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File: gccint.info,  Node: Addressing Modes,  Next: Condition Code,  Prev: Library Calls,  Up: Target Macros

Addressing Modes
================

   This is about addressing modes.

`HAVE_PRE_INCREMENT'
`HAVE_PRE_DECREMENT'
`HAVE_POST_INCREMENT'
`HAVE_POST_DECREMENT'
     A C expression that is nonzero if the machine supports
     pre-increment, pre-decrement, post-increment, or post-decrement
     addressing respectively.

`HAVE_PRE_MODIFY_DISP'
`HAVE_POST_MODIFY_DISP'
     A C expression that is nonzero if the machine supports pre- or
     post-address side-effect generation involving constants other than
     the size of the memory operand.

`HAVE_PRE_MODIFY_REG'
`HAVE_POST_MODIFY_REG'
     A C expression that is nonzero if the machine supports pre- or
     post-address side-effect generation involving a register
     displacement.

`CONSTANT_ADDRESS_P (X)'
     A C expression that is 1 if the RTX X is a constant which is a
     valid address.  On most machines, this can be defined as
     `CONSTANT_P (X)', but a few machines are more restrictive in which
     constant addresses are supported.

     `CONSTANT_P' accepts integer-values expressions whose values are
     not explicitly known, such as `symbol_ref', `label_ref', and
     `high' expressions and `const' arithmetic expressions, in addition
     to `const_int' and `const_double' expressions.

`MAX_REGS_PER_ADDRESS'
     A number, the maximum number of registers that can appear in a
     valid memory address.  Note that it is up to you to specify a
     value equal to the maximum number that `GO_IF_LEGITIMATE_ADDRESS'
     would ever accept.

`GO_IF_LEGITIMATE_ADDRESS (MODE, X, LABEL)'
     A C compound statement with a conditional `goto LABEL;' executed
     if X (an RTX) is a legitimate memory address on the target machine
     for a memory operand of mode MODE.

     It usually pays to define several simpler macros to serve as
     subroutines for this one.  Otherwise it may be too complicated to
     understand.

     This macro must exist in two variants: a strict variant and a
     non-strict one.  The strict variant is used in the reload pass.  It
     must be defined so that any pseudo-register that has not been
     allocated a hard register is considered a memory reference.  In
     contexts where some kind of register is required, a pseudo-register
     with no hard register must be rejected.

     The non-strict variant is used in other passes.  It must be
     defined to accept all pseudo-registers in every context where some
     kind of register is required.

     Compiler source files that want to use the strict variant of this
     macro define the macro `REG_OK_STRICT'.  You should use an `#ifdef
     REG_OK_STRICT' conditional to define the strict variant in that
     case and the non-strict variant otherwise.

     Subroutines to check for acceptable registers for various purposes
     (one for base registers, one for index registers, and so on) are
     typically among the subroutines used to define
     `GO_IF_LEGITIMATE_ADDRESS'.  Then only these subroutine macros
     need have two variants; the higher levels of macros may be the
     same whether strict or not.

     Normally, constant addresses which are the sum of a `symbol_ref'
     and an integer are stored inside a `const' RTX to mark them as
     constant.  Therefore, there is no need to recognize such sums
     specifically as legitimate addresses.  Normally you would simply
     recognize any `const' as legitimate.

     Usually `PRINT_OPERAND_ADDRESS' is not prepared to handle constant
     sums that are not marked with  `const'.  It assumes that a naked
     `plus' indicates indexing.  If so, then you _must_ reject such
     naked constant sums as illegitimate addresses, so that none of
     them will be given to `PRINT_OPERAND_ADDRESS'.

     On some machines, whether a symbolic address is legitimate depends
     on the section that the address refers to.  On these machines,
     define the macro `ENCODE_SECTION_INFO' to store the information
     into the `symbol_ref', and then check for it here.  When you see a
     `const', you will have to look inside it to find the `symbol_ref'
     in order to determine the section.  *Note Assembler Format::.

     The best way to modify the name string is by adding text to the
     beginning, with suitable punctuation to prevent any ambiguity.
     Allocate the new name in `saveable_obstack'.  You will have to
     modify `ASM_OUTPUT_LABELREF' to remove and decode the added text
     and output the name accordingly, and define `STRIP_NAME_ENCODING'
     to access the original name string.

     You can check the information stored here into the `symbol_ref' in
     the definitions of the macros `GO_IF_LEGITIMATE_ADDRESS' and
     `PRINT_OPERAND_ADDRESS'.

`REG_OK_FOR_BASE_P (X)'
     A C expression that is nonzero if X (assumed to be a `reg' RTX) is
     valid for use as a base register.  For hard registers, it should
     always accept those which the hardware permits and reject the
     others.  Whether the macro accepts or rejects pseudo registers
     must be controlled by `REG_OK_STRICT' as described above.  This
     usually requires two variant definitions, of which `REG_OK_STRICT'
     controls the one actually used.

`REG_MODE_OK_FOR_BASE_P (X, MODE)'
     A C expression that is just like `REG_OK_FOR_BASE_P', except that
     that expression may examine the mode of the memory reference in
     MODE.  You should define this macro if the mode of the memory
     reference affects whether a register may be used as a base
     register.  If you define this macro, the compiler will use it
     instead of `REG_OK_FOR_BASE_P'.

