MapValue support for MDNodes. This is similar to r109117, except

that it avoids a lot of unnecessary cloning by avoiding remapping
MDNode cycles when none of the nodes in the cycle actually need to
be remapped. Also it uses the new temporary MDNode mechanism.

llvm-svn: 111922

1 files changed, 27 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index 3f6a90c94eb..7f61c25d08e 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -27,17 +27,36 @@ Value *llvm::MapValue(const Value *V, ValueToValueMapTy &VM) {
   // NOTE: VMSlot can be invalidated by any reference to VM, which can grow the
   // DenseMap.  This includes any recursive calls to MapValue.
 
-  // Global values and non-function-local metadata do not need to be seeded into
-  // the VM if they are using the identity mapping.
-  if (isa<GlobalValue>(V) || isa<InlineAsm>(V) || isa<MDString>(V) ||
-      (isa<MDNode>(V) && !cast<MDNode>(V)->isFunctionLocal()))
+  // Global values do not need to be seeded into the VM if they
+  // are using the identity mapping.
+  if (isa<GlobalValue>(V) || isa<InlineAsm>(V) || isa<MDString>(V))
     return VMSlot = const_cast<Value*>(V);
 
   if (const MDNode *MD = dyn_cast<MDNode>(V)) {
-    SmallVector<Value*, 4> Elts;
-    for (unsigned i = 0, e = MD->getNumOperands(); i != e; ++i)
-      Elts.push_back(MD->getOperand(i) ? MapValue(MD->getOperand(i), VM) : 0);
-    return VM[V] = MDNode::get(V->getContext(), Elts.data(), Elts.size());
+    // Start by assuming that we'll use the identity mapping.
+    VMSlot = const_cast<Value*>(V);
+
+    // Check all operands to see if any need to be remapped.
+    for (unsigned i = 0, e = MD->getNumOperands(); i != e; ++i) {
+      Value *OP = MD->getOperand(i);
+      if (!OP || MapValue(OP, VM) == OP) continue;
+
+      // Ok, at least one operand needs remapping.
+      MDNode *Dummy = MDNode::getTemporary(V->getContext(), 0, 0);
+      VM[V] = Dummy;
+      SmallVector<Value*, 4> Elts;
+      Elts.reserve(MD->getNumOperands());
+      for (i = 0; i != e; ++i)
+        Elts.push_back(MD->getOperand(i) ? 
+                       MapValue(MD->getOperand(i), VM) : 0);
+      MDNode *NewMD = MDNode::get(V->getContext(), Elts.data(), Elts.size());
+      Dummy->replaceAllUsesWith(NewMD);
+      MDNode::deleteTemporary(Dummy);
+      return VM[V] = NewMD;
+    }
+
+    // No operands needed remapping; keep the identity map.
+    return const_cast<Value*>(V);
   }
 
   Constant *C = const_cast<Constant*>(dyn_cast<Constant>(V));