Index: llvm/trunk/test/BugPoint/named-md.ll
===================================================================
--- llvm/trunk/test/BugPoint/named-md.ll
+++ llvm/trunk/test/BugPoint/named-md.ll
@@ -0,0 +1,39 @@
+; RUN: bugpoint -load %llvmshlibdir/BugpointPasses%shlibext %s -output-prefix %t -bugpoint-crash-too-many-cus -silence-passes > /dev/null
+; RUN: llvm-dis %t-reduced-simplified.bc -o - | FileCheck %s
+; RUN-DISABLE: bugpoint -disable-namedmd-remove -load %llvmshlibdir/BugpointPasses%shlibext %s -output-prefix %t -bugpoint-crash-too-many-cus -silence-passes > /dev/null
+; RUN-DISABLE: llvm-dis %t-reduced-simplified.bc -o - | FileCheck %s
+; REQUIRES: loadable_module
+
+; CHECK: !llvm.dbg.cu = !{![[FIRST:[0-9]+]], ![[SECOND:[0-9]+]]}
+; CHECK-DISABLE:      !llvm.dbg.cu = !{![[FIRST:[0-9]+]], ![[SECOND:[0-9]+]],
+; CHECK-DISABLE-SAME: ![[THIRD:[0-9]+]], ![[FOURTH:[0-9]+]], ![[FIFTH:[0-9]+]]}
+!llvm.dbg.cu = !{!0, !1, !2, !3, !4, !5}
+; CHECK-NOT: !named
+; CHECK-DISABLE: !named
+!named = !{!0, !1, !2, !3, !4, !5}
+; CHECK: !llvm.module.flags = !{![[DIVERSION:[0-9]+]]}
+!llvm.module.flags = !{!6, !7}
+
+; CHECK-DAG: ![[FIRST]] = distinct !DICompileUnit(language: DW_LANG_Julia,
+; CHECK-DAG: ![[SECOND]] = distinct !DICompileUnit(language: DW_LANG_Julia,
+; CHECK-DAG: ![[DIVERSION]] = !{i32 2, !"Debug Info Version", i32 3}
+; CHECK-DAG: !DIFile(filename: "a", directory: "b")
+
+; 4 nodes survive. Due to renumbering !4 should not exist
+; CHECK-NOT: !4
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Julia,
+                             file: !8)
+!1 = distinct !DICompileUnit(language: DW_LANG_Julia,
+                             file: !8)
+!2 = distinct !DICompileUnit(language: DW_LANG_Julia,
+                             file: !8)
+!3 = distinct !DICompileUnit(language: DW_LANG_Julia,
+                             file: !8)
+!4 = distinct !DICompileUnit(language: DW_LANG_Julia,
+                             file: !8)
+!5 = distinct !DICompileUnit(language: DW_LANG_Julia,
+                             file: !8)
+!6 = !{i32 2, !"Dwarf Version", i32 2}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !DIFile(filename: "a", directory: "b")
Index: llvm/trunk/tools/bugpoint-passes/TestPasses.cpp
===================================================================
--- llvm/trunk/tools/bugpoint-passes/TestPasses.cpp
+++ llvm/trunk/tools/bugpoint-passes/TestPasses.cpp
@@ -76,20 +76,21 @@
 
 namespace {
   /// CrashOnDeclFunc - This pass is used to test bugpoint.  It intentionally
-  /// crash if the module has an undefined function (ie a function that is
-  /// defined in an external module).
-  class CrashOnDeclFunc : public ModulePass {
-  public:
-    static char ID; // Pass ID, replacement for typeid
-    CrashOnDeclFunc() : ModulePass(ID) {}
-  private:
-    bool runOnModule(Module &M) override {
-      for (auto &F : M.functions()) {
-        if (F.isDeclaration())
-          abort();
-      }
-      return false;
+/// crashes if the module has an undefined function (ie a function that is
+/// defined in an external module).
+class CrashOnDeclFunc : public ModulePass {
+public:
+  static char ID; // Pass ID, replacement for typeid
+  CrashOnDeclFunc() : ModulePass(ID) {}
+
+private:
+  bool runOnModule(Module &M) override {
+    for (auto &F : M.functions()) {
+      if (F.isDeclaration())
+        abort();
     }
+    return false;
+  }
   };
 }
 
