Implement Loop Optimizations

Loops Are Hot Optimization Targets

Most execution time sits in loops. LLVM's loop vectorizer, LICM, and induction variable strength reduction target loop nests. GCC's -O3 unrolls and vectorizes inner loops. Recognizing loop headers and induction variables is the first step.

LICM and Strength Reduction

Loop-Invariant Code Motion hoists t = a + b outside the loop if a and b do not change per iteration. Strength reduction replaces i * 4 with additive induction ptr += 4.

cCopy
Loading…

• Loop header: target of back edge
• Induction variable increases by constant each iter
• Invariant test: operands defined outside loop body
• Unrolling duplicates body to reduce branch overhead

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 loop optimizations including invariant code motion. This exercise asks you to detect loops in your CFG and hoist or rewrite computations that do not change per iteration.