SILGen: Don't emit default witness tables unless protocol is resilient

Author: slavapestov

lib/SILGen/SILGenType.cpp

@@ -827,7 +827,8 @@ class SILGenType : public TypeMemberVisitor<SILGenType> {
 
     // Build a default witness table if this is a protocol.
     if (auto protocol = dyn_cast<ProtocolDecl>(theType)) {
-      if (!protocol->isObjC())
+      if (!protocol->isObjC() &&
+          !protocol->hasFixedLayout())
         SGM.emitDefaultWitnessTable(protocol);
       return;
     }

lib/Sema/TypeChecker.cpp

@@ -678,7 +678,8 @@ void swift::finishTypeCheckingFile(SourceFile &SF) {
 
   for (auto D : SF.Decls)
     if (auto PD = dyn_cast<ProtocolDecl>(D))
-      TC.inferDefaultWitnesses(PD);
+      if (!PD->hasFixedLayout())
+        TC.inferDefaultWitnesses(PD);
 }
 
 void swift::performWholeModuleTypeChecking(SourceFile &SF) {

test/SILGen/protocol_resilience.swift

@@ -254,19 +254,6 @@ func inoutResilientProtocol(_ x: inout OtherConformingType) {
   inoutFunc(&OtherConformingType.staticPropertyInExtension)
 }
 
-// Protocol is not public -- make sure default witnesses have the right linkage
-protocol InternalProtocol {
-  func noDefaultF()
-  func defaultG()
-}
-
-extension InternalProtocol {
-
-  // CHECK-LABEL: sil private [transparent] [thunk] @_T019protocol_resilience16InternalProtocolP8defaultGyyF
-  // CHECK: return
-  func defaultG() {}
-}
-
 // CHECK-LABEL: sil_default_witness_table P {
 // CHECK-NEXT: }
 
@@ -328,8 +315,3 @@ extension InternalProtocol {
 // CHECK-NEXT:   method #ReabstractSelfRefined.callback!setter.1: {{.*}} : @_T019protocol_resilience21ReabstractSelfRefinedP8callbackxxcvs
 // CHECK-NEXT:   method #ReabstractSelfRefined.callback!materializeForSet.1: {{.*}} : @_T019protocol_resilience21ReabstractSelfRefinedP8callbackxxcvm
 // CHECK-NEXT: }
-
-// CHECK-LABEL: sil_default_witness_table hidden InternalProtocol {
-// CHECK-NEXT:   no_default
-// CHECK-NEXT:   method #InternalProtocol.defaultG!1: {{.*}} : @_T019protocol_resilience16InternalProtocolP8defaultGyyF
-// CHECK-NEXT: }

test/SILGen/witness_accessibility.swift

@@ -20,9 +20,9 @@ extension R {
 
 public struct S : R {}
 
-// CHECK-LABEL: sil private @_T021witness_accessibility1R{{.*}}AE18privateRequirementyyF
 // CHECK-LABEL: sil private @_T021witness_accessibility1R{{.*}}E17publicRequirementyyF
 // CHECK-LABEL: sil private @_T021witness_accessibility1R{{.*}}E19internalRequirementyyF
+// CHECK-LABEL: sil private @_T021witness_accessibility1R{{.*}}AE18privateRequirementyyF
 
 // CHECK-LABEL: sil private [transparent] [thunk] @_T021witness_accessibility1SVAA1R{{.*}}dELLP18privateRequirementyyFTW
 // CHECK-LABEL: sil private [transparent] [thunk] @_T021witness_accessibility1SVAA1QA2aDP19internalRequirementyyFTW

test/SILOptimizer/dead_function_elimination.swift

@@ -216,15 +216,3 @@ internal func donotEliminate() {
 
 // CHECK-TESTING-LABEL: sil_witness_table [serialized] Adopt: Prot
 // CHECK-TESTING: DeadWitness{{.*}}: @{{.*}}DeadWitness
-
-// CHECK-LABEL: sil_default_witness_table hidden Prot
-// CHECK:  no_default
-// CHECK:  no_default
-// CHECK:  method #Prot.aliveDefaultWitness!1: {{.*}} : @{{.*}}aliveDefaultWitness
-// CHECK:  no_default
-
-// CHECK-TESTING-LABEL: sil_default_witness_table Prot
-// CHECK-TESTING:  no_default
-// CHECK-TESTING:  no_default
-// CHECK-TESTING:  method #Prot.aliveDefaultWitness!1: {{.*}} : @{{.*}}aliveDefaultWitness
-// CHECK-TESTING:  method #Prot.DeadDefaultWitness!1: {{.*}} : @{{.*}}DeadDefaultWitness