IRGen: Don't emit generic witness table if conformance doesn't need one

The condition for "needs a generic witness table" was wrong; any
conformance with associated conformances would get one, even though
its only necessary if the associated conformances are dependent.

Fixing this also allows simplifying some code.

Author: slavapestov

lib/IRGen/GenProto.cpp

@@ -1284,7 +1284,6 @@ class AccessorConformanceInfo : public ConformanceInfo {
     // offsets, with conditional conformances closest to 0.
     unsigned NextPrivateDataIndex = 0;
     bool ResilientConformance;
-    bool RequiresSpecialization = false;
 
     const ProtocolInfo Π
 
@@ -1306,21 +1305,14 @@ class AccessorConformanceInfo : public ConformanceInfo {
           PI(IGM.getProtocolInfo(SILWT->getConformance()->getProtocol(),
                                  (ResilientConformance
                                   ? ProtocolInfoKind::RequirementSignature
-                                  : ProtocolInfoKind::Full))) {
-      // If the conformance is resilient, we require runtime instantiation.
-      if (ResilientConformance)
-        RequiresSpecialization = true;
-    }
+                                  : ProtocolInfoKind::Full))) {}
 
     /// The number of entries in the witness table.
     unsigned getTableSize() const { return TableSize; }
 
     /// The number of private entries in the witness table.
     unsigned getTablePrivateSize() const { return NextPrivateDataIndex; }
 
-    /// Whether this witness table must be specialized at runtime.
-    bool requiresSpecialization() const { return RequiresSpecialization; }
-
     /// The top-level entry point.
     void build();
 
@@ -1370,7 +1362,6 @@ class AccessorConformanceInfo : public ConformanceInfo {
       }
 
       // Otherwise, we'll need to derive it at instantiation time.
-      RequiresSpecialization = true;
       SpecializedBaseConformances.push_back({Table.size(), &conf});
       Table.addNullPointer(IGM.Int8PtrTy);
     }
@@ -1437,8 +1428,6 @@ class AccessorConformanceInfo : public ConformanceInfo {
       auto associate =
         Conformance.getTypeWitness(requirement.getAssociation(), nullptr)
           ->getCanonicalType();
-      if (associate->hasTypeParameter())
-        RequiresSpecialization = true;
       llvm::Constant *witness =
           IGM.getAssociatedTypeWitness(associate, /*inProtocolContext=*/false);
       Table.addBitCast(witness, IGM.Int8PtrTy);
@@ -1463,9 +1452,6 @@ class AccessorConformanceInfo : public ConformanceInfo {
           requirement.getAssociation(),
           requirement.getAssociatedRequirement());
 
-      if (requirement.getAssociation()->hasTypeParameter())
-        RequiresSpecialization = true;
-
 #ifndef NDEBUG
       assert(entry.getKind() == SILWitnessTable::AssociatedTypeProtocol
              && "sil witness table does not match protocol");
@@ -1516,7 +1502,6 @@ class AccessorConformanceInfo : public ConformanceInfo {
 
     /// Allocate another word of private data storage in the conformance table.
     unsigned getNextPrivateDataIndex() {
-      RequiresSpecialization = true;
       return NextPrivateDataIndex++;
     }
 
@@ -2309,7 +2294,9 @@ void IRGenModule::emitSILWitnessTable(SILWitnessTable *wt) {
   // descriptor.
   ConformanceDescription description(conf, wt, global, tableSize,
                                      wtableBuilder.getTablePrivateSize(),
-                                     wtableBuilder.requiresSpecialization(),
+                                     isDependentConformance(
+                                       conf,
+                                       /*considerResilience=*/true),
                                      isDependentConformance(
                                        conf,
                                        /*considerResilience=*/false));

