--- gcc/gcc.info-20 2018/04/24 18:12:15 1.1.1.2 +++ gcc/gcc.info-20 2018/04/24 18:42:27 1.1.1.5 @@ -1,12 +1,13 @@ -This is Info file gcc.info, produced by Makeinfo-1.54 from the input -file gcc.texi. +This is Info file gcc.info, produced by Makeinfo version 1.67 from the +input file gcc.texi. This file documents the use and the internals of the GNU compiler. - Published by the Free Software Foundation 675 Massachusetts Avenue -Cambridge, MA 02139 USA + Published by the Free Software Foundation 59 Temple Place - Suite 330 +Boston, MA 02111-1307 USA - Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc. + Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 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 +15,967 @@ 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: Leaf Functions, Next: Stack Registers, Prev: Values in Registers, Up: Registers -Condition Code Status -===================== +Handling Leaf Functions +----------------------- - 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 macro is not required if `EXTRA_CC_MODES' is not defined. + On some machines, a leaf function (i.e., one which makes no calls) +can run more efficiently if it does not make its own register window. +Often this means it is required to receive its arguments in the +registers where they are passed by the caller, instead of the registers +where they would normally arrive. + + The special treatment for leaf functions generally applies only when +other conditions are met; for example, often they may use only those +registers for its own variables and temporaries. We use the term "leaf +function" to mean a function that is suitable for this special +handling, so that functions with no calls are not necessarily "leaf +functions". + + GNU CC assigns register numbers before it knows whether the function +is suitable for leaf function treatment. So it needs to renumber the +registers in order to output a leaf function. The following macros +accomplish this. + +`LEAF_REGISTERS' + A C initializer for a vector, indexed by hard register number, + which contains 1 for a register that is allowable in a candidate + for leaf function treatment. + + If leaf function treatment involves renumbering the registers, + then the registers marked here should be the ones before + renumbering--those that GNU CC would ordinarily allocate. The + registers which will actually be used in the assembler code, after + renumbering, should not be marked with 1 in this vector. + + Define this macro only if the target machine offers a way to + optimize the treatment of leaf functions. + +`LEAF_REG_REMAP (REGNO)' + A C expression whose value is the register number to which REGNO + should be renumbered, when a function is treated as a leaf + function. + + If REGNO is a register number which should not appear in a leaf + function before renumbering, then the expression should yield -1, + which will cause the compiler to abort. + + Define this macro only if the target machine offers a way to + optimize the treatment of leaf functions, and registers need to be + renumbered to do this. + + Normally, `FUNCTION_PROLOGUE' and `FUNCTION_EPILOGUE' must treat +leaf functions specially. It can test the C variable `leaf_function' +which is nonzero for leaf functions. (The variable `leaf_function' is +defined only if `LEAF_REGISTERS' is defined.)  -File: gcc.info, Node: Costs, Next: Sections, Prev: Condition Code, Up: Target Macros +File: gcc.info, Node: Stack Registers, Next: Obsolete Register Macros, Prev: Leaf Functions, Up: Registers -Describing Relative Costs of Operations -======================================= +Registers That Form a Stack +--------------------------- - These macros let you describe the relative speed of various -operations on the target machine. + There are special features to handle computers where some of the +"registers" form a stack, as in the 80387 coprocessor for the 80386. +Stack registers are normally written by pushing onto the stack, and are +numbered relative to the top of the stack. -`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. + Currently, GNU CC can only handle one group of stack-like registers, +and they must be consecutively numbered. - -File: gcc.info, Node: Sections, Next: PIC, Prev: Costs, Up: Target Macros +`STACK_REGS' + Define this if the machine has any stack-like registers. -Dividing the Output into Sections (Texts, Data, ...) -==================================================== +`FIRST_STACK_REG' + The number of the first stack-like register. This one is the top + of the stack. - 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. +`LAST_STACK_REG' + The number of the last stack-like register. This one is the + bottom of the stack.  -File: gcc.info, Node: PIC, Next: Assembler Format, Prev: Sections, Up: Target Macros +File: gcc.info, Node: Obsolete Register Macros, Prev: Stack Registers, Up: Registers + +Obsolete Macros for Controlling Register Usage +---------------------------------------------- -Position Independent Code -========================= + These features do not work very well. They exist because they used +to be required to generate correct code for the 80387 coprocessor of the +80386. They are no longer used by that machine description and may be +removed in a later version of the compiler. Don't use them! + +`OVERLAPPING_REGNO_P (REGNO)' + If defined, this is a C expression whose value is nonzero if hard + register number REGNO is an overlapping register. This means a + hard register which overlaps a hard register with a different + number. (Such overlap is undesirable, but occasionally it allows + a machine to be supported which otherwise could not be.) This + macro must return nonzero for *all* the registers which overlap + each other. GNU CC can use an overlapping register only in + certain limited ways. It can be used for allocation within a + basic block, and may be spilled for reloading; that is all. + + If this macro is not defined, it means that none of the hard + registers overlap each other. This is the usual situation. + +`INSN_CLOBBERS_REGNO_P (INSN, REGNO)' + If defined, this is a C expression whose value should be nonzero if + the insn INSN has the effect of mysteriously clobbering the + contents of hard register number REGNO. By "mysterious" we mean + that the insn's RTL expression doesn't describe such an effect. + + If this macro is not defined, it means that no insn clobbers + registers mysteriously. This is the usual situation; all else + being equal, it is best for the RTL expression to show all the + activity. + +`PRESERVE_DEATH_INFO_REGNO_P (REGNO)' + If defined, this is a C expression whose value is nonzero if + accurate `REG_DEAD' notes are needed for hard register number REGNO + at the time of outputting the assembler code. When this is so, a + few optimizations that take place after register allocation and + could invalidate the death notes are not done when this register is + involved. + + You would arrange to preserve death info for a register when some + of the code in the machine description which is executed to write + the assembler code looks at the death notes. This is necessary + only when the actual hardware feature which GNU CC thinks of as a + register is not actually a register of the usual sort. (It might, + for example, be a hardware stack.) - 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. + If this macro is not defined, it means that no death notes need to + be preserved. This is the usual situation.  -File: gcc.info, Node: Assembler Format, Next: Debugging Info, Prev: PIC, Up: Target Macros +File: gcc.info, Node: Register Classes, Next: Stack and Calling, Prev: Registers, Up: Target Macros -Defining the Output Assembler Language -====================================== +Register Classes +================ - This section describes macros whose principal purpose is to describe -how to write instructions in assembler language-rather than what the -instructions do. + On many machines, the numbered registers are not all equivalent. +For example, certain registers may not be allowed for indexed +addressing; certain registers may not be allowed in some instructions. +These machine restrictions are described to the compiler using +"register classes". + + You define a number of register classes, giving each one a name and +saying which of the registers belong to it. Then you can specify +register classes that are allowed as operands to particular instruction +patterns. + + In general, each register will belong to several classes. In fact, +one class must be named `ALL_REGS' and contain all the registers. +Another class must be named `NO_REGS' and contain no registers. Often +the union of two classes will be another class; however, this is not +required. + + One of the classes must be named `GENERAL_REGS'. There is nothing +terribly special about the name, but the operand constraint letters `r' +and `g' specify this class. If `GENERAL_REGS' is the same as +`ALL_REGS', just define it as a macro which expands to `ALL_REGS'. + + Order the classes so that if class X is contained in class Y then X +has a lower class number than Y. + + The way classes other than `GENERAL_REGS' are specified in operand +constraints is through machine-dependent operand constraint letters. +You can define such letters to correspond to various classes, then use +them in operand constraints. + + You should define a class for the union of two classes whenever some +instruction allows both classes. For example, if an instruction allows +either a floating point (coprocessor) register or a general register +for a certain operand, you should define a class `FLOAT_OR_GENERAL_REGS' +which includes both of them. Otherwise you will get suboptimal code. + + You must also specify certain redundant information about the +register classes: for each class, which classes contain it and which +ones are contained in it; for each pair of classes, the largest class +contained in their union. + + When a value occupying several consecutive registers is expected in a +certain class, all the registers used must belong to that class. +Therefore, register classes cannot be used to enforce a requirement for +a register pair to start with an even-numbered register. The way to +specify this requirement is with `HARD_REGNO_MODE_OK'. + + Register classes used for input-operands of bitwise-and or shift +instructions have a special requirement: each such class must have, for +each fixed-point machine mode, a subclass whose registers can transfer +that mode to or from memory. For example, on some machines, the +operations for single-byte values (`QImode') are limited to certain +registers. When this is so, each register class that is used in a +bitwise-and or shift instruction must have a subclass consisting of +registers from which single-byte values can be loaded or stored. This +is so that `PREFERRED_RELOAD_CLASS' can always have a possible value to +return. + +`enum reg_class' + An enumeral type that must be defined with all the register class + names as enumeral values. `NO_REGS' must be first. `ALL_REGS' + must be the last register class, followed by one more enumeral + value, `LIM_REG_CLASSES', which is not a register class but rather + tells how many classes there are. + + Each register class has a number, which is the value of casting + the class name to type `int'. The number serves as an index in + many of