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UNIT-III

UNIT-III. By Mr. M. V. Nikum (B.E.I.T). Programming Language. Lexical and Syntactic features of a programming Language are specified by its grammar Language:- collection of valid sentences. Sentences: These are the sequence of words.

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UNIT-III

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  1. UNIT-III ByMr. M. V. Nikum (B.E.I.T)

  2. Programming Language • Lexical and Syntactic features of a programming Language are specified by its grammar • Language:- collection of valid sentences. • Sentences: These are the sequence of words. • Word:- Sequence of letters of graphic symbols. • The Language specified in this manner is called as formal Language.

  3. Programming Language Grammar • A formal Language is a set of rules which precisely specify the sentence of L. • Formal Grammar can be represented as :- • G= {∑ , NT, S, P} • ∑ set of terminals • NT set of non terminals • S Distinguished symbol (Starting symbol) • P set of productions.

  4. Terminal Symbol:- These are the symbols which can not further sub divided • Ex:- ∑= { a, b,c,d…….0,1,2,3……} • No terminal symbols:- These are the combination of terminal symbols which can be further sub divided. • Ex:- <A> or <Noun>

  5. Production :- It is called as re-writing rule • It can be represented as :- • Each production consists of a No terminal followed by an arrow (-) or equal to (=), followed by string of Non terminals and terminals • Ex:- A  b S  Aa

  6. Syntax Tree • A Graphical representation of any statement of a Language is called as syntax tree.

  7. id+id*id id

  8. Derivation • The replacement of Non terminal symbols according to the given production rule is called as derivation • Types of Derivation: • Leftmost derivation • Rightmost derivation

  9. Rules for English Language • <Sentence>  <NP><VP> • <NP>  <article><noun> • <VP>  <verb> • <VP>  <verb><adverb> • <article>  The • <noun>  student • <verb>  studies • <adverb>  hard • <adverb>  slowly

  10. Derivation • Structure Rules applied • <Sentence> • <NP><VP> (1) • <article><noun>< VP> (2) • <article><noun> <verb><adverb> (4) • The <noun> <verb><adverb> (5) • The student <verb> <adverb> (6) • The student studies <adverb> (7) • The student studies hard (8)

  11. Ex. Consider the full grammar, • E → E+E • E → E*E • E → id • Let us derive the string “ id + id * id”

  12. Using leftmost derivation:-

  13. Using Right most derivation:-

  14. Rules

  15. Required string is bbaa

  16. Derive the string • babbaaaba

  17. Required string is baab

  18. Reduction • It is the process of replacement of string or part of string by non terminal according to the production rule.

  19. Structure Rules applied • The student studies hard • <article> student studies hard (5) • <article><noun> studies hard (6) • <article><noun> <verb> hard (7) • <article><noun> <verb> <adverb> (8) • <NP> <verb> <adverb> (2) • <NP><VP> (4) • <Sentence> (1)

  20. Ambiguity of Grammar • The Grammar for a language is said to be ambiguous if there exists at least one string which can be generated (or, derived) in more than one way • i. e. there can be more than one leftmost derivations, more than one rightmost derivations & also more than one derivation trees associated with such a string.

  21. Ex. Consider the full grammar, • E → E+E • E → E*E • E → id • Let us derive the string “ id + id * id”

  22. id id

  23. Compiler

  24. Complier:- • These are the system programs which will automatically translate the High level language program in to the machine language program Target program / M/C Lang. Prog. Source program High level Lang. Prog. Compiler Database

  25. Cross Compiler:- • These are the system programs which will automatically translate the HLL program compatible with M/C A, in to the machine language program compatible with M/C A , but the underlying M/C is M/C B Target program / M/C Lang. Prog. Source program HLL Prog. Compatible with M/C A Cross Compiler M/C B

  26. P Code Compiler Source Program Compiler P-Code interpreter Obj Program Exexute P-Code interpreter

  27. Very similar in concept of Interpreter • In pseudo- code complier program is analyzed and converted into an intermediate form, which is then executed interpretively. • The source program is compiled, the resulted object program is in p-code. This p-code program is then read and executed under control of p-code interpreter.

  28. Compilation process overview • Compilation process is vast and complex. • Hence it is divided into a series of subtasks called as phases. • Each of which transform the source program form one representation to another. • The compilation process involves two major tasks.

  29. Compilation process overview Analysis of + Synthesis of = Translation source text Target text of prog in obj form

  30. Analysis of source text • Lexical Analysis (Scanner) • Syntax Analysis (Parser) • Semantic analysis. • Synthesis of target text • Storage allocation • Code generation

  31. Analysis of source text • Determine validity of source statement from the analysis view point. • Determine the content of source statement. • Construct the suitable representation of the source statement f0r use by the subsequent analysis phase or by the synthesis phase of compiler.

  32. Synthesis of target text • Memory allocation:- It is the simple task given to the presence of symbol table. The memory requirement of an identifier is computed from its length, type and dimension and memory is allocated to it. • Code generation:- the code generation uses the knowledge of target architecture , knowledge of instruction and also the addressing modes in the target computer to select the appropriate instruction.

  33. Synthesis of target text • The important issues in code generation are • Determine the space where the intermediate results should ne kept i.e. whether they should be kept in memory location or held in machine register. • Determine which instruction should be used for type conversion operation. • Determine which addressing mode should be used.

  34. Phase Structure of Compiler

  35. Code Optimization • This is an optional phase to improve the intermediate code so that ultimate object program can run faster and also take less phase. • The ultimate aim of this technique is to improve the execution efficiency of a program by • Eliminating redundancies • Rearranging the computation in the program with out affecting target machine.

  36. Code optimization techniques • Compile time evaluation • Elimination of common sub expressions • Frequency reduction • Strength reduction • Dead code elimination • Boolean sub expressions optimization • Local and Global optimization.

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