Factor out prelowerPhi for 32-bit targets. Disable adv phi lowering for ARM.

src/IceTargetLoweringARM32.h

 //===- subzero/src/IceTargetLoweringARM32.h - ARM32 lowering ----*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 85 matching lines @@
   /// I64 operations.
   void split64(Variable *Var);
   Operand *loOperand(Operand *Operand);
   Operand *hiOperand(Operand *Operand);
   void finishArgumentLowering(Variable *Arg, Variable *FramePtr,
                               size_t BasicFrameOffset, size_t &InArgsSizeBytes);
 
   bool hasCPUFeature(TargetARM32Features::ARM32InstructionSet I) const {
     return CPUFeatures.hasFeature(I);
   }
+  Operand *legalizeUndef(Operand *From, int32_t RegNum = Variable::NoRegister);
 
 protected:
   explicit TargetARM32(Cfg *Func);
 
   void postLower() override;
 
   void lowerAlloca(const InstAlloca *Inst) override;
   void lowerArithmetic(const InstArithmetic *Inst) override;
   void lowerAssign(const InstAssign *Inst) override;
   void lowerBr(const InstBr *Inst) override;
@@ skipping 23 matching lines @@
     Legal_Reg = 1 << 0,  /// physical register, not stack location
     Legal_Flex = 1 << 1, /// A flexible operand2, which can hold rotated
                          /// small immediates, or shifted registers.
     Legal_Mem = 1 << 2,  /// includes [r0, r1 lsl #2] as well as [sp, #12]
     Legal_All = ~Legal_None
   };
   typedef uint32_t LegalMask;
   Operand *legalize(Operand *From, LegalMask Allowed = Legal_All,
                     int32_t RegNum = Variable::NoRegister);
   Variable *legalizeToVar(Operand *From, int32_t RegNum = Variable::NoRegister);
-  Operand *legalizeUndef(Operand *From, int32_t RegNum = Variable::NoRegister);
   OperandARM32Mem *formMemoryOperand(Operand *Ptr, Type Ty);
 
   Variable *makeReg(Type Ty, int32_t RegNum = Variable::NoRegister);
   static Type stackSlotType();
   Variable *copyToReg(Operand *Src, int32_t RegNum = Variable::NoRegister);
   void alignRegisterPow2(Variable *Reg, uint32_t Align);
 
   /// Returns a vector in a register with the given constant entries.
   Variable *makeVectorOfZeros(Type Ty, int32_t RegNum = Variable::NoRegister);
 
@@ skipping 298 matching lines @@
 
 private:
   ~TargetHeaderARM32() = default;
 
   TargetARM32Features CPUFeatures;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGARM32_H