3 files changed, 14 insertions, 29 deletions

diff --git a/clang/lib/Sema/MultiplexExternalSemaSource.cpp b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
index 0f93421ac21..89eec242eb1 100644
--- a/clang/lib/Sema/MultiplexExternalSemaSource.cpp
+++ b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -204,7 +204,7 @@ void MultiplexExternalSemaSource::ReadKnownNamespaces(
 }
 
 void MultiplexExternalSemaSource::ReadUndefinedButUsed(
-                         llvm::DenseMap<NamedDecl*, SourceLocation> &Undefined){
+    llvm::MapVector<NamedDecl *, SourceLocation> &Undefined) {
   for(size_t i = 0; i < Sources.size(); ++i)
     Sources[i]->ReadUndefinedButUsed(Undefined);
 }
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 584dca1e387..997d967aa19 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -478,10 +478,8 @@ static bool ShouldRemoveFromUnused(Sema *SemaRef, const DeclaratorDecl *D) {
 /// Obtains a sorted list of functions that are undefined but ODR-used.
 void Sema::getUndefinedButUsed(
     SmallVectorImpl<std::pair<NamedDecl *, SourceLocation> > &Undefined) {
-  for (llvm::DenseMap<NamedDecl *, SourceLocation>::iterator
-         I = UndefinedButUsed.begin(), E = UndefinedButUsed.end();
-       I != E; ++I) {
-    NamedDecl *ND = I->first;
+  for (const auto &UndefinedUse : UndefinedButUsed) {
+    NamedDecl *ND = UndefinedUse.first;
 
     // Ignore attributes that have become invalid.
     if (ND->isInvalidDecl()) continue;
@@ -502,24 +500,8 @@ void Sema::getUndefinedButUsed(
         continue;
     }
 
-    Undefined.push_back(std::make_pair(ND, I->second));
+    Undefined.push_back(std::make_pair(ND, UndefinedUse.second));
   }
-
-  // Sort (in order of use site) so that we're not dependent on the iteration
-  // order through an llvm::DenseMap.
-  SourceManager &SM = Context.getSourceManager();
-  std::sort(Undefined.begin(), Undefined.end(),
-            [&SM](const std::pair<NamedDecl *, SourceLocation> &l,
-                  const std::pair<NamedDecl *, SourceLocation> &r) {
-    if (l.second.isValid() && !r.second.isValid())
-      return true;
-    if (!l.second.isValid() && r.second.isValid())
-      return false;
-    if (l.second != r.second)
-      return SM.isBeforeInTranslationUnit(l.second, r.second);
-    return SM.isBeforeInTranslationUnit(l.first->getLocation(),
-                                        r.first->getLocation());
-  });
 }
 
 /// checkUndefinedButUsed - Check for undefined objects with internal linkage
@@ -554,6 +536,8 @@ static void checkUndefinedButUsed(Sema &S) {
     if (I->second.isValid())
       S.Diag(I->second, diag::note_used_here);
   }
+
+  S.UndefinedButUsed.clear();
 }
 
 void Sema::LoadExternalWeakUndeclaredIdentifiers() {
@@ -749,6 +733,12 @@ void Sema::ActOnEndOfTranslationUnit() {
       !Diags.isIgnored(diag::warn_delegating_ctor_cycle, SourceLocation()))
     CheckDelegatingCtorCycles();
 
+  if (!Diags.hasErrorOccurred()) {
+    if (ExternalSource)
+      ExternalSource->ReadUndefinedButUsed(UndefinedButUsed);
+    checkUndefinedButUsed(*this);
+  }
+
   if (TUKind == TU_Module) {
     // If we are building a module, resolve all of the exported declarations
     // now.
@@ -882,10 +872,6 @@ void Sema::ActOnEndOfTranslationUnit() {
       }
     }
 
-    if (ExternalSource)
-      ExternalSource->ReadUndefinedButUsed(UndefinedButUsed);
-    checkUndefinedButUsed(*this);
-
     emitAndClearUnusedLocalTypedefWarnings();
   }
 
@@ -1271,8 +1257,7 @@ void ExternalSemaSource::ReadKnownNamespaces(
 }
 
 void ExternalSemaSource::ReadUndefinedButUsed(
-                       llvm::DenseMap<NamedDecl *, SourceLocation> &Undefined) {
-}
+    llvm::MapVector<NamedDecl *, SourceLocation> &Undefined) {}
 
 void ExternalSemaSource::ReadMismatchingDeleteExpressions(llvm::MapVector<
     FieldDecl *, llvm::SmallVector<std::pair<SourceLocation, bool>, 4>> &) {}
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index f730d6f4f20..d05cbeb2a1c 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -7254,7 +7254,7 @@ void ASTReader::ReadKnownNamespaces(
 }
 
 void ASTReader::ReadUndefinedButUsed(
-                        llvm::DenseMap<NamedDecl*, SourceLocation> &Undefined) {
+    llvm::MapVector<NamedDecl *, SourceLocation> &Undefined) {
   for (unsigned Idx = 0, N = UndefinedButUsed.size(); Idx != N;) {
     NamedDecl *D = cast<NamedDecl>(GetDecl(UndefinedButUsed[Idx++]));
     SourceLocation Loc =