--- gcc/gcc.info-20 2018/04/24 18:12:15 1.1.1.2 +++ gcc/gcc.info-20 2018/04/24 18:19:04 1.1.1.3 @@ -1,4 +1,4 @@ -This is Info file gcc.info, produced by Makeinfo-1.54 from the input +This is Info file gcc.info, produced by Makeinfo-1.55 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. @@ -6,7 +6,8 @@ file gcc.texi. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA - Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc. + Copyright (C) 1988, 1989, 1992, 1993, 1994 Free Software Foundation, +Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are @@ -14,1043 +15,1072 @@ preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also -that the sections entitled "GNU General Public License" and "Protect -Your Freedom--Fight `Look And Feel'" are included exactly as in the -original, and provided that the entire resulting derived work is -distributed under the terms of a permission notice identical to this -one. +that the sections entitled "GNU General Public License," "Funding for +Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are +included exactly as in the original, and provided that the entire +resulting derived work is distributed under the terms of a permission +notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "GNU General Public -License" and "Protect Your Freedom--Fight `Look And Feel'", and this -permission notice, may be included in translations approved by the Free -Software Foundation instead of in the original English. +License," "Funding for Free Software," and "Protect Your Freedom--Fight +`Look And Feel'", and this permission notice, may be included in +translations approved by the Free Software Foundation instead of in the +original English.  -File: gcc.info, Node: Condition Code, Next: Costs, Prev: Addressing Modes, Up: Target Macros +File: gcc.info, Node: Scalar Return, Next: Aggregate Return, Prev: Register Arguments, Up: Stack and Calling -Condition Code Status -===================== +How Scalar Function Values Are Returned +--------------------------------------- - 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 names to be used for additional modes for condition code - values in registers (*note Jump Patterns::.). These names are - added to `enum machine_mode' and all have class `MODE_CC'. By - convention, they should start with `CC' and end with `mode'. - - You should only define this macro if your machine does not use - `cc0' and only if additional modes are required. - -`EXTRA_CC_NAMES' - A list of C strings giving the names for the modes listed in - `EXTRA_CC_MODES'. For example, the Sparc defines this macro and - `EXTRA_CC_MODES' as - - #define EXTRA_CC_MODES CC_NOOVmode, CCFPmode - #define EXTRA_CC_NAMES "CC_NOOV", "CCFP" - - This macro is not required if `EXTRA_CC_MODES' is not defined. - -`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)) + This section discusses the macros that control returning scalars as +values--values that can fit in registers. - This macro is not required if `EXTRA_CC_MODES' is not defined. +`TRADITIONAL_RETURN_FLOAT' + Define this macro if `-traditional' should not cause functions + declared to return `float' to convert the value to `double'. + +`FUNCTION_VALUE (VALTYPE, FUNC)' + A C expression to create an RTX representing the place where a + function returns a value of data type VALTYPE. VALTYPE is a tree + node representing a data type. Write `TYPE_MODE (VALTYPE)' to get + the machine mode used to represent that type. On many machines, + only the mode is relevant. (Actually, on most machines, scalar + values are returned in the same place regardless of mode). + + If `PROMOTE_FUNCTION_RETURN' is defined, you must apply the same + promotion rules specified in `PROMOTE_MODE' if VALTYPE is a scalar + type. + + If the precise function being called is known, FUNC is a tree node + (`FUNCTION_DECL') for it; otherwise, FUNC is a null pointer. This + makes it possible to use a different value-returning convention + for specific functions when all their calls are known. + + `FUNCTION_VALUE' is not used for return vales with aggregate data + types, because these are returned in another way. See + `STRUCT_VALUE_REGNUM' and related macros, below. + +`FUNCTION_OUTGOING_VALUE (VALTYPE, FUNC)' + Define this macro if the target machine has "register windows" so + that the register in which a function returns its value is not the + same as the one in which the caller sees the value. + + For such machines, `FUNCTION_VALUE' computes the register in which + the caller will see the value. `FUNCTION_OUTGOING_VALUE' should be + defined in a similar fashion to tell the function where to put the + value. + + If `FUNCTION_OUTGOING_VALUE' is not defined, `FUNCTION_VALUE' + serves both purposes. + + `FUNCTION_OUTGOING_VALUE' is not used for return vales with + aggregate data types, because these are returned in another way. + See `STRUCT_VALUE_REGNUM' and related macros, below. + +`LIBCALL_VALUE (MODE)' + A C expression to create an RTX representing the place where a + library function returns a value of mode MODE. If the precise + function being called is known, FUNC is a tree node + (`FUNCTION_DECL') for it; otherwise, FUNC is a null pointer. This + makes it possible to use a different value-returning convention + for specific functions when all their calls are known. + + Note that "library function" in this context means a compiler + support routine, used to perform arithmetic, whose name is known + specially by the compiler and was not mentioned in the C code being + compiled. + + The definition of `LIBRARY_VALUE' need not be concerned aggregate + data types, because none of the library functions returns such + types. + +`FUNCTION_VALUE_REGNO_P (REGNO)' + A C expression that is nonzero if REGNO is the number of a hard + register in which the values of called function may come back. + + A register whose use for returning values is limited to serving as + the second of a pair (for a value of type `double', say) need not + be recognized by this macro. So for most machines, this definition + suffices: + + #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) + + If the machine has register windows, so that the caller and the + called function use different registers for the return value, this + macro should recognize only the caller's register numbers. + +`APPLY_RESULT_SIZE' + Define this macro if `untyped_call' and `untyped_return' need more + space than is implied by `FUNCTION_VALUE_REGNO_P' for saving and + restoring an arbitrary return value.  -File: gcc.info, Node: Costs, Next: Sections, Prev: Condition Code, Up: Target Macros +File: gcc.info, Node: Aggregate Return, Next: Caller Saves, Prev: Scalar Return, Up: Stack and Calling -Describing Relative Costs of Operations -======================================= +How Large Values Are Returned +----------------------------- - These macros let you describe the relative speed of various -operations on the target machine. + When a function value's mode is `BLKmode' (and in some other cases), +the value is not returned according to `FUNCTION_VALUE' (*note Scalar +Return::.). Instead, the caller passes the address of a block of +memory in which the value should be stored. This address is called the +"structure value address". + + This section describes how to control returning structure values in +memory. + +`RETURN_IN_MEMORY (TYPE)' + A C expression which can inhibit the returning of certain function + values in registers, based on the type of value. A nonzero value + says to return the function value in memory, just as large + structures are always returned. Here TYPE will be a C expression + of type `tree', representing the data type of the value. + + Note that values of mode `BLKmode' must be explicitly handled by + this macro. Also, the option `-fpcc-struct-return' takes effect + regardless of this macro. On most systems, it is possible to + leave the macro undefined; this causes a default definition to be + used, whose value is the constant 1 for `BLKmode' values, and 0 + otherwise. + + Do not use this macro to indicate that structures and unions + should always be returned in memory. You should instead use + `DEFAULT_PCC_STRUCT_RETURN' to indicate this. + +`DEFAULT_PCC_STRUCT_RETURN' + Define this macro to be 1 if all structure and union return values + must be in memory. Since this results in slower code, this should + be defined only if needed for compatibility with other compilers + or with an ABI. If you define this macro to be 0, then the + conventions used for structure and union return values are decided + by the `RETURN_IN_MEMORY' macro. + + If not defined, this defaults to the value 1. + +`STRUCT_VALUE_REGNUM' + If the structure value address is passed in a register, then + `STRUCT_VALUE_REGNUM' should be the number of that register. + +`STRUCT_VALUE' + If the structure value address is not passed in a register, define + `STRUCT_VALUE' as an expression returning an RTX for the place + where the address is passed. If it returns 0, the address is + passed as an "invisible" first argument. + +`STRUCT_VALUE_INCOMING_REGNUM' + On some architectures the place where the