llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h

//===-- RISCVAsmBackend.h - RISCV Assembler Backend -----------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_TARGET_RISCV_MCTARGETDESC_RISCVASMBACKEND_H
#define LLVM_LIB_TARGET_RISCV_MCTARGETDESC_RISCVASMBACKEND_H

#include "MCTargetDesc/RISCVFixupKinds.h"
#include "MCTargetDesc/RISCVMCTargetDesc.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCSubtargetInfo.h"

namespace llvm {
class MCAssembler;
class MCObjectTargetWriter;
class raw_ostream;

class RISCVAsmBackend : public MCAsmBackend {
  const MCSubtargetInfo &STI;
  uint8_t OSABI;
  bool Is64Bit;
  bool ForceRelocs = false;

public:
  RISCVAsmBackend(const MCSubtargetInfo &STI, uint8_t OSABI, bool Is64Bit)
      : MCAsmBackend(support::little), STI(STI), OSABI(OSABI),
        Is64Bit(Is64Bit) {}
  ~RISCVAsmBackend() override {}

  void setForceRelocs() { ForceRelocs = true; }

  // Generate diff expression relocations if the relax feature is enabled or had
  // previously been enabled, otherwise it is safe for the assembler to
  // calculate these internally.
  bool requiresDiffExpressionRelocations() const override {
    return STI.getFeatureBits()[RISCV::FeatureRelax] || ForceRelocs;
  }
  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                  const MCValue &Target, MutableArrayRef<char> Data,
                  uint64_t Value, bool IsResolved,
                  const MCSubtargetInfo *STI) const override;

  std::unique_ptr<MCObjectTargetWriter>
  createObjectTargetWriter() const override;

  // If linker relaxation is enabled, or the relax option had previously been
  // enabled, always emit relocations even if the fixup can be resolved. This is
  // necessary for correctness as offsets may change during relaxation.
  bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
                             const MCValue &Target) override {
    return STI.getFeatureBits()[RISCV::FeatureRelax] || ForceRelocs;
  }

  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
                            const MCRelaxableFragment *DF,
                            const MCAsmLayout &Layout) const override {
    llvm_unreachable("Handled by fixupNeedsRelaxationAdvanced");
  }

  bool fixupNeedsRelaxationAdvanced(const MCFixup &Fixup, bool Resolved,
                                    uint64_t Value,
                                    const MCRelaxableFragment *DF,
                                    const MCAsmLayout &Layout,
                                    const bool WasForced) const override;

  unsigned getNumFixupKinds() const override {
    return RISCV::NumTargetFixupKinds;
  }

  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override {
    const static MCFixupKindInfo Infos[] = {
      // This table *must* be in the order that the fixup_* kinds are defined in
      // RISCVFixupKinds.h.
      //
      // name                      offset bits  flags
      { "fixup_riscv_hi20",         12,     20,  0 },
      { "fixup_riscv_lo12_i",       20,     12,  0 },
      { "fixup_riscv_lo12_s",        0,     32,  0 },
      { "fixup_riscv_pcrel_hi20",   12,     20,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_pcrel_lo12_i", 20,     12,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_pcrel_lo12_s",  0,     32,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_jal",          12,     20,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_branch",        0,     32,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_rvc_jump",      2,     11,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_rvc_branch",    0,     16,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_call",          0,     64,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_relax",         0,      0,  0 }
    };
    static_assert((array_lengthof(Infos)) == RISCV::NumTargetFixupKinds,
                  "Not all fixup kinds added to Infos array");

    if (Kind < FirstTargetFixupKind)
      return MCAsmBackend::getFixupKindInfo(Kind);

    assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
           "Invalid kind!");
    return Infos[Kind - FirstTargetFixupKind];
  }

  bool mayNeedRelaxation(const MCInst &Inst,
                         const MCSubtargetInfo &STI) const override;
  unsigned getRelaxedOpcode(unsigned Op) const;

  void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                        MCInst &Res) const override;


  bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
};
}

#endif