Add LLVM codegen tests for new Rc implementation

Author: EFanZh

tests/codegen-llvm/lib-optimizations/array-of-dangling-weaks-uses-memset.rs

@@ -0,0 +1,16 @@
+// Ensures that we can create an array of `Weak`s using `memset`.
+
+//@ compile-flags: -Z merge-functions=disabled
+
+#![crate_type = "lib"]
+
+use std::rc;
+
+#[no_mangle]
+pub fn array_of_rc_weak() -> [rc::Weak<u32>; 100] {
+    // CHECK-LABEL: @array_of_rc_weak(
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: call void @llvm.memset.
+    // CHECK-NEXT: ret void
+    [(); 100].map(|()| rc::Weak::new())
+}

tests/codegen-llvm/lib-optimizations/option-rc-as-deref-no-cmp.rs

@@ -0,0 +1,16 @@
+// Ensures that we can acquire `Option<&T>` from `&Option<Rc<T>>` without checking for `None`.
+
+//@ compile-flags: -Z merge-functions=disabled
+
+#![crate_type = "lib"]
+
+use std::rc::Rc;
+
+#[no_mangle]
+pub fn option_rc_as_deref_no_cmp(rc: &Option<Rc<u32>>) -> Option<&u32> {
+    // CHECK-LABEL: @option_rc_as_deref_no_cmp(ptr
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: %[[RC:.+]] = load ptr, ptr %rc
+    // CHECK-NEXT: ret ptr %[[RC]]
+    rc.as_deref()
+}