Index: lib/Support/Windows/DynamicLibrary.inc
===================================================================
--- lib/Support/Windows/DynamicLibrary.inc
+++ lib/Support/Windows/DynamicLibrary.inc
@@ -12,16 +12,18 @@
 //===----------------------------------------------------------------------===//
 
 #include "WindowsSupport.h"
+#include "llvm/ADT/iterator_range.h"
 
 #ifdef __MINGW32__
  #include <imagehlp.h>
 #else
- #include <dbghelp.h>
+ #include <Psapi.h>
 #endif
 
 #ifdef _MSC_VER
  #include <ntverp.h>
 #endif
+#include <vector>
 
 namespace llvm {
 using namespace sys;
@@ -31,25 +33,9 @@
 //===          and must not be UNIX code.
 //===----------------------------------------------------------------------===//
 
-typedef BOOL (WINAPI *fpEnumerateLoadedModules)(HANDLE,PENUMLOADED_MODULES_CALLBACK64,PVOID);
-static fpEnumerateLoadedModules fEnumerateLoadedModules;
-static DenseSet<HMODULE> *OpenedHandles;
-
-static bool loadDebugHelp(void) {
-  HMODULE hLib = ::LoadLibraryW(L"Dbghelp.dll");
-  if (hLib) {
-    fEnumerateLoadedModules = (fpEnumerateLoadedModules)
-      ::GetProcAddress(hLib, "EnumerateLoadedModules64");
-  }
-  return fEnumerateLoadedModules != 0;
-}
-
-static BOOL CALLBACK
-ELM_Callback(PCSTR ModuleName, DWORD64 ModuleBase,
-             ULONG ModuleSize, PVOID UserContext) {
-  OpenedHandles->insert((HMODULE)ModuleBase);
-  return TRUE;
-}
+typedef std::vector<HMODULE> ModuleHandles;
+static std::unique_ptr<ModuleHandles> OpenedHandles;
+static bool KeepFront;
 
 DynamicLibrary DynamicLibrary::getPermanentLibrary(const char *filename,
                                                    std::string *errMsg) {
@@ -57,20 +43,58 @@
 
   if (!filename) {
     // When no file is specified, enumerate all DLLs and EXEs in the process.
-    if (OpenedHandles == 0)
-      OpenedHandles = new DenseSet<HMODULE>();
 
-    if (!fEnumerateLoadedModules) {
-      if (!loadDebugHelp()) {
-        assert(false && "These APIs should always be available");
+#ifdef _WIN64
+    const DWORD Flags = LIST_MODULES_64BIT;
+#else
+    const DWORD Flags = LIST_MODULES_32BIT;
+#endif
+
+    DWORD Bytes;
+    HMODULE Self = (HMODULE)GetCurrentProcess();
+    if (!EnumProcessModulesEx(Self, nullptr, 0, &Bytes, Flags)) {
+      MakeErrMsg(errMsg, "EnumProcessModulesEx failure");
+      return DynamicLibrary();
+    }
+
+    // Get the most recent list in case any modules added between calls.
+    ModuleHandles Current;
+    do {
+      assert(Bytes && ((Bytes % sizeof(HMODULE)) == 0) &&
+             "Should have at least one module and be aligned");
+      Current.resize(Bytes / sizeof(HMODULE));
+      if (!EnumProcessModulesEx(Self, Current.data(), Bytes, &Bytes, Flags)) {
+        MakeErrMsg(errMsg, "EnumProcessModulesEx failure");
         return DynamicLibrary();
       }
+    } while (Bytes != (Current.size() * sizeof(HMODULE)));
+
+#ifndef NDEBUG
+    if (OpenedHandles) {
+      auto Begin = Current.begin(), End = Current.end();
+      for (HMODULE Mod : *OpenedHandles) {
+        assert((std::find(Begin, End, Mod) != End) &&
+               "Module in older list that is not in newer one");
+      }
     }
+#endif
+
+    // Keep current process handle at top of list
+    if (Current.size() > 1) {
+      Self = Current.front();
+      memmove(Current.data(), Current.data()+1, Bytes - sizeof(HMODULE));
+      Current.back() = Self;
+    }
+    KeepFront = true;
+
+    if (!OpenedHandles)
+      OpenedHandles.reset(new ModuleHandles(std::move(Current)));
+    else
+      OpenedHandles->swap(Current);
 
-    fEnumerateLoadedModules(GetCurrentProcess(), ELM_Callback, 0);
     // Dummy library that represents "search all handles".
     // This is mostly to ensure that the return value still shows up as "valid".
-    return DynamicLibrary(&OpenedHandles);
+    return DynamicLibrary(OpenedHandles.get());
   }
 
   SmallVector<wchar_t, MAX_PATH> filenameUnicode;
@@ -79,7 +103,7 @@
     MakeErrMsg(errMsg, std::string(filename) + ": Can't convert to UTF-16");
     return DynamicLibrary();
   }
-  
+
   HMODULE a_handle = LoadLibraryW(filenameUnicode.data());
 
   if (a_handle == 0) {
@@ -87,13 +111,25 @@
     return DynamicLibrary();
   }
 
-  if (OpenedHandles == 0)
-    OpenedHandles = new DenseSet<HMODULE>();
+  if (OpenedHandles) {
+    // If we've already loaded this library, FreeLibrary() the handle in order
+    // to keep the internal refcount at +1.
+    auto It = std::find(OpenedHandles->begin(), OpenedHandles->end(), a_handle);
+    if (It != OpenedHandles->end()) {
+      FreeLibrary(a_handle);
+      return DynamicLibrary(a_handle);
+    }
+  } else
+    OpenedHandles.reset(new ModuleHandles);
 
-  // If we've already loaded this library, FreeLibrary() the handle in order to
-  // keep the internal refcount at +1.
-  if (!OpenedHandles->insert(a_handle).second)
-    FreeLibrary(a_handle);
+  OpenedHandles->push_back(a_handle);
+
+  if (KeepFront) {
+    // Keep current process handle at top of list
+    const size_t Len = OpenedHandles->size();
+    if (Len > 2)
+      std::swap((*OpenedHandles)[Len-1], (*OpenedHandles)[Len-2]);
+  }
 
   return DynamicLibrary(a_handle);
 }
@@ -134,11 +170,11 @@
       return i->second;
   }
 
-  // Now search the libraries.
+  // Now search the libraries (in reverse, newer symbols override oldest)
   if (OpenedHandles) {
-    for (DenseSet<HMODULE>::iterator I = OpenedHandles->begin(),
-         E = OpenedHandles->end(); I != E; ++I) {
-      FARPROC ptr = GetProcAddress((HMODULE)*I, symbolName);
+    for (HMODULE Module : llvm::make_range(OpenedHandles->rbegin(),
+                                           OpenedHandles->rend())) {
+      FARPROC ptr = GetProcAddress(Module, symbolName);
       if (ptr) {
         return (void *)(intptr_t)ptr;
       }
@@ -174,7 +210,7 @@
 void *DynamicLibrary::getAddressOfSymbol(const char *symbolName) {
   if (!isValid())
     return NULL;
-  if (Data == &OpenedHandles)
+  if (Data == OpenedHandles.get())
     return SearchForAddressOfSymbol(symbolName);
   return (void *)(intptr_t)GetProcAddress((HMODULE)Data, symbolName);
 }