`REG_OK_FOR_INDEX_P (X)'
     A C expression that is nonzero if X (assumed to be a `reg' RTX) is
     valid for use as an index register.

     The difference between an index register and a base register is
     that the index register may be scaled.  If an address involves the
     sum of two registers, neither one of them scaled, then either one
     may be labeled the "base" and the other the "index"; but whichever
     labeling is used must fit the machine's constraints of which
     registers may serve in each capacity.  The compiler will try both
     labelings, looking for one that is valid, and will reload one or
     both registers only if neither labeling works.

`FIND_BASE_TERM (X)'
     A C expression to determine the base term of address X.  This
     macro is used in only one place: `find_base_term' in alias.c.

     It is always safe for this macro to not be defined.  It exists so
     that alias analysis can understand machine-dependent addresses.

     The typical use of this macro is to handle addresses containing a
     label_ref or symbol_ref within an UNSPEC.

`LEGITIMIZE_ADDRESS (X, OLDX, MODE, WIN)'
     A C compound statement that attempts to replace X with a valid
     memory address for an operand of mode MODE.  WIN will be a C
     statement label elsewhere in the code; the macro definition may use

          GO_IF_LEGITIMATE_ADDRESS (MODE, X, WIN);

     to avoid further processing if the address has become legitimate.

     X will always be the result of a call to `break_out_memory_refs',
     and OLDX will be the operand that was given to that function to
     produce X.

     The code generated by this macro should not alter the substructure
     of X.  If it transforms X into a more legitimate form, it should
     assign X (which will always be a C variable) a new value.

     It is not necessary for this macro to come up with a legitimate
     address.  The compiler has standard ways of doing so in all cases.
     In fact, it is safe for this macro to do nothing.  But often a
     machine-dependent strategy can generate better code.

`LEGITIMIZE_RELOAD_ADDRESS (X, MODE, OPNUM, TYPE, IND_LEVELS, WIN)'
     A C compound statement that attempts to replace X, which is an
     address that needs reloading, with a valid memory address for an
     operand of mode MODE.  WIN will be a C statement label elsewhere
     in the code.  It is not necessary to define this macro, but it
     might be useful for performance reasons.

     For example, on the i386, it is sometimes possible to use a single
     reload register instead of two by reloading a sum of two pseudo
     registers into a register.  On the other hand, for number of RISC
     processors offsets are limited so that often an intermediate
     address needs to be generated in order to address a stack slot.
     By defining `LEGITIMIZE_RELOAD_ADDRESS' appropriately, the
     intermediate addresses generated for adjacent some stack slots can
     be made identical, and thus be shared.

     _Note_: This macro should be used with caution.  It is necessary
     to know something of how reload works in order to effectively use
     this, and it is quite easy to produce macros that build in too
     much knowledge of reload internals.

     _Note_: This macro must be able to reload an address created by a
     previous invocation of this macro.  If it fails to handle such
     addresses then the compiler may generate incorrect code or abort.

     The macro definition should use `push_reload' to indicate parts
     that need reloading; OPNUM, TYPE and IND_LEVELS are usually
     suitable to be passed unaltered to `push_reload'.

     The code generated by this macro must not alter the substructure of
     X.  If it transforms X into a more legitimate form, it should
     assign X (which will always be a C variable) a new value.  This
     also applies to parts that you change indirectly by calling
     `push_reload'.

     The macro definition may use `strict_memory_address_p' to test if
     the address has become legitimate.

     If you want to change only a part of X, one standard way of doing
     this is to use `copy_rtx'.  Note, however, that is unshares only a
     single level of rtl.  Thus, if the part to be changed is not at the
     top level, you'll need to replace first the top level.  It is not
     necessary for this macro to come up with a legitimate address;
     but often a machine-dependent strategy can generate better code.

`GO_IF_MODE_DEPENDENT_ADDRESS (ADDR, LABEL)'
     A C statement or compound statement with a conditional `goto
     LABEL;' executed if memory address X (an RTX) can have different
     meanings depending on the machine mode of the memory reference it
     is used for or if the address is valid for some modes but not
     others.

     Autoincrement and autodecrement addresses typically have
     mode-dependent effects because the amount of the increment or
     decrement is the size of the operand being addressed.  Some
     machines have other mode-dependent addresses.  Many RISC machines
     have no mode-dependent addresses.

     You may assume that ADDR is a valid address for the machine.

`LEGITIMATE_CONSTANT_P (X)'
     A C expression that is nonzero if X is a legitimate constant for
     an immediate operand on the target machine.  You can assume that X
     satisfies `CONSTANT_P', so you need not check this.  In fact, `1'
     is a suitable definition for this macro on machines where anything
     `CONSTANT_P' is valid.


File: gccint.info,  Node: Condition Code,  Next: Costs,  Prev: Addressing Modes,  Up: Target Macros

Condition Code Status
=====================

   This describes the condition code status.

   The file `conditions.h' defines a variable `cc_status' to describe
how the condition code was computed (in case the interpretation of the
condition code depends on the instruction that it was set by).  This
variable contains the RTL expressions on which the condition code is
currently based, and several standard flags.

   Sometimes additional machine-specific flags must be defined in the
machine description header file.  It can also add additional
machine-specific information by defining `CC_STATUS_MDEP'.

