commit 22a52dfddcefad4f275eb8ad1cc0e200074c2d8a
Author: Duncan P. N. Exon Smith <dexonsmith@apple.com>
Date:   Thu Feb 11 08:23:39 2021 -0800

    TransformUtils: Fix metadata handling in CloneModule (and improve CloneFunctionInto)
    
    This commit fixes how metadata is handled in CloneModule to be sound,
    and improves how it's handled in CloneFunctionInto (although the latter
    is still awkward when called within a module).
    
    Ruiling Song pointed out in PR48841 that CloneModule was changed to
    unsoundly use the RF_ReuseAndMutateDistinctMDs flag (renamed in
    fa35c1f80f0ea080a7cbc581416929b0a654f25c for clarity). This flag papered
    over a crash caused by other various changes made to CloneFunctionInto
    over the past few years that made it unsound to use cloning between
    different modules.
    
    (This commit partially addresses PR48841, fixing the repro from
    preprocessed source but not textual IR. MDNodeMapper::mapDistinctNode
    became unsound in df763188c9a1ecb1e7e5c4d4ea53a99fbb755903 and this
    commit does not address that regression.)
    
    RF_ReuseAndMutateDistinctMDs is designed for the IRMover to use,
    avoiding unnecessary clones of all referenced metadata when linking
    between modules (with IRMover, the source module is discarded after
    linking). It never makes sense to use when you're not discarding the
    source. This commit drops its incorrect use in CloneModule.
    
    Sadly, the right thing to do with metadata when cloning a function is
    complicated, and this patch doesn't totally fix it.
    
    The first problem is that there are two different types of referenceable
    metadata and it's not obvious what to with one of them when remapping.
    
    - `!0 = !{!1}` is metadata's version of a constant. Programatically it's
      called "uniqued" (probably a better term would be "constant") because,
      like `ConstantArray`, it's stored in uniquing tables. Once it's
      constructed, it's illegal to change its arguments.
    - `!0 = distinct !{!1}` is a bit closer to a global variable. It's legal
      to change the operands after construction.
    
    What should be done with distinct metadata when cloning functions within
    the same module?
    
    - Should new, cloned nodes be created?
    - Should all references point to the same, old nodes?
    
    The answer depends on whether that metadata is effectively owned by a
    function.
    
    And that's the second problem. Referenceable metadata's ownership model
    is not clear or explicit. Technically, it's all stored on an
    LLVMContext. However, any metadata that is `distinct`, that transitively
    references a `distinct` node, or that transitively references a
    GlobalValue is specific to a Module and is effectively owned by it. More
    specifically, some metadata is effectively owned by a specific Function
    within a module.
    
    Effectively function-local metadata was introduced somewhere around
    c10d0e5ccd12f049bddb24dcf8bbb7fbbc6c68f2, which made it illegal for two
    functions to share a DISubprogram attachment.
    
    When cloning a function within a module, you need to clone the
    function-local debug info and suppress cloning of global debug info (the
    status quo suppresses cloning some global debug info but not all). When
    cloning a function to a new/different module, you need to clone all of
    the debug info.
    
    Here's what I think we should do (eventually? soon? not this patch
    though):
    - Distinguish explicitly (somehow) between pure constant metadata owned
      by the LLVMContext, global metadata owned by the Module, and local
      metadata owned by a GlobalValue (such as a function).
    - Update CloneFunctionInto to trigger cloning of all "local" metadata
      (only), perhaps by adding a bit to RemapFlag. Alternatively, split
      out a separate function CloneFunctionMetadataInto to prime the
      metadata map that callers are updated to call ahead of time as
      appropriate.
    
