saturating-float-casts test from rustc test suite is panicking

[bjorn3]

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `170141183460469231731687303715884105727`,
 right: `0`: run-time f32 -> i128', example/saturating-float-casts.rs:95:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /home/bjorn/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.38/src/backtrace/libunwind.rs:88
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
./test.sh: regel 59: 17537 Afgebroken              ./target/out/saturating_float_casts

cc #381

[bjorn3]

170141183460469231731687303715884105727 == 0x7fffffffffffffffffffffffffffffff

[bjorn3]

Reduced to:

// cranelift doesn't inline
fn black_box<T>(a: T) -> T {
    a
}

pub fn main() {
    assert_eq!(black_box(std::f32::NAN) as i128, 0);
}

[bjorn3]

Opened rust-lang/rust#65245

[bjorn3]

Implementing something like:

https://github.com/rust-lang/rust/blob/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/librustc_codegen_ssa/mir/rvalue.rs#L774-L901

should fix this.

Edit(2022-03-25): since moved to https://github.com/rust-lang/rust/blob/4a56cbec59903a830a5fc06c5c81956de4199584/compiler/rustc_codegen_ssa/src/traits/builder.rs#L207-L378

[bjorn3]

Removed from MVP milestone as this is just an edge case.