diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 0d617bf8b10..886e1432acb 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -2073,6 +2073,10 @@ void LSRInstance::CollectFixupsAndInitialFormulae() {
         // x == y  -->  x - y == 0
         const SCEV *N = SE.getSCEV(NV);
         if (SE.isLoopInvariant(N, L)) {
+          // S is normalized, so normalize N before folding it into S
+          // to keep the result normalized.
+          N = TransformForPostIncUse(Normalize, N, CI, 0,
+                                     LF.PostIncLoops, SE, DT);
           Kind = LSRUse::ICmpZero;
           S = SE.getMinusSCEV(N, S);
         }
diff --git a/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll b/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
new file mode 100644
index 00000000000..294c0904194
--- /dev/null
+++ b/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
@@ -0,0 +1,91 @@
+; RUN: opt -loop-reduce -S < %s | FileCheck %s
+; PR9939
+
+; LSR should property handle the post-inc offset when folding the
+; non-IV operand of an icmp into the IV.
+
+; CHECK:   %tmp2 = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+; CHECK:   %tmp3 = lshr i64 %tmp2, 1
+; CHECK:   %tmp4 = mul i64 %tmp3, 2
+; CHECK:   br label %for.body
+; CHECK: for.body:
+; CHECK:   %lsr.iv5 = phi i64 [ %lsr.iv.next, %for.body ], [ %tmp4, %for.body.lr.ph ]
+; CHECK:   %lsr.iv.next = add i64 %lsr.iv5, -2
+; CHECK:   %lsr.iv.next6 = inttoptr i64 %lsr.iv.next to i16*
+; CHECK:   %cmp27 = icmp eq i16* %lsr.iv.next6, null
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.Vector2 = type { i16*, [64 x i16], i32 }
+
+@.str = private unnamed_addr constant [37 x i8] c"0123456789abcdefghijklmnopqrstuvwxyz\00"
+
+define void @_Z15IntegerToStringjjR7Vector2(i32 %i, i32 %radix, %struct.Vector2* nocapture %result) nounwind noinline {
+entry:
+  %buffer = alloca [33 x i16], align 16
+  %add.ptr = getelementptr inbounds [33 x i16]* %buffer, i64 0, i64 33
+  br label %do.body
+
+do.body:                                          ; preds = %do.body, %entry
+  %0 = phi i64 [ %indvar.next44, %do.body ], [ 0, %entry ]
+  %i.addr.0 = phi i32 [ %div, %do.body ], [ %i, %entry ]
+  %tmp51 = sub i64 32, %0
+  %incdec.ptr = getelementptr [33 x i16]* %buffer, i64 0, i64 %tmp51
+  %rem = urem i32 %i.addr.0, 10
+  %div = udiv i32 %i.addr.0, 10
+  %idxprom = zext i32 %rem to i64
+  %arrayidx = getelementptr inbounds [37 x i8]* @.str, i64 0, i64 %idxprom
+  %tmp5 = load i8* %arrayidx, align 1
+  %conv = sext i8 %tmp5 to i16
+  store i16 %conv, i16* %incdec.ptr, align 2
+  %1 = icmp ugt i32 %i.addr.0, 9
+  %indvar.next44 = add i64 %0, 1
+  br i1 %1, label %do.body, label %do.end
+
+do.end:                                           ; preds = %do.body
+  %xap.0 = inttoptr i64 %0 to i1*
+  %cap.0 = ptrtoint i1* %xap.0 to i64
+  %sub.ptr.lhs.cast = ptrtoint i16* %add.ptr to i64
+  %sub.ptr.rhs.cast = ptrtoint i16* %incdec.ptr to i64
+  %sub.ptr.sub = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+  %sub.ptr.div39 = lshr exact i64 %sub.ptr.sub, 1
+  %conv11 = trunc i64 %sub.ptr.div39 to i32
+  %mLength = getelementptr inbounds %struct.Vector2* %result, i64 0, i32 2
+  %idx.ext21 = bitcast i64 %sub.ptr.div39 to i64
+  %incdec.ptr.sum = add i64 %idx.ext21, -1
+  %cp.0.sum = sub i64 %incdec.ptr.sum, %0
+  %add.ptr22 = getelementptr [33 x i16]* %buffer, i64 1, i64 %cp.0.sum
+  %cmp2740 = icmp eq i64 %idx.ext21, 0
+  br i1 %cmp2740, label %for.end, label %for.body.lr.ph
+
+for.body.lr.ph:                                   ; preds = %do.end
+  %tmp16 = load i32* %mLength, align 4
+  %mBegin = getelementptr inbounds %struct.Vector2* %result, i64 0, i32 0
+  %tmp14 = load i16** %mBegin, align 8
+  %tmp48 = zext i32 %tmp16 to i64
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %for.body.lr.ph
+  %indvar = phi i64 [ 0, %for.body.lr.ph ], [ %indvar.next, %for.body ]
+  %tmp46 = add i64 %tmp51, %indvar
+  %p.042 = getelementptr [33 x i16]* %buffer, i64 0, i64 %tmp46
+  %tmp47 = sub i64 %indvar, %0
+  %incdec.ptr32 = getelementptr [33 x i16]* %buffer, i64 1, i64 %tmp47
+  %tmp49 = add i64 %tmp48, %indvar
+  %dst.041 = getelementptr i16* %tmp14, i64 %tmp49
+  %tmp29 = load i16* %p.042, align 2
+  store i16 %tmp29, i16* %dst.041, align 2
+  %cmp27 = icmp eq i16* %incdec.ptr32, %add.ptr22
+  %indvar.next = add i64 %indvar, 1
+  br i1 %cmp27, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:                                 ; preds = %for.body
+  br label %for.end
+
+for.end:                                          ; preds = %for.end.loopexit, %do.end
+  %tmp38 = load i32* %mLength, align 4
+  %add = add i32 %tmp38, %conv11
+  store i32 %add, i32* %mLength, align 4
+  ret void
+}