From 4ce307f96361d428bd332c2086ef42be359d9dd2 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Tue, 24 Aug 2010 17:10:10 +0000
Subject: 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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111922 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/ValueMapper.cpp | 35 +++++++++++++++++++++++++++--------
 1 file changed, 27 insertions(+), 8 deletions(-)

(limited to 'lib/Transforms/Utils/ValueMapper.cpp')

diff --git a/lib/Transforms/Utils/ValueMapper.cpp b/lib/Transforms/Utils/ValueMapper.cpp
index 3f6a90c94e..7f61c25d08 100644
--- a/lib/Transforms/Utils/ValueMapper.cpp
+++ b/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));
-- 
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