1 February 17, 2016 1 February 17, 2016February 17, 2016February 17, 2016 Azusa, CA Sheldon X. Liang Ph. D. Computer Science at Azusa Pacific University

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May 4, 20231

May 4, 2023May 4, 2023 Azusa, CAAzusa, CA

Sheldon X. Liang Ph. D.

Computer Science at Computer Science at Azusa Pacific UniversityAzusa Pacific University

Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278 Department of Computer Science, http://www.apu.edu/clas/computerscience/

CS400 Compiler ConstructionCS400 Compiler Construction

http://www.apu.edu/clas/computerscience/

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Static Checking and Type Systems

COP5621 Compiler ConstructionCopyright Robert van Engelen, Florida State University, 2007

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CS@APU: CS400 Compiler ConstructionCS@APU: CS400 Compiler Construction

Semantic Analysis


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The Structure of our Compiler Revisited

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Keep in mind following questionsKeep in mind following questions

• Semantic Checking– Static– Dynamic– One/multi pass checking

• Type expressions– Graph representations– Name equivalence – Structural equivalence

• Constructing graphs by Yacc– Construct type nodes– SDD – attributed type production – Yacc: auto tool for constructing

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Static versus Dynamic Checking

• Static checking: the compiler enforces programming language’s static semantics– Program properties that can be checked at compile

time• Dynamic semantics: checked at run time

– Compiler generates verification code to enforce programming language’s dynamic semantics

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Static Checking

• Typical examples of static checking are– Type checks– Flow-of-control checks– Uniqueness checks– Name-related checks

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Type Checks, Overloading, Coercion, and Polymorphism

int op(int), op(float);int f(float);int a, c[10], d;

d = c+d; // FAIL --> access c as an address*d = a; // FAIL --> d is not pointera = op(d); // OK: overloading (C++)a = f(d); // OK: coersion of d to floatvector<int> v; // OK: template instantiation

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• Type conversion is explicit, for example using type casts• Type coercion is implicitly performed by the compiler


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Flow-of-Control Checks

myfunc(){ … break; // ERROR}

myfunc(){ … switch (a) { case 0: … break; // OK case 1: … }}

myfunc(){ … while (n) { … if (i>10) break; // OK }}

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Uniqueness Checks

myfunc(){ int i, j, i; // ERROR …}

struct myrec{ int name;};struct myrec // ERROR{ int id;};

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cnufym(int a, int a) // ERROR{ …}


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Name-Related Checks

LoopA: for (int I = 0; I < n; I++) { … if (a[I] == 0) break LoopB; // Java labeled loop … }

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One-Pass versus Multi-Pass Static Checking

• One-pass compiler: static checking for C, Pascal, Fortran, and many other languages is performed in one pass while intermediate code is generated– Influences design of a language: placement constraints

• Multi-pass compiler: static checking for Ada, Java, and C# is performed in a separate phase, sometimes by traversing the syntax tree multiple times

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Type Expressions

• Type expressions are used in declarations and type casts to define or refer to a type– Primitive types, such as int and bool– Type constructors, such as pointer-to, array-of,

records and classes, templates, and functions– Type names, such as typedefs in C and named

types in Pascal, refer to type expressions

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Graph Representations for Type Expressions

int *f(char*,char*)

fun

args pointer

char

intpointer

char

pointer

Tree forms

fun

args pointer

char

intpointer

DAGsMay 4, 2023

13Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278 Department of Computer Science, http://www.apu.edu/clas/computerscience/


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Cyclic Graph Representations

struct Node{ int val; struct Node *next;};

struct

val

pointerint

Cyclic graph

next

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Name Equivalence

• Each type name is a distinct type, even when the type expressions the names refer to are the same

• Types are identical only if names match• Used by Pascal (inconsistently)

type link = ^node;var next : link; last : link; p : ^node; q, r : ^node;

With name equivalence in Pascal:p ≠ nextp ≠ lastp = q = rnext = last

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Structural Equivalence of Type Expressions

• Two types are the same if they are structurally identical

• Used in C, Java, C#

=

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Structural Equivalence of Type Expressions (cont’d)

• Two structurally equivalent type expressions have the same pointer address when constructing graphs by sharing nodes

struct Node{ int val; struct Node *next;};struct Node s, *p;

… p = &s; // OK… *p = s; // OK

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Constructing Type Graphs in Yacc

Type *mkint() construct int node if not alreadyconstructed

Type *mkarr(Type*,int) construct array-of-type nodeif not already constructed

Type *mkptr(Type*) construct pointer-of-type nodeif not already constructed

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Syntax-Directed Definitions for Constructing Type Graphs in Yacc%union{ Symbol *sym; int num; Type *typ;}%token INT%token <sym> ID%token <int> NUM%type <typ> type%%decl : type ID { addtype($2, $1); } | type ID ‘[’ NUM ‘]’ { addtype($2, mkarr($1, $4)); } ;type : INT { $$ = mkint(); } | type ‘*’ { $$ = mkptr($1); } | /* empty */ { $$ = mkint(); } ;

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Got it with following questionsGot it with following questions

• Semantic Checking– Static– Dynamic– One/multi pass checking

• Type expressions– Graph representations– Name equivalence – Structural equivalence

• Constructing graphs by Yacc– Construct type nodes– SDD – attributed type production – Yacc: auto tool for constructing


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Thank you very much!

Questions?

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Documents

1 February 17, 2016 1 February 17, 2016February 17, 2016February 17, 2016 Azusa, CA Sheldon X. Liang Ph. D. Computer Science at Azusa Pacific University