Index: tools/llc/llc.cpp
===================================================================
--- tools/llc/llc.cpp
+++ tools/llc/llc.cpp
@@ -96,6 +96,11 @@
                                 cl::desc("Add comments to directives."),
                                 cl::init(true));
 
+static cl::opt<bool> CompileTwice(
+    "compile-twice", cl::Hidden,
+    cl::desc("Run everything twice, re-using the same pass manager."),
+    cl::init(false));
+
 static int compileModule(char **, LLVMContext &);
 
 static std::unique_ptr<tool_output_file>
@@ -379,6 +384,11 @@
     cl::PrintOptionValues();
 
     PM.run(*M);
+
+    // If requested, run the pass manager over the same module again,
+    // to catch any bugs due to persistent state in the passes
+    if (CompileTwice)
+      PM.run(*M);
   }
 
   // Declare success.
Index: tools/opt/opt.cpp
===================================================================
--- tools/opt/opt.cpp
+++ tools/opt/opt.cpp
@@ -190,6 +190,11 @@
     cl::desc("Preserve use-list order when writing LLVM assembly."),
     cl::init(false), cl::Hidden);
 
+static cl::opt<bool>
+    RunTwice("run-twice",
+             cl::desc("Run all passes twice, re-using the same pass manager."),
+             cl::init(false), cl::Hidden);
+
 static inline void addPass(legacy::PassManagerBase &PM, Pass *P) {
   // Add the pass to the pass manager...
   PM.add(P);
@@ -598,6 +603,11 @@
   // Now that we have all of the passes ready, run them.
   Passes.run(*M);
 
+  // If requested, run all passes again with the same pass manager to catch
+  // bugs caused by persistent state in the passes
+  if (RunTwice)
+    Passes.run(*M);
+
   // Declare success.
   if (!NoOutput || PrintBreakpoints)
     Out->keep();