Index: llvm/trunk/lib/Analysis/ConstantFolding.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ConstantFolding.cpp
+++ llvm/trunk/lib/Analysis/ConstantFolding.cpp
@@ -784,7 +784,7 @@
 Constant* StripPtrCastKeepAS(Constant* Ptr, Type *&ElemTy) {
   assert(Ptr->getType()->isPointerTy() && "Not a pointer type");
   auto *OldPtrTy = cast<PointerType>(Ptr->getType());
-  Ptr = Ptr->stripPointerCasts();
+  Ptr = cast<Constant>(Ptr->stripPointerCastsNoFollowAliases());
   auto *NewPtrTy = cast<PointerType>(Ptr->getType());
 
   ElemTy = NewPtrTy->getPointerElementType();
Index: llvm/trunk/test/Analysis/ConstantFolding/gep-alias.ll
===================================================================
--- llvm/trunk/test/Analysis/ConstantFolding/gep-alias.ll
+++ llvm/trunk/test/Analysis/ConstantFolding/gep-alias.ll
@@ -0,0 +1,17 @@
+; RUN: opt -instcombine -S -o - %s | FileCheck %s
+; Test that we don't replace an alias with its aliasee when simplifying GEPs.
+; In this test case the transformation is invalid because it replaces the
+; reference to the symbol "b" (which refers to whichever instance of "b"
+; was chosen by the linker) with a reference to "a" (which refers to the
+; specific instance of "b" in this module).
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@a = internal global [3 x i8*] zeroinitializer
+@b = linkonce_odr alias [3 x i8*], [3 x i8*]* @a
+
+define i8** @f() {
+  ; CHECK: ret i8** getelementptr ([3 x i8*], [3 x i8*]* @b, i32 0, i32 1)
+  ret i8** getelementptr ([3 x i8*], [3 x i8*]* @b, i32 0, i32 1)
+}