add regression test for not memcpying padding bytes

1 files changed, 46 insertions, 0 deletions

diff --git a/tests/codegen/box-uninit-bytes.rs b/tests/codegen/box-uninit-bytes.rs
new file mode 100644
index 00000000000..732da0a1794
--- /dev/null
+++ b/tests/codegen/box-uninit-bytes.rs
@@ -0,0 +1,46 @@
+// compile-flags: -O
+#![crate_type = "lib"]
+
+use std::mem::MaybeUninit;
+
+// Boxing a `MaybeUninit` value should not copy junk from the stack
+#[no_mangle]
+pub fn box_uninitialized() -> Box<MaybeUninit<usize>> {
+    // CHECK-LABEL: @box_uninitialized
+    // CHECK-NOT: store
+    // CHECK-NOT: alloca
+    // CHECK-NOT: memcpy
+    // CHECK-NOT: memset
+    Box::new(MaybeUninit::uninit())
+}
+
+// https://github.com/rust-lang/rust/issues/58201
+#[no_mangle]
+pub fn box_uninitialized2() -> Box<MaybeUninit<[usize; 1024 * 1024]>> {
+    // CHECK-LABEL: @box_uninitialized2
+    // CHECK-NOT: store
+    // CHECK-NOT: alloca
+    // CHECK-NOT: memcpy
+    // CHECK-NOT: memset
+    Box::new(MaybeUninit::uninit())
+}
+
+#[repr(align(1024))]
+pub struct LotsaPadding(usize);
+
+// Boxing a value with padding should not copy junk from the stack
+#[no_mangle]
+pub fn box_lotsa_padding() -> Box<LotsaPadding> {
+    // CHECK-LABEL: @box_lotsa_padding
+    // CHECK-NOT: alloca
+    // CHECK-NOT: getelementptr
+    // CHECK-NOT: memcpy
+    // CHECK-NOT: memset
+    Box::new(LotsaPadding(42))
+}
+
+// Hide the `allocalign` attribute in the declaration of __rust_alloc
+// from the CHECK-NOT above, and also verify the attributes got set reasonably.
+// CHECK: declare {{(dso_local )?}}noalias noundef ptr @__rust_alloc(i{{[0-9]+}} noundef, i{{[0-9]+}} allocalign noundef) unnamed_addr [[RUST_ALLOC_ATTRS:#[0-9]+]]
+
+// CHECK-DAG: attributes [[RUST_ALLOC_ATTRS]] = { {{.*}} allockind("alloc,uninitialized,aligned") allocsize(0) {{(uwtable )?}}"alloc-family"="__rust_alloc" {{.*}} }