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    Syntax-Directed Translation and Intermediate Representations Notes for GATE CS

    Syntax-Directed Translation and Intermediate Representations notes for GATE CS: 47 study cards covering concepts, formulas, shortcuts and exam traps, plus sol

    syntax directed translation and intermediate representations notes

    Chapter Roadmap: Syntax-Directed Translation and IR

    Chapter Roadmap

    Your visual journey through the compiler's middle-end.

    Step 1: Syntax-Directed Definitions
    The Heavyweight (High Exam Yield)
    Attaching semantic rules to grammar. Inherited vs. Synthesized attributes. Dependency graphs.
    Step 2: Backpatching & Control Flow
    The Current Topic (Core Logic)
    Translating boolean logic and control structures (if, while) into Three-Address Code in a single pass.
    Step 3: Intermediate Representations
    The Formats (Direct Applications)
    Quadruples, Triples, and Indirect Triples. How the code is actually stored in memory.
    What you will master: Tracing how a high-level while loop is parsed and converted into low-level jump instructions without a second pass.

    The Forward Reference Problem in One-Pass Compilation

    The Forward Reference Problem

    When generating code for control structures like if or while, the compiler faces a dilemma in a single pass:

    if (x < y) {
      // ... 50 lines of code ...
    }
    // Target Line Unknown!

    The compiler evaluates x < y and needs to emit a jump for the false condition. But the target address (after the 50 lines) hasn't been generated yet.

    Two-Pass Compilation

    Pass 1 records block ends. Pass 2 generates code. Simple but slow and memory-heavy.

    Backpatching (One-Pass)

    Emit goto _ with a blank target. Record the location. "Patch" the address when the target is finally reached.

    The Backpatching Toolkit: Functions and Lists

    The Backpatching Toolkit

    To manage unresolved jumps, we use three core functions operating on linked lists of instruction indices.

    Function Signature Action
    makelist makelist(i) Creates a new list containing only index i. Returns pointer.
    merge merge(p1, p2) Concatenates lists p1 and p2. Returns pointer to combined list.
    backpatch backpatch(p, i) Fills blank target field of every instruction in list p with address i.
    Synthesized Attributes:
    B.truelist Jumps to execute when is true.
    B.falselist Jumps to execute when is false.
    S.nextlist Jumps to code immediately following statement .

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    Syntax-Directed Translation and Intermediate Representations Notes for GATE CS

    Syntax-Directed Translation and Intermediate Representations notes for GATE CS: 47 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice questions.

    Chapter Roadmap: Syntax-Directed Translation and IR

    Chapter Roadmap

    Your visual journey through the compiler's middle-end.

    Step 1: Syntax-Directed Definitions
    The Heavyweight (High Exam Yield)
    Attaching semantic rules to grammar. Inherited vs. Synthesized attributes. Dependency graphs.
    Step 2: Backpatching & Control Flow
    The Current Topic (Core Logic)
    Translating boolean logic and control structures (if, while) into Three-Address Code in a single pass.
    Step 3: Intermediate Representations
    The Formats (Direct Applications)
    Quadruples, Triples, and Indirect Triples. How the code is actually stored in memory.
    What you will master: Tracing how a high-level while loop is parsed and converted into low-level jump instructions without a second pass.

    The Forward Reference Problem in One-Pass Compilation

    The Forward Reference Problem

    When generating code for control structures like if or while, the compiler faces a dilemma in a single pass:

    if (x < y) {
      // ... 50 lines of code ...
    }
    // Target Line Unknown!

    The compiler evaluates x < y and needs to emit a jump for the false condition. But the target address (after the 50 lines) hasn't been generated yet.

    Two-Pass Compilation

    Pass 1 records block ends. Pass 2 generates code. Simple but slow and memory-heavy.

    Backpatching (One-Pass)

    Emit goto _ with a blank target. Record the location. "Patch" the address when the target is finally reached.

    The Backpatching Toolkit: Functions and Lists

    The Backpatching Toolkit

    To manage unresolved jumps, we use three core functions operating on linked lists of instruction indices.

    Function Signature Action
    makelist makelist(i) Creates a new list containing only index i. Returns pointer.
    merge merge(p1, p2) Concatenates lists p1 and p2. Returns pointer to combined list.
    backpatch backpatch(p, i) Fills blank target field of every instruction in list p with address i.
    Synthesized Attributes:
    B.truelist Jumps to execute when is true.
    B.falselist Jumps to execute when is false.
    S.nextlist Jumps to code immediately following statement .

    Translating Boolean Expressions

    Translating Basic Boolean Expressions

    For a relational expression , we generate two branch instructions with blank targets.

    B.truelist = makelist(nextquad)
    B.falselist = makelist(nextquad + 1)
    emit('if' E1.addr '<' E2.addr 'goto _')
    emit('goto _')

    Visualizing the TAC generated:

    Index Instruction Status
    100 if a < b goto _ Added to truelist
    101 goto _ Added to falselist

    The actual patching happens later when this Boolean expression is used inside a control structure.

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