Info file gcc.info, produced by Makeinfo, -*- Text -*- from input file gcc.texinfo. This file documents the use and the internals of the GNU compiler. Copyright (C) 1988, 1989, 1990 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 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. 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. File: gcc.info, Node: Register Classes, Next: Stack Layout, Prev: Registers, Up: Machine Macros Register Classes ================ 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'. 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 that 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'. `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 definition #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS is safe. 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. In a shift instruction or a bitwise-and instruction, the mode of X, the value being reloaded, may not be the same as the mode of the instruction's operand. (They will both be fixed-point modes, however.) In such a case, CLASS may not be a safe value to return. CLASS is certainly valid for the instruction, but it may not be valid for reloading X. This problem can occur on machines such as the 68000 and 80386 where some registers can handle full-word values but cannot handle single-byte values. On such machines, this macro must examine the mode of X and return a subclass of CLASS which can handle loads and stores of that mode. On the 68000, where address registers cannot handle `QImode', if X has `QImode' then you must return `DATA_REGS'. If CLASS is `ADDR_REGS', then there is no correct value to return; but the shift and bitwise-and instructions don't use `ADDR_REGS', so this fatal case never arises. `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. Two other special macros describe which constants 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 floating 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. File: gcc.info, Node: Stack Layout, Next: Library Names, Prev: Register Classes, Up: Machine Macros Describing Stack Layout ======================= `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. `STARTING_FRAME_OFFSET' Offset from the frame pointer to the first local variable slot to be allocated. If `FRAME_GROWS_DOWNWARD', the next slot's offset is found by subtracting the length of the first slot from `STARTING_FRAME_OFFSET'. Otherwise, it is found by adding the length of the first slot to the value `STARTING_FRAME_OFFSET'. `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) `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. (In the next version of GNU CC, the argument will be changed to the function data type rather than its declaration.) `FIRST_PARM_CALLER_OFFSET (FUNDECL)' Define this macro on machines where register parameters have shadow locations on the stack, at addresses below the nominal parameter. This matters because certain arguments cannot be passed on the stack. On these machines, such arguments must be stored into the shadow locations. This macro should expand into a C expression whose value is the offset of the first parameter's shadow location from the nominal stack pointer value. (That value is itself computed by adding the value of `STACK_POINTER_OFFSET' to the stack pointer register.) `REG_PARM_STACK_SPACE' Define this macro if functions should assume that stack space has been allocated for arguments even when their values are passed in registers. The actual allocation of such space would be done either by the call instruction or by the function prologue, or by defining `FIRST_PARM_CALLER_OFFSET'. `STACK_ARGS_ADJUST (SIZE)' Define this macro if the machine requires padding on the stack for certain function calls. This is padding on a per-function-call basis, not padding for individual arguments. The argument SIZE will be a C variable of type `struct arg_data' which contains two fields, an integer named `constant' and an RTX named `var'. These together represent a size measured in bytes which is the sum of the integer and the RTX. Most of the time `var' is 0, which means that the size is simply the integer. The definition should be a C statement or compound statement which alters the variable supplied in whatever way you wish. Note that the value you leave in the variable `size' will ultimately be rounded up to a multiple of `STACK_BOUNDARY' bits. This macro is not fully implemented for machines which have push instructions (i.e., on which `PUSH_ROUNDING' is defined). `RETURN_POPS_ARGS (FUNTYPE)' A C expression that should be 1 if a function pops its own arguments on returning, or 0 if the function pops no arguments and the caller must therefore pop them all after the function returns. 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. On the Vax, all functions always pop their arguments, so the definition of this macro is 1. 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. When this macro returns nonzero, the macro `FRAME_POINTER_REQUIRED' must also return nonzero for proper operation. `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 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_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, and `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. `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' are returned in memory regardless of 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 0. `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. `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. `FUNCTION_ARG (CUM, MODE, TYPE, NAMED)' A C expression that controls whether a function argument is passed in a register, and which register. The arguments are CUM, which summarizes all the previous arguments; MODE, the