Synthesized & Inherited Attributes Evaluation

Lecture 33 of CS606 Compiler Construction explores evaluation strategies for attribute grammars based on their dependency graphs. A Dependency Graph is a directed graph that depicts the flow of information between attribute instances: an edge from node a to node b indicates that attribute b depends on the value of attribute a, requiring a to be evaluated first. If the dependency graph contains a directed cycle, the grammar is circular and cannot be evaluated. Students examine two well-behaved classes of SDDs: S-Attributed definitions, where every attribute is synthesized, allowing all semantic rules to be evaluated naturally during bottom-up LR reduction passes; and L-Attributed definitions, where inherited attributes depend strictly on attributes of parents or left siblings, permitting evaluation in a single depth-first left-to-right tree traversal pass. The curriculum systematically bridges abstract automata theory with concrete systems programming techniques and modern compiler construction tools. Reviewing the accompanying lecture handouts and structural diagrams reinforces understanding of symbol tables, semantic type checking, and runtime memory layouts. Consistent evaluation of grammatical derivations, item closure sets, and shift-reduce actions ensures robust preparation for academic assessments. Students investigate the role of intermediate representations in decoupling front-end language syntax from target machine instruction architectures. The discussion highlights how syntax-directed definitions associate computable semantic attributes with context-free production rules. Key concepts such as viable prefixes, handle pruning, and parser stack configurations are analyzed to understand deterministic bottom-up parsing. The lecture details algorithmic subset construction and Hopcroft state minimization to produce space-efficient deterministic finite automata. Control flow graph analysis is demonstrated to partition linear three-address instruction sequences into maximal basic blocks. Directed acyclic graph representations provide deterministic frameworks for common subexpression elimination and local code optimization. Data flow equations and backward liveness analysis are formulated to determine the exact variable live ranges required for optimal register allocation. Automated compiler generation utilities such as Lex and YACC are presented as indispensable instruments for industrial language processing. Top-down and bottom-up parsing techniques are contrasted regarding grammatical expressive power, lookahead requirements, and implementation complexity.