    Here's the somewhat more isolated fix in this patch:
    - Converted the `ModuleLevelChanges` parameter to `CloneFunctionInto` to
      an enum called `CloneFunctionChangeType` that is one of
      LocalChangesOnly, GlobalChanges, DifferentModule, and ClonedModule.
    - The code maintaining the "functions uniquely own subprograms"
      invariant is now only active in the first two cases, where a function
      is being cloned within a single module. That's necessary because this
      code inhibits cloning of (some) "global" metadata that's effectively
      owned by the module.
    - The code maintaining the "all compile units must be explicitly
      referenced by !llvm.dbg.cu" invariant is now only active in the
      DifferentModule case, where a function is being cloned into a new
      module in isolation.
    - CoroSplit.cpp's call to CloneFunctionInto in CoroCloner::create
      uses LocalChangeOnly, since fa635d730f74f3285b77cc1537f1692184b8bf5b
      only set `ModuleLevelChanges` to trigger cloning of local metadata.
    - CloneModule drops its unsound use of RF_ReuseAndMutateDistinctMDs
      and special handling of !llvm.dbg.cu.
    - Fixed some outdated header docs and left a couple of FIXMEs.
    
    Differential Revision: https://reviews.llvm.org/D96531

diff --git a/llvm/include/llvm/Transforms/Utils/Cloning.h b/llvm/include/llvm/Transforms/Utils/Cloning.h
index 56aaa5d48e2a..401b235e3490 100644
--- a/llvm/include/llvm/Transforms/Utils/Cloning.h
+++ b/llvm/include/llvm/Transforms/Utils/Cloning.h
@@ -119,24 +119,45 @@ BasicBlock *CloneBasicBlock(const BasicBlock *BB, ValueToValueMapTy &VMap,
 /// values.  The final argument captures information about the cloned code if
 /// non-null.
 ///
-/// VMap contains no non-identity GlobalValue mappings and debug info metadata
-/// will not be cloned.
+/// \pre VMap contains no non-identity GlobalValue mappings.
 ///
 Function *CloneFunction(Function *F, ValueToValueMapTy &VMap,
                         ClonedCodeInfo *CodeInfo = nullptr);
 
+enum class CloneFunctionChangeType {
+  LocalChangesOnly,
+  GlobalChanges,
+  DifferentModule,
+  ClonedModule,
+};
+
 /// Clone OldFunc into NewFunc, transforming the old arguments into references
 /// to VMap values.  Note that if NewFunc already has basic blocks, the ones
 /// cloned into it will be added to the end of the function.  This function
 /// fills in a list of return instructions, and can optionally remap types
 /// and/or append the specified suffix to all values cloned.
 ///
-/// If ModuleLevelChanges is false, VMap contains no non-identity GlobalValue
-/// mappings.
+/// If \p Changes is \a CloneFunctionChangeType::LocalChangesOnly, VMap is
+/// required to contain no non-identity GlobalValue mappings. Otherwise,
+/// referenced metadata will be cloned.
+///
+/// If \p Changes is less than \a CloneFunctionChangeType::DifferentModule
+/// indicating cloning into the same module (even if it's LocalChangesOnly), if
+/// debug info metadata transitively references a \a DISubprogram, it will be
+/// cloned, effectively upgrading \p Changes to GlobalChanges while suppressing
+/// cloning of types and compile units.
+///
+/// If \p Changes is \a CloneFunctionChangeType::DifferentModule, the new
+/// module's \c !llvm.dbg.cu will get updated with any newly created compile
+/// units. (\a CloneFunctionChangeType::ClonedModule leaves that work for the
+/// caller.)
 ///
+/// FIXME: Consider simplifying this function by splitting out \a
+/// CloneFunctionMetadataInto() and expecting / updating callers to call it
+/// first when / how it's needed.
 void CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
-                       ValueToValueMapTy &VMap, bool ModuleLevelChanges,
-                       SmallVectorImpl<ReturnInst*> &Returns,
+                       ValueToValueMapTy &VMap, CloneFunctionChangeType Changes,
+                       SmallVectorImpl<ReturnInst *> &Returns,
                        const char *NameSuffix = "",
                        ClonedCodeInfo *CodeInfo = nullptr,
                        ValueMapTypeRemapper *TypeMapper = nullptr,
diff --git a/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp b/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp
index 1cfcf8ae943d..e8dd1bb90c9a 100644
--- a/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp
@@ -316,8 +316,9 @@ void moveFunctionBody(Function &OrigF, ValueToValueMapTy &VMap,
          "modules.");
 
