[IRGen] Narrow the “requires instantiation” bit for conformances.

lib/IRGen/GenDecl.cpp

@@ -2009,7 +2009,11 @@ llvm::Function *IRGenModule::getAddrOfSILFunction(SILFunction *f,
 
 static llvm::GlobalVariable *createGOTEquivalent(IRGenModule &IGM,
                                                  llvm::Constant *global,
-                                                 StringRef globalName) {
+                                                 LinkEntity entity) {
+  // Determine the name of this entity.
+  llvm::SmallString<64> globalName;
+  entity.mangle(globalName);
+
   if (IGM.Triple.getObjectFormat() == llvm::Triple::COFF) {
     if (cast<llvm::GlobalValue>(global)->hasDLLImportStorageClass()) {
       llvm::GlobalVariable *GV =
@@ -2178,7 +2182,7 @@ IRGenModule::getAddrOfLLVMVariable(LinkEntity entity,
 
     // Make a new GOT equivalent referring to the new variable with its
     // definition type.
-    auto newGOTEquiv = createGOTEquivalent(*this, var, var->getName());
+    auto newGOTEquiv = createGOTEquivalent(*this, var, entity);
     auto castGOTEquiv = llvm::ConstantExpr::getBitCast(newGOTEquiv,
                                                    existingGOTEquiv->getType());
     existingGOTEquiv->replaceAllUsesWith(castGOTEquiv);
@@ -2256,9 +2260,7 @@ IRGenModule::getAddrOfLLVMVariableOrGOTEquivalent(LinkEntity entity,
     auto global = cast<llvm::GlobalValue>(entry);
     // Use it as the initializer for an anonymous constant. LLVM can treat this as
     // equivalent to the global's GOT entry.
-    llvm::SmallString<64> name;
-    entity.mangle(name);
-    auto gotEquivalent = createGOTEquivalent(*this, global, name);
+    auto gotEquivalent = createGOTEquivalent(*this, global, entity);
     gotEntry = gotEquivalent;
     return {gotEquivalent, ConstantReference::Indirect};
   };

lib/IRGen/GenProto.cpp

@@ -961,6 +961,31 @@ static bool isResilientConformance(const NormalProtocolConformance *conformance)
   return true;
 }
 
+/// Whether this protocol conformance has a dependent type witness.
+static bool hasDependentTypeWitness(
+                                const NormalProtocolConformance *conformance) {
+  auto DC = conformance->getDeclContext();
+  // If the conforming type isn't dependent, the below check is never true.
+  if (!DC->isGenericContext())
+    return false;
+
+  // Check whether any of the associated types are dependent.
+  if (conformance->forEachTypeWitness(nullptr,
+        [&](AssociatedTypeDecl *requirement, Type type,
+            TypeDecl *explicitDecl) -> bool {
+          // Skip associated types that don't have witness table entries.
+          if (!requirement->getOverriddenDecls().empty())
+            return false;
+
+          // RESILIENCE: this could be an opaque conformance
+          return type->hasTypeParameter();
+       })) {
+    return true;
+  }
+
+  return false;
+}
+
 /// Is there anything about the given conformance that requires witness
 /// tables to be dependently-generated?
 bool irgen::isDependentConformance(const NormalProtocolConformance *conformance) {
@@ -984,20 +1009,8 @@ bool irgen::isDependentConformance(const NormalProtocolConformance *conformance)
       return true;
   }
 
-  auto DC = conformance->getDeclContext();
-  // If the conforming type isn't dependent, the below check is never true.
-  if (!DC->isGenericContext())
-    return false;
-
-  // Check whether any of the associated types are dependent.
-  if (conformance->forEachTypeWitness(nullptr,
-        [&](AssociatedTypeDecl *requirement, Type type,
-            TypeDecl *explicitDecl) -> bool {
-          // RESILIENCE: this could be an opaque conformance
-          return type->hasTypeParameter();
-       })) {
+  if (hasDependentTypeWitness(conformance))
     return true;
-  }
 
   // Check if there are any conditional conformances. Other forms of conditional
   // requirements don't exist in the witness table.
@@ -2184,7 +2197,7 @@ namespace {
       // WitnessTablePrivateSizeInWordsAndRequiresInstantiation
       B.addInt(IGM.Int16Ty,
                (Description.witnessTablePrivateSize << 1) |
-                Description.requiresSpecialization);
+                Description.hasDependentAssociatedTypeWitnesses);
       // RelativePointer<WitnessTable>
       B.addRelativeAddress(Description.pattern);
       // Instantiation function
@@ -2413,7 +2426,8 @@ void IRGenModule::emitSILWitnessTable(SILWitnessTable *wt) {
   ConformanceDescription description(conf, wt, global,
                                      wtableBuilder.getTableSize(),
                                      wtableBuilder.getTablePrivateSize(),
-                                     wtableBuilder.requiresSpecialization());
+                                     wtableBuilder.requiresSpecialization(),
+                                     hasDependentTypeWitness(conf));
 
