Enable saving SHARED_BASE to VCC.

This is observed when exhausting scalar registers in kernels with high register usage.

Author: carlobertolli

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -899,7 +899,8 @@ void SIInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
     }
 
     if (DestReg == AMDGPU::VCC) {
-      if (AMDGPU::SReg_64RegClass.contains(SrcReg)) {
+      if (AMDGPU::SReg_64RegClass.contains(SrcReg) ||
+      AMDGPU::SReg_64_EncodableRegClass.contains(SrcReg)) {
         BuildMI(MBB, MI, DL, get(AMDGPU::S_MOV_B64), AMDGPU::VCC)
           .addReg(SrcReg, getKillRegState(KillSrc));
       } else {

llvm/test/CodeGen/AMDGPU/sgpr-phys-copy.mir

@@ -58,6 +58,15 @@ body:             |
     $sgpr0_sgpr1 = COPY $src_shared_base
 ...
 
+---
+name: src_shared_base_to_vcc
+body:             |
+  bb.0:
+    ; GFX9-LABEL: name: src_shared_base_to_vcc
+    ; GFX9: $vcc = S_MOV_B64 $src_shared_base
+    $vcc = COPY $src_shared_base
+...
+
 ---
 name: sgpr96_aligned_src_dst
 body:             |