diff --git a/include/llvm/ADT/ilist.h b/include/llvm/ADT/ilist.h
index 1db648b0ff2..1a3571dea5a 100644
--- a/include/llvm/ADT/ilist.h
+++ b/include/llvm/ADT/ilist.h
@@ -39,8 +39,15 @@
 #define LLVM_ADT_ILIST_H
 
 #include "llvm/ADT/iterator.h"
+#include "llvm/Config/config.h"
 #include <cassert>
 
+#if defined(LLVM_COMPACT_SENTINELS) && LLVM_COMPACT_SENTINELS
+#   define sentinel_tail_assert(COND)
+#else
+#   define sentinel_tail_assert(COND) assert(COND)
+#endif
+
 namespace llvm {
 
 template<typename NodeTy, typename Traits> class iplist;
@@ -189,12 +196,12 @@ public:
 
   // Accessors...
   operator pointer() const {
-    assert(Traits::getNext(NodePtr) != 0 && "Dereferencing end()!");
+    sentinel_tail_assert(Traits::getNext(NodePtr) != 0 && "Dereferencing end()!");
     return NodePtr;
   }
 
   reference operator*() const {
-    assert(Traits::getNext(NodePtr) != 0 && "Dereferencing end()!");
+    sentinel_tail_assert(Traits::getNext(NodePtr) != 0 && "Dereferencing end()!");
     return *NodePtr;
   }
   pointer operator->() const { return &operator*(); }
@@ -215,7 +222,7 @@ public:
   }
   ilist_iterator &operator++() {      // preincrement - Advance
     NodePtr = Traits::getNext(NodePtr);
-    assert(NodePtr && "++'d off the end of an ilist!");
+    sentinel_tail_assert(NodePtr && "++'d off the end of an ilist!");
     return *this;
   }
   ilist_iterator operator--(int) {    // postdecrement operators...
diff --git a/include/llvm/ADT/ilist_node.h b/include/llvm/ADT/ilist_node.h
index dae7475ffa0..89e5b6ef482 100644
--- a/include/llvm/ADT/ilist_node.h
+++ b/include/llvm/ADT/ilist_node.h
@@ -15,33 +15,56 @@
 #ifndef LLVM_ADT_ILIST_NODE_H
 #define LLVM_ADT_ILIST_NODE_H
 
+#include "llvm/Config/config.h"
+
 namespace llvm {
 
 template<typename NodeTy>
-struct ilist_nextprev_traits;
+struct ilist_traits;
+
+/// ilist_half_node - Base class that provides prev services for sentinels.
+///
+template<typename NodeTy>
+class ilist_half_node {
+  friend struct ilist_traits<NodeTy>;
+  NodeTy *Prev;
+protected:
+  NodeTy *getPrev() { return Prev; }
+  const NodeTy *getPrev() const { return Prev; }
+  void setPrev(NodeTy *P) { Prev = P; }
+  ilist_half_node() : Prev(0) {}
+};
 
 template<typename NodeTy>
-struct ilist_traits;
+struct ilist_nextprev_traits;
 
 /// ilist_node - Base class that provides next/prev services for nodes
 /// that use ilist_nextprev_traits or ilist_default_traits.
 ///
 template<typename NodeTy>
-class ilist_node {
-private:
+class ilist_node : ilist_half_node<NodeTy> {
   friend struct ilist_nextprev_traits<NodeTy>;
   friend struct ilist_traits<NodeTy>;
-  NodeTy *Prev, *Next;
-  NodeTy *getPrev() { return Prev; }
+  NodeTy *Next;
   NodeTy *getNext() { return Next; }
-  const NodeTy *getPrev() const { return Prev; }
   const NodeTy *getNext() const { return Next; }
-  void setPrev(NodeTy *N) { Prev = N; }
   void setNext(NodeTy *N) { Next = N; }
 protected:
-  ilist_node() : Prev(0), Next(0) {}
+  ilist_node() : Next(0) {}
 };
 
