Index: llvm/include/llvm/Analysis/Utils/Local.h
===================================================================
--- llvm/include/llvm/Analysis/Utils/Local.h
+++ llvm/include/llvm/Analysis/Utils/Local.h
@@ -27,7 +27,7 @@
 /// overflowing is made.
 template <typename IRBuilderTy>
 Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &DL, User *GEP,
-                     bool NoAssumptions = false) {
+                     bool NoAssumptions = false, bool IsNonNegative = false) {
   GEPOperator *GEPOp = cast<GEPOperator>(GEP);
   Type *IntIdxTy = DL.getIndexType(GEP->getType());
   Value *Result = Constant::getNullValue(IntIdxTy);
@@ -35,6 +35,11 @@
   // If the GEP is inbounds, we know that none of the addressing operations will
   // overflow in a signed sense.
   bool isInBounds = GEPOp->isInBounds() && !NoAssumptions;
+  // If we additionally know that the result is non-negative, then operations
+  // also don't overflow in an unsigned sense. Just IsNonNegative is not
+  // sufficient here, as we may still overflow while yielding a non-negative
+  // final result.
+  bool isNUW = IsNonNegative && isInBounds;
 
   // Build a mask for high order bits.
   unsigned IntPtrWidth = IntIdxTy->getScalarType()->getIntegerBitWidth();
@@ -68,7 +73,7 @@
       Constant *Scale = ConstantInt::get(IntIdxTy, Size);
       Constant *OC = ConstantExpr::getIntegerCast(OpC, IntIdxTy, true /*SExt*/);
       Scale =
-          ConstantExpr::getMul(OC, Scale, false /*NUW*/, isInBounds /*NSW*/);
+          ConstantExpr::getMul(OC, Scale, isNUW /*NUW*/, isInBounds /*NSW*/);
       // Emit an add instruction.
       Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
       continue;
@@ -84,7 +89,7 @@
     if (Size != 1) {
       // We'll let instcombine(mul) convert this to a shl if possible.
       Op = Builder->CreateMul(Op, ConstantInt::get(IntIdxTy, Size),
-                              GEP->getName() + ".idx", false /*NUW*/,
+                              GEP->getName() + ".idx", isNUW /*NUW*/,
                               isInBounds /*NSW*/);
     }
 
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1585,7 +1585,7 @@
 ///  &A[10] - &A[0]: we should compile this to "10".  LHS/RHS are the pointer
 /// operands to the ptrtoint instructions for the LHS/RHS of the subtract.
 Value *InstCombiner::OptimizePointerDifference(Value *LHS, Value *RHS,
-                                               Type *Ty) {
+                                               Type *Ty, bool IsNUW) {
   // If LHS is a gep based on RHS or RHS is a gep based on LHS, we can optimize
   // this.
   bool Swapped = false;
@@ -1651,7 +1651,8 @@
   }
 
   // Emit the offset of the GEP and an intptr_t.
-  Value *Result = EmitGEPOffset(GEP1);
+  bool IsNonNegative = IsNUW && !GEP2 && !Swapped;
+  Value *Result = EmitGEPOffset(GEP1, IsNonNegative);
 
   // If we had a constant expression GEP on the other side offsetting the
   // pointer, subtract it from the offset we have.
@@ -1983,13 +1984,15 @@
   Value *LHSOp, *RHSOp;
   if (match(Op0, m_PtrToInt(m_Value(LHSOp))) &&
       match(Op1, m_PtrToInt(m_Value(RHSOp))))
-    if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType()))
+    if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType(),
+                                               I.hasNoUnsignedWrap()))
       return replaceInstUsesWith(I, Res);
 
   // trunc(p)-trunc(q) -> trunc(p-q)
   if (match(Op0, m_Trunc(m_PtrToInt(m_Value(LHSOp)))) &&
       match(Op1, m_Trunc(m_PtrToInt(m_Value(RHSOp)))))
-    if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType()))
+    if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType(),
+                                               /* IsNUW */ false))
       return replaceInstUsesWith(I, Res);
 
   // Canonicalize a shifty way to code absolute value to the common pattern.
Index: llvm/lib/Transforms/InstCombine/InstCombineInternal.h
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -369,7 +369,8 @@
   Instruction *visitFNeg(UnaryOperator &I);
   Instruction *visitAdd(BinaryOperator &I);
   Instruction *visitFAdd(BinaryOperator &I);
-  Value *OptimizePointerDifference(Value *LHS, Value *RHS, Type *Ty);
+  Value *OptimizePointerDifference(
+      Value *LHS, Value *RHS, Type *Ty, bool IsNUW);
   Instruction *visitSub(BinaryOperator &I);
   Instruction *visitFSub(BinaryOperator &I);
   Instruction *visitMul(BinaryOperator &I);
@@ -594,7 +595,7 @@
     }
   }
 
-  Value *EmitGEPOffset(User *GEP);
+  Value *EmitGEPOffset(User *GEP, bool IsNonNegative = false);
   Instruction *scalarizePHI(ExtractElementInst &EI, PHINode *PN);
   Instruction *foldCastedBitwiseLogic(BinaryOperator &I);
   Instruction *narrowBinOp(TruncInst &Trunc);
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -158,8 +158,9 @@
 static cl::opt<unsigned> ShouldLowerDbgDeclare("instcombine-lower-dbg-declare",
                                                cl::Hidden, cl::init(true));
 
-Value *InstCombiner::EmitGEPOffset(User *GEP) {
-  return llvm::EmitGEPOffset(&Builder, DL, GEP);
+Value *InstCombiner::EmitGEPOffset(User *GEP, bool IsNonNegative) {
+  return llvm::EmitGEPOffset(&Builder, DL, GEP, /* NoAssumptions */ false,
+                             IsNonNegative);
 }
 
 /// Return true if it is desirable to convert an integer computation from a
Index: llvm/test/Transforms/InstCombine/sub-gep.ll
===================================================================
--- llvm/test/Transforms/InstCombine/sub-gep.ll
+++ llvm/test/Transforms/InstCombine/sub-gep.ll
@@ -16,7 +16,7 @@
 
 define i64 @test_inbounds_nuw([0 x i32]* %base, i64 %idx) {
 ; CHECK-LABEL: @test_inbounds_nuw(
-; CHECK-NEXT:    [[P2_IDX:%.*]] = shl nsw i64 [[IDX:%.*]], 2
+; CHECK-NEXT:    [[P2_IDX:%.*]] = shl nuw nsw i64 [[IDX:%.*]], 2
 ; CHECK-NEXT:    ret i64 [[P2_IDX]]
 ;
   %p1 = getelementptr inbounds [0 x i32], [0 x i32]* %base, i64 0, i64 0