[AMDGPU][MachineRegisterInfo] Extend the MRI live-ins check by including

the check against the subregs for live-ins.

Author: vg0204

llvm/include/llvm/CodeGen/MachineRegisterInfo.h

@@ -1020,7 +1020,7 @@ class MachineRegisterInfo {
     return LiveIns;
   }
 
-  bool isLiveIn(Register Reg) const;
+  bool isLiveIn(Register Reg, bool CheckForSubreg = false) const;
 
   /// getLiveInPhysReg - If VReg is a live-in virtual register, return the
   /// corresponding live-in physical register.

llvm/lib/CodeGen/MachineRegisterInfo.cpp

@@ -447,10 +447,22 @@ void MachineRegisterInfo::clearKillFlags(Register Reg) const {
     MO.setIsKill(false);
 }
 
-bool MachineRegisterInfo::isLiveIn(Register Reg) const {
-  for (const std::pair<MCRegister, Register> &LI : liveins())
+bool MachineRegisterInfo::isLiveIn(Register Reg, bool CheckForSubreg) const {
+  for (const std::pair<MCRegister, Register> &LI : liveins()) {
     if ((Register)LI.first == Reg || LI.second == Reg)
       return true;
+
+    // Check if Reg is a subreg of live-in register
+    if (CheckForSubreg) {
+      MCRegister PhysReg = LI.first;
+      if (!PhysReg.isValid())
+        continue;
+
+      for (MCPhysReg SubReg : getTargetRegisterInfo()->subregs(PhysReg))
+        if (SubReg == Reg)
+          return true;
+    }
+  }
   return false;
 }