Clean up sub-register implementation by moving subReg information back to

MachineOperand auxInfo. Previous clunky implementation uses an external map
to track sub-register uses. That works because register allocator uses
a new virtual register for each spilled use. With interval splitting (coming
soon), we may have multiple uses of the same register some of which are
of using different sub-registers from others. It's too fragile to constantly
update the information.

llvm-svn: 44104

llvm/lib/CodeGen/MachineInstr.cpp

@@ -39,6 +39,7 @@ void MachineInstr::addImplicitDefUseOperands() {
       Op.IsKill = false;
       Op.IsDead = false;
       Op.contents.RegNo = *ImpDefs;
+      Op.auxInfo.subReg = 0;
       Operands.push_back(Op);
     }
   if (TID->ImplicitUses)
@@ -50,6 +51,7 @@ void MachineInstr::addImplicitDefUseOperands() {
       Op.IsKill = false;
       Op.IsDead = false;
       Op.contents.RegNo = *ImpUses;
+      Op.auxInfo.subReg = 0;
       Operands.push_back(Op);
     }
 }