mips.md

gcc-you can use this code to learn something about gcc, and inquire further into linux,

(define_insn "subsf3"
  [(set (match_operand:SF 0 "register_operand" "=f")
	(minus:SF (match_operand:SF 1 "register_operand" "f")
		  (match_operand:SF 2 "register_operand" "f")))]
  "TARGET_HARD_FLOAT"
  "sub.s\\t%0,%1,%2"
  [(set_attr "type"	"fadd")
   (set_attr "mode"	"SF")])

(define_expand "subsi3"
  [(set (match_operand:SI 0 "register_operand" "=d")
	(minus:SI (match_operand:SI 1 "reg_or_0_operand" "dJ")
		  (match_operand:SI 2 "arith_operand" "dI")))]
  ""
  "
{
  if (GET_CODE (operands[2]) == CONST_INT
      && (INTVAL (operands[2]) == -32768
	  || (TARGET_MIPS16
	      && INTVAL (operands[2]) == -0x4000)))
    operands[2] = force_reg (SImode, operands[2]);
}")

(define_insn "subsi3_internal"
  [(set (match_operand:SI 0 "register_operand" "=d")
	(minus:SI (match_operand:SI 1 "reg_or_0_operand" "dJ")
		  (match_operand:SI 2 "arith_operand" "dI")))]
  "!TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT || INTVAL (operands[2]) != -32768)"
  "subu\\t%0,%z1,%2"
  [(set_attr "type"	"arith")
   (set_attr "mode"	"SI")])

;; For the mips16, we need to recognize stack pointer subtractions
;; explicitly, since we don't have a constraint for $sp.  These insns
;; will be generated by the save_restore_insns functions.

(define_insn ""
  [(set (reg:SI 29)
	(minus:SI (reg:SI 29)
		  (match_operand:SI 0 "small_int" "I")))]
  "TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT || INTVAL (operands[2]) != -32768)"
  "addu\\t%$,%$,%n0"
  [(set_attr "type"	"arith")
   (set_attr "mode"	"SI")
   (set (attr "length")	(if_then_else (match_operand:VOID 0 "m16_nsimm8_8" "")
				      (const_int 4)
				      (const_int 8)))])

(define_insn ""
  [(set (match_operand:SI 0 "register_operand" "=d")
	(minus:SI (reg:SI 29)
		  (match_operand:SI 1 "small_int" "I")))]
  "TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT || INTVAL (operands[2]) != -32768)"
  "addu\\t%0,%$,%n1"
  [(set_attr "type"	"arith")
   (set_attr "mode"	"SI")
   (set (attr "length")	(if_then_else (match_operand:VOID 1 "m16_nuimm8_4" "")
				      (const_int 4)
				      (const_int 8)))])


(define_insn ""
  [(set (match_operand:SI 0 "register_operand" "=d,d,d")
	(minus:SI (match_operand:SI 1 "register_operand" "0,d,d")
		  (match_operand:SI 2 "arith_operand" "I,O,d")))]
  "TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT
       || (INTVAL (operands[2]) != -32768 && INTVAL (operands[2]) != -0x4000))"
  "*
{
  if (REGNO (operands[0]) == REGNO (operands[1]))
    return \"subu\\t%0,%2\";
  return \"subu\\t%0,%1,%2\";
}"
  [(set_attr "type"	"arith")
   (set_attr "mode"	"SI")
   (set_attr_alternative "length"
		[(if_then_else (match_operand:VOID 2 "m16_nsimm8_1" "")
			       (const_int 4)
			       (const_int 8))
		 (if_then_else (match_operand:VOID 2 "m16_nsimm4_1" "")
			       (const_int 4)
			       (const_int 8))
		 (const_int 4)])])

;; On the mips16, we can sometimes split an subtract of a constant
;; which is a 4 byte instruction into two adds which are both 2 byte
;; instructions.  There are two cases: one where we are setting a
;; register to a register minus a constant, and one where we are
;; simply subtracting a constant from a register.

