[CSKY 3/n] Add bare-bones C-SKY MCTargetDesc

[zixuan-wu]

Summary

Add basis of CSKY MCTargetDesc and it's enough to compile and link but doesn't yet do anything particularly useful.
Once an ASM parser and printer are added in the next two patches, the whole thing can be usefully tested.

[rengolin]

Looks like a standard mock implementation, basic infrastructure. I don't see anything wrong with it but I've also been far from this area for too long, so I'll let other people review it properly and approve.

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.h

13

Do you really need this include here?

[zixuan-wu]

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.h

13

Yes, class MCTargetOptions is introduced by it.

[rengolin]

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.h

13

Why not include "llvm/MC/MCTargetOptions.h" directly here?

Your target description header has some auto-generated code that could get really large.

[myhsu]

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCCodeEmitter.cpp

27

Are getOImmOpValue and getImmOpValue only gonna used in this file? Because if they're used in other files, there will be a linker error saying that it can't find the template-instantiated version of these two functions (unless you explicitly instantiate every possible template arguments here). And I think in general you should avoid splitting template definitions from its declarations.

And also, why num is not used in both functions?

[zixuan-wu]

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.h

13

Right. I move it to related cpp file CSKYAsmBackend.cpp which needs that header file.

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCCodeEmitter.cpp

27

Good. I think the num is not needed anymore.

Second, I think I can write template implementation in header in short version now. In future, the complex body of getImmOpValue can be departed into another function and its implementation is in cpp file.

[zixuan-wu]

Address comments.

[zixuan-wu]

Is it good to anybody to LGTM?

[rengolin]

LGTM, thanks!

[MaskRay]

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.cpp

76

No newline at end of file

llvm/lib/Target/CSKY/MCTargetDesc/CSKYELFObjectWriter.cpp

14

You may use csky-elf-writer or csky-elf-object-writer

The current generic name can be misleading.

[MaskRay]

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.cpp

37

No need to define since it has a default definition.

llvm/lib/Target/CSKY/MCTargetDesc/CSKYELFObjectWriter.cpp

36

Add a period for complete sentences in comments

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCCodeEmitter.cpp

22

The generic name can be misleading. Add a target prefix

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCCodeEmitter.h

45

clang-format this line

[zixuan-wu]

Address comments.

[zixuan-wu]

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCCodeEmitter.h

45

It's been clang-formatted.

llvm/lib/Target/CSKY/CMakeLists.txt

 add_llvm_component_group(CSKY)
 
 set(LLVM_TARGET_DEFINITIONS CSKY.td)
 
 tablegen(LLVM CSKYGenRegisterInfo.inc -gen-register-info)
 tablegen(LLVM CSKYGenInstrInfo.inc -gen-instr-info)
+tablegen(LLVM CSKYGenMCCodeEmitter.inc -gen-emitter)
 
 add_public_tablegen_target(CSKYCommonTableGen)
 
 add_llvm_target(CSKYCodeGen
   CSKYTargetMachine.cpp
 
   LINK_COMPONENTS
   Core
   CodeGen
   CSKYInfo
   Support
   Target
 
   ADD_TO_COMPONENT
   CSKY
   )
 
 add_subdirectory(TargetInfo)
+add_subdirectory(MCTargetDesc)

llvm/lib/Target/CSKY/CSKYInstrInfo.td

 // TODO: Add CSKY specific DAG Nodes.
 
 //===----------------------------------------------------------------------===//
 // Operand and SDNode transformation definitions.
 //===----------------------------------------------------------------------===//
 
 class oimm<int num> : Operand<i32>,
   ImmLeaf<i32, "return isUInt<"#num#">(Imm - 1);"> {
-  let EncoderMethod = "getOImmOpValue<"#num#">";
+  let EncoderMethod = "getOImmOpValue";
 }
 
 class uimm<int num, int shift = 0> : Operand<i32>,
   ImmLeaf<i32, "return isShiftedUInt<"#num#", "#shift#">(Imm);"> {
-  let EncoderMethod = "getImmOpValue<"#num#", "#shift#">";
+  let EncoderMethod = "getImmOpValue<"#shift#">";
 }
 
