IR `cast` from i32 to u32 produces MASM that does not support full u32 range

[Denys Zadorozhnyi]

Discovered in #49

Rust <= (le) op on u32 values compiles to the following IR:

module noname

const $0 = 0x00100000;

global external @__stack_pointer : i32 = $0 { id = 0 };
global external @gv1 : i32 = $0 { id = 1 };
global external @gv2 : i32 = $0 { id = 2 };

pub fn entrypoint(i32, i32) -> i32 {
block0(v0: i32, v1: i32):
    v3 = cast v0 : u32;
    v4 = cast v1 : u32;
    v5 = lt v3, v4 : i1;
    v6 = cast v5 : i32;
    br block1(v6);

block1(v2: i32):
    ret v2;
}

Which then generates the following MASM:

export.entrypoint
  dup.0
  push.2147483648
  u32.and
  eq.2147483648
  assertz
  swap.1
  dup.0
  push.2147483648
  u32.and
  eq.2147483648
  assertz
  u32.lt.checked

end
begin
    exec.entrypoint
end

Which fails on assert in VM in proptest with minimal example of (0, 2147483648).

EDIT: see commented test reproducing this issue in #49 in instructions.rs (any comparison test for u32).

[Denys Zadorozhnyi]

Nevermind. I did not convert the op result(u64) to the expected type (u32).