1 files changed, 74 insertions, 0 deletions
diff --git a/src/test/codegen/vec-in-place.rs b/src/test/codegen/vec-in-place.rs
new file mode 100644
index 000000000..62139aa9b
--- /dev/null
+++ b/src/test/codegen/vec-in-place.rs
@@ -0,0 +1,74 @@
+// min-llvm-version: 14.0
+// ignore-debug: the debug assertions get in the way
+// compile-flags: -O -Z merge-functions=disabled
+#![crate_type = "lib"]
+
+// Ensure that trivial casts of vec elements are O(1)
+
+pub struct Wrapper<T>(T);
+
+#[repr(C)]
+pub struct Foo {
+    a: u64,
+    b: u64,
+    c: u64,
+    d: u64,
+}
+
+// Going from an aggregate struct to another type currently requires Copy to
+// enable the TrustedRandomAccess specialization. Without it optimizations do not yet
+// reliably recognize the loops as noop for for repr(C) or non-Copy structs.
+#[derive(Copy, Clone)]
+pub struct Bar {
+    a: u64,
+    b: u64,
+    c: u64,
+    d: u64,
+}
+
+// CHECK-LABEL: @vec_iterator_cast_primitive
+#[no_mangle]
+pub fn vec_iterator_cast_primitive(vec: Vec<i8>) -> Vec<u8> {
+    // CHECK-NOT: loop
+    // CHECK-NOT: call
+    vec.into_iter().map(|e| e as u8).collect()
+}
+
+// CHECK-LABEL: @vec_iterator_cast_wrapper
+#[no_mangle]
+pub fn vec_iterator_cast_wrapper(vec: Vec<u8>) -> Vec<Wrapper<u8>> {
+    // CHECK-NOT: loop
+    // CHECK-NOT: call
+    vec.into_iter().map(|e| Wrapper(e)).collect()
+}
+
+// CHECK-LABEL: @vec_iterator_cast_unwrap
+#[no_mangle]
+pub fn vec_iterator_cast_unwrap(vec: Vec<Wrapper<u8>>) -> Vec<u8> {
+    // CHECK-NOT: loop
+    // CHECK-NOT: call
+    vec.into_iter().map(|e| e.0).collect()
+}
+
+// CHECK-LABEL: @vec_iterator_cast_aggregate
+#[no_mangle]
+pub fn vec_iterator_cast_aggregate(vec: Vec<[u64; 4]>) -> Vec<Foo> {
+    // FIXME These checks should be the same as other functions.
+    // CHECK-NOT: @__rust_alloc
+    // CHECK-NOT: @__rust_alloc
+    vec.into_iter().map(|e| unsafe { std::mem::transmute(e) }).collect()
+}
+
+// CHECK-LABEL: @vec_iterator_cast_deaggregate
+#[no_mangle]
+pub fn vec_iterator_cast_deaggregate(vec: Vec<Bar>) -> Vec<[u64; 4]> {
+    // FIXME These checks should be the same as other functions.
+    // CHECK-NOT: @__rust_alloc
+    // CHECK-NOT: @__rust_alloc
+
+    // Safety: For the purpose of this test we assume that Bar layout matches [u64; 4].
+    // This currently is not guaranteed for repr(Rust) types, but it happens to work here and
+    // the UCG may add additional guarantees for homogenous types in the future that would make this
+    // correct.
+    vec.into_iter().map(|e| unsafe { std::mem::transmute(e) }).collect()
+}