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

compiler/rustc_ty_utils/src/layout.rs

@@ -506,6 +506,8 @@ fn layout_of_uncached<'tcx>(
                 .checked_mul(e_len, dl)
                 .ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?;
 
+            let requested_align = def.repr().align.clone();
+
             let (abi, align) = if def.repr().packed() && !e_len.is_power_of_two() {
                 // Non-power-of-two vectors have padding up to the next power-of-two.
                 // If we're a packed repr, remove the padding while keeping the alignment as close
@@ -518,7 +520,13 @@ fn layout_of_uncached<'tcx>(
                     },
                 )
             } else {
-                (Abi::Vector { element: e_abi, count: e_len }, dl.vector_align(size))
+                let natural_align = dl.vector_align(size);
+                let align = if let Some(align) = requested_align {
+                    natural_align.max(AbiAndPrefAlign::new(align))
+                } else {
+                    natural_align
+                };
+                (Abi::Vector { element: e_abi, count: e_len }, align)
             };
             let size = size.align_to(align.abi);
 
@@ -536,7 +544,7 @@ fn layout_of_uncached<'tcx>(
                 largest_niche: e_ly.largest_niche,
                 size,
                 align,
-                max_repr_align: None,
+                max_repr_align: requested_align,
                 unadjusted_abi_align: align.abi,
             })
         }

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>());
+}