@@ -97,3 +98,29 @@
 static RegisterPass<CrashOnDeclFunc>
   Z("bugpoint-crash-decl-funcs",
     "BugPoint Test Pass - Intentionally crash on declared functions");
+
+#include <iostream>
+namespace {
+/// CrashOnOneCU - This pass is used to test bugpoint. It intentionally
+/// crashes if the Module has two or more compile units
+class CrashOnTooManyCUs : public ModulePass {
+public:
+  static char ID;
+  CrashOnTooManyCUs() : ModulePass(ID) {}
+
+private:
+  bool runOnModule(Module &M) override {
+    NamedMDNode *CU_Nodes = M.getNamedMetadata("llvm.dbg.cu");
+    if (!CU_Nodes)
+      return false;
+    if (CU_Nodes->getNumOperands() >= 2)
+      abort();
+    return false;
+  }
+};
+}
+
+char CrashOnTooManyCUs::ID = 0;
+static RegisterPass<CrashOnTooManyCUs>
+    A("bugpoint-crash-too-many-cus",
+      "BugPoint Test Pass - Intentionally crash on too many CUs");
Index: llvm/trunk/tools/bugpoint/CrashDebugger.cpp
===================================================================
--- llvm/trunk/tools/bugpoint/CrashDebugger.cpp
+++ llvm/trunk/tools/bugpoint/CrashDebugger.cpp
@@ -15,6 +15,7 @@
 #include "ListReducer.h"
 #include "ToolRunner.h"
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
@@ -49,6 +50,10 @@
   DontReducePassList("disable-pass-list-reduction",
                      cl::desc("Skip pass list reduction steps"),
                      cl::init(false));
+
+  cl::opt<bool> NoNamedMDRM("disable-namedmd-remove",
+                            cl::desc("Do not remove global named metadata"),
+                            cl::init(false));
 }
 
