diff --git a/include/swift/RemoteInspection/DescriptorFinder.h b/include/swift/RemoteInspection/DescriptorFinder.h
index 9335474be6fbb..8af44a4384656 100644
--- a/include/swift/RemoteInspection/DescriptorFinder.h
+++ b/include/swift/RemoteInspection/DescriptorFinder.h
@@ -93,26 +93,6 @@ struct FieldDescriptorBase {
   getFieldRecords() = 0;
 };
 
-struct MultiPayloadEnumDescriptorBase {
-  virtual ~MultiPayloadEnumDescriptorBase(){};
-
-  virtual llvm::StringRef getMangledTypeName() = 0;
-
-  virtual uint32_t getContentsSizeInWords() const = 0;
-
-  virtual size_t getSizeInBytes() const = 0;
-
-  virtual uint32_t getFlags() const = 0;
-
-  virtual bool usesPayloadSpareBits() const = 0;
-
-  virtual uint32_t getPayloadSpareBitMaskByteOffset() const = 0;
-
-  virtual uint32_t getPayloadSpareBitMaskByteCount() const = 0;
-
-  virtual const uint8_t *getPayloadSpareBits() const = 0;
-
-};
 /// Interface for finding type descriptors. Implementors may provide descriptors
 /// that live inside or outside reflection metadata.
 struct DescriptorFinder {
@@ -124,9 +104,6 @@ struct DescriptorFinder {
 
   virtual std::unique_ptr<FieldDescriptorBase>
   getFieldDescriptor(const TypeRef *TR) = 0;
-
-  virtual std::unique_ptr<MultiPayloadEnumDescriptorBase>
-  getMultiPayloadEnumDescriptor(const TypeRef *TR) = 0;
 };
 
 } // namespace reflection
diff --git a/include/swift/RemoteInspection/Records.h b/include/swift/RemoteInspection/Records.h
index aa08ce3ef5b6d..1c0ceeb976257 100644
--- a/include/swift/RemoteInspection/Records.h
+++ b/include/swift/RemoteInspection/Records.h
@@ -378,111 +378,6 @@ class BuiltinTypeDescriptor {
   }
 };
 
-class MultiPayloadEnumDescriptor {
-public:
-  const RelativeDirectPointer<const char> TypeName;
-
-private:
-  // This descriptor contains a series of 32-bit words
-  uint32_t contents[];
-
-  // Properties are stored in `contents` at particular indexes:
-
-  // uint32_t SizeFlags;
-  // Upper 16 bits are the size of the contents (in 32-bit words):
-  //  (This allows us to expand this structure in the future;
-  //  new fields should have accessors that test whether the
-  //  size is large enough and return "non-existent" if the
-  //  descriptor isn't large enough to have that field.)
-  // Lower 16 bits are flag bits
-
-  int getSizeFlagsIndex() const { return 0; }
-
-  // uint32_t PayloadSpareBitMaskByteOffsetCount;
-  // Number of bytes in "payload spare bits", and
-  // offset of them within the payload area
-  // Only present if `usePayloadSpareBits()`
-
-  int getPayloadSpareBitMaskByteCountIndex() const {
-    return getSizeFlagsIndex() + 1;
-  }
-
-  // uint8_t  *PayloadSpareBits;
-  // Variably-sized bitmask field (padded to a multiple of 4 bytes)
-  // Only present if `usePayloadSpareBits()`
-
-  int getPayloadSpareBitsIndex() const {
-    int PayloadSpareBitMaskByteCountFieldSize = usesPayloadSpareBits() ? 1 : 0;
-    return getPayloadSpareBitMaskByteCountIndex() + PayloadSpareBitMaskByteCountFieldSize;
-  }
-
-  // uint32_t foo;
-  // TODO: Some future field
-  // int getFooIndex() const {
-  //   int PayloadSpareBitMaskFieldSize = (getPayloadSpareBitMaskByteCount() + 3) / 4;
-  //   return getPayloadSpareBitsIndex() + PayloadSpareBitMaskFieldSize;
-  // }
-
-  // uint32_t getFoo() const {
-  //   if (getFooIndex() < getContentsSizeInWords()) {
-  //       return contents[getFooIndex()];
-  //   } else {
-  //       return 0; // Field isn't present
-  //   }
-  // }
-
-public:
-  //
-  // Data derived from the above...
-  //
-
-  uint32_t getContentsSizeInWords() const {
-    return contents[getSizeFlagsIndex()] >> 16;
-  }
-
-  size_t getSizeInBytes() const {
-//    assert(getContentsSizeInWords() > 0 && "Malformed MPEnum reflection record");
-    size_t sizeInBytes = sizeof(TypeName) + getContentsSizeInWords() * 4;
-    return sizeInBytes;
-  }
-
-  uint32_t getFlags() const {
-    assert(getContentsSizeInWords() > 0 && "Malformed MPEnum reflection record");
-    return contents[getSizeFlagsIndex()] & 0xffff;
-  }
-
-  bool usesPayloadSpareBits() const {
-    return getFlags() & 1;
-  }
-
-  uint32_t getPayloadSpareBitMaskByteOffset() const {
-    if (usesPayloadSpareBits()) {
-      return contents[getPayloadSpareBitMaskByteCountIndex()] >> 16;
-    } else {
-      return 0;
-    }
-  }
-
-  uint32_t getPayloadSpareBitMaskByteCount() const {
-    if (usesPayloadSpareBits()) {
-      auto byteCount = contents[getPayloadSpareBitMaskByteCountIndex()] & 0xffff;
-      assert(getContentsSizeInWords() >= 2 + (byteCount + 3) / 4
-            && "Malformed MPEnum reflection record: mask bigger than record");
-      return byteCount;
-    } else {
-      return 0;
-    }
-  }
-
-  const uint8_t *getPayloadSpareBits() const {
-    if (usesPayloadSpareBits()) {
-      return reinterpret_cast<const uint8_t *>(&contents[getPayloadSpareBitsIndex()]);
-    } else {
-      return nullptr;
-    }
-  }
-};
-
 class CaptureTypeRecord {
 public:
   const RelativeDirectPointer<const char> MangledTypeName;
diff --git a/include/swift/RemoteInspection/ReflectionContext.h b/include/swift/RemoteInspection/ReflectionContext.h
index e2384813ab4d7..8b0f109483251 100644
--- a/include/swift/RemoteInspection/ReflectionContext.h
+++ b/include/swift/RemoteInspection/ReflectionContext.h
@@ -335,8 +335,6 @@ class ReflectionContext
         ObjectFileFormat.getSectionName(ReflectionSectionKind::reflstr));
     auto ConformMdSec = findMachOSectionByName(
         ObjectFileFormat.getSectionName(ReflectionSectionKind::conform));
-    auto MPEnumMdSec = findMachOSectionByName(
-        ObjectFileFormat.getSectionName(ReflectionSectionKind::mpenum));
 