machine mode of the argument; TYPE, the data type of the argument as a tree node or 0 if that is not known (which happens for C support library functions); and NAMED, which is 1 for an ordinary argument and 0 for nameless arguments that correspond to `...' in the called function's prototype. The value of the expression should either be a `reg' RTX for the hard register in which to pass the argument, or zero to pass the argument on the stack. For the Vax and 68000, where normally all arguments are pushed, zero suffices as a definition. The usual way to make the ANSI library `stdarg.h' work on a machine where some arguments are usually passed in registers, is to cause nameless arguments to be passed on the stack instead. This is done by making `FUNCTION_ARG' return 0 whenever NAMED is 0. `FUNCTION_INCOMING_ARG (CUM, MODE, TYPE, NAMED)' Define this macro if the target machine has "register windows", so that the register in which a function sees an arguments is not necessarily the same as the one in which the caller passed the argument. For such machines, `FUNCTION_ARG' computes the register in which the caller passes the value, and `FUNCTION_INCOMING_ARG' should be defined in a similar fashion to tell the function being called where the arguments will arrive. If `FUNCTION_INCOMING_ARG' is not defined, `FUNCTION_ARG' serves both purposes. `FUNCTION_ARG_PARTIAL_NREGS (CUM, MODE, TYPE, NAMED)' A C expression for the number of words, at the beginning of an argument, must be put in registers. The value must be zero for arguments that are passed entirely in registers or that are entirely pushed on the stack. On some machines, certain arguments must be passed partially in registers and partially in memory. On these machines, typically the first N words of arguments are passed in registers, and the rest on the stack. If a multi-word argument (a `double' or a structure) crosses that boundary, its first few words must be passed in registers and the rest must be pushed. This macro tells the compiler when this occurs, and how many of the words should go in registers. `FUNCTION_ARG' for these arguments should return the first register to be used by the caller for this argument; likewise `FUNCTION_INCOMING_ARG', for the called function. `CUMULATIVE_ARGS' A C type for declaring a variable that is used as the first argument of `FUNCTION_ARG' and other related values. For some target machines, the type `int' suffices and can hold the number of bytes of argument so far. `INIT_CUMULATIVE_ARGS (CUM, FNTYPE)' A C statement (sans semicolon) for initializing the variable CUM for the state at the beginning of the argument list. The variable has type `CUMULATIVE_ARGS'. The value of FNTYPE is the tree node for the data type of the function which will receive the args, or 0 if the args are to a compiler support library function. `FUNCTION_ARG_ADVANCE (CUM, MODE, TYPE, NAMED)' A C statement (sans semicolon) to update the summarizer variable CUM to advance past an argument in the argument list. The values MODE, TYPE and NAMED describe that argument. Once this is done, the variable CUM is suitable for analyzing the *following* argument with `FUNCTION_ARG', etc. `FUNCTION_ARG_REGNO_P (REGNO)' A C expression that is nonzero if REGNO is the number of a hard register in which function arguments are sometimes passed. This does *not* include implicit arguments such as the static chain and the structure-value address. On many machines, no registers can be used for this purpose since all function arguments are pushed on the stack. `FUNCTION_ARG_PADDING (MODE, SIZE)' If defined, a C expression which determines whether, and in which direction, to pad out an argument with extra space. The value should be of type `enum direction': either `upward' to pad above the argument, `downward' to pad below, or `none' to inhibit padding. The argument SIZE is an RTX which describes the size of the argument, in bytes. It should be used only if MODE is `BLKmode'. Otherwise, SIZE is 0. This macro does not control the *amount* of padding; that is always just enough to reach the next multiple of `PARM_BOUNDARY'. This macro has a default definition which is right for most systems. For little-endian machines, the default is to pad upward. For big-endian machines, the default is to pad downward for an argument of constant size shorter than an `int', and upward otherwise. `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, but not if it is one of the call-used registers. 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. On machines where an argument may be passed partly in registers and partly in memory, this macro must examine the variable `current_function_pretend_args_size', and allocate that many bytes of uninitialized space on the stack just underneath the first argument arriving on the stack. (This may not be at the very end of the stack, 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.) `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. `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. `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 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. 