Index: llvm/lib/Target/AMDGPU/SIISelLowering.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -9586,7 +9586,16 @@
 
   // sub x, zext (setcc) => subcarry x, 0, setcc
   // sub x, sext (setcc) => addcarry x, 0, setcc
-  unsigned Opc = RHS.getOpcode();
+
+  bool Commuted = false;
+  unsigned Opc = LHS.getOpcode();
+  if (Opc == ISD::ZERO_EXTEND || Opc == ISD::SIGN_EXTEND ||
+      Opc == ISD::ANY_EXTEND) {
+    std::swap(RHS, LHS);
+    Commuted = true;
+  }
+
+  Opc = RHS.getOpcode();
   switch (Opc) {
   default: break;
   case ISD::ZERO_EXTEND:
@@ -9598,8 +9607,22 @@
     if (!isBoolSGPR(Cond))
       break;
     SDVTList VTList = DAG.getVTList(MVT::i32, MVT::i1);
-    SDValue Args[] = { LHS, DAG.getConstant(0, SL, MVT::i32), Cond };
-    Opc = (Opc == ISD::SIGN_EXTEND) ? ISD::ADDCARRY : ISD::SUBCARRY;
+    SDValue Zero = DAG.getConstant(0, SL, MVT::i32);
+    SDValue Args[3];
+    Args[2] = Cond;
+
+    if (Commuted) {
+      // sub zext (setcc), x => addcarry 0, x, setcc
+      // sub sext (setcc), x => subcarry 0, x, setcc
+      Args[0] = Zero;
+      Args[1] = LHS;
+      Opc = (Opc == ISD::SIGN_EXTEND) ? ISD::SUBCARRY : ISD::ADDCARRY;
+    } else {
+      Args[0] = LHS;
+      Args[1] = Zero;
+      Opc = (Opc == ISD::SIGN_EXTEND) ? ISD::ADDCARRY : ISD::SUBCARRY;
+    }
+
     return DAG.getNode(Opc, SL, VTList, Args);
   }
   }
Index: llvm/test/CodeGen/AMDGPU/combine-cond-add-sub.ll
===================================================================
--- llvm/test/CodeGen/AMDGPU/combine-cond-add-sub.ll
+++ llvm/test/CodeGen/AMDGPU/combine-cond-add-sub.ll
@@ -311,6 +311,48 @@
   ret void
 }
 
+; Check case where sub is commuted with sext
+; GCN-LABEL: {{^}}sub_zext_setcc_commute:
+; GCN: v_cmp_gt_u32_e32 vcc, v
+; GCN-NOT: vcc
+; GCN: v_addc_u32_e32 [[ADDC:v[0-9]+]], vcc, v{{[0-9]+}}, v{{[0-9]+}}, vcc
+; GCN: v_subrev_i32_e32 [[RESULT:v[0-9]+]], vcc, s{{[0-9]+}}, [[ADDC]]
+define amdgpu_kernel void @sub_zext_setcc_commute(i32 addrspace(1)* nocapture %arg, i32 %a, i32%b) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %gep = getelementptr inbounds i32, i32 addrspace(1)* %arg, i32 %x
+  %v = load i32, i32 addrspace(1)* %gep, align 4
+  %cmp = icmp ugt i32 %x, %y
+  %ext = zext i1 %cmp to i32
+  %adde = sub i32 %v, %ext
+  %sub = sub i32 %a, %adde
+  %sub2 = sub i32 %sub, %b
+  store i32 %sub2, i32 addrspace(1)* %gep, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}sub_sext_setcc_commute:
+; GCN: v_cmp_gt_u32_e32 vcc, v
+; GCN-NOT: vcc
+; GCN: v_subb_u32_e32 [[SUBB:v[0-9]+]], vcc, 0, v{{[0-9]+}}, vcc
+; GCN: v_add_i32_e32 [[ADD:v[0-9]+]], vcc, s{{[0-9]+}}, [[SUBB]]
+; GCN: v_subrev_i32_e32 [[RESULT:v[0-9]+]], vcc, s{{[0-9]+}}, [[ADD]]
+define amdgpu_kernel void @sub_sext_setcc_commute(i32 addrspace(1)* nocapture %arg, i32 %a, i32%b) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %gep = getelementptr inbounds i32, i32 addrspace(1)* %arg, i32 %x
+  %v = load i32, i32 addrspace(1)* %gep, align 4
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %adde = sub i32 %v, %ext
+  %sub = sub i32 %a, %adde
+  %sub2 = sub i32 %sub, %b
+  store i32 %sub2, i32 addrspace(1)* %gep, align 4
+  ret void
+}
+
 declare i1 @llvm.amdgcn.class.f32(float, i32) #0
 
 declare i32 @llvm.amdgcn.workitem.id.x() #0