--- gcc/gcc.info-15 2018/04/24 17:53:01 1.1.1.2 +++ gcc/gcc.info-15 2018/04/24 18:19:23 1.1.1.7 @@ -1,1058 +1,987 @@ -This is Info file gcc.info, produced by Makeinfo-1.44 from the input +This is Info file gcc.info, produced by Makeinfo-1.55 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. - Copyright (C) 1988, 1989, 1992 Free Software Foundation, Inc. + Published by the Free Software Foundation 675 Massachusetts Avenue +Cambridge, MA 02139 USA - 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. + Copyright (C) 1988, 1989, 1992, 1993, 1994 Free Software Foundation, +Inc. + + Permission is granted to make and distribute verbatim copies of this +manual provided the copyright notice and this permission notice are +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 section entitled "GNU General Public License" is 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 section entitled "GNU General Public -License" and this permission notice may be included in translations -approved by the Free Software Foundation instead of in the original -English. +versions, except that the sections entitled "GNU General Public +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: Output Statement, Next: Constraints, Prev: Output Template, Up: Machine Desc + +C Statements for Assembler Output +================================= + + Often a single fixed template string cannot produce correct and +efficient assembler code for all the cases that are recognized by a +single instruction pattern. For example, the opcodes may depend on the +kinds of operands; or some unfortunate combinations of operands may +require extra machine instructions. + + If the output control string starts with a `@', then it is actually +a series of templates, each on a separate line. (Blank lines and +leading spaces and tabs are ignored.) The templates correspond to the +pattern's constraint alternatives (*note Multi-Alternative::.). For +example, if a target machine has a two-address add instruction `addr' +to add into a register and another `addm' to add a register to memory, +you might write this pattern: + + (define_insn "addsi3" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (plus:SI (match_operand:SI 1 "general_operand" "0,0") + (match_operand:SI 2 "general_operand" "g,r")))] + "" + "@ + addr %2,%0 + addm %2,%0") + + If the output control string starts with a `*', then it is not an +output template but rather a piece of C program that should compute a +template. It should execute a `return' statement to return the +template-string you want. Most such templates use C string literals, +which require doublequote characters to delimit them. To include these +doublequote characters in the string, prefix each one with `\'. + + The operands may be found in the array `operands', whose C data type +is `rtx []'. + + It is very common to select different ways of generating assembler +code based on whether an immediate operand is within a certain range. +Be careful when doing this, because the result of `INTVAL' is an +integer on the host machine. If the host machine has more bits in an +`int' than the target machine has in the mode in which the constant +will be used, then some of the bits you get from `INTVAL' will be +superfluous. For proper results, you must carefully disregard the +values of those bits. + + It is possible to output an assembler instruction and then go on to +output or compute more of them, using the subroutine `output_asm_insn'. +This receives two arguments: a template-string and a vector of +operands. The vector may be `operands', or it may be another array of +`rtx' that you declare locally and initialize yourself. + + When an insn pattern has multiple alternatives in its constraints, +often the appearance of the assembler code is determined mostly by +which alternative was matched. When this is so, the C code can test +the variable `which_alternative', which is the ordinal number of the +alternative that was actually satisfied (0 for the first, 1 for the +second alternative, etc.). + + For example, suppose there are two opcodes for storing zero, `clrreg' +for registers and `clrmem' for memory locations. Here is how a pattern +could use `which_alternative' to choose between them: + + (define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + "* + return (which_alternative == 0 + ? \"clrreg %0\" : \"clrmem %0\"); + ") + + The example above, where the assembler code to generate was *solely* +determined by the alternative, could also have been specified as +follows, having the output control string start with a `@': + + (define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + "@ + clrreg %0 + clrmem %0") + + +File: gcc.info, Node: Constraints, Next: Standard Names, Prev: Output Statement, Up: Machine Desc + +Operand Constraints +=================== + + Each `match_operand' in an instruction pattern can specify a +constraint for the type of operands allowed. Constraints can say +whether an operand may be in a register, and which kinds of register; +whether the operand can be a memory reference, and which kinds of +address; whether the operand may be an immediate constant, and which +possible values it may have. Constraints can also require two operands +to match. + +* Menu: + +* Simple Constraints:: Basic use of constraints. +* Multi-Alternative:: When an insn has two alternative constraint-patterns. +* Class Preferences:: Constraints guide which hard register to put things in. +* Modifiers:: More precise control over effects of constraints. +* Machine Constraints:: Existing constraints for some particular machines. +* No Constraints:: Describing a clean machine without constraints. + + +File: gcc.info, Node: Simple Constraints, Next: Multi-Alternative, Up: Constraints + +Simple Constraints +------------------ + + The simplest kind of constraint is a string full of letters, each of +which describes one kind of operand that is permitted. Here are the +letters that are allowed: + +`m' + A memory operand is allowed, with any kind of address that the + machine supports in general. + +`o' + A memory operand is allowed, but