the tables described below. + +`N_REG_CLASSES' + The number of distinct register classes, defined as follows: + + #define N_REG_CLASSES (int) LIM_REG_CLASSES + +`REG_CLASS_NAMES' + An initializer containing the names of the register classes as C + string constants. These names are used in writing some of the + debugging dumps. + +`REG_CLASS_CONTENTS' + An initializer containing the contents of the register classes, as + integers which are bit masks. The Nth integer specifies the + contents of class N. The way the integer MASK is interpreted is + that register R is in the class if `MASK & (1 << R)' is 1. + + When the machine has more than 32 registers, an integer does not + suffice. Then the integers are replaced by sub-initializers, + braced groupings containing several integers. Each + sub-initializer must be suitable as an initializer for the type + `HARD_REG_SET' which is defined in `hard-reg-set.h'. + +`REGNO_REG_CLASS (REGNO)' + A C expression whose value is a register class containing hard + register REGNO. In general there is more than one such class; + choose a class which is "minimal", meaning that no smaller class + also contains the register. + +`BASE_REG_CLASS' + A macro whose definition is the name of the class to which a valid + base register must belong. A base register is one used in an + address which is the register value plus a displacement. + +`INDEX_REG_CLASS' + A macro whose definition is the name of the class to which a valid + index register must belong. An index register is one used in an + address where its value is either multiplied by a scale factor or + added to another register (as well as added to a displacement). + +`REG_CLASS_FROM_LETTER (CHAR)' + A C expression which defines the machine-dependent operand + constraint letters for register classes. If CHAR is such a + letter, the value should be the register class corresponding to + it. Otherwise, the value should be `NO_REGS'. The register + letter `r', corresponding to class `GENERAL_REGS', will not be + passed to this macro; you do not need to handle it. + +`REGNO_OK_FOR_BASE_P (NUM)' + A C expression which is nonzero if register number NUM is suitable + for use as a base register in operand addresses. It may be either + a suitable hard register or a pseudo register that has been + allocated such a hard register. + +`REGNO_OK_FOR_INDEX_P (NUM)' + A C expression which is nonzero if register number NUM is suitable + for use as an index register in operand addresses. It may be + either a suitable hard register or a pseudo register that has been + allocated such a hard 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. + +`PREFERRED_RELOAD_CLASS (X, CLASS)' + A C expression that places additional restrictions on the register + class to use when it is necessary to copy value X into a register + in class CLASS. The value is a register class; perhaps CLASS, or + perhaps another, smaller class. On many machines, the following + definition is safe: + + #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS + + Sometimes returning a more restrictive class makes better code. + For example, on the 68000, when X is an integer constant that is + in range for a `moveq' instruction, the value of this macro is + always `DATA_REGS' as long as CLASS includes the data registers. + Requiring a data register guarantees that a `moveq' will be used. + + If X is a `const_double', by returning `NO_REGS' you can force X + into a memory constant. This is useful on certain machines where + immediate floating values cannot be loaded into certain kinds of + registers. + +`PREFERRED_OUTPUT_RELOAD_CLASS (X, CLASS)' + Like `PREFERRED_RELOAD_CLASS', but for output reloads instead of + input reloads. If you don't define this macro, the default is to + use CLASS, unchanged. + +`LIMIT_RELOAD_CLASS (MODE, CLASS)' + A C expression that places additional restrictions on the register + class to use when it is necessary to be able to hold a value of + mode MODE in a reload register for which class CLASS would + ordinarily be used. + + Unlike `PREFERRED_RELOAD_CLASS', this macro should be used when + there are certain modes that simply can't go in certain reload + classes. + + The value is a register class; perhaps CLASS, or perhaps another, + smaller class. + + Don't define this macro unless the target machine has limitations + which require the macro to do something nontrivial. + +`SECONDARY_RELOAD_CLASS (CLASS, MODE, X)' +`SECONDARY_INPUT_RELOAD_CLASS (CLASS, MODE, X)' +`SECONDARY_OUTPUT_RELOAD_CLASS (CLASS, MODE, X)' + Many machines have some registers that cannot be copied directly + to or from memory or even from other types of registers. An + example is the `MQ' register, which on most machines, can only be + copied to or from general registers, but not memory. Some + machines allow copying all registers to and from memory, but + require a scratch register for stores to some memory locations + (e.g., those with symbolic address on the RT, and those with + certain symbolic address on the Sparc when compiling PIC). In + some cases, both an intermediate and a scratch register are + required. + + You should define these macros to indicate to the reload phase + that it may need to allocate at least one register for a reload in + addition to the register to contain the data. Specifically, if + copying X to a register CLASS in MODE requires an intermediate + register, you should define `SECONDARY_INPUT_RELOAD_CLASS' to + return the largest register class all of whose registers can be + used as intermediate registers or scratch registers. + + If copying a register CLASS in MODE to X requires an intermediate + or scratch register, `SECONDARY_OUTPUT_RELOAD_CLASS' should