     if (FieldMdSec.first == nullptr &&
         AssocTySec.first == nullptr &&
@@ -344,8 +342,7 @@ class ReflectionContext
         CaptureSec.first == nullptr &&
         TypeRefMdSec.first == nullptr &&
         ReflStrMdSec.first == nullptr &&
-        ConformMdSec.first == nullptr &&
-        MPEnumMdSec.first == nullptr)
+        ConformMdSec.first == nullptr)
       return {};
 
     ReflectionInfo info = {{FieldMdSec.first, FieldMdSec.second},
@@ -355,7 +352,6 @@ class ReflectionContext
                            {TypeRefMdSec.first, TypeRefMdSec.second},
                            {ReflStrMdSec.first, ReflStrMdSec.second},
                            {ConformMdSec.first, ConformMdSec.second},
-                           {MPEnumMdSec.first, MPEnumMdSec.second},
                            PotentialModuleNames};
 
     auto InfoID = this->addReflectionInfo(info);
@@ -470,8 +466,6 @@ class ReflectionContext
         ObjectFileFormat.getSectionName(ReflectionSectionKind::reflstr));
     auto ConformMdSec = findCOFFSectionByName(
         ObjectFileFormat.getSectionName(ReflectionSectionKind::conform));
-    auto MPEnumMdSec = findCOFFSectionByName(
-        ObjectFileFormat.getSectionName(ReflectionSectionKind::mpenum));
 
     if (FieldMdSec.first == nullptr &&
         AssocTySec.first == nullptr &&
@@ -479,8 +473,7 @@ class ReflectionContext
         CaptureSec.first == nullptr &&
         TypeRefMdSec.first == nullptr &&
         ReflStrMdSec.first == nullptr &&
-        ConformMdSec.first == nullptr &&
-        MPEnumMdSec.first == nullptr)
+        ConformMdSec.first == nullptr)
       return {};
 
     ReflectionInfo Info = {{FieldMdSec.first, FieldMdSec.second},
@@ -490,7 +483,6 @@ class ReflectionContext
                            {TypeRefMdSec.first, TypeRefMdSec.second},
                            {ReflStrMdSec.first, ReflStrMdSec.second},
                            {ConformMdSec.first, ConformMdSec.second},
-                           {MPEnumMdSec.first, MPEnumMdSec.second},
                            PotentialModuleNames};
     return this->addReflectionInfo(Info);
   }
@@ -687,9 +679,6 @@ class ReflectionContext
         ObjectFileFormat.getSectionName(ReflectionSectionKind::reflstr), true);
     auto ConformMdSec = findELFSectionByName(
         ObjectFileFormat.getSectionName(ReflectionSectionKind::conform), true);
-    auto MPEnumMdSec = findELFSectionByName(
-        ObjectFileFormat.getSectionName(ReflectionSectionKind::mpenum), true);
-
     if (Error)
       return {};
 
