres {};
     398forall(dtype U) scalar(U) ?+?(scalar(U) a, scalar(U) b) {
     399        return (scalar(U)){ a.value + b.value };
     402scalar(metres) half_marathon = { 21098 };
     403scalar(litres) pool = { 2500000 };
     404scalar(metres) marathon = half_marathon + half_marathon;
     405`marathon + pool;` $\C[4in]{// compiler ERROR, mismatched types}$
     408\section{Performance Experiments} \label{generic-performance-sec}
     410To validate the practicality of this generic type design I have conducted microbenchmark-based tests against a number of comparable code designs in C and \CC{}, first published in \cite{Moss18}.
     411Since all these languages are compiled with the same compiler backend and share a subset essentially comprising standard C, maximal-performance benchmarks should show little runtime variance, differing only in length and clarity of source code.
     412A more illustrative comparison measures the costs of idiomatic usage of each language's features.
     413The code below shows the \CFA{} benchmark tests for a generic stack based on a singly-linked list; the test suite is equivalent for the other other languages.
     414The experiment uses element types !int! and !pair(short, char)! and pushes $N = 40M$ elements on a generic stack, copies the stack, clears one of the stacks, and finds the maximum value in the other stack.
     417int main() {
     418        int max = 0, val = 42;
     419        stack( int ) si, ti;
     421        REPEAT_TIMED( "push_int", N, push( si, val ); )
     422        TIMED( "copy_int", ti{ si }; )
     423        TIMED( "clear_int", clear( si ); )
     424        REPEAT_TIMED( "pop_int", N, int x = pop( ti ); if ( x > max ) max = x; )
     426        pair( short, char ) max = { 0h, '\0' }, val = { 42h, 'a' };
     427        stack( pair( short, char ) ) sp, tp;
     429        REPEAT_TIMED( "push_pair", N, push( sp, val ); )
     430        TIMED( "copy_pair", tp{ sp }; )
     431        TIMED( "clear_pair", clear( sp ); )
     432        REPEAT_TIMED( "pop_pair", N, pair(short, char) x = pop( tp );
     433                if ( x > max ) max = x; )
     437The four versions of the benchmark implemented are C with !void*!-based polymorphism, \CFA{} with parameteric polymorphism, \CC{} with templates, and \CC{} using only class inheritance for polymorphism, denoted \CCV{}.
     438The \CCV{} variant illustrates an alternative object-oriented idiom where all objects inherit from a base !object! class, mimicking a Java-like interface; in particular, runtime checks are necessary to safely downcast objects.
     439The most notable difference among the implementations is the memory layout of generic types: \CFA{} and \CC{} inline the stack and pair elements into corresponding list and pair nodes, while C and \CCV{} lack such capability and, instead, must store generic objects via pointers to separately allocated objects.
     440Note that the C benchmark uses unchecked casts as C has no runtime mechanism to perform such checks, whereas \CFA{} and \CC{} provide type safety statically.
     442Figure~\ref{generic-eval-fig} and Table~\ref{generic-eval-table} show the results of running the described benchmark.
     443The graph plots the median of five consecutive runs of each program, with an initial warm-up run omitted.
     444All code is compiled at \texttt{-O2} by gcc or g++ 6.4.0, with all \CC{} code compiled as \CCfourteen{}.
     445The benchmarks are run on an Ubuntu 16.04 workstation with 16 GB of RAM and a 6-core AMD FX-6300 CPU with 3.5 GHz maximum clock frequency.
     446I conjecture that these results scale across most uses of generic types, given the constant underlying polymorphism implementation.
     451\caption{Benchmark timing results (smaller is better)} \label{generic-eval-fig}
     455\caption{Properties of benchmark code} \label{generic-eval-table}
     459                                                                        & \CT{C}        & \CT{\CFA}     & \CT{\CC}      & \CT{\CCV}             \\
     460maximum memory usage (MB)                       & 10\,001       & 2\,502        & 2\,503        & 11\,253               \\
     461source code size (lines)                        & 201           & 191           & 125           & 294                   \\
     462redundant type annotations (lines)      & 27            & 0                     & 2                     & 16                    \\
     463binary size (KB)                                        & 14            & 257           & 14            & 37                    \\
     467The C and \CCV{} variants are generally the slowest and have the largest memory footprint, due to their less-efficient memory layout and the pointer indirection necessary to implement generic types in those languages; this inefficiency is exacerbated by the second level of generic types in the pair benchmarks.
