Index: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -12652,7 +12652,13 @@
   // Check #2.
   if (!isLoad) {
     SDValue Val = cast<StoreSDNode>(N)->getValue();
-    if (Val == BasePtr || BasePtr.getNode()->isPredecessorOf(Val.getNode()))
+
+    // Would require a copy.
+    if (Val == BasePtr)
+      return false;
+
+    // Would create a cycle.
+    if (Val == Ptr || Ptr->isPredecessorOf(Val.getNode()))
       return false;
   }
 
Index: llvm/trunk/test/CodeGen/ARM/indexed-mem.ll
===================================================================
--- llvm/trunk/test/CodeGen/ARM/indexed-mem.ll
+++ llvm/trunk/test/CodeGen/ARM/indexed-mem.ll
@@ -0,0 +1,186 @@
+; RUN: llc -mtriple=thumbv8m.main %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V8M
+; RUN: llc -mtriple=armv8 %s -o - | FileCheck %s --check-prefix=CHECK-V8
+
+; CHECK-LABEL: pre_inc_ldr
+; CHECK: ldr{{.*}}, [r0, #4]!
+define i32* @pre_inc_ldr(i32* %base, i32 %a) {
+  %addr = getelementptr i32, i32* %base, i32 1
+  %ld = load i32, i32* %addr
+  %addr.1 = getelementptr i32, i32* %base, i32 2
+  %res = add i32 %ld, %a
+  store i32 %res, i32* %addr.1
+  ret i32* %addr
+}
+
+; CHECK-LABEL: pre_dec_ldr
+; CHECK: ldr{{.*}}, [r0, #-4]!
+define i32* @pre_dec_ldr(i32* %base, i32 %a) {
+  %addr = getelementptr i32, i32* %base, i32 -1
+  %ld = load i32, i32* %addr
+  %addr.1 = getelementptr i32, i32* %base, i32 2
+  %res = add i32 %ld, %a
+  store i32 %res, i32* %addr.1
+  ret i32* %addr
+}
+
+; CHECK-LABEL: post_inc_ldr
+; CHECK: ldr{{.*}}, [r0], #4
+define i32* @post_inc_ldr(i32* %base, i32* %addr.2, i32 %a) {
+  %addr = getelementptr i32, i32* %base, i32 0
+  %ld = load i32, i32* %addr
+  %addr.1 = getelementptr i32, i32* %base, i32 1
+  %res = add i32 %ld, %a
+  store i32 %res, i32* %addr.2
+  ret i32* %addr.1
+}
+
+; CHECK-LABEL: post_dec_ldr
+; CHECK: ldr{{.*}}, [r0], #-4
+define i32* @post_dec_ldr(i32* %base, i32* %addr.2, i32 %a) {
+  %addr = getelementptr i32, i32* %base, i32 0
+  %ld = load i32, i32* %addr
+  %addr.1 = getelementptr i32, i32* %base, i32 -1
+  %res = add i32 %ld, %a
+  store i32 %res, i32* %addr.2
+  ret i32* %addr.1
+}
+
+; CHECK-LABEL: pre_inc_str
+; CHECK: str{{.*}}, [r0, #4]!
+define i32* @pre_inc_str(i32* %base, i32 %a, i32 %b) {
+  %addr.1 = getelementptr i32, i32* %base, i32 1
+  %res = add i32 %a, %b
+  store i32 %res, i32* %addr.1
+  ret i32* %addr.1
+}
+
+; CHECK-LABEL: pre_dec_str
+; CHECK: str{{.*}}, [r0, #-4]!
+define i32* @pre_dec_str(i32* %base, i32 %a, i32 %b) {
+  %res = add i32 %a, %b
+  %addr.1 = getelementptr i32, i32* %base, i32 -1
+  store i32 %res, i32* %addr.1
+  ret i32* %addr.1
+}
+
+; CHECK-LABEL: post_inc_str
+; CHECK: str{{.*}}, [r0], #4
+define i32* @post_inc_str(i32* %base, i32 %a, i32 %b) {
+  %addr.1 = getelementptr i32, i32* %base, i32 1
+  %res = add i32 %a, %b
+  store i32 %res, i32* %base
+  ret i32* %addr.1
+}
+
+; CHECK-LABEL: post_dec_str
+; CHECK: str{{.*}}, [r0], #-4
+define i32* @post_dec_str(i32* %base, i32 %a, i32 %b) {
+  %addr.1 = getelementptr i32, i32* %base, i32 -1
+  %res = add i32 %a, %b
+  store i32 %res, i32* %base
+  ret i32* %addr.1
+}
+
+; TODO: Generate ldrd
+; CHECK-LABEL: pre_inc_ldrd
+; CHECK: ldr{{.*}}, #4]!
