FastISel: constrain the RegClass of operands when emitting instructions.

ARM64 suffered multiple -verify-machineinstr failures (principally over the
xsp/xzr issue) because FastISel was completely ignoring which subset of the
general-purpose registers each instruction required.

More fixes are coming in ARM64 specific FastISel, but this should cover the
generic problems.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206283 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMFastISel.cpp

@@ -166,8 +166,6 @@ class ARMFastISel final : public FastISel {
 
     // Utility routines.
   private:
-    unsigned constrainOperandRegClass(const MCInstrDesc &II, unsigned OpNum,
-                                      unsigned Op);
     bool isTypeLegal(Type *Ty, MVT &VT);
     bool isLoadTypeLegal(Type *Ty, MVT &VT);
     bool ARMEmitCmp(const Value *Src1Value, const Value *Src2Value,
@@ -283,23 +281,6 @@ ARMFastISel::AddOptionalDefs(const MachineInstrBuilder &MIB) {
   return MIB;
 }
 
-unsigned ARMFastISel::constrainOperandRegClass(const MCInstrDesc &II,
-                                               unsigned Op, unsigned OpNum) {
-  if (TargetRegisterInfo::isVirtualRegister(Op)) {
-    const TargetRegisterClass *RegClass =
-        TII.getRegClass(II, OpNum, &TRI, *FuncInfo.MF);
-    if (!MRI.constrainRegClass(Op, RegClass)) {
-      // If it's not legal to COPY between the register classes, something
-      // has gone very wrong before we got here.
-      unsigned NewOp = createResultReg(RegClass);
-      AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
-                              TII.get(TargetOpcode::COPY), NewOp).addReg(Op));
-      return NewOp;
-    }
-  }
-  return Op;
-}
-
 unsigned ARMFastISel::FastEmitInst_r(unsigned MachineInstOpcode,
                                      const TargetRegisterClass *RC,
                                      unsigned Op0, bool Op0IsKill) {