Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -809,6 +809,20 @@
   bool IsSigned = Cast->getOpcode() == Instruction::SExt;
   if (!IsSigned && Cast->getOpcode() != Instruction::ZExt)
     return;
+  
+  // If this is a zext, mark this IV as signed if it is known to be
+  // non-negative and the zext has a GEP user.
+  if (!IsSigned) {
+    const SCEV *NarrowIVSCEV = SE->getSCEV(WI.NarrowIV);
+    bool NeverNegative = 
+      SE->isKnownPredicate(ICmpInst::ICMP_SGE, NarrowIVSCEV,
+                           SE->getConstant(NarrowIVSCEV->getType(), 0));
+    if (NeverNegative && any_of(Cast->users(), [](User *U) {
+      auto* CastUser = cast<Instruction>(U);
+      return CastUser->getOpcode() == Instruction::GetElementPtr;
+    }))
+      IsSigned = true;
+  }
 
   Type *Ty = Cast->getType();
   uint64_t Width = SE->getTypeSizeInBits(Ty);