only if the address is + "offsettable". This means that adding a small integer (actually, + the width in bytes of the operand, as determined by its machine + mode) may be added to the address and the result is also a valid + memory address. + + For example, an address which is constant is offsettable; so is an + address that is the sum of a register and a constant (as long as a + slightly larger constant is also within the range of + address-offsets supported by the machine); but an autoincrement or + autodecrement address is not offsettable. More complicated + indirect/indexed addresses may or may not be offsettable depending + on the other addressing modes that the machine supports. + + Note that in an output operand which can be matched by another + operand, the constraint letter `o' is valid only when accompanied + by both `<' (if the target machine has predecrement addressing) + and `>' (if the target machine has preincrement addressing). + +`V' + A memory operand that is not offsettable. In other words, + anything that would fit the `m' constraint but not the `o' + constraint. + +`<' + A memory operand with autodecrement addressing (either + predecrement or postdecrement) is allowed. + +`>' + A memory operand with autoincrement addressing (either + preincrement or postincrement) is allowed. + +`r' + A register operand is allowed provided that it is in a general + register. + +`d', `a', `f', ... + Other letters can be defined in machine-dependent fashion to stand + for particular classes of registers. `d', `a' and `f' are defined + on the 68000/68020 to stand for data, address and floating point + registers. + +`i' + An immediate integer operand (one with constant value) is allowed. + This includes symbolic constants whose values will be known only at + assembly time. + +`n' + An immediate integer operand with a known numeric value is allowed. + Many systems cannot support assembly-time constants for operands + less than a word wide. Constraints for these operands should use + `n' rather than `i'. + +`I', `J', `K', ... `P' + Other letters in the range `I' through `P' may be defined in a + machine-dependent fashion to permit immediate integer operands with + explicit integer values in specified ranges. For example, on the + 68000, `I' is defined to stand for the range of values 1 to 8. + This is the range permitted as a shift count in the shift + instructions. + +`E' + An immediate floating operand (expression code `const_double') is + allowed, but only if the target floating point format is the same + as that of the host machine (on which the compiler is running). + +`F' + An immediate floating operand (expression code `const_double') is + allowed. + +`G', `H' + `G' and `H' may be defined in a machine-dependent fashion to + permit immediate floating operands in particular ranges of values. + +`s' + An immediate integer operand whose value is not an explicit + integer is allowed. + + This might appear strange; if an insn allows a constant operand + with a value not known at compile time, it certainly must allow + any known value. So why use `s' instead of `i'? Sometimes it + allows better code to be generated. + + For example, on the 68000 in a fullword instruction it is possible + to use an immediate operand; but if the immediate value is between + -128 and 127, better code results from loading the value into a + register and using the register. This is because the load into + the register can be done with a `moveq' instruction. We arrange + for this to happen by defining the letter `K' to mean "any integer + outside the range -128 to 127", and then specifying `Ks' in the + operand constraints. + +`g' + Any register, memory or immediate integer operand is allowed, + except for registers that are not general registers. + +`X' + Any operand whatsoever is allowed, even if it does not satisfy + `general_operand'. This is normally used in the constraint of a + `match_scratch' when certain alternatives will not actually + require a scratch register. + +`0', `1', `2', ... `9' + An operand that matches the specified operand number is allowed. + If a digit is used together with letters within the same + alternative, the digit should come last. + + This is called a "matching constraint" and what it really means is + that the assembler has only a single operand that fills two roles + considered separate in the RTL insn. For example, an add insn has + two input operands and one output operand in the RTL, but on most + CISC machines an add instruction really has only two operands, one + of them an input-output operand: + + addl #35,r12 + + Matching constraints are used in these circumstances. More + precisely, the two operands that match must include one input-only + operand and one output-only operand. Moreover, the digit must be a + smaller number than the number of the operand that uses it in the + constraint. + + For operands to match in a particular case usually means that they + are identical-looking RTL expressions. But in a few special cases + specific kinds of dissimilarity are allowed. For example, `*x' as + an input operand will match `*x++' as an output operand. For + proper results in such cases, the output template should always + use the output-operand's number when printing the operand. + +`p' + An operand that is a valid memory address is allowed. This is for + "load address" and "push address" instructions. + + `p' in the constraint must be accompanied by `address_operand' as + the predicate in the `match_operand'. This predicate interprets + the mode specified in the `match_operand' as the mode of the memory + reference for which the address would be valid. + +`Q', `R', `S', ... `U' + Letters in the range `Q' through `U' may be defined in a + machine-dependent fashion to stand for arbitrary operand types. + The machine description macro `EXTRA_CONSTRAINT' is passed the + operand as its first argument and the constraint letter as its + second operand. + + A typical use for this would be to distinguish certain types of + memory references that affect other insn operands. + + Do not define these