diff --git a/lib/CodeGen/SlotIndexes.cpp b/lib/CodeGen/SlotIndexes.cpp
index f3ad0d1cc0a..bf66367865d 100644
--- a/lib/CodeGen/SlotIndexes.cpp
+++ b/lib/CodeGen/SlotIndexes.cpp
@@ -51,8 +51,6 @@ bool SlotIndexes::runOnMachineFunction(MachineFunction &fn) {
   mf = &fn;
   initList();
 
-  const unsigned gap = 1;
-
   // Check that the list contains only the sentinal.
   assert(indexListHead->getNext() == 0 &&
          "Index list non-empty at initial numbering?");
@@ -64,14 +62,6 @@ bool SlotIndexes::runOnMachineFunction(MachineFunction &fn) {
          "MachineInstr -> Index mapping non-empty at initial numbering?");
 
   functionSize = 0;
-  /*  
-  for (unsigned s = 0; s < SlotIndex::NUM; ++s) {  
-    indexList.push_back(createEntry(0, s));
-  }
-
-  unsigned index = gap * SlotIndex::NUM;
-  */
-
   unsigned index = 0;
 
   // Iterate over the the function.
@@ -83,7 +73,7 @@ bool SlotIndexes::runOnMachineFunction(MachineFunction &fn) {
     push_back(createEntry(0, index));
     SlotIndex blockStartIndex(back(), SlotIndex::LOAD);
 
-    index += gap * SlotIndex::NUM;
+    index += SlotIndex::NUM;
 
     for (MachineBasicBlock::iterator miItr = mbb->begin(), miEnd = mbb->end();
          miItr != miEnd; ++miItr) {
@@ -93,7 +83,7 @@ bool SlotIndexes::runOnMachineFunction(MachineFunction &fn) {
         push_back(createEntry(0, index));
         terminatorGaps.insert(
           std::make_pair(mbb, SlotIndex(back(), SlotIndex::PHI_BIT)));
-        index += gap * SlotIndex::NUM;
+        index += SlotIndex::NUM;
       }
 
       // Insert a store index for the instr.
@@ -109,14 +99,14 @@ bool SlotIndexes::runOnMachineFunction(MachineFunction &fn) {
       if (Slots == 0)
         Slots = 1;
 
-      index += (Slots + 1) * gap * SlotIndex::NUM;
+      index += (Slots + 1) * SlotIndex::NUM;
     }
 
     if (mbb->getFirstTerminator() == mbb->end()) {
       push_back(createEntry(0, index));
       terminatorGaps.insert(
         std::make_pair(mbb, SlotIndex(back(), SlotIndex::PHI_BIT)));
-      index += gap * SlotIndex::NUM;
+      index += SlotIndex::NUM;
     }
 
     SlotIndex blockEndIndex(back(), SlotIndex::STORE);
@@ -139,20 +129,36 @@ bool SlotIndexes::runOnMachineFunction(MachineFunction &fn) {
 }
 
 void SlotIndexes::renumber() {
-  assert(false && "SlotIndexes::runmuber is not fully implemented yet.");
 
-  // Compute numbering as follows:
-  // Grab an iterator to the start of the index list.
-  // Iterate over all MBBs, and within each MBB all MIs, keeping the MI
-  // iterator in lock-step (though skipping it over indexes which have
-  // null pointers in the instruction field).
-  // At each iteration assert that the instruction pointed to in the index
-  // is the same one pointed to by the MI iterator. This 
+  // Renumber updates the index of every element of the index list.
+  // If all instrs in the function have been allocated an index (which has been
+  // placed in the index list in the order of instruction iteration) then the
+  // resulting numbering will match what would have been generated by the
+  // pass during the initial numbering of the function if the new instructions
+  // had been present.
 
-  // FIXME: This can be simplified. The mi2iMap_, Idx2MBBMap, etc. should
-  // only need to be set up once - when the first numbering is computed.
+  functionSize = 0;
+  unsigned index = 0;
 
-  assert(false && "Renumbering not supported yet.");
+  for (IndexListEntry *curEntry = front(); curEntry != getTail();
+       curEntry = curEntry->getNext()) {
+
+    curEntry->setIndex(index);
+
+    if (curEntry->getInstr() == 0) {
+      // MBB start entry or terminator gap. Just step index by 1.
+      index += SlotIndex::NUM;
+    }
+    else {
+      ++functionSize;
+      unsigned Slots = curEntry->getInstr()->getDesc().getNumDefs();
+      if (Slots == 0)
+        Slots = 1;
+
+      index += (Slots + 1) * SlotIndex::NUM;
+
+    }
+  }
 }
 
 void SlotIndexes::dump() const {