More on this - LLVM-IR has no official formal semantics and it's riddled with UB. RISC-V has a formal model in Sail, but it's an ISA so you throw away the structured control flow and types which we want for proving.
Wasm has different levels we can validate against - starting with W3C test suite, then later full verification against the SpecTec-generated Lean semantics so that we can drop our interpreter from the trusted base.