(define_split
  [(set (match_operand:SI 0 "register_operand" "")
	(minus:SI (match_dup 0)
		  (match_operand:SI 1 "const_int_operand" "")))]
  "TARGET_MIPS16 && reload_completed && !TARGET_DEBUG_D_MODE
   && GET_CODE (operands[0]) == REG
   && M16_REG_P (REGNO (operands[0]))
   && GET_CODE (operands[1]) == CONST_INT
   && ((INTVAL (operands[1]) > 0x80
	&& INTVAL (operands[1]) <= 0x80 + 0x80)
       || (INTVAL (operands[1]) < - 0x7f
	   && INTVAL (operands[1]) >= - 0x7f - 0x7f))"
  [(set (match_dup 0) (minus:SI (match_dup 0) (match_dup 1)))
   (set (match_dup 0) (minus:SI (match_dup 0) (match_dup 2)))]
  "
{
  HOST_WIDE_INT val = INTVAL (operands[1]);

  if (val >= 0)
    {
      operands[1] = GEN_INT (0x80);
      operands[2] = GEN_INT (val - 0x80);
    }
  else
    {
      operands[1] = GEN_INT (- 0x7f);
      operands[2] = GEN_INT (val + 0x7f);
    }
}")

(define_split
  [(set (match_operand:SI 0 "register_operand" "")
	(minus:SI (match_operand:SI 1 "register_operand" "")
		  (match_operand:SI 2 "const_int_operand" "")))]
  "TARGET_MIPS16 && reload_completed && !TARGET_DEBUG_D_MODE
   && GET_CODE (operands[0]) == REG
   && M16_REG_P (REGNO (operands[0]))
   && GET_CODE (operands[1]) == REG
   && M16_REG_P (REGNO (operands[1]))
   && REGNO (operands[0]) != REGNO (operands[1])
   && GET_CODE (operands[2]) == CONST_INT
   && ((INTVAL (operands[2]) > 0x8
	&& INTVAL (operands[2]) <= 0x8 + 0x80)
       || (INTVAL (operands[2]) < - 0x7
	   && INTVAL (operands[2]) >= - 0x7 - 0x7f))"
  [(set (match_dup 0) (minus:SI (match_dup 1) (match_dup 2)))
   (set (match_dup 0) (minus:SI (match_dup 0) (match_dup 3)))]
  "
{
  HOST_WIDE_INT val = INTVAL (operands[2]);

  if (val >= 0)
    {
      operands[2] = GEN_INT (0x8);
      operands[3] = GEN_INT (val - 0x8);
    }
  else
    {
      operands[2] = GEN_INT (- 0x7);
      operands[3] = GEN_INT (val + 0x7);
    }
}")

(define_expand "subdi3"
  [(parallel [(set (match_operand:DI 0 "register_operand" "=d")
		   (minus:DI (match_operand:DI 1 "se_register_operand" "d")
			     (match_operand:DI 2 "se_register_operand" "d")))
	      (clobber (match_dup 3))])]
  "TARGET_64BIT || (!TARGET_DEBUG_G_MODE && !TARGET_MIPS16)"
  "
{
  if (TARGET_64BIT)
    {
      emit_insn (gen_subdi3_internal_3 (operands[0], operands[1],
					operands[2]));
      DONE;
    }

  operands[3] = gen_reg_rtx (SImode);
}")

(define_insn "subdi3_internal"
  [(set (match_operand:DI 0 "register_operand" "=d")
	(minus:DI (match_operand:DI 1 "register_operand" "d")
		  (match_operand:DI 2 "register_operand" "d")))
   (clobber (match_operand:SI 3 "register_operand" "=d"))]
  "!TARGET_64BIT && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16"
  "sltu\\t%3,%L1,%L2\;subu\\t%L0,%L1,%L2\;subu\\t%M0,%M1,%M2\;subu\\t%M0,%M0,%3"
  [(set_attr "type"	"darith")
   (set_attr "mode"	"DI")
   (set_attr "length"	"16")])

(define_split
  [(set (match_operand:DI 0 "register_operand" "")
	(minus:DI (match_operand:DI 1 "register_operand" "")
		  (match_operand:DI 2 "register_operand" "")))
   (clobber (match_operand:SI 3 "register_operand" ""))]
  "reload_completed && !WORDS_BIG_ENDIAN && !TARGET_64BIT
   && !TARGET_DEBUG_D_MODE && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
   && GET_CODE (operands[0]) == REG && GP_REG_P (REGNO (operands[0]))
   && GET_CODE (operands[1]) == REG && GP_REG_P (REGNO (operands[1]))
   && GET_CODE (operands[2]) == REG && GP_REG_P (REGNO (operands[2]))"

  [(set (match_dup 3)
	(ltu:SI (subreg:SI (match_dup 1) 0)
		(subreg:SI (match_dup 2) 0)))

   (set (subreg:SI (match_dup 0) 0)
	(minus:SI (subreg:SI (match_dup 1) 0)
		  (subreg:SI (match_dup 2) 0)))

