I can be 99.99999999% certain when I write an if statement like "if (x > 1) do y" that the compiler will turn that into the equivalent machine code. So, yes, unless I hit some crazy performance bottleneck, I'm not concerned about reviewing the machine code.
However, LLM outputs change with slight re-wording of prompts and with each new model release. I could hand write a test that says if x > 1 make sure y happens, but then what productivity was gained?