`CC_STATUS_MDEP'
     C code for a data type which is used for declaring the `mdep'
     component of `cc_status'.  It defaults to `int'.

     This macro is not used on machines that do not use `cc0'.

`CC_STATUS_MDEP_INIT'
     A C expression to initialize the `mdep' field to "empty".  The
     default definition does nothing, since most machines don't use the
     field anyway.  If you want to use the field, you should probably
     define this macro to initialize it.

     This macro is not used on machines that do not use `cc0'.

`NOTICE_UPDATE_CC (EXP, INSN)'
     A C compound statement to set the components of `cc_status'
     appropriately for an insn INSN whose body is EXP.  It is this
     macro's responsibility to recognize insns that set the condition
     code as a byproduct of other activity as well as those that
     explicitly set `(cc0)'.

     This macro is not used on machines that do not use `cc0'.

     If there are insns that do not set the condition code but do alter
     other machine registers, this macro must check to see whether they
     invalidate the expressions that the condition code is recorded as
     reflecting.  For example, on the 68000, insns that store in address
     registers do not set the condition code, which means that usually
     `NOTICE_UPDATE_CC' can leave `cc_status' unaltered for such insns.
     But suppose that the previous insn set the condition code based
     on location `a4@(102)' and the current insn stores a new value in
     `a4'.  Although the condition code is not changed by this, it will
     no longer be true that it reflects the contents of `a4@(102)'.
     Therefore, `NOTICE_UPDATE_CC' must alter `cc_status' in this case
     to say that nothing is known about the condition code value.

     The definition of `NOTICE_UPDATE_CC' must be prepared to deal with
     the results of peephole optimization: insns whose patterns are
     `parallel' RTXs containing various `reg', `mem' or constants which
     are just the operands.  The RTL structure of these insns is not
     sufficient to indicate what the insns actually do.  What
     `NOTICE_UPDATE_CC' should do when it sees one is just to run
     `CC_STATUS_INIT'.

     A possible definition of `NOTICE_UPDATE_CC' is to call a function
     that looks at an attribute (*note Insn Attributes::) named, for
     example, `cc'.  This avoids having detailed information about
     patterns in two places, the `md' file and in `NOTICE_UPDATE_CC'.

`EXTRA_CC_MODES'
     A list of additional modes for condition code values in registers
     (*note Jump Patterns::).  This macro should expand to a sequence of
     calls of the macro `CC' separated by white space.  `CC' takes two
     arguments.  The first is the enumeration name of the mode, which
     should begin with `CC' and end with `mode'.  The second is a C
     string giving the printable name of the mode; it should be the
     same as the first argument, but with the trailing `mode' removed.

     You should only define this macro if additional modes are required.

     A sample definition of `EXTRA_CC_MODES' is:
          #define EXTRA_CC_MODES            \
              CC(CC_NOOVmode, "CC_NOOV")    \
              CC(CCFPmode, "CCFP")          \
              CC(CCFPEmode, "CCFPE")

`SELECT_CC_MODE (OP, X, Y)'
     Returns a mode from class `MODE_CC' to be used when comparison
     operation code OP is applied to rtx X and Y.  For example, on the
     Sparc, `SELECT_CC_MODE' is defined as (see *note Jump Patterns::
     for a description of the reason for this definition)

          #define SELECT_CC_MODE(OP,X,Y) \
            (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT          \
             ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode)    \
             : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS    \
                 || GET_CODE (X) == NEG) \
                ? CC_NOOVmode : CCmode))

     You need not define this macro if `EXTRA_CC_MODES' is not defined.

`CANONICALIZE_COMPARISON (CODE, OP0, OP1)'
     On some machines not all possible comparisons are defined, but you
     can convert an invalid comparison into a valid one.  For example,
     the Alpha does not have a `GT' comparison, but you can use an `LT'
     comparison instead and swap the order of the operands.

     On such machines, define this macro to be a C statement to do any
     required conversions.  CODE is the initial comparison code and OP0
     and OP1 are the left and right operands of the comparison,
     respectively.  You should modify CODE, OP0, and OP1 as required.

     GCC will not assume that the comparison resulting from this macro
     is valid but will see if the resulting insn matches a pattern in
     the `md' file.

     You need not define this macro if it would never change the
     comparison code or operands.

`REVERSIBLE_CC_MODE (MODE)'
     A C expression whose value is one if it is always safe to reverse a
     comparison whose mode is MODE.  If `SELECT_CC_MODE' can ever
     return MODE for a floating-point inequality comparison, then
     `REVERSIBLE_CC_MODE (MODE)' must be zero.