   // Build the instantiation function, we if need one.
   description.instantiationFn = wtableBuilder.buildInstantiationFunction();

lib/IRGen/IRGenModule.h

@@ -470,6 +470,9 @@ struct ConformanceDescription {
   /// Whether this witness table requires runtime specialization.
   const unsigned requiresSpecialization : 1;
 
+  /// Whether this witness table contains dependent associated type witnesses.
+  const unsigned hasDependentAssociatedTypeWitnesses : 1;
+
   /// The instantiation function, to be run at the end of witness table
   /// instantiation.
   llvm::Constant *instantiationFn = nullptr;
@@ -482,11 +485,15 @@ struct ConformanceDescription {
                          llvm::Constant *pattern,
                          uint16_t witnessTableSize,
                          uint16_t witnessTablePrivateSize,
-                         bool requiresSpecialization)
+                         bool requiresSpecialization,
+                         bool hasDependentAssociatedTypeWitnesses)
     : conformance(conformance), wtable(wtable), pattern(pattern),
       witnessTableSize(witnessTableSize),
       witnessTablePrivateSize(witnessTablePrivateSize),
-      requiresSpecialization(requiresSpecialization) { }
+      requiresSpecialization(requiresSpecialization),
+      hasDependentAssociatedTypeWitnesses(hasDependentAssociatedTypeWitnesses)
+  {
+  }
 };
 
 /// IRGenModule - Primary class for emitting IR for global declarations.

test/IRGen/associated_type_witness.swift

@@ -167,7 +167,7 @@ struct UsesVoid : HasSimpleAssoc {
 //   Protocol conformance descriptor for GenericComputed : DerivedFromSimpleAssoc.
 // GLOBAL-LABEL: @"$s23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocAAMc" = hidden constant
 // GLOBAL-SAME:    i16 2,
-// GLOBAL-SAME:    i16 1,
+// GLOBAL-SAME:    i16 0,
 
 //   Relative reference to witness table template
 // GLOBAL-SAME:    i32 trunc (i64 sub (i64 ptrtoint ([2 x i8*]* @"$s23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocAAWp" to i64

test/IRGen/protocol_conformance_records.swift

@@ -137,6 +137,10 @@ extension Int : OtherResilientProtocol { }
 // CHECK-SAME:           @"$s28protocol_conformance_records9DependentVyxGAA9AssociateAAWa"
 // -- flags
 // CHECK-SAME:           i32 1
+// -- number of words in witness table
+// CHECK-SAME:           i16 2,
+// -- number of private words in witness table + bit for "needs instantiation"
+// CHECK-SAME:           i16 1
 // CHECK-SAME:         }
 extension Dependent : Associate {
   public typealias X = (T, T)

test/IRGen/protocol_resilience.sil

@@ -106,8 +106,8 @@ protocol InternalProtocol {
 // -- number of witness table entries
 // CHECK-SAME:   i16 1,
 
-// -- size of private area + 'needs instantiation' bit
-// CHECK-SAME:   i16 1,
+// -- size of private area + 'requires instantiation' bit (not set)
+// CHECK-SAME:   i16 0,
 
 // -- the template
 // CHECK-SAME:   @"$s19protocol_resilience23ResilientConformingTypeV010resilient_A005OtherC8ProtocolAAWp"
@@ -139,8 +139,8 @@ protocol InternalProtocol {
 // -- number of witness table entries
 // CHECK-SAME:   i16 1,
 
-// -- size of private area + 'needs instantiation' bit
-// CHECK-SAME:   i16 1,
+// -- size of private area + 'requires instantiation' bit (not set)
+// CHECK-SAME:   i16 0,
 
 // -- the template
 // CHECK-SAME:   @"$s19protocol_resilience24ConformsWithRequirementsV010resilient_A008ProtocoldE0AAWp"

test/IRGen/protocol_resilience_descriptors.swift

@@ -56,6 +56,12 @@ public protocol P { }
 public struct ConditionallyConforms<Element> { }
 public struct Y { }
 
+// CHECK-USAGE-LABEL: @"$s31protocol_resilience_descriptors1YV010resilient_A022OtherResilientProtocolAAMc" =
+// CHECK-USAGE-SAME: i32 131073,
+// CHECK-USAGE-SAME: i16 1,
+// CHECK-USAGE-SAME: i16 0
+extension Y: OtherResilientProtocol { }
+
 // CHECK-USAGE: @"$s31protocol_resilience_descriptors29ConformsWithAssocRequirementsV010resilient_A008ProtocoleF12TypeDefaultsAAMc" =
 // CHECK-USAGE-SAME: $s18resilient_protocol29ProtocolWithAssocTypeDefaultsP2T2AC_AA014OtherResilientC0Tn
 // CHECK-USAGE-SAME: $s31protocol_resilience_descriptors29ConformsWithAssocRequirementsV010resilient_A008ProtocoleF12TypeDefaultsAA2T2AdEP_AD014OtherResilientI0PWT