[DebugInfo] Make DIArgList inherit from Metadata and always unique (#72147)

This patch changes the `DIArgList` class's inheritance from `MDNode` to
`Metadata, ReplaceableMetadataImpl`, and ensures that it is always
unique, i.e. a distinct DIArgList should never be produced.

This should not result in any changes to IR or bitcode parsing and
printing, as the format for DIArgList is unchanged, and the order in which it
appears should also be identical. As a minor note, this patch also fixes
a gap in the verifier, where the ValueAsMetadata operands to a DIArgList
would not be visited.

Author: SLTozer

llvm/include/llvm/AsmParser/LLParser.h

@@ -548,6 +548,7 @@ namespace llvm {
     bool parseMetadataAsValue(Value *&V, PerFunctionState &PFS);
     bool parseValueAsMetadata(Metadata *&MD, const Twine &TypeMsg,
                               PerFunctionState *PFS);
+    bool parseDIArgList(Metadata *&MD, PerFunctionState *PFS);
     bool parseMetadata(Metadata *&MD, PerFunctionState *PFS);
     bool parseMDTuple(MDNode *&MD, bool IsDistinct = false);
     bool parseMDNode(MDNode *&N);
@@ -569,8 +570,6 @@ namespace llvm {
 #define HANDLE_SPECIALIZED_MDNODE_LEAF(CLASS)                                  \
   bool parse##CLASS(MDNode *&Result, bool IsDistinct);
 #include "llvm/IR/Metadata.def"
-    bool parseDIArgList(MDNode *&Result, bool IsDistinct,
-                        PerFunctionState *PFS);
 
     // Function Parsing.
     struct ArgInfo {

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -3753,51 +3753,40 @@ class DIMacroFile : public DIMacroNode {
 
 /// List of ValueAsMetadata, to be used as an argument to a dbg.value
 /// intrinsic.
-class DIArgList : public MDNode {
+class DIArgList : public Metadata, ReplaceableMetadataImpl {
+  friend class ReplaceableMetadataImpl;
   friend class LLVMContextImpl;
-  friend class MDNode;
   using iterator = SmallVectorImpl<ValueAsMetadata *>::iterator;
 
   SmallVector<ValueAsMetadata *, 4> Args;
 
-  DIArgList(LLVMContext &C, StorageType Storage,
-            ArrayRef<ValueAsMetadata *> Args)
-      : MDNode(C, DIArgListKind, Storage, std::nullopt),
+  DIArgList(LLVMContext &Context, ArrayRef<ValueAsMetadata *> Args)
+      : Metadata(DIArgListKind, Uniqued), ReplaceableMetadataImpl(Context),
         Args(Args.begin(), Args.end()) {
     track();
   }
   ~DIArgList() { untrack(); }
 
-  static DIArgList *getImpl(LLVMContext &Context,
-                            ArrayRef<ValueAsMetadata *> Args,
-                            StorageType Storage, bool ShouldCreate = true);
-
-  TempDIArgList cloneImpl() const {
-    return getTemporary(getContext(), getArgs());
-  }
-
   void track();
   void untrack();
-  void dropAllReferences();
+  void dropAllReferences(bool Untrack);
 
 public:
-  DEFINE_MDNODE_GET(DIArgList, (ArrayRef<ValueAsMetadata *> Args), (Args))
-
-  TempDIArgList clone() const { return cloneImpl(); }
+  static DIArgList *get(LLVMContext &Context, ArrayRef<ValueAsMetadata *> Args);
 
   ArrayRef<ValueAsMetadata *> getArgs() const { return Args; }
 
   iterator args_begin() { return Args.begin(); }
   iterator args_end() { return Args.end(); }
 
-  ReplaceableMetadataImpl *getReplaceableUses() {
-    return Context.getReplaceableUses();
-  }
-
   static bool classof(const Metadata *MD) {
     return MD->getMetadataID() == DIArgListKind;
   }
 