be + defined to return the largest register class required. If the + requirements for input and output reloads are the same, the macro + `SECONDARY_RELOAD_CLASS' should be used instead of defining both + macros identically. + + The values returned by these macros are often `GENERAL_REGS'. + Return `NO_REGS' if no spare register is needed; i.e., if X can be + directly copied to or from a register of CLASS in MODE without + requiring a scratch register. Do not define this macro if it + would always return `NO_REGS'. + + If a scratch register is required (either with or without an + intermediate register), you should define patterns for + `reload_inM' or `reload_outM', as required (*note Standard + Names::.. These patterns, which will normally be implemented with + a `define_expand', should be similar to the `movM' patterns, + except that operand 2 is the scratch register. + + Define constraints for the reload register and scratch register + that contain a single register class. If the original reload + register (whose class is CLASS) can meet the constraint given in + the pattern, the value returned by these macros is used for the + class of the scratch register. Otherwise, two additional reload + registers are required. Their classes are obtained from the + constraints in the insn pattern. + + X might be a pseudo-register or a `subreg' of a pseudo-register, + which could either be in a hard register or in memory. Use + `true_regnum' to find out; it will return -1 if the pseudo is in + memory and the hard register number if it is in a register. + + These macros should not be used in the case where a particular + class of registers can only be copied to memory and not to another + class of registers. In that case, secondary reload registers are + not needed and would not be helpful. Instead, a stack location + must be used to perform the copy and the `movM' pattern should use + memory as a intermediate storage. This case often occurs between + floating-point and general registers. + +`SECONDARY_MEMORY_NEEDED (CLASS1, CLASS2, M)' + Certain machines have the property that some registers cannot be + copied to some other registers without using memory. Define this + macro on those machines to be a C expression that is non-zero if + objects of mode M in registers of CLASS1 can only be copied to + registers of class CLASS2 by storing a register of CLASS1 into + memory and loading that memory location into a register of CLASS2. + + Do not define this macro if its value would always be zero. + +`SECONDARY_MEMORY_NEEDED_RTX (MODE)' + Normally when `SECONDARY_MEMORY_NEEDED' is defined, the compiler + allocates a stack slot for a memory location needed for register + copies. If this macro is defined, the compiler instead uses the + memory location defined by this macro. + + Do not define this macro if you do not define + `SECONDARY_MEMORY_NEEDED'. + +`SECONDARY_MEMORY_NEEDED_MODE (MODE)' + When the compiler needs a secondary memory location to copy + between two registers of mode MODE, it normally allocates + sufficient memory to hold a quantity of `BITS_PER_WORD' bits and + performs the store and load operations in a mode that many bits + wide and whose class is the same as that of MODE. + + This is right thing to do on most machines because it ensures that + all bits of the register are copied and prevents accesses to the + registers in a narrower mode, which some machines prohibit for + floating-point registers. + + However, this default behavior is not correct on some machines, + such as the DEC Alpha, that store short integers in floating-point + registers differently than in integer registers. On those + machines, the default widening will not work correctly and you + must define this macro to suppress that widening in some cases. + See the file `alpha.h' for details. + + Do not define this macro if you do not define + `SECONDARY_MEMORY_NEEDED' or if widening MODE to a mode that is + `BITS_PER_WORD' bits wide is correct for your machine. + +`SMALL_REGISTER_CLASSES' + Normally the compiler avoids choosing registers that have been + explicitly mentioned in the rtl as spill registers (these + registers are normally those used to pass parameters and return + values). However, some machines have so few registers of certain + classes that there would not be enough registers to use as spill + registers if this were done. + + Define `SMALL_REGISTER_CLASSES' on these machines. When it is + defined, the compiler allows registers explicitly used in the rtl + to be used as spill registers but avoids extending the lifetime of + these registers. + + It is always safe to define this macro, but if you unnecessarily + define it, you will reduce the amount of optimizations that can be + performed in some cases. If you do not define this macro when it + is required, the compiler will run out of spill registers and + print a fatal error message. For most machines, you should not + define this macro. + +`CLASS_LIKELY_SPILLED_P (CLASS)' + A C expression whose value is nonzero if pseudos that have been + assigned to registers of class CLASS would likely be spilled + because registers of CLASS are needed for spill registers. + + The default value of this macro returns 1 if CLASS has exactly one + register and zero otherwise. On most machines, this default + should be used. Only define this macro to some other expression + if pseudo allocated by `local-alloc.c' end up in memory because + their hard registers were needed for spill registers. If this + macro returns nonzero for those classes, those pseudos will only + be allocated by `global.c', which knows how to reallocate the + pseudo to another register. If there would not be another + register available for reallocation, you should not change the + definition of this macro since the only effect of such a + definition would be to slow down register allocation. + +`CLASS_MAX_NREGS (CLASS, MODE)' + A C expression for the maximum number of consecutive registers of + class CLASS needed to hold a value of mode MODE. + + This is closely related to the macro `HARD_REGNO_NREGS'. In fact, + the value of the macro `CLASS_MAX_NREGS (CLASS, MODE)' should be + the maximum value of `HARD_REGNO_NREGS (REGNO, MODE)' for all + REGNO values in the class CLASS. + + This macro helps control the handling of multiple-word values in + the reload pass. + +`CLASS_CANNOT_CHANGE_SIZE' + If defined, a C expression for a class that contains registers + which the compiler must always access in a mode that is the same + size as the mode in which it loaded the register. + + For the example, loading 32-bit integer or floating-point objects + into floating-point registers on the Alpha extends them to 64-bits. + Therefore loading a 64-bit object and then storing it as a 32-bit + object does not store the low-order 32-bits, as would be the case + for a normal register. Therefore, `alpha.h' defines this macro as + `FLOAT_REGS'. + + Three other special macros describe which operands fit which +constraint letters. + +`CONST_OK_FOR_LETTER_P (VALUE, C)' + A C expression that defines the machine-dependent operand + constraint letters that specify particular ranges of integer + values. If C is one of those letters, the expression should check + that VALUE, an integer, is in the appropriate range and return 1 + if so, 0 otherwise. If C is not one of those letters, the value + should be 0 regardless of VALUE. + +`CONST_DOUBLE_OK_FOR_LETTER_P (VALUE, C)' + A C expression that defines the machine-dependent operand + constraint letters that specify particular ranges of + `const_double' values. + + If C is one of those letters, the expression should check that + VALUE, an RTX of code `const_double', is in the appropriate range + and return 1 if so, 0 otherwise. If C is not one of those + letters, the value should be 0 regardless of VALUE. + + `const_double' is used for all floating-point constants and for + `DImode' fixed-point constants. A given letter can accept either + or both kinds of values. It can use `GET_MODE' to distinguish + between these kinds. + +`EXTRA_CONSTRAINT (VALUE, C)' + A C expression that defines the optional machine-dependent + constraint letters that can be used to segregate specific types of + operands, usually memory references, for the target machine. + Normally this macro will not be defined. If it is required for a + particular target machine, it should return 1 if VALUE corresponds + to the operand type represented by the constraint letter C. If C + is not defined as an extra constraint, the value returned should + be 0 regardless of VALUE. + + For example, on the ROMP, load instructions cannot have their + output in r0 if the memory reference contains a symbolic address. + Constraint letter `Q' is defined as representing a memory address + that does *not* contain a symbolic address. An alternative is + specified with a `Q' constraint on the input and `r' on the + output. The next alternative specifies `m' on the input and a + register class that does not include r0 on the output. -* Menu: + +File: gcc.info, Node: Stack and Calling, Next: Varargs, Prev: Register Classes, Up: Target Macros -* 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. +Stack Layout and Calling Conventions +==================================== - -File: gcc.info, Node: File Framework, Next: Data Output, Up: Assembler Format + This describes the stack layout and calling conventions. -The Overall Framework of an Assembler File ------------------------------------------- +* Menu: -`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. +* Frame Layout:: +* Frame Registers:: +* Elimination:: +* Stack Arguments:: +* Register Arguments:: +* Scalar Return:: +* Aggregate Return:: +* Caller Saves:: +* Function Entry:: +* Profiling::  -File: gcc.info, Node: Data Output, Next: Uninitialized Data, Prev: File Framework, Up: Assembler Format +File: gcc.info, Node: Frame Layout, Next: Frame Registers, Up: Stack and Calling -Output of Data --------------- +Basic Stack Layout +------------------ -`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. + Here is the basic stack layout. - The argument FORMAT is a `printf'-specification that serves as a - suggestion for how to format the output string. +`STACK_GROWS_DOWNWARD' + Define this macro if pushing a word onto the stack moves the stack + pointer to a smaller address. + + When we say, "define this macro if ...," it means that the + compiler checks this macro only with `#ifdef' so the precise + definition used does not matter. + +`FRAME_GROWS_DOWNWARD' + Define this macro if the addresses of local variable slots are at + negative offsets from the frame pointer. + +`ARGS_GROW_DOWNWARD' + Define this macro if successive arguments to a function occupy + decreasing addresses on the stack. + +`STARTING_FRAME_OFFSET' + Offset from the frame pointer to the first local variable slot to + be allocated. + + If `FRAME_GROWS_DOWNWARD', find the next slot's offset by + subtracting the first slot's length from `STARTING_FRAME_OFFSET'. + Otherwise, it is found by adding the length of the first slot to + the value `STARTING_FRAME_OFFSET'. + +`STACK_POINTER_OFFSET' + Offset from the stack pointer register to the first location at + which outgoing arguments are placed. If not specified, the + default value of zero is used. This is the proper value for most + machines. + + If `ARGS_GROW_DOWNWARD', this is the offset to