+define i32* @pre_inc_ldrd(i32* %base) {
+  %addr = getelementptr i32, i32* %base, i32 1
+  %addr.1 = getelementptr i32, i32* %base, i32 2
+  %addr.2 = getelementptr i32, i32* %base, i32 3
+  %ld = load i32, i32* %addr
+  %ld.1 = load i32, i32* %addr.1
+  %res = add i32 %ld, %ld.1
+  store i32 %res, i32* %addr.2
+  ret i32* %addr
+}
+
+; TODO: Generate ldrd
+; CHECK-LABEL: pre_dec_ldrd
+; CHECK: ldr{{.*}}, #-4]!
+define i32* @pre_dec_ldrd(i32* %base) {
+  %addr = getelementptr i32, i32* %base, i32 -1
+  %addr.1 = getelementptr i32, i32* %base, i32 -2
+  %addr.2 = getelementptr i32, i32* %base, i32 -3
+  %ld = load i32, i32* %addr
+  %ld.1 = load i32, i32* %addr.1
+  %res = add i32 %ld, %ld.1
+  store i32 %res, i32* %addr.2
+  ret i32* %addr
+}
+
+; TODO: Generate post inc
+; CHECK-LABEL: post_inc_ldrd
+; CHECK-V8M: ldrd{{.*}}, [r0]
+; CHECK-V8: ldm
+; CHECK: add{{.*}}, #8
+define i32* @post_inc_ldrd(i32* %base, i32* %addr.3) {
+  %addr = getelementptr i32, i32* %base, i32 0
+  %ld = load i32, i32* %addr
+  %addr.1 = getelementptr i32, i32* %base, i32 1
+  %ld.1 = load i32, i32* %addr.1
+  %addr.2 = getelementptr i32, i32* %base, i32 2
+  %res = add i32 %ld, %ld.1
+  store i32 %res, i32* %addr.3
+  ret i32* %addr.2
+}
+
+; CHECK-LABEL: pre_inc_str_multi
+; CHECK: str{{.*}}, #8]!
+define i32* @pre_inc_str_multi(i32* %base) {
+  %addr = getelementptr i32, i32* %base, i32 0
+  %addr.1 = getelementptr i32, i32* %base, i32 1
+  %ld = load i32, i32* %addr
+  %ld.1 = load i32, i32* %addr.1
+  %res = add i32 %ld, %ld.1
+  %addr.2 = getelementptr i32, i32* %base, i32 2
+  store i32 %res, i32* %addr.2
+  ret i32* %addr.2
+}
+
+; CHECK-LABEL: pre_dec_str_multi
+; CHECK: str{{.*}}, #-4]!
+define i32* @pre_dec_str_multi(i32* %base) {
+  %addr = getelementptr i32, i32* %base, i32 0
+  %addr.1 = getelementptr i32, i32* %base, i32 1
+  %ld = load i32, i32* %addr
+  %ld.1 = load i32, i32* %addr.1
+  %res = add i32 %ld, %ld.1
+  %addr.2 = getelementptr i32, i32* %base, i32 -1
+  store i32 %res, i32* %addr.2
+  ret i32* %addr.2
+}
+
+; CHECK-LABEL: illegal_pre_inc_store_1
+; CHECK-NOT: str{{.*}} ]!
+define i32* @illegal_pre_inc_store_1(i32* %base) {
+entry:
+  %ptr.to.use = getelementptr i32, i32* %base, i32 2
+  %ptr.to.store = ptrtoint i32* %base to i32
+  store i32 %ptr.to.store, i32* %ptr.to.use, align 4
+  ret i32* %ptr.to.use
+}
+
+; TODO: The mov should be unecessary
+; CHECK-LABEL: legal_pre_inc_store_needs_copy_1
+; CHECK: add{{.*}}, #8
+; CHECK-NOT: str{{.*}}]!
+; CHECK: mov
+define i32* @legal_pre_inc_store_needs_copy_1(i32* %base) {
+entry:
+  %ptr.to.use = getelementptr i32, i32* %base, i32 2
+  %ptr.to.store = ptrtoint i32* %ptr.to.use to i32
+  store i32 %ptr.to.store, i32* %ptr.to.use, align 4
+  ret i32* %ptr.to.use
+}
+
+; CHECK-LABEL: legal_pre_inc_store_needs_copy_2
+; CHECK-NOT: mov
+; CHECK-NOT: str{{.*}}]!
+define i32* @legal_pre_inc_store_needs_copy_2(i32 %base) {
+entry:
+  %ptr = inttoptr i32 %base to i32*
+  %ptr.to.use = getelementptr i32, i32* %ptr, i32 2
+  store i32 %base, i32* %ptr.to.use, align 4
+  ret i32* %ptr.to.use
+}