Add codegen test for remainder match

tests/codegen-llvm/issues/rem-match-unreachable.rs

@@ -0,0 +1,32 @@
+// Matching every possible result of `x % 5` should not keep unreachable
+// fallback panic code.
+
+//@ compile-flags: -Copt-level=3
+//@ only-64bit
+
+#![crate_type = "lib"]
+
+unsafe extern "C" {
+    fn rem_arm0(x: usize) -> usize;
+    fn rem_arm1(x: usize) -> usize;
+    fn rem_arm2(x: usize) -> usize;
+    fn rem_arm3(x: usize) -> usize;
+    fn rem_arm4(x: usize) -> usize;
+}
+
+// CHECK-LABEL: @rem_match_unreachable
+// CHECK-NOT: core::panicking::panic
+// CHECK-NOT: entered unreachable code
+#[no_mangle]
+pub fn rem_match_unreachable(x: usize) -> usize {
+    unsafe {
+        match x % 5 {
+            0 => rem_arm0(x),
+            1 => rem_arm1(x),
+            2 => rem_arm2(x),
+            3 => rem_arm3(x),
+            4 => rem_arm4(x),
+            _ => unreachable!(),
+        }
+    }
+}