     468By contrast, the \CFA{} and \CC{} variants run in roughly equivalent time for both the integer and pair because of the equivalent storage layout, with the inlined libraries (\ie{} no separate compilation) and greater maturity of the \CC{} compiler contributing to its lead.
     469\CCV{} is slower than C largely due to the cost of runtime type checking of downcasts (implemented with !dynamic_cast!); the outlier for \CFA{}, pop !pair!, results from the complexity of the generated-C polymorphic code.
     470The gcc compiler is unable to optimize some dead code and condense nested calls; a compiler designed for \CFA{} could more easily perform these optimizations.
     471Finally, the binary size for \CFA{} is larger because of static linking with \CFA{} libraries.
     473\CFA{} is also competitive in terms of source code size, measured as a proxy for programmer effort.
     474The line counts in Table~\ref{generic-eval-table} include implementations of !pair! and !stack! types for all four languages for purposes of direct comparison, although it should be noted that \CFA{} and \CC{} have prewritten data structures in their standard libraries that programmers would generally use instead.
     475Use of these standard library types has minimal impact on the performance benchmarks, but shrinks the \CFA{} and \CC{} code to 39 and 42 lines, respectively.
     476The difference between the \CFA{} and \CC{} line counts is primarily declaration duplication to implement separate compilation; a header-only \CFA{} library is similar in length to the \CC{} version.
     477On the other hand, due to the language shortcomings mentioned at the beginning of the chapter, C does not have a generic collections library in its standard distribution, resulting in frequent reimplementation of such collection types by C programmers.
     478\CCV{} does not use the \CC{} standard template library by construction, and, in fact, includes the definition of !object! and wrapper classes for !char!, !short!, and !int! in its line count, which inflates this count somewhat, as an actual object-oriented language would include these in the standard library.
     479I justify the given line count by noting that many object-oriented languages do not allow implementing new interfaces on library types without subclassing or wrapper types, which may be similarly verbose.
     481Line count is a fairly rough measure of code complexity; another important factor is how much type information the programmer must specify manually, especially where that information is not type-checked.
     482Such unchecked type information produces a heavier documentation burden and increased potential for runtime bugs and is much less common in \CFA{} than C, with its manually specified function pointer arguments and format codes, or \CCV{}, with its extensive use of un-type-checked downcasts, \eg{} !object! to !integer! when popping a stack.
     483To quantify this manual typing, the ``redundant type annotations'' line in Table~\ref{generic-eval-table} counts the number of lines on which the known type of a variable is respecified, either as a format specifier, explicit downcast, type-specific function, or by name in a !sizeof!, !struct! literal, or !new! expression.
     484The \CC{} benchmark uses two redundant type annotations to create new stack nodes, whereas the C and \CCV{} benchmarks have several such annotations spread throughout their code.
     485The \CFA{} benchmark is able to eliminate \emph{all} redundant type annotations through use of the return-type polymorphic !alloc! function in the \CFA{} standard library.
     487\section{Future Work}
     489The generic types design presented here is already sufficiently expressive to implement a variety of useful library types.
     490However, some other features based on this design could further improve \CFA{}.
     492The most pressing addition is the ability to have non-type generic parameters.
     493C already supports fixed-length array types, \eg{} !int[10]!; these types are essentially generic types with unsigned integer parameters, and allowing \CFA{} users the capability to build similar types is a requested feature.
     494More exotically, the ability to have these non-type parameters depend on dynamic runtime values rather than static compile-time constants opens up interesting opportunities for type-checking problematic code patterns.
     495For example, if a collection iterator was parameterized over the pointer to the collection it was drawn from, then a sufficiently powerful static analysis pass could ensure that that iterator was only used for that collection, eliminating one source of hard-to-find bugs.
