--- gcc/gcc.info-16 2018/04/24 17:56:26 1.1.1.3 +++ gcc/gcc.info-16 2018/04/24 18:11:35 1.1.1.6 @@ -1,9 +1,12 @@ -This is Info file gcc.info, produced by Makeinfo-1.47 from the input +This is Info file gcc.info, produced by Makeinfo-1.54 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 + + Copyright (C) 1988, 1989, 1992, 1993 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 @@ -11,1118 +14,1038 @@ 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 "Boycott" -are included exactly as in the original, and provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. +that the sections entitled "GNU General Public License" 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 "Boycott", and this permission notice, may be included in -translations approved by the Free Software Foundation instead of in the -original English. +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: Costs, Next: Sections, Prev: Condition Code, Up: Target Macros - -Describing Relative Costs of Operations -======================================= +File: gcc.info, Node: Expander Definitions, Next: Insn Splitting, Prev: Peephole Definitions, Up: Machine Desc - These macros let you describe the relative speed of various -operations on the target machine. +Defining RTL Sequences for Code Generation +========================================== -`CONST_COSTS (X, CODE, OUTER_CODE)' - A part of a C `switch' statement that describes the relative costs - of constant RTL expressions. It must contain `case' labels for - expression codes `const_int', `const', `symbol_ref', `label_ref' - and `const_double'. Each case must ultimately reach a `return' - statement to return the relative cost of the use of that kind of - constant value in an expression. The cost may depend on the - precise value of the constant, which is available for examination - in X, and the rtx code of the expression in which it is contained, - found in OUTER_CODE. - - CODE is the expression code--redundant, since it can be obtained - with `GET_CODE (X)'. - -`RTX_COSTS (X, CODE, OUTER_CODE)' - Like `CONST_COSTS' but applies to nonconstant RTL expressions. - This can be used, for example, to indicate how costly a multiply - instruction is. In writing this macro, you can use the construct - `COSTS_N_INSNS (N)' to specify a cost equal to N fast - instructions. OUTER_CODE is the code of the expression in which X - is contained. - - This macro is optional; do not define it if the default cost - assumptions are adequate for the target machine. - -`ADDRESS_COST (ADDRESS)' - An expression giving the cost of an addressing mode that contains - ADDRESS. If not defined, the cost is computed from the ADDRESS - expression and the `CONST_COSTS' values. - - For most CISC machines, the default cost is a good approximation - of the true cost of the addressing mode. However, on RISC - machines, all instructions normally have the same length and - execution time. Hence all addresses will have equal costs. - - In cases where more than one form of an address is known, the form - with the lowest cost will be used. If multiple forms have the - same, lowest, cost, the one that is the most complex will be used. - - For example, suppose an address that is equal to the sum of a - register and a constant is used twice in the same basic block. - When this macro is not defined, the address will be computed in a - register and memory references will be indirect through that - register. On machines where the cost of the addressing mode - containing the sum is no higher than that of a simple indirect - reference, this will produce an additional instruction and - possibly require an additional register. Proper specification of - this macro eliminates this overhead for such machines. - - Similar use of this macro is made in strength reduction of loops. - - ADDRESS need not be valid as an address. In such a case, the cost - is not relevant and can be any value; invalid addresses need not be - assigned a different cost. - - On machines where an address involving more than one register is as - cheap as an address computation involving only one register, - defining `ADDRESS_COST' to reflect this can cause two registers to - be live over a region of code where only one would have been if - `ADDRESS_COST' were not defined in that manner. This effect should - be considered in the definition of this macro. Equivalent costs - should probably only be given to addresses with different numbers - of registers on machines with lots of registers. - - This macro will normally either not be defined or be defined as a - constant. - -`REGISTER_MOVE_COST (FROM, TO)' - A C expression for the cost of moving data from a register in class - FROM to one in class TO. The classes are expressed using the - enumeration values such as `GENERAL_REGS'. A value of 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. + On some target machines, some standard pattern names for RTL +generation cannot be handled with single insn, but a sequence of RTL +insns can represent them. For these target machines, you can write a +`define_expand' to specify how to generate the sequence of RTL. + + A `define_expand' is an RTL expression that looks almost like a +`define_insn'; but, unlike the latter, a `define_expand' is used only +for RTL generation and it can produce more than one RTL insn. + + A `define_expand' RTX has four operands: + + * The name. Each `define_expand' must have a name, since the only + use for it is to refer to it by name. + + * The RTL template. This is just like the RTL template for a + `define_peephole' in that it is a vector of RTL expressions each + being one insn. + + * The condition, a string containing a C expression. This + expression is used to express how the availability of this pattern + depends on subclasses of target machine, selected by command-line + options when GNU CC is run. This is just like the condition of a + `define_insn' that has a standard name. + + * The preparation statements, a string containing zero or more C + statements which are to be executed before RTL code is generated + from the RTL template. + + Usually these statements prepare temporary registers for use as + internal operands in the RTL template, but they can also generate + RTL insns directly by calling routines such as `emit_insn', etc. + Any such insns precede the ones that come from the RTL template. + + Every RTL insn emitted by a `define_expand' must match some +`define_insn' in the machine description. Otherwise, the compiler will +crash when trying to generate code for the insn or trying to optimize +it. + + The RTL template, in addition to controlling generation of RTL insns, +also describes the operands that need to be specified when this pattern +is used. In particular, it gives a predicate for each operand. + + A true operand, which needs to be specified in order to generate RTL +from the pattern, should be described with a `match_operand' in its +first occurrence in the RTL template. This enters information on the +operand's predicate into the tables that record such