   (set (subreg:SI (match_dup 0) 4)
	(minus:SI (subreg:SI (match_dup 1) 4)
		  (subreg:SI (match_dup 2) 4)))

   (set (subreg:SI (match_dup 0) 4)
	(minus:SI (subreg:SI (match_dup 0) 4)
		  (match_dup 3)))]
  "")

(define_split
  [(set (match_operand:DI 0 "register_operand" "")
	(minus:DI (match_operand:DI 1 "register_operand" "")
		  (match_operand:DI 2 "register_operand" "")))
   (clobber (match_operand:SI 3 "register_operand" ""))]
  "reload_completed && WORDS_BIG_ENDIAN && !TARGET_64BIT
   && !TARGET_DEBUG_D_MODE && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
   && GET_CODE (operands[0]) == REG && GP_REG_P (REGNO (operands[0]))
   && GET_CODE (operands[1]) == REG && GP_REG_P (REGNO (operands[1]))
   && GET_CODE (operands[2]) == REG && GP_REG_P (REGNO (operands[2]))"

  [(set (match_dup 3)
	(ltu:SI (subreg:SI (match_dup 1) 4)
	        (subreg:SI (match_dup 2) 4)))

   (set (subreg:SI (match_dup 0) 4)
	(minus:SI (subreg:SI (match_dup 1) 4)
		  (subreg:SI (match_dup 2) 4)))

   (set (subreg:SI (match_dup 0) 0)
	(minus:SI (subreg:SI (match_dup 1) 0)
		  (subreg:SI (match_dup 2) 0)))

   (set (subreg:SI (match_dup 0) 0)
	(minus:SI (subreg:SI (match_dup 0) 0)
		  (match_dup 3)))]
  "")

(define_insn "subdi3_internal_2"
  [(set (match_operand:DI 0 "register_operand" "=d,d,d")
	(minus:DI (match_operand:DI 1 "register_operand" "d,d,d")
		  (match_operand:DI 2 "small_int" "P,J,N")))
   (clobber (match_operand:SI 3 "register_operand" "=d,d,d"))]
  "!TARGET_64BIT && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
   && INTVAL (operands[2]) != -32768"
  "@
   sltu\\t%3,%L1,%2\;subu\\t%L0,%L1,%2\;subu\\t%M0,%M1,%3
   move\\t%L0,%L1\;move\\t%M0,%M1
   sltu\\t%3,%L1,%2\;subu\\t%L0,%L1,%2\;subu\\t%M0,%M1,1\;subu\\t%M0,%M0,%3"
  [(set_attr "type"	"darith")
   (set_attr "mode"	"DI")
   (set_attr "length"	"12,8,16")])

(define_split
  [(set (match_operand:DI 0 "register_operand" "")
	(minus:DI (match_operand:DI 1 "register_operand" "")
		  (match_operand:DI 2 "small_int" "")))
   (clobber (match_operand:SI 3 "register_operand" ""))]
  "reload_completed && !WORDS_BIG_ENDIAN && !TARGET_64BIT
   && !TARGET_DEBUG_D_MODE && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
   && GET_CODE (operands[0]) == REG && GP_REG_P (REGNO (operands[0]))
   && GET_CODE (operands[1]) == REG && GP_REG_P (REGNO (operands[1]))
   && INTVAL (operands[2]) > 0"

  [(set (match_dup 3)
	(ltu:SI (subreg:SI (match_dup 1) 0)
		(match_dup 2)))

   (set (subreg:SI (match_dup 0) 0)
	(minus:SI (subreg:SI (match_dup 1) 0)
		  (match_dup 2)))

   (set (subreg:SI (match_dup 0) 4)
	(minus:SI (subreg:SI (match_dup 1) 4)
		  (match_dup 3)))]
  "")

(define_split
  [(set (match_operand:DI 0 "register_operand" "")
	(minus:DI (match_operand:DI 1 "register_operand" "")
		  (match_operand:DI 2 "small_int" "")))
   (clobber (match_operand:SI 3 "register_operand" ""))]
  "reload_completed && WORDS_BIG_ENDIAN && !TARGET_64BIT
   && !TARGET_DEBUG_D_MODE && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
   && GET_CODE (operands[0]) == REG && GP_REG_P (REGNO (operands[0]))
   && GET_CODE (operands[1]) == REG && GP_REG_P (REGNO (operands[1]))
   && INTVAL (operands[2]) > 0"

  [(set (match_dup 3)
	(ltu:SI (subreg:SI (match_dup 1) 4)
		(match_dup 2)))

