This fixes bug 35064, though it needs a reduced testcase still.
ConstantExpr are not handled by FastISel.
Similar checks should be added inside WebAssemblyFastISel::selectSExt and WebAssemblyFastISel::selectZExt
Fixed in r319144, along with selectSExt and selectZExt, and I fixed a few other places that needed similar changes as well. Thanks!