things. GNU CC +uses the information to preload the operand into a register if that is +required for valid RTL code. If the operand is referred to more than +once, subsequent references should use `match_dup'. + + The RTL template may also refer to internal "operands" which are +temporary registers or labels used only within the sequence made by the +`define_expand'. Internal operands are substituted into the RTL +template with `match_dup', never with `match_operand'. The values of +the internal operands are not passed in as arguments by the compiler +when it requests use of this pattern. Instead, they are computed +within the pattern, in the preparation statements. These statements +compute the values and store them into the appropriate elements of +`operands' so that `match_dup' can find them. + + There are two special macros defined for use in the preparation +statements: `DONE' and `FAIL'. Use them with a following semicolon, as +a statement. + +`DONE' + Use the `DONE' macro to end RTL generation for the pattern. The + only RTL insns resulting from the pattern on this occasion will be + those already emitted by explicit calls to `emit_insn' within the + preparation statements; the RTL template will not be generated. + +`FAIL' + Make the pattern fail on this occasion. When a pattern fails, it + means that the pattern was not truly available. The calling + routines in the compiler will try other strategies for code + generation using other patterns. + + Failure is currently supported only for binary (addition, + multiplication, shifting, etc.) and bitfield (`extv', `extzv', and + `insv') operations. + + Here is an example, the definition of left-shift for the SPUR chip: + + (define_expand "ashlsi3" + [(set (match_operand:SI 0 "register_operand" "") + (ashift:SI + + (match_operand:SI 1 "register_operand" "") + (match_operand:SI 2 "nonmemory_operand" "")))] + "" + " + + { + if (GET_CODE (operands[2]) != CONST_INT + || (unsigned) INTVAL (operands[2]) > 3) + FAIL; + }") + +This example uses `define_expand' so that it can generate an RTL insn +for shifting when the shift-count is in the supported range of 0 to 3 +but fail in other cases where machine insns aren't available. When it +fails, the compiler tries another strategy using different patterns +(such as, a library call). + + If the compiler were able to handle nontrivial condition-strings in +patterns with names, then it would be possible to use a `define_insn' +in that case. Here is another case (zero-extension on the 68000) which +makes more use of the power of `define_expand': + + (define_expand "zero_extendhisi2" + [(set (match_operand:SI 0 "general_operand" "") + (const_int 0)) + (set (strict_low_part + (subreg:HI + (match_dup 0) + 0)) + (match_operand:HI 1 "general_operand" ""))] + "" + "operands[1] = make_safe_from (operands[1], operands[0]);") + +Here two RTL insns are generated, one to clear the entire output operand +and the other to copy the input operand into its low half. This +sequence is incorrect if the input operand refers to [the old value of] +the output operand, so the preparation statement makes sure this isn't +so. The function `make_safe_from' copies the `operands[1]' into a +temporary register if it refers to `operands[0]'. It does this by +emitting another RTL insn. + + Finally, a third example shows the use of an internal operand. +Zero-extension on the SPUR chip is done by `and'-ing the result against +a halfword mask. But this mask cannot be represented by a `const_int' +because the constant value is too large to be legitimate on this +machine. So it must be copied into a register with `force_reg' and +then the register used in the `and'. + + (define_expand "zero_extendhisi2" + [(set (match_operand:SI 0 "register_operand" "") + (and:SI (subreg:SI + (match_operand:HI 1 "register_operand" "") + 0) + (match_dup 2)))] + "" + "operands[2] + = force_reg (SImode, gen_rtx (CONST_INT, + VOIDmode, 65535)); ") + + *Note:* If the `define_expand' is used to serve a standard binary or +unary arithmetic operation or a bitfield operation, then the last insn +it generates must not be a `code_label', `barrier' or `note'. It must +be an `insn', `jump_insn' or `call_insn'. If you don't need a real insn +at the end, emit an insn to copy the result of the operation into +itself. Such an insn will generate no code, but it can avoid problems +in the compiler.  -File: gcc.info, Node: Sections, Next: PIC, Prev: Costs, Up: Target Macros +File: gcc.info, Node: Insn Splitting, Next: Insn Attributes, Prev: Expander Definitions, Up: Machine Desc -Dividing the Output into Sections (Texts, Data, ...) -==================================================== +Defining How to Split Instructions +================================== - 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). + There are two cases where you should specify how to split a pattern +into multiple insns. On machines that have instructions requiring delay +slots (*note Delay Slots::.) or that have instructions whose output is +not available for multiple cycles (*note Function Units::.), the +compiler phases that optimize these cases need to be able to move insns +into one-instruction delay slots. However, some insns may generate +more than one machine instruction. These insns cannot be placed into a +delay slot. + + Often you can rewrite the single insn as a list of individual insns, +each corresponding to one machine instruction. The disadvantage of +doing so is that it will cause the compilation to be slower and require +more space. If the resulting insns are too complex, it may also +suppress some optimizations. The compiler splits the insn if there is a +reason to believe that it might improve instruction or delay slot +scheduling. + + The insn combiner phase also splits putative insns. If three insns +are merged into one insn with a complex expression that cannot be +matched by some `define_insn' pattern, the combiner phase attempts to +split the complex pattern into two insns that are recognized. Usually +it can break the complex pattern into two patterns by splitting out some +subexpression. However, in some other cases, such as performing an +addition of a large constant in two insns on a RISC machine, the way to +split the addition into two insns is machine-dependent. + + The `define_split' definition tells the compiler how to split a +complex insn into several simpler insns. It looks like this: + + (define_split + [INSN-PATTERN] + "CONDITION" + [NEW-INSN-PATTERN-1 + NEW-INSN-PATTERN-2 + ...] + "PREPARATION STATEMENTS") + + INSN-PATTERN is a pattern that needs to be split and CONDITION is +the final condition to be tested, as in a `define_insn'. When an insn +matching INSN-PATTERN and satisfying CONDITION is found, it is replaced +in the insn list with the insns given by NEW-INSN-PATTERN-1, +NEW-INSN-PATTERN-2, etc. + + The PREPARATION STATEMENTS are similar to those statements that are +specified for `define_expand' (*note Expander Definitions::.) and are +executed before the new RTL is generated to prepare for the generated +code or