   (set (subreg:SI (match_dup 0) 4)
	(minus:SI (subreg:SI (match_dup 1) 4)
		  (match_dup 2)))

   (set (subreg:SI (match_dup 0) 0)
	(minus:SI (subreg:SI (match_dup 1) 0)
		  (match_dup 3)))]
  "")

(define_insn "subdi3_internal_3"
  [(set (match_operand:DI 0 "register_operand" "=d")
	(minus:DI (match_operand:DI 1 "se_reg_or_0_operand" "dJ")
		  (match_operand:DI 2 "se_arith_operand" "dI")))]
  "TARGET_64BIT && !TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT || INTVAL (operands[2]) != -32768)"
  "*
{
  return (GET_CODE (operands[2]) == CONST_INT && INTVAL (operands[2]) < 0)
    ? \"daddu\\t%0,%z1,%n2\"
    : \"dsubu\\t%0,%z1,%2\";
}"
  [(set_attr "type"	"darith")
   (set_attr "mode"	"DI")])

;; For the mips16, we need to recognize stack pointer subtractions
;; explicitly, since we don't have a constraint for $sp.  These insns
;; will be generated by the save_restore_insns functions.

(define_insn ""
  [(set (reg:DI 29)
	(minus:DI (reg:DI 29)
		  (match_operand:DI 0 "small_int" "I")))]
  "TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT || INTVAL (operands[2]) != -32768)"
  "daddu\\t%$,%$,%n0"
  [(set_attr "type"	"arith")
   (set_attr "mode"	"DI")
   (set (attr "length")	(if_then_else (match_operand:VOID 0 "m16_nsimm8_8" "")
				      (const_int 4)
				      (const_int 8)))])

(define_insn ""
  [(set (match_operand:DI 0 "register_operand" "=d")
	(minus:DI (reg:DI 29)
		  (match_operand:DI 1 "small_int" "I")))]
  "TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT || INTVAL (operands[2]) != -32768)"
  "daddu\\t%0,%$,%n1"
  [(set_attr "type"	"arith")
   (set_attr "mode"	"DI")
   (set (attr "length")	(if_then_else (match_operand:VOID 0 "m16_nuimm5_4" "")
				      (const_int 4)
				      (const_int 8)))])

(define_insn ""
  [(set (match_operand:DI 0 "register_operand" "=d,d,d")
	(minus:DI (match_operand:DI 1 "register_operand" "0,d,d")
		  (match_operand:DI 2 "arith_operand" "I,O,d")))]
  "TARGET_MIPS16
   && (GET_CODE (operands[2]) != CONST_INT
       || (INTVAL (operands[2]) != -32768 && INTVAL (operands[2]) != -0x4000))"
  "*
{
  if (REGNO (operands[0]) == REGNO (operands[1]))
    return \"dsubu\\t%0,%2\";
  return \"dsubu\\t%0,%1,%2\";
}"
  [(set_attr "type"	"arith")
   (set_attr "mode"	"DI")
   (set_attr_alternative "length"
		[(if_then_else (match_operand:VOID 2 "m16_nsimm5_1" "")
			       (const_int 4)
			       (const_int 8))
		 (if_then_else (match_operand:VOID 2 "m16_nsimm4_1" "")
			       (const_int 4)
			       (const_int 8))
		 (const_int 4)])])

;; On the mips16, we can sometimes split an add of a constant which is
;; a 4 byte instruction into two adds which are both 2 byte
;; instructions.  There are two cases: one where we are adding a
;; constant plus a register to another register, and one where we are
;; simply adding a constant to a register.

(define_split
  [(set (match_operand:DI 0 "register_operand" "")
	(minus:DI (match_dup 0)
		  (match_operand:DI 1 "const_int_operand" "")))]
  "TARGET_MIPS16 && TARGET_64BIT && reload_completed && !TARGET_DEBUG_D_MODE
   && GET_CODE (operands[0]) == REG
   && M16_REG_P (REGNO (operands[0]))
   && GET_CODE (operands[1]) == CONST_INT
   && ((INTVAL (operands[1]) > 0x10
	&& INTVAL (operands[1]) <= 0x10 + 0x10)
       || (INTVAL (operands[1]) < - 0xf
	   && INTVAL (operands[1]) >= - 0xf - 0xf))"
  [(set (match_dup 0) (minus:DI (match_dup 0) (match_dup 1)))
   (set (match_dup 0) (minus:DI (match_dup 0) (match_dup 2)))]
  "
{
  HOST_WIDE_INT val = INTVAL (operands[1]);

  if (val >= 0)