 class simm<int num, int shift = 0> : Operand<i32>,
   ImmLeaf<i32, "return isShiftedInt<"#num#", "#shift#">(Imm);"> {
-  let EncoderMethod = "getImmOpValue<"#num#", "#shift#">";
+  let EncoderMethod = "getImmOpValue<"#shift#">";
 }
 
 def nimm_XFORM : SDNodeXForm<imm, [{
   return CurDAG->getTargetConstant(~N->getSExtValue(), SDLoc(N), MVT::i32);
 }]>;
 class nimm<int num> : Operand<i32>,
   ImmLeaf<i32, "return isUInt<"#num#">(~Imm);", nimm_XFORM> {
 }

llvm/lib/Target/CSKY/MCTargetDesc/CMakeLists.txt

+add_llvm_component_library(LLVMCSKYDesc
+  CSKYAsmBackend.cpp
+  CSKYELFObjectWriter.cpp
+  CSKYMCAsmInfo.cpp
+  CSKYMCTargetDesc.cpp
+  CSKYMCCodeEmitter.cpp
+
+  LINK_COMPONENTS
+  MC
+  CSKYInfo
+  Support
+
+  ADD_TO_COMPONENT
+  CSKY
+)

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.h

+//===-- CSKYAsmBackend.h - CSKY Assembler Backend -------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYASMBACKEND_H
+#define LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYASMBACKEND_H
+
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCTargetOptions.h"
+
+namespace llvm {
+
+class CSKYAsmBackend : public MCAsmBackend {
+
+public:
+  CSKYAsmBackend(const MCSubtargetInfo &STI, const MCTargetOptions &OP)
+      : MCAsmBackend(support::little) {}
+
+  unsigned int getNumFixupKinds() const override;
+  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
+                  const MCValue &Target, MutableArrayRef<char> Data,
+                  uint64_t Value, bool IsResolved,
+                  const MCSubtargetInfo *STI) const override;
+  bool mayNeedRelaxation(const MCInst &Inst,
+                         const MCSubtargetInfo &STI) const override;
+  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
+                            const MCRelaxableFragment *DF,
+                            const MCAsmLayout &Layout) const override;
+  void relaxInstruction(MCInst &Inst,
+                        const MCSubtargetInfo &STI) const override;
+  bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
+  std::unique_ptr<MCObjectTargetWriter>
+  createObjectTargetWriter() const override;
+};
+} // namespace llvm
+
+#endif // LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYASMBACKEND_H

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.cpp

+//===-- CSKYAsmBackend.cpp - CSKY Assembler Backend -----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "CSKYAsmBackend.h"
+#include "MCTargetDesc/CSKYMCTargetDesc.h"
+#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCFixupKindInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "asmbackend"
+
+using namespace llvm;
+
+std::unique_ptr<MCObjectTargetWriter>
+CSKYAsmBackend::createObjectTargetWriter() const {
+  return createCSKYELFObjectWriter();
+}
+
+unsigned int CSKYAsmBackend::getNumFixupKinds() const { return 1; }
+
+void CSKYAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
+                                const MCValue &Target,
+                                MutableArrayRef<char> Data, uint64_t Value,
+                                bool IsResolved,
+                                const MCSubtargetInfo *STI) const {
+  return;
+}
+
+bool CSKYAsmBackend::mayNeedRelaxation(const MCInst &Inst,
+                                       const MCSubtargetInfo &STI) const {
+
+  return false;
+}
+
+bool CSKYAsmBackend::fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
+                                          const MCRelaxableFragment *DF,
+                                          const MCAsmLayout &Layout) const {
+  return false;
+}
+
+void CSKYAsmBackend::relaxInstruction(MCInst &Inst,
+                                      const MCSubtargetInfo &STI) const {
+  llvm_unreachable("CSKYAsmBackend::relaxInstruction() unimplemented");
+}
+
+bool CSKYAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
+  if (Count % 2)
+    return false;
+
+  // MOV32 r0, r0
+  while (Count >= 4) {
+    OS.write("\xc4\x00\x48\x20", 4);
+    Count -= 4;
+  }
+  // MOV16 r0, r0
+  if (Count)
+    OS.write("\x6c\x03", 2);
+
+  return true;
+}
+
+MCAsmBackend *llvm::createCSKYAsmBackend(const Target &T,
+                                         const MCSubtargetInfo &STI,
+                                         const MCRegisterInfo &MRI,
+                                         const MCTargetOptions &Options) {
+  return new CSKYAsmBackend(STI, Options);
+}
 No newline at end of file