emit some insns whose pattern is not fixed. Unlike those in +`define_expand', however, these statements must not generate any new +pseudo-registers. Once reload has completed, they also must not +allocate any space in the stack frame. + + Patterns are matched against INSN-PATTERN in two different +circumstances. If an insn needs to be split for delay slot scheduling +or insn scheduling, the insn is already known to be valid, which means +that it must have been matched by some `define_insn' and, if +`reload_completed' is non-zero, is known to satisfy the constraints of +that `define_insn'. In that case, the new insn patterns must also be +insns that are matched by some `define_insn' and, if `reload_completed' +is non-zero, must also satisfy the constraints of those definitions. + + As an example of this usage of `define_split', consider the following +example from `a29k.md', which splits a `sign_extend' from `HImode' to +`SImode' into a pair of shift insns: + + (define_split + [(set (match_operand:SI 0 "gen_reg_operand" "") + (sign_extend:SI (match_operand:HI 1 "gen_reg_operand" "")))] + "" + [(set (match_dup 0) + (ashift:SI (match_dup 1) + (const_int 16))) + (set (match_dup 0) + (ashiftrt:SI (match_dup 0) + (const_int 16)))] + " + { operands[1] = gen_lowpart (SImode, operands[1]); }") + + When the combiner phase tries to split an insn pattern, it is always +the case that the pattern is *not* matched by any `define_insn'. The +combiner pass first tries to split a single `set' expression and then +the same `set' expression inside a `parallel', but followed by a +`clobber' of a pseudo-reg to use as a scratch register. In these +cases, the combiner expects exactly two new insn patterns to be +generated. It will verify that these patterns match some `define_insn' +definitions, so you need not do this test in the `define_split' (of +course, there is no point in writing a `define_split' that will never +produce insns that match). + + Here is an example of this use of `define_split', taken from +`rs6000.md': + + (define_split + [(set (match_operand:SI 0 "gen_reg_operand" "") + (plus:SI (match_operand:SI 1 "gen_reg_operand" "") + (match_operand:SI 2 "non_add_cint_operand" "")))] + "" + [(set (match_dup 0) (plus:SI (match_dup 1) (match_dup 3))) + (set (match_dup 0) (plus:SI (match_dup 0) (match_dup 4)))] + " + { + int low = INTVAL (operands[2]) & 0xffff; + int high = (unsigned) INTVAL (operands[2]) >> 16; + + if (low & 0x8000) + high++, low |= 0xffff0000; + + operands[3] = gen_rtx (CONST_INT, VOIDmode, high << 16); + operands[4] = gen_rtx (CONST_INT, VOIDmode, low); + }") + + Here the predicate `non_add_cint_operand' matches any `const_int' +that is *not* a valid operand of a single add insn. The add with the +smaller displacement is written so that it can be substituted into the +address of a subsequent operation. + + An example that uses a scratch register, from the same file, +generates an equality comparison of a register and a large constant: + + (define_split + [(set (match_operand:CC 0 "cc_reg_operand" "") + (compare:CC (match_operand:SI 1 "gen_reg_operand" "") + (match_operand:SI 2 "non_short_cint_operand" ""))) + (clobber (match_operand:SI 3 "gen_reg_operand" ""))] + "find_single_use (operands[0], insn, 0) + && (GET_CODE (*find_single_use (operands[0], insn, 0)) == EQ + || GET_CODE (*find_single_use (operands[0], insn, 0)) == NE)" + [(set (match_dup 3) (xor:SI (match_dup 1) (match_dup 4))) + (set (match_dup 0) (compare:CC (match_dup 3) (match_dup 5)))] + " + { + /* Get the constant we are comparing against, C, and see what it + looks like sign-extended to 16 bits. Then see what constant + could be XOR'ed with C to get the sign-extended value. */ + + int c = INTVAL (operands[2]); + int sextc = (c << 16) >> 16; + int xorv = c ^ sextc; + + operands[4] = gen_rtx (CONST_INT, VOIDmode, xorv); + operands[5] = gen_rtx (CONST_INT, VOIDmode, sextc); + }") + + To avoid confusion, don't write a single `define_split' that accepts +some insns that match some `define_insn' as well as some insns that +don't. Instead, write two separate `define_split' definitions, one for +the insns that are valid and one for the insns that are not valid.  -File: gcc.info, Node: PIC, Next: Assembler Format, Prev: Sections, Up: Target Macros +File: gcc.info, Node: Insn Attributes, Prev: Insn Splitting, Up: Machine Desc + +Instruction Attributes +====================== -Position Independent Code -========================= + In addition to describing the instruction supported by the target +machine, the `md' file also defines a group of "attributes" and a set of +values for each. Every generated insn is assigned a value for each +attribute. One possible attribute would be the effect that the insn +has on the machine's condition code. This attribute can then be used +by `NOTICE_UPDATE_CC' to track the condition codes. - 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.) +* Menu: + +* Defining Attributes:: Specifying attributes and their values. +* Expressions:: Valid expressions for attribute values. +* Tagging Insns:: Assigning attribute values to insns. +* Attr Example:: An example of assigning attributes. +* Insn Lengths:: Computing the length of insns. +* Constant Attributes:: Defining attributes that are constant. +* Delay Slots:: Defining delay slots required for a machine. +* Function Units:: Specifying information for insn scheduling.  -File: gcc.info, Node: Assembler Format, Next: Debugging Info, Prev: PIC, Up: Target Macros +File: gcc.info, Node: Defining Attributes, Next: Expressions, Up: Insn Attributes -Defining the Output Assembler Language -====================================== +Defining Attributes and their Values +------------------------------------ - This section describes macros whose principal purpose is to describe -how to write instructions in assembler language--rather than what the -instructions do. + The `define_attr' expression is used to define each attribute +required by the target machine. It looks like: -* Menu: + (define_attr NAME LIST-OF-VALUES DEFAULT) -* 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. + NAME is a string specifying the name of the attribute being defined. - -File: gcc.info, Node: File Framework, Next: Data Output, Up: Assembler Format + LIST-OF-VALUES is either a string that specifies a comma-separated +list of values that can be assigned to the attribute, or a null string +to indicate that the attribute takes numeric values. -The Overall Framework of an Assembler File ------------------------------------------- + DEFAULT is an attribute expression that gives the value of this +attribute for insns that match patterns whose definition does not +include an explicit value for this attribute. *Note Attr Example::, +for more information on the handling of defaults. *Note Constant +Attributes::, for information on attributes that do not depend on any +particular insn. -`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. + For each defined attribute, a number of definitions are written to +the `insn-attr.h' file. For cases where