1 files changed, 24 insertions, 0 deletions
diff --git a/tests/ui/numbers-arithmetic/overflowing-lsh-4.rs b/tests/ui/numbers-arithmetic/overflowing-lsh-4.rs
new file mode 100644
index 00000000000..1042bfcb34d
--- /dev/null
+++ b/tests/ui/numbers-arithmetic/overflowing-lsh-4.rs
@@ -0,0 +1,24 @@
+// build-fail
+// compile-flags: -C debug-assertions
+
+// This function is checking that our automatic truncation does not
+// sidestep the overflow checking.
+
+#![deny(arithmetic_overflow)]
+
+fn main() {
+    // this signals overflow when checking is on
+    let x = 1_i8 << 17;
+    //~^ ERROR: this arithmetic operation will overflow
+
+    // ... but when checking is off, the fallback will truncate the
+    // input to its lower three bits (= 1). Note that this is *not*
+    // the behavior of the x86 processor for 8- and 16-bit types,
+    // but it is necessary to avoid undefined behavior from LLVM.
+    //
+    // We check that here, by ensuring the result has only been
+    // shifted by one place; if overflow checking is turned off, then
+    // this assertion will pass (and the compiletest driver will
+    // report that the test did not produce the error expected above).
+    assert_eq!(x, 2_i8);
+}