Add test for alloca addrspacecast

Add a test to check that `alloca`s are casted to `addrspace(0)` before a
pointer to an `alloca` is used.

tests/codegen/amdgpu-addrspacecast.rs

@@ -0,0 +1,22 @@
+// Check that pointers are casted to addrspace(0) before they are used
+
+//@ compile-flags: --crate-type=rlib --target=amdgcn-amd-amdhsa -Ctarget-cpu=gfx900
+//@ needs-llvm-components: amdgpu
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "freeze"]
+trait Freeze {}
+#[lang = "copy"]
+trait Copy {}
+
+// CHECK-LABEL: @ref_of_local
+// CHECK: [[alloca:%[0-9]]] = alloca
+// CHECK: %i = addrspacecast ptr addrspace(5) [[alloca]] to ptr
+#[no_mangle]
+pub fn ref_of_local(f: fn(&i32)) {
+    let i = 0;
+    f(&i);
+}