@@ -699,7 +688,7 @@ class ReflectionContext
     // ELF executable.
     if (FieldMdSec.first || AssocTySec.first || BuiltinTySec.first ||
         CaptureSec.first || TypeRefMdSec.first || ReflStrMdSec.first ||
-        ConformMdSec.first || MPEnumMdSec.first) {
+        ConformMdSec.first) {
       ReflectionInfo info = {{FieldMdSec.first, FieldMdSec.second},
                              {AssocTySec.first, AssocTySec.second},
                              {BuiltinTySec.first, BuiltinTySec.second},
@@ -707,7 +696,6 @@ class ReflectionContext
                              {TypeRefMdSec.first, TypeRefMdSec.second},
                              {ReflStrMdSec.first, ReflStrMdSec.second},
                              {ConformMdSec.first, ConformMdSec.second},
-                             {MPEnumMdSec.first, MPEnumMdSec.second},
                              PotentialModuleNames};
       result = this->addReflectionInfo(info);
     }
@@ -730,15 +718,13 @@ class ReflectionContext
         ObjectFileFormat.getSectionName(ReflectionSectionKind::reflstr), false);
     ConformMdSec = findELFSectionByName(
         ObjectFileFormat.getSectionName(ReflectionSectionKind::conform), false);
-    MPEnumMdSec = findELFSectionByName(
-        ObjectFileFormat.getSectionName(ReflectionSectionKind::mpenum), false);
 
     if (Error)
       return {};
 
     if (FieldMdSec.first || AssocTySec.first || BuiltinTySec.first ||
         CaptureSec.first || TypeRefMdSec.first || ReflStrMdSec.first ||
-        ConformMdSec.first || MPEnumMdSec.first) {
+        ConformMdSec.first) {
       ReflectionInfo info = {{FieldMdSec.first, FieldMdSec.second},
                              {AssocTySec.first, AssocTySec.second},
                              {BuiltinTySec.first, BuiltinTySec.second},
@@ -746,7 +732,6 @@ class ReflectionContext
                              {TypeRefMdSec.first, TypeRefMdSec.second},
                              {ReflStrMdSec.first, ReflStrMdSec.second},
                              {ConformMdSec.first, ConformMdSec.second},
-                             {MPEnumMdSec.first, MPEnumMdSec.second},
                              PotentialModuleNames};
       auto rid = this->addReflectionInfo(info);
       if (!result)
@@ -861,7 +846,8 @@ class ReflectionContext
         ReflectionSectionKind::fieldmd, ReflectionSectionKind::assocty,
         ReflectionSectionKind::builtin, ReflectionSectionKind::capture,
         ReflectionSectionKind::typeref, ReflectionSectionKind::reflstr,
-        ReflectionSectionKind::conform, ReflectionSectionKind::mpenum};
+        ReflectionSectionKind::conform
+    };
 
     llvm::SmallVector<std::pair<RemoteRef<void>, uint64_t>, 6> Pairs;
     for (auto Section : Sections) {
@@ -887,7 +873,6 @@ class ReflectionContext
                            {Pairs[4].first, Pairs[4].second},
                            {Pairs[5].first, Pairs[5].second},
                            {Pairs[6].first, Pairs[6].second},
-                           {Pairs[7].first, Pairs[7].second},
                            PotentialModuleNames};
     return addReflectionInfo(Info);
   }
diff --git a/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/Swift.def b/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/Swift.def
index 05b60e40632cd..1ea0bc548b37e 100644
--- a/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/Swift.def
+++ b/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/Swift.def
@@ -30,4 +30,3 @@ HANDLE_SWIFT_SECTION(protocs, "__swift5_protos", "swift5_protocols",
                      ".sw5prt$B")
 HANDLE_SWIFT_SECTION(acfuncs, "__swift5_acfuncs", "swift5_accessible_functions",
                      ".sw5acfn$B")
-HANDLE_SWIFT_SECTION(mpenum, "__swift5_mpenum", "swift5_mpenum", ".sw5mpen$B")
diff --git a/include/swift/RemoteInspection/TypeRefBuilder.h b/include/swift/RemoteInspection/TypeRefBuilder.h
index 0a98b782d05c2..b787b8522ded5 100644
--- a/include/swift/RemoteInspection/TypeRefBuilder.h
+++ b/include/swift/RemoteInspection/TypeRefBuilder.h
@@ -231,21 +231,6 @@ class CaptureDescriptorIterator
 };
 using CaptureSection = ReflectionSection<CaptureDescriptorIterator>;
 
