Assertion failure at lib/Backend/NativeCodeGenerator.cpp:957

The debug build crashes due to assertion failure at lib/Backend/NativeCodeGenerator.cpp:957

PoC:
```
function func_0() {
var wasmCode = new Uint8Array([0,97,115,109,1,0,0,0,1,6,1,96,1,127,1,127,3,2,1,0,5,4,1,1,1,1,7,8,1,4,108,111,97,100,0,0,10,9,1,7,0,32,0,40,0,0,11,0,7,1,5,4,108,111,97,100]);
var wasmModule = new WebAssembly.Module(wasmCode);
for (var var_0 of [0, 12, 192]) {
var wasmInstance = new WebAssembly.Instance(wasmModule, { mod: { offset: var_0 } });
for (var var_2 = var_0 - 20; var_2 < var_0 + 20; var_2 += 4) {
if (var_2 >= 0)
wasmInstance.exports.load(var_2)
}
}
}
for(i = 0; i < 0x10000; i ++)
func_0();
```

Commit: e055dbb
Build Option: None
OS: Ubuntu 18.04.1 LTS
Arch: x86_64