diff --git a/lib/IRGen/GenProto.cpp b/lib/IRGen/GenProto.cpp
index 0d142b5415e..91f6a595824 100644
--- a/lib/IRGen/GenProto.cpp
+++ b/lib/IRGen/GenProto.cpp
@@ -1114,7 +1114,7 @@ static llvm::Value *emitWitnessTableAccessorCall(
 
   // Emit the source metadata if we haven't yet.
   if (!*srcMetadataCache) {
-    *srcMetadataCache = IGF.emitTypeMetadataRef(
+    *srcMetadataCache = IGF.emitAbstractTypeMetadataRef(
       conformance->getType()->getCanonicalType());
   }
 
diff --git a/test/IRGen/witness_method.sil b/test/IRGen/witness_method.sil
index a98294707ed..654271cab7d 100644
--- a/test/IRGen/witness_method.sil
+++ b/test/IRGen/witness_method.sil
@@ -64,12 +64,14 @@ struct SyncUp<Deliverable> : Synergy {
 
 // CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc void @testGenericWitnessMethod(%swift.opaque* noalias nocapture sret, %T14witness_method6SyncUpV* noalias nocapture, %swift.type* %T)
 // CHECK: entry:
-// CHECK:   [[TMP:%.*]] = call swiftcc %swift.metadata_response @"$s14witness_method6SyncUpVMa"([[INT]] 0, %swift.type* %T)
+// CHECK:   [[TMP:%.*]] = call swiftcc %swift.metadata_response @"$s14witness_method6SyncUpVMa"([[INT]] 255, %swift.type* %T)
 // CHECK:   [[METADATA:%.*]] = extractvalue %swift.metadata_response [[TMP]], 0
 // CHECK:   [[WTABLE:%.*]] = call i8** @swift_getWitnessTable(
 // CHECK:   [[WITNESS_ADDR:%.*]] = getelementptr inbounds i8*, i8** [[WTABLE]], i32 2
 // CHECK:   [[WITNESS_FN:%.*]] = load i8*, i8** [[WITNESS_ADDR]]
 // CHECK:   [[WITNESS:%.*]] = bitcast i8* [[WITNESS_FN]] to void (%swift.opaque*, %swift.opaque*, %swift.type*, i8**)*
+// CHECK:   [[TMP:%.*]] = call swiftcc %swift.metadata_response @swift_checkMetadataState(i64 0, %swift.type* [[METADATA]])
+// CHECK:   [[METADATA:%.*]] = extractvalue %swift.metadata_response [[TMP]], 0
 // CHECK:   [[ARG:%.*]] = bitcast %T14witness_method6SyncUpV* %1 to %swift.opaque*
 // CHECK:   call swiftcc void [[WITNESS]](%swift.opaque* noalias nocapture sret %0, %swift.opaque* noalias nocapture swiftself [[ARG]], %swift.type* [[METADATA]], i8** [[WTABLE]])
 // CHECK:   ret void
diff --git a/test/Inputs/conditional_conformance_basic_conformances.swift b/test/Inputs/conditional_conformance_basic_conformances.swift
index 06cc8202dc5..028e512ba3c 100644
--- a/test/Inputs/conditional_conformance_basic_conformances.swift
+++ b/test/Inputs/conditional_conformance_basic_conformances.swift
@@ -84,10 +84,10 @@ public func single_concrete() {
 // CHECK-NEXT:    br i1 [[IS_NULL]], label %cacheIsNull, label %cont
 
 // CHECK:       cacheIsNull:
-// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s42conditional_conformance_basic_conformances6SingleVyAA4IsP2VGMa"(i64 0)
+// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s42conditional_conformance_basic_conformances6SingleVyAA4IsP2VGMa"(i64 255)
 // CHECK-NEXT:    [[Single_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0
 
-// CHECK-NEXT:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
+// CHECK:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
 // CHECK-NEXT:    [[A_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0
 // CHECK-NEXT:    store i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"$s42conditional_conformance_basic_conformances4IsP2VAA0F0AAWP", i32 0, i32 0), i8*** [[A_P2_PTR]], align 8
 
@@ -219,10 +219,10 @@ public func double_concrete_concrete() {
 // CHECK-NEXT:    br i1 [[IS_NULL]], label %cacheIsNull, label %cont
 
 // CHECK:       cacheIsNull:
-// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s42conditional_conformance_basic_conformances6DoubleVyAA4IsP2VAA0F2P3VGMa"(i64 0)
+// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s42conditional_conformance_basic_conformances6DoubleVyAA4IsP2VAA0F2P3VGMa"(i64 255)
 // CHECK-NEXT:    [[Double_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0
 
-// CHECK-NEXT:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [2 x i8**], [2 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
+// CHECK:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [2 x i8**], [2 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
 // CHECK-NEXT:    [[B_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0
 // CHECK-NEXT:    store i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"$s42conditional_conformance_basic_conformances4IsP2VAA0F0AAWP", i32 0, i32 0), i8*** [[B_P2_PTR]], align 8
 // CHECK-NEXT:    [[C_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 1
diff --git a/test/Inputs/conditional_conformance_subclass.swift b/test/Inputs/conditional_conformance_subclass.swift
index f3c6c2683a8..3684ac6771d 100644
--- a/test/Inputs/conditional_conformance_subclass.swift
+++ b/test/Inputs/conditional_conformance_subclass.swift
@@ -83,9 +83,9 @@ public func subclassgeneric_concrete() {
 // CHECK-NEXT:    br i1 [[IS_NULL]], label %cacheIsNull, label %cont
 
