Introduce a new temporary MDNode concept. Temporary MDNodes are

not part of the IR, are not uniqued, and may be safely RAUW'd.
This replaces a variety of alternate mechanisms for achieving
the same effect.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111681 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/DebugInfo.h

@@ -272,6 +272,10 @@ namespace llvm {
     StringRef getFilename() const    { return getCompileUnit().getFilename();}
     StringRef getDirectory() const   { return getCompileUnit().getDirectory();}
 
+    /// replaceAllUsesWith - Replace all uses of debug info referenced by
+    /// this descriptor.
+    void replaceAllUsesWith(DIDescriptor &D);
+
     /// print - print type.
     void print(raw_ostream &OS) const;
 
@@ -314,10 +318,6 @@ namespace llvm {
 
     /// dump - print derived type to dbgs() with a newline.
     void dump() const;
-
-    /// replaceAllUsesWith - Replace all uses of debug info referenced by
-    /// this descriptor.
-    void replaceAllUsesWith(DIDescriptor &D);
   };
 
   /// DICompositeType - This descriptor holds a type that can refer to multiple
@@ -654,6 +654,9 @@ namespace llvm {
                                         unsigned RunTimeLang = 0,
                                         MDNode *ContainingType = 0);
 
+    /// CreateTemporaryType - Create a temporary forward-declared type.
+    DIType CreateTemporaryType(DIDescriptor Context);
+
     /// CreateArtificialType - Create a new DIType with "artificial" flag set.
     DIType CreateArtificialType(DIType Ty);
 

include/llvm/Metadata.h

@@ -128,6 +128,16 @@ public:
                                        
   static MDNode *getIfExists(LLVMContext &Context, Value *const *Vals,
                              unsigned NumVals);
+
+  /// getTemporary - Return a temporary MDNode, for use in constructing
+  /// cyclic MDNode structures. A temporary MDNode is not uniqued,
+  /// may be RAUW'd, and must be manually deleted with deleteTemporary.
+  static MDNode *getTemporary(LLVMContext &Context, Value *const *Vals,
+                              unsigned NumVals);
+
+  /// deleteTemporary - Deallocate a node created by getTemporary. The
+  /// node must not have any users.
+  static void deleteTemporary(MDNode *N);
   
   /// getOperand - Return specified operand.
   Value *getOperand(unsigned i) const;

lib/Analysis/DebugInfo.cpp

@@ -22,6 +22,7 @@
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Dwarf.h"
 #include "llvm/Support/raw_ostream.h"
@@ -260,7 +261,7 @@ unsigned DIArray::getNumElements() const {
 
 /// replaceAllUsesWith - Replace all uses of debug info referenced by
 /// this descriptor.
-void DIDerivedType::replaceAllUsesWith(DIDescriptor &D) {
+void DIType::replaceAllUsesWith(DIDescriptor &D) {
   if (!DbgNode)
     return;
 
@@ -274,6 +275,7 @@ void DIDerivedType::replaceAllUsesWith(DIDescriptor &D) {
     const MDNode *DN = D;
     const Value *V = cast_or_null<Value>(DN);
     Node->replaceAllUsesWith(const_cast<Value*>(V));
+    MDNode::deleteTemporary(Node);
   }
 }
 
@@ -934,6 +936,18 @@ DICompositeType DIFactory::CreateCompositeType(unsigned Tag,
 }
 
 
+/// CreateTemporaryType - Create a temporary forward-declared type.
+DIType DIFactory::CreateTemporaryType(DIDescriptor Context) {
+  // Give the temporary MDNode a tag. It doesn't matter what tag we
+  // use here as long as DIType accepts it.
+  Value *Elts[] = {
+    GetTagConstant(DW_TAG_base_type)
+  };
+  MDNode *Node = MDNode::getTemporary(VMContext, Elts, array_lengthof(Elts));
+  return DIType(Node);
+}
+
+
 /// CreateCompositeType - Create a composite type like array, struct, etc.
 DICompositeType DIFactory::CreateCompositeTypeEx(unsigned Tag,
                                                  DIDescriptor Context,

lib/AsmParser/LLParser.cpp

@@ -517,11 +517,7 @@ bool LLParser::ParseMDNodeID(MDNode *&Result) {
   if (Result) return false;
 
