Index: lib/Target/AMDGPU/SIISelLowering.cpp
===================================================================
--- lib/Target/AMDGPU/SIISelLowering.cpp
+++ lib/Target/AMDGPU/SIISelLowering.cpp
@@ -454,7 +454,6 @@
   }
 
   case AMDGPUAS::PRIVATE_ADDRESS:
-  case AMDGPUAS::UNKNOWN_ADDRESS_SPACE:
     return isLegalMUBUFAddressingMode(AM);
 
   case AMDGPUAS::LOCAL_ADDRESS:
@@ -475,6 +474,12 @@
     return false;
   }
   case AMDGPUAS::FLAT_ADDRESS:
+  case AMDGPUAS::UNKNOWN_ADDRESS_SPACE:
+    // For an unknown address space, this usually means that this is for some
+    // reason being used for pure arithmetic, and not based on some addressing
+    // computation. We don't have instructions that compute pointers with any
+    // addressing modes, so treat them as having no offset like flat
+    // instructions.
     return isLegalFlatAddressingMode(AM);
 
   default:
Index: test/Transforms/LoopStrengthReduce/AMDGPU/lsr-postinc-pos-addrspace.ll
===================================================================
--- test/Transforms/LoopStrengthReduce/AMDGPU/lsr-postinc-pos-addrspace.ll
+++ test/Transforms/LoopStrengthReduce/AMDGPU/lsr-postinc-pos-addrspace.ll
@@ -9,10 +9,11 @@
 ; CHECK: bb11:
 ; CHECK: %lsr.iv1 = phi i32 [ %lsr.iv.next2, %bb ], [ -2, %entry ]
 ; CHECK: %lsr.iv = phi i32 [ %lsr.iv.next, %bb ], [ undef, %entry ]
-
-; CHECK: bb:
 ; CHECK: %lsr.iv.next = add i32 %lsr.iv, -1
 ; CHECK: %lsr.iv.next2 = add i32 %lsr.iv1, 2
+; CHECK: br i1
+
+; CHECK: bb:
 ; CHECK: %scevgep = getelementptr i8, i8 addrspace(3)* %t, i32 %lsr.iv.next2
 ; CHECK: %c1 = icmp ult i8 addrspace(3)* %scevgep, undef
 define void @local_cmp_user() nounwind {
@@ -37,8 +38,13 @@
 }
 
 ; CHECK-LABEL: @global_cmp_user(
+; CHECK: %lsr.iv1 = phi i64
+; CHECK: %lsr.iv = phi i64
 ; CHECK: %lsr.iv.next = add i64 %lsr.iv, -1
 ; CHECK: %lsr.iv.next2 = add i64 %lsr.iv1, 2
+; CHECK: br i1
+
+; CHECK: bb:
 ; CHECK: %scevgep = getelementptr i8, i8 addrspace(1)* %t, i64 %lsr.iv.next2
 define void @global_cmp_user() nounwind {
 entry:
@@ -62,9 +68,14 @@
 }
 
 ; CHECK-LABEL: @global_gep_user(
-; CHECK: %p = getelementptr i8, i8 addrspace(1)* %t, i32 %lsr.iv1
+; CHECK: %lsr.iv1 = phi i32 [ %lsr.iv.next2, %bb ], [ 0, %entry ]
+; CHECK: %lsr.iv = phi i32 [ %lsr.iv.next, %bb ], [ undef, %entry ]
 ; CHECK: %lsr.iv.next = add i32 %lsr.iv, -1
 ; CHECK: %lsr.iv.next2 = add i32 %lsr.iv1, 2
+; CHECK: br i1
+
+; CHECK: bb:
+; CHECK: %p = getelementptr i8, i8 addrspace(1)* %t, i32 %lsr.iv1
 define void @global_gep_user() nounwind {
 entry:
   br label %bb11
@@ -87,9 +98,14 @@
 }
 
 ; CHECK-LABEL: @global_sext_scale_user(
-; CHECK: %p = getelementptr i8, i8 addrspace(1)* %t, i64 %ii.ext
+; CHECK: %lsr.iv1 = phi i32 [ %lsr.iv.next2, %bb ], [ 0, %entry ]
+; CHECK: %lsr.iv = phi i32 [ %lsr.iv.next, %bb ], [ undef, %entry ]
 ; CHECK: %lsr.iv.next = add i32 %lsr.iv, -1
 ; CHECK: %lsr.iv.next2 = add i32 %lsr.iv1, 2
+; CHECK: br i1
+
+; CHECK: bb
+; CHECK: %p = getelementptr i8, i8 addrspace(1)* %t, i64 %ii.ext
 define void @global_sext_scale_user() nounwind {
 entry:
   br label %bb11