structure value address + is found by the called function is not the same place that the + caller put it. This can be due to register windows, or it could + be because the function prologue moves it to a different place. + + If the incoming location of the structure value address is in a + register, define this macro as the register number. + +`STRUCT_VALUE_INCOMING' + If the incoming location is not a register, then you should define + `STRUCT_VALUE_INCOMING' as an expression for an RTX for where the + called function should find the value. If it should find the + value on the stack, define this to create a `mem' which refers to + the frame pointer. A definition of 0 means that the address is + passed as an "invisible" first argument. + +`PCC_STATIC_STRUCT_RETURN' + Define this macro if the usual system convention on the target + machine for returning structures and unions is for the called + function to return the address of a static variable containing the + value. -`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. - -`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 (FROM, TO)' - A C expression for the cost of moving data 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 4 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 (M)' - A C expression for the cost of moving data of mode M between a - register and memory. A value of 2 is the default; 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. - -`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 GNU CC -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_ZERO_EXTEND' - Define this macro if zero-extension (of a `char' or `short' to an - `int') can be done faster if the destination is a register that is - known to be zero. - - If you define this macro, you must have instruction patterns that - recognize RTL structures like this: - - (set (strict_low_part (subreg:QI (reg:SI ...) 0)) ...) - - and likewise for `HImode'. - -`SLOW_UNALIGNED_ACCESS' - Define this macro to be the value 1 if unaligned accesses have a - cost many times greater than aligned accesses, for example if they - are emulated in a trap handler. - - When this macro is non-zero, the compiler will act as if - `STRICT_ALIGNMENT' were non-zero when generating code for block - moves. This can cause significantly more instructions to be - produced. Therefore, do not set this macro non-zero 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. - -`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 number of scalar move insns which 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. - - If you don't define this, a reasonable default is used. - -`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. - -`ADJUST_COST (INSN, LINK, DEP_INSN, COST)' - A C statement (sans semicolon) to update the integer variable COST - based on the relationship between INSN that is dependent on - DEP_INSN through the dependence LINK. 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. + Do not define this if the usual system convention is for the + caller to pass an address to the subroutine. + + This macro has effect in `-fpcc-struct-return' mode, but it does + nothing when you use `-freg-struct-return' mode.  -File: gcc.info, Node: Sections, Next: PIC, Prev: Costs, Up: Target Macros +File: gcc.info, Node: Caller Saves, Next: Function Entry, Prev: Aggregate Return, Up: Stack and Calling + +Caller-Saves Register Allocation +-------------------------------- -Dividing the Output into Sections (Texts, Data, ...) -==================================================== + If you enable it, GNU CC can save registers around function calls. +This makes it possible to use call-clobbered registers to hold +variables that must live across calls. + +`DEFAULT_CALLER_SAVES' + Define this macro if function calls on the target machine do not + preserve any registers; in other words, if `CALL_USED_REGISTERS' + has 1 for all registers. This macro enables `-fcaller-saves' by + default. Eventually that option will be enabled by default on all + machines and both the option and this macro will be eliminated. + +`CALLER_SAVE_PROFITABLE (REFS, CALLS)' + A C expression to determine whether it is worthwhile to consider + placing a pseudo-register in a call-clobbered hard register and + saving and restoring it around each function call. The expression + should be 1 when this is worth doing, and 0 otherwise. - 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 containing the assembler - operation that should precede instructions and read-only data. - Normally `".text"' is right. - -`DATA_SECTION_ASM_OP' - A C expression whose value is a string containing the assembler - operation to identify the following data as writable initialized - data. Normally `".data"' is right. - -`SHARED_SECTION_ASM_OP' - if defined, a C expression whose value is a string containing the - assembler operation to identify the following data as shared data. - If not defined, `DATA_SECTION_ASM_OP' will be used. - -`INIT_SECTION_ASM_OP' - if defined, a C expression whose value is a string containing the - assembler operation to identify the following data as - initialization code. If not defined, GNU CC will assume such a - section does not exist. - -`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)' - 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. Select the - section by calling `text_section' or one of the alternatives for - other sections. - - 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)' - 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. - - Do not define this macro if you put all constants in the read-only - data section. - -`JUMP_TABLES_IN_TEXT_SECTION' - Define this macro 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 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 immediately after the - rtl for DECL 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 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. + If you don't define this macro, a default is used which is good on + most machines: `4 * CALLS < REFS'.  -File: gcc.info, Node: PIC, Next: Assembler Format, Prev: Sections, Up: Target Macros +File: gcc.info, Node: Function Entry, Next: Profiling, Prev: Caller Saves, Up: Stack and Calling -Position Independent Code -========================= +Function Entry and Exit +----------------------- - 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). - -`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. + This section describes the macros that output function entry +("prologue") and exit ("epilogue") code. - -File: gcc.info, Node: Assembler Format, Next: Debugging Info, Prev: PIC, Up: Target Macros +`FUNCTION_PROLOGUE (FILE, SIZE)' + A C compound statement that outputs the assembler code for entry + to a function. The prologue is responsible for setting up the + stack frame, initializing the frame pointer register, saving + registers that must be saved, and allocating SIZE additional bytes + of storage for the local variables. SIZE is an integer. FILE is + a stdio stream to which the assembler code should be output. + + The label for the beginning of the function need not be output by + this macro. That has already been done when the macro is run. + + To determine which registers to save, the macro can refer to the + array `regs_ever_live': element R is nonzero if hard register R is + used anywhere within the function. This implies the function + prologue should save register R, provided it is not one of the + call-used registers. (`FUNCTION_EPILOGUE' must likewise use + `regs_ever_live'.) + + On machines that have "register windows", the function entry code + does not save on the stack the registers that are in the windows, + even if they are supposed to be preserved by function calls; + instead it takes appropriate steps to "push" the register stack, + if any non-call-used registers are used in the function. + + On machines where functions may or may not have frame-pointers, the + function entry code must vary accordingly; it must set up the frame + pointer if one is wanted, and not otherwise. To determine whether + a frame pointer is in wanted, the macro can refer to the variable + `frame_pointer_needed'. The variable's value will be 1 at run + time in a function that needs a frame pointer. *Note + Elimination::. + + The function entry code is responsible for allocating any stack + space required for the function. This stack space consists of the + regions listed below. In most cases, these regions are allocated + in the order listed, with the last listed region closest to the + top of the stack (the lowest address if `STACK_GROWS_DOWNWARD' is + defined, and the highest address if it is not defined). You can + use a different order for a machine if doing so is more convenient + or required for compatibility reasons. Except in cases where + required by standard or by a debugger, there is no reason why the + stack layout used by GCC need agree with that used by other + compilers for a machine. + + * A region of `current_function_pretend_args_size' bytes of + uninitialized space just underneath the first argument + arriving on the stack. (This may not be at