[Runtime] Extract some layout string functionality into separate functions (#66577)

We want to re-use them for enum layout string instantiation, so best to pull them into separate functions.

Author: drexin

include/swift/Runtime/Metadata.h

@@ -666,6 +666,36 @@ void swift_initStructMetadataWithLayoutString(StructMetadata *self,
                                               const uint8_t *fieldTags,
                                               uint32_t *fieldOffsets);
 
+SWIFT_RUNTIME_STDLIB_INTERNAL
+size_t _swift_refCountBytesForMetatype(const Metadata *type);
+
+enum LayoutStringFlags : uint64_t {
+  Empty = 0,
+  // TODO: Track other useful information tha can be used to optimize layout
+  //       strings, like different reference kinds contained in the string
+  //       number of ref counting operations (maybe up to 4), so we can
+  //       use witness functions optimized for these cases.
+  HasRelativePointers = (1ULL << 63),
+};
+
+inline bool operator&(LayoutStringFlags a, LayoutStringFlags b) {
+  return (uint64_t(a) & uint64_t(b)) != 0;
+}
+inline LayoutStringFlags operator|(LayoutStringFlags a, LayoutStringFlags b) {
+  return LayoutStringFlags(uint64_t(a) | uint64_t(b));
+}
+inline LayoutStringFlags &operator|=(LayoutStringFlags &a, LayoutStringFlags b) {
+  return a = (a | b);
+}
+
+SWIFT_RUNTIME_STDLIB_INTERNAL
+void _swift_addRefCountStringForMetatype(uint8_t *layoutStr,
+                                         size_t &layoutStrOffset,
+                                         LayoutStringFlags &flags,
+                                         const Metadata *fieldType,
+                                         size_t &fullOffset,
+                                         size_t &previousFieldOffset);
+
 /// Allocate the metadata for a class and copy fields from the given pattern.
 /// The final size of the metadata is calculated at runtime from the metadata
 /// bounds in the class descriptor.

stdlib/public/runtime/Enum.cpp

@@ -214,6 +214,66 @@ swift::swift_initEnumMetadataMultiPayload(EnumMetadata *enumType,
   vwtable->publishLayout(layout);
 }
 
+// void
+// swift::swift_initEnumMetadataMultiPayloadWithLayoutString(EnumMetadata *enumType,
+//                                      EnumLayoutFlags layoutFlags,
+//                                      unsigned numPayloads,
+//                                      const TypeLayout * const *payloadLayouts) {
+  // // Accumulate the layout requirements of the payloads.
+  // size_t payloadSize = 0, alignMask = 0;
+  // bool isPOD = true, isBT = true;
+  // for (unsigned i = 0; i < numPayloads; ++i) {
+  //   const TypeLayout *payloadLayout = payloadLayouts[i];
+  //   payloadSize
+  //     = std::max(payloadSize, (size_t)payloadLayout->size);
+  //   alignMask |= payloadLayout->flags.getAlignmentMask();
+  //   isPOD &= payloadLayout->flags.isPOD();
+  //   isBT &= payloadLayout->flags.isBitwiseTakable();
+  // }
+
+  // // Store the max payload size in the metadata.
+  // assignUnlessEqual(enumType->getPayloadSize(), payloadSize);
+
+  // // The total size includes space for the tag.
+  // auto tagCounts = getEnumTagCounts(payloadSize,
+  //                               enumType->getDescription()->getNumEmptyCases(),
+  //                               numPayloads);
+  // unsigned totalSize = payloadSize + tagCounts.numTagBytes;
+
+  // // See whether there are extra inhabitants in the tag.
+  // unsigned numExtraInhabitants = tagCounts.numTagBytes == 4
+  //   ? INT_MAX
+  //   : (1 << (tagCounts.numTagBytes * 8)) - tagCounts.numTags;
+  // numExtraInhabitants = std::min(numExtraInhabitants,
+  //                         unsigned(ValueWitnessFlags::MaxNumExtraInhabitants));
+
+  // auto vwtable = getMutableVWTableForInit(enumType, layoutFlags);
+
+  // // Set up the layout info in the vwtable.
+  // auto rawStride = (totalSize + alignMask) & ~alignMask;
+  // TypeLayout layout{totalSize,
+  //                   rawStride == 0 ? 1 : rawStride,
+  //                   ValueWitnessFlags()
+  //                    .withAlignmentMask(alignMask)
+  //                    .withPOD(isPOD)
+  //                    .withBitwiseTakable(isBT)
+  //                    .withEnumWitnesses(true)
+  //                    .withInlineStorage(ValueWitnessTable::isValueInline(
+  //                        isBT, totalSize, alignMask + 1)),
+  //                   numExtraInhabitants};
+
+  // installCommonValueWitnesses(layout, vwtable);
+
+  // // Unconditionally overwrite the enum-tag witnesses.
+  // // The compiler does not generate meaningful enum-tag witnesses for
+  // // enums in this state.
+  // vwtable->getEnumTagSinglePayload = swift_getMultiPayloadEnumTagSinglePayload;
+  // vwtable->storeEnumTagSinglePayload =
+  //     swift_storeMultiPayloadEnumTagSinglePayload;
+
+  // vwtable->publishLayout(layout);
+//}
+
 namespace {
 struct MultiPayloadLayout {
   size_t payloadSize;