the location above + the first location at which outgoing arguments are placed. + +`FIRST_PARM_OFFSET (FUNDECL)' + Offset from the argument pointer register to the first argument's + address. On some machines it may depend on the data type of the + function. + + If `ARGS_GROW_DOWNWARD', this is the offset to the location above + the first argument's address. + +`STACK_DYNAMIC_OFFSET (FUNDECL)' + Offset from the stack pointer register to an item dynamically + allocated on the stack, e.g., by `alloca'. + + The default value for this macro is `STACK_POINTER_OFFSET' plus the + length of the outgoing arguments. The default is correct for most + machines. See `function.c' for details. + +`DYNAMIC_CHAIN_ADDRESS (FRAMEADDR)' + A C expression whose value is RTL representing the address in a + stack frame where the pointer to the caller's frame is stored. + Assume that FRAMEADDR is an RTL expression for the address of the + stack frame itself. + + If you don't define this macro, the default is to return the value + of FRAMEADDR--that is, the stack frame address is also the address + of the stack word that points to the previous frame. + +`SETUP_FRAME_ADDRESSES ()' + If defined, a C expression that produces the machine-specific code + to setup the stack so that arbitrary frames can be accessed. For + example, on the Sparc, we must flush all of the register windows + to the stack before we can access arbitrary stack frames. This + macro will seldom need to be defined. + +`RETURN_ADDR_RTX (COUNT, FRAMEADDR)' + A C expression whose value is RTL representing the value of the + return address for the frame COUNT steps up from the current frame. + FRAMEADDR is the frame pointer of the COUNT frame, or the frame + pointer of the COUNT - 1 frame if `RETURN_ADDR_IN_PREVIOUS_FRAME' + is defined. + +`RETURN_ADDR_IN_PREVIOUS_FRAME' + Define this if the return address of a particular stack frame is + accessed from the frame pointer of the previous stack frame.  -File: gcc.info, Node: Uninitialized Data, Next: Label Output, Prev: Data Output, Up: Assembler Format +File: gcc.info, Node: Frame Registers, Next: Elimination, Prev: Frame Layout, Up: Stack and Calling + +Registers That Address the Stack Frame +-------------------------------------- -Output of Uninitialized Variables ---------------------------------- + This discusses registers that address the stack frame. - Each of the macros in this section is used to do the whole job of -outputting a single uninitialized variable. +`STACK_POINTER_REGNUM' + The register number of the stack pointer register, which must also + be a fixed register according to `FIXED_REGISTERS'. On most + machines, the hardware determines which register this is. + +`FRAME_POINTER_REGNUM' + The register number of the frame pointer register, which is used to + access automatic variables in the stack frame. On some machines, + the hardware determines which register this is. On other + machines, you can choose any register you wish for this purpose. + +`HARD_FRAME_POINTER_REGNUM' + On some machines the offset between the frame pointer and starting + offset of the automatic variables is not known until after register + allocation has been done (for example, because the saved registers + are between these two locations). On those machines, define + `FRAME_POINTER_REGNUM' the number of a special, fixed register to + be used internally until the offset is known, and define + `HARD_FRAME_POINTER_REGNUM' to be actual the hard register number + used for the frame pointer. + + You should define this macro only in the very rare circumstances + when it is not possible to calculate the offset between the frame + pointer and the automatic variables until after register + allocation has been completed. When this macro is defined, you + must also indicate in your definition of `ELIMINABLE_REGS' how to + eliminate `FRAME_POINTER_REGNUM' into either + `HARD_FRAME_POINTER_REGNUM' or `STACK_POINTER_REGNUM'. + + Do not define this macro if it would be the same as + `FRAME_POINTER_REGNUM'. + +`ARG_POINTER_REGNUM' + The register number of the arg pointer register, which is used to + access the function's argument list. On some machines, this is + the same as the frame pointer register. On some machines, the + hardware determines which register this is. On other machines, + you can choose any register you wish for this purpose. If this is + not the same register as the frame pointer register, then you must + mark it as a fixed register according to `FIXED_REGISTERS', or + arrange to be able to eliminate it (*note Elimination::.). + +`STATIC_CHAIN_REGNUM' +`STATIC_CHAIN_INCOMING_REGNUM' + Register numbers used for passing a function's static chain + pointer. If register windows are used, the register number as + seen by the called function is `STATIC_CHAIN_INCOMING_REGNUM', + while the register number as seen by the calling function is + `STATIC_CHAIN_REGNUM'. If these registers are the same, + `STATIC_CHAIN_INCOMING_REGNUM' need not be defined. + + The static chain register need not be a fixed register. + + If the static chain is passed in memory, these macros should not be + defined; instead, the next two macros should be defined. + +`STATIC_CHAIN' +`STATIC_CHAIN_INCOMING' + If the static chain is passed in memory, these macros provide rtx + giving `mem' expressions that denote where they are stored. + `STATIC_CHAIN' and `STATIC_CHAIN_INCOMING' give the locations as + seen by the calling and called functions, respectively. Often the + former will be at an offset from the stack pointer and the latter + at an offset from the frame pointer. + + The variables `stack_pointer_rtx', `frame_pointer_rtx', and + `arg_pointer_rtx' will have been initialized prior to the use of + these macros and should be used to refer to those items. -`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. + If the static chain is passed in a register, the two previous + macros should be defined instead.  -File: gcc.info, Node: Label Output, Next: Initialization, Prev: Uninitialized Data, Up: Assembler Format +File: gcc.info, Node: Elimination, Next: Stack Arguments, Prev: Frame Registers, Up: Stack and Calling -Output and Generation of Labels -------------------------------- +Eliminating Frame Pointer and Arg Pointer +----------------------------------------- -`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. + This is about eliminating the frame pointer and arg pointer. - If this macro is not defined, then the function size is not +`FRAME_POINTER_REQUIRED' + A C expression which is nonzero if a function must have and use a + frame pointer. This expression is evaluated in the reload pass. + If its value is nonzero the function will have a frame pointer. + + The expression can in principle examine the current function and + decide according to the facts, but on most machines the constant 0 + or the constant 1 suffices. Use 0 when the machine allows code to + be generated with no frame pointer, and doing so saves some time + or space. Use 1 when there is no possible advantage to avoiding a + frame pointer. + + In certain cases, the compiler does not know how to produce valid + code without a frame pointer. The compiler recognizes those cases + and automatically gives the function a frame pointer regardless of + what `FRAME_POINTER_REQUIRED' says. You don't need to worry about + them. + + In a function that does not require a frame pointer, the frame + pointer register can be allocated for ordinary usage, unless you + mark it as a fixed register. See `FIXED_REGISTERS' for more + information. + +`INITIAL_FRAME_POINTER_OFFSET (DEPTH-VAR)' + A C statement to store in the variable DEPTH-VAR the difference + between the frame pointer and the stack pointer values immediately + after the function prologue. The value would be computed from + information such as the result of `get_frame_size ()' and the + tables of registers `regs_ever_live' and `call_used_regs'. + + If `ELIMINABLE_REGS' is defined, this macro will be not be used and + need not be defined. Otherwise, it must be defined even if + `FRAME_POINTER_REQUIRED' is defined to always be true; in that + case, you may set DEPTH-VAR to anything. + +`ELIMINABLE_REGS' + If defined, this macro specifies a table of register pairs used to + eliminate unneeded registers that point into the stack frame. If + it is not defined, the only elimination attempted by the compiler + is to replace references to the frame pointer with references to + the stack pointer. + + The definition of this macro is a list of structure + initializations, each of which specifies an original and + replacement register. + + On some machines, the position of the argument pointer is not + known until the compilation is completed. In such a case, a + separate hard register must be used for the argument pointer. + This register can be eliminated by replacing it with either the + frame pointer or the argument pointer, depending on whether or not + the frame pointer has been eliminated. + + In this case, you might specify: + #define ELIMINABLE_REGS \ + {{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM}, \ + {ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM}, \ + {FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM}} + + Note that the elimination of the argument pointer with the stack + pointer is specified first since that is the preferred elimination. + +`CAN_ELIMINATE (FROM-REG, TO-REG)' + A C expression that returns non-zero if the compiler is allowed to + try to replace register number FROM-REG with register number + TO-REG. This macro need only be defined if `ELIMINABLE_REGS' is + defined, and will usually be the constant 1, since most of the + cases preventing register elimination are things that the compiler + already knows about. + +`INITIAL_ELIMINATION_OFFSET (FROM-REG, TO-REG, OFFSET-VAR)' + This macro is similar to `INITIAL_FRAME_POINTER_OFFSET'. It + specifies the initial difference between the specified pair of + registers. This macro must be defined if `ELIMINABLE_REGS' is 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. - - On systems where the assembler can handle quoted names, you can - use this macro to provide more human-readable names. +`LONGJMP_RESTORE_FROM_STACK' + Define this macro if the `longjmp' function restores registers from + the stack frames, rather than from those saved specifically by + `setjmp'. Certain quantities must not be kept in registers across + a call to `setjmp' on such machines.  -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. - -`svr4.h' - For System V Release 4 and similar systems using `ELF' format. +File: gcc.info, Node: Stack Arguments, Next: Register Arguments, Prev: Elimination, Up: Stack and Calling -`vms.h' - For the VMS operating system. +Passing Function Arguments on the Stack +--------------------------------------- - The following section describes the specific macros that control and -customize the handling of initialization and termination functions. + The macros in this section control how arguments are passed on the +stack. See the following section for other macros that control passing +certain arguments in registers. + +`PROMOTE_PROTOTYPES' + Define this macro if an argument declared in a prototype as an + integral type smaller than `int' should actually be passed as an + `int'. In addition to avoiding errors in certain cases of + mismatch, it also makes for better