     497The implementation mechanisms behind this generic types design can also be used to add new features to \CFA{}.
     498One such potential feature would be to add \emph{field assertions} to the existing function and variable assertions on polymorphic type variables.
     499Implementation of these field assertions would be based on the same code that supports member access by dynamic offset calculation for dynamic generic types.
     500Simulating field access can already be done more flexibly in \CFA{} by declaring a trait containing an accessor function to be called from polymorphic code, but these accessor functions impose some overhead both to write and call, and directly providing field access via an implicit offset parameter would be both more concise and more efficient.
     501Of course, there are language design trade-offs to such an approach, notably that providing the two similar features of field and function assertions would impose a burden of choice on programmers writing traits, with field assertions more efficient, but function assertions more general; given this open design question we have deferred a decision on field assertions until we have more experience using \CFA{}.
     502If field assertions are included in the language, a natural extension would be to provide a structural inheritance mechanism for every !struct! type that simply turns the list of !struct! fields into a list of field assertions, allowing monomorphic functions over that type to be generalized to polymorphic functions over other similar types with added or reordered fields.
     503\CFA{} could also support a packed or otherwise size-optimized representation for generic types based on a similar mechanism --- the layout function would need to be re-written, but nothing in the use of the offset arrays implies that the field offsets need be monotonically increasing.
     505With respect to the broader \CFA{} polymorphism design, the experimental results in Section~\ref{generic-performance-sec} demonstrate that though the runtime impact of \CFA{}'s dynamic virtual dispatch is low, it is not as low as the static dispatch of \CC{} template inlining.
     506However, rather than subject all \CFA{} users to the compile-time costs of ubiquitous template expansion, we are considering more targeted mechanisms for performance-sensitive code.
     507Two promising approaches are are an !inline! annotation at polymorphic function call sites to create a template specialization of the function (provided the code is visible) or placing a different !inline! annotation on polymorphic function definitions to instantiate a specialized version of the function for some set of types.
     508These approaches are not mutually exclusive and allow performance optimizations to be applied only when necessary, without suffering global code bloat.
     509In general, the \CFA{} team believes that separate compilation works well with loaded hardware caches by producing smaller code, which may offset the benefit of larger inlined code.
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    7 \label{tiobe-table}
    8 \caption[TIOBE index over time]{Current top 5 places in the TIOBE index averaged over years}
     7\caption[TIOBE index over time]{Current top 5 places in the TIOBE index averaged over years} \label{tiobe-table}
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    1212\newcommand{\CCseventeen}{\textrm{C}\kern-.1em\hbox{+\kern-.25em+}17} % C++17 symbolic name
    1313\newcommand{\CCtwenty}{\textrm{C}\kern-.1em\hbox{+\kern-.25em+}20} % C++20 symbolic name
     14\newcommand{\CCV}{\rm C\kern-.1em\hbox{+\kern-.25em+}obj} % C++ virtual symbolic name
    1415\newcommand{\Csharp}{C\raisebox{-0.7ex}{\Large$^\sharp$}} % C# symbolic name
    2124\newcommand{\TODO}[1]{\textbf{TODO:} \textit{#1}}
    2225\newcommand{\cit}{\textsuperscript{[citation needed]}}
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    2222\usepackage{amsmath,amssymb,amstext} % Lots of math symbols and environments
    23 \usepackage[pdftex]{graphicx} % For including graphics N.B. pdftex graphics driver
     23% \usepackage[pdftex]{graphicx} % For including graphics N.B. pdftex graphics driver
     26\usepackage{footmisc} % for double refs to the same footnote
    2528% Hyperlinks make it very easy to navigate an electronic document.
    2831% Use the "hyperref" package
    30 \usepackage[pdftex,pagebackref=false]{hyperref} % with basic options
     33%\usepackage[pdftex,pagebackref=false]{hyperref} % with basic options
    3135% N.B. pagebackref=true provides links back from the References to the body text. This can cause trouble for printing.
    123 \input{resolution-heuristics}
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    4 Talk about the type environment data structure. Pull from your presentation.