an explicit set of values is +specified for an attribute, the following are defined: - -File: gcc.info, Node: Data Output, Next: Uninitialized Data, Prev: File Framework, Up: Assembler Format + * A `#define' is written for the symbol `HAVE_ATTR_NAME'. -Output of Data --------------- + * An enumeral class is defined for `attr_NAME' with elements of the + form `UPPER-NAME_UPPER-VALUE' where the attribute name and value + are first converted to upper case. -`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: + * A function `get_attr_NAME' is defined that is passed an insn and + returns the attribute value for that insn. - #define ASM_OPEN_PAREN "(" - #define ASM_CLOSE_PAREN ")" + For example, if the following is present in the `md' file: - -File: gcc.info, Node: Uninitialized Data, Next: Label Output, Prev: Data Output, Up: Assembler Format + (define_attr "type" "branch,fp,load,store,arith" ...) -Output of Uninitialized Variables ---------------------------------- +the following lines will be written to the file `insn-attr.h'. - Each of the macros in this section is used to do the whole job of -outputting a single uninitialized variable. + #define HAVE_ATTR_type + enum attr_type {TYPE_BRANCH, TYPE_FP, TYPE_LOAD, + TYPE_STORE, TYPE_ARITH}; + extern enum attr_type get_attr_type (); -`ASM_OUTPUT_COMMON (STREAM, NAME, SIZE, ROUNDED)' - A C statement (sans semicolon) to output to the stdio stream - STREAM the assembler definition of a common-label named NAME whose - size is SIZE bytes. The variable ROUNDED is the size rounded up - to whatever alignment the caller wants. - - Use the expression `assemble_name (STREAM, NAME)' to output the - name itself; before and after that, output the additional - assembler syntax for defining the name, and a newline. - - This macro controls how the assembler definitions of uninitialized - global variables are output. - -`ASM_OUTPUT_ALIGNED_COMMON (STREAM, NAME, SIZE, ALIGNMENT)' - Like `ASM_OUTPUT_COMMON' except takes the required alignment as a - separate, explicit argument. If you define this macro, it is used - in place of `ASM_OUTPUT_COMMON', and gives you more flexibility in - handling the required alignment of the variable. - -`ASM_OUTPUT_SHARED_COMMON (STREAM, NAME, SIZE, ROUNDED)' - If defined, it is similar to `ASM_OUTPUT_COMMON', except that it - is used when NAME is shared. If not defined, `ASM_OUTPUT_COMMON' - will be used. - -`ASM_OUTPUT_LOCAL (STREAM, NAME, SIZE, ROUNDED)' - A C statement (sans semicolon) to output to the stdio stream - STREAM the assembler definition of a local-common-label named NAME - whose size is SIZE bytes. The variable ROUNDED is the size - rounded up to whatever alignment the caller wants. - - Use the expression `assemble_name (STREAM, NAME)' to output the - name itself; before and after that, output the additional - assembler syntax for defining the name, and a newline. - - This macro controls how the assembler definitions of uninitialized - static variables are output. - -`ASM_OUTPUT_ALIGNED_LOCAL (STREAM, NAME, SIZE, ALIGNMENT)' - Like `ASM_OUTPUT_LOCAL' except takes the required alignment as a - separate, explicit argument. If you define this macro, it is used - in place of `ASM_OUTPUT_LOCAL', and gives you more flexibility in - handling the required alignment of the variable. - -`ASM_OUTPUT_SHARED_LOCAL (STREAM, NAME, SIZE, ROUNDED)' - If defined, it is similar to `ASM_OUTPUT_LOCAL', except that it is - used when NAME is shared. If not defined, `ASM_OUTPUT_LOCAL' will - be used. + If the attribute takes numeric values, no `enum' type will be +defined and the function to obtain the attribute's value will return +`int'.  -File: gcc.info, Node: Label Output, Next: Constructor Output, Prev: Uninitialized Data, Up: Assembler Format +File: gcc.info, Node: Expressions, Next: Tagging Insns, Prev: Defining Attributes, Up: Insn Attributes -Output and Generation of Labels -------------------------------- +Attribute Expressions +--------------------- -`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. + RTL expressions used to define attributes use the codes described +above plus a few specific to attribute definitions, to be discussed +below. Attribute value expressions must have one of the following +forms: + +`(const_int I)' + The integer I specifies the value of a numeric attribute. I must + be non-negative. + + The value of a numeric attribute can be specified either with a + `const_int' or as an integer represented as a string in + `const_string', `eq_attr' (see below), and `set_attr' (*note + Tagging Insns::.) expressions. + +`(const_string VALUE)' + The string VALUE specifies a constant attribute value. If VALUE + is specified as `"*"', it means that the default value of the + attribute is to be used for the insn containing this expression. + `"*"' obviously cannot be used in the DEFAULT expression of a + `define_attr'. + + If the attribute whose value is being specified is numeric, VALUE + must be a string containing a non-negative integer (normally + `const_int' would be used in this case). Otherwise, it must + contain one of the valid values for the attribute. + +`(if_then_else TEST TRUE-VALUE FALSE-VALUE)' + TEST specifies an attribute test, whose format is defined below. + The value of this expression is TRUE-VALUE if TEST is true, + otherwise it is FALSE-VALUE. + +`(cond [TEST1 VALUE1 ...] DEFAULT)' + The first operand of this expression is a vector containing an even + number of expressions and consisting of pairs of TEST and VALUE + expressions. The value of the `cond' expression is that of the + VALUE corresponding to the first true TEST expression. If none of + the TEST expressions are true, the value of the `cond' expression + is that of the DEFAULT expression. + + TEST expressions can have one of the following forms: + +`(const_int I)' + This test is true if I is non-zero and false otherwise. + +`(not TEST)' +`(ior TEST1 TEST2)' +`(and TEST1 TEST2)' + These tests are true if the indicated logical function is true. + +`(match_operand:M N PRED CONSTRAINTS)' + This test is true if operand N of the insn whose attribute value + is being determined has mode M (this part of the test is ignored + if M is `VOIDmode') and the function specified by the string PRED + returns a non-zero value when passed operand N and mode M (this + part of the test is ignored if PRED is the null string). + + The CONSTRAINTS operand is ignored and should be the null string. + +`(le ARITH1 ARITH2)' +`(leu ARITH1 ARITH2)' +`(lt ARITH1 ARITH2)' +`(ltu ARITH1 ARITH2)' +`(gt ARITH1 ARITH2)' +`(gtu ARITH1 ARITH2)' +`(ge ARITH1 ARITH2)' +`(geu ARITH1 ARITH2)' +`(ne ARITH1 ARITH2)' +`(eq ARITH1 ARITH2)' + These tests are true if the indicated comparison of the two + arithmetic expressions is true. Arithmetic expressions are formed + with `plus', `minus', `mult', `div', `mod', `abs', `neg', `and', + `ior', `xor', `not', `lshift', `ashift', `lshiftrt', and `ashiftrt' + expressions. + + `const_int' and `symbol_ref' are always valid terms (*note Insn + Lengths::.,for additional forms). `symbol_ref' is a