IRGen: Emit fixed type descriptors for structs and enums with @_alignment attributes

This attribute is used in the simd overlay. To ensure we can layout
SIMD types correctly, emit a fixed type descriptor instead of a
field type descriptor for these types.

Author: slavapestov

lib/IRGen/GenEnum.cpp

@@ -5684,6 +5684,12 @@ const TypeInfo *TypeConverter::convertEnumType(TypeBase *key, CanType type,
 void IRGenModule::emitEnumDecl(EnumDecl *theEnum) {
   emitEnumMetadata(*this, theEnum);
   emitNestedTypeDecls(theEnum->getMembers());
+
+  if (shouldEmitOpaqueTypeMetadataRecord(theEnum)) {
+    emitOpaqueTypeMetadataRecord(theEnum);
+    return;
+  }
+
   emitFieldMetadataRecord(theEnum);
 }
 

lib/IRGen/GenReflection.cpp

@@ -557,6 +557,17 @@ void IRGenModule::emitOpaqueTypeMetadataRecord(const NominalTypeDecl *nominalDec
   builder.emit();
 }
 
+bool IRGenModule::shouldEmitOpaqueTypeMetadataRecord(
+    const NominalTypeDecl *nominalDecl) {
+  if (nominalDecl->getAttrs().hasAttribute<AlignmentAttr>()) {
+    auto &ti = getTypeInfoForUnlowered(nominalDecl->getDeclaredTypeInContext());
+    if (isa<FixedTypeInfo>(ti))
+      return true;
+  }
+
+  return false;
+}
+
 /// Builds a constant LLVM struct describing the layout of a fixed-size
 /// SIL @box. These look like closure contexts, but without any necessary
 /// bindings or metadata sources, and only a single captured value.

lib/IRGen/GenStruct.cpp

@@ -839,6 +839,12 @@ unsigned irgen::getPhysicalStructFieldIndex(IRGenModule &IGM, SILType baseType,
 void IRGenModule::emitStructDecl(StructDecl *st) {
   emitStructMetadata(*this, st);
   emitNestedTypeDecls(st->getMembers());
+
+  if (shouldEmitOpaqueTypeMetadataRecord(st)) {
+    emitOpaqueTypeMetadataRecord(st);
+    return;
+  }
+
   emitFieldMetadataRecord(st);
 }
 

lib/IRGen/IRGenModule.h

@@ -771,6 +771,10 @@ class IRGenModule {
   /// from this module.
   void emitOpaqueTypeMetadataRecord(const NominalTypeDecl *nominalDecl);
 
+  /// Some nominal type declarations require us to emit a fixed-size type
+  /// descriptor, because they have special layout considerations.
+  bool shouldEmitOpaqueTypeMetadataRecord(const NominalTypeDecl *nominalDecl);
+
   /// Emit reflection metadata records for builtin and imported types referenced
   /// from this module.
   void emitBuiltinReflectionMetadata();