     You need not define this macro if it would always returns zero or
     if the floating-point format is anything other than
     `IEEE_FLOAT_FORMAT'.  For example, here is the definition used on
     the Sparc, where floating-point inequality comparisons are always
     given `CCFPEmode':

          #define REVERSIBLE_CC_MODE(MODE)  ((MODE) != CCFPEmode)

     A C expression whose value is reversed condition code of the CODE
     for comparison done in CC_MODE MODE.  The macro is used only in
     case `REVERSIBLE_CC_MODE (MODE)' is nonzero.  Define this macro in
     case machine has some non-standard way how to reverse certain
     conditionals.  For instance in case all floating point conditions
     are non-trapping, compiler may freely convert unordered compares
     to ordered one.  Then definition may look like:

          #define REVERSE_CONDITION(CODE, MODE) \
             ((MODE) != CCFPmode ? reverse_condition (CODE) \
              : reverse_condition_maybe_unordered (CODE))

`REVERSE_CONDEXEC_PREDICATES_P (CODE1, CODE2)'
     A C expression that returns true if the conditional execution
     predicate CODE1 is the inverse of CODE2 and vice versa.  Define
     this to return 0 if the target has conditional execution
     predicates that cannot be reversed safely.  If no expansion is
     specified, this macro is defined as follows:

          #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
             ((x) == reverse_condition (y))



File: gccint.info,  Node: Costs,  Next: Scheduling,  Prev: Condition Code,  Up: Target Macros

Describing Relative Costs of Operations
=======================================

   These macros let you describe the relative speed of various
operations on the target machine.

`CONST_COSTS (X, CODE, OUTER_CODE)'
     A part of a C `switch' statement that describes the relative costs
     of constant RTL expressions.  It must contain `case' labels for
     expression codes `const_int', `const', `symbol_ref', `label_ref'
     and `const_double'.  Each case must ultimately reach a `return'
     statement to return the relative cost of the use of that kind of
     constant value in an expression.  The cost may depend on the
     precise value of the constant, which is available for examination
     in X, and the rtx code of the expression in which it is contained,
     found in OUTER_CODE.

     CODE is the expression code--redundant, since it can be obtained
     with `GET_CODE (X)'.

`RTX_COSTS (X, CODE, OUTER_CODE)'
     Like `CONST_COSTS' but applies to nonconstant RTL expressions.
     This can be used, for example, to indicate how costly a multiply
     instruction is.  In writing this macro, you can use the construct
     `COSTS_N_INSNS (N)' to specify a cost equal to N fast
     instructions.  OUTER_CODE is the code of the expression in which X
     is contained.

     This macro is optional; do not define it if the default cost
     assumptions are adequate for the target machine.

`DEFAULT_RTX_COSTS (X, CODE, OUTER_CODE)'
     This macro, if defined, is called for any case not handled by the
     `RTX_COSTS' or `CONST_COSTS' macros.  This eliminates the need to
     put case labels into the macro, but the code, or any functions it
     calls, must assume that the RTL in X could be of any type that has
     not already been handled.  The arguments are the same as for
     `RTX_COSTS', and the macro should execute a return statement giving
     the cost of any RTL expressions that it can handle.  The default
     cost calculation is used for any RTL for which this macro does not
     return a value.

     This macro is optional; do not define it if the default cost
     assumptions are adequate for the target machine.

`ADDRESS_COST (ADDRESS)'
     An expression giving the cost of an addressing mode that contains
     ADDRESS.  If not defined, the cost is computed from the ADDRESS
     expression and the `CONST_COSTS' values.

     For most CISC machines, the default cost is a good approximation
     of the true cost of the addressing mode.  However, on RISC
     machines, all instructions normally have the same length and
     execution time.  Hence all addresses will have equal costs.

     In cases where more than one form of an address is known, the form
     with the lowest cost will be used.  If multiple forms have the
     same, lowest, cost, the one that is the most complex will be used.

     For example, suppose an address that is equal to the sum of a
     register and a constant is used twice in the same basic block.
     When this macro is not defined, the address will be computed in a
     register and memory references will be indirect through that
     register.  On machines where the cost of the addressing mode
     containing the sum is no higher than that of a simple indirect
     reference, this will produce an additional instruction and
     possibly require an additional register.  Proper specification of
     this macro eliminates this overhead for such machines.

     Similar use of this macro is made in strength reduction of loops.

     ADDRESS need not be valid as an address.  In such a case, the cost
     is not relevant and can be any value; invalid addresses need not be
     assigned a different cost.

     On machines where an address involving more than one register is as
     cheap as an address computation involving only one register,
     defining `ADDRESS_COST' to reflect this can cause two registers to
     be live over a region of code where only one would have been if
     `ADDRESS_COST' were not defined in that manner.  This effect should
     be considered in the definition of this macro.  Equivalent costs
     should probably only be given to addresses with different numbers
     of registers on machines with lots of registers.

     This macro will normally either not be defined or be defined as a
     constant.

`REGISTER_MOVE_COST (MODE, FROM, TO)'
     A C expression for the cost of moving data of mode MODE from a
     register in class FROM to one in class TO.  The classes are
     expressed using the enumeration values such as `GENERAL_REGS'.  A
     value of 2 is the default; other values are interpreted relative to
     that.

     It is not required that the cost always equal 2 when FROM is the
     same as TO; on some machines it is expensive to move between
     registers if they are not general registers.

     If reload sees an insn consisting of a single `set' between two
     hard registers, and if `REGISTER_MOVE_COST' applied to their
     classes returns a value of 2, reload does not check to ensure that
     the constraints of the insn are met.  Setting a cost of other than
     2 will allow reload to verify that the constraints are met.  You
     should do this if the `movM' pattern's constraints do not allow
     such copying.

`MEMORY_MOVE_COST (MODE, CLASS, IN)'
     A C expression for the cost of moving data of mode MODE between a
     register of class CLASS and memory; IN is zero if the value is to
     be written to memory, nonzero if it is to be read in.  This cost
     is relative to those in `REGISTER_MOVE_COST'.  If moving between
     registers and memory is more expensive than between two registers,
     you should define this macro to express the relative cost.

