Index: include/llvm/Transforms/Utils/LoopUtils.h
===================================================================
--- include/llvm/Transforms/Utils/LoopUtils.h
+++ include/llvm/Transforms/Utils/LoopUtils.h
@@ -376,6 +376,10 @@
                                   DominatorTree *, Loop *, AliasSetTracker *,
                                   LICMSafetyInfo *);
 
+/// \brief Check whether a constant expression is used by any instruction
+/// in a given loop.
+bool isConstantExprUsedInLoop(ConstantExpr* CE, Loop *CurLoop);
+
 /// \brief Computes safety information for a loop
 /// checks loop body & header for the possibility of may throw
 /// exception, it takes LICMSafetyInfo and loop as argument.
Index: lib/Transforms/Scalar/LICM.cpp
===================================================================
--- lib/Transforms/Scalar/LICM.cpp
+++ lib/Transforms/Scalar/LICM.cpp
@@ -837,6 +837,28 @@
   };
 } // end anon namespace
 
+/// Check whether a constant expression is used by any instruction
+/// in a given loop. This, unforunately, requires a recursive lookup.
+bool llvm::isConstantExprUsedInLoop(ConstantExpr *CE, Loop *CurLoop) {
+  SmallVector<ConstantExpr *, 4> WorkList;
+  WorkList.push_back(CE);
+
+  while (!WorkList.empty()) {
+    auto Curr = WorkList.pop_back_val();
+    // We only care if the user is an instruction or a constant expression.
+    // Check if instructions are in the loop, and recurse down ConstantExpr.
+    for (auto U : Curr->users()) {
+      if (auto UI = dyn_cast<Instruction>(U)) {
+        if (CurLoop->contains(UI))
+          return true;
+      } else if (auto UCE = dyn_cast<ConstantExpr>(U))
+        WorkList.push_back(UCE);
+    }
+  }
+
+  return false;
+}
+
 /// Try to promote memory values to scalars by sinking stores out of the
 /// loop and moving loads to before the loop.  We do this by looping over
 /// the stores in the loop, looking for stores to Must pointers which are
@@ -907,6 +929,14 @@
       return Changed;
 
     for (User *U : ASIV->users()) {
+      // If we encounter a constant expression which is used by an instruction
+      // inside the loop, bail.
+      // FIXME: This is somewhat too conservative, but for now, err on the side
+      // of correctness.
+      if (auto UCE = dyn_cast<ConstantExpr>(U))
+        if (isConstantExprUsedInLoop(UCE, CurLoop))
+          return Changed;
+
       // Ignore instructions that are outside the loop.
       Instruction *UI = dyn_cast<Instruction>(U);
       if (!UI || !CurLoop->contains(UI))
Index: test/Transforms/LICM/pr26843.ll
===================================================================
--- test/Transforms/LICM/pr26843.ll
+++ test/Transforms/LICM/pr26843.ll
@@ -0,0 +1,32 @@
+; RUN: opt -S -basicaa -licm < %s | FileCheck %s
+
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.0"
+
+@v = common global [4 x i32] zeroinitializer, align 4 
+
+; Make sure the store to v[1] is not sunk past the memset to v[1]-v[3].
+; CHECK-LABEL: @main
+; CHECK: for.body:
+; CHECK-NEXT: store i32 1, i32* getelementptr inbounds ([4 x i32], [4 x i32]* @v, i32 0, i32 1)
+; CHECK-NEXT: tail call void @llvm.memset
+; CHECK: end:
+; CHECK-NEXT: ret i32 0
+
+define i32 @main(i1 %k) {
+entry:
+  br label %for.body
+ 
+for.body:
+  store i32 1, i32* getelementptr inbounds ([4 x i32], [4 x i32]* @v, i32 0, i32 1), align 4
+  tail call void @llvm.memset.p0i8.i32(i8* bitcast (i32* getelementptr inbounds ([4 x i32], [4 x i32]* @v, i32 0, i32 1) to i8*), i8 0, i32 12, i32 4, i1 false)
+  br label %for.latch
+  
+for.latch:
+  br i1 %k, label %for.body, label %end
+
+end:
+  ret i32 0
+}
+
+declare void @llvm.memset.p0i8.i32(i8* nocapture, i8, i32, i32, i1)