i386.h

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

{ 0xffffffff,0x1fffff }							\
}

/* The same information, inverted:
   Return the class number of the smallest class containing
   reg number REGNO.  This could be a conditional expression
   or could index an array.  */

#define REGNO_REG_CLASS(REGNO) (regclass_map[REGNO])

/* When defined, the compiler allows registers explicitly used in the
   rtl to be used as spill registers but prevents the compiler from
   extending the lifetime of these registers.  */

#define SMALL_REGISTER_CLASSES 1

#define QI_REG_P(X) \
  (REG_P (X) && REGNO (X) < 4)

#define GENERAL_REGNO_P(N) \
  ((N) < 8 || REX_INT_REGNO_P (N))

#define GENERAL_REG_P(X) \
  (REG_P (X) && GENERAL_REGNO_P (REGNO (X)))

#define ANY_QI_REG_P(X) (TARGET_64BIT ? GENERAL_REG_P(X) : QI_REG_P (X))

#define NON_QI_REG_P(X) \
  (REG_P (X) && REGNO (X) >= 4 && REGNO (X) < FIRST_PSEUDO_REGISTER)

#define REX_INT_REGNO_P(N) ((N) >= FIRST_REX_INT_REG && (N) <= LAST_REX_INT_REG)
#define REX_INT_REG_P(X) (REG_P (X) && REX_INT_REGNO_P (REGNO (X)))

#define FP_REG_P(X) (REG_P (X) && FP_REGNO_P (REGNO (X)))
#define FP_REGNO_P(N) ((N) >= FIRST_STACK_REG && (N) <= LAST_STACK_REG)
#define ANY_FP_REG_P(X) (REG_P (X) && ANY_FP_REGNO_P (REGNO (X)))
#define ANY_FP_REGNO_P(N) (FP_REGNO_P (N) || SSE_REGNO_P (N))

#define SSE_REGNO_P(N) \
  (((N) >= FIRST_SSE_REG && (N) <= LAST_SSE_REG) \
   || ((N) >= FIRST_REX_SSE_REG && (N) <= LAST_REX_SSE_REG))

#define SSE_REGNO(N) \
  ((N) < 8 ? FIRST_SSE_REG + (N) : FIRST_REX_SSE_REG + (N) - 8)
#define SSE_REG_P(N) (REG_P (N) && SSE_REGNO_P (REGNO (N)))

#define SSE_FLOAT_MODE_P(MODE) \
  ((TARGET_SSE && (MODE) == SFmode) || (TARGET_SSE2 && (MODE) == DFmode))

#define MMX_REGNO_P(N) ((N) >= FIRST_MMX_REG && (N) <= LAST_MMX_REG)
#define MMX_REG_P(XOP) (REG_P (XOP) && MMX_REGNO_P (REGNO (XOP)))

#define STACK_REG_P(XOP)		\
  (REG_P (XOP) &&		       	\
   REGNO (XOP) >= FIRST_STACK_REG &&	\
   REGNO (XOP) <= LAST_STACK_REG)

#define NON_STACK_REG_P(XOP) (REG_P (XOP) && ! STACK_REG_P (XOP))

#define STACK_TOP_P(XOP) (REG_P (XOP) && REGNO (XOP) == FIRST_STACK_REG)

#define CC_REG_P(X) (REG_P (X) && CC_REGNO_P (REGNO (X)))
#define CC_REGNO_P(X) ((X) == FLAGS_REG || (X) == FPSR_REG)

/* Indicate whether hard register numbered REG_NO should be converted
   to SSA form.  */
#define CONVERT_HARD_REGISTER_TO_SSA_P(REG_NO) \
  ((REG_NO) == FLAGS_REG || (REG_NO) == ARG_POINTER_REGNUM)