     If you do not define this macro, GCC uses a default cost of 4 plus
     the cost of copying via a secondary reload register, if one is
     needed.  If your machine requires a secondary reload register to
     copy between memory and a register of CLASS but the reload
     mechanism is more complex than copying via an intermediate, define
     this macro to reflect the actual cost of the move.

     GCC defines the function `memory_move_secondary_cost' if secondary
     reloads are needed.  It computes the costs due to copying via a
     secondary register.  If your machine copies from memory using a
     secondary register in the conventional way but the default base
     value of 4 is not correct for your machine, define this macro to
     add some other value to the result of that function.  The
     arguments to that function are the same as to this macro.

`BRANCH_COST'
     A C expression for the cost of a branch instruction.  A value of 1
     is the default; other values are interpreted relative to that.

   Here are additional macros which do not specify precise relative
costs, but only that certain actions are more expensive than GCC would
ordinarily expect.

`SLOW_BYTE_ACCESS'
     Define this macro as a C expression which is nonzero if accessing
     less than a word of memory (i.e. a `char' or a `short') is no
     faster than accessing a word of memory, i.e., if such access
     require more than one instruction or if there is no difference in
     cost between byte and (aligned) word loads.

     When this macro is not defined, the compiler will access a field by
     finding the smallest containing object; when it is defined, a
     fullword load will be used if alignment permits.  Unless bytes
     accesses are faster than word accesses, using word accesses is
     preferable since it may eliminate subsequent memory access if
     subsequent accesses occur to other fields in the same word of the
     structure, but to different bytes.

`SLOW_UNALIGNED_ACCESS (MODE, ALIGNMENT)'
     Define this macro to be the value 1 if memory accesses described
     by the MODE and ALIGNMENT parameters have a cost many times greater
     than aligned accesses, for example if they are emulated in a trap
     handler.

     When this macro is nonzero, the compiler will act as if
     `STRICT_ALIGNMENT' were nonzero when generating code for block
     moves.  This can cause significantly more instructions to be
     produced.  Therefore, do not set this macro nonzero if unaligned
     accesses only add a cycle or two to the time for a memory access.

     If the value of this macro is always zero, it need not be defined.
     If this macro is defined, it should produce a nonzero value when
     `STRICT_ALIGNMENT' is nonzero.

`DONT_REDUCE_ADDR'
     Define this macro to inhibit strength reduction of memory
     addresses.  (On some machines, such strength reduction seems to do
     harm rather than good.)

`MOVE_RATIO'
     The threshold of number of scalar memory-to-memory move insns,
     _below_ which a sequence of insns should be generated instead of a
     string move insn or a library call.  Increasing the value will
     always make code faster, but eventually incurs high cost in
     increased code size.

     Note that on machines where the corresponding move insn is a
     `define_expand' that emits a sequence of insns, this macro counts
     the number of such sequences.

     If you don't define this, a reasonable default is used.

`MOVE_BY_PIECES_P (SIZE, ALIGNMENT)'
     A C expression used to determine whether `move_by_pieces' will be
     used to copy a chunk of memory, or whether some other block move
     mechanism will be used.  Defaults to 1 if `move_by_pieces_ninsns'
     returns less than `MOVE_RATIO'.

`MOVE_MAX_PIECES'
     A C expression used by `move_by_pieces' to determine the largest
     unit a load or store used to copy memory is.  Defaults to
     `MOVE_MAX'.

`USE_LOAD_POST_INCREMENT (MODE)'
     A C expression used to determine whether a load postincrement is a
     good thing to use for a given mode.  Defaults to the value of
     `HAVE_POST_INCREMENT'.

`USE_LOAD_POST_DECREMENT (MODE)'
     A C expression used to determine whether a load postdecrement is a
     good thing to use for a given mode.  Defaults to the value of
     `HAVE_POST_DECREMENT'.

`USE_LOAD_PRE_INCREMENT (MODE)'
     A C expression used to determine whether a load preincrement is a
     good thing to use for a given mode.  Defaults to the value of
     `HAVE_PRE_INCREMENT'.

`USE_LOAD_PRE_DECREMENT (MODE)'
     A C expression used to determine whether a load predecrement is a
     good thing to use for a given mode.  Defaults to the value of
     `HAVE_PRE_DECREMENT'.

`USE_STORE_POST_INCREMENT (MODE)'
     A C expression used to determine whether a store postincrement is
     a good thing to use for a given mode.  Defaults to the value of
     `HAVE_POST_INCREMENT'.

`USE_STORE_POST_DECREMENT (MODE)'
     A C expression used to determine whether a store postdecrement is
     a good thing to use for a given mode.  Defaults to the value of
     `HAVE_POST_DECREMENT'.

`USE_STORE_PRE_INCREMENT (MODE)'
     This macro is used to determine whether a store preincrement is a
     good thing to use for a given mode.  Defaults to the value of
     `HAVE_PRE_INCREMENT'.

`USE_STORE_PRE_DECREMENT (MODE)'
     This macro is used to determine whether a store predecrement is a
     good thing to use for a given mode.  Defaults to the value of
     `HAVE_PRE_DECREMENT'.

