Auto merge of #57998 - niklasf:align-enum, r=nagisa

Allow #[repr(align(x))] on enums (#57996)

Tracking issue: #57996

Implements an extension of [RFC 1358](https://github.com/rust-lang/rfcs/blob/master/text/1358-repr-align.md) behind a feature flag (`repr_align_enum`). Originally introduced here for structs: #39999.

It seems like only HIR-level changes are required, since enums are already aware of their alignment (due to alignment of their limbs).

cc @bitshifter

1 files changed, 36 insertions, 0 deletions

diff --git a/src/test/codegen/align-enum.rs b/src/test/codegen/align-enum.rs
new file mode 100644
index 00000000000..2251c54229e
--- /dev/null
+++ b/src/test/codegen/align-enum.rs
@@ -0,0 +1,36 @@
+// compile-flags: -C no-prepopulate-passes
+// ignore-tidy-linelength
+// min-llvm-version 7.0
+
+#![crate_type = "lib"]
+#![feature(repr_align_enum)]
+
+#[repr(align(64))]
+pub enum Align64 {
+    A(u32),
+    B(u32),
+}
+// CHECK: %Align64 = type { [0 x i32], i32, [15 x i32] }
+
+pub struct Nested64 {
+    a: u8,
+    b: Align64,
+    c: u16,
+}
+
+// CHECK-LABEL: @align64
+#[no_mangle]
+pub fn align64(a: u32) -> Align64 {
+// CHECK: %a64 = alloca %Align64, align 64
+// CHECK: call void @llvm.memcpy.{{.*}}(i8* align 64 %{{.*}}, i8* align 64 %{{.*}}, i{{[0-9]+}} 64, i1 false)
+    let a64 = Align64::A(a);
+    a64
+}
+
+// CHECK-LABEL: @nested64
+#[no_mangle]
+pub fn nested64(a: u8, b: u32, c: u16) -> Nested64 {
+// CHECK: %n64 = alloca %Nested64, align 64
+    let n64 = Nested64 { a, b: Align64::B(b), c };
+    n64
+}