string + denoting a C expression that yields an `int' when evaluated by the + `get_attr_...' routine. It should normally be a global variable. + +`(eq_attr NAME VALUE)' + NAME is a string specifying the name of an attribute. + + VALUE is a string that is either a valid value for attribute NAME, + a comma-separated list of values, or `!' followed by a value or + list. If VALUE does not begin with a `!', this test is true if + the value of the NAME attribute of the current insn is in the list + specified by VALUE. If VALUE begins with a `!', this test is true + if the attribute's value is *not* in the specified list. + + For example, + + (eq_attr "type" "load,store") + + is equivalent to + + (ior (eq_attr "type" "load") (eq_attr "type" "store")) + + If NAME specifies an attribute of `alternative', it refers to the + value of the compiler variable `which_alternative' (*note Output + Statement::.) and the values must be small integers. For example, + + (eq_attr "alternative" "2,3") + + is equivalent to + + (ior (eq (symbol_ref "which_alternative") (const_int 2)) + (eq (symbol_ref "which_alternative") (const_int 3))) + + Note that, for most attributes, an `eq_attr' test is simplified in + cases where the value of the attribute being tested is known for + all insns matching a particular pattern. This is by far the most + common case. + +`(attr_flag NAME)' + The value of an `attr_flag' expression is true if the flag + specified by NAME is true for the `insn' currently being scheduled. + + NAME is a string specifying one of a fixed set of flags to test. + Test the flags `forward' and `backward' to determine the direction + of a conditional branch. Test the flags `very_likely', `likely', + `very_unlikely', and `unlikely' to determine if a conditional + branch is expected to be taken. + + If the `very_likely' flag is true, then the `likely' flag is also + true. Likewise for the `very_unlikely' and `unlikely' flags. + + This example describes a conditional branch delay slot which can + be nullified for forward branches that are taken (annul-true) or + for backward branches which are not taken (annul-false). + + (define_delay (eq_attr "type" "cbranch") + [(eq_attr "in_branch_delay" "true") + (and (eq_attr "in_branch_delay" "true") + (attr_flag "forward")) + (and (eq_attr "in_branch_delay" "true") + (attr_flag "backward"))]) + + The `forward' and `backward' flags are false if the current `insn' + being scheduled is not a conditional branch. + + The `very_likely' and `likely' flags are true if the `insn' being + scheduled is not a conditional branch. The The `very_unlikely' + and `unlikely' flags are false if the `insn' being scheduled is + not a conditional branch. - On systems where the assembler can handle quoted names, you can - use this macro to provide more human-readable names. + `attr_flag' is only used during delay slot scheduling and has no + meaning to other passes of the compiler.  -File: gcc.info, Node: Constructor Output, Next: Instruction Output, Prev: Label Output, Up: Assembler Format +File: gcc.info, Node: Tagging Insns, Next: Attr Example, Prev: Expressions, Up: Insn Attributes -Output of Initialization Routines ---------------------------------- +Assigning Attribute Values to Insns +----------------------------------- - 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. - - If your system uses `collect2' as the means of processing -constructors, then that program normally uses `nm' to scan an object -file for constructor functions to be called. On certain kinds of -systems, you can define these macros to make `collect2' work faster -(and, in some cases, make it work at all): - -`OBJECT_FORMAT_COFF' - Define this macro if the system uses COFF (Common Object File - Format) object files, so that `collect2' can assume this format - and scan object files directly for dynamic constructor/destructor - functions. - -`OBJECT_FORMAT_ROSE' - Define this macro if the system uses ROSE format object files, so - that `collect2' can assume this format and scan object files - directly for dynamic constructor/destructor functions. - - These macros are effective only in a native compiler; `collect2' as -part of a cross compiler always uses `nm'. - -`REAL_NM_FILE_NAME' - Define this macro as a C string constant containing the file name - to use to execute `nm'. The default is to search the path - normally for `nm'. + The value assigned to an attribute of an insn is primarily +determined by which pattern is matched by that insn (or which +`define_peephole' generated it). Every `define_insn' and +`define_peephole' can have an optional last argument to specify the +values of attributes for matching insns. The value of any attribute +not specified in a particular insn is set to the default value for that +attribute, as specified in its `define_attr'. Extensive use of default +values for attributes permits the specification of the values for only +one or two attributes in the definition of most insn patterns, as seen +in the example in the next section. + + The optional last argument of `define_insn' and `define_peephole' is +a vector of expressions, each of which defines the value for a single +attribute. The most general way of assigning an attribute's value is +to use a `set' expression whose first operand is an `attr' expression +giving the name of the attribute being set. The second operand of the +`set' is an attribute expression (*note Expressions::.) giving the +value of the attribute. + + When the attribute value depends on the `alternative' attribute +(i.e., which is the applicable alternative in the constraint of the +insn), the `set_attr_alternative' expression can be used. It allows +the specification of a vector of attribute expressions, one for each +alternative. + + When the generality of arbitrary attribute expressions is not +required, the simpler `set_attr' expression can be used, which allows +specifying a string giving either a single attribute value or a list of +attribute values, one for each alternative. + + The form of each of the above specifications is shown below. In +each case, NAME is a string specifying the attribute to be set. + +`(set_attr NAME VALUE-STRING)' + VALUE-STRING is either a string giving the desired attribute value, + or a string containing a comma-separated list giving the values for + succeeding alternatives. The number of elements must match the + number of alternatives in the constraint of the insn pattern. + + Note that it may be useful to specify `*' for some alternative, in + which case the attribute will assume its default value for insns + matching that alternative. + +`(set_attr_alternative NAME [VALUE1 VALUE2 ...])' + Depending on the alternative of the insn, the value will be one of + the specified values. This is a shorthand for using a `cond' with + tests on the `alternative' attribute. + +`(set (attr NAME) VALUE)' + The first operand of this `set' must be the special RTL expression + `attr', whose sole operand is a string giving the name of the + attribute being set. VALUE is the value of the attribute. + + The