Revert "Reinstate [SILGen] Implement NSString -> String bridging through _ObjectiveCBridgeable."

This reverts commit b25019c. The
builders are failing in ways that are clearly related to my changes
but I'm unable to replicate locally.

Author: DougGregor

lib/AST/Type.cpp

@@ -798,9 +798,9 @@ Type TypeBase::replaceCovariantResultType(Type newResultType,
                                           bool preserveOptionality) {
   if (uncurryLevel == 0) {
     if (preserveOptionality) {
+      assert(!newResultType->getAnyOptionalObjectType());
       OptionalTypeKind resultOTK;
       if (auto objectType = getAnyOptionalObjectType(resultOTK)) {
-        assert(!newResultType->getAnyOptionalObjectType());
         return OptionalType::get(
             resultOTK,
             objectType->replaceCovariantResultType(

lib/SILGen/SILGen.cpp

@@ -203,37 +203,6 @@ FuncDecl *SILGenModule::getBridgeToObjectiveCRequirement(SILLocation loc) {
   return found;
 }
 
-FuncDecl *SILGenModule::getUnconditionallyBridgeFromObjectiveCRequirement(
-    SILLocation loc) {
-  if (UnconditionallyBridgeFromObjectiveCRequirement)
-    return *UnconditionallyBridgeFromObjectiveCRequirement;
-
-  // Find the _ObjectiveCBridgeable protocol.
-  auto proto = getObjectiveCBridgeable(loc);
-  if (!proto) {
-    UnconditionallyBridgeFromObjectiveCRequirement = nullptr;
-    return nullptr;
-  }
-
-  // Look for _bridgeToObjectiveC().
-  auto &ctx = getASTContext();
-  FuncDecl *found = nullptr;
-  DeclName name(ctx, ctx.getIdentifier("_unconditionallyBridgeFromObjectiveC"),
-                llvm::makeArrayRef(Identifier()));
-  for (auto member : proto->lookupDirect(name, true)) {
-    if (auto func = dyn_cast<FuncDecl>(member)) {
-      found = func;
-      break;
-    }
-  }
-
-  if (!found)
-    diagnose(loc, diag::bridging_objcbridgeable_broken, name);
-
-  UnconditionallyBridgeFromObjectiveCRequirement = found;
-  return found;
-}
-
 AssociatedTypeDecl *
 SILGenModule::getBridgedObjectiveCTypeRequirement(SILLocation loc) {
   if (BridgedObjectiveCType)

lib/SILGen/SILGen.h

@@ -126,7 +126,6 @@ class LLVM_LIBRARY_VISIBILITY SILGenModule : public ASTVisitor<SILGenModule> {
 
   Optional<ProtocolDecl*> ObjectiveCBridgeable;
   Optional<FuncDecl*> BridgeToObjectiveCRequirement;
-  Optional<FuncDecl*> UnconditionallyBridgeFromObjectiveCRequirement;
   Optional<AssociatedTypeDecl*> BridgedObjectiveCType;
 
 public:
@@ -359,11 +358,6 @@ class LLVM_LIBRARY_VISIBILITY SILGenModule : public ASTVisitor<SILGenModule> {
   /// Retrieve the _ObjectiveCBridgeable._bridgeToObjectiveC requirement.
   FuncDecl *getBridgeToObjectiveCRequirement(SILLocation loc);
 
-  /// Retrieve the
-  /// _ObjectiveCBridgeable._unconditionallyBridgeFromObjectiveC
-  /// requirement.
-  FuncDecl *getUnconditionallyBridgeFromObjectiveCRequirement(SILLocation loc);
-
   /// Retrieve the _ObjectiveCBridgeable._ObjectiveCType requirement.
   AssociatedTypeDecl *getBridgedObjectiveCTypeRequirement(SILLocation loc);
 

lib/SILGen/SILGenBridging.cpp

@@ -28,10 +28,10 @@ using namespace Lowering;
 /// object, using the appropriate witness for the
 /// _ObjectiveCBridgeable._bridgeToObjectiveC requirement.
 static Optional<ManagedValue>
-emitBridgeNativeToObjectiveC(SILGenFunction &gen,
-                             SILLocation loc,
-                             ManagedValue swiftValue,
-                             ProtocolConformance *conformance) {
+emitBridgeToObjectiveC(SILGenFunction &gen,
+                       SILLocation loc,
+                       ManagedValue swiftValue,
+                       ProtocolConformance *conformance) {
   // Dig out the nominal type we're bridging from.
   Type swiftValueType = swiftValue.getSwiftType()->getRValueType();
 
