diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -3523,24 +3523,24 @@
   ISD::CondCode CCOpcode = cast<CondCodeSDNode>(Cond.getOperand(2))->get();
   SDValue CmpLHS = Cond.getOperand(0);
 
-  unsigned Opc = isCttzOpc(RHS.getOpcode()) ? AMDGPUISD::FFBL_B32 :
-                                           AMDGPUISD::FFBH_U32;
-
   // select (setcc x, 0, eq), -1, (ctlz_zero_undef x) -> ffbh_u32 x
   // select (setcc x, 0, eq), -1, (cttz_zero_undef x) -> ffbl_u32 x
   if (CCOpcode == ISD::SETEQ &&
       (isCtlzOpc(RHS.getOpcode()) || isCttzOpc(RHS.getOpcode())) &&
-      RHS.getOperand(0) == CmpLHS &&
-      isNegativeOne(LHS)) {
+      RHS.getOperand(0) == CmpLHS && isNegativeOne(LHS)) {
+    unsigned Opc =
+        isCttzOpc(RHS.getOpcode()) ? AMDGPUISD::FFBL_B32 : AMDGPUISD::FFBH_U32;
     return getFFBX_U32(DAG, CmpLHS, SL, Opc);
   }
 
   // select (setcc x, 0, ne), (ctlz_zero_undef x), -1 -> ffbh_u32 x
   // select (setcc x, 0, ne), (cttz_zero_undef x), -1 -> ffbl_u32 x
   if (CCOpcode == ISD::SETNE &&
-      (isCtlzOpc(LHS.getOpcode()) || isCttzOpc(RHS.getOpcode())) &&
-      LHS.getOperand(0) == CmpLHS &&
-      isNegativeOne(RHS)) {
+      (isCtlzOpc(LHS.getOpcode()) || isCttzOpc(LHS.getOpcode())) &&
+      LHS.getOperand(0) == CmpLHS && isNegativeOne(RHS)) {
+    unsigned Opc =
+        isCttzOpc(LHS.getOpcode()) ? AMDGPUISD::FFBL_B32 : AMDGPUISD::FFBH_U32;
+
     return getFFBX_U32(DAG, CmpLHS, SL, Opc);
   }
 
diff --git a/llvm/test/CodeGen/AMDGPU/cttz_zero_undef.ll b/llvm/test/CodeGen/AMDGPU/cttz_zero_undef.ll
--- a/llvm/test/CodeGen/AMDGPU/cttz_zero_undef.ll
+++ b/llvm/test/CodeGen/AMDGPU/cttz_zero_undef.ll
@@ -198,8 +198,8 @@
 }
 
 ; FUNC-LABEL: {{^}}v_cttz_i32_sel_eq_neg1:
-; SI: v_ffbl_b32_e32 v{{[0-9]+}}, [[VAL:v[0-9]+]]
-; SI: v_cmp_ne_u32_e32 vcc, 0, [[VAL]]
+; SI: v_ffbl_b32_e32 [[VAL:v[0-9]+]], v{{[0-9]+}}
+; SI: buffer_store_dword [[VAL]],
 ; SI: s_endpgm
 ; EG: MEM_RAT_CACHELESS STORE_RAW
 ; EG: FFBL_INT
@@ -213,8 +213,8 @@
 }
 
 ; FUNC-LABEL: {{^}}v_cttz_i32_sel_ne_neg1:
-; SI: v_ffbl_b32_e32 v{{[0-9]+}}, [[VAL:v[0-9]+]]
-; SI: v_cmp_ne_u32_e32 vcc, 0, [[VAL]]
+; SI: v_ffbl_b32_e32 [[VAL:v[0-9]+]], v{{[0-9]+}}
+; SI: buffer_store_dword [[VAL]],
 ; SI: s_endpgm
 ; EG: MEM_RAT_CACHELESS STORE_RAW
 ; EG: FFBL_INT
diff --git a/llvm/test/CodeGen/AMDGPU/select-constant-cttz.ll b/llvm/test/CodeGen/AMDGPU/select-constant-cttz.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/select-constant-cttz.ll
@@ -0,0 +1,42 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -march=amdgcn -verify-machineinstrs -o - %s | FileCheck -check-prefix=GCN %s
+
+declare i32 @llvm.cttz.i32(i32, i1) nounwind readnone
+declare i32 @llvm.amdgcn.sffbh.i32(i32) nounwind readnone speculatable
+define amdgpu_kernel void @select_constant_cttz(i32 addrspace(1)* noalias %out, i32 addrspace(1)* nocapture readonly %arrayidx) nounwind {
+; GCN-LABEL: select_constant_cttz:
+; GCN:       ; %bb.0:
+; GCN-NEXT:    s_load_dwordx2 s[2:3], s[0:1], 0xb
+; GCN-NEXT:    s_waitcnt lgkmcnt(0)
+; GCN-NEXT:    s_load_dword s8, s[2:3], 0x0
+; GCN-NEXT:    s_load_dwordx2 s[4:5], s[0:1], 0x9
+; GCN-NEXT:    s_mov_b32 s7, 0xf000
+; GCN-NEXT:    s_waitcnt lgkmcnt(0)
+; GCN-NEXT:    s_lshr_b32 s0, 1, s8
+; GCN-NEXT:    s_ff1_i32_b32 s0, s0
+; GCN-NEXT:    s_mov_b32 s6, -1
+; GCN-NEXT:    v_mov_b32_e32 v0, s0
+; GCN-NEXT:    v_cmp_ne_u32_e64 s[2:3], s8, 0
+; GCN-NEXT:    v_cndmask_b32_e64 v0, v0, -1, s[2:3]
+; GCN-NEXT:    v_ffbh_i32_e32 v1, v0
+; GCN-NEXT:    v_cmp_eq_u32_e64 s[0:1], 0, v0
+; GCN-NEXT:    v_sub_i32_e32 v0, vcc, 31, v1
+; GCN-NEXT:    s_or_b64 s[0:1], s[2:3], s[0:1]
+; GCN-NEXT:    v_cndmask_b32_e64 v0, v0, -1, s[0:1]
+; GCN-NEXT:    buffer_store_dword v0, off, s[4:7], 0
+; GCN-NEXT:    s_endpgm
+  %v    = load i32, i32 addrspace(1)* %arrayidx, align 4
+  %sr   = lshr i32 1, %v
+  %cmp  = icmp ne i32 %v, 0
+  %cttz = call i32 @llvm.cttz.i32(i32 %sr, i1 true), !range !0
+  %sel  = select i1 %cmp, i32 -1, i32 %cttz
+  %ffbh = call i32 @llvm.amdgcn.sffbh.i32(i32 %sel)
+  %sub  = sub i32 31, %ffbh
+  %cmp2 = icmp eq i32 %sel, 0
+  %or   = or i1 %cmp, %cmp2
+  %sel2 = select i1 %or, i32 -1, i32 %sub
+  store i32 %sel2, i32 addrspace(1)* %out
+  ret void
+}
+
+!0 = !{i32 0, i32 33}