64 bit shift is broken in nightly build for MIPS

[mcroomp]

I tried this code:

const SHIFTVALUE : i64 = 10000000000i64;

fn main() {

    fn shiftleft(a : i64, b : i64) -> i64 {
        a << b
    }

    assert_eq!(shiftleft(black_box(SHIFTVALUE), black_box(2)), SHIFTVALUE << 2);
}

Nightly fails running on MIPS emulator

assertion left == right failed
left: 35705032704
right: 40000000000

Stable succeeds

Looks like the top and bottom dwords are mixed up

target is mips-unknown-linux-musl
emulator is qemu-mips-static

[nikic]

This is probably related to llvm/llvm-project#64794.

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium