Control Flow Graphs (CFG) & Basic Block Partitioning

Lecture 43 of CS606 Compiler Construction explores Control Flow Graphs (CFG) and the algorithmic partitioning of intermediate code into Basic Blocks. A Basic Block is a sequence of consecutive three-address instructions in which control enters strictly at the first instruction and leaves strictly at the last instruction, with no branches or halting operations in the middle. Students master the Leader Identification algorithm: the first three-address instruction is a leader; any instruction that is the target of a conditional or unconditional jump is a leader; and any instruction that immediately follows a jump is a leader. Each basic block extends from one leader up to, but not including, the next leader. A Control Flow Graph CFG = (V, E) is constructed where vertices V are basic blocks and directed edges E represent possible control transfers between blocks. 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. By engaging with solved past papers by Moaaz and Waqar Siddhu, learners gain actionable insights into recurrent university exam questions. Interactive quiz assessments on VU SIGMA facilitate rapid knowledge verification and retention of critical compiler engineering terminology. Comprehensive coverage of IEEE and ACM curricula standards ensures learners communicate with technical precision across global systems engineering teams. Detailed analysis of machine code selection highlights the imperative of generating instruction sequences that maximize hardware pipeline throughput. Intermediate representation taxonomy categorizes structural formats into graphical ASTs, linear tuples, and hybrid tree-address models. The strategic role of peephole optimization is evaluated as a final localized pass to eliminate redundant loads, stores, and jumps. In this lecture, students examine formal language translation principles and architectural compiler pipelines to understand automated code generation. Through detailed theoretical derivations and algorithmic walkthroughs, the lesson explores lexical tokenization, grammatical parse trees, and syntax trees.