Rollup merge of #144665 - scottmcm:restore-sroa-simd-check, r=compiler-errors

Re-block SRoA on SIMD types

Fixes rust-lang/rust#144621

compiler/rustc_mir_transform/src/sroa.rs

@@ -72,8 +72,12 @@ fn escaping_locals<'tcx>(
             return true;
         }
         if let ty::Adt(def, _args) = ty.kind()
-            && tcx.is_lang_item(def.did(), LangItem::DynMetadata)
+            && (def.repr().simd() || tcx.is_lang_item(def.did(), LangItem::DynMetadata))
         {
+            // Exclude #[repr(simd)] types so that they are not de-optimized into an array
+            // (MCP#838 banned projections into SIMD types, but if the value is unused
+            // this pass sees "all the uses are of the fields" and expands it.)
+
             // codegen wants to see the `DynMetadata<T>`,
             // not the inner reference-to-opaque-type.
             return true;