compiler: Fix handling of repr(align(N), simd)

The attributes may not be sensible to combine in user code, but
they should still work.

Author: workingjubilee

Diff for: compiler/rustc_ty_utils/src/layout.rs

@@ -517,6 +517,10 @@ fn layout_of_uncached<'tcx>(
                         pref: dl.vector_align(size).pref,
                     },
                 )
+            } else if let Some(align) = def.repr().align {
+                let natural_align = dl.vector_align(size);
+                let align = natural_align.max(AbiAndPrefAlign::new(align));
+                (Abi::Vector { element: e_abi, count: e_len }, align)
             } else {
                 (Abi::Vector { element: e_abi, count: e_len }, dl.vector_align(size))
             };

Diff for: tests/ui/simd/repr-align-and-simd.rs

@@ -0,0 +1,19 @@
+//@ run-pass
+// A regression test for https://github.com/rust-lang/rust/issues/130402
+// Our SIMD representation did not combine correctly with the repr(align) attribute,
+// and this will remain a concern regardless of what we do with SIMD types.
+#![feature(repr_simd)]
+use std::mem::{size_of, align_of};
+
+#[repr(simd, align(64))]
+struct IntelsIdeaOfWhatAvx512Means([u8; 32]);
+
+#[repr(transparent)]
+struct DesignValidation(IntelsIdeaOfWhatAvx512Means);
+
+fn main() {
+    assert_eq!(64, size_of::<IntelsIdeaOfWhatAvx512Means>());
+    assert_eq!(64, align_of::<IntelsIdeaOfWhatAvx512Means>());
+    assert_eq!(64, size_of::<DesignValidation>());
+    assert_eq!(64, align_of::<DesignValidation>());
+}