Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
A set of digital notes on Compiler Design, a course offered in the B.Tech III Year - I Sem program at Malla Reddy College of Engineering & Technology. The notes cover topics such as language translation, lexical analysis, syntax analysis, semantic analysis, intermediate code generation, and symbol tables. an initial understanding of language translators, knowledge of various techniques used in compiler construction, and the use of automated tools available in compilers construction.
Typology: Study notes
1 / 127
This page cannot be seen from the preview
Don't miss anything!
(Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‘A’ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad – 500100, Telangana State, INDIA.
S. No Unit Topic Page no 1 1 language processing system 1 2 1 Phases 0 f a Compiler 4 3 1 Automata^16 4 1 Lex-lexical Analyzer generator^19 5 2 Top down parsing^27 6 2 Bottom up parsing^40 7 2 LR Parsers^52 8 2 CALR PARSER^69 9 3 Intermediate code forms^75 10 3 Type Checking^81 11 3 Syntax Directed Translation^84 12 3 Symbol table^91 13 4 Activation Records^96 14 4 Code optimization^102 15 4 Common Sub Expression Elimination^103
Executing a program written n HLL programming language is basically of two parts. the source program must first be compiled translated into a object program. Then the results object program is loaded into a memory executed. ASSEMBLER : programmers found it difficult to write or read programs in machine language. They begin to use a mnemonic (symbols) for each machine instruction, which they would subsequently translate into machine language. Such a mnemonic machine language is now called an assembly language. Programs known as assembler were written to automate the translation of assembly language in to machine language. The input to an assembler program is called source program, the output is a machine language translation (object program). INTERPRETER : An interpreter is a program that appears to execute a source program as if it were machine language. Languages such as BASIC, SNOBOL, LISP can be translated using interpreters. JAVA also uses interpreter. The process of interpretation can be carried out in following phases.
Loader and Link-editor: Once the assembler procedures an object program, that program must be p laced into memory and executed. The assembler could place the object program directly in memory and transfer control to it, thereby causing the machine language program to be execute. This would waste core by leaving the assembler in memory while the user’s program was being executed. Also the programmer would have to retranslate his program with each execution, thus wasting translation time. To overcome this problems of wasted translation time and memory. System programmers developed another component called loader. “A loader is a program that places programs into memory and prepares them for execution.” It would be more efficient if subroutines could be translated into object form the loader could ”relocate” directly behind the user’s program. The task of adjusting programs o they may be placed in arbitrary core locations is called relocation. Relocation loaders perform four functions. TRANSLATOR A translator is a program that takes as input a program written in one language and produces as output a program in another language. Beside program translation, the translator performs another very important role, the error-detection. Any violation of d HLL specification would be detected and reported to the programmers. Important role of translator are: 1.Translating the hll program input into an equivalent ml program. 2.Providing diagnostic messages wherever the programmer violates specification of TYPE OF TRANSLATORS :-
Intermediate Code Generations: - An intermediate representation of the final machine language code is produced. This phase bridges the analysis and synthesis phases of translation. Code Optimization : - This is optional phase described to improve the intermediate code so that the output runs faster and takes less space. Code Generation:- The last phase of translation is code generation. A number of optimizations to Reduce the length of machine language program are carried out during this phase. The output of the code generator is the machine language program of the specified computer. Table Management (or) Book-keeping:- This is the portion to keep the names used by the program and records essential information about each. The data structure used to record this information called a ‘Symbol Table’. Error Handlers:- It is invoked when a flaw error in the source program is detected. The output of LA is a stream of tokens, which is passed to the next phase, the syntax analyzer or parser. The SA groups the tokens together into syntactic structure called as expression. Expression may further be combined to form statements. The syntactic structure can be regarded as a tree whose leaves are the token called as parse trees. The parser has two functions. It checks if the tokens from lexical analyzer, occur in pattern that are permitted by the specification for the source language. It also imposes on tokens a tree-like structure that is used by the sub-sequent phases of the compiler. Example , if a program contains the expression A+/B after lexical analysis this expression might appear to the syntax analyzer as the token sequence id+/id. On seeing the /, the syntax analyzer should detect an error situation, because the presence of these two adjacent binary operators violates the formulations rule of an expression. Syntax analysis is to make explicit the hierarchical structure of the incoming token stream by identifying which parts of the token stream should be grouped. Example, (A/B*C has two possible interpretations.) 1 - divide A by B and then multiply by C or 2 - multiply B by C and then use the result to divide A. Each of these two interpretations can be represented in terms of a parse tree. Intermediate Code Generation:- The intermediate code generation uses the structure produced by the syntax analyzer to create a stream of simple instructions. Many styles of intermediate code are