 namespace llvm {
@@ -497,6 +502,149 @@
   return false;
 }
 
+namespace {
+// Reduce the list of Named Metadata nodes. We keep this as a list of
+// names to avoid having to convert back and forth every time.
+class ReduceCrashingNamedMD : public ListReducer<std::string> {
+  BugDriver &BD;
+  bool (*TestFn)(const BugDriver &, Module *);
+
+public:
+  ReduceCrashingNamedMD(BugDriver &bd,
+                        bool (*testFn)(const BugDriver &, Module *))
+      : BD(bd), TestFn(testFn) {}
+
+  TestResult doTest(std::vector<std::string> &Prefix,
+                    std::vector<std::string> &Kept,
+                    std::string &Error) override {
+    if (!Kept.empty() && TestNamedMDs(Kept))
+      return KeepSuffix;
+    if (!Prefix.empty() && TestNamedMDs(Prefix))
+      return KeepPrefix;
+    return NoFailure;
+  }
+
+  bool TestNamedMDs(std::vector<std::string> &NamedMDs);
+};
+}
+
+bool ReduceCrashingNamedMD::TestNamedMDs(std::vector<std::string> &NamedMDs) {
+
+  ValueToValueMapTy VMap;
+  Module *M = CloneModule(BD.getProgram(), VMap);
+
+  outs() << "Checking for crash with only these named metadata nodes:";
+  unsigned NumPrint = std::min<size_t>(NamedMDs.size(), 10);
+  for (unsigned i = 0, e = NumPrint; i != e; ++i)
+    outs() << " " << NamedMDs[i];
+  if (NumPrint < NamedMDs.size())
+    outs() << "... <" << NamedMDs.size() << " total>";
+  outs() << ": ";
+
+  // Make a StringMap for faster lookup
+  StringSet<> Names;
+  for (const std::string &Name : NamedMDs)
+    Names.insert(Name);
+
+  // First collect all the metadata to delete in a vector, then
+  // delete them all at once to avoid invalidating the iterator
+  std::vector<NamedMDNode *> ToDelete;
+  ToDelete.reserve(M->named_metadata_size() - Names.size());
+  for (auto &NamedMD : M->named_metadata())
+    if (!Names.count(NamedMD.getName()))
+      ToDelete.push_back(&NamedMD);
+
+  for (auto *NamedMD : ToDelete)
+    NamedMD->eraseFromParent();
+
+  // Verify that this is still valid.
+  legacy::PassManager Passes;
+  Passes.add(createVerifierPass());
+  Passes.run(*M);
+
+  // Try running on the hacked up program...
+  if (TestFn(BD, M)) {
+    BD.setNewProgram(M); // It crashed, keep the trimmed version...
+    return true;
+  }
+  delete M; // It didn't crash, try something else.
+  return false;
+}
+
+namespace {
+// Reduce the list of operands to named metadata nodes
+class ReduceCrashingNamedMDOps : public ListReducer<const MDNode *> {
+  BugDriver &BD;
+  bool (*TestFn)(const BugDriver &, Module *);
+
+public:
+  ReduceCrashingNamedMDOps(BugDriver &bd,
+                           bool (*testFn)(const BugDriver &, Module *))
+      : BD(bd), TestFn(testFn) {}
+
+  TestResult doTest(std::vector<const MDNode *> &Prefix,
+                    std::vector<const MDNode *> &Kept,
+                    std::string &Error) override {
+    if (!Kept.empty() && TestNamedMDOps(Kept))
+      return KeepSuffix;
+    if (!Prefix.empty() && TestNamedMDOps(Prefix))
+      return KeepPrefix;
+    return NoFailure;
+  }
+
+  bool TestNamedMDOps(std::vector<const MDNode *> &NamedMDOps);
+};
+}
+
+bool ReduceCrashingNamedMDOps::TestNamedMDOps(
+    std::vector<const MDNode *> &NamedMDOps) {
+  // Convert list to set for fast lookup...
+  SmallPtrSet<const MDNode *, 64> OldMDNodeOps;
+  for (unsigned i = 0, e = NamedMDOps.size(); i != e; ++i) {
+    OldMDNodeOps.insert(NamedMDOps[i]);
+  }
+
+  outs() << "Checking for crash with only " << OldMDNodeOps.size();
+  if (OldMDNodeOps.size() == 1)
+    outs() << " named metadata operand: ";
+  else
+    outs() << " named metadata operands: ";
+
+  ValueToValueMapTy VMap;
+  Module *M = CloneModule(BD.getProgram(), VMap);
+
+  // This is a little wasteful. In the future it might be good if we could have
+  // these dropped during cloning.
+  for (auto &NamedMD : BD.getProgram()->named_metadata()) {
+    // Drop the old one and create a new one
+    M->eraseNamedMetadata(M->getNamedMetadata(NamedMD.getName()));
+    NamedMDNode *NewNamedMDNode =
+        M->getOrInsertNamedMetadata(NamedMD.getName());
+    for (MDNode *op : NamedMD.operands())
+      if (OldMDNodeOps.count(op))
+        NewNamedMDNode->addOperand(cast<MDNode>(MapMetadata(op, VMap)));
+  }
+
+  // Verify that this is still valid.
+  legacy::PassManager Passes;
+  Passes.add(createVerifierPass());
+  Passes.run(*M);
+
+  // Try running on the hacked up program...
+  if (TestFn(BD, M)) {
+    // Make sure to use instruction pointers that point into the now-current
+    // module, and that they don't include any deleted blocks.
+    NamedMDOps.clear();
+    for (const MDNode *Node : OldMDNodeOps)
+      NamedMDOps.push_back(cast<MDNode>(VMap.MD()[Node].get()));
+
+    BD.setNewProgram(M); // It crashed, keep the trimmed version...
+    return true;
+  }
+  delete M; // It didn't crash, try something else.
+  return false;
+}
+
 /// DebugACrash - Given a predicate that determines whether a component crashes
 /// on a program, try to destructively reduce the program while still keeping
 /// the predicate true.
@@ -661,6 +809,31 @@
     }
 
   } while (Simplification);
+
+  if (!NoNamedMDRM) {
+    BD.EmitProgressBitcode(BD.getProgram(), "reduced-instructions");
+
+    if (!BugpointIsInterrupted) {
+      // Try to reduce the amount of global metadata (particularly debug info),
+      // by dropping global named metadata that anchors them
+      outs() << "\n*** Attempting to remove named metadata: ";
+      std::vector<std::string> NamedMDNames;
+      for (auto &NamedMD : BD.getProgram()->named_metadata())
+        NamedMDNames.push_back(NamedMD.getName().str());
+      ReduceCrashingNamedMD(BD, TestFn).reduceList(NamedMDNames, Error);
+    }
+
+    if (!BugpointIsInterrupted) {
+      // Now that we quickly dropped all the named metadata that doesn't
+      // contribute to the crash, bisect the operands of the remaining ones
+      std::vector<const MDNode *> NamedMDOps;
+      for (auto &NamedMD : BD.getProgram()->named_metadata())
+        NamedMDOps.insert(NamedMDOps.end(), NamedMD.op_begin(),
+                          NamedMD.op_end());
+      ReduceCrashingNamedMDOps(BD, TestFn).reduceList(NamedMDOps, Error);
+    }
+  }
+
 ExitLoops:
 
   // Try to clean up the testcase by running funcresolve and globaldce...