gcc源代码分析，genemit由i386.md文件生成insn-emit.c文件

第一部分输入的：

;; Call subroutine returning no value.
(define_insn "call"
  [(call (match_operand:QI 0 "indirect_operand" "m")
     (match_operand:SI 1 "general_operand" "g"))]
  ;; Operand 1 not really used on the m68000.
  ""
  "*
{
  if (GET_CODE (operands[0]) == MEM
      && ! CONSTANT_ADDRESS_P (XEXP (operands[0], 0)))
    {
      operands[0] = XEXP (operands[0], 0);
      return \"call %*%0\";
    }
  else
    return \"call %0\";
}")

;; Call subroutine, returning value in operand 0
;; (which must be a hard register).
(define_insn "call_value"
  [(set (match_operand 0 "" "=rf")
    (call (match_operand:QI 1 "indirect_operand" "m")
          (match_operand:SI 2 "general_operand" "g")))]
  ;; Operand 2 not really used on the m68000.
  ""
  "*
{
  if (GET_CODE (operands[1]) == MEM
      && ! CONSTANT_ADDRESS_P (XEXP (operands[1], 0)))
    {
      operands[1] = XEXP (operands[1], 0);
      output_asm_insn (\"call %*%1\", operands);
    }
  else
    output_asm_insn (\"call %1\", operands);

  if (GET_MODE (operands[0]) == DFmode
      || GET_MODE (operands[0]) == SFmode)
    {
/*      fp_pop_level++; */
      /* pop if reg dead */
      if (!FP_REG_P (operands[0]))
    abort ();
      if (top_dead_p (insn))
    {
      POP_ONE_FP;
    }
    }
  RET;
}")

(define_insn "nop"
  [(const_int 0)]
  ""
  "nop")

第二部分是生成的：

rtx

gen_call (operand0, operand1)
     rtx operand0;
     rtx operand1;
{
  return gen_rtx (CALL, VOIDmode, operand0, operand1);
}

rtx
gen_call_value (operand0, operand1, operand2)
     rtx operand0;
     rtx operand1;
     rtx operand2;
{
  return gen_rtx (SET, VOIDmode, operand0, gen_rtx (CALL, VOIDmode, operand1, operand2));
}

rtx
gen_nop ()
{
  return const0_rtx;
}

在编译gcc的时候先生成可执行文件genemit，然后再由genemit和i386.md生成insn-emit.c文件。

也就是在编译之前没有insn-*文件，编译之后就有了insn-*文件。

那么hello.s文件和i386.md就没有关系了，和insn-* 文件有关。

还是把main函数列出来：

int
main (argc, argv)
     int argc;
     char **argv;
{
  rtx desc;
  FILE *infile;
  extern rtx read_rtx ();
  register int c;

  obstack_init (rtl_obstack);

  if (argc <= 1)
    fatal ("No input file name.");

  infile = fopen (argv[1], "r");
  if (infile == 0)
    {
      perror (argv[1]);
      exit (FATAL_EXIT_CODE);
    }

  init_rtl ();

  /* Assign sequential codes to all entries in the machine description
     in parallel with the tables in insn-output.c.  */

  insn_code_number = 0;

  printf ("/* Generated automatically by the program `genemit'\n\
from the machine description file `md'.  */\n\n");

  printf ("#include \"config.h\"\n");
  printf ("#include \"rtl.h\"\n");
  printf ("#include \"expr.h\"\n");
  printf ("#include \"real.h\"\n");
  printf ("#include \"insn-config.h\"\n\n");
  printf ("#include \"insn-flags.h\"\n\n");
  printf ("extern char *insn_operand_constraint[][MAX_RECOG_OPERANDS];\n\n");
  printf ("extern rtx recog_operand[];\n");
  printf ("#define operands emit_operand\n\n");
  printf ("#define FAIL do { end_sequence (); return 0;} while (0)\n\n");
  printf ("#define DONE goto _done\n\n");

  /* Read the machine description.  */

  while (1)
    {
      c = read_skip_spaces (infile);
      if (c == EOF)
    break;
      ungetc (c, infile);

      desc = read_rtx (infile);
      if (GET_CODE (desc) == DEFINE_INSN)
    {
      gen_insn (desc);
      ++insn_code_number;
    }
      if (GET_CODE (desc) == DEFINE_EXPAND)
    {
      gen_expand (desc);
      ++insn_code_number;
    }
      if (GET_CODE (desc) == DEFINE_PEEPHOLE)
    {
      ++insn_code_number;
    }
    }

  fflush (stdout);
  exit (ferror (stdout) != 0 ? FATAL_EXIT_CODE : SUCCESS_EXIT_CODE);
}