Add support to fallback on operator new when a placement operator new[] is called for which there is no valid declaration.  This fallback only happens in Microsoft compatibility mode.  This patch addresses PR13164, and improves support for the WDK.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182905 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaExprCXX.cpp b/lib/Sema/SemaExprCXX.cpp
index 21f00b2..439fc16 100644
--- a/lib/Sema/SemaExprCXX.cpp
+++ b/lib/Sema/SemaExprCXX.cpp
@@ -1554,13 +1554,28 @@
                                /*AllowMissing=*/true, OperatorNew))
       return true;
   }
+
   if (!OperatorNew) {
     // Didn't find a member overload. Look for a global one.
     DeclareGlobalNewDelete();
     DeclContext *TUDecl = Context.getTranslationUnitDecl();
+    bool FallbackEnabled = IsArray && Context.getLangOpts().MicrosoftMode;
     if (FindAllocationOverload(StartLoc, Range, NewName, AllocArgs, TUDecl,
+                               /*AllowMissing=*/FallbackEnabled, OperatorNew,
+                               /*Diagnose=*/!FallbackEnabled)) {
+      if (!FallbackEnabled)
+        return true;
+
+      // MSVC will fall back on trying to find a matching global operator new
+      // if operator new[] cannot be found.  Also, MSVC will leak by not
+      // generating a call to operator delete or operator delete[], but we
+      // will not replicate that bug.
+      NewName = Context.DeclarationNames.getCXXOperatorName(OO_New);
+      DeleteName = Context.DeclarationNames.getCXXOperatorName(OO_Delete);
+      if (FindAllocationOverload(StartLoc, Range, NewName, AllocArgs, TUDecl,
                                /*AllowMissing=*/false, OperatorNew))
       return true;
+    }
   }
 
   // We don't need an operator delete if we're running under