     4One key data structure for expression resolution is the \emph{type environment}.
     5As discussed in Chapter~\ref{resolution-chap}, being able to efficiently determine which type variables are bound to which concrete types or whether two type environments are compatible is a core requirement of the resolution algorithm.
     6Furthermore, expression resolution involves a search through many related possible solutions, so being able to re-use shared subsets of type environment data and to switch between environments quickly is desirable for performance.
     7In this chapter I discuss and empirically compare a number of type environment data structure variants, including some novel variations on the union-find\cit{} data structure introduced in this thesis.
     11For purposes of this chapter, a \emph{type environment} $T$ is a set of \emph{type classes} $\myset{T_1, T_2, \cdots, T_{|T|}}$.
     12Each type class $T_i$ contains a set of \emph{type variables} $\myset{v_{i,1}, v_{i,2}, \cdots, v_{i,|T_i|}}$; note that the sets of variables contained in two distinct classes in the same environment must be disjoint.
     13Each individual type class $T_i$ may also be associated with a \emph{bound}, $b_i$; this bound contains the \emph{bound type} which the variables in the type class are replaced with, but also includes other information in \CFACC{}, including whether type conversions are permissible on the bound type and what sort of type variables are contained in the class (data types, function types, or variadic tuples).
     16\caption[Type environment operation summary]{Summary of type environment operations.}
     19\begin{tabular}{r@{\hskip 0.25em}ll}
     20        $find(T, v_{i,j})$ & $\rightarrow T_i | \bot$           & Locate class for variable             \\
     21        $report(T_i)$ & $\rightarrow \{ v_{i,j} \cdots \}$      & List variables for class              \\
     22        $bound(T_i)$ & $\rightarrow b_i | \bot$                         & Get bound for class                   \\
     23        $insert(v_{i,1})$ &                                                                     & New single-variable class             \\
     24        $add(T_i, v_{i,j})$ &                                                           & Add variable to class                 \\
     25        $bind(T_i, b_i)$ &                                                                      & Set or update class bound             \\
     26        $remove(T, T_i)$ &                                                                      & Remove class from environment \\
     27        $unify(T, T_i, T_j)$ & $\rightarrow \top | \bot$        & Combine two type classes              \\
     28        $combine(T, T')$ & $\rightarrow \top | \bot$            & Merge two environments                \\
     29        $save(T)$ & $\rightarrow H$                                                     & Get handle for current state  \\
     30        $backtrack(T, H)$ &                                                                     & Return to handle state
     34Given this basic structure, type environments in \CFACC{} need to support eleven basic operations, summarized in Table~\ref{env-op-table}.
     35The first seven operations are straightforward queries and updates on these data structures:
     36The lookup operation $find(T, v_{i,j})$ produces $T_i$, the type class in $T$ which contains variable $v_{i,j}$, or an invalid sentinel value for no such class.
     37The other two query operations act on type classes, where $report(T_i)$ produces the set $\myset{v_{i,1}, v_{i,2}, \cdots, v_{i,|T_i|}}$ of all type variables in a class $T_i$ and $bound(T_i)$ produces the bound $b_i$ of that class, or a sentinel indicating no bound is set.
     39The update operation $insert(T, v_{i,1})$ creates a new type class $T_i$ in $T$ that contains only the variable $v_{i,1}$ and no bound; due to the disjointness property $v_{i,1}$ cannot belong to any other type class in $T$.
     40The $add(T_i, v_{i,j})$ operation adds a new type variable $v_{i,j}$ to class $T_i$; again, $v_{i,j}$ cannot exist elsewhere in $T$.
     41$bind(T_i, b_i)$ mutates the bound for a type class, setting or updating the current bound.
     42The final basic mutation operation is $remove(T, T_i)$, which removes a class $T_i$ and all its type variables from an environment $T$.
     44The $unify$ operation is the fundamental non-trivial operation a type environment data structure must support.
     45$unify(T, T_i, T_j)$ merges a type class $T_j$ into another $T_i$, producing a failure result and leaving $T$ in an invalid state if this merge fails.