the very start of + the allocated stack region if the calling sequence has pushed + anything else since pushing the stack arguments. But + usually, on such machines, nothing else has been pushed yet, + because the function prologue itself does all the pushing.) + This region is used on machines where an argument may be + passed partly in registers and partly in memory, and, in some + cases to support the features in `varargs.h' and `stdargs.h'. + + * An area of memory used to save certain registers used by the + function. The size of this area, which may also include + space for such things as the return address and pointers to + previous stack frames, is machine-specific and usually + depends on which registers have been used in the function. + Machines with register windows often do not require a save + area. + + * A region of at least SIZE bytes, possibly rounded up to an + allocation boundary, to contain the local variables of the + function. On some machines, this region and the save area + may occur in the opposite order, with the save area closer to + the top of the stack. + + * Optionally, when `ACCUMULATE_OUTGOING_ARGS' is defined, a + region of `current_function_outgoing_args_size' bytes to be + used for outgoing argument lists of the function. *Note + Stack Arguments::. + + Normally, it is necessary for the macros `FUNCTION_PROLOGUE' and + `FUNCTION_EPILOGUE' to treat leaf functions specially. The C + variable `leaf_function' is nonzero for such a function. + +`EXIT_IGNORE_STACK' + Define this macro as a C expression that is nonzero if the return + instruction or the function epilogue ignores the value of the stack + pointer; in other words, if it is safe to delete an instruction to + adjust the stack pointer before a return from the function. + + Note that this macro's value is relevant only for functions for + which frame pointers are maintained. It is never safe to delete a + final stack adjustment in a function that has no frame pointer, + and the compiler knows this regardless of `EXIT_IGNORE_STACK'. + +`FUNCTION_EPILOGUE (FILE, SIZE)' + A C compound statement that outputs the assembler code for exit + from a function. The epilogue is responsible for restoring the + saved registers and stack pointer to their values when the + function was called, and returning control to the caller. This + macro takes the same arguments as the macro `FUNCTION_PROLOGUE', + and the registers to restore are determined from `regs_ever_live' + and `CALL_USED_REGISTERS' in the same way. + + On some machines, there is a single instruction that does all the + work of returning from the function. On these machines, give that + instruction the name `return' and do not define the macro + `FUNCTION_EPILOGUE' at all. + + Do not define a pattern named `return' if you want the + `FUNCTION_EPILOGUE' to be used. If you want the target switches + to control whether return instructions or epilogues are used, + define a `return' pattern with a validity condition that tests the + target switches appropriately. If the `return' pattern's validity + condition is false, epilogues will be used. + + On machines where functions may or may not have frame-pointers, the + function exit code must vary accordingly. Sometimes the code for + these two cases is completely different. To determine whether a + frame pointer is wanted, the macro can refer to the variable + `frame_pointer_needed'. The variable's value will be 1 when + compiling a function that needs a frame pointer. + + Normally, `FUNCTION_PROLOGUE' and `FUNCTION_EPILOGUE' must treat + leaf functions specially. The C variable `leaf_function' is + nonzero for such a function. *Note Leaf Functions::. + + On some machines, some functions pop their arguments on exit while + others leave that for the caller to do. For example, the 68020 + when given `-mrtd' pops arguments in functions that take a fixed + number of arguments. + + Your definition of the macro `RETURN_POPS_ARGS' decides which + functions pop their own arguments. `FUNCTION_EPILOGUE' needs to + know what was decided. The variable that is called + `current_function_pops_args' is the number of bytes of its + arguments that a function should pop. *Note Scalar Return::. + +`DELAY_SLOTS_FOR_EPILOGUE' + Define this macro if the function epilogue contains delay slots to + which instructions from the rest of the function can be "moved". + The definition should be a C expression whose value is an integer + representing the number of delay slots there. + +`ELIGIBLE_FOR_EPILOGUE_DELAY (INSN, N)' + A C expression that returns 1 if INSN can be placed in delay slot + number N of the epilogue. + + The argument N is an integer which identifies the delay slot now + being considered (since different slots may have different rules of + eligibility). It is never negative and is always less than the + number of epilogue delay slots (what `DELAY_SLOTS_FOR_EPILOGUE' + returns). If you reject a particular insn for a given delay slot, + in principle, it may be reconsidered for a subsequent delay slot. + Also, other insns may (at least in principle) be considered for + the so far unfilled delay slot. + + The insns accepted to fill the epilogue delay slots are put in an + RTL list made with `insn_list' objects, stored in the variable + `current_function_epilogue_delay_list'. The insn for the first + delay slot comes first in the list. Your definition of the macro + `FUNCTION_EPILOGUE' should fill the delay slots by outputting the + insns in this list, usually by calling `final_scan_insn'. -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. -* Alignment Output:: Pseudo ops for alignment and skipping data. + You need not define this macro if you did not define + `DELAY_SLOTS_FOR_EPILOGUE'.  -File: gcc.info, Node: File Framework, Next: Data Output, Up: Assembler Format +File: gcc.info, Node: Profiling, Prev: Function Entry, Up: Stack and Calling -The Overall Framework of an Assembler File ------------------------------------------- +Generating Code for Profiling +----------------------------- -`ASM_FILE_START (STREAM)' - A C expression which outputs to the stdio stream STREAM some - appropriate text to go at the start of an assembler file. - - Normally this macro is defined to output a line containing - `#NO_APP', which is a comment that has no effect on most - assemblers but tells the GNU assembler that it can save time by not - checking for certain assembler constructs. - - On systems that use SDB, it is necessary to output certain - commands; see `attasm.h'. - -`ASM_FILE_END (STREAM)' - A C expression which outputs to the stdio stream STREAM some - appropriate text to go at the end of an assembler file. - - If this macro is not defined, the default is to output nothing - special at the end of the file. Most systems don't require any - definition. - - On systems that use SDB, it is necessary to output certain - commands; see `attasm.h'. - -`ASM_IDENTIFY_GCC (FILE)' - A C statement to output assembler commands which will identify the - object file as having been compiled with GNU CC (or another GNU - compiler). - - If you don't define this macro, the string `gcc_compiled.:' is - output. This string is calculated to define a symbol which, on - BSD systems, will never be defined for any other reason. GDB - checks for the presence of this symbol when reading the symbol - table of an executable. - - On non-BSD systems, you must arrange communication with GDB in - some other fashion. If GDB is not used on your system, you can - define this macro with an empty body. - -`ASM_COMMENT_START' - A C string constant describing how to begin a comment in the target - assembler language. The compiler assumes that the comment will - end at the end of the line. - -`ASM_APP_ON' - A C string constant for text to be output before each `asm' - statement or group of consecutive ones. Normally this is - `"#APP"', which is a comment that has no effect on most assemblers - but tells the GNU assembler that it must check the lines that - follow for all valid assembler constructs. - -`ASM_APP_OFF' - A C string constant for text to be output after each `asm' - statement or group of consecutive ones. Normally this is - `"#NO_APP"', which tells the GNU assembler to resume making the - time-saving assumptions that are valid for ordinary compiler - output. - -`ASM_OUTPUT_SOURCE_FILENAME (STREAM, NAME)' - A C statement to output COFF information or DWARF debugging - information which indicates that filename NAME is the current - source file to the stdio stream STREAM. - - This macro need not be defined if the standard form of output for - the file format in use is appropriate. - -`ASM_OUTPUT_SOURCE_LINE (STREAM, LINE)' - A C statement to output DBX or SDB debugging information before - code for line number LINE of the current source file to the stdio - stream STREAM. - - This macro need not be defined if the standard form of debugging - information for the debugger in use is appropriate. - -`ASM_OUTPUT_IDENT (STREAM, STRING)' - A C statement to output something to the assembler file to handle a - `#ident' directive containing the text STRING. If this macro is - not defined, nothing is output for a `#ident' directive. - -`OBJC_PROLOGUE' - A C statement to output any assembler statements which are - required to precede any Objective C object definitions or message - sending. The statement is executed only when compiling an - Objective C program. + These macros will help you generate code for profiling. - -File: gcc.info, Node: Data Output, Next: Uninitialized Data, Prev: File Framework, Up: Assembler Format +`FUNCTION_PROFILER (FILE, LABELNO)' + A C statement or compound statement to output to FILE some + assembler code to call the profiling subroutine `mcount'. Before + calling, the assembler code must load the address of a counter + variable into a register where `mcount' expects to find the + address. The name of this variable is `LP' followed by the number + LABELNO, so you would generate the name using `LP%d' in a + `fprintf'. + + The details of how the address should be passed to `mcount' are + determined by your operating system environment, not by GNU CC. To + figure them out, compile a small program for profiling using the + system's installed C compiler and look at the assembler code that + results. + +`PROFILE_BEFORE_PROLOGUE' + Define this macro if the code for function profiling should come + before the function prologue. Normally, the profiling code comes + after. + +`FUNCTION_BLOCK_PROFILER (FILE, LABELNO)' + A C statement or compound statement to output to FILE some + assembler code to initialize basic-block profiling for the current + object module. This code should call the subroutine + `__bb_init_func' once per object module, passing it as its sole + argument the address of a block allocated in the object module. + + The name of the block is a local symbol made with this statement: + + ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 0); + + Of course, since you are writing the definition of + `ASM_GENERATE_INTERNAL_LABEL' as well as that of this macro, you + can take a short cut in the definition of this macro and use the + name that you know will result. + + The first word of this block is a flag which will be nonzero if the + object module has already been initialized. So test this word + first, and do not call `__bb_init_func' if the flag is nonzero. + +`BLOCK_PROFILER (FILE, BLOCKNO)' + A C statement or compound statement to increment the count + associated with the basic block number BLOCKNO. Basic blocks are + numbered separately from zero within each compilation. The count + associated with block number BLOCKNO is at index BLOCKNO in a + vector of words; the name of this array is a local symbol made + with this statement: + + ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 2); + + Of course, since you are writing the definition of + `ASM_GENERATE_INTERNAL_LABEL' as well as that of this macro, you + can take a short cut in the definition of this macro and use the + name that you know will result. + +`BLOCK_PROFILER_CODE' + A C function or functions which are needed in the library to + support block profiling. -Output of Data --------------- + +File: gcc.info, Node: Varargs, Next: Trampolines, Prev: Stack and Calling, Up: Target Macros -`ASM_OUTPUT_LONG_DOUBLE (STREAM, VALUE)' -`ASM_OUTPUT_DOUBLE (STREAM, VALUE)' -`ASM_OUTPUT_FLOAT (STREAM, VALUE)' - A C statement to output to the stdio stream STREAM an assembler - instruction to assemble a floating-point constant of `TFmode', - `DFmode' or `SFmode', respectively, whose value is VALUE. VALUE - will be a C expression of type `REAL_VALUE_TYPE'. Macros such as - `REAL_VALUE_TO_TARGET_DOUBLE' are useful for writing these - definitions. - -`ASM_OUTPUT_QUADRUPLE_INT (STREAM, EXP)' -`ASM_OUTPUT_DOUBLE_INT (STREAM, EXP)' -`ASM_OUTPUT_INT (STREAM, EXP)' -`ASM_OUTPUT_SHORT (STREAM, EXP)' -`ASM_OUTPUT_CHAR (STREAM, EXP)' - A C statement to output to the stdio stream STREAM an assembler - instruction to assemble an integer of 16, 8, 4, 2 or 1 bytes, - respectively, whose value is VALUE. The argument EXP will be an - RTL expression which represents a constant value. Use - `output_addr_const (STREAM, EXP)' to output this value as an - assembler expression. - - For sizes larger than `UNITS_PER_WORD', if the action of a macro - would be identical to repeatedly calling the macro corresponding to - a size of `UNITS_PER_WORD', once for each word, you need not define - the macro. - -`ASM_OUTPUT_BYTE (STREAM, VALUE)' - A C statement to output to the stdio stream STREAM an assembler - instruction to assemble a single byte containing the number VALUE. - -`ASM_BYTE_OP' - A C string constant giving the pseudo-op to use for a sequence of - single-byte constants. If this macro is not defined, the default - is `"byte"'. - -`ASM_OUTPUT_ASCII (STREAM, PTR, LEN)' - A C statement to output to the stdio stream STREAM an assembler - instruction to assemble a string constant containing the LEN bytes - at PTR. PTR will be a C expression of type `char *' and LEN a C - expression of type `int'. - - If the assembler has a `.ascii' pseudo-op as found in the Berkeley - Unix assembler, do not define the macro `ASM_OUTPUT_ASCII'. - -`ASM_OUTPUT_POOL_PROLOGUE (FILE FUNNAME FUNDECL SIZE)' - A C statement to output assembler commands to define the start of - the constant pool for a function. FUNNAME is a string giving the - name of the function. Should the return type of the function be - required, it can be obtained via FUNDECL. SIZE is the size, in - bytes, of the constant pool that will be written immediately after - this call. - - If no constant-pool prefix is required, the usual case, this macro - need not be defined. - -`ASM_OUTPUT_SPECIAL_POOL_ENTRY (FILE, X, MODE, ALIGN, LABELNO, JUMPTO)' - A C statement (with or without semicolon) to output a constant in - the constant pool, if it needs special treatment. (This macro - need not do anything for RTL expressions that can be output - normally.) - - The argument FILE is the standard I/O stream to output the - assembler code on. X is the RTL expression for the constant to - output, and MODE is the machine mode (in case X is a `const_int'). - ALIGN is the required alignment for the value X; you should - output an assembler directive to force this much alignment. - - The argument LABELNO is a number to use in an internal label for - the address of this pool entry. The definition of this macro is - responsible for outputting the label definition at the proper - place. Here is how to do this: - - ASM_OUTPUT_INTERNAL_LABEL (FILE, "LC", LABELNO); - - When you output a pool entry specially, you should end with a - `goto' to the label JUMPTO. This will prevent the same pool entry - from being output a second time in the usual manner. - - You need not define this macro if it would do nothing. - -`ASM_OPEN_PAREN' -`ASM_CLOSE_PAREN' - These macros are defined as C string constant, describing the - syntax in the assembler for grouping arithmetic expressions. The - following definitions are correct for most assemblers: - - #define ASM_OPEN_PAREN "(" - #define ASM_CLOSE_PAREN ")" - - These macros are provided by `real.h' for writing the definitions of -`ASM_OUTPUT_DOUBLE' and the like: - -`REAL_VALUE_TO_TARGET_SINGLE (X, L)' -`REAL_VALUE_TO_TARGET_DOUBLE (X, L)' -`REAL_VALUE_TO_TARGET_LONG_DOUBLE (X, L)' - These translate X, of type `REAL_VALUE_TYPE', to the target's - floating point representation, and store its bit pattern in the - array of `long int' whose address is L. The number of elements in - the output array is determined by the size of the desired target - floating point data type: 32 bits of it go in each `long int' array - element. Each array element holds 32 bits of the result, even if - `long int' is wider than 32 bits on the host machine. - - The array element values are designed so that you can print them - out using `fprintf' in the order they should appear in the target - machine's memory. - -`REAL_VALUE_TO_DECIMAL (X, FORMAT, STRING)' - This macro converts X, of type `REAL_VALUE_TYPE', to a decimal - number and stores it as a string into STRING. You must pass, as - STRING, the address of a long enough block of space to hold the - result. +Implementing the Varargs Macros +=============================== - The argument FORMAT is a `printf'-specification that serves as a - suggestion for how to format the output string. + GNU CC comes with an implementation of `varargs.h' and `stdarg.h' +that work without change on machines that pass arguments on the stack. +Other machines require their own implementations of varargs, and the +two machine independent header files must have conditionals to include +it. + + ANSI `stdarg.h' differs from traditional `varargs.h' mainly in the +calling convention for `va_start'. The traditional implementation +takes just one argument, which is the variable in which to store the +argument pointer. The ANSI implementation of `va_start' takes an +additional second argument. The user is supposed to write the last +named argument of the function here. + + However, `va_start' should not use this argument. The way to find +the end of the named arguments is with the built-in functions described +below. + +`__builtin_saveregs ()' + Use this built-in function to save the argument registers in + memory so that the varargs mechanism can access them. Both ANSI + and traditional versions of `va_start' must use + `__builtin_saveregs', unless you use `SETUP_INCOMING_VARARGS' (see + below) instead. + + On some machines, `__builtin_saveregs' is open-coded under the + control of the macro `EXPAND_BUILTIN_SAVEREGS'. On other machines, + it calls a routine written in assembler language, found in + `libgcc2.c'. + + Code generated for the call to `__builtin_saveregs' appears at the + beginning of the function, as opposed to where the call to + `__builtin_saveregs' is written, regardless of what the code is. + This is because the registers must be saved before the function + starts to use them for its own purposes. + +`__builtin_args_info (CATEGORY)' + Use this built-in function to find the first anonymous arguments in + registers. + + In general, a machine may have several categories of registers + used for arguments, each for a particular category of data types. + (For example, on some machines, floating-point registers are used + for floating-point arguments while other arguments are passed in + the general registers.) To make non-varargs functions use the + proper calling convention, you have defined the `CUMULATIVE_ARGS' + data type to record how many registers in each category have been + used so far + + `__builtin_args_info' accesses the same data structure of type + `CUMULATIVE_ARGS' after the ordinary argument layout is finished + with it, with CATEGORY specifying which word to access. Thus, the + value indicates the first unused register in a given category. + + Normally, you would use `__builtin_args_info' in the implementation + of `va_start', accessing each category just once and storing the + value in the `va_list' object. This is because `va_list' will + have to update the values, and there is no way to alter the values + accessed by `__builtin_args_info'. + +`__builtin_next_arg (LASTARG)' + This is the equivalent of `__builtin_args_info', for stack + arguments. It returns the address of the first anonymous stack + argument, as type `void *'. If `ARGS_GROW_DOWNWARD', it returns + the address of the location above the first anonymous stack + argument. Use it in `va_start' to initialize the pointer for + fetching arguments from the stack. Also use it in `va_start' to + verify that the second parameter LASTARG is the last named argument + of the current function. + +`__builtin_classify_type (OBJECT)' + Since each machine has its own conventions for which data types are + passed in which kind of register, your implementation of `va_arg' + has to embody these conventions. The easiest way to categorize the + specified data type is to use `__builtin_classify_type' together + with `sizeof' and `__alignof__'. + + `__builtin_classify_type' ignores the value of OBJECT, considering + only its data type. It returns an integer describing what kind of + type that is--integer, floating, pointer, structure, and so on. + + The file `typeclass.h' defines an enumeration that you can use to + interpret the values of `__builtin_classify_type'. + + These machine description macros help implement varargs: + +`EXPAND_BUILTIN_SAVEREGS (ARGS)' + If defined, is a C expression that produces the machine-specific + code for a call to `__builtin_saveregs'. This code will be moved + to the very beginning of the function, before any parameter access + are made. The return value of this function should be an RTX that + contains the value to use as the return of `__builtin_saveregs'. + + The argument ARGS is a `tree_list' containing the arguments that + were passed to `__builtin_saveregs'. + + If this macro is not defined, the compiler will output an ordinary + call to the library function `__builtin_saveregs'. + +`SETUP_INCOMING_VARARGS (ARGS_SO_FAR, MODE, TYPE,' + PRETEND_ARGS_SIZE, SECOND_TIME) This macro offers an alternative + to using `__builtin_saveregs' and defining the macro + `EXPAND_BUILTIN_SAVEREGS'. Use it to store the anonymous register + arguments into the stack so that all the arguments appear to have + been passed consecutively on the stack. Once this is done, you + can use the standard implementation of varargs that works for + machines that pass all their arguments on the stack. + + The argument ARGS_SO_FAR is the `CUMULATIVE_ARGS' data structure, + containing the values that obtain after processing of the named + arguments. The arguments MODE and TYPE describe the last named + argument--its machine mode and its data type as a tree node. + + The macro implementation should do two things: first, push onto the + stack all the argument registers *not* used for the named + arguments, and second, store the size of the data thus pushed into + the `int'-valued variable whose name is supplied as the argument + PRETEND_ARGS_SIZE. The value that you store here will serve as + additional offset for setting up the stack frame. + + Because you must generate code to push the anonymous arguments at + compile time without knowing their data types, + `SETUP_INCOMING_VARARGS' is only useful on machines that have just + a single category of argument register and use it uniformly for + all data types. + + If the argument SECOND_TIME is nonzero, it means that the + arguments of the function are being analyzed for the second time. + This happens for an inline function, which is not actually + compiled until the end of the source file. The macro + `SETUP_INCOMING_VARARGS' should not generate any instructions in + this case.  -File: gcc.info, Node: Uninitialized Data, Next: Label Output, Prev: Data Output, Up: Assembler Format - -Output of Uninitialized Variables ---------------------------------- +File: gcc.info, Node: Trampolines, Next: Library Calls, Prev: Varargs, Up: Target Macros - Each of the macros in this section is used to do the whole job of -outputting a single uninitialized variable. +Trampolines for Nested Functions +================================ -`ASM_OUTPUT_COMMON (STREAM, NAME, SIZE, ROUNDED)' - A C statement (sans semicolon) to output to the stdio stream - STREAM the assembler definition of a common-label named NAME whose - size is SIZE bytes. The variable ROUNDED is the size rounded up - to whatever alignment the caller wants. - - Use the expression `assemble_name (STREAM, NAME)' to output the - name itself; before and after that, output the additional - assembler syntax for defining the name, and a newline. - - This macro controls how the assembler definitions of uninitialized - global variables are output. - -`ASM_OUTPUT_ALIGNED_COMMON (STREAM, NAME, SIZE, ALIGNMENT)' - Like `ASM_OUTPUT_COMMON' except takes the required alignment as a - separate, explicit argument. If you define this macro, it is used - in place of `ASM_OUTPUT_COMMON', and gives you more flexibility in - handling the required alignment of the variable. - -`ASM_OUTPUT_SHARED_COMMON (STREAM, NAME, SIZE, ROUNDED)' - If defined, it is similar to `ASM_OUTPUT_COMMON', except that it - is used when NAME is shared. If not defined, `ASM_OUTPUT_COMMON' - will be used. - -`ASM_OUTPUT_LOCAL (STREAM, NAME, SIZE, ROUNDED)' - A C statement (sans semicolon) to output to the stdio stream - STREAM the assembler definition of a local-common-label named NAME - whose size is SIZE bytes. The variable ROUNDED is the size - rounded up to whatever alignment the caller wants. - - Use the expression `assemble_name (STREAM, NAME)' to output the - name itself; before and after that, output the additional - assembler syntax for defining the name, and a newline. - - This macro controls how the assembler definitions of uninitialized - static variables are output. - -`ASM_OUTPUT_ALIGNED_LOCAL (STREAM, NAME, SIZE, ALIGNMENT)' - Like `ASM_OUTPUT_LOCAL' except takes the required alignment as a - separate, explicit argument. If you define this macro, it is used - in place of `ASM_OUTPUT_LOCAL', and gives you more flexibility in - handling the required alignment of the variable. - -`ASM_OUTPUT_SHARED_LOCAL (STREAM, NAME, SIZE, ROUNDED)' - If defined, it is similar to `ASM_OUTPUT_LOCAL', except that it is - used when NAME is shared. If not defined, `ASM_OUTPUT_LOCAL' will - be used. + A "trampoline" is a small piece of code that is created at run time +when the address of a nested function is taken. It normally resides on +the stack, in the stack frame of the containing function. These macros +tell GNU CC how to generate code to allocate and initialize a +trampoline. + + The instructions in the trampoline must do two things: load a +constant address into the static chain register, and jump to the real +address of the nested function. On CISC machines such as the m68k, +this requires two instructions, a move immediate and a jump. Then the +two addresses exist in the trampoline as word-long immediate operands. +On RISC machines, it is often necessary to load each address into a +register in two parts. Then pieces of each address form separate +immediate operands. + + The code generated to initialize the trampoline must store the +variable parts--the static chain value and the function address--into +the immediate operands of the instructions. On a CISC machine, this is +simply a matter of copying each address to a memory reference at the +proper offset from the start of the trampoline. On a RISC machine, it +may be necessary to take out pieces of the address and store them +separately. + +`TRAMPOLINE_TEMPLATE (FILE)' + A C statement to output, on the stream FILE, assembler code for a + block of data that contains the constant parts of a trampoline. + This code should not include a label--the label is taken care of + automatically. + +`TRAMPOLINE_SECTION' + The name of a subroutine to switch to the section in which the + trampoline template is to be placed (*note Sections::.). The + default is a value of `readonly_data_section', which places the + trampoline in the section containing read-only data. + +`TRAMPOLINE_SIZE' + A C expression for the size in bytes of the trampoline, as an + integer. + +`TRAMPOLINE_ALIGNMENT' + Alignment required for trampolines, in bits. + + If you don't define this macro, the value of `BIGGEST_ALIGNMENT' + is used for aligning trampolines. + +`INITIALIZE_TRAMPOLINE (ADDR, FNADDR, STATIC_CHAIN)' + A C statement to initialize the variable parts of a trampoline. + aDDR is an RTX for the address of the trampoline; FNADDR is an RTX + for the address of the nested function; STATIC_CHAIN is an RTX for + the static chain value that should be passed to the function when + it is called. + +`ALLOCATE_TRAMPOLINE (FP)' + A C expression to allocate run-time space for a trampoline. The + expression value should be an RTX representing a memory reference + to the space for the trampoline. + + If this macro is not defined, by default the trampoline is + allocated as a stack slot. This default is right for most + machines. The exceptions are machines where it is impossible to + execute instructions in the stack area. On such machines, you may + have to implement a separate stack, using this macro in + conjunction with `FUNCTION_PROLOGUE' and `FUNCTION_EPILOGUE'. + + FP points to a data structure, a `struct function', which + describes the compilation status of the immediate containing + function of the function which the trampoline is for. Normally + (when `ALLOCATE_TRAMPOLINE' is not defined), the stack slot for the + trampoline is in the stack frame of this containing function. + Other allocation strategies probably must do something analogous + with this information. + + Implementing trampolines is difficult on many machines because they +have separate instruction and data caches. Writing into a stack +location fails to clear the memory in the instruction cache, so when +the program jumps to that location, it executes the old contents. + + Here are two possible solutions. One is to clear the relevant parts +of the instruction cache whenever a trampoline is set up. The other is +to make all trampolines identical, by having them jump to a standard +subroutine. The former technique makes trampoline execution faster; the +latter makes initialization faster. + + To clear the instruction cache when a trampoline is initialized, +define the following macros which describe the shape of the cache. + +`INSN_CACHE_SIZE' + The total size in bytes of the cache. + +`INSN_CACHE_LINE_WIDTH' + The length in bytes of each cache line. The cache is divided into + cache lines which are disjoint slots, each holding a contiguous + chunk of data fetched from memory. Each time data is brought into + the cache, an entire line is read at once. The data loaded into a + cache line is always aligned on a boundary equal to the line size. + +`INSN_CACHE_DEPTH' + The number of alternative cache lines that can hold any particular + memory location. + + Alternatively, if the machine has system calls or instructions to +clear the instruction cache directly, you can define the following +macro. + +`CLEAR_INSN_CACHE (BEG, END)' + If defined, expands to a C expression clearing the *instruction + cache* in the specified interval. If it is not defined, and the + macro INSN_CACHE_SIZE is defined, some generic code is generated + to clear the cache. The definition of this macro would typically + be a series of `asm' statements. Both BEG and END are both pointer + expressions. + + To use a standard subroutine, define the following macro. In +addition, you must make sure that the instructions in a trampoline fill +an entire cache line with identical instructions, or else ensure that +the beginning of the trampoline code is always aligned at the same +point in its cache line. Look in `m68k.h' as a guide. + +`TRANSFER_FROM_TRAMPOLINE' + Define this macro if trampolines need a special subroutine to do + their work. The macro should expand to a series of `asm' + statements which will be compiled with GNU CC. They go in a + library function named `__transfer_from_trampoline'. + + If you need to avoid executing the ordinary prologue code of a + compiled C function when you jump to the subroutine, you can do so + by placing a special label of your own in the assembler code. Use + one `asm' statement to generate an assembler label, and another to + make the label global. Then trampolines can use that label to + jump directly to your special assembler code.  -File: gcc.info, Node: Label Output, Next: Initialization, Prev: Uninitialized Data, Up: Assembler Format +File: gcc.info, Node: Library Calls, Next: Addressing Modes, Prev: Trampolines, Up: Target Macros -Output and Generation of Labels -------------------------------- +Implicit Calls to Library Routines +================================== -`ASM_OUTPUT_LABEL (STREAM, NAME)' - A C statement (sans semicolon) to output to the stdio stream - STREAM the assembler definition of a label named NAME. Use the - expression `assemble_name (STREAM, NAME)' to output the name - itself; before and after that, output the additional assembler - syntax for defining the name, and a newline. - -`ASM_DECLARE_FUNCTION_NAME (STREAM, NAME, DECL)' - A C statement (sans semicolon) to output to the stdio stream - STREAM any text necessary for declaring the name NAME of a - function which is being defined. This macro is responsible for - outputting the label definition (perhaps using - `ASM_OUTPUT_LABEL'). The argument DECL is the `FUNCTION_DECL' - tree node representing the function. - - If this macro is not defined, then the function name is defined in - the usual manner as a label (by means of `ASM_OUTPUT_LABEL'). - -`ASM_DECLARE_FUNCTION_SIZE (STREAM, NAME, DECL)' - A C statement (sans semicolon) to output to the stdio stream - STREAM any text necessary for declaring the size of a function - which is being defined. The argument NAME is the name of the - function. The argument DECL is the `FUNCTION_DECL' tree node - representing the function. - - If this macro is not defined, then the function size is not - defined. - -`ASM_DECLARE_OBJECT_NAME (STREAM, NAME, DECL)' - A C statement (sans semicolon) to output to the stdio stream - STREAM any text necessary for declaring the name NAME of an - initialized variable which is being defined. This macro must - output the label definition (perhaps using `ASM_OUTPUT_LABEL'). - The argument DECL is the `VAR_DECL' tree node representing the - variable. - - If this macro is not defined, then the variable name is defined in - the usual manner as a label (by means of `ASM_OUTPUT_LABEL'). - -`ASM_FINISH_DECLARE_OBJECT (STREAM, DECL, TOPLEVEL, ATEND)' - A C statement (sans semicolon) to finish up declaring a variable - name once the compiler has processed its initializer fully and - thus has had a chance to determine the size of an array when - controlled by an initializer. This is used on systems where it's - necessary to declare something about the size of the object. - - If you don't define this macro, that is equivalent to defining it - to do nothing. - -`ASM_GLOBALIZE_LABEL (STREAM, NAME)' - A C statement (sans semicolon) to output to the stdio stream - STREAM some commands that will make the label NAME global; that - is, available for reference from other files. Use the expression - `assemble_name (STREAM, NAME)' to output the name itself; before - and after that, output the additional assembler syntax for making - that name global, and a newline. - -`ASM_OUTPUT_EXTERNAL (STREAM, DECL, NAME)' - A C statement (sans semicolon) to output to the stdio stream - STREAM any text necessary for declaring the name of an external - symbol named NAME which is referenced in this compilation but not - defined. The value of DECL is the tree node for the declaration. - - This macro need not be defined if it does not need to output - anything. The GNU assembler and most Unix assemblers don't - require anything. - -`ASM_OUTPUT_EXTERNAL_LIBCALL (STREAM, SYMREF)' - A C statement (sans semicolon) to output on STREAM an assembler - pseudo-op to declare a library function name external. The name - of the library function is given by SYMREF, which has type `rtx' - and is a `symbol_ref'. - - This macro need not be defined if it does not need to output - anything. The GNU assembler and most Unix assemblers don't - require anything. - -`ASM_OUTPUT_LABELREF (STREAM, NAME)' - A