code on certain machines. + +`PUSH_ROUNDING (NPUSHED)' + A C expression that is the number of bytes actually pushed onto the + stack when an instruction attempts to push NPUSHED bytes. + + If the target machine does not have a push instruction, do not + define this macro. That directs GNU CC to use an alternate + strategy: to allocate the entire argument block and then store the + arguments into it. + + On some machines, the definition + + #define PUSH_ROUNDING(BYTES) (BYTES) + + will suffice. But on other machines, instructions that appear to + push one byte actually push two bytes in an attempt to maintain + alignment. Then the definition should be + + #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) + +`ACCUMULATE_OUTGOING_ARGS' + If defined, the maximum amount of space required for outgoing + arguments will be computed and placed into the variable + `current_function_outgoing_args_size'. No space will be pushed + onto the stack for each call; instead, the function prologue should + increase the stack frame size by this amount. + + Defining both `PUSH_ROUNDING' and `ACCUMULATE_OUTGOING_ARGS' is + not proper. + +`REG_PARM_STACK_SPACE (FNDECL)' + Define this macro if functions should assume that stack space has + been allocated for arguments even when their values are passed in + registers. + + The value of this macro is the size, in bytes, of the area + reserved for arguments passed in registers for the function + represented by FNDECL. + + This space can be allocated by the caller, or be a part of the + machine-dependent stack frame: `OUTGOING_REG_PARM_STACK_SPACE' says + which. + +`MAYBE_REG_PARM_STACK_SPACE' +`FINAL_REG_PARM_STACK_SPACE (CONST_SIZE, VAR_SIZE)' + Define these macros in addition to the one above if functions might + allocate stack space for arguments even when their values are + passed in registers. These should be used when the stack space + allocated for arguments in registers is not a simple constant + independent of the function declaration. + + The value of the first macro is the size, in bytes, of the area + that we should initially assume would be reserved for arguments + passed in registers. + + The value of the second macro is the actual size, in bytes, of the + area that will be reserved for arguments passed in registers. + This takes two arguments: an integer representing the number of + bytes of fixed sized arguments on the stack, and a tree + representing the number of bytes of variable sized arguments on + the stack. + + When these macros are defined, `REG_PARM_STACK_SPACE' will only be + called for libcall functions, the current function, or for a + function being called when it is known that such stack space must + be allocated. In each case this value can be easily computed. + + When deciding whether a called function needs such stack space, + and how much space to reserve, GNU CC uses these two macros + instead of `REG_PARM_STACK_SPACE'. + +`OUTGOING_REG_PARM_STACK_SPACE' + Define this if it is the responsibility of the caller to allocate + the area reserved for arguments passed in registers. + + If `ACCUMULATE_OUTGOING_ARGS' is defined, this macro controls + whether the space for these arguments counts in the value of + `current_function_outgoing_args_size'. + +`STACK_PARMS_IN_REG_PARM_AREA' + Define this macro if `REG_PARM_STACK_SPACE' is defined, but the + stack parameters don't skip the area specified by it. + + Normally, when a parameter is not passed in registers, it is + placed on the stack beyond the `REG_PARM_STACK_SPACE' area. + Defining this macro suppresses this behavior and causes the + parameter to be passed on the stack in its natural location. + +`RETURN_POPS_ARGS (FUNDECL, FUNTYPE, STACK-SIZE)' + A C expression that should indicate the number of bytes of its own + arguments that a function pops on returning, or 0 if the function + pops no arguments and the caller must therefore pop them all after + the function returns. + + FUNDECL is a C variable whose value is a tree node that describes + the function in question. Normally it is a node of type + `FUNCTION_DECL' that describes the declaration of the function. + From this it is possible to obtain the DECL_MACHINE_ATTRIBUTES of + the function. + + FUNTYPE is a C variable whose value is a tree node that describes + the function in question. Normally it is a node of type + `FUNCTION_TYPE' that describes the data type of the function. + From this it is possible to obtain the data types of the value and + arguments (if known). + + When a call to a library function is being considered, FUNTYPE + will contain an identifier node for the library function. Thus, if + you need to distinguish among various library functions, you can + do so by their names. Note that "library function" in this + context means a function used to perform arithmetic, whose name is + known specially in the compiler and was not mentioned in the C + code being compiled. + + STACK-SIZE is the number of bytes of arguments passed on the + stack. If a variable number of bytes is passed, it is zero, and + argument popping will always be the responsibility of the calling + function. + + On the Vax, all functions always pop their arguments, so the + definition of this macro is STACK-SIZE. On the 68000, using the + standard calling convention, no functions pop their arguments, so + the value of the macro is always 0 in this case. But an + alternative calling convention is available in which functions + that take a fixed number of arguments pop them but other functions + (such as `printf') pop nothing (the caller pops all). When this + convention is in use, FUNTYPE is examined to determine whether a + function takes a fixed number of arguments.