Basic Block Analysis

Analyzing Block Structure

Basic blocks are straight-line code with single entry and exit. Analyses partition the CFG into blocks, then compute properties per block: predecessors, successors, dominators, loop membership. LLVM's LoopInfo and GCC's loop passes depend on this foundation.

Block-Level Facts

For each block: list of instructions, predecessor and successor sets, whether it is a loop header, whether it dominates its successors' join nodes.

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• Leaders define block boundaries
• Critical edge: pred has multiple succs and succ has multiple preds
• Loop header: block with back edge from descendant
• Block frequency estimates guide code layout

Connecting to real compilers

Production compilers embed this step inside a longer pipeline. GCC flows through cpp, cc1, assembly, and ld; Clang uses the driver, Sema, LLVM IR passes, and a target backend. LLVM bitcode, JVM bytecode, and WASM are other familiar IRs at the same layer. The exercise isolates one pass so you can test it alone before chaining it to the next stage.

Why for this exercise

You will implement basic block analysis on your CFG. This exercise requires identifying blocks, computing predecessor and successor lists, and preparing data structures for loop and dominance analyses.