Index: lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- lib/Transforms/Scalar/JumpThreading.cpp
+++ lib/Transforms/Scalar/JumpThreading.cpp
@@ -160,10 +160,12 @@
 
   FindLoopHeaders(F);
 
-  bool Changed, EverChanged = false;
+  unsigned UpdatedBBCount;
+  SmallPtrSet<BasicBlock *, 16> UpdatedBB;
   do {
-    Changed = false;
+    UpdatedBBCount = UpdatedBB.size();
     for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
+      bool Changed = false;
       BasicBlock *BB = I;
       // Thread all of the branches we can over this block.
       while (ProcessBlock(BB))
@@ -180,7 +182,7 @@
         LoopHeaders.erase(BB);
         LVI->eraseBlock(BB);
         DeleteDeadBlock(BB);
-        Changed = true;
+        UpdatedBB.insert(BB);
         continue;
       }
 
@@ -214,12 +216,13 @@
         if (ErasedFromLoopHeaders)
           LoopHeaders.insert(BB);
       }
+      if (Changed)
+        UpdatedBB.insert(BB);
     }
-    EverChanged |= Changed;
-  } while (Changed);
+  } while (UpdatedBBCount < UpdatedBB.size());
 
   LoopHeaders.clear();
-  return EverChanged;
+  return UpdatedBBCount > 0;
 }
 
 /// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
Index: test/Transforms/JumpThreading/pr15851_hang.ll
===================================================================
--- test/Transforms/JumpThreading/pr15851_hang.ll
+++ test/Transforms/JumpThreading/pr15851_hang.ll
@@ -0,0 +1,27 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f() {
+entry:
+  call void @f()
+  unreachable
+
+for.cond1:                                        ; preds = %for.cond1, %for.inc
+  %i.0 = phi i32 [ %inc, %for.inc ], [ 0, %for.cond1 ]
+  %cmp = icmp slt i32 %i.0, 2
+  br i1 %cmp, label %for.body, label %for.cond1
+
+for.body:                                         ; preds = %for.cond1
+  %div = sdiv i32 %i.0, 2
+  %i.0.off = add i32 %i.0, 1
+  %0 = icmp ugt i32 %i.0.off, 2
+  br i1 %0, label %land.rhs, label %for.inc
+
+land.rhs:                                         ; preds = %for.body
+  store i32 0, i32* undef, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body
+  %inc = add nsw i32 %div, 1
+  br label %for.cond1
+}