llvm/lib/Target/CSKY/MCTargetDesc/CSKYELFObjectWriter.cpp

+//===-- CSKYELFObjectWriter.cpp - CSKY ELF Writer -------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "CSKYMCTargetDesc.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCELFObjectWriter.h"
+#include "llvm/MC/MCObjectWriter.h"
+
+#define DEBUG_TYPE "elfobjectwriter"
+
+using namespace llvm;
+
+namespace {
+
+class CSKYELFObjectWriter : public MCELFObjectTargetWriter {
+public:
+  CSKYELFObjectWriter(uint8_t OSABI = 0)
+      : MCELFObjectTargetWriter(false, OSABI, ELF::EM_CSKY, true){};
+  ~CSKYELFObjectWriter() {}
+
+  unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
+                        const MCFixup &Fixup, bool IsPCRel) const override;
+};
+
+} // namespace
+
+unsigned CSKYELFObjectWriter::getRelocType(MCContext &Ctx,
+                                           const MCValue &Target,
+                                           const MCFixup &Fixup,
+                                           bool IsPCRel) const {
+  // Determine the type of the relocation
+  switch ((unsigned)Fixup.getKind()) {
+  default:
+    llvm_unreachable("invalid fixup kind!");
+  }
+}
+
+std::unique_ptr<MCObjectTargetWriter> llvm::createCSKYELFObjectWriter() {
+  return std::make_unique<CSKYELFObjectWriter>();
+}

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCAsmInfo.h

+//===-- CSKYMCAsmInfo.h - CSKY Asm Info ------------------------*- C++ -*--===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the declaration of the CSKYMCAsmInfo class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCASMINFO_H
+#define LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCASMINFO_H
+
+#include "llvm/MC/MCAsmInfoELF.h"
+
+namespace llvm {
+class Triple;
+
+class CSKYMCAsmInfo : public MCAsmInfoELF {
+  void anchor() override;
+
+public:
+  explicit CSKYMCAsmInfo(const Triple &TargetTriple);
+};
+} // namespace llvm
+
+#endif // LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCASMINFO_H

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCAsmInfo.cpp

+//===-- CSKYMCAsmInfo.cpp - CSKY Asm properties ---------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the declarations of the CSKYMCAsmInfo properties.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CSKYMCAsmInfo.h"
+#include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/MC/MCStreamer.h"
+
+using namespace llvm;
+
+void CSKYMCAsmInfo::anchor() {}
+
+CSKYMCAsmInfo::CSKYMCAsmInfo(const Triple &TargetTriple) {
+  AlignmentIsInBytes = false;
+  SupportsDebugInformation = true;
+  CommentString = "#";
+}

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCCodeEmitter.h

+//===-- CSKYMCCodeEmitter.cpp - CSKY Code Emitter interface ---------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CSKYMCCodeEmitter class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCCODEEMITTER_H
+#define LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCCODEEMITTER_H
+
+#include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCContext.h"
+
+namespace llvm {
+
+class CSKYMCCodeEmitter : public MCCodeEmitter {
+  MCContext &Ctx;
+  const MCInstrInfo &MII;
+
+public:
+  CSKYMCCodeEmitter(MCContext &Ctx, const MCInstrInfo &MII)
+      : Ctx(Ctx), MII(MII) {}
+
+  ~CSKYMCCodeEmitter() {}
+
+  void encodeInstruction(const MCInst &Inst, raw_ostream &OS,
+                         SmallVectorImpl<MCFixup> &Fixups,
+                         const MCSubtargetInfo &STI) const override;
+
+  // Generated by tablegen.
+  uint64_t getBinaryCodeForInstr(const MCInst &MI,
+                                 SmallVectorImpl<MCFixup> &Fixups,
+                                 const MCSubtargetInfo &STI) const;
+
+  // Default encoding method used by tablegen.
+  unsigned getMachineOpValue(const MCInst &MI, const MCOperand &MO,
+                             SmallVectorImpl<MCFixup> &Fixups,
+                             const MCSubtargetInfo &STI) const;
+
+  template <int shift = 0>
+  unsigned getImmOpValue(const MCInst &MI, unsigned Idx,
+                         SmallVectorImpl<MCFixup> &Fixups,
+                         const MCSubtargetInfo &STI) const {
+    const MCOperand &MO = MI.getOperand(Idx);
+    assert(MO.isImm() && "Unexpected MO type.");
+    return (MO.getImm() >> shift);
+  }
+
+  unsigned getOImmOpValue(const MCInst &MI, unsigned Idx,
+                          SmallVectorImpl<MCFixup> &Fixups,
+                          const MCSubtargetInfo &STI) const;
+};
+
+} // namespace llvm
+
+#endif // LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCCODEEMITTER_H