@@ -80,10 +80,9 @@ emitBridgeNativeToObjectiveC(SILGenFunction &gen,
 /// Bridge the given Swift value to its corresponding Objective-C
 /// object, using the appropriate witness for the
 /// _ObjectiveCBridgeable._bridgeToObjectiveC requirement.
-static Optional<ManagedValue>
-emitBridgeNativeToObjectiveC(SILGenFunction &gen,
-                             SILLocation loc,
-                             ManagedValue swiftValue) {
+static Optional<ManagedValue> emitBridgeToObjectiveC(SILGenFunction &gen,
+                                                     SILLocation loc,
+                                                     ManagedValue swiftValue) {
   // Dig out the nominal type we're bridging from.
   Type swiftValueType = swiftValue.getSwiftType()->getRValueType();
 
@@ -92,7 +91,7 @@ emitBridgeNativeToObjectiveC(SILGenFunction &gen,
       gen.SGM.getConformanceToObjectiveCBridgeable(loc, swiftValueType);
   if (!conformance) return None;
 
-  return emitBridgeNativeToObjectiveC(gen, loc, swiftValue, conformance);
+  return emitBridgeToObjectiveC(gen, loc, swiftValue, conformance);
 }
 
 static ManagedValue emitBridgeStringToNSString(SILGenFunction &gen,
@@ -101,80 +100,26 @@ static ManagedValue emitBridgeStringToNSString(SILGenFunction &gen,
   llvm_unreachable("Handled via the _bridgeToObjectiveC witness");
 }
 
-/// Bridge the given Objective-C object to its corresponding Swift
-/// value, using the appropriate witness for the
-/// _ObjectiveCBridgeable._unconditionallyBridgeFromObjectiveC requirement.
-static Optional<ManagedValue>
-emitBridgeObjectiveCToNative(SILGenFunction &gen,
-                             SILLocation loc,
-                             ManagedValue objcValue,
-                             ProtocolConformance *conformance) {
-  // Find the _unconditionallyBridgeFromObjectiveC requirement.
-  auto requirement =
-    gen.SGM.getUnconditionallyBridgeFromObjectiveCRequirement(loc);
-  if (!requirement) return None;
-
-  // Retrieve the _unconditionallyBridgeFromObjectiveC witness.
-  auto witness = conformance->getWitness(requirement, nullptr);
-  assert(witness);
-
-  // Create a reference to the witness.
-  SILDeclRef witnessConstant(witness.getDecl());
-  auto witnessRef = gen.emitGlobalFunctionRef(loc, witnessConstant);
-
-  // Determine the substitutions.
-  ArrayRef<Substitution> substitutions;
-  auto witnessFnTy = witnessRef->getType().castTo<SILFunctionType>();
-
-  Type swiftValueType = conformance->getType();
-  if (auto valueTypeBGT = swiftValueType->getAs<BoundGenericType>()) {
-    // Compute the substitutions.
-    substitutions = valueTypeBGT->getSubstitutions(gen.SGM.SwiftModule,
-                                                   nullptr);
-  }
-
-  // Substitute into the witness function type.
-  if (!substitutions.empty())
-    witnessFnTy = witnessFnTy->substGenericArgs(gen.SGM.M, gen.SGM.SwiftModule,
-                                                substitutions);
+static ManagedValue emitBridgeNSStringToString(SILGenFunction &gen,
+                                               SILLocation loc,
+                                               ManagedValue nsstr) {
+  SILValue bridgeFn =
+      gen.emitGlobalFunctionRef(loc, gen.SGM.getNSStringToStringFn());
 
-  // If the Objective-C value isn't optional, wrap it in an optional.
-  Type objcValueType = objcValue.getType().getSwiftRValueType();
-  if (!objcValueType->getOptionalObjectType()) {
-    SILType loweredOptTy =
-        gen.SGM.getLoweredType(OptionalType::get(objcValueType));
+  Type inputType = nsstr.getType().getSwiftRValueType();
+  if (!inputType->getOptionalObjectType()) {
+    SILType loweredOptTy = gen.SGM.getLoweredType(OptionalType::get(inputType));
     auto *someDecl = gen.getASTContext().getOptionalSomeDecl();
-    auto *enumInst = gen.B.createEnum(loc, objcValue.getValue(), someDecl,
+    auto *enumInst = gen.B.createEnum(loc, nsstr.getValue(), someDecl,
                                       loweredOptTy);
-    objcValue = ManagedValue(enumInst, objcValue.getCleanup());
+    nsstr = ManagedValue(enumInst, nsstr.getCleanup());
   }
 