   SmallVector<ReturnInst *, 8> Returns; // Ignore returns cloned.
-  CloneFunctionInto(NewF, &OrigF, VMap, /*ModuleLevelChanges=*/true, Returns,
-                    "", nullptr, nullptr, Materializer);
+  CloneFunctionInto(NewF, &OrigF, VMap,
+                    CloneFunctionChangeType::DifferentModule, Returns, "",
+                    nullptr, nullptr, Materializer);
   OrigF.deleteBody();
 }
 
diff --git a/llvm/lib/Target/AMDGPU/R600OpenCLImageTypeLoweringPass.cpp b/llvm/lib/Target/AMDGPU/R600OpenCLImageTypeLoweringPass.cpp
index 5fd912e0fb39..8f1a069c232d 100644
--- a/llvm/lib/Target/AMDGPU/R600OpenCLImageTypeLoweringPass.cpp
+++ b/llvm/lib/Target/AMDGPU/R600OpenCLImageTypeLoweringPass.cpp
@@ -301,7 +301,8 @@ class R600OpenCLImageTypeLoweringPass : public ModulePass {
       }
     }
     SmallVector<ReturnInst*, 8> Returns;
-    CloneFunctionInto(NewF, F, VMap, /*ModuleLevelChanges=*/false, Returns);
+    CloneFunctionInto(NewF, F, VMap, CloneFunctionChangeType::LocalChangesOnly,
+                      Returns);
 
     // Build new MDNode.
     SmallVector<Metadata *, 6> KernelMDArgs;
diff --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
index 5cafe8c5021c..04f426db8421 100644
--- a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -840,7 +840,8 @@ void CoroCloner::create() {
   auto savedLinkage = NewF->getLinkage();
   NewF->setLinkage(llvm::GlobalValue::ExternalLinkage);
 
-  CloneFunctionInto(NewF, &OrigF, VMap, /*ModuleLevelChanges=*/true, Returns);
+  CloneFunctionInto(NewF, &OrigF, VMap,
+                    CloneFunctionChangeType::LocalChangesOnly, Returns);
 
   NewF->setLinkage(savedLinkage);
   NewF->setVisibility(savedVisibility);
diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index ba2423ab6b5e..ecbe59a7f360 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -1527,7 +1527,8 @@ static Function *internalizeFunction(Function &F) {
   SmallVector<ReturnInst *, 8> Returns;
 
   // Copy the body of the original function to the new one
-  CloneFunctionInto(Copied, &F, VMap, /* ModuleLevelChanges */ false, Returns);
+  CloneFunctionInto(Copied, &F, VMap, CloneFunctionChangeType::LocalChangesOnly,
+                    Returns);
 
   // Set the linakage and visibility late as CloneFunctionInto has some implicit
   // requirements.
diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index a953ba5c6b14..dd3d535850bc 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -83,8 +83,8 @@ BasicBlock *llvm::CloneBasicBlock(const BasicBlock *BB, ValueToValueMapTy &VMap,
 //
 void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
                              ValueToValueMapTy &VMap,
-                             bool ModuleLevelChanges,
-                             SmallVectorImpl<ReturnInst*> &Returns,
+                             CloneFunctionChangeType Changes,
+                             SmallVectorImpl<ReturnInst *> &Returns,
                              const char *NameSuffix, ClonedCodeInfo *CodeInfo,
                              ValueMapTypeRemapper *TypeMapper,
                              ValueMaterializer *Materializer) {
@@ -95,6 +95,8 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
     assert(VMap.count(&I) && "No mapping from source argument specified!");
 #endif
 