-class MultiPayloadEnumDescriptorIterator
-    : public ReflectionSectionIteratorBase<MultiPayloadEnumDescriptorIterator,
-                                           MultiPayloadEnumDescriptor> {
-public:
-  MultiPayloadEnumDescriptorIterator(RemoteRef<void> Cur, uint64_t Size)
-      : ReflectionSectionIteratorBase(Cur, Size, "MultiPayloadEnum") {}
-
-  static uint64_t
-  getCurrentRecordSize(RemoteRef<MultiPayloadEnumDescriptor> MPER) {
-    return MPER->getSizeInBytes();
-  }
-};
-using MultiPayloadEnumSection =
-    ReflectionSection<MultiPayloadEnumDescriptorIterator>;
-
 using GenericSection = ReflectionSection<const void *>;
 
 struct ReflectionInfo {
@@ -256,7 +241,6 @@ struct ReflectionInfo {
   GenericSection TypeReference;
   GenericSection ReflectionString;
   GenericSection Conformance;
-  MultiPayloadEnumSection MultiPayloadEnum;
   llvm::SmallVector<llvm::StringRef, 1> PotentialModuleNames;
 };
 
@@ -490,10 +474,6 @@ class TypeRefBuilder {
     /// Get the unsubstituted capture types for a closure context.
     ClosureContextInfo getClosureContextInfo(RemoteRef<CaptureDescriptor> CD);
 
-    /// Get the multipayload enum projection information for a given TR
-    std::unique_ptr<MultiPayloadEnumDescriptorBase>
-    getMultiPayloadEnumDescriptor(const TypeRef *TR) override;
-
     const TypeRef *lookupTypeWitness(const std::string &MangledTypeName,
                                      const std::string &Member,
                                      StringRef Protocol);
@@ -516,8 +496,6 @@ class TypeRefBuilder {
     /// Load unsubstituted field types for a nominal type.
     RemoteRef<FieldDescriptor> getFieldTypeInfo(const TypeRef *TR);
 
-    RemoteRef<MultiPayloadEnumDescriptor> getMultiPayloadEnumInfo(const TypeRef *TR);
-
     void populateFieldTypeInfoCacheWithReflectionAtIndex(size_t Index);
 
     std::optional<RemoteRef<FieldDescriptor>>
@@ -567,8 +545,7 @@ class TypeRefBuilder {
 
   public:
     ///
-    /// Dumping typerefs, field declarations, builtin types, captures,
-    /// multi-payload enums
+    /// Dumping typerefs, field declarations, builtin types, captures
     ///
     void dumpTypeRef(RemoteRef<char> MangledName, std::ostream &stream,
                      bool printTypeName = false);
@@ -577,7 +554,6 @@ class TypeRefBuilder {
     void dumpFieldSection(std::ostream &stream);
     void dumpBuiltinTypeSection(std::ostream &stream);
     void dumpCaptureSection(std::ostream &stream);
-    void dumpMultiPayloadEnumSection(std::ostream &stream);
 
     template <template <typename Runtime> class ObjCInteropKind,
               unsigned PointerSize>
@@ -817,10 +793,6 @@ class TypeRefBuilder {
       stream << "=============\n";
       dumpConformanceSection<ObjCInteropKind, PointerSize>(stream);
       stream << "\n";
-      stream << "MULTI-PAYLOAD ENUM DESCRIPTORS:\n";
-      stream << "===============================\n";
-      dumpMultiPayloadEnumSection(stream);
-      stream << "\n";
     }
   };
   friend struct ReflectionTypeDescriptorFinder;
@@ -1577,17 +1549,10 @@ class TypeRefBuilder {
     return RDF.getClosureContextInfo(CD);
   }
 
-  /// Get the multipayload enum projection information for a given TR
-  std::unique_ptr<MultiPayloadEnumDescriptorBase>
-  getMultiPayloadEnumDescriptor(const TypeRef *TR);
-
 private:
   /// Get the primitive type lowering for a builtin type.
   RemoteRef<BuiltinTypeDescriptor> getBuiltinTypeInfo(const TypeRef *TR);
 
-  RemoteRef<MultiPayloadEnumDescriptor>
-  getMultiPayloadEnumInfo(const TypeRef *TR);
-
   std::optional<uint64_t> multiPayloadEnumPointerMask;
 
 public:
@@ -1617,6 +1582,7 @@ class TypeRefBuilder {
     }
     return multiPayloadEnumPointerMask.value();
   }
+
   FieldTypeCollectionResult
   collectFieldTypes(std::optional<std::string> forMangledTypeName) {
     return RDF.collectFieldTypes(forMangledTypeName);
diff --git a/lib/IRGen/GenReflection.cpp b/lib/IRGen/GenReflection.cpp
index e3020f98e0b32..27d366c941ebb 100644
--- a/lib/IRGen/GenReflection.cpp
+++ b/lib/IRGen/GenReflection.cpp
@@ -37,7 +37,6 @@
 #include "GenMeta.h"
 #include "GenProto.h"
 #include "GenType.h"
-#include "GenValueWitness.h"
 #include "IRGenDebugInfo.h"
 #include "IRGenFunction.h"
 #include "IRGenMangler.h"
@@ -1131,74 +1130,6 @@ void IRGenModule::emitBuiltinTypeMetadataRecord(CanType builtinType) {
   builder.emit();
 }
 
