IRGen: Initialize single case enum extrainhabitant value witness in generated code

lib/IRGen/GenEnum.cpp

@@ -630,6 +630,18 @@ namespace {
       IGF.Builder.CreateCall(
                     IGF.IGM.getInitEnumMetadataSingleCaseFn(),
                     {metadata, flags, payloadLayout});
+
+      // Pre swift-5.1 runtimes were missing the initialization of the
+      // the extraInhabitantCount field. Do it here instead.
+      auto payloadRef = IGF.Builder.CreateBitOrPointerCast(
+          payloadLayout, IGF.IGM.TypeLayoutTy->getPointerTo());
+      auto payloadExtraInhabitantCount =
+          IGF.Builder.CreateLoad(IGF.Builder.CreateStructGEP(
+              Address(payloadRef, Alignment(1)), 3,
+              Size(IGF.IGM.DataLayout.getTypeAllocSize(IGF.IGM.SizeTy) * 2 +
+                   IGF.IGM.DataLayout.getTypeAllocSize(IGF.IGM.Int32Ty))));
+      emitStoreOfExtraInhabitantCount(IGF, payloadExtraInhabitantCount,
+                                      metadata);
     }
 
     bool mayHaveExtraInhabitants(IRGenModule &IGM) const override {

lib/IRGen/GenOpaque.cpp

@@ -343,11 +343,9 @@ llvm::Value *irgen::emitInvariantLoadOfOpaqueWitness(IRGenFunction &IGF,
   return witness;
 }
 
-/// Given a value witness table, load one of the value witnesses.
-/// The result has the appropriate type for the witness.
-static llvm::Value *emitLoadOfValueWitnessValue(IRGenFunction &IGF,
-                                                llvm::Value *table,
-                                                ValueWitness witness) {
+static Address emitAddressOfValueWitnessTableValue(IRGenFunction &IGF,
+                                                   llvm::Value *table,
+                                                   ValueWitness witness) {
   assert(!isValueWitnessFunction(witness));
   assert(unsigned(witness) <= unsigned(ValueWitness::ExtraInhabitantCount) &&
          "extraInhabitantCount not the last non-function value witness");
@@ -368,7 +366,15 @@ static llvm::Value *emitLoadOfValueWitnessValue(IRGenFunction &IGF,
   Address addr = Address(table, IGF.IGM.getPointerAlignment());
   addr = IGF.Builder.CreateBitCast(addr, IGF.IGM.getValueWitnessTablePtrTy());
   addr = IGF.Builder.CreateStructGEP(addr, unsigned(witness), offset);
+  return addr;
+}
 
+/// Given a value witness table, load one of the value witnesses.
+/// The result has the appropriate type for the witness.
+static llvm::Value *emitLoadOfValueWitnessValue(IRGenFunction &IGF,
+                                                llvm::Value *table,
+                                                ValueWitness witness) {
+  auto addr = emitAddressOfValueWitnessTableValue(IGF, table, witness);
   auto load = IGF.Builder.CreateLoad(addr, getValueWitnessLabel(witness));
   IGF.setInvariantLoad(load);
   return load;
@@ -912,6 +918,15 @@ llvm::Value *irgen::emitLoadOfExtraInhabitantCount(IRGenFunction &IGF,
   return IGF.emitValueWitnessValue(T, ValueWitness::ExtraInhabitantCount);
 }
 
+void irgen::emitStoreOfExtraInhabitantCount(IRGenFunction &IGF,
+                                            llvm::Value *value,
+                                            llvm::Value *metadata) {
+  auto vwTable = IGF.emitValueWitnessTableRefForMetadata(metadata);
+  auto addr = emitAddressOfValueWitnessTableValue(
+      IGF, vwTable, ValueWitness::ExtraInhabitantCount);
+  IGF.Builder.CreateStore(value, addr);
+}
+
 std::pair<llvm::Value *, llvm::Value *>
 irgen::emitLoadOfIsInline(IRGenFunction &IGF, llvm::Value *metadata) {
   auto *flags = emitLoadOfValueWitnessValueFromMetadata(IGF, metadata,

lib/IRGen/GenOpaque.h

@@ -215,6 +215,10 @@ namespace irgen {
   /// Emit a load of the 'extraInhabitantCount' value witness.
   llvm::Value *emitLoadOfExtraInhabitantCount(IRGenFunction &IGF, SILType T);
 