 // CHECK:       cacheIsNull:
-// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s32conditional_conformance_subclass15SubclassGenericCyAA4IsP2VGMa"(i64 0)
+// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s32conditional_conformance_subclass15SubclassGenericCyAA4IsP2VGMa"(i64 255)
 // CHECK-NEXT:    [[SubclassGeneric_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0
-// CHECK-NEXT:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
+// CHECK:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
 // CHECK-NEXT:    [[A_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0
 // CHECK-NEXT:    store i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"$s32conditional_conformance_subclass4IsP2VAA0E0AAWP", i32 0, i32 0), i8*** [[A_P2_PTR]], align 8
 // CHECK-NEXT:    [[Base_P1:%.*]] = call i8** @swift_getWitnessTable
@@ -118,9 +118,9 @@ public func subclassconcrete() {
 // CHECK-NEXT:    br i1 [[IS_NULL]], label %cacheIsNull, label %cont
 
 // CHECK:       cacheIsNull:
-// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s32conditional_conformance_subclass16SubclassConcreteCMa"(i64 0)
+// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s32conditional_conformance_subclass16SubclassConcreteCMa"(i64 255)
 // CHECK-NEXT:    [[SubclassConcrete_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0
-// CHECK-NEXT:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
+// CHECK:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
 // CHECK-NEXT:    [[A_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0
 // CHECK-NEXT:    store i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"$s32conditional_conformance_subclass4IsP2VAA0E0AAWP", i32 0, i32 0), i8*** [[A_P2_PTR]], align 8
 // CHECK-NEXT:    [[Base_P1:%.*]] = call i8** @swift_getWitnessTable
@@ -153,9 +153,9 @@ public func subclassgenericconcrete() {
 // CHECK-NEXT:    br i1 [[IS_NULL]], label %cacheIsNull, label %cont
 
 // CHECK:       cacheIsNull:
-// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s32conditional_conformance_subclass23SubclassGenericConcreteCMa"(i64 0)
+// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s32conditional_conformance_subclass23SubclassGenericConcreteCMa"(i64 255)
 // CHECK-NEXT:    [[SubclassGenericConcrete_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0
-// CHECK-NEXT:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
+// CHECK:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [1 x i8**], [1 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
 // CHECK-NEXT:    [[A_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0
 // CHECK-NEXT:    store i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"$s32conditional_conformance_subclass4IsP2VAA0E0AAWP", i32 0, i32 0), i8*** [[A_P2_PTR]], align 8
 // CHECK-NEXT:    [[Base_P1:%.*]] = call i8** @swift_getWitnessTable
diff --git a/test/Inputs/conditional_conformance_with_assoc.swift b/test/Inputs/conditional_conformance_with_assoc.swift
index 23a30093865..b356a60122d 100644
--- a/test/Inputs/conditional_conformance_with_assoc.swift
+++ b/test/Inputs/conditional_conformance_with_assoc.swift
@@ -200,9 +200,9 @@ public func concrete_concrete() {
 // CHECK-NEXT:    br i1 [[IS_NULL]], label %cacheIsNull, label %cont
 
 // CHECK:       cacheIsNull:
-// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGMa"(i64 0)
+// CHECK-NEXT:    [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGMa"(i64 255)
 // CHECK-NEXT:    [[Double_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0
-// CHECK-NEXT:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [3 x i8**], [3 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
+// CHECK:    [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [3 x i8**], [3 x i8**]* %conditional.requirement.buffer, i32 0, i32 0
 // CHECK-NEXT:    [[C_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0
 // CHECK-NEXT:    store i8** getelementptr inbounds ([2 x i8*], [2 x i8*]* @"$s34conditional_conformance_with_assoc4IsP3VAA0F0AAWP", i32 0, i32 0), i8*** [[C_P3_PTR]], align 8
 // CHECK-NEXT:    [[B_AT2_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 1
diff --git a/test/Runtime/lazy_witness_table_cycle.swift b/test/Runtime/lazy_witness_table_cycle.swift
new file mode 100644
index 00000000000..05bd44924a0
--- /dev/null
+++ b/test/Runtime/lazy_witness_table_cycle.swift
@@ -0,0 +1,31 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+// SR-5958
+import Foundation
+
+public struct Property: Equatable, Hashable, Codable {
+    public var value: PropertyValue<Property>
+}
+
+public enum PropertyValue<P>: Equatable, Hashable where P: Equatable & Hashable {
+    case invalid
+    case date(date: Date?)
+}
+
+extension PropertyValue: Codable where P: Codable {
+    public func encode(to encoder: Encoder) throws {}
+    public init(from decoder: Decoder) throws { self = .invalid }
+}
+
+extension String: Error {}
+
+let encoder = JSONEncoder()
+let json = try! encoder.encode(
+  Property(value: .invalid)
+)
+
+let decoder = JSONDecoder()
+let result = try! decoder.decode(Property.self, from: json)
+print(result)