[AMDGPU][GlobalISel] Clean up selectCOPY_SCC_VCC function (#165797)

Follow-up patch to address the comments in
#165355.

Author: vangthao95

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -224,13 +224,12 @@ bool AMDGPUInstructionSelector::selectCOPY_SCC_VCC(MachineInstr &I) const {
   Register VCCReg = I.getOperand(1).getReg();
   MachineInstr *Cmp;
 
-  if (STI.getGeneration() >= AMDGPUSubtarget::VOLCANIC_ISLANDS) {
+  // Set SCC as a side effect with S_CMP or S_OR.
+  if (STI.hasScalarCompareEq64()) {
     unsigned CmpOpc =
         STI.isWave64() ? AMDGPU::S_CMP_LG_U64 : AMDGPU::S_CMP_LG_U32;
     Cmp = BuildMI(*BB, &I, DL, TII.get(CmpOpc)).addReg(VCCReg).addImm(0);
   } else {
-    // For gfx7 and earlier, S_CMP_LG_U64 doesn't exist, so we use S_OR_B64
-    // which sets SCC as a side effect.
     Register DeadDst = MRI->createVirtualRegister(&AMDGPU::SReg_64RegClass);
     Cmp = BuildMI(*BB, &I, DL, TII.get(AMDGPU::S_OR_B64), DeadDst)
               .addReg(VCCReg)

llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-copy-scc-vcc.ll

@@ -1,7 +1,7 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
-; RUN: llc -global-isel -new-reg-bank-select -mtriple=amdgcn -mcpu=gfx700 -verify-machineinstrs < %s | FileCheck -check-prefixes=GFX7 %s
-; RUN: llc -global-isel -new-reg-bank-select -mtriple=amdgcn -mcpu=gfx803 -verify-machineinstrs < %s | FileCheck -check-prefixes=GFX8 %s
-; RUN: llc -global-isel -new-reg-bank-select -mtriple=amdgcn -mcpu=gfx1100 -verify-machineinstrs < %s | FileCheck -check-prefixes=GFX11 %s
+; RUN: llc -global-isel -new-reg-bank-select -mtriple=amdgcn -mcpu=gfx700 < %s | FileCheck -check-prefixes=GFX7 %s
+; RUN: llc -global-isel -new-reg-bank-select -mtriple=amdgcn -mcpu=gfx803 < %s | FileCheck -check-prefixes=GFX8 %s
+; RUN: llc -global-isel -new-reg-bank-select -mtriple=amdgcn -mcpu=gfx1100 < %s | FileCheck -check-prefixes=GFX11 %s
 
 define amdgpu_kernel void @fcmp_uniform_select(float %a, i32 %b, i32 %c, ptr addrspace(1) %out) {
 ; GFX7-LABEL: fcmp_uniform_select:

llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-copy-scc-vcc.mir

@@ -1,7 +1,7 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -mtriple=amdgcn -mcpu=gfx700 -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck -check-prefixes=GFX7 %s
-# RUN: llc -mtriple=amdgcn -mcpu=gfx803 -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck -check-prefixes=GF8 %s
-# RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck -check-prefixes=GFX11 %s
+# RUN: llc -mtriple=amdgcn -mcpu=gfx700 -run-pass=instruction-select %s -o - | FileCheck -check-prefixes=GFX7 %s
+# RUN: llc -mtriple=amdgcn -mcpu=gfx803 -run-pass=instruction-select %s -o - | FileCheck -check-prefixes=GF8 %s
+# RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -run-pass=instruction-select %s -o - | FileCheck -check-prefixes=GFX11 %s
 
 ---
 name: test_copy_scc_vcc