constraint letters to accept register + references (`reg'); the reload pass does not expect this and would + not handle it properly. + + In order to have valid assembler code, each operand must satisfy its +constraint. But a failure to do so does not prevent the pattern from +applying to an insn. Instead, it directs the compiler to modify the +code so that the constraint will be satisfied. Usually this is done by +copying an operand into a register. + + Contrast, therefore, the two instruction patterns that follow: + + (define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r") + (plus:SI (match_dup 0) + (match_operand:SI 1 "general_operand" "r")))] + "" + "...") + +which has two operands, one of which must appear in two places, and + + (define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r") + (plus:SI (match_operand:SI 1 "general_operand" "0") + (match_operand:SI 2 "general_operand" "r")))] + "" + "...") + +which has three operands, two of which are required by a constraint to +be identical. If we are considering an insn of the form + + (insn N PREV NEXT + (set (reg:SI 3) + (plus:SI (reg:SI 6) (reg:SI 109))) + ...) + +the first pattern would not apply at all, because this insn does not +contain two identical subexpressions in the right place. The pattern +would say, "That does not look like an add instruction; try other +patterns." The second pattern would say, "Yes, that's an add +instruction, but there is something wrong with it." It would direct +the reload pass of the compiler to generate additional insns to make +the constraint true. The results might look like this: + + (insn N2 PREV N + (set (reg:SI 3) (reg:SI 6)) + ...) + + (insn N N2 NEXT + (set (reg:SI 3) + (plus:SI (reg:SI 3) (reg:SI 109))) + ...) + + It is up to you to make sure that each operand, in each pattern, has +constraints that can handle any RTL expression that could be present for +that operand. (When multiple alternatives are in use, each pattern +must, for each possible combination of operand expressions, have at +least one alternative which can handle that combination of operands.) +The constraints don't need to *allow* any possible operand--when this is +the case, they do not constrain--but they must at least point the way to +reloading any possible operand so that it will fit. + + * If the constraint accepts whatever operands the predicate permits, + there is no problem: reloading is never necessary for this operand. + + For example, an operand whose constraints permit everything except + registers is safe provided its predicate rejects registers. + + An operand whose predicate accepts only constant values is safe + provided its constraints include the letter `i'. If any possible + constant value is accepted, then nothing less than `i' will do; if + the predicate is more selective, then the constraints may also be + more selective. + + * Any operand expression can be reloaded by copying it into a + register. So if an operand's constraints allow some kind of + register, it is certain to be safe. It need not permit all + classes of registers; the compiler knows how to copy a register + into another register of the proper class in order to make an + instruction valid. + + * A nonoffsettable memory reference can be reloaded by copying the + address into a register. So if the constraint uses the letter + `o', all memory references are taken care of. + + * A constant operand can be reloaded by allocating space in memory to + hold it as preinitialized data. Then the memory reference can be + used in place of the constant. So if the constraint uses the + letters `o' or `m', constant operands are not a problem. + + * If the constraint permits a constant and a pseudo register used in + an insn was not allocated to a hard register and is equivalent to + a constant, the register will be replaced with the constant. If + the predicate does not permit a constant and the insn is + re-recognized for some reason, the compiler will crash. Thus the + predicate must always recognize any objects allowed by the + constraint. + + If the operand's predicate can recognize registers, but the +constraint does not permit them, it can make the compiler crash. When +this operand happens to be a register, the reload pass will be stymied, +because it does not know how to copy a register temporarily into memory.  -File: gcc.info, Node: Costs, Next: Sections, Prev: Condition Code, Up: Target Macros +File: gcc.info, Node: Multi-Alternative, Next: Class Preferences, Prev: Simple Constraints, Up: Constraints -Describing Relative Costs of Operations -======================================= +Multiple Alternative Constraints +-------------------------------- - These macros let you describe the relative speed of various -operations on the target machine. + Sometimes a single instruction has multiple alternative sets of +possible operands. For example, on the 68000, a logical-or instruction +can combine register or an immediate value into memory, or it can +combine any kind of operand into a register; but it cannot combine one +memory location into another. -`CONST_COSTS (X, 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. - - CODE is the expression code--redundant, since it can be obtained - with `GET_CODE (X)'. - -`RTX_COSTS (X, 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. + These constraints are represented as multiple alternatives. An +alternative can be described by a series of letters for each operand. +The overall constraint for an operand is made from the letters for this +operand from the first alternative, a comma, the letters for this +operand from the second alternative, a comma, and so on until the last +alternative. Here is how it is done for fullword logical-or on the +68000: - This macro is optional; do not define it if the default cost - assumptions are adequate for the target machine. + (define_insn "iorsi3" + [(set (match_operand:SI 0 "general_operand" "=m,d") + (ior:SI (match_operand:SI 1 "general_operand" "%0,0") + (match_operand:SI 2 "general_operand" "dKs,dmKs")))] + ...) -`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 