possible. One common style uses instruction with one operator and a small number of operands.The output of the syntax analyzer is some representation of a parse tree. The intermediate code generation phase transforms this parse tree into an intermediate language representation of the source program. Code Optimization:- This is optional phase described to improve the intermediate code so that the output runs faster and takes less space. Its output is another intermediate code program that does the same job as the original, but in a way that saves time and / or spaces. /* 1, Local Optimization:- There are local transformations that can be applied to a program to make an improvement. For example, If A > B goto L Goto L3 L2 : This can be replaced by a single statement If A < B goto L Another important local optimization is the elimination of common sub-expressions A := B + C + D E := B + C + F Might be evaluated as T1 := B + C A := T1 + D E := T1 + F Take this advantage of the common sub-expressions B + C. Loop Optimization:- Another important source of optimization concerns about increasing the speed of loops. A typical loop improvement is to move a computation that produces the same result each time around the loop to a point, in the program just before the loop is entered.*/ Code generator :- C produces the object code by deciding on the memory locations for data, selecting code to access each data and selecting the registers in which each computation is to be done. Many computers have only a few high speed registers in which computations can be performed quickly. A good code generator would attempt to utilize registers as efficiently as possible. Error Handing :- One of the most important functions of a compiler is the detection and reporting of errors in the source program. The error message should allow the programmer to determine exactly where the errors have occurred. Errors may occur in all or the phases of a compiler.
Code Generator Temp1: = id3 * 60. Id1:= id2 +temp Lexical Analyzer: The LA is the first phase of a compiler. Lexical analysis is called as linear analysis or scanning. In this phase the stream of characters making up the source program is read from left-to-right and grouped into tokens that are sequences of characters having a collective meaning. Upon receiving a ‘get next token’ command form the parser, the lexical analyzer reads the input character until it can identify the next token. The LA return to the parser representation for the token it has found. The representation will be an integer code, if the token is a simple construct such as parenthesis, comma or colon. LA may also perform certain secondary tasks as the user interface. One such task is striping out from the source program the commands and white spaces in the form of blank, tab and new line characters. Another is correlating error message from the compiler with the source program. Code Optimizer
Lexical Analysis Vs Parsing: Token, Lexeme, Pattern: Token: Token is a sequence of characters that can be treated as a single logical entity. Typical tokens are,
countable set of strings over some fixed alphabet. In language theory, the terms "sentence" and "word" are often used as synonyms for "string." The length of a string s, usually written |s|, is the number of occurrences of symbols in s. For example, banana is a string of length six. The empty string, denoted ε, is the string of length zero. Operations on strings The following string-related terms are commonly used:
Regular Expressions: Each regular expression r denotes a language L(r). Here are the rules that define the regular expressions over some alphabet Σ and the languages that those expressions denote:
Lexeme Token Name Attribute Value Any ws _ if if _ then then _ else _ Any id id pointer to table entry Any number number pointer^ to^ table entry < relop LT <= relop LE = relop ET < > relop NE TRANSITION DIAGRAM: Transition Diagram has a collection of nodes or circles, called states. Each state represents a condition that could occur during the process of scanning the input looking for a lexeme that matches one of several patterns .Edges are directed from one state of the transition diagram to another. each edge is labeled by a symbol or set of symbols.If we are in one state s, and the next input symbol is a, we look for an edge out of state s labeled by a. if we find such an edge ,we advance the forward pointer and enter the state of the transition diagram to which that edge leads. Some important conventions about transition diagrams are
As an intermediate step in the construction of a LA, we first produce a stylized flowchart, called a transition diagram. Position in a transition diagram, are drawn as circles and are called as states. The above TD for an identifier, defined to be a letter followed by any no of letters or digits.A sequence of transition diagram can be converted into program to look for the tokens specified by the diagrams. Each state gets a segment of code. Automata : Automation is defined as a system where information is transmitted and used for performing some functions without direct participation of man.
1. An automation in which the output depends only on the input is called automation without memory.
