Implement Static Single Assignment (SSA) Form

SSA: One Assignment Per Variable

Static Single Assignment form gives each variable exactly one definition site, simplifying dataflow analysis. LLVM IR, GCC's SSA GIMPLE, and HotSpot's C1 IR all use SSA. The Cytron algorithm inserts phi-nodes at control-flow joins to merge values.

Converting to SSA

Rename each assignment to a fresh version: x becomes x1, x2. At join points after if/else, insert x3 = phi(x1, x2). Optimizations like constant propagation and dead code elimination become trivial on SSA.

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• Phi-nodes go at dominance frontiers of definitions
• SSA enables sparse dataflow analyses
• Destruction phase lowers phi to copies before codegen
• Each SSA name has a single reaching definition

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 convert your IR to static single assignment form. This exercise asks you to rename variables and insert phi-nodes at merge points so each SSA name is assigned exactly once.