Implement Function Inline Expansion

Inlining Removes Call Overhead

Function inlining replaces a call site with the callee's body, enabling further optimization across the old boundary. LLVM's inliner uses cost heuristics; C++ inline and LTO push this aggressively. Too much inlining blows code size.

When to Inline

Small callees, hot call sites, and functions marked always_inline are candidates. Copy parameters to locals, rename to avoid clashes, insert return handling at the call site.

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• Size budget prevents code bloat
• Recursive inlining needs depth limits
• Tail calls may not need full frame setup
• Inlining exposes constants to inter-procedural opts

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 function inline expansion on your IR. This exercise requires copying a callee's instructions to the call site, mapping arguments to parameters, and splicing the result back into the caller.