add initial tests for placement new changes

Author: jwong101

Diff for: tests/codegen/placement-new.rs

@@ -0,0 +1,27 @@
+//@ compile-flags: -O
+#![crate_type = "lib"]
+
+// Test to check that types with "complex" destructors, but trivial `Default` impls
+// are constructed directly into the allocation in `Box::default` and `Arc::default`.
+
+use std::sync::Arc;
+
+// CHECK-LABEL: @box_default_inplace
+#[no_mangle]
+pub fn box_default_inplace() -> Box<(String, String)> {
+    // CHECK: [[ALLOCA:%.*]] = alloca
+    // CHECK: [[BOX:%.*]] = {{.*}}call {{.*}}__rust_alloc(
+    // CHECK: call void @llvm.memcpy.p0.p0.i64(ptr {{.*}}[[BOX]], ptr {{.*}}[[ALLOCA]]
+    // CHECK: ret ptr [[BOX]]
+    Box::default()
+}
+
+// CHECK-LABEL: @arc_default_inplace
+#[no_mangle]
+pub fn arc_default_inplace() -> Arc<(String, String)> {
+    // CHECK: [[ALLOCA:%.*]] = alloca
+    // CHECK: [[ARC:%.*]] = {{.*}}call {{.*}}__rust_alloc(
+    // CHECK: call void @llvm.memcpy.p0.p0.i64(
+    // CHECK: ret ptr [[ARC]]
+    Arc::default()
+}