+  SmallVector<DPValue *> getAllDPValueUsers() {
+    return ReplaceableMetadataImpl::getAllDPValueUsers();
+  }
+
   void handleChangedOperand(void *Ref, Metadata *New);
 };
 

llvm/include/llvm/IR/Metadata.def

@@ -77,6 +77,7 @@ HANDLE_METADATA_BRANCH(ValueAsMetadata)
 HANDLE_METADATA_LEAF(ConstantAsMetadata)
 HANDLE_METADATA_LEAF(LocalAsMetadata)
 HANDLE_METADATA_LEAF(DistinctMDOperandPlaceholder)
+HANDLE_METADATA_LEAF(DIArgList)
 HANDLE_MDNODE_BRANCH(MDNode)
 HANDLE_MDNODE_LEAF_UNIQUABLE(MDTuple)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DILocation)
@@ -115,7 +116,6 @@ HANDLE_SPECIALIZED_MDNODE_BRANCH(DIMacroNode)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIMacro)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIMacroFile)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DICommonBlock)
-HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIArgList)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIStringType)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIGenericSubrange)
 

llvm/include/llvm/IR/Metadata.h

@@ -1037,7 +1037,6 @@ struct TempMDNodeDeleter {
 class MDNode : public Metadata {
   friend class ReplaceableMetadataImpl;
   friend class LLVMContextImpl;
-  friend class DIArgList;
 
   /// The header that is coallocated with an MDNode along with its "small"
   /// operands. It is located immediately before the main body of the node.
@@ -1220,9 +1219,7 @@ class MDNode : public Metadata {
   bool isDistinct() const { return Storage == Distinct; }
   bool isTemporary() const { return Storage == Temporary; }
 
-  bool isReplaceable() const {
-    return isTemporary() || getMetadataID() == DIArgListKind;
-  }
+  bool isReplaceable() const { return isTemporary(); }
 
   /// RAUW a temporary.
   ///

llvm/lib/AsmParser/LLParser.cpp

@@ -5486,13 +5486,9 @@ bool LLParser::parseDIExpression(MDNode *&Result, bool IsDistinct) {
   return false;
 }
 
-bool LLParser::parseDIArgList(MDNode *&Result, bool IsDistinct) {
-  return parseDIArgList(Result, IsDistinct, nullptr);
-}
 /// ParseDIArgList:
 ///   ::= !DIArgList(i32 7, i64 %0)
-bool LLParser::parseDIArgList(MDNode *&Result, bool IsDistinct,
-                              PerFunctionState *PFS) {
+bool LLParser::parseDIArgList(Metadata *&MD, PerFunctionState *PFS) {
   assert(PFS && "Expected valid function state");
   assert(Lex.getKind() == lltok::MetadataVar && "Expected metadata type name");
   Lex.Lex();
@@ -5512,7 +5508,7 @@ bool LLParser::parseDIArgList(MDNode *&Result, bool IsDistinct,
   if (parseToken(lltok::rparen, "expected ')' here"))
     return true;
 
-  Result = GET_OR_DISTINCT(DIArgList, (Context, Args));
+  MD = DIArgList::get(Context, Args);
   return false;
 }
 
@@ -5626,13 +5622,17 @@ bool LLParser::parseValueAsMetadata(Metadata *&MD, const Twine &TypeMsg,
 ///  ::= !DILocation(...)
 bool LLParser::parseMetadata(Metadata *&MD, PerFunctionState *PFS) {
   if (Lex.getKind() == lltok::MetadataVar) {
-    MDNode *N;
     // DIArgLists are a special case, as they are a list of ValueAsMetadata and
     // so parsing this requires a Function State.
     if (Lex.getStrVal() == "DIArgList") {
-      if (parseDIArgList(N, false, PFS))
+      Metadata *AL;
+      if (parseDIArgList(AL, PFS))
         return true;
-    } else if (parseSpecializedMDNode(N)) {
+      MD = AL;
+      return false;
+    }
+    MDNode *N;
+    if (parseSpecializedMDNode(N)) {
       return true;
     }
     MD = N;

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -336,8 +336,7 @@ class ModuleBitcodeWriter : public ModuleBitcodeWriterBase {
                     unsigned Abbrev);
   void writeDIMacroFile(const DIMacroFile *N, SmallVectorImpl<uint64_t> &Record,
                         unsigned Abbrev);
-  void writeDIArgList(const DIArgList *N, SmallVectorImpl<uint64_t> &Record,
-                      unsigned Abbrev);
+  void writeDIArgList(const DIArgList *N, SmallVectorImpl<uint64_t> &Record);
   void writeDIModule(const DIModule *N, SmallVectorImpl<uint64_t> &Record,
                      unsigned Abbrev);
   void writeDIAssignID(const DIAssignID *N, SmallVectorImpl<uint64_t> &Record,
@@ -1975,13 +1974,12 @@ void ModuleBitcodeWriter::writeDIMacroFile(const DIMacroFile *N,
 }
 
 void ModuleBitcodeWriter::writeDIArgList(const DIArgList *N,
-                                         SmallVectorImpl<uint64_t> &Record,
-                                         unsigned Abbrev) {
+                                         SmallVectorImpl<uint64_t> &Record) {
   Record.reserve(N->getArgs().size());
   for (ValueAsMetadata *MD : N->getArgs())
     Record.push_back(VE.getMetadataID(MD));
 
