We designed Iago to be a drop-in replacement for Souper—a state-of-the-art superoptimizer for LLVM IR—we can perform a direct comparison between Iago’s synthesis by LLM and Souper’s synthesis by enumeration. We evaluated both Iago and Souper on a random sample of the synthesis problems encountered when optimizing the SPEC CPU 2017 benchmark suite. We found that while Iago finds 7.4% fewer optimizations than Souper does, 35.7% of the optimizations found by Iago were not found by Souper: most of these required synthesizing two or more new instructions and multiple fresh constants. Therefore, Iago’s ability to find more complex optimizations complements Souper’s completeness in finding simpler ones.