non-const-visitor.cc

// Copyright 2014, VIXL authors
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#include "non-const-visitor.h"

#include <regex>

#include "examples.h"

using namespace vixl;
using namespace vixl::aarch64;

#define __ masm->


void SwitchAddSubRegisterSources::Visit(Metadata* metadata,
                                        const Instruction* instr) {
  const std::string& form = (*metadata)["form"];

  // Match the forms for 32/64-bit add/subtract with shift, with optional flag
  // setting.
  if (std::regex_match(form,  // NOLINT: avoid clang-tidy-4.0 errors.
                       std::regex("(?:add|sub)s?_(?:32|64)_addsub_shift"))) {
    int rn = instr->GetRn();
    int rm = instr->GetRm();
    // Only non-const visitors are allowed to discard constness of the visited
    // instruction.
    Instruction* mutable_instr = MutableInstruction(instr);
    Instr instr_bits = mutable_instr->GetInstructionBits();

    // Switch the bitfields for the `rn` and `rm` registers.
    instr_bits &= ~(Rn_mask | Rm_mask);
    instr_bits |= (rn << Rm_offset) | (rm << Rn_offset);

    // Rewrite the instruction.
    mutable_instr->SetInstructionBits(instr_bits);
  }
}


void GenerateNonConstVisitorTestCode(MacroAssembler* masm) {
  // int64_t foo(int64_t a, int64_t b)
  //  Argument locations:
  //    a -> x0
  //    b -> x1
  __ Sub(x0, x0, x1);
  // The return value is in x0.
  __ Ret();
}


int64_t RunNonConstVisitorTestGeneratedCode(const Instruction* start_instr) {
#ifdef VIXL_INCLUDE_SIMULATOR_AARCH64
  Decoder simulator_decoder;
  Simulator simulator(&simulator_decoder);

  int64_t a = 5;
  int64_t b = 2;
  simulator.WriteXRegister(0, a);
  simulator.WriteXRegister(1, b);
  simulator.RunFrom(start_instr);
  int64_t res = simulator.ReadXRegister(0);
  printf("foo(%" PRId64 ", %" PRId64 ") = %" PRId64 "\n", a, b, res);

  return res;
#else
  // Without the simulator there is nothing to test.
  USE(start_instr);
  return 0;
#endif
}


#ifndef TEST_EXAMPLES
#ifdef VIXL_INCLUDE_SIMULATOR_AARCH64
int main(void) {
  MacroAssembler masm;

  // Generate the code.
  Label code_start, code_end;
  masm.Bind(&code_start);
  GenerateNonConstVisitorTestCode(&masm);
  masm.Bind(&code_end);
  masm.FinalizeCode();
  Instruction* instr_start = masm.GetLabelAddress<Instruction*>(&code_start);
  Instruction* instr_end = masm.GetLabelAddress<Instruction*>(&code_end);

  // Run the code a first time.
  RunNonConstVisitorTestGeneratedCode(instr_start);

  // Instantiate a decoder, disassembler, and our custom modifying visitor.
  Decoder decoder;
  PrintDisassembler disasm(stdout);
  SwitchAddSubRegisterSources modifying_visitor;

  // Register visitors in such a way that when visiting instructions, the
  // decoder will first disassemble the original instruction, modify it, and
  // then disassemble the modified instruction.
  decoder.AppendVisitor(&disasm);
  decoder.AppendVisitor(&modifying_visitor);
  decoder.AppendVisitor(&disasm);

  // Iterate through the instructions.
  Instruction* instr;
  for (instr = instr_start; instr < instr_end; instr += kInstructionSize) {
    printf("---\n");
    decoder.Decode(instr);
  }

  // Run the modified code and observe the different output from before.
  RunNonConstVisitorTestGeneratedCode(instr_start);

  return 0;
}
#else
// Without the simulator there is nothing to test.
int main(void) { return 0; }
#endif  // VIXL_INCLUDE_SIMULATOR_AARCH64
#endif  // TEST_EXAMPLES


// This is only used by the testing code.
void ModifyNonConstVisitorTestGeneratedCode(Instruction* start,
                                            Instruction* end) {
  Decoder decoder;
  SwitchAddSubRegisterSources modifying_visitor;
  decoder.AppendVisitor(&modifying_visitor);

  Instruction* instr;
  for (instr = start; instr < end; instr += kInstructionSize) {
    printf("---\n");
    decoder.Decode(instr);
  }
}