diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -1388,12 +1388,16 @@
       // in 8-bits, it can use a smaller encoding.
       if (!isUInt<32>(AM.BaseOffs / 4))
         return false;
-    } else if (Subtarget->getGeneration() >= AMDGPUSubtarget::VOLCANIC_ISLANDS) {
+    } else if (Subtarget->getGeneration() < AMDGPUSubtarget::GFX9) {
       // On VI, these use the SMEM format and the offset is 20-bit in bytes.
       if (!isUInt<20>(AM.BaseOffs))
         return false;
-    } else
-      llvm_unreachable("unhandled generation");
+    } else {
+      // On GFX9 the offset is signed 21-bit in bytes (but must not be negative
+      // for S_BUFFER_* instructions).
+      if (!isInt<21>(AM.BaseOffs))
+        return false;
+    }
 
     if (AM.Scale == 0) // r + i or just i, depending on HasBaseReg.
       return true;
diff --git a/llvm/test/CodeGen/AMDGPU/cgp-addressing-modes-smem.ll b/llvm/test/CodeGen/AMDGPU/cgp-addressing-modes-smem.ll
--- a/llvm/test/CodeGen/AMDGPU/cgp-addressing-modes-smem.ll
+++ b/llvm/test/CodeGen/AMDGPU/cgp-addressing-modes-smem.ll
@@ -167,19 +167,31 @@
 }
 
 define amdgpu_cs void @test_sink_smem_offset_neg400(ptr addrspace(4) inreg %ptr, i32 inreg %val) {
-; GFX6789-LABEL: test_sink_smem_offset_neg400:
-; GFX6789:       ; %bb.0: ; %entry
-; GFX6789-NEXT:    s_add_u32 s0, s0, 0xfffffe70
-; GFX6789-NEXT:    s_addc_u32 s1, s1, -1
-; GFX6789-NEXT:  .LBB4_1: ; %loop
-; GFX6789-NEXT:    ; =>This Inner Loop Header: Depth=1
-; GFX6789-NEXT:    s_waitcnt lgkmcnt(0)
-; GFX6789-NEXT:    s_load_dword s3, s[0:1], 0x0
-; GFX6789-NEXT:    s_add_i32 s2, s2, -1
-; GFX6789-NEXT:    s_cmp_lg_u32 s2, 0
-; GFX6789-NEXT:    s_cbranch_scc1 .LBB4_1
-; GFX6789-NEXT:  ; %bb.2: ; %end
-; GFX6789-NEXT:    s_endpgm
+; GFX678-LABEL: test_sink_smem_offset_neg400:
+; GFX678:       ; %bb.0: ; %entry
+; GFX678-NEXT:    s_add_u32 s0, s0, 0xfffffe70
+; GFX678-NEXT:    s_addc_u32 s1, s1, -1
+; GFX678-NEXT:  .LBB4_1: ; %loop
+; GFX678-NEXT:    ; =>This Inner Loop Header: Depth=1
+; GFX678-NEXT:    s_waitcnt lgkmcnt(0)
+; GFX678-NEXT:    s_load_dword s3, s[0:1], 0x0
+; GFX678-NEXT:    s_add_i32 s2, s2, -1
+; GFX678-NEXT:    s_cmp_lg_u32 s2, 0
+; GFX678-NEXT:    s_cbranch_scc1 .LBB4_1
+; GFX678-NEXT:  ; %bb.2: ; %end
+; GFX678-NEXT:    s_endpgm
+;
+; GFX9-LABEL: test_sink_smem_offset_neg400:
+; GFX9:       ; %bb.0: ; %entry
+; GFX9-NEXT:  .LBB4_1: ; %loop
+; GFX9-NEXT:    ; =>This Inner Loop Header: Depth=1
+; GFX9-NEXT:    s_waitcnt lgkmcnt(0)
+; GFX9-NEXT:    s_load_dword s3, s[0:1], -0x190
+; GFX9-NEXT:    s_add_i32 s2, s2, -1
+; GFX9-NEXT:    s_cmp_lg_u32 s2, 0
+; GFX9-NEXT:    s_cbranch_scc1 .LBB4_1
+; GFX9-NEXT:  ; %bb.2: ; %end
+; GFX9-NEXT:    s_endpgm
 entry:
   %gep = getelementptr i8, ptr addrspace(4) %ptr, i64 -400
   br label %loop
@@ -194,6 +206,3 @@
 end:
   ret void
 }
-;; NOTE: These prefixes are unused and the list is autogenerated. Do not add tests below this line:
-; GFX678: {{.*}}
-; GFX9: {{.*}}