+  bool ModuleLevelChanges = Changes > CloneFunctionChangeType::LocalChangesOnly;
+
   // Copy all attributes other than those stored in the AttributeList.  We need
   // to remap the parameter indices of the AttributeList.
   AttributeList NewAttrs = NewFunc->getAttributes();
@@ -123,21 +125,37 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
       AttributeList::get(NewFunc->getContext(), OldAttrs.getFnAttributes(),
                          OldAttrs.getRetAttributes(), NewArgAttrs));
 
-  bool MustCloneSP =
-      OldFunc->getParent() && OldFunc->getParent() == NewFunc->getParent();
-  DISubprogram *SP = OldFunc->getSubprogram();
-  if (SP) {
-    assert(!MustCloneSP || ModuleLevelChanges);
-    // Add mappings for some DebugInfo nodes that we don't want duplicated
-    // even if they're distinct.
-    auto &MD = VMap.MD();
-    MD[SP->getUnit()].reset(SP->getUnit());
-    MD[SP->getType()].reset(SP->getType());
-    MD[SP->getFile()].reset(SP->getFile());
-    // If we're not cloning into the same module, no need to clone the
-    // subprogram
-    if (!MustCloneSP)
-      MD[SP].reset(SP);
+  // When we remap instructions within the same module, we want to avoid
+  // duplicating inlined DISubprograms, so record all subprograms we find as we
+  // duplicate instructions and then freeze them in the MD map. We also record
+  // information about dbg.value and dbg.declare to avoid duplicating the
+  // types.
+  Optional<DebugInfoFinder> DIFinder;
+
+  // Track the subprogram attachment that needs to be cloned to fine-tune the
+  // mapping within the same module.
+  DISubprogram *SPClonedWithinModule = nullptr;
+  if (Changes < CloneFunctionChangeType::DifferentModule) {
+    assert((NewFunc->getParent() == nullptr ||
+            NewFunc->getParent() == OldFunc->getParent()) &&
+           "Expected NewFunc to have the same parent, or no parent");
+
+    // Need to find subprograms, types, and compile units.
+    DIFinder.emplace();
+
+    SPClonedWithinModule = OldFunc->getSubprogram();
+  } else {
+    assert((NewFunc->getParent() == nullptr ||
+            NewFunc->getParent() != OldFunc->getParent()) &&
+           "Set SameModule to true if the new function is in the same module");
+
+    if (Changes == CloneFunctionChangeType::DifferentModule) {
+      assert(NewFunc->getParent() &&
+             "Need parent of new function to maintain debug info invariants");
+
+      // Need to find all the compile units.
+      DIFinder.emplace();
+    }
   }
 
   // Everything else beyond this point deals with function instructions,
@@ -145,13 +163,6 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
   if (OldFunc->isDeclaration())
     return;
 
-  // When we remap instructions, we want to avoid duplicating inlined
-  // DISubprograms, so record all subprograms we find as we duplicate
-  // instructions and then freeze them in the MD map.
-  // We also record information about dbg.value and dbg.declare to avoid
-  // duplicating the types.
-  DebugInfoFinder DIFinder;
-
   // Loop over all of the basic blocks in the function, cloning them as
   // appropriate.  Note that we save BE this way in order to handle cloning of
   // recursive functions into themselves.
@@ -161,7 +172,7 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
 
     // Create a new basic block and copy instructions into it!
     BasicBlock *CBB = CloneBasicBlock(&BB, VMap, NameSuffix, NewFunc, CodeInfo,
-                                      ModuleLevelChanges ? &DIFinder : nullptr);
+                                      DIFinder ? &*DIFinder : nullptr);
 
     // Add basic block mapping.
     VMap[&BB] = CBB;
@@ -183,15 +194,38 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
       Returns.push_back(RI);
   }
 
