foo.ll

; ModuleID = 'foo0-8787f43e282added376259c1adb08b80.rs'
source_filename = "foo0-8787f43e282added376259c1adb08b80.rs"
target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
target triple = "wasm32-unknown-unknown"

; Function Attrs: nounwind
define void @test() unnamed_addr #0 {
start:
  %0 = call i32 @return_one()
  br label %bb1

bb1:                                              ; preds = %start
  %1 = icmp eq i32 %0, 1
  %2 = xor i1 %1, true
  br i1 %2, label %bb2, label %bb3

bb2:                                              ; preds = %bb1
  call void @panic()
  unreachable

bb3:                                              ; preds = %bb1
  %3 = xor i1 %2, true
  br i1 %3, label %bb4, label %bb5

bb4:                                              ; preds = %bb3
  call void @panic()
  unreachable

bb5:                                              ; preds = %bb3
  ret void
}

; Function Attrs: nounwind
declare i32 @return_one() unnamed_addr #0

; Function Attrs: noreturn nounwind
declare void @panic() unnamed_addr #1

attributes #0 = { nounwind }
attributes #1 = { noreturn nounwind }

foo.rs

extern {
    fn return_one() -> u32;
    fn panic() -> !;
}

#[no_mangle]
pub unsafe extern fn test() {
    let tmp: bool = !(return_one() == 1);
    if tmp { panic() }
    if !tmp { panic() }
}