Translate an AST into Your IR

Lowering AST to IR

Code generation traditionally walks the AST and emits IR instructions. Clang's CodeGenFunction::EmitStmt and LLVM's IRBuilder follow this pattern: recursive descent on the tree, emitting instructions as you return from subtrees. Expression results land in temporaries.

Post-Order Walk

For a + b, generate code for a and b first, obtaining operands, then emit t = a + b. For statements, emit side-effecting instructions in order. Control flow creates labels and conditional branches.

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• Each expression node yields an operand (temp, var, or const)
• Short-circuit && needs labels, not naive eager eval
• Declarations may emit alloca or variable binding
• Attach IR to function nodes, not just expressions

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 translate an AST into your IR by walking the tree and emitting instructions. This exercise requires implementing the lowering pass that converts expressions and statements into a linear instruction list.