2 is - the default; other values are interpreted relative to that. - - It is not required that the cost always equal 2 when FROM is the - same as TO; on some machines it is expensive to move between - registers if they are not general registers. - - If reload sees an insn consisting of a single `set' between two - hard registers, and if `REGISTER_MOVE_COST' applied to their - classes returns a value of 2, reload does not check to ensure - that the constraints of the insn are met. Setting a cost of - other than 2 will allow reload to verify that the constraints are - met. You should do this if the `movM' pattern's constraints do - not allow such copying. - -`MEMORY_MOVE_COST (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. + The first alternative has `m' (memory) for operand 0, `0' for +operand 1 (meaning it must match operand 0), and `dKs' for operand 2. +The second alternative has `d' (data register) for operand 0, `0' for +operand 1, and `dmKs' for operand 2. The `=' and `%' in the +constraints apply to all the alternatives; their meaning is explained +in the next section (*note Class Preferences::.). - -File: gcc.info, Node: Sections, Next: PIC, Prev: Costs, Up: Target Macros + If all the operands fit any one alternative, the instruction is +valid. Otherwise, for each alternative, the compiler counts how many +instructions must be added to copy the operands so that that +alternative applies. The alternative requiring the least copying is +chosen. If two alternatives need the same amount of copying, the one +that comes first is chosen. These choices can be altered with the `?' +and `!' characters: + +`?' + Disparage slightly the alternative that the `?' appears in, as a + choice when no alternative applies exactly. The compiler regards + this alternative as one unit more costly for each `?' that appears + in it. -Dividing the Output into Sections (Texts, Data, ...) -==================================================== +`!' + Disparage severely the alternative that the `!' appears in. This + alternative can still be used if it fits without reloading, but if + reloading is needed, some other alternative will be used. - 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 string constant for the assembler operation that should - precede instructions and read-only data. Normally `".text"' is - right. - -`DATA_SECTION_ASM_OP' - A C string constant for the assembler operation to identify the - following data as writable initialized data. Normally `".data"' - is right. - -`SHARED_SECTION_ASM_OP' - If defined, a C string constant for 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 string constant for 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). + When an insn pattern has multiple alternatives in its constraints, +often the appearance of the assembler code is determined mostly by which +alternative was matched. When this is so, the C code for writing the +assembler code can use the variable `which_alternative', which is the +ordinal number of the alternative that was actually satisfied (0 for +the first, 1 for the second alternative, etc.). *Note Output +Statement::.  -File: gcc.info, Node: PIC, Next: Assembler Format, Prev: Sections, Up: Target Macros +File: gcc.info, Node: Class Preferences, Next: Modifiers, Prev: Multi-Alternative, Up: Constraints -Position Independent Code -========================= +Register Class Preferences +-------------------------- - 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 `LEGITIMIZE_ADDRESS', and -`PRINT_OPERAND_ADDRESS' as well. 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.) + The operand constraints have another function: they enable the +compiler to decide which kind of hardware register a pseudo register is +best allocated to. The compiler examines the constraints that apply to +the insns that use the pseudo register, looking for the +machine-dependent letters such as `d' and `a' that specify classes of +registers. The pseudo register is put in whichever class gets the most +"votes". The constraint letters `g' and `r' also vote: they vote in +favor of a general register. The machine description says which +registers are considered general. + + Of course, on some machines all registers are equivalent, and no +register classes are defined. Then none of this complexity is relevant.  -File: gcc.info, Node: Assembler Format, Next: Debugging Info, Prev: PIC, Up: Target Macros +File: gcc.info, Node: Modifiers, Next: Machine Constraints, Prev: Class Preferences, Up: Constraints -Defining the Output Assembler Language -====================================== +Constraint Modifier Characters +------------------------------ - This section describes macros whose principal purpose is to -describe how to write instructions in assembler language--rather than -what the instructions do. + Here are constraint modifier characters. -* Menu: +`=' + Means that this operand is write-only for this instruction: the + previous value is discarded and replaced by output data. -* 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. -* Constructor Output:: Output 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. +`+' + Means that this operand is both read and written by the + instruction. - -File: gcc.info, Node: File Framework, Next: Data Output, Up: Assembler Format + When the compiler fixes up the operands to satisfy the constraints, + it needs to know which operands are inputs to the instruction and + which are outputs from it. `=' identifies an output; `+' + identifies an operand that is both input and output; all other + operands are assumed to be input only. -The Overall Framework of an Assembler File ------------------------------------------- +`&' + Means (in a particular alternative) that this operand is written + before the instruction is finished using the input operands. + Therefore, this operand may not lie in a register that is used as + an input operand or as part of any memory address. -`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. + `&' applies only to the alternative in which it is written. In + constraints with multiple