diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -50,6 +50,9 @@
 using namespace clang;
 using namespace llvm;
 
+static llvm::cl::opt<bool> ClearASTBeforeBackend("clear-clang-ast",
+                                                 llvm::cl::init(false));
+
 namespace clang {
   class BackendConsumer;
   class ClangDiagnosticHandler final : public DiagnosticHandler {
@@ -301,6 +304,9 @@
       if (!getModule())
         return;
 
+      if (ClearASTBeforeBackend)
+        this->Context->getAllocator().Reset();
+
       LLVMContext &Ctx = getModule()->getContext();
       std::unique_ptr<DiagnosticHandler> OldDiagnosticHandler =
           Ctx.getDiagnosticHandler();