Index: llvm/trunk/include/llvm/IR/Attributes.h
===================================================================
--- llvm/trunk/include/llvm/IR/Attributes.h
+++ llvm/trunk/include/llvm/IR/Attributes.h
@@ -511,6 +511,9 @@
   /// \brief Return the attributes at the given slot.
   AttributeList getSlotAttributes(unsigned Slot) const;
 
+  /// \brief Return the attributes at the given slot.
+  AttributeSet getSlotSet(unsigned Slot) const;
+
   void dump() const;
 };
 
Index: llvm/trunk/lib/Bitcode/Writer/BitcodeWriter.cpp
===================================================================
--- llvm/trunk/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ llvm/trunk/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -726,54 +726,50 @@
 }
 
 void ModuleBitcodeWriter::writeAttributeGroupTable() {
-  const std::vector<AttributeList> &AttrGrps = VE.getAttributeGroups();
+  const std::vector<ValueEnumerator::IndexAndAttrSet> &AttrGrps =
+      VE.getAttributeGroups();
   if (AttrGrps.empty()) return;
 
   Stream.EnterSubblock(bitc::PARAMATTR_GROUP_BLOCK_ID, 3);
 
   SmallVector<uint64_t, 64> Record;
-  for (unsigned i = 0, e = AttrGrps.size(); i != e; ++i) {
-    AttributeList AS = AttrGrps[i];
-    for (unsigned i = 0, e = AS.getNumSlots(); i != e; ++i) {
-      AttributeList A = AS.getSlotAttributes(i);
-
-      Record.push_back(VE.getAttributeGroupID(A));
-      Record.push_back(AS.getSlotIndex(i));
-
-      for (AttributeList::iterator I = AS.begin(0), E = AS.end(0); I != E;
-           ++I) {
-        Attribute Attr = *I;
-        if (Attr.isEnumAttribute()) {
-          Record.push_back(0);
-          Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
-        } else if (Attr.isIntAttribute()) {
-          Record.push_back(1);
-          Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
-          Record.push_back(Attr.getValueAsInt());
-        } else {
-          StringRef Kind = Attr.getKindAsString();
-          StringRef Val = Attr.getValueAsString();
+  for (ValueEnumerator::IndexAndAttrSet Pair : AttrGrps) {
+    unsigned AttrListIndex = Pair.first;
+    AttributeSet AS = Pair.second;
+    Record.push_back(VE.getAttributeGroupID(Pair));
+    Record.push_back(AttrListIndex);
+
+    for (Attribute Attr : AS) {
+      if (Attr.isEnumAttribute()) {
+        Record.push_back(0);
+        Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
+      } else if (Attr.isIntAttribute()) {
+        Record.push_back(1);
+        Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
+        Record.push_back(Attr.getValueAsInt());
+      } else {
+        StringRef Kind = Attr.getKindAsString();
+        StringRef Val = Attr.getValueAsString();
 
-          Record.push_back(Val.empty() ? 3 : 4);
-          Record.append(Kind.begin(), Kind.end());
+        Record.push_back(Val.empty() ? 3 : 4);
+        Record.append(Kind.begin(), Kind.end());
+        Record.push_back(0);
+        if (!Val.empty()) {
+          Record.append(Val.begin(), Val.end());
           Record.push_back(0);
-          if (!Val.empty()) {
-            Record.append(Val.begin(), Val.end());
-            Record.push_back(0);
-          }
         }
       }
-
-      Stream.EmitRecord(bitc::PARAMATTR_GRP_CODE_ENTRY, Record);
-      Record.clear();
     }
+
+    Stream.EmitRecord(bitc::PARAMATTR_GRP_CODE_ENTRY, Record);
+    Record.clear();
   }
 
   Stream.ExitBlock();
 }
 
 void ModuleBitcodeWriter::writeAttributeTable() {
-  const std::vector<AttributeList> &Attrs = VE.getAttributes();
+  const std::vector<AttributeList> &Attrs = VE.getAttributeLists();
   if (Attrs.empty()) return;
 