C statement (sans semicolon) to output to the stdio stream - STREAM a reference in assembler syntax to a label named NAME. - This should add `_' to the front of the name, if that is customary - on your operating system, as it is in most Berkeley Unix systems. - This macro is used in `assemble_name'. - -`ASM_OUTPUT_INTERNAL_LABEL (STREAM, PREFIX, NUM)' - A C statement to output to the stdio stream STREAM a label whose - name is made from the string PREFIX and the number NUM. - - It is absolutely essential that these labels be distinct from the - labels used for user-level functions and variables. Otherwise, - certain programs will have name conflicts with internal labels. - - It is desirable to exclude internal labels from the symbol table - of the object file. Most assemblers have a naming convention for - labels that should be excluded; on many systems, the letter `L' at - the beginning of a label has this effect. You should find out what - convention your system uses, and follow it. - - The usual definition of this macro is as follows: - - fprintf (STREAM, "L%s%d:\n", PREFIX, NUM) - -`ASM_GENERATE_INTERNAL_LABEL (STRING, PREFIX, NUM)' - A C statement to store into the string STRING a label whose name - is made from the string PREFIX and the number NUM. - - This string, when output subsequently by `assemble_name', should - produce the output that `ASM_OUTPUT_INTERNAL_LABEL' would produce - with the same PREFIX and NUM. - - If the string begins with `*', then `assemble_name' will output - the rest of the string unchanged. It is often convenient for - `ASM_GENERATE_INTERNAL_LABEL' to use `*' in this way. If the - string doesn't start with `*', then `ASM_OUTPUT_LABELREF' gets to - output the string, and may change it. (Of course, - `ASM_OUTPUT_LABELREF' is also part of your machine description, so - you should know what it does on your machine.) - -`ASM_FORMAT_PRIVATE_NAME (OUTVAR, NAME, NUMBER)' - A C expression to assign to OUTVAR (which is a variable of type - `char *') a newly allocated string made from the string NAME and - the number NUMBER, with some suitable punctuation added. Use - `alloca' to get space for the string. - - The string will be used as an argument to `ASM_OUTPUT_LABELREF' to - produce an assembler label for an internal static variable whose - name is NAME. Therefore, the string must be such as to result in - valid assembler code. The argument NUMBER is different each time - this macro is executed; it prevents conflicts between - similarly-named internal static variables in different scopes. - - Ideally this string should not be a valid C identifier, to prevent - any conflict with the user's own symbols. Most assemblers allow - periods or percent signs in assembler symbols; putting at least - one of these between the name and the number will suffice. - -`OBJC_GEN_METHOD_LABEL (BUF, IS_INST, CLASS_NAME, CAT_NAME, SEL_NAME)' - Define this macro to override the default assembler names used for - Objective C methods. - - The default name is a unique method number followed by the name of - the class (e.g. `_1_Foo'). For methods in categories, the name of - the category is also included in the assembler name (e.g. - `_1_Foo_Bar'). - - These names are safe on most systems, but make debugging difficult - since the method's selector is not present in the name. - Therefore, particular systems define other ways of computing names. - - BUF is an expression of type `char *' which gives you a buffer in - which to store the name; its length is as long as CLASS_NAME, - CAT_NAME and SEL_NAME put together, plus 50 characters extra. - - The argument IS_INST specifies whether the method is an instance - method or a class method; CLASS_NAME is the name of the class; - CAT_NAME is the name of the category (or NULL if the method is not - in a category); and SEL_NAME is the name of the selector. + Here is an explanation of implicit calls to library routines. - On systems where the assembler can handle quoted names, you can - use this macro to provide more human-readable names. +`MULSI3_LIBCALL' + A C string constant giving the name of the function to call for + multiplication of one signed full-word by another. If you do not + define this macro, the default name is used, which is `__mulsi3', + a function defined in `libgcc.a'. + +`DIVSI3_LIBCALL' + A C string constant giving the name of the function to call for + division of one signed full-word by another. If you do not define + this macro, the default name is used, which is `__divsi3', a + function defined in `libgcc.a'. + +`UDIVSI3_LIBCALL' + A C string constant giving the name of the function to call for + division of one unsigned full-word by another. If you do not + define this macro, the default name is used, which is `__udivsi3', + a function defined in `libgcc.a'. + +`MODSI3_LIBCALL' + A C string constant giving the name of the function to call for the + remainder in division of one signed full-word by another. If you + do not define this macro, the default name is used, which is + `__modsi3', a function defined in `libgcc.a'. + +`UMODSI3_LIBCALL' + A C string constant giving the name of the function to call for the + remainder in division of one unsigned full-word by another. If + you do not define this macro, the default name is used, which is + `__umodsi3', a function defined in `libgcc.a'. + +`MULDI3_LIBCALL' + A C string constant giving the name of the function to call for + multiplication of one signed double-word by another. If you do not + define this macro, the default name is used, which is `__muldi3', + a function defined in `libgcc.a'. + +`DIVDI3_LIBCALL' + A C string constant giving the name of the function to call for + division of one signed double-word by another. If you do not + define this macro, the default name is used, which is `__divdi3', a + function defined in `libgcc.a'. + +`UDIVDI3_LIBCALL' + A C string constant giving the name of the function to call for + division of one unsigned full-word by another. If you do not + define this macro, the default name is used, which is `__udivdi3', + a function defined in `libgcc.a'. + +`MODDI3_LIBCALL' + A C string constant giving the name of the function to call for the + remainder in division of one signed double-word by another. If + you do not define this macro, the default name is used, which is + `__moddi3', a function defined in `libgcc.a'. + +`UMODDI3_LIBCALL' + A C string constant giving the name of the function to call for the + remainder in division of one unsigned full-word by another. If + you do not define this macro, the default name is used, which is + `__umoddi3', a function defined in `libgcc.a'. + +`INIT_TARGET_OPTABS' + Define this macro as a C statement that declares additional library + routines renames existing ones. `init_optabs' calls this macro + after initializing all the normal library routines. + +`TARGET_EDOM' + The value of `EDOM' on the target machine, as a C integer constant + expression. If you don't define this macro, GNU CC does not + attempt to deposit the value of `EDOM' into `errno' directly. + Look in `/usr/include/errno.h' to find the value of `EDOM' on your + system. + + If you do not define `TARGET_EDOM', then compiled code reports + domain errors by calling the library function and letting it + report the error. If mathematical functions on your system use + `matherr' when there is an error, then you should leave + `TARGET_EDOM' undefined so that `matherr' is used normally. + +`GEN_ERRNO_RTX' + Define this macro as a C expression to create an rtl expression + that refers to the global "variable" `errno'. (On certain systems, + `errno' may not actually be a variable.) If you don't define this + macro, a reasonable default is used. + +`TARGET_MEM_FUNCTIONS' + Define this macro if GNU CC should generate calls to the System V + (and ANSI C) library functions `memcpy' and `memset' rather than + the BSD functions `bcopy' and `bzero'. + +`LIBGCC_NEEDS_DOUBLE' + Define this macro if only `float' arguments cannot be passed to + library routines (so they must be converted to `double'). This + macro affects both how library calls are generated and how the + library routines in `libgcc1.c' accept their arguments. It is + useful on machines where floating and fixed point arguments are + passed differently, such as the i860. + +`FLOAT_ARG_TYPE' + Define this macro to override the type used by the library + routines to pick up arguments of type `float'. (By default, they + use a union of `float' and `int'.) + + The obvious choice would be `float'--but that won't work with + traditional C compilers that expect all arguments declared as + `float' to arrive as `double'. To avoid this conversion, the + library routines ask for the value as some other type and then + treat it as a `float'. + + On some systems, no other type will work for this. For these + systems, you must use `LIBGCC_NEEDS_DOUBLE' instead, to force + conversion of the values `double' before they are passed. + +`FLOATIFY (PASSED-VALUE)' + Define this macro to override the way library routines redesignate + a `float' argument as a `float' instead of the type it was passed + as. The default is an expression which takes the `float' field of + the union. + +`FLOAT_VALUE_TYPE' + Define this macro to override the type used by the library + routines to return values that ought to have type `float'. (By + default, they use `int'.) + + The obvious choice would be `float'--but that won't work with + traditional C compilers gratuitously convert values declared as + `float' into `double'. + +`INTIFY (FLOAT-VALUE)' + Define this macro to override the way the value of a + `float'-returning library routine should be packaged in order to + return it. These functions are actually declared to return type + `FLOAT_VALUE_TYPE' (normally `int'). + + These values can't be returned as type `float' because traditional + C compilers would gratuitously convert the value to a `double'. + + A local variable named `intify' is always available when the macro + `INTIFY' is used. It is a union of a `float' field named `f' and + a field named `i' whose type is `FLOAT_VALUE_TYPE' or `int'. + + If you don't define this macro, the default definition works by + copying the value through that union. + +`nongcc_SI_type' + Define this macro as the name of the data type corresponding to + `SImode' in the system's own C compiler. + + You need not define this macro if that type is `long int', as it + usually is. + +`nongcc_word_type' + Define this macro as the name of the data type corresponding to the + word_mode in the system's own C compiler. + + You need not define this macro if that type is `long int', as it + usually is. + +`perform_...' + Define these macros to supply explicit C statements to carry out + various arithmetic operations on types `float' and `double' in the + library routines in `libgcc1.c'. See that file for a full list of + these macros and their arguments. + + On most machines, you don't need to define any of these macros, + because the C compiler that comes with the system takes care of + doing them. + +`NEXT_OBJC_RUNTIME' + Define this macro to generate code for Objective C message sending + using the calling convention of the NeXT system. This calling + convention involves passing the object, the selector and the + method arguments all at once to the method-lookup library function. + + The default calling convention passes just the object and the + selector to the lookup function, which returns a pointer to the + method.  -File: gcc.info, Node: Initialization, Next: Macros for Initialization, Prev: Label Output, Up: Assembler Format - -How Initialization Functions Are Handled ----------------------------------------- - - The compiled code for certain languages includes "constructors" -(also called "initialization routines")--functions to initialize data -in the program when the program is started. These functions need to be -called before the program is "started"--that is to say, before `main' -is called. - - Compiling some languages generates "destructors" (also called -"termination routines") that should be called when the program -terminates. - - To make the initialization and termination functions work, the -compiler must output something in the assembler code to cause those -functions to be called at the appropriate time. When you port the -compiler to a new system, you need to specify how to do this. - - There are two major ways that GCC currently supports the execution of -initialization and termination functions. Each way has two variants. -Much of the structure is common to all four variations. - - The linker must build two lists of these functions--a list of -initialization functions, called `__CTOR_LIST__', and a list of -termination functions, called `__DTOR_LIST__'. - - Each list always begins with an ignored function pointer (which may -hold 0, -1, or a count of the function pointers after it, depending on -the environment). This is followed by a series of zero or more function -pointers to constructors (or destructors), followed by a function -pointer containing zero. - - Depending on the operating system and its executable file format, -either `crtstuff.c' or `libgcc2.c' traverses these lists at startup -time and exit time. Constructors are called in forward order of the -list; destructors in reverse order. - - The best way to handle static constructors works only for object file -formats which provide arbitrarily-named sections. A section is set -aside for a list of constructors, and another for a list of destructors. -Traditionally these are called `.ctors' and `.dtors'. Each object file -that defines an initialization function also puts a word in the -constructor section to point to that function. The linker accumulates -all these words into one contiguous `.ctors' section. Termination -functions are handled similarly. - - To use this method, you need appropriate definitions of the macros -`ASM_OUTPUT_CONSTRUCTOR' and `ASM_OUTPUT_DESTRUCTOR'. Usually you can -get them by including `svr4.h'. - - When arbitrary sections are available, there are two variants, -depending upon how the code in `crtstuff.c' is called. On systems that -support an "init" section which is executed at program startup, parts -of `crtstuff.c' are compiled into that section. The program is linked -by the `gcc' driver like this: - - ld -o OUTPUT_FILE crtbegin.o ... crtend.o -lgcc - - The head of a function (`__do_global_ctors') appears in the init -section of `crtbegin.o'; the remainder of the function appears in the -init section of `crtend.o'. The linker will pull these two parts of -the section together, making a whole function. If any of the user's -object files linked into the middle of it contribute code, then that -code will be executed as part of the body of `__do_global_ctors'. - - To use this variant, you must define the `INIT_SECTION_ASM_OP' macro -properly. - - If no init section is available, do not define -`INIT_SECTION_ASM_OP'. Then `__do_global_ctors' is built into the text -section like all other functions, and resides in `libgcc.a'. When GCC -compiles any function called `main', it inserts a procedure call to -`__main' as the first executable code after the function prologue. The -`__main' function, also defined in `libgcc2.c', simply calls -`__do_global_ctors'. - - In file formats that don't support arbitrary sections, there are -again two variants. In the simplest variant, the GNU linker (GNU `ld') -and an `a.out' format must be used. In this case, -`ASM_OUTPUT_CONSTRUCTOR' is defined to produce a `.stabs' entry of type -`N_SETT', referencing the name `__CTOR_LIST__', and with the address of -the void function containing the initialization code as its value. The -GNU linker recognizes this as a request to add the value to a "set"; -the values are accumulated, and are eventually placed in the executable -as a vector in the format described above, with a leading (ignored) -count and a trailing zero element. `ASM_OUTPUT_DESTRUCTOR' is handled -similarly. Since no init section is available, the absence of -`INIT_SECTION_ASM_OP' causes the compilation of `main' to call `__main' -as above, starting the initialization process. - - The last variant uses neither arbitrary sections nor the GNU linker. -This is preferable when you want to do dynamic linking and when using -file formats which the GNU linker does not support, such as `ECOFF'. In -this case, `ASM_OUTPUT_CONSTRUCTOR' does not produce an `N_SETT' -symbol; initialization and termination functions are recognized simply -by their names. This requires an extra program in the linkage step, -called `collect2'. This program pretends to be the linker, for use -with GNU CC; it does its job by running the ordinary linker, but also -arranges to include the vectors of initialization and termination -functions. These functions are called via `__main' as described above. - - Choosing among these configuration options has been simplified by a -set of operating-system-dependent files in the `config' subdirectory. -These files define all of the relevant parameters. Usually it is -sufficient to include one into your specific machine-dependent -configuration file. These files are: - -`aoutos.h' - For operating systems using the `a.out' format. - -`next.h' - For operating systems using the `MachO' format. - -`svr3.h' - For System V Release 3 and similar systems using `COFF' format. +File: gcc.info, Node: Addressing Modes, Next: Condition Code, Prev: Library Calls, Up: Target Macros -`svr4.h' - For System V Release 4 and similar systems using `ELF' format. +Addressing Modes +================ -`vms.h' - For the VMS operating system. + This is about addressing modes. - The following section describes the specific macros that control and -customize the handling of initialization and termination functions. +`HAVE_POST_INCREMENT' + Define this macro if the machine supports post-increment + addressing. + +`HAVE_PRE_INCREMENT' +`HAVE_POST_DECREMENT' +`HAVE_PRE_DECREMENT' + Similar for other kinds of addressing. + +`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_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. + +`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. + +`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.