Compilation Phases & Parse Trees

Lecture 3 of CS606 Compiler Construction investigates the graphical representations used by compilers to model program structure during translation. The lecture demonstrates how grammatical derivations are represented as hierarchical trees: concrete parse trees and compact Abstract Syntax Trees (AST). In a concrete parse tree, every terminal and non-terminal grammar symbol is explicitly represented, preserving exact grammatical derivation steps. In contrast, an Abstract Syntax Tree retains only essential syntactic operators and operands, stripping redundant punctuation and parentheses to provide a streamlined representation for semantic analysis and intermediate code generation. Students examine the central role of the Symbol Table as a shared database that records variable identifiers, data types, scope depths, memory offsets, and function signatures across all compilation phases. The lecture traces how semantic analysis annotates the syntax tree with type information, paving the way for linear three-address intermediate code. 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. Shift-reduce and reduce-reduce grammatical conflicts are analyzed alongside operator precedence declarations to eliminate parsing ambiguities. The curriculum traces the progressive transformation of source text through tokens, parse trees, abstract syntax trees, and linear three-address tuples. Practical considerations for short-circuit boolean evaluation and label backpatching provide rigorous quantitative decision support for control flow compilation. Scholars examine how type checking systems enforce static semantic consistency across arithmetic expressions, assignments, and function signatures. Memory management techniques spanning static allocation, stack-based activation records, and heap allocation are evaluated in detail. The lesson explores register allocation heuristics, demonstrating how Chaitin graph coloring minimizes memory spills in CPU register starved environments. Quadruple, triple, and indirect triple data structures are compared regarding memory overhead and ease of compiler instruction reordering. Students study intermediate code generation for multidimensional array references, evaluating base addresses and row-major displacement calculations. Key compiler optimization passes spanning loop invariant code motion, constant folding, and dead code elimination are systematically demystified.