following shows three different ways of representing the same +attribute value specification: + + (set_attr "type" "load,store,arith") + + (set_attr_alternative "type" + [(const_string "load") (const_string "store") + (const_string "arith")]) + + (set (attr "type") + (cond [(eq_attr "alternative" "1") (const_string "load") + (eq_attr "alternative" "2") (const_string "store")] + (const_string "arith"))) + + The `define_asm_attributes' expression provides a mechanism to +specify the attributes assigned to insns produced from an `asm' +statement. It has the form: + + (define_asm_attributes [ATTR-SETS]) + +where ATTR-SETS is specified the same as for both the `define_insn' and +the `define_peephole' expressions. + + These values will typically be the "worst case" attribute values. +For example, they might indicate that the condition code will be +clobbered. + + A specification for a `length' attribute is handled specially. The +way to compute the length of an `asm' insn is to multiply the length +specified in the expression `define_asm_attributes' by the number of +machine instructions specified in the `asm' statement, determined by +counting the number of semicolons and newlines in the string. +Therefore, the value of the `length' attribute specified in a +`define_asm_attributes' should be the maximum possible length of a +single machine instruction.  -File: gcc.info, Node: Instruction Output, Next: Dispatch Tables, Prev: Constructor Output, Up: Assembler Format +File: gcc.info, Node: Attr Example, Next: Insn Lengths, Prev: Tagging Insns, Up: Insn Attributes -Output of Assembler Instructions --------------------------------- +Example of Attribute Specifications +----------------------------------- -`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. + The judicious use of defaulting is important in the efficient use of +insn attributes. Typically, insns are divided into "types" and an +attribute, customarily called `type', is used to represent this value. +This attribute is normally used only to define the default value for +other attributes. An example will clarify this usage. + + Assume we have a RISC machine with a condition code and in which only +full-word operations are performed in registers. Let us assume that we +can divide all insns into loads, stores, (integer) arithmetic +operations, floating point operations, and branches. + + Here we will concern ourselves with determining the effect of an +insn on the condition code and will limit ourselves to the following +possible effects: The condition code can be set unpredictably +(clobbered), not be changed, be set to agree with the results of the +operation, or only changed if the item previously set into the +condition code has been modified. + + Here is part of a sample `md' file for such a machine: + + (define_attr "type" "load,store,arith,fp,branch" (const_string "arith")) + + (define_attr "cc" "clobber,unchanged,set,change0" + (cond [(eq_attr "type" "load") + (const_string "change0") + (eq_attr "type" "store,branch") + (const_string "unchanged") + (eq_attr "type" "arith") + (if_then_else (match_operand:SI 0 "" "") + (const_string "set") + (const_string "clobber"))] + (const_string "clobber"))) + + (define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,r,m") + (match_operand:SI 1 "general_operand" "r,m,r"))] + "" + "@ + move %0,%1 + load %0,%1 + store %0,%1" + [(set_attr "type" "arith,load,store")]) + + Note that we assume in the above example that arithmetic operations +performed on quantities smaller than a machine word clobber the +condition code since they will set the condition code to a value +corresponding to the full-word result.  -File: gcc.info, Node: Dispatch Tables, Next: Alignment Output, Prev: Instruction Output, Up: Assembler Format +File: gcc.info, Node: Insn Lengths, Next: Constant Attributes, Prev: Attr Example, Up: Insn Attributes -Output of Dispatch Tables -------------------------- - -`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. +Computing the Length of an Insn +------------------------------- - If this macro is not defined, nothing special is output at the end - of the jump-table. + For many machines, multiple types of branch instructions are +provided, each for different length branch displacements. In most +cases, the assembler will choose the correct instruction to use. +However, when the assembler cannot do so, GCC can when a special +attribute, the `length' attribute, is defined. This attribute must be +defined to have numeric values by specifying a null string in its +`define_attr'. + + In the case of the `length' attribute, two additional forms of +arithmetic terms are allowed in test expressions: + +`(match_dup N)' + This refers to the address of operand N of the current insn, which + must be a `label_ref'. + +`(pc)' + This refers to the address of the *current* insn. It might have + been more consistent with other usage to make this the address of + the *next* insn but this would be confusing because the length of + the current insn is to be computed. + + For normal insns, the length will be determined by value of the +`length' attribute. In the case of `addr_vec' and `addr_diff_vec' insn +patterns, the length is computed as the number of vectors multiplied by +the size of each vector. + + Lengths are measured in addressable storage units (bytes). + + The following macros can be used to refine the length computation: + +`FIRST_INSN_ADDRESS' + When the `length' insn attribute is used, this macro specifies the + value to be assigned to the address of the first insn in a + function. If not specified, 0 is used. + +`ADJUST_INSN_LENGTH (INSN, LENGTH)' + If defined, modifies the length assigned to instruction INSN as a + function of the context in which it is used. LENGTH is an lvalue + that contains the initially computed length of the insn and should + be updated with the correct length of the insn. If updating is + required, INSN must not be a varying-length insn. + + This macro will normally not be required. A case in which it is + required is the ROMP. On this machine, the size of an `addr_vec' + insn must be increased by two to compensate for the fact that + alignment may be required. + + The routine that returns `get_attr_length' (the value of the +`length' attribute) can be used by the output routine to determine the +form of the branch instruction to be written, as the example below +illustrates. + + As an example of the specification of variable-length branches, +consider the IBM 360. If we adopt the convention that a register will +be set to the starting address of a function, we can jump to labels +within 4k of the start using a four-byte instruction. Otherwise, we +need a six-byte sequence to load the address from memory and then +branch to it. + + On such a machine, a pattern for a branch instruction might be +specified as follows: + + (define_insn "jump" + [(set (pc) + (label_ref (match_operand 0 "" "")))] + "" + "* + { + return (get_attr_length (insn) == 4 + ? \"b %l0\" : \"l r15,=a(%l0); br r15\"); + }" + [(set (attr "length") (if_then_else (lt (match_dup 0) (const_int 4096)) + (const_int 4) + (const_int 6)))])  -File: gcc.info, Node: Alignment Output, Prev: Dispatch Tables, Up: Assembler Format +File: gcc.info, Node: Constant Attributes, Next: Delay Slots, Prev: Insn Lengths, Up: Insn Attributes -Assembler Commands for Alignment --------------------------------- +Constant Attributes +------------------- -`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'. + A special form of `define_attr', where the expression for the +default value is a `const' expression, indicates an attribute that is +constant for a given run of the compiler. Constant attributes may be +used to specify which variety of processor is used. For example, + + (define_attr "cpu" "m88100,m88110,m88000" + (const + (cond [(symbol_ref "TARGET_88100") (const_string "m88100") + (symbol_ref "TARGET_88110") (const_string "m88110")] + (const_string "m88000")))) + + (define_attr "memory" "fast,slow" + (const + (if_then_else (symbol_ref "TARGET_FAST_MEM") + (const_string "fast") + (const_string "slow")))) + + The routine generated for constant attributes has no parameters as it +does not depend on any particular insn. RTL expressions used to define +the value of a constant attribute may use the `symbol_ref' form, but +may not use either the `match_operand' form or `eq_attr' forms +involving insn attributes.  -File: gcc.info, Node: Debugging Info, Next: Cross-compilation, Prev: Assembler Format, Up: Target Macros +File: gcc.info, Node: Delay Slots, Next: Function Units, Prev: Constant Attributes, Up: Insn Attributes -Controlling Debugging Information Format -======================================== +Delay Slot Scheduling +--------------------- -* Menu: + The insn attribute mechanism can be used to specify the requirements +for delay slots, if any, on a target machine. An instruction is said to +require a "delay slot" if some instructions that are physically after +the instruction are executed as if they were located before it. +Classic examples are branch and call instructions, which often execute +the following instruction before the branch or call is performed. + + On some machines, conditional branch instructions can optionally +"annul" instructions in the delay slot. This means that the +instruction will not be executed for certain branch outcomes. Both +instructions that annul if the branch is true and instructions that +annul if the branch is false are supported. + + Delay slot scheduling differs from instruction scheduling in that +determining whether an instruction needs a delay slot is dependent only +on the type of instruction being generated, not on data flow between the +instructions. See the next section for a discussion of data-dependent +instruction scheduling. + + The requirement of an insn needing one or more delay slots is +indicated via the `define_delay' expression. It has the following form: + + (define_delay TEST + [DELAY-1 ANNUL-TRUE-1 ANNUL-FALSE-1 + DELAY-2 ANNUL-TRUE-2 ANNUL-FALSE-2 + ...]) + + TEST is an attribute test that indicates whether this `define_delay' +applies to a particular insn. If so, the number of required delay +slots is determined by the length of the vector specified as the second +argument. An insn placed in delay slot N must satisfy attribute test +DELAY-N. ANNUL-TRUE-N is an attribute test that specifies which insns +may be annulled if the branch is true. Similarly, ANNUL-FALSE-N +specifies which insns in the delay slot may be annulled if the branch +is false. If annulling is not supported for that delay slot, `(nil)' +should be coded. + + For example, in the common case where branch and call insns require +a single delay slot, which may contain any insn other than a branch or +call, the following would be placed in the `md' file: + + (define_delay (eq_attr "type" "branch,call") + [(eq_attr "type" "!branch,call") (nil) (nil)]) + + Multiple `define_delay' expressions may be specified. In this case, +each such expression specifies different delay slot requirements and +there must be no insn for which tests in two `define_delay' expressions +are both true. + + For example, if we have a machine that requires one delay slot for +branches but two for calls, no delay slot can contain a branch or call +insn, and any valid insn in the delay slot for the branch can be +annulled if the branch is true, we might represent this as follows: + + (define_delay (eq_attr "type" "branch") + [(eq_attr "type" "!branch,call") + (eq_attr "type" "!branch,call") + (nil)]) + + (define_delay (eq_attr "type" "call") + [(eq_attr "type" "!branch,call") (nil) (nil) + (eq_attr "type" "!branch,call") (nil) (nil)]) + + +File: gcc.info, Node: Function Units, Prev: Delay Slots, Up: Insn Attributes -* All Debuggers:: Macros that affect all debugging formats uniformly. -* DBX Options:: Macros enabling specific options in DBX format. -* DBX Hooks:: Hook macros for varying DBX format. -* File Names and DBX:: Macros controlling output of file names in DBX format. -* SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. +Specifying Function Units +------------------------- + + On most RISC machines, there are instructions whose results are not +available for a specific number of cycles. Common cases are +instructions that load data from memory. On many machines, a pipeline +stall will result if the data is referenced too soon after the load +instruction. + + In addition, many newer microprocessors have multiple function +units, usually one for integer and one for floating point, and often +will incur pipeline stalls when a result that is needed is not yet +ready. + + The descriptions in this section allow the specification of how much +time must elapse between the execution of an instruction and the time +when its result is used. It also allows specification of when the +execution of an instruction will delay execution of similar instructions +due to function unit conflicts. + + For the purposes of the specifications in this section, a machine is +divided into "function units", each of which execute a specific class +of instructions in first-in-first-out order. Function units that +accept one instruction each cycle and allow a result to be used in the +succeeding instruction (usually via forwarding) need not be specified. +Classic RISC microprocessors will normally have a single function unit, +which we can call `memory'. The newer "superscalar" processors will +often have function units for floating point operations, usually at +least a floating point adder and multiplier. + + Each usage of a function units by a class of insns is specified with +a `define_function_unit' expression, which looks like this: + + (define_function_unit NAME MULTIPLICITY SIMULTANEITY + TEST READY-DELAY ISSUE-DELAY + [CONFLICT-LIST]) + + NAME is a string giving the name of the function unit. + + MULTIPLICITY is an integer specifying the number of identical units +in the processor. If more than one unit is specified, they will be +scheduled independently. Only truly independent units should be +counted; a pipelined unit should be