`NO_FUNCTION_CSE'
     Define this macro if it is as good or better to call a constant
     function address than to call an address kept in a register.

`NO_RECURSIVE_FUNCTION_CSE'
     Define this macro if it is as good or better for a function to call
     itself with an explicit address than to call an address kept in a
     register.


File: gccint.info,  Node: Scheduling,  Next: Sections,  Prev: Costs,  Up: Target Macros

Adjusting the Instruction Scheduler
===================================

   The instruction scheduler may need a fair amount of machine-specific
adjustment in order to produce good code.  GCC provides several target
hooks for this purpose.  It is usually enough to define just a few of
them: try the first ones in this list first.

 - Target Hook: int TARGET_SCHED_ISSUE_RATE (void)
     This hook returns the maximum number of instructions that can ever
     issue at the same time on the target machine.  The default is one.
     This value must be constant over the entire compilation.  If you
     need it to vary depending on what the instructions are, you must
     use `TARGET_SCHED_VARIABLE_ISSUE'.

 - Target Hook: int TARGET_SCHED_VARIABLE_ISSUE (FILE *FILE, int
          VERBOSE, rtx INSN, int MORE)
     This hook is executed by the scheduler after it has scheduled an
     insn from the ready list.  It should return the number of insns
     which can still be issued in the current cycle.  Normally this is
     `MORE - 1'.  You should define this hook if some insns take more
     machine resources than others, so that fewer insns can follow them
     in the same cycle.  FILE is either a null pointer, or a stdio
     stream to write any debug output to.  VERBOSE is the verbose level
     provided by `-fsched-verbose-N'.  INSN is the instruction that was
     scheduled.

 - Target Hook: int TARGET_SCHED_ADJUST_COST (rtx INSN, rtx LINK, rtx
          DEP_INSN, int COST)
     This function corrects the value of COST based on the relationship
     between INSN and DEP_INSN through the dependence LINK.  It should
     return the new value.  The default is to make no adjustment to
     COST.  This can be used for example to specify to the scheduler
     that an output- or anti-dependence does not incur the same cost as
     a data-dependence.

 - Target Hook: int TARGET_SCHED_ADJUST_PRIORITY (rtx INSN, int
          PRIORITY)
     This hook adjusts the integer scheduling priority PRIORITY of
     INSN.  It should return the new priority.  Reduce the priority to
     execute INSN earlier, increase the priority to execute INSN later.
     Do not define this hook if you do not need to adjust the
     scheduling priorities of insns.

 - Target Hook: int TARGET_SCHED_REORDER (FILE *FILE, int VERBOSE, rtx
          *READY, int *N_READYP, int CLOCK)
     This hook is executed by the scheduler after it has scheduled the
     ready list, to allow the machine description to reorder it (for
     example to combine two small instructions together on `VLIW'
     machines).  FILE is either a null pointer, or a stdio stream to
     write any debug output to.  VERBOSE is the verbose level provided
     by `-fsched-verbose-N'.  READY is a pointer to the ready list of
     instructions that are ready to be scheduled.  N_READYP is a
     pointer to the number of elements in the ready list.  The scheduler
     reads the ready list in reverse order, starting with
     READY[*N_READYP-1] and going to READY[0].  CLOCK is the timer tick
     of the scheduler.  You may modify the ready list and the number of
     ready insns.  The return value is the number of insns that can
     issue this cycle; normally this is just `issue_rate'.  See also
     `TARGET_SCHED_REORDER2'.

 - Target Hook: int TARGET_SCHED_REORDER2 (FILE *FILE, int VERBOSE, rtx
          *READY, int *N_READY, CLOCK)
     Like `TARGET_SCHED_REORDER', but called at a different time.  That
     function is called whenever the scheduler starts a new cycle.
     This one is called once per iteration over a cycle, immediately
     after `TARGET_SCHED_VARIABLE_ISSUE'; it can reorder the ready list
     and return the number of insns to be scheduled in the same cycle.
     Defining this hook can be useful if there are frequent situations
     where scheduling one insn causes other insns to become ready in
     the same cycle.  These other insns can then be taken into account
     properly.

 - Target Hook: void TARGET_SCHED_INIT (FILE *FILE, int VERBOSE, int
          MAX_READY)
     This hook is executed by the scheduler at the beginning of each
     block of instructions that are to be scheduled.  FILE is either a
     null pointer, or a stdio stream to write any debug output to.
     VERBOSE is the verbose level provided by `-fsched-verbose-N'.
     MAX_READY is the maximum number of insns in the current scheduling
     region that can be live at the same time.  This can be used to
     allocate scratch space if it is needed, e.g. by
     `TARGET_SCHED_REORDER'.

 - Target Hook: void TARGET_SCHED_FINISH (FILE *FILE, int VERBOSE)
     This hook is executed by the scheduler at the end of each block of
     instructions that are to be scheduled.  It can be used to perform
     cleanup of any actions done by the other scheduling hooks.  FILE
     is either a null pointer, or a stdio stream to write any debug
     output to.  VERBOSE is the verbose level provided by
     `-fsched-verbose-N'.

 - Target Hook: rtx TARGET_SCHED_CYCLE_DISPLAY (int CLOCK, rtx LAST)
     This hook is called in verbose mode only, at the beginning of each
     pass over a basic block.  It should insert an insn into the chain
     after LAST, which has no effect, but records the value CLOCK in
     RTL dumps and assembly output.  Define this hook only if you need
     this level of detail about what the scheduler is doing.