-  // Call the witness.
-  Type metatype = MetatypeType::get(swiftValueType);
-  SILValue metatypeValue = gen.B.createMetatype(loc,
-                                                gen.getLoweredType(metatype));
-
-  auto witnessCI = gen.getConstantInfo(witnessConstant);
-  CanType formalResultTy = witnessCI.LoweredInterfaceType.getResult();
-
-  // Set up the generic signature.
-  CanGenericSignature witnessGenericSignature;
-  if (auto genericSig =
-        cast<AbstractFunctionDecl>(witness.getDecl())->getGenericSignature())
-    witnessGenericSignature = genericSig->getCanonicalSignature();
-
-  GenericContextScope genericContextScope(gen.SGM.Types,
-                                          witnessGenericSignature);
-  return gen.emitApply(loc, ManagedValue::forUnmanaged(witnessRef),
-                       substitutions,
-                       { objcValue, ManagedValue::forUnmanaged(metatypeValue) },
-                       witnessFnTy,
-                       AbstractionPattern(witnessGenericSignature,
-                                          formalResultTy),
-                       swiftValueType->getCanonicalType(),
-                       ApplyOptions::None, None, None,
-                       SGFContext())
-    .getAsSingleValue(gen, loc);
+  SILType nativeTy = gen.getLoweredType(gen.SGM.Types.getStringType());
+  SILValue str = gen.B.createApply(loc, bridgeFn, bridgeFn->getType(), nativeTy,
+                                   {}, { nsstr.forward(gen) });
+
+  return gen.emitManagedRValueWithCleanup(str);
 }
 
 static ManagedValue emitBridgeCollectionToNative(SILGenFunction &gen,
@@ -431,7 +376,7 @@ static ManagedValue emitNativeToCBridgedNonoptionalValue(SILGenFunction &gen,
   // hardcoding String -> NSString.
   if (loweredNativeTy == gen.SGM.Types.getStringType()
       && loweredBridgedTy == gen.SGM.Types.getNSStringType()) {
-    if (auto result = emitBridgeNativeToObjectiveC(gen, loc, v))
+    if (auto result = emitBridgeToObjectiveC(gen, loc, v))
       return *result;
 
     return gen.emitUndef(loc, bridgedTy);
@@ -468,7 +413,7 @@ static ManagedValue emitNativeToCBridgedNonoptionalValue(SILGenFunction &gen,
   // _bridgeToObjectiveC witness.
   if (auto conformance =
           gen.SGM.getConformanceToObjectiveCBridgeable(loc, loweredNativeTy)) {
-    if (auto result = emitBridgeNativeToObjectiveC(gen, loc, v, conformance))
+    if (auto result = emitBridgeToObjectiveC(gen, loc, v, conformance))
       return *result;
 
     return gen.emitUndef(loc, bridgedTy);
@@ -662,14 +607,7 @@ static ManagedValue emitCBridgedToNativeValue(SILGenFunction &gen,
   // Bridge NSString to String.
   if (auto stringDecl = gen.getASTContext().getStringDecl()) {
     if (nativeTy.getSwiftRValueType()->getAnyNominal() == stringDecl) {
-      auto conformance =
-        gen.SGM.getConformanceToObjectiveCBridgeable(loc, loweredNativeTy);
-      assert(conformance &&
-             "Missing String conformation to _ObjectiveCBridgeable?");
-      if (auto result = emitBridgeObjectiveCToNative(gen, loc, v, conformance))
-        return *result;
-
-      return gen.emitUndef(loc, nativeTy);
+      return emitBridgeNSStringToString(gen, loc, v);
     }
   }
 

lib/Sema/CSApply.cpp

@@ -1276,11 +1276,9 @@ namespace {
       // Find the conformance of the value type to _BridgedToObjectiveC.
       Type valueType = value->getType()->getRValueType();
       ProtocolConformance *conformance = nullptr;
-      bool conforms =
-        tc.conformsToProtocol(valueType, bridgedProto, cs.DC,
-                              (ConformanceCheckFlags::InExpression|
-                               ConformanceCheckFlags::Used),
-                              &conformance);
+      bool conforms = tc.conformsToProtocol(valueType, bridgedProto, cs.DC,
+                                            ConformanceCheckFlags::InExpression,
+                                            &conformance);
       assert(conforms && "Should already have checked the conformance");
       (void)conforms;
 
@@ -1320,8 +1318,7 @@ namespace {
         = tc.conformsToProtocol(valueType,
                                 bridgedProto,
                                 cs.DC,
-                                (ConformanceCheckFlags::InExpression|
-                                 ConformanceCheckFlags::Used),
+                                ConformanceCheckFlags::InExpression,
                                 &conformance);
 
       FuncDecl *fn = nullptr;