/* The class value for index registers, and the one for base regs.  */

#define INDEX_REG_CLASS INDEX_REGS
#define BASE_REG_CLASS GENERAL_REGS

/* Get reg_class from a letter such as appears in the machine description.  */

#define REG_CLASS_FROM_LETTER(C)	\
  ((C) == 'r' ? GENERAL_REGS :					\
   (C) == 'R' ? LEGACY_REGS :					\
   (C) == 'q' ? TARGET_64BIT ? GENERAL_REGS : Q_REGS :		\
   (C) == 'Q' ? Q_REGS :					\
   (C) == 'f' ? (TARGET_80387 || TARGET_FLOAT_RETURNS_IN_80387	\
		 ? FLOAT_REGS					\
		 : NO_REGS) :					\
   (C) == 't' ? (TARGET_80387 || TARGET_FLOAT_RETURNS_IN_80387	\
		 ? FP_TOP_REG					\
		 : NO_REGS) :					\
   (C) == 'u' ? (TARGET_80387 || TARGET_FLOAT_RETURNS_IN_80387	\
		 ? FP_SECOND_REG				\
		 : NO_REGS) :					\
   (C) == 'a' ? AREG :						\
   (C) == 'b' ? BREG :						\
   (C) == 'c' ? CREG :						\
   (C) == 'd' ? DREG :						\
   (C) == 'x' ? TARGET_SSE ? SSE_REGS : NO_REGS :		\
   (C) == 'Y' ? TARGET_SSE2? SSE_REGS : NO_REGS :		\
   (C) == 'y' ? TARGET_MMX ? MMX_REGS : NO_REGS :		\
   (C) == 'A' ? AD_REGS :					\
   (C) == 'D' ? DIREG :						\
   (C) == 'S' ? SIREG : NO_REGS)

/* The letters I, J, K, L and M in a register constraint string
   can be used to stand for particular ranges of immediate operands.
   This macro defines what the ranges are.
   C is the letter, and VALUE is a constant value.
   Return 1 if VALUE is in the range specified by C.

   I is for non-DImode shifts.
   J is for DImode shifts.
   K is for signed imm8 operands.
   L is for andsi as zero-extending move.
   M is for shifts that can be executed by the "lea" opcode.
   N is for immedaite operands for out/in instructions (0-255)
   */

#define CONST_OK_FOR_LETTER_P(VALUE, C)				\
  ((C) == 'I' ? (VALUE) >= 0 && (VALUE) <= 31			\
   : (C) == 'J' ? (VALUE) >= 0 && (VALUE) <= 63			\
   : (C) == 'K' ? (VALUE) >= -128 && (VALUE) <= 127		\
   : (C) == 'L' ? (VALUE) == 0xff || (VALUE) == 0xffff		\
   : (C) == 'M' ? (VALUE) >= 0 && (VALUE) <= 3			\
   : (C) == 'N' ? (VALUE) >= 0 && (VALUE) <= 255		\
   : 0)

/* Similar, but for floating constants, and defining letters G and H.
   Here VALUE is the CONST_DOUBLE rtx itself.  We allow constants even if
   TARGET_387 isn't set, because the stack register converter may need to
   load 0.0 into the function value register.  */

#define CONST_DOUBLE_OK_FOR_LETTER_P(VALUE, C)  \
  ((C) == 'G' ? standard_80387_constant_p (VALUE) \
   : 0)

/* A C expression that defines the optional machine-dependent
   constraint letters that can be used to segregate specific types of
   operands, usually memory references, for the target machine.  Any
   letter that is not elsewhere defined and not matched by
   `REG_CLASS_FROM_LETTER' may be used.  Normally this macro will not
   be defined.