-  for (DISubprogram *ISP : DIFinder.subprograms())
-    if (ISP != SP)
-      VMap.MD()[ISP].reset(ISP);
+  if (Changes < CloneFunctionChangeType::DifferentModule &&
+      (SPClonedWithinModule || DIFinder->subprogram_count() > 0)) {
+    // Turn on module-level changes, since we need to clone (some of) the
+    // debug info metadata.
+    //
+    // FIXME: Metadata effectively owned by a function should be made
+    // local, and only that local metadata should be cloned.
+    ModuleLevelChanges = true;
+
+    auto mapToSelfIfNew = [&VMap](MDNode *N) {
+      // Avoid clobbering an existing mapping.
+      (void)VMap.MD().try_emplace(N, N);
+    };
+
+    // Avoid cloning what the subprogram references.
+    if (SPClonedWithinModule) {
+      mapToSelfIfNew(SPClonedWithinModule->getUnit());
+      mapToSelfIfNew(SPClonedWithinModule->getType());
+      mapToSelfIfNew(SPClonedWithinModule->getFile());
+    }
+
+    // Avoid cloning other subprograms, compile units, and types.
+    for (DISubprogram *ISP : DIFinder->subprograms())
+      if (ISP != SPClonedWithinModule)
+        mapToSelfIfNew(ISP);
 
-  for (DICompileUnit *CU : DIFinder.compile_units())
-    VMap.MD()[CU].reset(CU);
+    for (DICompileUnit *CU : DIFinder->compile_units())
+      mapToSelfIfNew(CU);
 
-  for (DIType *Type : DIFinder.types())
-    VMap.MD()[Type].reset(Type);
+    for (DIType *Type : DIFinder->types())
+      mapToSelfIfNew(Type);
+  }
 
   // Duplicate the metadata that is attached to the cloned function.
   // Subprograms/CUs/types that were already mapped to themselves won't be
@@ -218,19 +252,33 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
                        ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges,
                        TypeMapper, Materializer);
 
-  // Register all DICompileUnits of the old parent module in the new parent module
-  auto* OldModule = OldFunc->getParent();
+  // Only update !llvm.dbg.cu for DifferentModule (not CloneModule). In the
+  // same module, the compile unit will already be listed (or not). When
+  // cloning a module, CloneModule() will handle creating the named metadata.
+  if (Changes != CloneFunctionChangeType::DifferentModule)
+    return;
+
+  // Update !llvm.dbg.cu with compile units added to the new module if this
+  // function is being cloned in isolation.
+  //
+  // FIXME: This is making global / module-level changes, which doesn't seem
+  // like the right encapsulation  Consider dropping the requirement to update
+  // !llvm.dbg.cu (either obsoleting the node, or restricting it to
+  // non-discardable compile units) instead of discovering compile units by
+  // visiting the metadata attached to global values, which would allow this
+  // code to be deleted. Alternatively, perhaps give responsibility for this
+  // update to CloneFunctionInto's callers.
   auto* NewModule = NewFunc->getParent();
-  if (OldModule && NewModule && OldModule != NewModule && DIFinder.compile_unit_count()) {
-    auto* NMD = NewModule->getOrInsertNamedMetadata("llvm.dbg.cu");
-    // Avoid multiple insertions of the same DICompileUnit to NMD.
-    SmallPtrSet<const void*, 8> Visited;
-    for (auto* Operand : NMD->operands())
-      Visited.insert(Operand);
-    for (auto* Unit : DIFinder.compile_units())
-      // VMap.MD()[Unit] == Unit
-      if (Visited.insert(Unit).second)
-        NMD->addOperand(Unit);
+  auto *NMD = NewModule->getOrInsertNamedMetadata("llvm.dbg.cu");
+  // Avoid multiple insertions of the same DICompileUnit to NMD.
+  SmallPtrSet<const void *, 8> Visited;
+  for (auto *Operand : NMD->operands())
+    Visited.insert(Operand);
+  for (auto *Unit : DIFinder->compile_units()) {
+    MDNode *MappedUnit =
+        MapMetadata(Unit, VMap, RF_None, TypeMapper, Materializer);
+    if (Visited.insert(MappedUnit).second)
+      NMD->addOperand(MappedUnit);
   }
 }
 