File: gccint.info,  Node: Sections,  Next: PIC,  Prev: Scheduling,  Up: Target Macros

Dividing the Output into Sections (Texts, Data, ...)
====================================================

   An object file is divided into sections containing different types of
data.  In the most common case, there are three sections: the "text
section", which holds instructions and read-only data; the "data
section", which holds initialized writable data; and the "bss section",
which holds uninitialized data.  Some systems have other kinds of
sections.

   The compiler must tell the assembler when to switch sections.  These
macros control what commands to output to tell the assembler this.  You
can also define additional sections.

`TEXT_SECTION_ASM_OP'
     A C expression whose value is a string, including spacing,
     containing the assembler operation that should precede
     instructions and read-only data.  Normally `"\t.text"' is right.

`TEXT_SECTION'
     A C statement that switches to the default section containing
     instructions.  Normally this is not needed, as simply defining
     `TEXT_SECTION_ASM_OP' is enough.  The MIPS port uses this to sort
     all functions after all data declarations.

`DATA_SECTION_ASM_OP'
     A C expression whose value is a string, including spacing,
     containing the assembler operation to identify the following data
     as writable initialized data.  Normally `"\t.data"' is right.

`SHARED_SECTION_ASM_OP'
     If defined, a C expression whose value is a string, including
     spacing, containing the assembler operation to identify the
     following data as shared data.  If not defined,
     `DATA_SECTION_ASM_OP' will be used.

`BSS_SECTION_ASM_OP'
     If defined, a C expression whose value is a string, including
     spacing, containing the assembler operation to identify the
     following data as uninitialized global data.  If not defined, and
     neither `ASM_OUTPUT_BSS' nor `ASM_OUTPUT_ALIGNED_BSS' are defined,
     uninitialized global data will be output in the data section if
     `-fno-common' is passed, otherwise `ASM_OUTPUT_COMMON' will be
     used.

`SHARED_BSS_SECTION_ASM_OP'
     If defined, a C expression whose value is a string, including
     spacing, containing the assembler operation to identify the
     following data as uninitialized global shared data.  If not
     defined, and `BSS_SECTION_ASM_OP' is, the latter will be used.

`INIT_SECTION_ASM_OP'
     If defined, a C expression whose value is a string, including
     spacing, containing the assembler operation to identify the
     following data as initialization code.  If not defined, GCC will
     assume such a section does not exist.

`FINI_SECTION_ASM_OP'
     If defined, a C expression whose value is a string, including
     spacing, containing the assembler operation to identify the
     following data as finalization code.  If not defined, GCC will
     assume such a section does not exist.

`CRT_CALL_STATIC_FUNCTION (SECTION_OP, FUNCTION)'
     If defined, an ASM statement that switches to a different section
     via SECTION_OP, calls FUNCTION, and switches back to the text
     section.  This is used in `crtstuff.c' if `INIT_SECTION_ASM_OP' or
     `FINI_SECTION_ASM_OP' to calls to initialization and finalization
     functions from the init and fini sections.  By default, this macro
     uses a simple function call.  Some ports need hand-crafted
     assembly code to avoid dependencies on registers initialized in
     the function prologue or to ensure that constant pools don't end
     up too far way in the text section.

`FORCE_CODE_SECTION_ALIGN'
     If defined, an ASM statement that aligns a code section to some
     arbitrary boundary.  This is used to force all fragments of the
     `.init' and `.fini' sections to have to same alignment and thus
     prevent the linker from having to add any padding.

`EXTRA_SECTIONS'
     A list of names for sections other than the standard two, which are
     `in_text' and `in_data'.  You need not define this macro on a
     system with no other sections (that GCC needs to use).

`EXTRA_SECTION_FUNCTIONS'
     One or more functions to be defined in `varasm.c'.  These
     functions should do jobs analogous to those of `text_section' and
     `data_section', for your additional sections.  Do not define this
     macro if you do not define `EXTRA_SECTIONS'.

`READONLY_DATA_SECTION'
     On most machines, read-only variables, constants, and jump tables
     are placed in the text section.  If this is not the case on your
     machine, this macro should be defined to be the name of a function
     (either `data_section' or a function defined in `EXTRA_SECTIONS')
     that switches to the section to be used for read-only items.

     If these items should be placed in the text section, this macro
     should not be defined.

`SELECT_SECTION (EXP, RELOC, ALIGN)'
     A C statement or statements to switch to the appropriate section
     for output of EXP.  You can assume that EXP is either a `VAR_DECL'
     node or a constant of some sort.  RELOC indicates whether the
     initial value of EXP requires link-time relocations.  Bit 1 is set
     when variable contains local relocations only, while bit 2 is set
     for global relocations.  Select the section by calling
     `text_section' or one of the alternatives for other sections.
     ALIGN is the constant alignment in bits.

     Do not define this macro if you put all read-only variables and
     constants in the read-only data section (usually the text section).

`SELECT_RTX_SECTION (MODE, RTX, ALIGN)'
     A C statement or statements to switch to the appropriate section
     for output of RTX in mode MODE.  You can assume that RTX is some
     kind of constant in RTL.  The argument MODE is redundant except in
     the case of a `const_int' rtx.  Select the section by calling
     `text_section' or one of the alternatives for other sections.
     ALIGN is the constant alignment in bits.

