Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -136,7 +136,9 @@
   SmallVector<WeakTrackingVH, 16> DeadInsts;
   bool Changed = false;
 
+#ifndef NDEBUG
   bool isValidRewrite(Value *FromVal, Value *ToVal);
+#endif
 
   void handleFloatingPointIV(Loop *L, PHINode *PH);
   void rewriteNonIntegerIVs(Loop *L);
@@ -166,10 +168,10 @@
 
 } // end anonymous namespace
 
+#ifndef NDEBUG
 /// Return true if the SCEV expansion generated by the rewriter can replace the
 /// original value. SCEV guarantees that it produces the same value, but the way
-/// it is produced may be illegal IR.  Ideally, this function will only be
-/// called for verification.
+/// it is produced may be illegal IR.
 bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
   // If an SCEV expression subsumed multiple pointers, its expansion could
   // reassociate the GEP changing the base pointer. This is illegal because the
@@ -217,6 +219,7 @@
   }
   return true;
 }
+#endif
 
 /// Determine the insertion point for this user. By default, insert immediately
 /// before the user. SCEVExpander or LICM will hoist loop invariants out of the
@@ -656,10 +659,7 @@
                           << '\n'
                           << "  LoopVal = " << *Inst << "\n");
 
-        if (!isValidRewrite(Inst, ExitVal)) {
-          DeadInsts.push_back(ExitVal);
-          continue;
-        }
+        assert(isValidRewrite(Inst, ExitVal) && "Must be!");
 
         // Collect all the candidate PHINodes to be rewritten.
         RewritePhiSet.emplace_back(PN, i, ExitVal, HighCost);