   // Otherwise, create MDNode forward reference.
-
-  // FIXME: This is not unique enough!
-  std::string FwdRefName = "llvm.mdnode.fwdref." + utostr(MID);
-  Value *V = MDString::get(Context, FwdRefName);
-  MDNode *FwdNode = MDNode::get(Context, &V, 1);
+  MDNode *FwdNode = MDNode::getTemporary(Context, 0, 0);
   ForwardRefMDNodes[MID] = std::make_pair(FwdNode, Lex.getLoc());
   
   if (NumberedMetadata.size() <= MID)
@@ -585,7 +581,9 @@ bool LLParser::ParseStandaloneMetadata() {
   std::map<unsigned, std::pair<TrackingVH<MDNode>, LocTy> >::iterator
     FI = ForwardRefMDNodes.find(MetadataID);
   if (FI != ForwardRefMDNodes.end()) {
-    FI->second.first->replaceAllUsesWith(Init);
+    MDNode *Temp = FI->second.first;
+    Temp->replaceAllUsesWith(Init);
+    MDNode::deleteTemporary(Temp);
     ForwardRefMDNodes.erase(FI);
     
     assert(NumberedMetadata[MetadataID] == Init && "Tracking VH didn't work");

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -333,9 +333,9 @@ void BitcodeReaderMDValueList::AssignValue(Value *V, unsigned Idx) {
   }
 
   // If there was a forward reference to this value, replace it.
-  Value *PrevVal = OldV;
+  MDNode *PrevVal = cast<MDNode>(OldV);
   OldV->replaceAllUsesWith(V);
-  delete PrevVal;
+  MDNode::deleteTemporary(PrevVal);
   // Deleting PrevVal sets Idx value in MDValuePtrs to null. Set new
   // value for Idx.
   MDValuePtrs[Idx] = V;
@@ -351,7 +351,7 @@ Value *BitcodeReaderMDValueList::getValueFwdRef(unsigned Idx) {
   }
 
   // Create and return a placeholder, which will later be RAUW'd.
-  Value *V = new Argument(Type::getMetadataTy(Context));
+  Value *V = MDNode::getTemporary(Context, 0, 0);
   MDValuePtrs[Idx] = V;
   return V;
 }

lib/VMCore/Metadata.cpp

@@ -20,6 +20,7 @@
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/SmallString.h"
 #include "SymbolTableListTraitsImpl.h"
+#include "llvm/Support/LeakDetector.h"
 #include "llvm/Support/ValueHandle.h"
 using namespace llvm;
 
@@ -244,6 +245,28 @@ MDNode *MDNode::getIfExists(LLVMContext &Context, Value *const *Vals,
   return getMDNode(Context, Vals, NumVals, FL_Unknown, false);
 }
 
+MDNode *MDNode::getTemporary(LLVMContext &Context, Value *const *Vals,
+                             unsigned NumVals) {
+  MDNode *N = (MDNode *)malloc(sizeof(MDNode)+NumVals*sizeof(MDNodeOperand));
+  N = new (N) MDNode(Context, Vals, NumVals, FL_No);
+  N->setValueSubclassData(N->getSubclassDataFromValue() |
+                          NotUniquedBit);
+  LeakDetector::addGarbageObject(N);
+  return N;
+}
+
+void MDNode::deleteTemporary(MDNode *N) {
+  assert(N->use_empty() && "Temporary MDNode has uses!");
+  assert((N->getSubclassDataFromValue() & NotUniquedBit) &&
+         "Temporary MDNode does not have NotUniquedBit set!");
+  assert((N->getSubclassDataFromValue() & DestroyFlag) == 0 &&
+         "Temporary MDNode does has DestroyFlag set!");
+  N->setValueSubclassData(N->getSubclassDataFromValue() |
+                          DestroyFlag);
+  LeakDetector::removeGarbageObject(N);
+  delete N;
+}
+
 /// getOperand - Return specified operand.
 Value *MDNode::getOperand(unsigned i) const {
   return *getOperandPtr(const_cast<MDNode*>(this), i);