     46It is always possible to unify the type variables of both classes by simply taking the union of both sets; given the disjointness property, no checks for set containment are required, and the variable sets can simply be concatenated if supported by the underlying data structure.
     47$unify$ depends on an internal $unify_bound$ operation which may fail.
     48In \CFACC{}, $unify_bound(b_i, b_j) \rightarrow b'_i|\bot$ checks that the type classes contain the same sort of variable, takes the tighter of the two conversion permissions, and checks if the bound types can be unified.
     49If the bound types cannot be unified (\eg{} !struct A! with !int*!), then $unify_bound$ fails, while other combinations of bound types may result in recursive calls.
     50For instance, unifying !R*! with !S*! for type variables !R! and !S! will result in a call to $unify(T, find($!R!$), find($!S!$))$, while unifying !R*! with !int*! will result in a call to $unify_bound$ on !int! and the bound type of the class containing !R!.
     51As such, a call to $unify(T, T_i, T_j)$ may touch every type class in $T$, not just $T_i$ and $T_j$, collapsing the entirety of $T$ into a single type class in extreme cases.
     53Given the nature of the expression resolution problem as backtracking search, caching and concurrency are both useful tools to decrease runtime.
     54However, both of these approaches may produce multiple distinct descendants of the same initial type environment, which have possibly been mutated in incompatible ways.
     55As such, to effectively employ either concurrency or caching, the type environment data structure must support an efficient method to check if two type environments are compatible and merge them if so.
     56$combine(T,T')$ attempts to merge an environment $T'$ into another environment $T$, producing $\top$ if successful or leaving $T$ in an invalid state and producing $\bot$ otherwise.
     57The invalid state of $T$ on failure is not important, given that a combination failure will result in the resolution algorithm backtracking to a different environment.
     58$combine$ proceeds by calls to $insert$, $add$, and $unify$ as needed, and can be roughly thought of as calling $unify$ on every pair of classes in $T$ that have variables $v'_{i,j}$ and $v'_{i,k}$ in the same class $T'_i$ in $T'$.
     59Like for $unify$, $combine$ can always find a mutually-consistent division of type variables into classes (in the extreme case, all type variables from $T$ and $T'$ in a single type class), but may fail due to inconsistent bounds on merged type classes.
     61Finally, the backtracking access patterns of the compiler can be exploited to reduce memory usage or runtime through use of an appropriately designed data structure.
     62The set of mutations to a type environment across the execution of the resolution algorithm produce an implicit tree of related environments, and the backtracking search typically focuses only on one leaf of the tree at once, or at most a small number of closely-related nodes as arguments to $combine$.
     63As such, the ability to save and restore particular type environment states is useful, and supported by the $save(T) \rightarrow H$ and $backtrack(T, H)$ operations, which produce a handle for the current environment state and mutate an environment back to a previous state, respectively.
     64These operations can be naively implemented by a deep copy of $T$ into $H$ and vice versa, but have more efficient implementations in persistency-aware data structures.
