Invalid codegen for wasm at opt-level=0

[alexcrichton]

I've reported an upstream LLVM bug for this but I want to track it on our side as well to track pulling in the fix. The gist of the issue is that this code:

extern {
    fn return_one() -> u32;
    fn panic() -> !;
}

#[no_mangle]
pub unsafe extern fn test() {
    let tmp: bool = !(return_one() == 1);
    if tmp { panic() }
    if !tmp { panic() }
}

will execute successfully when compiled at O0:

<html>
  <head>
    <script>
const imports = {
  env: {
    return_one: function() { return 1; },
    panic: function() { throw 'bad'; }
  }
};
fetch('foo.wasm')
  .then(r => r.arrayBuffer())
  .then(r => WebAssembly.instantiate(r, imports))
  .then(m => {
    console.log('start');
    m.instance.exports.test()
    console.log('end');
  })
  .catch(e => console.error(e));
    </script>
  </head>
  <body>
  </body>
</html>

And it should certainly panic!

I'm currently hoping we can fix this upstream in LLVM before we need to work around it in rustc!