+/// When assertions are off, the Next field of sentinels
+/// will not be accessed. So it is not necessary to allocate
+/// space for it. The following macro selects the most
+/// efficient traits class. The LLVM_COMPACT_SENTINELS
+/// configuration variable controls this.
+///
+#if defined(LLVM_COMPACT_SENTINELS) && LLVM_COMPACT_SENTINELS
+#   define ILIST_NODE ilist_half_node
+#else
+#   define ILIST_NODE ilist_node
+#endif
+
 } // End llvm namespace
 
 #endif
diff --git a/include/llvm/BasicBlock.h b/include/llvm/BasicBlock.h
index 3ba4e360f71..16f680d2438 100644
--- a/include/llvm/BasicBlock.h
+++ b/include/llvm/BasicBlock.h
@@ -47,7 +47,7 @@ template<> struct ilist_traits<Instruction>
   Instruction *ensureHead(Instruction*) const { return createSentinel(); }
   static void noteHead(Instruction*, Instruction*) {}
 private:
-  mutable ilist_node<Instruction> Sentinel;
+  mutable ILIST_NODE<Instruction> Sentinel;
 };
 
 /// This represents a single basic block in LLVM. A basic block is simply a
diff --git a/include/llvm/CodeGen/MachineBasicBlock.h b/include/llvm/CodeGen/MachineBasicBlock.h
index 9b989b2304f..52e56422c8c 100644
--- a/include/llvm/CodeGen/MachineBasicBlock.h
+++ b/include/llvm/CodeGen/MachineBasicBlock.h
@@ -26,7 +26,7 @@ class raw_ostream;
 template <>
 struct ilist_traits<MachineInstr> : public ilist_default_traits<MachineInstr> {
 private:
-  mutable ilist_node<MachineInstr> Sentinel;
+  mutable ILIST_NODE<MachineInstr> Sentinel;
 
   // this is only set by the MachineBasicBlock owning the LiveList
   friend class MachineBasicBlock;
diff --git a/include/llvm/CodeGen/MachineFunction.h b/include/llvm/CodeGen/MachineFunction.h
index 51200cb2bbe..92f46b070f5 100644
--- a/include/llvm/CodeGen/MachineFunction.h
+++ b/include/llvm/CodeGen/MachineFunction.h
@@ -38,7 +38,7 @@ class TargetRegisterClass;
 template <>
 struct ilist_traits<MachineBasicBlock>
     : public ilist_default_traits<MachineBasicBlock> {
-  mutable ilist_node<MachineBasicBlock> Sentinel;
+  mutable ILIST_NODE<MachineBasicBlock> Sentinel;
 public:
   MachineBasicBlock *createSentinel() const {
     return static_cast<MachineBasicBlock*>(&Sentinel);
diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index 5f5498158d8..b0fb5d8b1f2 100644
--- a/include/llvm/CodeGen/SelectionDAG.h
+++ b/include/llvm/CodeGen/SelectionDAG.h
@@ -37,7 +37,7 @@ class FunctionLoweringInfo;
 
 template<> struct ilist_traits<SDNode> : public ilist_default_traits<SDNode> {
 private:
-  mutable ilist_node<SDNode> Sentinel;
+  mutable ILIST_NODE<SDNode> Sentinel;
 public:
   SDNode *createSentinel() const {
     return static_cast<SDNode*>(&Sentinel);
diff --git a/include/llvm/Function.h b/include/llvm/Function.h
index 90d9b0ee46e..6c3d41e21af 100644
--- a/include/llvm/Function.h
+++ b/include/llvm/Function.h
@@ -45,7 +45,7 @@ template<> struct ilist_traits<BasicBlock>
 
   static ValueSymbolTable *getSymTab(Function *ItemParent);
 private:
-  mutable ilist_node<BasicBlock> Sentinel;
+  mutable ILIST_NODE<BasicBlock> Sentinel;
 };
 
 template<> struct ilist_traits<Argument>
@@ -62,7 +62,7 @@ template<> struct ilist_traits<Argument>
 
   static ValueSymbolTable *getSymTab(Function *ItemParent);
 private:
-  mutable ilist_node<Argument> Sentinel;
+  mutable ILIST_NODE<Argument> Sentinel;
 };
 
 class Function : public GlobalValue,