   If it is required for a particular target machine, it should
   return 1 if VALUE corresponds to the operand type represented by
   the constraint letter C.  If C is not defined as an extra
   constraint, the value returned should be 0 regardless of VALUE.  */

#define EXTRA_CONSTRAINT(VALUE, D)				\
  ((D) == 'e' ? x86_64_sign_extended_value (VALUE)		\
   : (D) == 'Z' ? x86_64_zero_extended_value (VALUE)		\
   : (D) == 'C' ? standard_sse_constant_p (VALUE)		\
   : 0)

/* Place additional restrictions on the register class to use when it
   is necessary to be able to hold a value of mode MODE in a reload
   register for which class CLASS would ordinarily be used.  */

#define LIMIT_RELOAD_CLASS(MODE, CLASS) 			\
  ((MODE) == QImode && !TARGET_64BIT				\
   && ((CLASS) == ALL_REGS || (CLASS) == GENERAL_REGS		\
       || (CLASS) == LEGACY_REGS || (CLASS) == INDEX_REGS)	\
   ? Q_REGS : (CLASS))

/* Given an rtx X being reloaded into a reg required to be
   in class CLASS, return the class of reg to actually use.
   In general this is just CLASS; but on some machines
   in some cases it is preferable to use a more restrictive class.
   On the 80386 series, we prevent floating constants from being
   reloaded into floating registers (since no move-insn can do that)
   and we ensure that QImodes aren't reloaded into the esi or edi reg.  */

/* Put float CONST_DOUBLE in the constant pool instead of fp regs.
   QImode must go into class Q_REGS.
   Narrow ALL_REGS to GENERAL_REGS.  This supports allowing movsf and
   movdf to do mem-to-mem moves through integer regs.  */

#define PREFERRED_RELOAD_CLASS(X, CLASS) \
   ix86_preferred_reload_class ((X), (CLASS))

/* If we are copying between general and FP registers, we need a memory
   location. The same is true for SSE and MMX registers.  */
#define SECONDARY_MEMORY_NEEDED(CLASS1, CLASS2, MODE) \
  ix86_secondary_memory_needed ((CLASS1), (CLASS2), (MODE), 1)

/* QImode spills from non-QI registers need a scratch.  This does not
   happen often -- the only example so far requires an uninitialized
   pseudo.  */

#define SECONDARY_OUTPUT_RELOAD_CLASS(CLASS, MODE, OUT)			\
  (((CLASS) == GENERAL_REGS || (CLASS) == LEGACY_REGS			\
    || (CLASS) == INDEX_REGS) && !TARGET_64BIT && (MODE) == QImode	\
   ? Q_REGS : NO_REGS)

/* Return the maximum number of consecutive registers
   needed to represent mode MODE in a register of class CLASS.  */
/* On the 80386, this is the size of MODE in words,
   except in the FP regs, where a single reg is always enough.
   The TFmodes are really just 80bit values, so we use only 3 registers
   to hold them, instead of 4, as the size would suggest.
 */
#define CLASS_MAX_NREGS(CLASS, MODE)					\
 (!MAYBE_INTEGER_CLASS_P (CLASS)					\
  ? (COMPLEX_MODE_P (MODE) ? 2 : 1)					\
  : ((GET_MODE_SIZE ((MODE) == TFmode ? XFmode : (MODE))		\
     + UNITS_PER_WORD - 1) / UNITS_PER_WORD))

/* A C expression whose value is nonzero if pseudos that have been
   assigned to registers of class CLASS would likely be spilled
   because registers of CLASS are needed for spill registers.

   The default value of this macro returns 1 if CLASS has exactly one
   register and zero otherwise.  On most machines, this default
   should be used.  Only define this macro to some other expression
   if pseudo allocated by `local-alloc.c' end up in memory because
   their hard registers were needed for spill registers.  If this
   macro returns nonzero for those classes, those pseudos will only
   be allocated by `global.c', which knows how to reallocate the
   pseudo to another register.  If there would not be another
   register available for reallocation, you should not change the
   definition of this macro since the only effect of such a
   definition would be to slow down register allocation.  */

#define CLASS_LIKELY_SPILLED_P(CLASS)					\
  (((CLASS) == AREG)							\
   || ((CLASS) == DREG)							\
   || ((CLASS) == CREG)							\
   || ((CLASS) == BREG)							\
   || ((CLASS) == AD_REGS)						\
   || ((CLASS) == SIREG)						\
   || ((CLASS) == DIREG))