-class MultiPayloadEnumDescriptorBuilder : public ReflectionMetadataBuilder {
-  CanType type;
-  CanType typeInContext;
-  const FixedTypeInfo *ti;
-
-public:
-  MultiPayloadEnumDescriptorBuilder(IRGenModule &IGM,
-                                    const NominalTypeDecl *nominalDecl)
-    : ReflectionMetadataBuilder(IGM) {
-    type = nominalDecl->getDeclaredType()->getCanonicalType();
-    typeInContext = nominalDecl->getDeclaredTypeInContext()->getCanonicalType();
-    ti = &cast<FixedTypeInfo>(IGM.getTypeInfoForUnlowered(typeInContext));
-  }
-
-  void layout() override {
-    auto &strategy = getEnumImplStrategy(IGM, typeInContext);
-    bool isMPE = strategy.getElementsWithPayload().size() > 1;
-    assert(isMPE && "Cannot emit Multi-Payload Enum data for an enum that "
-                    "doesn't have multiple payloads");
-
-    const TypeInfo &TI = strategy.getTypeInfo();
-    auto fixedTI = dyn_cast<FixedTypeInfo>(&TI);
-    assert(fixedTI != nullptr &&
-           "MPE reflection records can only be emitted for fixed-layout enums");
-
-    auto spareBitsMaskInfo = strategy.calculateSpareBitsMask();
-
-    // Never write an MPE descriptor bigger than 16k
-    // The runtime will fall back on its own internal
-    // spare bits calculation for this (very rare) case.
-    if (!spareBitsMaskInfo)
-      return;
-
-    auto bits = spareBitsMaskInfo->bits;
-
-    addTypeRef(type, CanGenericSignature());
-
-    bool usesPayloadSpareBits = spareBitsMaskInfo->bytesInMask > 0;
-
-    // MPE record contents are a multiple of 32-bits
-    uint32_t contentsSizeInWords = 1; /* Size + flags is mandatory */
-    if (usesPayloadSpareBits) {
-      contentsSizeInWords += 1 /* SpareBits byte count */
-                             + spareBitsMaskInfo->wordsInMask();
-    }
-
-    uint32_t flags = usesPayloadSpareBits ? 1 : 0;
-
-    B.addInt32((contentsSizeInWords << 16) | flags);
-
-    if (usesPayloadSpareBits) {
-      B.addInt32((spareBitsMaskInfo->byteOffset << 16) |
-                 spareBitsMaskInfo->bytesInMask);
-      // TODO: Endianness??
-      for (unsigned i = 0; i < spareBitsMaskInfo->wordsInMask(); ++i) {
-        uint32_t nextWord = bits.extractBitsAsZExtValue(32, 0);
-        B.addInt32(nextWord);
-        bits.lshrInPlace(32);
-      }
-    }
-  }
-
-  llvm::GlobalVariable *emit() {
-    auto section = IGM.getMultiPayloadEnumDescriptorSectionName();
-    return ReflectionMetadataBuilder::emit(std::nullopt, section);
-  }
-};
-
 /// 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.
@@ -1563,12 +1494,6 @@ const char *IRGenModule::getReflectionTypeRefSectionName() {
   return ReflectionTypeRefSection.c_str();
 }
 
-const char *IRGenModule::getMultiPayloadEnumDescriptorSectionName() {
-  if (MultiPayloadEnumDescriptorSection.empty())
-    MultiPayloadEnumDescriptorSection = getReflectionSectionName(*this, "mpenum", "mpen");
-  return MultiPayloadEnumDescriptorSection.c_str();
-}
-
 llvm::Constant *IRGenModule::getAddrOfFieldName(StringRef Name) {
   auto &entry = FieldNames[Name];
   if (entry.second)
@@ -1694,7 +1619,6 @@ void IRGenModule::emitFieldDescriptor(const NominalTypeDecl *D) {
   auto T = D->getDeclaredTypeInContext()->getCanonicalType();
 
   bool needsOpaqueDescriptor = false;
-  bool needsMPEDescriptor = false;
   bool needsFieldDescriptor = true;
 
   if (auto *ED = dyn_cast<EnumDecl>(D)) {
@@ -1708,13 +1632,11 @@ void IRGenModule::emitFieldDescriptor(const NominalTypeDecl *D) {
     }
 
     // If this is a fixed-size multi-payload enum, we have to emit a descriptor
-    // with the size and alignment of the type and another with the spare bit
-    // mask data, because the reflection library cannot consistently derive this
-    // information at runtime.
+    // with the size and alignment of the type, because the reflection library
+    // cannot derive this information at runtime.
     if (strategy.getElementsWithPayload().size() > 1 &&
         !strategy.needsPayloadSizeInMetadata()) {
       needsOpaqueDescriptor = true;
-      needsMPEDescriptor = true;
     }
   }
 
