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Overview of Compilation The Compiler BACK End

Overview of Compilation The Compiler BACK End. COP4620 – Programming Language Translators Dr. Manuel E. Bermudez. Analyze static semantics : V ariables declared before they are used ? Assignment compatibility? e.g ., a :=3 Operator type compatibility ? e.g., a+3

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Overview of Compilation The Compiler BACK End

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  1. Overview of CompilationThe Compiler BACK End COP4620 – Programming Language Translators Dr. Manuel E. Bermudez Translators

  2. Analyze static semantics: Variables declared before they are used ? Assignment compatibility? e.g., a:=3 Operator type compatibility ? e.g., a+3 Do actual and formal parameter types match? e.g. intf(int n, char c) {…} ... f('x', 3); Enforcement of scope rules. PHASE 3: Contextual Constraint Analysis Translators

  3. Traverse the tree recursively Deduce type information at the bottom, Pass type information up the tree. Each node verifies the types below. Make use of a DECLARATION TABLE, to keep track of names and their meaning. Contextual Constraint Analysis Translators

  4. Enter x into the DCLN table, with its type. Check type compatibility for x=5. x2 not declared! Verify type of ’>’ is boolean. Check type compatibility for ‘+’. Check type compatibility between x and int, for assignment. Contextual Constraint Analysis Translators

  5. Goal: Convert syntax tree to target code. Target code could be: Machine language. Assembly language. Quadruples for a fictional machine: Label, opcode, operands (1 or 2) PHASE 4: code generation   Translators

  6. Tradeoffs: “gcc” generates assembly code. “javac” generates bytecodes, to be interpreted by the JVM. “gcc”: slow compilation, fast running code. “javac”: fast compilation, slow running code. Speed depends on implementation strategy, not the language ! Code Generation: Traverse the tree again. Code Generation Translators

  7. Code generation (stack machine) • Text Level 1 • Text Level 2 • Text Level 3 LOAD 5 STORE X LOAD X LOAD 10 BGT COND L1 L2 L1 LOAD X LOAD 1 BADD STORE X GOTO L3 L2 ... L3 Translators

  8. Reduce the size of the target program. Decrease the running time of the target. “Optimization” a misnomer. “Code improvement” ? Two types of optimization: Peephole optimization (local). Global optimization (improve loops, etc.). Code Optimization Translators

  9. LOAD 5 STORE X LOAD X is replaced with LOAD 5 STND X STND: Store non-destructive Code Optimization LOAD 5 STORE X LOAD X LOAD 10 BGT COND L1 L2 L1 LOAD X LOAD 1 BADD STORE X GOTO L3 L2 ... L3 Translators

  10. Summary Source Scanner Tokens Screener Tokens Error Routines Table Routines Parser Tree Constrainer Tree Code Generator Code Interpreter Input Output Translators

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