+  /// Emit a stored to the 'extraInhabitantCount' value witness.
+  void emitStoreOfExtraInhabitantCount(IRGenFunction &IGF, llvm::Value *val,
+                                       llvm::Value *metadata);
+
   /// Returns the IsInline flag and the loaded flags value.
   std::pair<llvm::Value *, llvm::Value *>
   emitLoadOfIsInline(IRGenFunction &IGF, llvm::Value *metadata);

lib/IRGen/IRGenModule.cpp

@@ -228,6 +228,13 @@ IRGenModule::IRGenModule(IRGenerator &irgen,
     SizeTy  // extra inhabitant flags (optional)
   });
 
+  TypeLayoutTy = createStructType(*this, "swift.type_layout", {
+    SizeTy, // size
+    SizeTy, // stride
+    Int32Ty, // flags
+    Int32Ty // extra inhabitant count
+  });
+
   // A protocol descriptor describes a protocol. It is not type metadata in
   // and of itself, but is referenced in the structure of existential type
   // metadata records.

lib/IRGen/IRGenModule.h

@@ -579,6 +579,7 @@ class IRGenModule {
   };
   llvm::StructType *OffsetPairTy;      /// { iSize, iSize }
   llvm::StructType *FullTypeLayoutTy;  /// %swift.full_type_layout = { ... }
+  llvm::StructType *TypeLayoutTy;  /// %swift.type_layout = { ... }
   llvm::PointerType *TupleTypeMetadataPtrTy; /// %swift.tuple_type*
   llvm::StructType *FullHeapMetadataStructTy; /// %swift.full_heapmetadata = type { ... }
   llvm::PointerType *FullHeapMetadataPtrTy;/// %swift.full_heapmetadata*

test/IRGen/enum.sil

@@ -2683,6 +2683,15 @@ entry(%x : $*MyOptional):
 // CHECK:   [[T_VWT:%.*]] = load i8**, i8*** [[T_VWT_ADDR]]
 // CHECK:   [[T_LAYOUT:%.*]] = getelementptr inbounds i8*, i8** [[T_VWT]], i32 8
 // CHECK:   call void @swift_initEnumMetadataSingleCase(%swift.type* [[METADATA]], [[WORD]] 0, i8** [[T_LAYOUT]])
+// CHECK:   [[PAYLOAD_TYPELAYOUT:%.*]] = bitcast i8** [[T_LAYOUT]] to %swift.type_layout*
+// CHECK:   [[PAYLOAD_EXTRAINHABITANTCNT:%.*]] = getelementptr inbounds %swift.type_layout, %swift.type_layout* [[PAYLOAD_TYPELAYOUT]], i32 0, i32 3
+// CHECK:   [[CNT:%.*]] = load i32, i32* [[PAYLOAD_EXTRAINHABITANTCNT]]
+// CHECK:   [[METADATA2:%.*]] = bitcast %swift.type* [[METADATA]] to i8***
+// CHECK:   [[VWT_ADDR:%.*]] = getelementptr inbounds i8**, i8*** [[METADATA2]], [[WORD]] -1
+// CHECK:   [[VWT:%.*]] = load i8**, i8*** [[VWT_ADDR]]
+// CHECK:   [[VWT2:%.*]] = bitcast i8** [[VWT]] to %swift.vwtable*
+// CHECK:   [[XIC_ADDR:%.*]] = getelementptr inbounds %swift.vwtable, %swift.vwtable* [[VWT2]], i32 0, i32 11
+// CHECK:   store i32 [[CNT]], i32* [[XIC_ADDR]]
 // CHECK:   ret %swift.metadata_response
 
 // -- Fill function for dynamic single-payload. Call into the runtime to