   Stream.EnterSubblock(bitc::PARAMATTR_BLOCK_ID, 3);
@@ -782,7 +778,8 @@
   for (unsigned i = 0, e = Attrs.size(); i != e; ++i) {
     const AttributeList &A = Attrs[i];
     for (unsigned i = 0, e = A.getNumSlots(); i != e; ++i)
-      Record.push_back(VE.getAttributeGroupID(A.getSlotAttributes(i)));
+      Record.push_back(
+          VE.getAttributeGroupID({A.getSlotIndex(i), A.getSlotSet(i)}));
 
     Stream.EmitRecord(bitc::PARAMATTR_CODE_ENTRY, Record);
     Record.clear();
@@ -1270,7 +1267,7 @@
     Vals.push_back(F.getCallingConv());
     Vals.push_back(F.isDeclaration());
     Vals.push_back(getEncodedLinkage(F));
-    Vals.push_back(VE.getAttributeID(F.getAttributes()));
+    Vals.push_back(VE.getAttributeListID(F.getAttributes()));
     Vals.push_back(Log2_32(F.getAlignment())+1);
     Vals.push_back(F.hasSection() ? SectionMap[F.getSection()] : 0);
     Vals.push_back(getEncodedVisibility(F));
@@ -2616,7 +2613,7 @@
 
     Code = bitc::FUNC_CODE_INST_INVOKE;
 
-    Vals.push_back(VE.getAttributeID(II->getAttributes()));
+    Vals.push_back(VE.getAttributeListID(II->getAttributes()));
     Vals.push_back(II->getCallingConv() | 1 << 13);
     Vals.push_back(VE.getValueID(II->getNormalDest()));
     Vals.push_back(VE.getValueID(II->getUnwindDest()));
@@ -2808,7 +2805,7 @@
 
     Code = bitc::FUNC_CODE_INST_CALL;
 
-    Vals.push_back(VE.getAttributeID(CI.getAttributes()));
+    Vals.push_back(VE.getAttributeListID(CI.getAttributes()));
 
     unsigned Flags = getOptimizationFlags(&I);
     Vals.push_back(CI.getCallingConv() << bitc::CALL_CCONV |
Index: llvm/trunk/lib/Bitcode/Writer/ValueEnumerator.h
===================================================================
--- llvm/trunk/lib/Bitcode/Writer/ValueEnumerator.h
+++ llvm/trunk/lib/Bitcode/Writer/ValueEnumerator.h
@@ -48,6 +48,10 @@
   // For each value, we remember its Value* and occurrence frequency.
   typedef std::vector<std::pair<const Value*, unsigned> > ValueList;
 
+  /// Attribute groups as encoded in bitcode are almost AttributeSets, but they
+  /// include the AttributeList index, so we have to track that in our map.
+  typedef std::pair<unsigned, AttributeSet> IndexAndAttrSet;
+
   UseListOrderStack UseListOrders;
 
 private:
@@ -102,13 +106,13 @@
 
   bool ShouldPreserveUseListOrder;
 
-  typedef DenseMap<AttributeList, unsigned> AttributeGroupMapType;
+  typedef DenseMap<IndexAndAttrSet, unsigned> AttributeGroupMapType;
   AttributeGroupMapType AttributeGroupMap;
-  std::vector<AttributeList> AttributeGroups;
+  std::vector<IndexAndAttrSet> AttributeGroups;
 
-  typedef DenseMap<AttributeList, unsigned> AttributeMapType;
-  AttributeMapType AttributeMap;
-  std::vector<AttributeList> Attribute;
+  typedef DenseMap<AttributeList, unsigned> AttributeListMapType;
+  AttributeListMapType AttributeListMap;
+  std::vector<AttributeList> AttributeLists;
 
