[IRGen] Emit base protocol witnesses as mangled names.

Rather than setting the witness tables for base protocols in a witness
table’s instantiation function, use mangled names as we do for
associated conformances. The runtime will eagerly realize them so clients
of witness tables are not affected.

For now, only do this for unconditional conformances: conditional
conformances won’t work yet because the instantiation function currently
copies the instantiation arguments (which satisfy the conditional
requirements) in to the private area. The runtime will need to take over
this responsibility for conditional conformances to work.

Part of rdar://problem/46282080.

(cherry picked from commit 3fce389)

Author: DougGregor

lib/IRGen/GenProto.cpp

@@ -995,14 +995,9 @@ static bool hasDependentTypeWitness(
   return false;
 }
 
-static bool hasDependentTypeWitness(const RootProtocolConformance *root) {
-  if (auto normal = dyn_cast<NormalProtocolConformance>(root))
-    return hasDependentTypeWitness(normal);
-  return false; // no associated types
-}
-
 static bool isDependentConformance(
               const RootProtocolConformance *rootConformance,
+              bool considerResilience,
               llvm::SmallPtrSet<const NormalProtocolConformance *, 4> &visited){
   // Self-conformances are never dependent.
   auto conformance = dyn_cast<NormalProtocolConformance>(rootConformance);
@@ -1015,7 +1010,7 @@ static bool isDependentConformance(
     return false;
 
   // If the conformance is resilient, this is always true.
-  if (isResilientConformance(conformance))
+  if (considerResilience && isResilientConformance(conformance))
     return true;
 
   // Check whether any of the conformances are dependent.
@@ -1033,6 +1028,7 @@ static bool isDependentConformance(
     if (assocConformance.isAbstract() ||
         isDependentConformance(assocConformance.getConcrete()
                                  ->getRootConformance(),
+                               considerResilience,
                                visited))
       return true;
   }
@@ -1048,9 +1044,10 @@ static bool isDependentConformance(
 
 /// Is there anything about the given conformance that requires witness
 /// tables to be dependently-generated?
-static bool isDependentConformance(const RootProtocolConformance *conformance) {
+static bool isDependentConformance(const RootProtocolConformance *conformance,
+                                   bool considerResilience) {
   llvm::SmallPtrSet<const NormalProtocolConformance *, 4> visited;
-  return ::isDependentConformance(conformance, visited);
+  return ::isDependentConformance(conformance, considerResilience, visited);
 }
 
 static bool isSynthesizedNonUnique(const RootProtocolConformance *conformance) {
@@ -1349,6 +1346,25 @@ class AccessorConformanceInfo : public ConformanceInfo {
         return;
       }
 
+      // If this isn't a conditional conformance, we can emit a mangled name.
+      // FIXME: Conditional conformances won't currently work because the
+      // witness tables for conditional requirements won't have been written
+      // into the private area yet.
+      if (SILConditionalConformances.empty()) {
+        if (isDependentConformance(astConf->getRootConformance(),
+                                   /*considerResilience=*/false))
+          RequiresSpecialization = true;
+
+        auto proto = Conformance.getProtocol();
+        CanType selfType = proto->getProtocolSelfType()->getCanonicalType();
+        AssociatedConformance requirement(proto, selfType, baseProto);
+        llvm::Constant *witnessEntry =
+          getAssociatedConformanceWitness(requirement, ConcreteType,
+                                          ProtocolConformanceRef(astConf));
+        Table.addBitCast(witnessEntry, IGM.Int8PtrTy);
+        return;
+      }
+
       // Otherwise, we'll need to derive it at instantiation time.
       RequiresSpecialization = true;
       SpecializedBaseConformances.push_back({Table.size(), &conf});
@@ -2152,7 +2168,7 @@ IRGenModule::getConformanceInfo(const ProtocolDecl *protocol,
   // so in theory we could allocate them on a BumpPtrAllocator. But there's not
   // a good one for us to use. (The ASTContext's outlives the IRGenModule in
   // batch mode.)
-  if (isDependentConformance(rootConformance) ||
+  if (isDependentConformance(rootConformance, /*considerResilience=*/true) ||
       // Foreign types need to go through the accessor to unique the witness
       // table.
       isSynthesizedNonUnique(rootConformance)) {
@@ -2220,7 +2236,7 @@ void IRGenModule::emitSILWitnessTable(SILWitnessTable *wt) {
   // Produce the initializer value.
   auto initializer = wtableContents.finishAndCreateFuture();
 