-  Stream.EmitRecord(bitc::METADATA_ARG_LIST, Record, Abbrev);
+  Stream.EmitRecord(bitc::METADATA_ARG_LIST, Record);
   Record.clear();
 }
 
@@ -2264,6 +2262,10 @@ void ModuleBitcodeWriter::writeMetadataRecords(
 #include "llvm/IR/Metadata.def"
       }
     }
+    if (auto *AL = dyn_cast<DIArgList>(MD)) {
+      writeDIArgList(AL, Record);
+      continue;
+    }
     writeValueAsMetadata(cast<ValueAsMetadata>(MD), Record);
   }
 }

llvm/lib/IR/AsmWriter.cpp

@@ -1265,9 +1265,8 @@ void SlotTracker::CreateFunctionSlot(const Value *V) {
 void SlotTracker::CreateMetadataSlot(const MDNode *N) {
   assert(N && "Can't insert a null Value into SlotTracker!");
 
-  // Don't make slots for DIExpressions or DIArgLists. We just print them inline
-  // everywhere.
-  if (isa<DIExpression>(N) || isa<DIArgList>(N))
+  // Don't make slots for DIExpressions. We just print them inline everywhere.
+  if (isa<DIExpression>(N))
     return;
 
   unsigned DestSlot = mdnNext;
@@ -3516,8 +3515,6 @@ void AssemblyWriter::printNamedMDNode(const NamedMDNode *NMD) {
     // Write DIExpressions inline.
     // FIXME: Ban DIExpressions in NamedMDNodes, they will serve no purpose.
     MDNode *Op = NMD->getOperand(i);
-    assert(!isa<DIArgList>(Op) &&
-           "DIArgLists should not appear in NamedMDNodes");
     if (auto *Expr = dyn_cast<DIExpression>(Op)) {
       writeDIExpression(Out, Expr, AsmWriterContext::getEmpty());
       continue;
@@ -4918,7 +4915,7 @@ static void printMetadataImplRec(raw_ostream &ROS, const Metadata &MD,
   WriteAsOperandInternal(OS, &MD, WriterCtx, /* FromValue */ true);
 
   auto *N = dyn_cast<MDNode>(&MD);
-  if (!N || isa<DIExpression>(MD) || isa<DIArgList>(MD))
+  if (!N || isa<DIExpression>(MD))
     return;
 
   OS << " = ";
@@ -4986,7 +4983,7 @@ static void printMetadataImpl(raw_ostream &ROS, const Metadata &MD,
   WriteAsOperandInternal(OS, &MD, *WriterCtx, /* FromValue */ true);
 
   auto *N = dyn_cast<MDNode>(&MD);
-  if (OnlyAsOperand || !N || isa<DIExpression>(MD) || isa<DIArgList>(MD))
+  if (OnlyAsOperand || !N || isa<DIExpression>(MD))
     return;
 
   OS << " = ";

llvm/lib/IR/DebugInfoMetadata.cpp

@@ -2115,24 +2115,24 @@ DIMacroFile *DIMacroFile::getImpl(LLVMContext &Context, unsigned MIType,
   DEFINE_GETIMPL_STORE(DIMacroFile, (MIType, Line), Ops);
 }
 
-DIArgList *DIArgList::getImpl(LLVMContext &Context,
-                              ArrayRef<ValueAsMetadata *> Args,
-                              StorageType Storage, bool ShouldCreate) {
-  DEFINE_GETIMPL_LOOKUP(DIArgList, (Args));
-  DEFINE_GETIMPL_STORE_NO_OPS(DIArgList, (Args));
+DIArgList *DIArgList::get(LLVMContext &Context,
+                          ArrayRef<ValueAsMetadata *> Args) {
+  auto ExistingIt = Context.pImpl->DIArgLists.find_as(DIArgListKeyInfo(Args));
+  if (ExistingIt != Context.pImpl->DIArgLists.end())
+    return *ExistingIt;
+  DIArgList *NewArgList = new DIArgList(Context, Args);
+  Context.pImpl->DIArgLists.insert(NewArgList);
+  return NewArgList;
 }
 
