1 files changed, 28 insertions, 0 deletions
diff --git a/tests/codegen-llvm/box-default-debug-copies.rs b/tests/codegen-llvm/box-default-debug-copies.rs
new file mode 100644
index 00000000000..06cc41b21c0
--- /dev/null
+++ b/tests/codegen-llvm/box-default-debug-copies.rs
@@ -0,0 +1,28 @@
+//@ compile-flags: -Copt-level=0
+
+// Test to make sure that `<Box<T>>::default` does not create too many copies of `T` on the stack.
+// in debug mode. This regressed in dd0620b86721ae8cae86736443acd3f72ba6fc32 to
+// four `T` allocas.
+//
+// See https://github.com/rust-lang/rust/issues/136043 for more context.
+//
+// FIXME: This test only wants to ensure that there are at most two allocas of `T` created, instead
+// of checking for exactly two.
+
+#![crate_type = "lib"]
+
+#[allow(dead_code)]
+pub struct Thing([u8; 1000000]);
+
+impl Default for Thing {
+    fn default() -> Self {
+        Thing([0; 1000000])
+    }
+}
+
+// CHECK-COUNT-2: %{{.*}} = alloca {{.*}}1000000
+// CHECK-NOT: %{{.*}} = alloca {{.*}}1000000
+#[no_mangle]
+pub fn box_default_single_copy() -> Box<Thing> {
+    Box::default()
+}