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCCodeEmitter.cpp

+//===-- CSKYMCCodeEmitter.cpp - CSKY Code Emitter interface ---------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CSKYMCCodeEmitter class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CSKYMCCodeEmitter.h"
+#include "MCTargetDesc/CSKYMCTargetDesc.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/MC/MCInstBuilder.h"
+#include "llvm/MC/MCInstrInfo.h"
+#include "llvm/Support/EndianStream.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "mccodeemitter"
+
+STATISTIC(MCNumEmitted, "Number of MC instructions emitted");
+
+unsigned CSKYMCCodeEmitter::getOImmOpValue(const MCInst &MI, unsigned Idx,
+                                           SmallVectorImpl<MCFixup> &Fixups,
+                                           const MCSubtargetInfo &STI) const {
+  const MCOperand &MO = MI.getOperand(Idx);
+  assert(MO.isImm() && "Unexpected MO type.");
+  return MO.getImm() - 1;
+}
+
+void CSKYMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
+                                          SmallVectorImpl<MCFixup> &Fixups,
+                                          const MCSubtargetInfo &STI) const {
+  const MCInstrDesc &Desc = MII.get(MI.getOpcode());
+  unsigned Size = Desc.getSize();
+  uint32_t Bin = getBinaryCodeForInstr(MI, Fixups, STI);
+
+  uint16_t LO16 = static_cast<uint16_t>(Bin);
+  uint16_t HI16 = static_cast<uint16_t>(Bin >> 16);
+
+  if (Size == 4)
+    support::endian::write<uint16_t>(OS, HI16, support::little);
+
+  support::endian::write<uint16_t>(OS, LO16, support::little);
+  ++MCNumEmitted; // Keep track of the # of mi's emitted.
+}
+
+unsigned
+CSKYMCCodeEmitter::getMachineOpValue(const MCInst &MI, const MCOperand &MO,
+                                     SmallVectorImpl<MCFixup> &Fixups,
+                                     const MCSubtargetInfo &STI) const {
+  if (MO.isReg())
+    return Ctx.getRegisterInfo()->getEncodingValue(MO.getReg());
+
+  if (MO.isImm())
+    return static_cast<unsigned>(MO.getImm());
+
+  llvm_unreachable("Unhandled expression!");
+  return 0;
+}
+
+MCCodeEmitter *llvm::createCSKYMCCodeEmitter(const MCInstrInfo &MCII,
+                                             const MCRegisterInfo &MRI,
+                                             MCContext &Ctx) {
+  return new CSKYMCCodeEmitter(Ctx, MCII);
+}
+
+#include "CSKYGenMCCodeEmitter.inc"