specified as a single unit. (The +only common example of a machine that has multiple function units for a +single instruction class that are truly independent and not pipelined +are the two multiply and two increment units of the CDC 6600.) + + SIMULTANEITY specifies the maximum number of insns that can be +executing in each instance of the function unit simultaneously or zero +if the unit is pipelined and has no limit. + + All `define_function_unit' definitions referring to function unit +NAME must have the same name and values for MULTIPLICITY and +SIMULTANEITY. + + TEST is an attribute test that selects the insns we are describing +in this definition. Note that an insn may use more than one function +unit and a function unit may be specified in more than one +`define_function_unit'. + + READY-DELAY is an integer that specifies the number of cycles after +which the result of the instruction can be used without introducing any +stalls. + + ISSUE-DELAY is an integer that specifies the number of cycles after +the instruction matching the TEST expression begins using this unit +until a subsequent instruction can begin. A cost of N indicates an N-1 +cycle delay. A subsequent instruction may also be delayed if an +earlier instruction has a longer READY-DELAY value. This blocking +effect is computed using the SIMULTANEITY, READY-DELAY, ISSUE-DELAY, +and CONFLICT-LIST terms. For a normal non-pipelined function unit, +SIMULTANEITY is one, the unit is taken to block for the READY-DELAY +cycles of the executing insn, and smaller values of ISSUE-DELAY are +ignored. + + CONFLICT-LIST is an optional list giving detailed conflict costs for +this unit. If specified, it is a list of condition test expressions to +be applied to insns chosen to execute in NAME following the particular +insn matching TEST that is already executing in NAME. For each insn in +the list, ISSUE-DELAY specifies the conflict cost; for insns not in the +list, the cost is zero. If not specified, CONFLICT-LIST defaults to +all instructions that use the function unit. + + Typical uses of this vector are where a floating point function unit +can pipeline either single- or double-precision operations, but not +both, or where a memory unit can pipeline loads, but not stores, etc. + + As an example, consider a classic RISC machine where the result of a +load instruction is not available for two cycles (a single "delay" +instruction is required) and where only one load instruction can be +executed simultaneously. This would be specified as: + + (define_function_unit "memory" 1 1 (eq_attr "type" "load") 2 0) + + For the case of a floating point function unit that can pipeline +either single or double precision, but not both, the following could be +specified: + + (define_function_unit + "fp" 1 0 (eq_attr "type" "sp_fp") 4 4 [(eq_attr "type" "dp_fp")]) + (define_function_unit + "fp" 1 0 (eq_attr "type" "dp_fp") 4 4 [(eq_attr "type" "sp_fp")]) + + *Note:* The scheduler attempts to avoid function unit conflicts and +uses all the specifications in the `define_function_unit' expression. +It has recently come to our attention that these specifications may not +allow modeling of some of the newer "superscalar" processors that have +insns using multiple pipelined units. These insns will cause a +potential conflict for the second unit used during their execution and +there is no way of representing that conflict. We welcome any examples +of how function unit conflicts work in such processors and suggestions +for their representation.  -File: gcc.info, Node: All Debuggers, Next: DBX Options, Up: Debugging Info +File: gcc.info, Node: Target Macros, Next: Config, Prev: Machine Desc, Up: Top + +Target Description Macros +************************* -Macros Affecting All Debugging Formats --------------------------------------- + In addition to the file `MACHINE.md', a machine description includes +a C header file conventionally given the name `MACHINE.h'. This header +file defines numerous macros that convey the information about the +target machine that does not fit into the scheme of the `.md' file. +The file `tm.h' should be a link to `MACHINE.h'. The header file +`config.h' includes `tm.h' and most compiler source files include +`config.h'. + +* Menu: -`DBX_REGISTER_NUMBER (REGNO)' - A C expression that returns the DBX register number for the - compiler register number REGNO. In simple cases, the value of this - expression may be REGNO itself. But sometimes there are some - registers that the compiler knows about and DBX does not, or vice - versa. In such cases, some register may need to have one number in - the compiler and another for DBX. - - If two registers have consecutive numbers inside GNU CC, and they - can be used as a pair to hold a multiword value, then they *must* - have consecutive numbers after renumbering with - `DBX_REGISTER_NUMBER'. Otherwise, debuggers will be unable to - access such a pair, because they expect register pairs to be - consecutive in their own numbering scheme. - - If you find yourself defining `DBX_REGISTER_NUMBER' in way that - does not preserve register pairs, then what you must do instead is - redefine the actual register numbering scheme. - -`DEBUGGER_AUTO_OFFSET (X)' - A C expression that returns the integer offset value for an - automatic variable having address X (an RTL expression). The - default computation assumes that X is based on the frame-pointer - and gives the offset from the frame-pointer. This is required for - targets that produce debugging output for DBX or COFF-style - debugging output for SDB and allow the frame-pointer to be - eliminated when the `-g' options is used. - -`DEBUGGER_ARG_OFFSET (OFFSET, X)' - A C expression that returns the integer offset value for an - argument having address X (an RTL expression). The nominal offset - is OFFSET. +* Driver:: Controlling how the driver runs the compilation passes. +* Run-time Target:: Defining `-m' options like `-m68000' and `-m68020'. +* Storage Layout:: Defining sizes and alignments of data. +* Type Layout:: Defining sizes and properties of basic user data types. +* Registers:: Naming and describing the hardware registers. +* Register Classes:: Defining the classes of hardware registers. +* Stack and Calling:: Defining which way the stack grows and by how much. +* Varargs:: Defining the varargs macros. +* Trampolines:: Code set up at run time to enter a nested function. +* Library Calls:: Controlling how library routines are implicitly called. +* Addressing Modes:: Defining addressing modes valid for memory operands. +* Condition Code:: Defining how insns update the condition code. +* Costs:: Defining relative costs of different operations. +* Sections:: Dividing storage into text, data, and other sections. +* PIC:: Macros for position independent code. +* Assembler Format:: Defining how to write insns and pseudo-ops to output. +* Debugging Info:: Defining the format of debugging output. +* Cross-compilation:: Handling floating point for cross-compilers. +* Misc:: Everything else. - \ No newline at end of file