@@ -1761,11 +1683,6 @@ void IRGenModule::emitFieldDescriptor(const NominalTypeDecl *D) {
     builder.emit();
   }
 
-  if (needsMPEDescriptor) {
-    MultiPayloadEnumDescriptorBuilder builder(*this, D);
-    builder.emit();
-  }
-
   if (needsFieldDescriptor) {
     FieldTypeMetadataBuilder builder(*this, D);
     builder.emit();
diff --git a/lib/IRGen/IRGenModule.h b/lib/IRGen/IRGenModule.h
index 9b1e8bf8386d8..4bfaaf5f294e5 100644
--- a/lib/IRGen/IRGenModule.h
+++ b/lib/IRGen/IRGenModule.h
@@ -1396,7 +1396,6 @@ class IRGenModule {
   std::string CaptureDescriptorSection;
   std::string ReflectionStringsSection;
   std::string ReflectionTypeRefSection;
-  std::string MultiPayloadEnumDescriptorSection;
 
   /// Builtin types referenced by types in this module when emitting
   /// reflection metadata.
@@ -1476,7 +1475,6 @@ class IRGenModule {
   const char *getCaptureDescriptorMetadataSectionName();
   const char *getReflectionStringsSectionName();
   const char *getReflectionTypeRefSectionName();
-  const char *getMultiPayloadEnumDescriptorSectionName();
 
   /// Returns the special builtin types that should be emitted in the stdlib
   /// module.
diff --git a/stdlib/public/RemoteInspection/TypeLowering.cpp b/stdlib/public/RemoteInspection/TypeLowering.cpp
index 2bdb4c85b85b2..a74889afb2450 100644
--- a/stdlib/public/RemoteInspection/TypeLowering.cpp
+++ b/stdlib/public/RemoteInspection/TypeLowering.cpp
@@ -29,8 +29,6 @@
 #include "swift/RemoteInspection/TypeRefBuilder.h"
 #include "swift/Basic/Unreachable.h"
 #include <iostream>
-#include <sstream>
-#include <limits>
 
 #ifdef DEBUG_TYPE_LOWERING
   #define DEBUG_LOG(expr) expr;
diff --git a/stdlib/public/RemoteInspection/TypeRefBuilder.cpp b/stdlib/public/RemoteInspection/TypeRefBuilder.cpp
index 9e2a02871f541..7eef905e149c9 100644
--- a/stdlib/public/RemoteInspection/TypeRefBuilder.cpp
+++ b/stdlib/public/RemoteInspection/TypeRefBuilder.cpp
@@ -574,113 +574,6 @@ TypeRefBuilder::getBuiltinTypeDescriptor(const TypeRef *TR) {
   return nullptr;
 }
 