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 `current_function_pops_args' is nonzero if the function should pop its own arguments. If so, use the variable `current_function_args_size' as the number of bytes to pop. `FIX_FRAME_POINTER_ADDRESS (ADDR, DEPTH)' A C compound statement to alter a memory address that uses the frame pointer register so that it uses the stack pointer register instead. This must be done in the instructions that load parameter values into registers, when the reload pass determines that a frame pointer is not necessary for the function. ADDR will be a C variable name, and the updated address should be stored in that variable. DEPTH will be the current depth of stack temporaries (number of bytes of arguments currently pushed). The change in offset between a frame-pointer-relative address and a stack-pointer-relative address must include DEPTH. Even if your machine description specifies there will always be a frame pointer in the frame pointer register, you must still define `FIX_FRAME_POINTER_ADDRESS', but the definition will never be executed at run time, so it may be empty. `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: Library Names, Next: Addressing Modes, Prev: Stack Layout, Up: Machine Macros Library Subroutine 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 `gnulib'. `UMULSI3_LIBCALL' A C string constant giving the name of the function to call for multiplication of one unsigned full-word by another. If you do not define this macro, the default name is used, which is `__umulsi3', a function defined in `gnulib'. `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 `gnulib'. `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 `gnulib'. `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 `gnulib'. `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 `gnulib'. `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'. File: gcc.info, Node: Addressing Modes, Next: Delayed Branch, Prev: Library Names, Up: Machine Macros Addressing Modes ================ `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 whose value is an integer. This includes integers whose values are not explicitly known, such as `symbol_ref' and `label_ref' expressions and `const' arithmetic expressions. On most machines, this can be defined as `CONSTANT_P (X)', but a few machines are more restrictive in which constant addresses are supported. `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. Typically among the subroutines used to define `GO_IF_LEGITIMATE_ADDRESS' are subroutines to check for acceptable registers for various purposes (one for base registers, one for index registers, and so on). 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 as legitimate addresses. 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'. `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. 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 either X is a `const_double' or it satisfies `CONSTANT_P', so you need not check these things. In fact, `1' is a suitable definition for this macro on machines where any `const_double' is valid and anything `CONSTANT_P' is valid. File: gcc.info, Node: Delayed Branch, Next: Condition Code, Prev: Addressing Modes, Up: Machine Macros Parameters for Delayed Branch Optimization ========================================== `HAVE_DELAYED_BRANCH' Define this macro if the target machine has delayed branches, that is, a branch does not take effect immediately, and the actual branch instruction may be followed by one or more instructions that will be issued before the PC is actually changed. If defined, this allows a special scheduling pass to be run after the second jump optimization to attempt to reorder instructions to exploit this. Defining this macro also requires the definition of certain other macros described below. `DBR_SLOTS_AFTER (INSN)' This macro must be defined if `HAVE_DELAYED_BRANCH' is defined. Its definition should be a C expression returning the number of available delay slots following the instruction(s) output by the pattern for INSN. The definition of "slot" is machine-dependent, and may denote instructions, bytes, or whatever. `DBR_INSN_SLOTS (INSN)' This macro must be defined if `HAVE_DELAYED_BRANCH' is defined. It should be a C expression returning the number of slots (typically the number of machine instructions) consumed by INSN. You may assume that INSN is truly an insn, not a note, label, barrier, dispatch table, `use', or `clobber'. `DBR_INSN_ELIGIBLE_P (INSN, DINSN)' A C expression whose value is non-zero if it is legitimate to put INSN in the delay slot following DINSN. You do not need to take account of data flow considerations in the definition of this macro, because the delayed branch optimizer always does that. This macro is needed only when certain insns may not be placed in certain delay slots for reasons not evident from the RTL expressions themselves. If there are no such problems, you don't need to define this macro. You may assume that INSN is truly an insn, not a note, label, barrier, dispatch table, `use', or `clobber'. You may assume that DINSN is a jump insn with a delay slot. `DBR_OUTPUT_SEQEND(FILE)' A C statement, to be executed after all slot-filler instructions have been output. If necessary, call `dbr_sequence_length' to determine the number of slots filled in a sequence (zero if not currently outputting a sequence), to decide how many no-ops to output, or whatever. Don't define this macro if it has nothing to do, but it is helpful in reading assembly output if the extent of the delay sequence is made explicit (e.g. with white space). Note that output routines for instructions with delay slots must be prepared to deal with not being output as part of a sequence (i.e. when the scheduling pass is not run, or when no slot fillers could be found.) The variable `final_sequence' is null when not processing a sequence, otherwise it contains the `sequence' rtx being output. File: gcc.info, Node: Condition Code, Next: Cross-compilation, Prev: Delayed Branch, Up: Machine Macros Condition Code Information ========================== 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'. `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. `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)'. If there are insn 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'.