     66% Future work: design multi-threaded version of C&F persistent map --- core idea is some sort of thread-boundary edit node
  • doc/user/Makefile

    r2a75572 r9507ce3  
    44Figures = figures
    55Macros = ../LaTeXmacros
    6 TeXLIB = .:${Macros}:${Build}:../bibliography:
     6TeXLIB = .:${Macros}:${Build}:
    77LaTeX  = TEXINPUTS=${TeXLIB} && export TEXINPUTS && latex -halt-on-error -output-directory=${Build}
    8 BibTeX = BIBINPUTS=${TeXLIB} && export BIBINPUTS && bibtex
     8BibTeX = BIBINPUTS=../bibliography: && export BIBINPUTS && bibtex
    1010MAKEFLAGS = --no-print-directory --silent #
  • driver/

    r2a75572 r9507ce3  
    1010// Created On       : Tue Aug 20 13:44:49 2002
    1111// Last Modified By : Peter A. Buhr
    12 // Last Modified On : Mon Sep  3 16:47:59 2018
    13 // Update Count     : 275
     12// Last Modified On : Fri Sep 14 23:02:59 2018
     13// Update Count     : 277
    114114        bool std_flag = false;                                                          // -std= flag
    115115        bool noincstd_flag = false;                                                     // -no-include-stdhdr= flag
    116         bool xflag = false;                                                                     // user supplied -x flag
    117116        bool debugging __attribute(( unused )) = false;         // -g flag
    118117        bool m32 = false;                                    // -m32 flag
    291290                        } // if
    292291                        nonoptarg = true;
    293                         xflag = false;
    294292                } // if
    295293        } // for
    297     args[nargs] = "-x";                                 // turn off language
     295    args[nargs] = "-x";                                                                 // turn off language
    298296    nargs += 1;
    299297    args[nargs] = "none";
  • libcfa/src/time.hfa

    r2a75572 r9507ce3  
    1010// Created On       : Wed Mar 14 23:18:57 2018
    1111// Last Modified By : Peter A. Buhr
    12 // Last Modified On : Sat Aug 11 13:55:33 2018
    13 // Update Count     : 642
     12// Last Modified On : Sat Sep 22 12:25:34 2018
     13// Update Count     : 643
    2323#include <sys/time.h>                                                                   // timeval
    25 #include <time_t.hfa>                                                                           // Duration/Time types
     25#include <time_t.hfa>                                                                   // Duration/Time types
    2727enum { TIMEGRAN = 1_000_000_000LL };                                    // nanosecond granularity, except for timeval
    105105        timeval ?=?( timeval & t, zero_t ) { return t{ 0 }; }
    106         timeval ?+?( timeval & lhs, timeval rhs ) { return (timeval)@{ lhs.tv_sec + rhs.tv_sec, lhs.tv_usec + rhs.tv_usec }; }
    107         timeval ?-?( timeval & lhs, timeval rhs ) { return (timeval)@{ lhs.tv_sec - rhs.tv_sec, lhs.tv_usec - rhs.tv_usec }; }
     106        timeval ?+?( timeval lhs, timeval rhs ) { return (timeval)@{ lhs.tv_sec + rhs.tv_sec, lhs.tv_usec + rhs.tv_usec }; }
     107        timeval ?-?( timeval lhs, timeval rhs ) { return (timeval)@{ lhs.tv_sec - rhs.tv_sec, lhs.tv_usec - rhs.tv_usec }; }
    108108        bool ?==?( timeval lhs, timeval rhs ) { return lhs.tv_sec == rhs.tv_sec && lhs.tv_usec == rhs.tv_usec; }
    109109        bool ?!=?( timeval lhs, timeval rhs ) { return lhs.tv_sec != rhs.tv_sec || lhs.tv_usec != rhs.tv_usec; }
    120120        timespec ?=?( timespec & t, zero_t ) { return t{ 0 }; }
    121         timespec ?+?( timespec & lhs, timespec rhs ) { return (timespec)@{ lhs.tv_sec + rhs.tv_sec, lhs.tv_nsec + rhs.tv_nsec }; }
    122         timespec ?-?( timespec & lhs, timespec rhs ) { return (timespec)@{ lhs.tv_sec - rhs.tv_sec, lhs.tv_nsec - rhs.tv_nsec }; }
     121        timespec ?+?( timespec lhs, timespec rhs ) { return (timespec)@{ lhs.tv_sec + rhs.tv_sec, lhs.tv_nsec + rhs.tv_nsec }; }
     122        timespec ?-?( timespec lhs, timespec rhs ) { return (timespec)@{ lhs.tv_sec - rhs.tv_sec, lhs.tv_nsec - rhs.tv_nsec }; }
    123123        bool ?==?( timespec lhs, timespec rhs ) { return lhs.tv_sec == rhs.tv_sec && lhs.tv_nsec == rhs.tv_nsec; }
    124124        bool ?!=?( timespec lhs, timespec rhs ) { return lhs.tv_sec != rhs.tv_sec || lhs.tv_nsec != rhs.tv_nsec; }
  • src/CodeTools/

    r2a75572 r9507ce3  
    204204                /// ensures type inst names are uppercase
    205205                static void ti_name( const std::string& name, std::stringstream& ss ) {
     206                        // replace built-in wide character types with named types
     207                        if ( name == "char16_t" || name == "char32_t" || name == "wchar_t" ) {