-namespace {
-/// A builtin type descriptor implementation that wraps a reflection builtin
-/// type descriptor.
-class MultiPayloadEnumDescriptorImpl : public MultiPayloadEnumDescriptorBase {
-  RemoteRef<MultiPayloadEnumDescriptor> MPED;
-  TypeRefBuilder &Builder;
-
-public:
-  MultiPayloadEnumDescriptorImpl(RemoteRef<MultiPayloadEnumDescriptor> MPED,
-                                 TypeRefBuilder &Builder)
-      : MultiPayloadEnumDescriptorBase(), MPED(MPED), Builder(Builder) {}
-
-  ~MultiPayloadEnumDescriptorImpl() override {}
-
-  StringRef getMangledTypeName() override {
-    return Builder.getTypeRefString(Builder.readTypeRef(MPED, MPED->TypeName));
-  };
-
-  uint32_t getContentsSizeInWords() const override {
-    return MPED->getContentsSizeInWords();
-  }
-
-  size_t getSizeInBytes() const override { return MPED->getSizeInBytes(); }
-
-  uint32_t getFlags() const override { return MPED->getFlags(); }
-
-  bool usesPayloadSpareBits() const override {
-    return MPED->usesPayloadSpareBits();
-  }
-
-  uint32_t getPayloadSpareBitMaskByteOffset() const override {
-    return MPED->getPayloadSpareBitMaskByteOffset();
-  }
-
-  uint32_t getPayloadSpareBitMaskByteCount() const override {
-    return MPED->getPayloadSpareBitMaskByteCount();
-  }
-
-  const uint8_t *getPayloadSpareBits() const override {
-    return MPED->getPayloadSpareBits();
-  }
-};
-} // namespace
-  
-RemoteRef<MultiPayloadEnumDescriptor>
-TypeRefBuilder::ReflectionTypeDescriptorFinder::getMultiPayloadEnumInfo(
-    const TypeRef *TR) {
-  std::string MangledName;
-  if (auto B = dyn_cast<BuiltinTypeRef>(TR))
-    MangledName = B->getMangledName();
-  else if (auto N = dyn_cast<NominalTypeRef>(TR))
-    MangledName = N->getMangledName();
-  else if (auto B = dyn_cast<BoundGenericTypeRef>(TR))
-    MangledName = B->getMangledName();
-  else
-    return nullptr;
-
-  for (auto Info : ReflectionInfos) {
-    for (auto MultiPayloadEnumDescriptor : Info.MultiPayloadEnum) {
-
-      // Assert that descriptor size is sound...
-      assert(MultiPayloadEnumDescriptor->getContentsSizeInWords() >= 1);
-      // We're limited to 64k of spare bits mask...
-      assert(MultiPayloadEnumDescriptor->getContentsSizeInWords() < 16384);
-      assert(MultiPayloadEnumDescriptor->getSizeInBytes() ==
-             4 + MultiPayloadEnumDescriptor->getContentsSizeInWords() * 4);
-      // Must have a non-empty spare bits mask iff spare bits are used...
-      assert(
-          MultiPayloadEnumDescriptor->usesPayloadSpareBits() ==
-          (MultiPayloadEnumDescriptor->getPayloadSpareBitMaskByteCount() != 0));
-      // BitMask must fit within the advertised size...
-      if (MultiPayloadEnumDescriptor->usesPayloadSpareBits()) {
-        assert(
-            MultiPayloadEnumDescriptor->getContentsSizeInWords() >=
-            2 + (MultiPayloadEnumDescriptor->getPayloadSpareBitMaskByteCount() +
-                 3) /
-                    4);
-      }
-
-      auto CandidateMangledName = readTypeRef(
-          MultiPayloadEnumDescriptor, MultiPayloadEnumDescriptor->TypeName);
-      if (!reflectionNameMatches(CandidateMangledName, MangledName))
-        continue;
-      return MultiPayloadEnumDescriptor;
-    }
-  }
-
-  return nullptr;
-}
-
-std::unique_ptr<MultiPayloadEnumDescriptorBase>
-TypeRefBuilder::ReflectionTypeDescriptorFinder::getMultiPayloadEnumDescriptor(
-    const TypeRef *TR) {
-  if (auto BTI = getMultiPayloadEnumInfo(TR))
-    return std::make_unique<MultiPayloadEnumDescriptorImpl>(BTI, Builder);
-  return nullptr;
-}
-
-std::unique_ptr<MultiPayloadEnumDescriptorBase>
-TypeRefBuilder::getMultiPayloadEnumDescriptor(const TypeRef *TR) {
-  for (auto *DF : getDescriptorFinders())
-    if (auto descriptor = DF->getMultiPayloadEnumDescriptor(TR))
-      return descriptor;
-
-  return nullptr;
-}
-
 RemoteRef<CaptureDescriptor>
 TypeRefBuilder::ReflectionTypeDescriptorFinder::getCaptureDescriptor(
     uint64_t RemoteAddress) {
@@ -895,39 +788,4 @@ void TypeRefBuilder::ReflectionTypeDescriptorFinder::dumpCaptureSection(
   }
 }
 
-void TypeRefBuilder::ReflectionTypeDescriptorFinder::
-    dumpMultiPayloadEnumSection(std::ostream &stream) {
-  for (const auto &sections : ReflectionInfos) {
-    for (const auto descriptor : sections.MultiPayloadEnum) {
-      TypeRefBuilder::ScopedNodeFactoryCheckpoint checkpoint(&Builder);
-      auto typeNode = Builder.demangleTypeRef(
-          readTypeRef(descriptor, descriptor->TypeName));
-      auto typeName = nodeToString(typeNode);
-
-      stream << "\n- " << typeName << ":\n";
-      stream << "  Descriptor Size: " << descriptor->getSizeInBytes() << "\n";
-      stream << "  Flags: " << std::hex << descriptor->getFlags() << std::dec;
-      if (descriptor->usesPayloadSpareBits()) {
-        stream << " usesPayloadSpareBits";
-      }
-      stream << "\n";
-      auto maskBytes = descriptor->getPayloadSpareBitMaskByteCount();
-      auto maskOffset = descriptor->getPayloadSpareBitMaskByteOffset();
-      if (maskBytes > 0) {
-        if (maskOffset > 0) {
-          stream << "  Spare bit mask: (offset " << maskOffset << " bytes) 0x";
-        } else {
-          stream << "  Spare bit mask: 0x";
-        }
-        const uint8_t *p = descriptor->getPayloadSpareBits();
-        for (unsigned i = 0; i < maskBytes; i++) {
-          stream << std::hex << std::setw(2) << std::setfill('0') << (int)p[i];
-        }
-        stream << std::dec << "\n";
-      }
-      stream << "\n";
-    }
-  }
-}
-
 #endif
diff --git a/stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp b/stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp
index 23d5ced5d0b22..4957abedfd378 100644
--- a/stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp
+++ b/stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp
@@ -271,7 +271,6 @@ swift_reflection_addReflectionInfo(SwiftReflectionContextRef ContextRef,
         sectionFromInfo<const void *>(Info, Info.type_references),
         sectionFromInfo<const void *>(Info, Info.reflection_strings),
         ReflectionSection<const void *>(nullptr, 0),
-        ReflectionSection<MultiPayloadEnumDescriptorIterator>(0, 0),
         {}};
 