@@ -269,8 +317,8 @@ Function *llvm::CloneFunction(Function *F, ValueToValueMapTy &VMap,
     }
 
   SmallVector<ReturnInst*, 8> Returns;  // Ignore returns cloned.
-  CloneFunctionInto(NewF, F, VMap, F->getSubprogram() != nullptr, Returns, "",
-                    CodeInfo);
+  CloneFunctionInto(NewF, F, VMap, CloneFunctionChangeType::LocalChangesOnly,
+                    Returns, "", CodeInfo);
 
   return NewF;
 }
diff --git a/llvm/lib/Transforms/Utils/CloneModule.cpp b/llvm/lib/Transforms/Utils/CloneModule.cpp
index 487cd4eae957..eb226b9b246d 100644
--- a/llvm/lib/Transforms/Utils/CloneModule.cpp
+++ b/llvm/lib/Transforms/Utils/CloneModule.cpp
@@ -120,13 +120,8 @@ std::unique_ptr<Module> llvm::CloneModule(
 
     SmallVector<std::pair<unsigned, MDNode *>, 1> MDs;
     G.getAllMetadata(MDs);
-
-    // FIXME: Stop using RF_ReuseAndMutateDistinctMDs here, since it's unsound
-    // to mutate metadata that is still referenced by the source module unless
-    // the source is about to be discarded (see IRMover for a valid use).
     for (auto MD : MDs)
-      GV->addMetadata(MD.first, *MapMetadata(MD.second, VMap,
-                                             RF_ReuseAndMutateDistinctMDs));
+      GV->addMetadata(MD.first, *MapMetadata(MD.second, VMap));
 
     if (G.isDeclaration())
       continue;
@@ -165,7 +160,8 @@ std::unique_ptr<Module> llvm::CloneModule(
     }
 
     SmallVector<ReturnInst *, 8> Returns; // Ignore returns cloned.
-    CloneFunctionInto(F, &I, VMap, /*ModuleLevelChanges=*/true, Returns);
+    CloneFunctionInto(F, &I, VMap, CloneFunctionChangeType::ClonedModule,
+                      Returns);
 
     if (I.hasPersonalityFn())
       F->setPersonalityFn(MapValue(I.getPersonalityFn(), VMap));
@@ -185,25 +181,13 @@ std::unique_ptr<Module> llvm::CloneModule(
   }
 
   // And named metadata....
-  const auto* LLVM_DBG_CU = M.getNamedMetadata("llvm.dbg.cu");
   for (Module::const_named_metadata_iterator I = M.named_metadata_begin(),
                                              E = M.named_metadata_end();
        I != E; ++I) {
     const NamedMDNode &NMD = *I;
     NamedMDNode *NewNMD = New->getOrInsertNamedMetadata(NMD.getName());
-    if (&NMD == LLVM_DBG_CU) {
-      // Do not insert duplicate operands.
-      SmallPtrSet<const void*, 8> Visited;
-      for (const auto* Operand : NewNMD->operands())
-        Visited.insert(Operand);
-      for (const auto* Operand : NMD.operands()) {
-        auto* MappedOperand = MapMetadata(Operand, VMap);
-        if (Visited.insert(MappedOperand).second)
-          NewNMD->addOperand(MappedOperand);
-      }
-    } else
-      for (unsigned i = 0, e = NMD.getNumOperands(); i != e; ++i)
-        NewNMD->addOperand(MapMetadata(NMD.getOperand(i), VMap));
+    for (unsigned i = 0, e = NMD.getNumOperands(); i != e; ++i)
+      NewNMD->addOperand(MapMetadata(NMD.getOperand(i), VMap));
   }
 
   return New;
diff --git a/llvm/unittests/Transforms/Utils/CloningTest.cpp b/llvm/unittests/Transforms/Utils/CloningTest.cpp
index 016e772c2257..6bab80215c0b 100644
--- a/llvm/unittests/Transforms/Utils/CloningTest.cpp
+++ b/llvm/unittests/Transforms/Utils/CloningTest.cpp
@@ -177,7 +177,8 @@ TEST_F(CloneInstruction, Attributes) {
   ValueToValueMapTy VMap;
   VMap[A] = UndefValue::get(A->getType());
 
