[RISCV] Add preferred function and loop alignment RISCVSubtarget. NFC

[craig.topper]

Summary

These seem like properties we will want to adjust based on -mtune.
Move them to subtarget like is done on ARM and AArch64. Don't add
any overrides yet.

Note there's a slight change here. We are now passing Align(1) for
preferred function alignment where we previously passed the minimum
alignment. As far as I could tell, it will be maxed with min when
it used so this should be ok.

[reames]

LGTM

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

setOperationAction(
          ISD::ATOMIC_LOAD_XOR, ISD::ATOMIC_LOAD_NAND, ISD::ATOMIC_LOAD_MIN,
          ISD::ATOMIC_LOAD_MAX, ISD::ATOMIC_LOAD_UMIN, ISD::ATOMIC_LOAD_UMAX},
         XLenVT, Expand);
   }
 
   // Function alignments.
   const Align FunctionAlignment(Subtarget.hasStdExtCOrZca() ? 2 : 4);
   setMinFunctionAlignment(FunctionAlignment);
-  setPrefFunctionAlignment(FunctionAlignment);
+  // Set preferred alignments.
+  setPrefFunctionAlignment(Subtarget.getPrefFunctionAlignment());
+  setPrefLoopAlignment(Subtarget.getPrefLoopAlignment());
 
   setMinimumJumpTableEntries(5);
 
   // Jumps are expensive, compared to logic
   setJumpIsExpensive();
 
   setTargetDAGCombine({ISD::INTRINSIC_WO_CHAIN, ISD::ADD, ISD::SUB, ISD::AND,
                        ISD::OR, ISD::XOR, ISD::SETCC, ISD::SELECT});

llvm/lib/Target/RISCV/RISCVSubtarget.h

#include "RISCVGenSubtargetInfo.inc"
   unsigned XLen = 32;
   unsigned ZvlLen = 0;
   MVT XLenVT = MVT::i32;
   unsigned RVVVectorBitsMin;
   unsigned RVVVectorBitsMax;
   uint8_t MaxInterleaveFactor = 2;
   RISCVABI::ABI TargetABI = RISCVABI::ABI_Unknown;
   std::bitset<RISCV::NUM_TARGET_REGS> UserReservedRegister;
+  Align PrefFunctionAlignment;
+  Align PrefLoopAlignment;
+
   RISCVFrameLowering FrameLowering;
   RISCVInstrInfo InstrInfo;
   RISCVRegisterInfo RegInfo;
   RISCVTargetLowering TLInfo;
   SelectionDAGTargetInfo TSInfo;
 
   /// Initializes using the passed in CPU and feature strings so that we can
   /// use initializer lists for subtarget initialization.
public:
   const RISCVTargetLowering *getTargetLowering() const override {
     return &TLInfo;
   }
   const SelectionDAGTargetInfo *getSelectionDAGInfo() const override {
     return &TSInfo;
   }
   bool enableMachineScheduler() const override { return true; }
 
+  Align getPrefFunctionAlignment() const { return PrefFunctionAlignment; }
+  Align getPrefLoopAlignment() const { return PrefLoopAlignment; }
+
   /// Returns RISCV processor family.
   /// Avoid this function! CPU specifics should be kept local to this class
   /// and preferably modeled with SubtargetFeatures or properties in
   /// initializeProperties().
   RISCVProcFamilyEnum getProcFamily() const { return RISCVProcFamily; }
 
 #define GET_SUBTARGETINFO_MACRO(ATTRIBUTE, DEFAULT, GETTER) \
   bool GETTER() const { return ATTRIBUTE; }