     208                                ss << "#" << name;
     209                                return;
     210                        }
     212                        // strip leading underscore
    206213                        unsigned i = 0;
    207214                        while ( i < name.size() && name[i] == '_' ) { ++i; }
    210217                                return;
    211218                        }
    212                         ss << (char)std::toupper( static_cast<unsigned char>(name[i]) )
    213                            << (name.c_str() + i + 1);
     220                        std::string stripped = name.substr(i);
     221                        // strip trailing "_generic_" from autogen names (avoids some user-generation issues)
     222                        char generic[] = "_generic_"; size_t n_generic = sizeof(generic) - 1;
     223                        if ( stripped.size() >= n_generic
     224                                        && stripped.substr( stripped.size() - n_generic ) == generic ) {
     225                                stripped.resize( stripped.size() - n_generic );
     226                        }
     228                        // uppercase first character
     229                        ss << (char)std::toupper( static_cast<unsigned char>(stripped[0]) )
     230                           << (stripped.c_str() + 1);
    214231                }
    304321                        }
    306                         // TODO support VarArgsType
     323                        // TODO support variable args for functions
     324                        void previsit( VarArgsType* ) {
     325                                // only include varargs for top level (argument type)
     326                                if ( depth == 0 ) { ss << "#$varargs"; }
     327                        }
    308329                        // replace 0 and 1 with int
    397418                        }
     420                        /// Handle already-resolved variables as type constants
     421                        void previsit( VariableExpr* expr ) {
     422                                PassVisitor<TypePrinter> tyPrinter{ closed, ss };
     423                                expr->var->get_type()->accept( tyPrinter );
     424                                visit_children = false;
     425                        }
    399427                        /// Calls handled as calls
    400428                        void previsit( UntypedExpr* expr ) {
    426454                        }
    428                         /// Already-resolved calls skipped
    429                         void previsit( ApplicationExpr* ) {
     456                        /// Already-resolved calls reduced to their type constant
     457                        void previsit( ApplicationExpr* expr ) {
     458                                PassVisitor<TypePrinter> tyPrinter{ closed, ss };
     459                                expr->result->accept( tyPrinter );
    430460                                visit_children = false;
    431461                        }
    532562                                for ( Initializer* it : li->initializers ) {
    533563                                        build( it, ss );
    534                                         ss << ' ';
    535564                                }
    536565                        }
    539568                /// Adds an object initializer to the list of expressions
    540569                void build( const std::string& name, Initializer* init, std::stringstream& ss ) {
    541                         ss << "$constructor( ";
     570                        ss << "$constructor( &";
    542571                        rp_name( name, ss );
    543                         ss << "() ";
     572                        ss << ' ';
    544573                        build( init, ss );
    545574                        ss << ')';
    676705                }
     707                void previsit( AsmStmt* ) {
     708                        // skip asm statements
     709                        visit_children = false;
     710                }
    678712                void previsit( Expression* expr ) {
    679713                        std::stringstream ss;
    686720                /// Print non-prelude global declarations for resolv proto
    687721                void printGlobals() const {
    688                         std::cout << "#ptr<T> $addr T" << std::endl;  // &?
     722                        std::cout << "#$ptr<T> $addr T" << std::endl;  // &?
    689723                        int i = (int)BasicType::SignedInt;
    690724                        std::cout << i << " $and " << i << ' ' << i << std::endl;  // ?&&?
