[Coverage] Always emit unused coverage mappings in the same order.

[efriedma]

Summary

Non-determinism is confusing at best.

[vsk]

Thanks, lgtm!

cfe/trunk/lib/CodeGen/CodeGenModule.h

private:
   llvm::Constant *LifetimeEndFn = nullptr;
 
   GlobalDecl initializedGlobalDecl;
 
   std::unique_ptr<SanitizerMetadata> SanitizerMD;
 
   /// @}
 
-  llvm::DenseMap<const Decl *, bool> DeferredEmptyCoverageMappingDecls;
+  llvm::MapVector<const Decl *, bool> DeferredEmptyCoverageMappingDecls;
 
   std::unique_ptr<CoverageMappingModuleGen> CoverageMapping;
 
   /// Mapping from canonical types to their metadata identifiers. We need to
   /// maintain this mapping because identifiers may be formed from distinct
   /// MDNodes.
   typedef llvm::DenseMap<QualType, llvm::Metadata *> MetadataTypeMap;
   MetadataTypeMap MetadataIdMap;

cfe/trunk/lib/CodeGen/CodeGenModule.cpp

void CodeGenModule::ClearUnusedCoverageMapping(const Decl *D) {
   auto I = DeferredEmptyCoverageMappingDecls.find(D);
   if (I == DeferredEmptyCoverageMappingDecls.end())
     DeferredEmptyCoverageMappingDecls[D] = false;
   else
     I->second = false;
 }
 
 void CodeGenModule::EmitDeferredUnusedCoverageMappings() {
-  std::vector<const Decl *> DeferredDecls;
-  for (const auto &I : DeferredEmptyCoverageMappingDecls) {
-    if (!I.second)
+  for (const auto &Entry : DeferredEmptyCoverageMappingDecls) {
+    if (!Entry.second)
       continue;
-    DeferredDecls.push_back(I.first);
-  }
-  // Sort the declarations by their location to make sure that the tests get a
-  // predictable order for the coverage mapping for the unused declarations.
-  if (CodeGenOpts.DumpCoverageMapping)
-    std::sort(DeferredDecls.begin(), DeferredDecls.end(),
-              [] (const Decl *LHS, const Decl *RHS) {
-      return LHS->getLocStart() < RHS->getLocStart();
-    });
-  for (const auto *D : DeferredDecls) {
+    const Decl *D = Entry.first;
     switch (D->getKind()) {
     case Decl::CXXConversion:
     case Decl::CXXMethod:
     case Decl::Function:
     case Decl::ObjCMethod: {
       CodeGenPGO PGO(*this);
       GlobalDecl GD(cast<FunctionDecl>(D));
       PGO.emitEmptyCounterMapping(D, getMangledName(GD),