diff --git a/llvm/include/llvm/CodeGen/LiveInterval.h b/llvm/include/llvm/CodeGen/LiveInterval.h
--- a/llvm/include/llvm/CodeGen/LiveInterval.h
+++ b/llvm/include/llvm/CodeGen/LiveInterval.h
@@ -521,11 +521,11 @@
       removeSegment(S.start, S.end, RemoveDeadValNo);
     }
 
-    /// Remove segment pointed to by iterator @p I from this range.  This does
-    /// not remove dead value numbers.
-    iterator removeSegment(iterator I) {
-      return segments.erase(I);
-    }
+    /// Remove segment pointed to by iterator @p I from this range.
+    iterator removeSegment(iterator I, bool RemoveDeadValNo = false);
+
+    /// Mark \p ValNo for deletion if no segments in this range use it.
+    void removeValNoIfDead(VNInfo *ValNo);
 
     /// Query Liveness at Idx.
     /// The sub-instruction slot of Idx doesn't matter, only the instruction
diff --git a/llvm/lib/CodeGen/LiveInterval.cpp b/llvm/lib/CodeGen/LiveInterval.cpp
--- a/llvm/lib/CodeGen/LiveInterval.cpp
+++ b/llvm/lib/CodeGen/LiveInterval.cpp
@@ -592,21 +592,10 @@
   VNInfo *ValNo = I->valno;
   if (I->start == Start) {
     if (I->end == End) {
-      if (RemoveDeadValNo) {
-        // Check if val# is dead.
-        bool isDead = true;
-        for (const_iterator II = begin(), EE = end(); II != EE; ++II)
-          if (II != I && II->valno == ValNo) {
-            isDead = false;
-            break;
-          }
-        if (isDead) {
-          // Now that ValNo is dead, remove it.
-          markValNoForDeletion(ValNo);
-        }
-      }
-
       segments.erase(I);  // Removed the whole Segment.
+
+      if (RemoveDeadValNo)
+        removeValNoIfDead(ValNo);
     } else
       I->start = End;
     return;
@@ -627,6 +616,19 @@
   segments.insert(std::next(I), Segment(End, OldEnd, ValNo));
 }
 
+LiveRange::iterator LiveRange::removeSegment(iterator I, bool RemoveDeadValNo) {
+  VNInfo *ValNo = I->valno;
+  I = segments.erase(I);
+  if (RemoveDeadValNo)
+    removeValNoIfDead(ValNo);
+  return I;
+}
+
+void LiveRange::removeValNoIfDead(VNInfo *ValNo) {
+  if (none_of(*this, [=](const Segment &S) { return S.valno == ValNo; }))
+    markValNoForDeletion(ValNo);
+}
+
 /// removeValNo - Remove all the segments defined by the specified value#.
 /// Also remove the value# from value# list.
 void LiveRange::removeValNo(VNInfo *ValNo) {
diff --git a/llvm/lib/CodeGen/LiveIntervals.cpp b/llvm/lib/CodeGen/LiveIntervals.cpp
--- a/llvm/lib/CodeGen/LiveIntervals.cpp
+++ b/llvm/lib/CodeGen/LiveIntervals.cpp
@@ -1607,17 +1607,9 @@
       if (MO.isDef()) {
         if (!isStartValid) {
           if (LII->end.isDead()) {
-            SlotIndex prevStart;
+            LII = LR.removeSegment(LII, true);
             if (LII != LR.begin())
-              prevStart = std::prev(LII)->start;
-
-            // FIXME: This could be more efficient if there was a
-            // removeSegment method that returned an iterator.
-            LR.removeSegment(*LII, true);
-            if (prevStart.isValid())
-              LII = LR.find(prevStart);
-            else
-              LII = LR.begin();
+              --LII;
           } else {
             LII->start = instrIdx.getRegSlot();
             LII->valno->def = instrIdx.getRegSlot();