alternatives, sometimes one alternative + requires `&' while others do not. See, for example, the `movdf' + insn of the 68000. - -File: gcc.info, Node: Data Output, Next: Uninitialized Data, Prev: File Framework, Up: Assembler Format + `&' does not obviate the need to write `='. + +`%' + Declares the instruction to be commutative for this operand and the + following operand. This means that the compiler may interchange + the two operands if that is the cheapest way to make all operands + fit the constraints. This is often used in patterns for addition + instructions that really have only two operands: the result must + go in one of the arguments. Here for example, is how the 68000 + halfword-add instruction is defined: + + (define_insn "addhi3" + [(set (match_operand:HI 0 "general_operand" "=m,r") + (plus:HI (match_operand:HI 1 "general_operand" "%0,0") + (match_operand:HI 2 "general_operand" "di,g")))] + ...) -Output of Data --------------- +`#' + Says that all following characters, up to the next comma, are to be + ignored as a constraint. They are significant only for choosing + register preferences. -`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', usually - `double'. - -`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: +`*' + Says that the following character should be ignored when choosing + register preferences. `*' has no effect on the meaning of the + constraint as a constraint, and no effect on reloading. - #define ASM_OPEN_PAREN "(" - #define ASM_CLOSE_PAREN ")" + Here is an example: the 68000 has an instruction to sign-extend a + halfword in a data register, and can also sign-extend a value by + copying it into an address register. While either kind of + register is acceptable, the constraints on an address-register + destination are less strict, so it is best if register allocation + makes an address register its goal. Therefore, `*' is used so + that the `d' constraint letter (for data register) is ignored when + computing register preferences. + + (define_insn "extendhisi2" + [(set (match_operand:SI 0 "general_operand" "=*d,a") + (sign_extend:SI + (match_operand:HI 1 "general_operand" "0,g")))] + ...)  -File: gcc.info, Node: Uninitialized Data, Next: Label Output, Prev: Data Output, Up: Assembler Format +File: gcc.info, Node: Machine Constraints, Next: No Constraints, Prev: Modifiers, Up: Constraints -Output of Uninitialized Variables ---------------------------------- +Constraints for Particular Machines +----------------------------------- - Each of the macros in this section is used to do the whole job of -outputting a single uninitialized variable. + Whenever possible, you should use the general-purpose constraint +letters in `asm' arguments, since they will convey meaning more readily +to people reading your code. Failing that, use the constraint letters +that usually have very similar meanings across architectures. The most +commonly used constraints are `m' and `r' (for memory and +general-purpose registers respectively; *note Simple Constraints::.), +and `I', usually the letter indicating the most common +immediate-constant format. -`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. + For each machine architecture, the `config/MACHINE.h' file defines +additional constraints. These constraints are used by the compiler +itself for instruction generation, as well as for `asm' statements; +therefore, some of the constraints are not particularly interesting for +`asm'. The constraints are defined through these macros: - -File: gcc.info, Node: Label Output, Next: Constructor Output, Prev: Uninitialized Data, Up: Assembler Format +`REG_CLASS_FROM_LETTER' + Register class constraints (usually lower case). -Output and Generation of Labels -------------------------------- +`CONST_OK_FOR_LETTER_P' + Immediate constant constraints, for non-floating point constants of + word size or smaller precision (usually upper case). -`ASM_OUTPUT_LABEL (STREAM, NAME)' - A C statement (sans semicolon) to output to the stdio stream - STREAM the assembler definition of a label named NAME. Use the - expression `assemble_name (STREAM, NAME)' to output the name - itself; before and after that, output the additional assembler - syntax for defining the name, and a newline. - -`ASM_DECLARE_FUNCTION_NAME (STREAM, NAME, DECL)' - A C statement (sans semicolon) to output to the stdio stream - STREAM any text necessary for declaring the name NAME of a - function which is being defined. This macro is responsible for - outputting the label definition (perhaps using - `ASM_OUTPUT_LABEL'). The argument DECL is the `FUNCTION_DECL' - tree node representing the function. - - If this macro is not defined, then the function name is defined - in the usual manner as a label (by means of `ASM_OUTPUT_LABEL'). - -`ASM_DECLARE_FUNCTION_SIZE (STREAM, NAME, DECL)' - A C statement (sans semicolon) to output to the stdio stream - STREAM any text necessary for declaring the size of a function - which is being defined. The argument NAME is the name of the - function. The argument DECL is the `FUNCTION_DECL' tree node - representing the function. - - If this macro is not defined, then the function size is not - defined. - -`ASM_DECLARE_OBJECT_NAME (STREAM, NAME, DECL)' - A C statement (sans semicolon) to output to the stdio stream - STREAM any text necessary for declaring the name NAME of an - initialized variable which is being defined. This macro must - output the label definition (perhaps using `ASM_OUTPUT_LABEL'). - The argument DECL is the `VAR_DECL' tree node representing the - variable. - - If this macro is not defined, then the variable name is defined - in the usual manner as a label (by means of `ASM_OUTPUT_LABEL'). - -`ASM_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_LABELREF_AS_INT (FILE, LABEL)' - Define this macro for systems that use the program `collect2'. - The definition should be a C statement to output a word containing - a reference to the label LABEL. - -`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 same 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. - - This string will be used as the 