Index: lib/Analysis/LazyValueInfo.cpp
===================================================================
--- lib/Analysis/LazyValueInfo.cpp
+++ lib/Analysis/LazyValueInfo.cpp
@@ -1401,6 +1401,14 @@
   return LVILatticeVal::getOverdefined();
 }
 
+// Return true if the instruction type of Val is supported by
+// constantFoldUser(). Currently CastInst and BinaryOperator only.  Call this
+// before calling constantFoldUser() to find out if it's even worth attempting
+// to call it.
+static bool canConstantFoldUser(Value *Val) {
+  return isa<CastInst>(Val) || isa<BinaryOperator>(Val);
+}
+
 /// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
 /// Val is not constrained on the edge.  Result is unspecified if return value
 /// is false.
@@ -1436,7 +1444,7 @@
         assert(Result.isOverdefined() && "Result isn't overdefined");
         if (isa<IntegerType>(Val->getType())) {
           const DataLayout &DL = BBTo->getModule()->getDataLayout();
-          if (usesOperand(Usr, Condition)) {
+          if (canConstantFoldUser(Val) && usesOperand(Usr, Condition)) {
             // If Val has Condition as an operand and Val can be folded into a
             // constant with either Condition == true or Condition == false,
             // propagate the constant.
@@ -1454,13 +1462,18 @@
             //    %Val = add i8 %Op, 1
             //    %Condition = icmp eq i8 %Op, 93
             //    br i1 %Condition, label %then, label %else
-            for (unsigned i = 0; i < Usr->getNumOperands(); ++i) {
-              Value *Op = Usr->getOperand(i);
-              LVILatticeVal OpLatticeVal =
-                  getValueFromCondition(Op, Condition, isTrueDest);
-              if (Optional<APInt> OpConst = OpLatticeVal.asConstantInteger()) {
-                Result = constantFoldUser(Val, Op, OpConst.getValue(), DL);
-                break;
+            // Check with canConstantFoldUser() first to avoid checking the
+            // operands which can be expensive for a large phi, etc.
+            if (canConstantFoldUser(Val)) {
+              for (unsigned i = 0; i < Usr->getNumOperands(); ++i) {
+                Value *Op = Usr->getOperand(i);
+                LVILatticeVal OpLatticeVal =
+                    getValueFromCondition(Op, Condition, isTrueDest);
+                if (Optional<APInt> OpConst =
+                    OpLatticeVal.asConstantInteger()) {
+                  Result = constantFoldUser(Val, Op, OpConst.getValue(), DL);
+                  break;
+                }
               }
             }
           }