     Context->addReflectionInfo(ContextInfo);
@@ -295,7 +294,6 @@ void swift_reflection_addReflectionMappingInfo(
         reflectionSectionFromLocalAndRemote<const void *>(
             Info.reflection_strings),
         ReflectionSection<const void *>(nullptr, 0),
-        MultiPayloadEnumSection(0, 0),
         {}};
 
     Context->addReflectionInfo(ContextInfo);
diff --git a/stdlib/public/SwiftShims/swift/shims/MetadataSections.h b/stdlib/public/SwiftShims/swift/shims/MetadataSections.h
index 1e419e4b8f763..e7baba432d4bb 100644
--- a/stdlib/public/SwiftShims/swift/shims/MetadataSections.h
+++ b/stdlib/public/SwiftShims/swift/shims/MetadataSections.h
@@ -95,7 +95,6 @@ struct MetadataSections {
   MetadataSectionRange swift5_replac2;
   MetadataSectionRange swift5_builtin;
   MetadataSectionRange swift5_capture;
-  MetadataSectionRange swift5_mpenum;
   MetadataSectionRange swift5_accessible_functions;
   MetadataSectionRange swift5_runtime_attributes;
   MetadataSectionRange swift5_tests;
diff --git a/stdlib/public/runtime/SwiftRT-COFF.cpp b/stdlib/public/runtime/SwiftRT-COFF.cpp
index 2e64204d0ab1a..f581f53dca76d 100644
--- a/stdlib/public/runtime/SwiftRT-COFF.cpp
+++ b/stdlib/public/runtime/SwiftRT-COFF.cpp
@@ -52,7 +52,6 @@ DECLARE_SWIFT_SECTION(sw5repl)
 DECLARE_SWIFT_SECTION(sw5reps)
 DECLARE_SWIFT_SECTION(sw5bltn)
 DECLARE_SWIFT_SECTION(sw5cptr)
-DECLARE_SWIFT_SECTION(sw5mpen)
 DECLARE_SWIFT_SECTION(sw5acfn)
 DECLARE_SWIFT_SECTION(sw5ratt)
 DECLARE_SWIFT_SECTION(sw5test)
@@ -86,7 +85,6 @@ static void swift_image_constructor() {
       SWIFT_SECTION_RANGE(sw5reps),
       SWIFT_SECTION_RANGE(sw5bltn),
       SWIFT_SECTION_RANGE(sw5cptr),
-      SWIFT_SECTION_RANGE(sw5mpen),
       SWIFT_SECTION_RANGE(sw5acfn),
       SWIFT_SECTION_RANGE(sw5ratt),
       SWIFT_SECTION_RANGE(sw5test),
diff --git a/stdlib/public/runtime/SwiftRT-ELF-WASM.cpp b/stdlib/public/runtime/SwiftRT-ELF-WASM.cpp
index 032a97cd442e4..53006d036b5ac 100644
--- a/stdlib/public/runtime/SwiftRT-ELF-WASM.cpp
+++ b/stdlib/public/runtime/SwiftRT-ELF-WASM.cpp
@@ -68,7 +68,6 @@ DECLARE_SWIFT_REFLECTION_SECTION(swift5_assocty)
 DECLARE_SWIFT_REFLECTION_SECTION(swift5_capture)
 DECLARE_SWIFT_REFLECTION_SECTION(swift5_reflstr)
 DECLARE_SWIFT_REFLECTION_SECTION(swift5_typeref)
-DECLARE_SWIFT_REFLECTION_SECTION(swift5_mpenum)
 
 DECLARE_SWIFT_SECTION(swift5_replace)
 DECLARE_SWIFT_SECTION(swift5_replac2)
@@ -109,7 +108,6 @@ static void swift_image_constructor() {
       SWIFT_SECTION_RANGE(swift5_replac2),
       SWIFT_SECTION_RANGE(swift5_builtin),
       SWIFT_SECTION_RANGE(swift5_capture),
-      SWIFT_SECTION_RANGE(swift5_mpenum),
       SWIFT_SECTION_RANGE(swift5_accessible_functions),
       SWIFT_SECTION_RANGE(swift5_runtime_attributes),
       SWIFT_SECTION_RANGE(swift5_tests),