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. +`CONST_DOUBLE_OK_FOR_LETTER_P' + Immediate constant constraints, for all floating point constants + and for constants of greater than word size precision (usually + upper case). - On systems where the assembler can handle quoted names, you can - use this macro to provide more human-readable names. +`EXTRA_CONSTRAINT' + Special cases of registers or memory. This macro is not required, + and is only defined for some machines. - -File: gcc.info, Node: Constructor Output, Next: Instruction Output, Prev: Label Output, Up: Assembler Format + Inspecting these macro definitions in the compiler source for your +machine is the best way to be certain you have the right constraints. +However, here is a summary of the machine-dependent constraints +available on some particular machines. -Output of Initialization Routines ---------------------------------- +*ARM family--`arm.h'* + `f' + Floating-point register - 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 what assembler code is -needed to do this. - - Here are the two macros you should define if necessary: - -`ASM_OUTPUT_CONSTRUCTOR (STREAM, NAME)' - Define this macro as a C statement to output on the stream STREAM - the assembler code to arrange to call the function named NAME at - initialization time. - - Assume that NAME is the name of a C function generated - automatically by the compiler. This function takes no arguments. - Use the function `assemble_name' to output the name NAME; this - performs any system-specific syntactic transformations such as - adding an underscore. - - If you don't define this macro, nothing special is output to - arrange to call the function. This is correct when the function - will be called in some other manner--for example, by means of the - `collect' program, which looks through the symbol table to find - these functions by their names. If you want to use `collect', - then you need to arrange for it to be built and installed and - used on your system. - -`ASM_OUTPUT_DESTRUCTOR (STREAM, NAME)' - This is like `ASM_OUTPUT_CONSTRUCTOR' but used for termination - functions rather than initialization functions. + `F' + One of the floating-point constants 0.0, 0.5, 1.0, 2.0, 3.0, + 4.0, 5.0 or 10.0 - -File: gcc.info, Node: Instruction Output, Next: Dispatch Tables, Prev: Constructor Output, Up: Assembler Format + `G' + Floating-point constant that would satisfy the constraint `F' + if it were negated -Output of Assembler Instructions --------------------------------- + `I' + Integer that is valid as an immediate operand in a data + processing instruction. That is, an integer in the range 0 + to 255 rotated by a multiple of 2 -`REGISTER_NAMES' - A C initializer containing the assembler's names for the machine - registers, each one as a C string constant. This is what - translates register numbers in the compiler into assembler - language. - -`ADDITIONAL_REGISTER_NAMES' - If defined, a C initializer for an array of structures containing - a name and a register number. This macro defines additional - names for hard registers, thus allowing the `asm' option in - declarations to refer to registers using alternate names. - -`ASM_OUTPUT_OPCODE (STREAM, PTR)' - Define this macro if you are using an unusual assembler that - requires different names for the machine instructions. - - The definition is a C statement or statements which output an - assembler instruction opcode to the stdio stream STREAM. The - macro-operand PTR is a variable of type `char *' which points to - the opcode name in its "internal" form--the form that is written - in the machine description. The definition should output the - opcode name to STREAM, performing any translation you desire, and - increment the variable PTR to point at the end of the opcode so - that it will not be output twice. - - In fact, your macro definition may process less than the entire - opcode name, or more than the opcode name; but if you want to - process text that includes `%'-sequences to substitute operands, - you must take care of the substitution yourself. Just be sure to - increment PTR over whatever text should not be output normally. - - If you need to look at the operand values, they can be found as - the elements of `recog_operand'. - - If the macro definition does nothing, the instruction is output - in the usual way. - -`FINAL_PRESCAN_INSN (INSN, OPVEC, NOPERANDS)' - If defined, a C statement to be executed just prior to the output - of assembler code for INSN, to modify the extracted operands so - they will be output differently. - - Here the argument OPVEC is the vector containing the operands - extracted from INSN, and NOPERANDS is the number of elements of - the vector which contain meaningful data for this insn. The - contents of this vector are what will be used to convert the insn - template into assembler code, so you can change the assembler - output by changing the contents of the vector. - - This macro is useful when various assembler syntaxes share a - single file of instruction patterns; by defining this macro - differently, you can cause a large class of instructions to be - output differently (such as with rearranged operands). - Naturally, variations in assembler syntax affecting individual - insn patterns ought to be handled by writing conditional output - routines in those patterns. - - If this macro is not defined, it is equivalent to a null - statement. - -`PRINT_OPERAND (STREAM, X, CODE)' - A C compound statement to output to stdio stream STREAM the - assembler syntax for an instruction operand X. X is an RTL - expression. - - CODE is a value that can be used to specify one of several ways - of printing the operand. It is used when identical operands must - be printed differently depending on the context. CODE comes from - the `%' specification that was used to request printing of the - operand. If the specification was just `%DIGIT' then CODE is 0; - if the specification was `%LTR DIGIT' then CODE is the ASCII code - for LTR. - - If X is a register, this macro should print the register's name. - The names