     Do not define this macro if you put all constants in the read-only
     data section.

`JUMP_TABLES_IN_TEXT_SECTION'
     Define this macro to be an expression with a nonzero value if jump
     tables (for `tablejump' insns) should be output in the text
     section, along with the assembler instructions.  Otherwise, the
     readonly data section is used.

     This macro is irrelevant if there is no separate readonly data
     section.

`ENCODE_SECTION_INFO (DECL)'
     Define this macro if references to a symbol or a constant must be
     treated differently depending on something about the variable or
     function named by the symbol (such as what section it is in).

     The macro definition, if any, is executed under two circumstances.
     One is immediately after the rtl for DECL that represents a
     variable or a function has been created and stored in `DECL_RTL
     (DECL)'.  The value of the rtl will be a `mem' whose address is a
     `symbol_ref'.  The other is immediately after the rtl for DECL
     that represents a constant has been created and stored in
     `TREE_CST_RTL (DECL)'.  The macro is called once for each distinct
     constant in a source file.

     The usual thing for this macro to do is to record a flag in the
     `symbol_ref' (such as `SYMBOL_REF_FLAG') or to store a modified
     name string in the `symbol_ref' (if one bit is not enough
     information).

`STRIP_NAME_ENCODING (VAR, SYM_NAME)'
     Decode SYM_NAME and store the real name part in VAR, sans the
     characters that encode section info.  Define this macro if
     `ENCODE_SECTION_INFO' alters the symbol's name string.

`UNIQUE_SECTION (DECL, RELOC)'
     A C statement to build up a unique section name, expressed as a
     `STRING_CST' node, and assign it to `DECL_SECTION_NAME (DECL)'.
     RELOC indicates whether the initial value of EXP requires
     link-time relocations.  If you do not define this macro, GCC will
     use the symbol name prefixed by `.' as the section name.  Note -
     this macro can now be called for uninitialized data items as well
     as initialized data and functions.


File: gccint.info,  Node: PIC,  Next: Assembler Format,  Prev: Sections,  Up: Target Macros

Position Independent Code
=========================

   This section describes macros that help implement generation of
position independent code.  Simply defining these macros is not enough
to generate valid PIC; you must also add support to the macros
`GO_IF_LEGITIMATE_ADDRESS' and `PRINT_OPERAND_ADDRESS', as well as
`LEGITIMIZE_ADDRESS'.  You must modify the definition of `movsi' to do
something appropriate when the source operand contains a symbolic
address.  You may also need to alter the handling of switch statements
so that they use relative addresses.

`PIC_OFFSET_TABLE_REGNUM'
     The register number of the register used to address a table of
     static data addresses in memory.  In some cases this register is
     defined by a processor's "application binary interface" (ABI).
     When this macro is defined, RTL is generated for this register
     once, as with the stack pointer and frame pointer registers.  If
     this macro is not defined, it is up to the machine-dependent files
     to allocate such a register (if necessary).  Note that this
     register must be fixed when in use (e.g.  when `flag_pic' is true).

`PIC_OFFSET_TABLE_REG_CALL_CLOBBERED'
     Define this macro if the register defined by
     `PIC_OFFSET_TABLE_REGNUM' is clobbered by calls.  Do not define
     this macro if `PIC_OFFSET_TABLE_REGNUM' is not defined.

`FINALIZE_PIC'
     By generating position-independent code, when two different
     programs (A and B) share a common library (libC.a), the text of
     the library can be shared whether or not the library is linked at
     the same address for both programs.  In some of these
     environments, position-independent code requires not only the use
     of different addressing modes, but also special code to enable the
     use of these addressing modes.

     The `FINALIZE_PIC' macro serves as a hook to emit these special
     codes once the function is being compiled into assembly code, but
     not before.  (It is not done before, because in the case of
     compiling an inline function, it would lead to multiple PIC
     prologues being included in functions which used inline functions
     and were compiled to assembly language.)

`LEGITIMATE_PIC_OPERAND_P (X)'
     A C expression that is nonzero if X is a legitimate immediate
     operand on the target machine when generating position independent
     code.  You can assume that X satisfies `CONSTANT_P', so you need
     not check this.  You can also assume FLAG_PIC is true, so you need
     not check it either.  You need not define this macro if all
     constants (including `SYMBOL_REF') can be immediate operands when
     generating position independent code.


File: gccint.info,  Node: Assembler Format,  Next: Debugging Info,  Prev: PIC,  Up: Target Macros

Defining the Output Assembler Language
======================================

   This section describes macros whose principal purpose is to describe
how to write instructions in assembler language--rather than what the
instructions do.

* Menu:

* File Framework::       Structural information for the assembler file.
* Data Output::          Output of constants (numbers, strings, addresses).
* Uninitialized Data::   Output of uninitialized variables.
* Label Output::         Output and generation of labels.
* Initialization::       General principles of initialization
			   and termination routines.
* Macros for Initialization::
			 Specific macros that control the handling of
			   initialization and termination routines.
* Instruction Output::   Output of actual instructions.
* Dispatch Tables::      Output of jump tables.
* Exception Region Output:: Output of exception region code.
* Alignment Output::     Pseudo ops for alignment and skipping data.

