AMDGPU/GlobalISel: Better code for one case of G_SHUFFLE_VECTOR on v2i16

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

if (IsVALU) {
       BuildMI(*MBB, MI, DL, TII.get(AMDGPU::V_LSHRREV_B32_e64), DstReg)
         .addImm(16)
         .addReg(SrcVec);
     } else {
       BuildMI(*MBB, MI, DL, TII.get(AMDGPU::S_LSHR_B32), DstReg)
         .addReg(SrcVec)
         .addImm(16);
     }
-  } else if (isZeroOrUndef(Mask[0]) && Mask[1] == 0) {
+  } else if (Mask[0] == -1 && Mask[1] == 0) {
+    if (IsVALU) {
+      BuildMI(*MBB, MI, DL, TII.get(AMDGPU::V_LSHLREV_B32_e64), DstReg)
+        .addImm(16)
+        .addReg(SrcVec);
+    } else {
+      BuildMI(*MBB, MI, DL, TII.get(AMDGPU::S_LSHL_B32), DstReg)
+        .addReg(SrcVec)
+        .addImm(16);
+    }
+  } else if (Mask[0] == 0 && Mask[1] == 0) {
     if (IsVALU) {
       // Write low half of the register into the high half.
       MachineInstr *MovSDWA =
         BuildMI(*MBB, MI, DL, TII.get(AMDGPU::V_MOV_B32_sdwa), DstReg)
         .addImm(0)                             // $src0_modifiers
         .addReg(SrcVec)                        // $src0
         .addImm(0)                             // $clamp
         .addImm(AMDGPU::SDWA::WORD_1)          // $dst_sel

llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-shuffle-vector.v2s16.mir

 
 body: |
   bb.0:
     liveins: $vgpr0, $vgpr1
 
     ; GFX9-LABEL: name: v_shufflevector_v2s16_v2s16_u_0
     ; GFX9: liveins: $vgpr0, $vgpr1
     ; GFX9: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
-    ; GFX9: [[V_MOV_B32_sdwa:%[0-9]+]]:vgpr_32 = V_MOV_B32_sdwa 0, [[COPY]], 0, 5, 2, 4, implicit $exec, implicit [[COPY]](tied-def 0)
-    ; GFX9: $vgpr0 = COPY [[V_MOV_B32_sdwa]]
+    ; GFX9: [[V_LSHLREV_B32_e64_:%[0-9]+]]:vgpr_32 = V_LSHLREV_B32_e64 16, [[COPY]], implicit $exec
+    ; GFX9: $vgpr0 = COPY [[V_LSHLREV_B32_e64_]]
     %0:vgpr(<2 x s16>) = COPY $vgpr0
     %1:vgpr(<2 x s16>) = COPY $vgpr1
     %2:vgpr(<2 x s16>) = G_SHUFFLE_VECTOR %0, %1, shufflemask(undef, 0)
     $vgpr0 = COPY %2
 
 ...
 
 ---

 
 body: |
   bb.0:
     liveins: $vgpr0, $vgpr1
 
     ; GFX9-LABEL: name: v_shufflevector_v2s16_v2s16_u_2
     ; GFX9: liveins: $vgpr0, $vgpr1
     ; GFX9: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr1
-    ; GFX9: [[V_MOV_B32_sdwa:%[0-9]+]]:vgpr_32 = V_MOV_B32_sdwa 0, [[COPY]], 0, 5, 2, 4, implicit $exec, implicit [[COPY]](tied-def 0)
-    ; GFX9: $vgpr0 = COPY [[V_MOV_B32_sdwa]]
+    ; GFX9: [[V_LSHLREV_B32_e64_:%[0-9]+]]:vgpr_32 = V_LSHLREV_B32_e64 16, [[COPY]], implicit $exec
+    ; GFX9: $vgpr0 = COPY [[V_LSHLREV_B32_e64_]]
     %0:vgpr(<2 x s16>) = COPY $vgpr0
     %1:vgpr(<2 x s16>) = COPY $vgpr1
     %2:vgpr(<2 x s16>) = G_SHUFFLE_VECTOR %0, %1, shufflemask(undef, 2)
     $vgpr0 = COPY %2
 
 ...
 
 ---

 
 body: |
   bb.0:
     liveins: $sgpr0, $sgpr1
 
     ; GFX9-LABEL: name: s_shufflevector_v2s16_v2s16_u_0
     ; GFX9: liveins: $sgpr0, $sgpr1
     ; GFX9: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
-    ; GFX9: [[S_PACK_LL_B32_B16_:%[0-9]+]]:sreg_32 = S_PACK_LL_B32_B16 [[COPY]], [[COPY]]
-    ; GFX9: $sgpr0 = COPY [[S_PACK_LL_B32_B16_]]
+    ; GFX9: [[S_LSHL_B32_:%[0-9]+]]:sreg_32 = S_LSHL_B32 [[COPY]], 16, implicit-def $scc
+    ; GFX9: $sgpr0 = COPY [[S_LSHL_B32_]]
     %0:sgpr(<2 x s16>) = COPY $sgpr0
     %1:sgpr(<2 x s16>) = COPY $sgpr1
     %2:sgpr(<2 x s16>) = G_SHUFFLE_VECTOR %0, %1, shufflemask(undef, 0)
     $sgpr0 = COPY %2
 
 ...
 
 ---

 
 body: |
   bb.0:
     liveins: $sgpr0, $sgpr1
 
     ; GFX9-LABEL: name: s_shufflevector_v2s16_v2s16_u_2
     ; GFX9: liveins: $sgpr0, $sgpr1
     ; GFX9: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr1
-    ; GFX9: [[S_PACK_LL_B32_B16_:%[0-9]+]]:sreg_32 = S_PACK_LL_B32_B16 [[COPY]], [[COPY]]
-    ; GFX9: $sgpr0 = COPY [[S_PACK_LL_B32_B16_]]
+    ; GFX9: [[S_LSHL_B32_:%[0-9]+]]:sreg_32 = S_LSHL_B32 [[COPY]], 16, implicit-def $scc
+    ; GFX9: $sgpr0 = COPY [[S_LSHL_B32_]]
     %0:sgpr(<2 x s16>) = COPY $sgpr0
     %1:sgpr(<2 x s16>) = COPY $sgpr1
     %2:sgpr(<2 x s16>) = G_SHUFFLE_VECTOR %0, %1, shufflemask(undef, 2)
     $sgpr0 = COPY %2
 
 ...
 
 ---