can be found in an array `reg_names' whose type is - `char *[]'. `reg_names' is initialized from `REGISTER_NAMES'. - - When the machine description has a specification `%PUNCT' (a `%' - followed by a punctuation character), this macro is called with a - null pointer for X and the punctuation character for CODE. - -`PRINT_OPERAND_PUNCT_VALID_P (CODE)' - A C expression which evaluates to true if CODE is a valid - punctuation character for use in the `PRINT_OPERAND' macro. If - `PRINT_OPERAND_PUNCT_VALID_P' is not defined, it means that no - punctuation characters (except for the standard one, `%') are used - in this way. - -`PRINT_OPERAND_ADDRESS (STREAM, X)' - A C compound statement to output to stdio stream STREAM the - assembler syntax for an instruction operand that is a memory - reference whose address is X. X is an RTL expression. - - On some machines, the syntax for a symbolic address depends on the - section that the address refers to. On these machines, define - the macro `ENCODE_SECTION_INFO' to store the information into the - `symbol_ref', and then check for it here. *Note Assembler - Format::. - -`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. - -`REGISTER_PREFIX' -`LOCAL_LABEL_PREFIX' -`USER_LABEL_PREFIX' -`IMMEDIATE_PREFIX' - If defined, C string expressions to be used for the `%R', `%L', - `%U', and `%I' options of `asm_fprintf' (see `final.c'). These - are useful when a single `md' file must support multiple - assembler formats. In that case, the various `tm.h' files can - define these macros differently. - -`ASM_OUTPUT_REG_PUSH (STREAM, REGNO)' - A C expression to output to STREAM some assembler code which will - push hard register number REGNO onto the stack. The code need - not be optimal, since this macro is used only when profiling. - -`ASM_OUTPUT_REG_POP (STREAM, REGNO)' - A C expression to output to STREAM some assembler code which will - pop hard register number REGNO off of the stack. The code need - not be optimal, since this macro is used only when profiling. + `J' + Integer in the range -4095 to 4095 - -File: gcc.info, Node: Dispatch Tables, Next: Alignment Output, Prev: Instruction Output, Up: Assembler Format + `K' + Integer that satisfies constraint `I' when inverted (ones + complement) + + `L' + Integer that satisfies constraint `I' when negated (twos + complement) + + `M' + Integer in the range 0 to 32 + + `Q' + A memory reference where the exact address is in a single + register (``m'' is preferable for `asm' statements) + + `R' + An item in the constant pool + + `S' + A symbol in the text segment of the current file + +*AMD 29000 family--`a29k.h'* + `l' + Local register 0 + + `b' + Byte Pointer (`BP') register + + `q' + `Q' register + + `h' + Special purpose register + + `A' + First accumulator register + + `a' + Other accumulator register + + `f' + Floating point register + + `I' + Constant greater than 0, less than 0x100 + + `J' + Constant greater than 0, less than 0x10000 + + `K' + Constant whose high 24 bits are on (1) + + `L' + 16 bit constant whose high 8 bits are on (1) + + `M' + 32 bit constant whose high 16 bits are on (1) + + `N' + 32 bit negative constant that fits in 8 bits + + `O' + The constant 0x80000000 or, on the 29050, any 32 bit constant + whose low 16 bits are 0. + + `P' + 16 bit negative constant that fits in 8 bits + + `G' + `H' + A floating point constant (in `asm' statements, use the + machine independent `E' or `F' instead) + +*IBM RS6000--`rs6000.h'* + `b' + Address base register + + `f' + Floating point register + + `h' + `MQ', `CTR', or `LINK' register + + `q' + `MQ' register + + `c' + `CTR' register + + `l' + `LINK' register + + `x' + `CR' register (condition register) number 0 + + `y' + `CR' register (condition register) + + `I' + Signed 16 bit constant + + `J' + Constant whose low 16 bits are 0 + + `K' + Constant whose high 16 bits are 0 + + `L' + Constant suitable as a mask operand + + `M' + Constant larger than 31 + + `N' + Exact power of 2 + + `O' + Zero + + `P' + Constant whose negation is a signed 16 bit constant + + `G' + Floating point constant that can be loaded into a register + with one instruction per word + + `Q' + Memory operand that is an offset from a register (`m' is + preferable for `asm' statements) + +*Intel 386--`i386.h'* + `q' + `a', `b', `c', or `d' register + + `A' + `a', or `d' register (for 64-bit ints) + + `f' + Floating point register -Output of Dispatch Tables -------------------------- + `t' + First (top of stack) floating point register -`ASM_OUTPUT_ADDR_DIFF_ELT (STREAM, VALUE, REL)' - This macro should be provided on machines where the addresses in - a dispatch table are relative to the table's own address. - - The definition should be a C statement to output to the stdio - stream STREAM an assembler pseudo-instruction to generate a - difference between two labels. VALUE and REL are the numbers of - two internal labels. The definitions of these labels are output - using `ASM_OUTPUT_INTERNAL_LABEL', and they must be printed in - the same way here. For example, - - fprintf (STREAM, "\t.word L%d-L%d\n", - VALUE, REL) - -`ASM_OUTPUT_ADDR_VEC_ELT (STREAM, VALUE)' - This macro should be provided on machines where the addresses in - a dispatch table are absolute. - - The definition should be a C statement to output to the stdio - stream STREAM an assembler pseudo-instruction to generate a - reference to a label. VALUE is the number of an internal label - whose definition is output using `ASM_OUTPUT_INTERNAL_LABEL'. - For example, - - fprintf (STREAM, "\t.word L%d\n", VALUE) - -`ASM_OUTPUT_CASE_LABEL (STREAM, PREFIX, NUM, TABLE)' - Define this if the label before a jump-table needs to be output - specially. The first three arguments are the same as for - `ASM_OUTPUT_INTERNAL_LABEL'; the fourth argument is the - jump-table which follows (a `jump_insn' containing an `addr_vec' - or `addr_diff_vec'). - - This feature is used on system V to output a `swbeg' statement - for the table. - - If this macro is not defined, these labels are output with - `ASM_OUTPUT_INTERNAL_LABEL'. - -`ASM_OUTPUT_CASE_END (STREAM, NUM, TABLE)' - Define