Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -4768,7 +4768,7 @@
   if (!Root)
     return false;
 
-  if (Root->getParent() != BB)
+  if (Root->getParent() != BB || isa<PHINode>(Root))
     return false;
   // Start analysis starting from Root instruction. If horizontal reduction is
   // found, try to vectorize it. If it is not a horizontal reduction or
@@ -4789,7 +4789,7 @@
     if (!V)
       continue;
     auto *Inst = dyn_cast<Instruction>(V);
-    if (!Inst || isa<PHINode>(Inst))
+    if (!Inst)
       continue;
     if (auto *BI = dyn_cast<BinaryOperator>(Inst)) {
       HorizontalReduction HorRdx;
@@ -4825,7 +4825,10 @@
     // Try to vectorize operands.
     if (++Level < RecursionMaxDepth)
       for (auto *Op : Inst->operand_values())
-        Stack.emplace_back(Op, Level);
+        if (VisitedInstrs.insert(Op).second)
+          if (auto *I = dyn_cast<Instruction>(Op))
+            if (!isa<PHINode>(Inst) && I->getParent() == BB)
+              Stack.emplace_back(Op, Level);
   }
   return Res;
 }