[Serialization] Avoid some non-determinism in the serializer.

Unfortunately, we still have non-determinism coming from elsewhere, so we
can't start trying to test this yet.

Motivated by rdar://problem/20539158

Swift SVN r28576

Author: jrose-apple

lib/Serialization/Serialization.cpp

@@ -1023,7 +1023,16 @@ void Serializer::writeNormalConformance(
     return false;
   });
 
-  for (auto defaulted : conformance->getDefaultedDefinitions()) {
+  SmallVector<ValueDecl *, 4> defaultedDefinitions{
+    conformance->getDefaultedDefinitions().begin(),
+    conformance->getDefaultedDefinitions().end()
+  };
+  llvm::array_pod_sort(defaultedDefinitions.begin(), defaultedDefinitions.end(),
+                       [](ValueDecl * const *left, ValueDecl * const *right) {
+    return (*left)->getFullName().compare((*right)->getFullName());
+  });
+
+  for (auto defaulted : defaultedDefinitions) {
     data.push_back(addDeclRef(defaulted));
     ++numDefaultedDefinitions;
   }

lib/Serialization/Serialization.h

@@ -22,6 +22,7 @@
 #include "swift/Subsystems.h"
 #include "swift/AST/Identifier.h"
 #include "swift/Basic/LLVM.h"
+#include "llvm/ADT/MapVector.h"
 #include <array>
 #include <queue>
 #include <tuple>
@@ -110,7 +111,7 @@ class Serializer {
   using DeclTableData = SmallVector<std::pair<uint8_t, DeclID>, 4>;
   /// The in-memory representation of what will eventually be an on-disk hash
   /// table.
-  using DeclTable = llvm::DenseMap<Identifier, DeclTableData>;
+  using DeclTable = llvm::MapVector<Identifier, DeclTableData>;
 
   /// Returns the declaration the given generic parameter list is associated
   /// with.

lib/Serialization/SerializeSIL.cpp

@@ -18,6 +18,7 @@
 #include "swift/SIL/SILModule.h"
 #include "swift/SIL/SILUndef.h"
 
+#include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/CommandLine.h"
@@ -123,7 +124,7 @@ namespace {
 
   public:
     using TableData = FuncTableInfo::data_type;
-    using Table = llvm::DenseMap<FuncTableInfo::key_type, TableData>;
+    using Table = llvm::MapVector<FuncTableInfo::key_type, TableData>;
   private:
     /// FuncTable maps function name to an ID.
     Table FuncTable;