test/IRGen/protocol_conformance_records.swift

@@ -22,8 +22,7 @@ public protocol Runcible {
 // -- witness table
 // CHECK-SAME:           @"$s28protocol_conformance_records15NativeValueTypeVAA8RuncibleAAWP"
 // -- flags
-// CHECK-SAME:           i32 0
-// CHECK-SAME:         },
+// CHECK-SAME:           i32 0 },
 public struct NativeValueType: Runcible {
   public func runce() {}
 }
@@ -36,8 +35,7 @@ public struct NativeValueType: Runcible {
 // -- witness table
 // CHECK-SAME:           @"$s28protocol_conformance_records15NativeClassTypeCAA8RuncibleAAWP"
 // -- flags
-// CHECK-SAME:           i32 0
-// CHECK-SAME:         },
+// CHECK-SAME:           i32 0 },
 public class NativeClassType: Runcible {
   public func runce() {}
 }
@@ -50,8 +48,7 @@ public class NativeClassType: Runcible {
 // -- witness table
 // CHECK-SAME:           @"$s28protocol_conformance_records17NativeGenericTypeVyxGAA8RuncibleAAWP"
 // -- flags
-// CHECK-SAME:           i32 0
-// CHECK-SAME:         },
+// CHECK-SAME:           i32 0 },
 public struct NativeGenericType<T>: Runcible {
   public func runce() {}
 }
@@ -87,6 +84,30 @@ extension Size: Runcible {
   public func runce() {}
 }
 
+// A non-dependent type conforming to a protocol with associated conformances
+// does not require a generic witness table.
+public protocol Simple {}
+
+public protocol AssociateConformance {
+  associatedtype X : Simple
+}
+
+public struct Other : Simple {}
+
+public struct Concrete : AssociateConformance {
+  public typealias X = Other
+}
+
+// CHECK-LABEL: @"$s28protocol_conformance_records8ConcreteVAA20AssociateConformanceAAMc" ={{ dllexport | protected | }}constant
+// -- protocol descriptor
+// CHECK-SAME:           @"$s28protocol_conformance_records20AssociateConformanceMp"
+// -- nominal type descriptor
+// CHECK-SAME:           @"$s28protocol_conformance_records8ConcreteVMn"
+// -- witness table
+// CHECK-SAME:           @"$s28protocol_conformance_records8ConcreteVAA20AssociateConformanceAAWP"
+// -- no flags are set, and no generic witness table follows
+// CHECK-SAME:           i32 0 }
+
 // CHECK-LABEL: @"\01l_protocols"
 // CHECK-SAME: @"$s28protocol_conformance_records8RuncibleMp"
 // CHECK-SAME: @"$s28protocol_conformance_records5SpoonMp"
@@ -136,7 +157,7 @@ extension Int : OtherResilientProtocol { }
 // -- witness table pattern
 // CHECK-SAME:           @"$s28protocol_conformance_records9DependentVyxGAA9AssociateAAWp"
 // -- flags
-// CHECK-SAME:           i32 0
+// CHECK-SAME:           i32 131072,
 // -- number of words in witness table
 // CHECK-SAME:           i16 2,
 // -- number of private words in witness table + bit for "needs instantiation"
@@ -151,5 +172,6 @@ extension Dependent : Associate {
 // CHECK-SAME: @"$s28protocol_conformance_records15NativeClassTypeCAA8RuncibleAAMc"
 // CHECK-SAME: @"$s28protocol_conformance_records17NativeGenericTypeVyxGAA8RuncibleAAMc"
 // CHECK-SAME: @"$s16resilient_struct4SizeV28protocol_conformance_records8RuncibleADMc"
+// CHECK-SAME: @"$s28protocol_conformance_records8ConcreteVAA20AssociateConformanceAAMc"
 // CHECK-SAME: @"$s28protocol_conformance_records17NativeGenericTypeVyxGAA5SpoonA2aERzlMc"
-// CHECK-SAME: @"$sSi18resilient_protocol22OtherResilientProtocol0B20_conformance_recordsMc"
+// CHECK-SAME: @"$sSi18resilient_protocol22OtherResilientProtocol0B20_conformance_recordsMc"