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCTargetDesc.h

+//===-- CSKYMCTargetDesc.h - CSKY Target Descriptions -----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides CSKY specific target descriptions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCTARGETDESC_H
+#define LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCTARGETDESC_H
+
+#include "llvm/MC/MCTargetOptions.h"
+#include <memory>
+
+namespace llvm {
+class MCAsmBackend;
+class MCCodeEmitter;
+class MCContext;
+class MCInstrInfo;
+class MCRegisterInfo;
+class MCObjectTargetWriter;
+class MCRegisterInfo;
+class MCSubtargetInfo;
+class Target;
+class Triple;
+
+std::unique_ptr<MCObjectTargetWriter> createCSKYELFObjectWriter();
+
+MCAsmBackend *createCSKYAsmBackend(const Target &T, const MCSubtargetInfo &STI,
+                                   const MCRegisterInfo &MRI,
+                                   const MCTargetOptions &Options);
+
+MCCodeEmitter *createCSKYMCCodeEmitter(const MCInstrInfo &MCII,
+                                       const MCRegisterInfo &MRI,
+                                       MCContext &Ctx);
+} // namespace llvm
+
+#define GET_REGINFO_ENUM
+#include "CSKYGenRegisterInfo.inc"
+
+#define GET_INSTRINFO_ENUM
+#include "CSKYGenInstrInfo.inc"
+
+#endif // LLVM_LIB_TARGET_CSKY_MCTARGETDESC_CSKYMCTARGETDESC_H

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCTargetDesc.cpp

+//===-- CSKYMCTargetDesc.cpp - CSKY Target Descriptions -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// This file provides CSKY specific target descriptions.
+///
+//===----------------------------------------------------------------------===//
+
+#include "CSKYMCTargetDesc.h"
+#include "CSKYAsmBackend.h"
+#include "CSKYMCAsmInfo.h"
+#include "CSKYMCCodeEmitter.h"
+#include "TargetInfo/CSKYTargetInfo.h"
+#include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/MC/MCSubtargetInfo.h"
+#include "llvm/Support/TargetRegistry.h"
+
+#define GET_INSTRINFO_MC_DESC
+#include "CSKYGenInstrInfo.inc"
+
+#define GET_REGINFO_MC_DESC
+#include "CSKYGenRegisterInfo.inc"
+
+using namespace llvm;
+
+static MCAsmInfo *createCSKYMCAsmInfo(const MCRegisterInfo &MRI,
+                                      const Triple &TT,
+                                      const MCTargetOptions &Options) {
+  MCAsmInfo *MAI = new CSKYMCAsmInfo(TT);
+
+  // Initial state of the frame pointer is SP.
+  unsigned Reg = MRI.getDwarfRegNum(CSKY::R14, true);
+  MCCFIInstruction Inst = MCCFIInstruction::cfiDefCfa(nullptr, Reg, 0);
+  MAI->addInitialFrameState(Inst);
+  return MAI;
+}
+
+static MCInstrInfo *createCSKYMCInstrInfo() {
+  MCInstrInfo *Info = new MCInstrInfo();
+  InitCSKYMCInstrInfo(Info);
+  return Info;
+}
+
+static MCRegisterInfo *createCSKYMCRegisterInfo(const Triple &TT) {
+  MCRegisterInfo *Info = new MCRegisterInfo();
+  InitCSKYMCRegisterInfo(Info, CSKY::R15);
+  return Info;
+}
+
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeCSKYTargetMC() {
+  auto &CSKYTarget = getTheCSKYTarget();
+  TargetRegistry::RegisterMCAsmBackend(CSKYTarget, createCSKYAsmBackend);
+  TargetRegistry::RegisterMCAsmInfo(CSKYTarget, createCSKYMCAsmInfo);
+  TargetRegistry::RegisterMCInstrInfo(CSKYTarget, createCSKYMCInstrInfo);
+  TargetRegistry::RegisterMCRegInfo(CSKYTarget, createCSKYMCRegisterInfo);
+  TargetRegistry::RegisterMCCodeEmitter(CSKYTarget, createCSKYMCCodeEmitter);
+}

llvm/lib/Target/CSKY/TargetInfo/CSKYTargetInfo.cpp

 Target &llvm::getTheCSKYTarget() {
   static Target TheCSKYTarget;
   return TheCSKYTarget;
 }
 
 extern "C" void LLVMInitializeCSKYTargetInfo() {
   RegisterTarget<Triple::csky> X(getTheCSKYTarget(), "csky", "C-SKY", "CSKY");
 }
-
-// FIXME: Temporary stub - this function must be defined for linking
-// to succeed and will be called unconditionally by llc, so must be a no-op.
-// Remove once this function is properly implemented.
-extern "C" void LLVMInitializeCSKYTargetMC() {}