WASM/WebAssembly bug when compiling with opt-level=0

[adiba]

extern {
    fn log_i32(val: i32);
}

#[no_mangle]
pub fn run() {
    let s = "Tre".as_bytes();
    let len = s.len();
    unsafe {
        log_i32(len as i32);
    }
}

This should yield 3. It however gives 0 when compiling with the following command:
rustc +nightly -C opt-level=0 --target wasm32-unknown-unknown --crate-type=cdylib src/main.rs
Any opt-level above 0 is fine though. (eg rustc +nightly -C opt-level=1 --target wasm32-unknown-unknown --crate-type=cdylib src/main.rs)

The fat pointer of s contains the correct length in memory, just the len method returns the wrong value.
I only have access to the mangled opt-level=0 WAT so I cannot investigate what WASM or LLVM-IR is doing there.

[alexcrichton]

I'm gona close this in favor of #46367 as I believe it's the same issue as that, but thanks for the report!