-  bool isDependent = isDependentConformance(conf);
+  bool isDependent = isDependentConformance(conf, /*considerResilience=*/true);
   auto global = cast<llvm::GlobalVariable>(
     isDependent
       ? getAddrOfWitnessTablePattern(cast<NormalProtocolConformance>(conf),
@@ -2235,7 +2251,9 @@ void IRGenModule::emitSILWitnessTable(SILWitnessTable *wt) {
                                      wtableBuilder.getTableSize(),
                                      wtableBuilder.getTablePrivateSize(),
                                      wtableBuilder.requiresSpecialization(),
-                                     hasDependentTypeWitness(conf));
+                                     isDependentConformance(
+                                       conf,
+                                       /*considerResilience=*/false));
 
   // Build the instantiation function, we if need one.
   description.instantiationFn = wtableBuilder.buildInstantiationFunction();

test/IRGen/associated_type_witness.swift

@@ -97,15 +97,6 @@ struct Computed<T, U> : Assocked {
   typealias Assoc = Pair<T, U>
 }
 
-//   Instantiation function for GenericComputed : DerivedFromSimpleAssoc.
-// CHECK-LABEL: define internal void @"$s23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocAAWI"(i8**, %swift.type* %"GenericComputed<T>", i8**)
-// CHECK:         [[T0:%.*]] = call i8** @swift_getWitnessTable({{.*}}@"$s23associated_type_witness15GenericComputedVyxGAA14HasSimpleAssocAAMc"
-// CHECK-NEXT:    [[T1:%.*]] = bitcast i8** [[T0]] to i8*
-// CHECK-NEXT:    [[T2:%.*]] = getelementptr inbounds i8*, i8** %0, i32 1
-// CHECK-NEXT:    store i8* [[T1]], i8** [[T2]], align 8
-// CHECK-NEXT:    ret void
-
-
 struct PBox<T: P> {}
 protocol HasSimpleAssoc {
   associatedtype Assoc
@@ -115,7 +106,7 @@ protocol DerivedFromSimpleAssoc : HasSimpleAssoc {}
 //   Generic witness table pattern for GenericComputed : DerivedFromSimpleAssoc.
 // GLOBAL-LABEL: @"$s23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocAAWp" = internal constant [2 x i8*]
 // GLOBAL-SAME: @"$s23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocAAMc"
-// GLOBAL-SAME: i8* null
+// GLOBAL-SAME: @"associated conformance 23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocA2A03HashI0"
 
 //   Relative reference to private data
 struct GenericComputed<T: P> : DerivedFromSimpleAssoc {
@@ -146,7 +137,7 @@ struct UsesVoid : HasSimpleAssoc {
 //   Protocol conformance descriptor for GenericComputed : DerivedFromSimpleAssoc.
 // GLOBAL-LABEL: @"$s23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocAAMc" = hidden constant
 // GLOBAL-SAME:    i16 2,
-// GLOBAL-SAME:    i16 0,
+// GLOBAL-SAME:    i16 1,
 
-//   Relative reference to instantiator function
-// GLOBAL-SAME:    i32 trunc (i64 sub (i64 ptrtoint (void (i8**, %swift.type*, i8**)* @"$s23associated_type_witness15GenericComputedVyxGAA22DerivedFromSimpleAssocAAWI" to i64),
+//   No instantiator function needed
+// GLOBAL-SAME:    i32 0

test/IRGen/deserialize-clang-importer-witness-tables.swift

@@ -9,8 +9,8 @@ public func foo(line: String) {
   // from the default argument expression passed to `RegEx(pattern:options:)`
   // below. Ensure that a local copy of the definition was deserialized
   // and lowered to IR.
-  // CHECK-LABEL: define {{.*}} void @"$sSo26NSRegularExpressionOptionsVs10SetAlgebraSCsACPxycfCTW"
   // CHECK-LABEL: define {{.*}} i8** @"$sSo26NSRegularExpressionOptionsVABSQSCWl"()
+  // CHECK-LABEL: define {{.*}} void @"$sSo26NSRegularExpressionOptionsVs10SetAlgebraSCsACPxycfCTW"
   let versionRegex = try! RegEx(pattern: "Apple")
   _ = versionRegex.firstMatch(in: line)  
 }

test/IRGen/generic_wt_linkage.sil

@@ -44,6 +44,6 @@ sil_default_witness_table hidden DerivedFromSimpleAssoc {
   no_default
 }
 
-// CHECK: define internal void @"$s4test15GenericComputedVyxGAA22DerivedFromSimpleAssocAAWI"
+// CHECK: define internal swiftcc i8** @"$s4test15GenericComputedVyxGAA22DerivedFromSimpleAssocAAxAA03HasfG0PWT"