 void DIArgList::handleChangedOperand(void *Ref, Metadata *New) {
   ValueAsMetadata **OldVMPtr = static_cast<ValueAsMetadata **>(Ref);
   assert((!New || isa<ValueAsMetadata>(New)) &&
          "DIArgList must be passed a ValueAsMetadata");
   untrack();
-  bool Uniq = isUniqued();
-  if (Uniq) {
-    // We need to update the uniqueness once the Args are updated since they
-    // form the key to the DIArgLists store.
-    eraseFromStore();
-  }
+  // We need to update the set storage once the Args are updated since they
+  // form the key to the DIArgLists store.
+  getContext().pImpl->DIArgLists.erase(this);
   ValueAsMetadata *NewVM = cast_or_null<ValueAsMetadata>(New);
   for (ValueAsMetadata *&VM : Args) {
     if (&VM == OldVMPtr) {
@@ -2142,28 +2142,19 @@ void DIArgList::handleChangedOperand(void *Ref, Metadata *New) {
         VM = ValueAsMetadata::get(PoisonValue::get(VM->getValue()->getType()));
     }
   }
-  if (Uniq) {
-    // In the RemoveDIs project (eliminating debug-info-intrinsics), DIArgLists
-    // can be referred to by DebugValueUser objects, which necessitates them
-    // being unique and replaceable metadata. This causes a slight
-    // performance regression that's to be avoided during the early stages of
-    // the RemoveDIs prototype, see D154080.
-#ifdef EXPERIMENTAL_DEBUGINFO_ITERATORS
-    MDNode *UniqueArgList = uniquify();
-    if (UniqueArgList != this) {
-      replaceAllUsesWith(UniqueArgList);
-      // Clear this here so we don't try to untrack in the destructor.
-      Args.clear();
-      delete this;
-      return;
-    }
-#else
-    // Otherwise, don't fully unique, become distinct instead. See D108968,
-    // there's a latent bug that presents here as nondeterminism otherwise.
-    if (uniquify() != this)
-      storeDistinctInContext();
-#endif
+  // We've changed the contents of this DIArgList, and the set storage may
+  // already contain a DIArgList with our new set of args; if it does, then we
+  // must RAUW this with the existing DIArgList, otherwise we simply insert this
+  // back into the set storage.
+  DIArgList *ExistingArgList = getUniqued(getContext().pImpl->DIArgLists, this);
+  if (ExistingArgList) {
+    replaceAllUsesWith(ExistingArgList);
+    // Clear this here so we don't try to untrack in the destructor.
+    Args.clear();
+    delete this;
+    return;
   }
+  getContext().pImpl->DIArgLists.insert(this);
   track();
 }
 void DIArgList::track() {
@@ -2176,8 +2167,9 @@ void DIArgList::untrack() {
     if (VAM)
       MetadataTracking::untrack(&VAM, *VAM);
 }
-void DIArgList::dropAllReferences() {
-  untrack();
+void DIArgList::dropAllReferences(bool Untrack) {
+  if (Untrack)
+    untrack();
   Args.clear();
-  MDNode::dropAllReferences();
+  ReplaceableMetadataImpl::resolveAllUses(/* ResolveUsers */ false);
 }

llvm/lib/IR/LLVMContextImpl.cpp

@@ -68,15 +68,8 @@ LLVMContextImpl::~LLVMContextImpl() {
 
   // Drop references for MDNodes.  Do this before Values get deleted to avoid
   // unnecessary RAUW when nodes are still unresolved.
-  for (auto *I : DistinctMDNodes) {
-    // We may have DIArgList that were uniqued, and as it has a custom
-    // implementation of dropAllReferences, it needs to be explicitly invoked.
-    if (auto *AL = dyn_cast<DIArgList>(I)) {
-      AL->dropAllReferences();
-      continue;
-    }
+  for (auto *I : DistinctMDNodes)
     I->dropAllReferences();
-  }
 #define HANDLE_MDNODE_LEAF_UNIQUABLE(CLASS)                                    \
   for (auto *I : CLASS##s)                                                     \
     I->dropAllReferences();
@@ -87,6 +80,10 @@ LLVMContextImpl::~LLVMContextImpl() {
     Pair.second->dropUsers();
   for (auto &Pair : MetadataAsValues)
     Pair.second->dropUse();
+  // Do not untrack ValueAsMetadata references for DIArgLists, as they have
+  // already been more efficiently untracked above.
+  for (DIArgList *AL : DIArgLists)
+    AL->dropAllReferences(/* Untrack */ false);
 
   // Destroy MDNodes.
   for (MDNode *I : DistinctMDNodes)