/* Return a class of registers that cannot change FROM mode to TO mode.
  
   x87 registers can't do subreg as all values are reformated to extended
   precision.  XMM registers does not support with nonzero offsets equal
   to 4, 8 and 12 otherwise valid for integer registers. Since we can't
   determine these, prohibit all nonparadoxical subregs changing size.  */

#define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS)	\
  (GET_MODE_SIZE (TO) < GET_MODE_SIZE (FROM)		\
   ? reg_classes_intersect_p (FLOAT_SSE_REGS, (CLASS))	\
     || MAYBE_MMX_CLASS_P (CLASS) 			\
   : GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO)		\
   ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)

/* A C statement that adds to CLOBBERS any hard regs the port wishes
   to automatically clobber for all asms.

   We do this in the new i386 backend to maintain source compatibility
   with the old cc0-based compiler.  */

#define MD_ASM_CLOBBERS(CLOBBERS)					\
  do {									\
    (CLOBBERS) = tree_cons (NULL_TREE, build_string (5, "flags"),	\
			    (CLOBBERS));				\
    (CLOBBERS) = tree_cons (NULL_TREE, build_string (4, "fpsr"),	\
			    (CLOBBERS));				\
    (CLOBBERS) = tree_cons (NULL_TREE, build_string (7, "dirflag"),	\
			    (CLOBBERS));				\
  } while (0)

/* Stack layout; function entry, exit and calling.  */

/* Define this if pushing a word on the stack
   makes the stack pointer a smaller address.  */
#define STACK_GROWS_DOWNWARD

/* Define this if the nominal address of the stack frame
   is at the high-address end of the local variables;
   that is, each additional local variable allocated
   goes at a more negative offset in the frame.  */
#define FRAME_GROWS_DOWNWARD

/* Offset within stack frame to start allocating local variables at.
   If FRAME_GROWS_DOWNWARD, this is the offset to the END of the
   first local allocated.  Otherwise, it is the offset to the BEGINNING
   of the first local allocated.  */
#define STARTING_FRAME_OFFSET 0

/* If we generate an insn to push BYTES bytes,
   this says how many the stack pointer really advances by.
   On 386 pushw decrements by exactly 2 no matter what the position was.
   On the 386 there is no pushb; we use pushw instead, and this
   has the effect of rounding up to 2.

   For 64bit ABI we round up to 8 bytes.
 */

#define PUSH_ROUNDING(BYTES) \
  (TARGET_64BIT		     \
   ? (((BYTES) + 7) & (-8))  \
   : (((BYTES) + 1) & (-2)))

/* If defined, the maximum amount of space required for outgoing arguments will
   be computed and placed into the variable
   `current_function_outgoing_args_size'.  No space will be pushed onto the
   stack for each call; instead, the function prologue should increase the stack
   frame size by this amount.  */

#define ACCUMULATE_OUTGOING_ARGS TARGET_ACCUMULATE_OUTGOING_ARGS

/* If defined, a C expression whose value is nonzero when we want to use PUSH
   instructions to pass outgoing arguments.  */

#define PUSH_ARGS (TARGET_PUSH_ARGS && !ACCUMULATE_OUTGOING_ARGS)

/* We want the stack and args grow in opposite directions, even if
   PUSH_ARGS is 0.  */
#define PUSH_ARGS_REVERSED 1

/* Offset of first parameter from the argument pointer register value.  */
#define FIRST_PARM_OFFSET(FNDECL) 0

/* Define this macro if functions should assume that stack space has been
   allocated for arguments even when their values are passed in registers.

   The value of this macro is the size, in bytes, of the area reserved for
   arguments passed in registers for the function represented by FNDECL.

   This space can be allocated by the caller, or be a part of the
   machine-dependent stack frame: `OUTGOING_REG_PARM_STACK_SPACE' says
   which.  */
#define REG_PARM_STACK_SPACE(FNDECL) 0

/* Define as a C expression that evaluates to nonzero if we