   /// GlobalBasicBlockIDs - This map memoizes the basic block ID's referenced by
   /// the "getGlobalBasicBlockID" method.
@@ -166,16 +170,17 @@
   unsigned getInstructionID(const Instruction *I) const;
   void setInstructionID(const Instruction *I);
 
-  unsigned getAttributeID(AttributeList PAL) const {
+  unsigned getAttributeListID(AttributeList PAL) const {
     if (PAL.isEmpty()) return 0;  // Null maps to zero.
-    AttributeMapType::const_iterator I = AttributeMap.find(PAL);
-    assert(I != AttributeMap.end() && "Attribute not in ValueEnumerator!");
+    AttributeListMapType::const_iterator I = AttributeListMap.find(PAL);
+    assert(I != AttributeListMap.end() && "Attribute not in ValueEnumerator!");
     return I->second;
   }
 
-  unsigned getAttributeGroupID(AttributeList PAL) const {
-    if (PAL.isEmpty()) return 0;  // Null maps to zero.
-    AttributeGroupMapType::const_iterator I = AttributeGroupMap.find(PAL);
+  unsigned getAttributeGroupID(IndexAndAttrSet Group) const {
+    if (!Group.second.hasAttributes())
+      return 0; // Null maps to zero.
+    AttributeGroupMapType::const_iterator I = AttributeGroupMap.find(Group);
     assert(I != AttributeGroupMap.end() && "Attribute not in ValueEnumerator!");
     return I->second;
   }
@@ -206,8 +211,8 @@
   const std::vector<const BasicBlock*> &getBasicBlocks() const {
     return BasicBlocks;
   }
-  const std::vector<AttributeList> &getAttributes() const { return Attribute; }
-  const std::vector<AttributeList> &getAttributeGroups() const {
+  const std::vector<AttributeList> &getAttributeLists() const { return AttributeLists; }
+  const std::vector<IndexAndAttrSet> &getAttributeGroups() const {
     return AttributeGroups;
   }
 
Index: llvm/trunk/lib/Bitcode/Writer/ValueEnumerator.cpp
===================================================================
--- llvm/trunk/lib/Bitcode/Writer/ValueEnumerator.cpp
+++ llvm/trunk/lib/Bitcode/Writer/ValueEnumerator.cpp
@@ -891,19 +891,19 @@
   if (PAL.isEmpty()) return;  // null is always 0.
 
   // Do a lookup.
-  unsigned &Entry = AttributeMap[PAL];
+  unsigned &Entry = AttributeListMap[PAL];
   if (Entry == 0) {
     // Never saw this before, add it.
-    Attribute.push_back(PAL);
-    Entry = Attribute.size();
+    AttributeLists.push_back(PAL);
+    Entry = AttributeLists.size();
   }
 
   // Do lookups for all attribute groups.
   for (unsigned i = 0, e = PAL.getNumSlots(); i != e; ++i) {
-    AttributeList AS = PAL.getSlotAttributes(i);
-    unsigned &Entry = AttributeGroupMap[AS];
+    IndexAndAttrSet Pair = {PAL.getSlotIndex(i), PAL.getSlotSet(i)};
+    unsigned &Entry = AttributeGroupMap[Pair];
     if (Entry == 0) {
-      AttributeGroups.push_back(AS);
+      AttributeGroups.push_back(Pair);
       Entry = AttributeGroups.size();
     }
   }
Index: llvm/trunk/lib/IR/Attributes.cpp
===================================================================
--- llvm/trunk/lib/IR/Attributes.cpp
+++ llvm/trunk/lib/IR/Attributes.cpp
@@ -1257,6 +1257,12 @@
   return pImpl->getSlotAttributes(Slot);
 }
 
+AttributeSet AttributeList::getSlotSet(unsigned Slot) const {
+  assert(pImpl && Slot < pImpl->getNumSlots() &&
+         "Slot # out of range!");
+  return pImpl->getSlotNode(Slot);
+}
+
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void AttributeList::dump() const {
   dbgs() << "PAL[\n";