SIL: Sort associated types in witness table layouts

This allows them to be re-ordered resiliently.

Author: slavapestov

include/swift/SIL/SILWitnessVisitor.h

@@ -58,12 +58,21 @@ template <class T> class SILWitnessVisitor : public ASTVisitor<T> {
       if (haveAddedAssociatedTypes) return;
       haveAddedAssociatedTypes = true;
 
+      SmallVector<AssociatedTypeDecl *, 2> associatedTypes;
       for (Decl *member : protocol->getMembers()) {
         if (auto associatedType = dyn_cast<AssociatedTypeDecl>(member)) {
-          // TODO: only add associated types when they're new?
-          asDerived().addAssociatedType(AssociatedType(associatedType));
+          associatedTypes.push_back(associatedType);
         }
       }
+
+      // Sort associated types by name, for resilience.
+      llvm::array_pod_sort(associatedTypes.begin(), associatedTypes.end(),
+                           TypeDecl::compare);
+
+      for (auto *associatedType : associatedTypes) {
+        // TODO: only add associated types when they're new?
+        asDerived().addAssociatedType(AssociatedType(associatedType));
+      }
     };
 
     for (const auto &reqt : protocol->getRequirementSignature()) {

test/IRGen/associated_type_witness.swift

@@ -12,7 +12,7 @@ protocol Assocked {
 
 struct Universal : P, Q {}
 
-// CHECK: [[ASSOC_TYPE_NAMES:@.*]] = private constant [29 x i8] c"OneAssoc TwoAssoc ThreeAssoc\00"
+// CHECK: [[ASSOC_TYPE_NAMES:@.*]] = private constant [29 x i8] c"OneAssoc ThreeAssoc TwoAssoc\00"
 // CHECK: @"$S23associated_type_witness18HasThreeAssocTypesMp" =
 // CHECK-SAME: [[ASSOC_TYPE_NAMES]] to i64
 

test/IRGen/associated_types.swift

@@ -75,7 +75,7 @@ func testFastRuncible<T: Runcible, U: FastRuncible>(_ t: T, u: U)
 //   1. Get the type metadata for U.RuncerType.Runcee.
 //     1a. Get the type metadata for U.RuncerType.
 //         Note that we actually look things up in T, which is going to prove unfortunate.
-// CHECK:      [[T0_GEP:%.*]] = getelementptr inbounds i8*, i8** %T.Runcible, i32 1
+// CHECK:      [[T0_GEP:%.*]] = getelementptr inbounds i8*, i8** %T.Runcible, i32 2
 // CHECK:      [[T0:%.*]] = load i8*, i8** [[T0_GEP]]
 // CHECK-NEXT: [[T1:%.*]] = bitcast i8* [[T0]] to %swift.metadata_response ([[INT]], %swift.type*, i8**)*
 // CHECK-NEXT: [[T2:%.*]] = call swiftcc %swift.metadata_response [[T1]]([[INT]] 0, %swift.type* %T, i8** %T.Runcible)