Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1937,16 +1937,17 @@
   // addrspacecast between types is canonicalized as a bitcast, then an
   // addrspacecast. To take advantage of the below bitcast + struct GEP, look
   // through the addrspacecast.
+  Value *ASCStrippedPtrOp = PtrOp;
   if (auto *ASC = dyn_cast<AddrSpaceCastInst>(PtrOp)) {
     //   X = bitcast A addrspace(1)* to B addrspace(1)*
     //   Y = addrspacecast A addrspace(1)* to B addrspace(2)*
     //   Z = gep Y, <...constant indices...>
     // Into an addrspacecasted GEP of the struct.
     if (auto *BC = dyn_cast<BitCastInst>(ASC->getOperand(0)))
-      PtrOp = BC;
+      ASCStrippedPtrOp = BC;
   }
 
-  if (auto *BCI = dyn_cast<BitCastInst>(PtrOp)) {
+  if (auto *BCI = dyn_cast<BitCastInst>(ASCStrippedPtrOp)) {
     Value *SrcOp = BCI->getOperand(0);
     PointerType *SrcType = cast<PointerType>(BCI->getSrcTy());
     Type *SrcEltType = SrcType->getElementType();
Index: test/Transforms/InstCombine/gep-addrspace.ll
===================================================================
--- test/Transforms/InstCombine/gep-addrspace.ll
+++ test/Transforms/InstCombine/gep-addrspace.ll
@@ -32,3 +32,22 @@
   ret void
 }
 
+declare void @escape_alloca(i16*)
+
+; check that addrspacecast is not ignored (leading to an assertion failure)
+; when trying to mark a GEP as inbounds
+define { i8, i8 } @inbounds_after_addrspacecast() {
+top:
+; CHECK-LABEL: @inbounds_after_addrspacecast
+  %0 = alloca i16, align 2
+  call void @escape_alloca(i16* %0)
+  %tmpcast = bitcast i16* %0 to [2 x i8]*
+; CHECK: addrspacecast [2 x i8]* %tmpcast to [2 x i8] addrspace(11)*
+  %1 = addrspacecast [2 x i8]* %tmpcast to [2 x i8] addrspace(11)*
+; CHECK: getelementptr [2 x i8], [2 x i8] addrspace(11)* %1, i64 0, i64 1
+  %2 = getelementptr [2 x i8], [2 x i8] addrspace(11)* %1, i64 0, i64 1
+; CHECK: addrspace(11)
+  %3 = load i8, i8 addrspace(11)* %2, align 1
+  %.fca.1.insert = insertvalue { i8, i8 } zeroinitializer, i8 %3, 1
+  ret { i8, i8 } %.fca.1.insert
+}