-  CloneFunctionInto(F2, F1, VMap, false, Returns);
+  CloneFunctionInto(F2, F1, VMap, CloneFunctionChangeType::LocalChangesOnly,
+                    Returns);
   EXPECT_FALSE(F2->arg_begin()->hasNoCaptureAttr());
 
   delete F1;
@@ -200,7 +201,8 @@ TEST_F(CloneInstruction, CallingConvention) {
   ValueToValueMapTy VMap;
   VMap[&*F1->arg_begin()] = &*F2->arg_begin();
 
-  CloneFunctionInto(F2, F1, VMap, false, Returns);
+  CloneFunctionInto(F2, F1, VMap, CloneFunctionChangeType::LocalChangesOnly,
+                    Returns);
   EXPECT_EQ(CallingConv::Cold, F2->getCallingConv());
 
   delete F1;
@@ -663,6 +665,28 @@ static int GetDICompileUnitCount(const Module& M) {
   return 0;
 }
 
+static bool haveCompileUnitsInCommon(const Module &LHS, const Module &RHS) {
+  const NamedMDNode *LHSCUs = LHS.getNamedMetadata("llvm.dbg.cu");
+  if (!LHSCUs)
+    return false;
+
+  const NamedMDNode *RHSCUs = RHS.getNamedMetadata("llvm.dbg.cu");
+  if (!RHSCUs)
+    return false;
+
+  SmallPtrSet<const MDNode *, 8> Found;
+  for (int I = 0, E = LHSCUs->getNumOperands(); I != E; ++I)
+    if (const MDNode *N = LHSCUs->getOperand(I))
+      Found.insert(N);
+
+  for (int I = 0, E = RHSCUs->getNumOperands(); I != E; ++I)
+    if (const MDNode *N = RHSCUs->getOperand(I))
+      if (Found.count(N))
+        return true;
+
+  return false;
+}
+
 TEST(CloneFunction, CloneEmptyFunction) {
   StringRef ImplAssembly = R"(
     define void @foo() {
@@ -684,7 +708,8 @@ TEST(CloneFunction, CloneEmptyFunction) {
   ValueToValueMapTy VMap;
   SmallVector<ReturnInst *, 8> Returns;
   ClonedCodeInfo CCI;
-  CloneFunctionInto(ImplFunction, DeclFunction, VMap, true, Returns, "", &CCI);
+  CloneFunctionInto(ImplFunction, DeclFunction, VMap,
+                    CloneFunctionChangeType::GlobalChanges, Returns, "", &CCI);
 
   EXPECT_FALSE(verifyModule(*ImplModule, &errs()));
   EXPECT_FALSE(CCI.ContainsCalls);
@@ -715,7 +740,8 @@ TEST(CloneFunction, CloneFunctionWithInalloca) {
   ValueToValueMapTy VMap;
   SmallVector<ReturnInst *, 8> Returns;
   ClonedCodeInfo CCI;
-  CloneFunctionInto(DeclFunction, ImplFunction, VMap, true, Returns, "", &CCI);
+  CloneFunctionInto(DeclFunction, ImplFunction, VMap,
+                    CloneFunctionChangeType::GlobalChanges, Returns, "", &CCI);
 
   EXPECT_FALSE(verifyModule(*ImplModule, &errs()));
   EXPECT_TRUE(CCI.ContainsCalls);
@@ -764,7 +790,8 @@ TEST(CloneFunction, CloneFunctionWithSubprograms) {
   ValueToValueMapTy VMap;
   SmallVector<ReturnInst *, 8> Returns;
   ClonedCodeInfo CCI;
-  CloneFunctionInto(NewFunc, OldFunc, VMap, true, Returns, "", &CCI);
+  CloneFunctionInto(NewFunc, OldFunc, VMap,
+                    CloneFunctionChangeType::GlobalChanges, Returns, "", &CCI);
 
