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Compiler Construction

Compiler Construction. Objectives. Given a context-free grammar, G, and the grammar-independent functions for a recursive-descent parser, complete the recursive-descent parser by adding the grammar-dependent functions.

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Compiler Construction

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  1. Compiler Construction

  2. Objectives • Given a context-free grammar, G, and the grammar-independent functions for a recursive-descent parser, complete the recursive-descent parser by adding the grammar-dependent functions. • Given naive intermediate code for a C loop, hand-optimize the code, reducing by at least 20% the number of intermediate code instructions needed while maintaining semantic correctness of the program. • Define "register assignment" in the context of a compiler. Explain why register assignment is an important compiler optimization.

  3. Compiler Tasks Code Generation Tokens Source Intermediate Intermediate Lexor Parser Optimizer Assembler or Binary or Source

  4. CFGs: Example Simplified description of English grammar: G = S  NP VP NP  N | Adj NP N car | dog Adj big | green VP  V | V NP V is | eats Example derivation: S G NP VP G Adj NP VP G Adj N VP G Adj N V G Adj N eatsGbig N eatsGbigdogeats Production form: LHS = variable. RHS = string of variables and/or terminals.

  5. CFGs: Formal Definition G = (V, S, P, S) V = variables a finite set S = alphabet or terminals a finite set P = productions a finite set S = start variable SV Productions’ form, where AV, a(VS)*: • A  a

  6. CFGs: Example 1 {anbn | n0} S e | a S b Formally: G = ({S}, {a,b}, {S e, S a S b}, S)

  7. CFGs & CFLs: Example 2 all strings of balanced parentheses A core idea of most programming languages. P e | ( P ) | P P

  8. CFGs: Example 2 Language of Assignment Statements P  S P P  S S  id = E; E  expressions (expressions left as “exercise”)

  9. Example Languages • Set of strings over {a,b} with an even number of a’s • Arithmetic expressions using +, *, /, -, (,) Assume that all operands are called “id”

  10. Recursive Descent Parser • Built from a context-free grammar • Simple rules build recursive program • Grammar independent part (see pdf file) • Grammar dependent • Include a function for each non-terminal (lhs) • Generate code for each rule, left to right • “Call” non-terminals • “Match” terminals • Use if statement to choose between multiple rules with the same lhs (non-terminal) symbol

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