diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 6fdf4afebc2..b292af6cee7 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1821,13 +1821,16 @@ unsigned ComputeNumSignBits(Value *V, const DataLayout *TD,
 
   case Instruction::PHI: {
     PHINode *PN = cast<PHINode>(U);
+    unsigned NumIncomingValues = PN->getNumIncomingValues();
     // Don't analyze large in-degree PHIs.
-    if (PN->getNumIncomingValues() > 4) break;
+    if (NumIncomingValues > 4) break;
+    // Unreachable blocks may have zero-operand PHI nodes.
+    if (NumIncomingValues == 0) break;
 
     // Take the minimum of all incoming values.  This can't infinitely loop
     // because of our depth threshold.
     Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1, Q);
-    for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
+    for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
       if (Tmp == 1) return Tmp;
       Tmp = std::min(Tmp,
                      ComputeNumSignBits(PN->getIncomingValue(i), TD,
diff --git a/test/Transforms/JumpThreading/pr22086.ll b/test/Transforms/JumpThreading/pr22086.ll
new file mode 100644
index 00000000000..35d9aa5b184
--- /dev/null
+++ b/test/Transforms/JumpThreading/pr22086.ll
@@ -0,0 +1,28 @@
+; RUN: opt -S -jump-threading < %s | FileCheck %s
+
+
+; CHECK-LABEL: @f(
+; CHECK-LABEL: entry:
+; CHECK-NEXT:  br label %[[loop:.*]]
+; CHECK:       [[loop]]:
+; CHECK-NEXT:  br label %[[loop]]
+
+define void @f() {
+entry:
+  br label %for.cond1
+
+if.end16:
+  %phi1 = phi i32 [ undef, %for.cond1 ]
+  %g.3 = phi i32 [ %g.1, %for.cond1 ]
+  %sext = shl i32 %g.3, 16
+  %conv20 = ashr exact i32 %sext, 16
+  %tobool21 = icmp eq i32 %phi1, 0
+  br i1 %tobool21, label %lor.rhs, label %for.cond1
+
+for.cond1:
+  %g.1 = phi i32 [ 0, %entry ], [ 0, %lor.rhs ], [ %g.3, %if.end16 ]
+  br i1 undef, label %lor.rhs, label %if.end16
+
+lor.rhs:
+  br label %for.cond1
+}