   // This fails if the scopes in the llvm.dbg.declare variable and location
   // aren't the same.
@@ -812,12 +839,14 @@ TEST(CloneFunction, CloneFunctionToDifferentModule) {
   VMap[ImplFunction] = DeclFunction;
   // No args to map
   SmallVector<ReturnInst*, 8> Returns;
-  CloneFunctionInto(DeclFunction, ImplFunction, VMap, true, Returns);
+  CloneFunctionInto(DeclFunction, ImplFunction, VMap,
+                    CloneFunctionChangeType::DifferentModule, Returns);
 
   EXPECT_FALSE(verifyModule(*ImplModule, &errs()));
   EXPECT_FALSE(verifyModule(*DeclModule, &errs()));
-  // DICompileUnit !2 shall be inserted into DeclModule.
+  // DICompileUnit !2 shall be cloned into DeclModule.
   EXPECT_TRUE(GetDICompileUnitCount(*DeclModule) == 1);
+  EXPECT_FALSE(haveCompileUnitsInCommon(*ImplModule, *DeclModule));
 }
 
 class CloneModule : public ::testing::Test {
@@ -840,6 +869,16 @@ protected:
     GV->addMetadata(LLVMContext::MD_type, *MDNode::get(C, {}));
     GV->setComdat(CD);
 
+    {
+      // Add an empty compile unit first that isn't otherwise referenced, to
+      // confirm that compile units get cloned in the correct order.
+      DIBuilder EmptyBuilder(*OldM);
+      auto *File = EmptyBuilder.createFile("empty.c", "/file/dir/");
+      (void)EmptyBuilder.createCompileUnit(dwarf::DW_LANG_C99, File,
+                                           "EmptyUnit", false, "", 0);
+      EmptyBuilder.finalize();
+    }
+
     DIBuilder DBuilder(*OldM);
     IRBuilder<> IBuilder(C);
 
@@ -894,6 +933,10 @@ protected:
 };
 
 TEST_F(CloneModule, Verify) {
+  // Confirm the old module is (still) valid.
+  EXPECT_FALSE(verifyModule(*OldM));
+
+  // Check the new module.
   EXPECT_FALSE(verifyModule(*NewM));
 }
 
@@ -944,10 +987,19 @@ TEST_F(CloneModule, CompileUnit) {
   // Find DICompileUnit listed in llvm.dbg.cu
   auto *NMD = NewM->getNamedMetadata("llvm.dbg.cu");
   EXPECT_TRUE(NMD != nullptr);
-  EXPECT_EQ(NMD->getNumOperands(), 1U);
+  EXPECT_EQ(NMD->getNumOperands(), 2U);
+  EXPECT_FALSE(haveCompileUnitsInCommon(*OldM, *NewM));
+
+  // Check that the empty CU is first, even though it's not referenced except
+  // from named metadata.
+  DICompileUnit *EmptyCU = dyn_cast<llvm::DICompileUnit>(NMD->getOperand(0));
+  EXPECT_TRUE(EmptyCU != nullptr);
+  EXPECT_EQ("EmptyUnit", EmptyCU->getProducer());
 
-  DICompileUnit *CU = dyn_cast<llvm::DICompileUnit>(NMD->getOperand(0));
+  // Get the interesting CU.
+  DICompileUnit *CU = dyn_cast<llvm::DICompileUnit>(NMD->getOperand(1));
   EXPECT_TRUE(CU != nullptr);
+  EXPECT_EQ("CloneModule", CU->getProducer());
 
   // Assert this CU is consistent with the cloned function debug info
   DISubprogram *SP = NewM->getFunction("f")->getSubprogram();