  • src/SynTree/

    r2a75572 r9507ce3  
    1010// Created On       : Mon May 18 07:44:20 2015
    1111// Last Modified By : Andrew Beach
    12 // Last Modified On : Fri Jul 14 14:50:00 2017
    13 // Update Count     : 29
     12// Last Modified On : Fri Spt 28 14:49:00 2018
     13// Update Count     : 30
    2020#include "Constant.h"
     21#include "Expression.h" // for ConstantExpr
    2122#include "Type.h"    // for BasicType, Type, Type::Qualifiers, PointerType
    4849Constant Constant::from_double( double d ) {
    4950        return Constant( new BasicType( Type::Qualifiers(), BasicType::Double ), std::to_string( d ), d );
     53Constant Constant::from_string( std::string const & str ) {
     54        return Constant(
     55                new ArrayType(
     56                        noQualifiers,
     57                        new BasicType( Type::Qualifiers( Type::Const ), BasicType::Char ),
     58                        new ConstantExpr( Constant::from_int( str.size() + 1 /* \0 */ )),
     59                        false, false ),
     60                std::string("\"") + str + "\"", (unsigned long long int)0 );
  • src/SynTree/Constant.h

    r2a75572 r9507ce3  
    99// Author           : Richard C. Bilson
    1010// Created On       : Mon May 18 07:44:20 2015
    11 // Last Modified By : Peter A. Buhr
    12 // Last Modified On : Sat Jul 22 09:54:46 2017
    13 // Update Count     : 17
     11// Last Modified By : Andrew Beach
     12// Last Modified On : Fri Spt 28 14:48:00 2018
     13// Update Count     : 18
    5151        /// generates a floating point constant of the given double
    5252        static Constant from_double( double d );
     53        /// generates an array of chars constant of the given string
     54        static Constant from_string( std::string const & s );
    5456        /// generates a null pointer value for the given type. void * if omitted.
  • tests/.expect/forctrl.txt

    r2a75572 r9507ce3  
    2222(0 0)(1 1)(2 2)(3 3)(4 4)(5 5)(6 6)(7 7)(8 8)(9 9)
    2323(0 0)(1 1)(2 2)(3 3)(4 4)(5 5)(6 6)(7 7)(8 8)(9 9)
     24(0 0)(1 1)(2 2)(3 3)(4 4)(5 5)(6 6)(7 7)(8 8)(9 9)
  • tests/concurrent/coroutineYield.c

    r2a75572 r9507ce3  
    11#include <fstream.hfa>
    2 #include <kernel.hfa>hfa>
     2#include <kernel.hfa>
    33#include <stdlib.hfa>
    44#include <thread.hfa>
  • tests/concurrent/preempt.c

    r2a75572 r9507ce3  
    1 #include <kernel.hfa>hfa>
     1#include <kernel.hfa>
    22#include <thread.hfa>
    33#include <time.hfa>
  • tests/concurrent/signal/block.c

    r2a75572 r9507ce3  
    99#include <fstream.hfa>
    10 #include <kernel.hfa>hfa>
     10#include <kernel.hfa>
    1111#include <monitor.hfa>
    1212#include <stdlib.hfa>
  • tests/concurrent/signal/disjoint.c

    r2a75572 r9507ce3  
    11#include <fstream.hfa>
    2 #include <kernel.hfa>hfa>
     2#include <kernel.hfa>
    33#include <monitor.hfa>
    44#include <thread.hfa>
  • tests/concurrent/signal/wait.c

    r2a75572 r9507ce3  
    77#include <fstream.hfa>
    8 #include <kernel.hfa>hfa>
     8#include <kernel.hfa>
    99#include <monitor.hfa>
    1010#include <stdlib.hfa>
  • tests/forctrl.c

    r2a75572 r9507ce3  
    1010// Created On       : Wed Aug  8 18:32:59 2018
    1111// Last Modified By : Peter A. Buhr
    12 // Last Modified On : Thu Aug 30 17:12:12 2018
    13 // Update Count     : 43
     12// Last Modified On : Tue Sep 25 17:43:47 2018
     13// Update Count     : 44
    6060        for ( S s = (S){0}; s < (S){10,10}; s += (S){1} ) { sout | s; } sout | endl;
    61 //      for ( s; (S){10,10} ) { sout | s; } sout | endl;
     61        for ( s; (S){10,10} ) { sout | s; } sout | endl;
    6262        for ( s; (S){0} ~ (S){10,10} ) { sout | s; } sout | endl;
    6363        for ( s; (S){0} ~ (S){10,10} ~ (S){1} ) { sout | s; } sout | endl;
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