Add a test for 128-bit return values

src/test/codegen/return-value-in-reg.rs

@@ -0,0 +1,32 @@
+//! This test checks that types of up to 128 bits are returned by-value instead of via out-pointer.
+
+// compile-flags: -C no-prepopulate-passes -O
+// only-x86_64
+
+#![crate_type = "lib"]
+
+pub struct S {
+    a: u64,
+    b: u32,
+    c: u32,
+}
+
+// CHECK: define i128 @modify(%S* noalias nocapture dereferenceable(16) %s)
+#[no_mangle]
+pub fn modify(s: S) -> S {
+    S { a: s.a + s.a, b: s.b + s.b, c: s.c + s.c }
+}
+
+#[repr(packed)]
+pub struct TooBig {
+    a: u64,
+    b: u32,
+    c: u32,
+    d: u8,
+}
+
+// CHECK: define void @m_big(%TooBig* [[ATTRS:.*sret.*]], %TooBig* [[ATTRS2:.*]] %s)
+#[no_mangle]
+pub fn m_big(s: TooBig) -> TooBig {
+    TooBig { a: s.a + s.a, b: s.b + s.b, c: s.c + s.c, d: s.d + s.d }
+}