PR19598: Provide the ability to RAUW a declaration with itself, creating a non-temporary copy and using that to RAUW.

Also, provide the ability to create temporary and non-temporary
declarations, as not all declarations may be replaced by definitions
later on.

This provides the necessary infrastructure for Clang to fix PR19598,
leaking temporary MDNodes in Clang's debug info generation.

llvm-svn: 208054

llvm/include/llvm/IR/DIBuilder.h

@@ -434,7 +434,7 @@ namespace llvm {
     /// flag set.
     DIType createObjectPointerType(DIType Ty);
 
-    /// createForwardDecl - Create a temporary forward-declared type.
+    /// \brief Create a permanent forward-declared type.
     DICompositeType createForwardDecl(unsigned Tag, StringRef Name,
                                       DIDescriptor Scope, DIFile F,
                                       unsigned Line, unsigned RuntimeLang = 0,
@@ -442,6 +442,12 @@ namespace llvm {
                                       uint64_t AlignInBits = 0,
                                       StringRef UniqueIdentifier = StringRef());
 
+    /// \brief Create a temporary forward-declared type.
+    DICompositeType createReplaceableForwardDecl(
+        unsigned Tag, StringRef Name, DIDescriptor Scope, DIFile F,
+        unsigned Line, unsigned RuntimeLang = 0, uint64_t SizeInBits = 0,
+        uint64_t AlignInBits = 0, StringRef UniqueIdentifier = StringRef());
+
     /// retainType - Retain DIType in a module even if it is not referenced
     /// through debug info anchors.
     void retainType(DIType T);

llvm/include/llvm/IR/DebugInfo.h

@@ -339,7 +339,7 @@ public:
 
   /// replaceAllUsesWith - Replace all uses of debug info referenced by
   /// this descriptor.
-  void replaceAllUsesWith(DIDescriptor &D);
+  void replaceAllUsesWith(LLVMContext &VMContext, DIDescriptor D);
   void replaceAllUsesWith(MDNode *D);
 };
 

llvm/lib/IR/DIBuilder.cpp

@@ -901,6 +901,40 @@ DIBuilder::createForwardDecl(unsigned Tag, StringRef Name, DIDescriptor Scope,
     UniqueIdentifier.empty() ? nullptr
                              : MDString::get(VMContext, UniqueIdentifier)
   };
+  MDNode *Node = MDNode::get(VMContext, Elts);
+  DICompositeType RetTy(Node);
+  assert(RetTy.isCompositeType() &&
+         "createForwardDecl result should be a DIType");
+  if (!UniqueIdentifier.empty())
+    retainType(RetTy);
+  return RetTy;
+}
+
+/// createForwardDecl - Create a temporary forward-declared type that
+/// can be RAUW'd if the full type is seen.
+DICompositeType DIBuilder::createReplaceableForwardDecl(
+    unsigned Tag, StringRef Name, DIDescriptor Scope, DIFile F, unsigned Line,
+    unsigned RuntimeLang, uint64_t SizeInBits, uint64_t AlignInBits,
+    StringRef UniqueIdentifier) {
+  // Create a temporary MDNode.
+  Value *Elts[] = {
+    GetTagConstant(VMContext, Tag),
+    F.getFileNode(),
+    DIScope(getNonCompileUnitScope(Scope)).getRef(),
+    MDString::get(VMContext, Name),
+    ConstantInt::get(Type::getInt32Ty(VMContext), Line),
+    ConstantInt::get(Type::getInt64Ty(VMContext), SizeInBits),
+    ConstantInt::get(Type::getInt64Ty(VMContext), AlignInBits),
+    ConstantInt::get(Type::getInt32Ty(VMContext), 0), // Offset
+    ConstantInt::get(Type::getInt32Ty(VMContext), DIDescriptor::FlagFwdDecl),
+    nullptr,
+    DIArray(),
+    ConstantInt::get(Type::getInt32Ty(VMContext), RuntimeLang),
+    nullptr,
+    nullptr, //TemplateParams
+    UniqueIdentifier.empty() ? nullptr
+                             : MDString::get(VMContext, UniqueIdentifier)
+  };
   MDNode *Node = MDNode::getTemporary(VMContext, Elts);
   DICompositeType RetTy(Node);
   assert(RetTy.isCompositeType() &&

llvm/lib/IR/DebugInfo.cpp

@@ -335,7 +335,7 @@ unsigned DIArray::getNumElements() const {
 
 /// replaceAllUsesWith - Replace all uses of the MDNode used by this
 /// type with the one in the passed descriptor.
-void DIType::replaceAllUsesWith(DIDescriptor &D) {
+void DIType::replaceAllUsesWith(LLVMContext &VMContext, DIDescriptor D) {
 
   assert(DbgNode && "Trying to replace an unverified type!");
 
@@ -344,13 +344,19 @@ void DIType::replaceAllUsesWith(DIDescriptor &D) {
   // which, due to uniquing, has merged with the source. We shield clients from
   // this detail by allowing a value to be replaced with replaceAllUsesWith()
   // itself.
-  if (DbgNode != D) {
-    MDNode *Node = const_cast<MDNode *>(DbgNode);
-    const MDNode *DN = D;
-    const Value *V = cast_or_null<Value>(DN);
-    Node->replaceAllUsesWith(const_cast<Value *>(V));
-    MDNode::deleteTemporary(Node);
+  const MDNode *DN = D;
+  if (DbgNode == DN) {
+    SmallVector<Value*, 10> Ops(DbgNode->getNumOperands());
+    for (size_t i = 0; i != Ops.size(); ++i)
+      Ops[i] = DbgNode->getOperand(i);
+    DN = MDNode::get(VMContext, Ops);
   }
+
+  MDNode *Node = const_cast<MDNode *>(DbgNode);
+  const Value *V = cast_or_null<Value>(DN);
+  Node->replaceAllUsesWith(const_cast<Value *>(V));
+  MDNode::deleteTemporary(Node);
+  DbgNode = D;
 }
 
 /// replaceAllUsesWith - Replace all uses of the MDNode used by this
@@ -358,19 +364,12 @@ void DIType::replaceAllUsesWith(DIDescriptor &D) {
 void DIType::replaceAllUsesWith(MDNode *D) {
 
   assert(DbgNode && "Trying to replace an unverified type!");
-
-  // Since we use a TrackingVH for the node, its easy for clients to manufacture
-  // legitimate situations where they want to replaceAllUsesWith() on something
-  // which, due to uniquing, has merged with the source. We shield clients from
-  // this detail by allowing a value to be replaced with replaceAllUsesWith()
-  // itself.
-  if (DbgNode != D) {
-    MDNode *Node = const_cast<MDNode *>(DbgNode);
-    const MDNode *DN = D;
-    const Value *V = cast_or_null<Value>(DN);
-    Node->replaceAllUsesWith(const_cast<Value *>(V));
-    MDNode::deleteTemporary(Node);
-  }
+  assert(DbgNode != D && "This replacement should always happen");
+  MDNode *Node = const_cast<MDNode *>(DbgNode);
+  const MDNode *DN = D;
+  const Value *V = cast_or_null<Value>(DN);
+  Node->replaceAllUsesWith(const_cast<Value *>(V));
+  MDNode::deleteTemporary(Node);
 }
 
 /// Verify - Verify that a compile unit is well formed.