this if something special must be output at the end of a - jump-table. The definition should be a C statement to be executed - after the assembler code for the table is written. It should - write the appropriate code to stdio stream STREAM. The argument - TABLE is the jump-table insn, and NUM is the label-number of the - preceding label. + `u' + Second floating point register - If this macro is not defined, nothing special is output at the - end of the jump-table. + `a' + `a' register + + `b' + `b' register + + `c' + `c' register + + `d' + `d' register + + `D' + `di' register + + `S' + `si' register + + `I' + Constant in range 0 to 31 (for 32 bit shifts) + + `J' + Constant in range 0 to 63 (for 64 bit shifts) + + `K' + `0xff' + + `L' + `0xffff' + + `M' + 0, 1, 2, or 3 (shifts for `lea' instruction) + + `G' + Standard 80387 floating point constant + +*Intel 960--`i960.h'* + `f' + Floating point register (`fp0' to `fp3') + + `l' + Local register (`r0' to `r15') + + `b' + Global register (`g0' to `g15') + + `d' + Any local or global register + + `I' + Integers from 0 to 31 + + `J' + 0 + + `K' + Integers from -31 to 0 + + `G' + Floating point 0 + + `H' + Floating point 1 + +*MIPS--`mips.h'* + `d' + General-purpose integer register + + `f' + Floating-point register (if available) + + `h' + `Hi' register + + `l' + `Lo' register + + `x' + `Hi' or `Lo' register + + `y' + General-purpose integer register + + `z' + Floating-point status register + + `I' + Signed 16 bit constant (for arithmetic instructions) + + `J' + Zero + + `K' + Zero-extended 16-bit constant (for logic instructions) + + `L' + Constant with low 16 bits zero (can be loaded with `lui') + + `M' + 32 bit constant which requires two instructions to load (a + constant which is not `I', `K', or `L') + + `N' + Negative 16 bit constant + + `O' + Exact power of two + + `P' + Positive 16 bit constant + + `G' + Floating point zero + + `Q' + Memory reference that can be loaded with more than one + instruction (`m' is preferable for `asm' statements) + + `R' + Memory reference that can be loaded with one instruction (`m' + is preferable for `asm' statements) + + `S' + Memory reference in external OSF/rose PIC format (`m' is + preferable for `asm' statements) + +*Motorola 680x0--`m68k.h'* + `a' + Address register + + `d' + Data register + + `f' + 68881 floating-point register, if available + + `x' + Sun FPA (floating-point) register, if available + + `y' + First 16 Sun FPA registers, if available + + `I' + Integer in the range 1 to 8 + + `J' + 16 bit signed number + + `K' + Signed number whose magnitude is greater than 0x80 + + `L' + Integer in the range -8 to -1 + + `G' + Floating point constant that is not a 68881 constant + + `H' + Floating point constant that can be used by Sun FPA + +*SPARC--`sparc.h'* + `f' + Floating-point register + + `I' + Signed 13 bit constant + + `J' + Zero + + `K' + 32 bit constant with the low 12 bits clear (a constant that + can be loaded with the `sethi' instruction) + + `G' + Floating-point zero + + `H' + Signed 13 bit constant, sign-extended to 32 or 64 bits + + `Q' + Memory reference that can be loaded with one instruction + (`m' is more appropriate for `asm' statements) + + `S' + Constant, or memory address + + `T' + Memory address aligned to an 8-byte boundary + + `U' + Even register  -File: gcc.info, Node: Alignment Output, Prev: Dispatch Tables, Up: Assembler Format +File: gcc.info, Node: No Constraints, Prev: Machine Constraints, Up: Constraints -Assembler Commands for Alignment --------------------------------- +Not Using Constraints +--------------------- + + Some machines are so clean that operand constraints are not +required. For example, on the Vax, an operand valid in one context is +valid in any other context. On such a machine, every operand +constraint would be `g', excepting only operands of "load address" +instructions which are written as if they referred to a memory +location's contents but actual refer to its address. They would have +constraint `p'. + + For such machines, instead of writing `g' and `p' for all the +constraints, you can choose to write a description with empty +constraints. Then you write `""' for the constraint in every +`match_operand'. Address operands are identified by writing an +`address' expression around the `match_operand', not by their +constraints. -`ASM_OUTPUT_ALIGN_CODE (FILE)' - A C expression to output text to align the location counter in - the way that is desirable at a point in the code that is reached - only by jumping. - - This macro need not be defined if you don't want any special - alignment to be done at such a time. Most machine descriptions - do not currently define the macro. - -`ASM_OUTPUT_LOOP_ALIGN (FILE)' - A C expression to output text to align the location counter in - the way that is desirable at the beginning of a loop. - - This macro need not be defined if you don't want any special - alignment to be done at such a time. Most machine descriptions - do not currently define the macro. - -`ASM_OUTPUT_SKIP (STREAM, NBYTES)' - A C statement to output to the stdio stream STREAM an assembler - instruction to advance the location counter by NBYTES bytes. - Those bytes should be zero when loaded. NBYTES will be a C - expression of type `int'. - -`ASM_NO_SKIP_IN_TEXT' - Define this macro if `ASM_OUTPUT_SKIP' should not be used in the - text section because it fails put zeros in the bytes that are - skipped. This is true on many Unix systems, where the pseudo--op - to skip bytes produces no-op instructions rather than zeros when - used in the text section. - -`ASM_OUTPUT_ALIGN (STREAM, POWER)' - A C statement to output to the stdio stream STREAM an assembler - command to advance the location counter to a multiple of 2 to the - POWER bytes. POWER will be a C expression of type `int'. + When the machine description has just empty constraints, certain +parts of compilation are skipped, making the compiler faster. However, +few machines actually do not need constraints; all machine descriptions +now in existence use constraints. - \ No newline at end of file