--- gcc/gcc.info-10 2018/04/24 16:53:39 1.1 +++ gcc/gcc.info-10 2018/04/24 16:59:07 1.1.1.4 @@ -1,29 +1,584 @@ Info file gcc.info, produced by Makeinfo, -*- Text -*- from input file gcc.texinfo. -This file documents the use and the internals of the GNU compiler. + This file documents the use and the internals of the GNU compiler. -Copyright (C) 1988, 1989 Free Software Foundation, Inc. + Copyright (C) 1988, 1989, 1990 Free Software Foundation, Inc. -Permission is granted to make and distribute verbatim copies of this -manual provided the copyright notice and this permission notice are -preserved on all copies. + Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. -Permission is granted to copy and distribute modified versions of + Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also -that the sections entitled ``GNU General Public License'' and -``Protect Your Freedom--Fight `Look And Feel''' are included exactly -as in the original, and provided that the entire resulting derived -work is distributed under the terms of a permission notice identical -to this one. +that the sections entitled "GNU General Public License" 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 + Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified -versions, except that the sections entitled ``GNU General Public -License'' and ``Protect Your Freedom--Fight `Look And Feel''' and -this permission notice may be included in translations approved by -the Free Software Foundation instead of in the original English. +versions, except that the sections entitled "GNU General Public +License" and "Protect Your Freedom--Fight `Look And Feel'" and this +permission notice may be included in translations approved by the +Free Software Foundation instead of in the original English. + +File: gcc.info, Node: Addressing Modes, Next: Delayed Branch, Prev: Library Calls, Up: Machine Macros + +Addressing Modes +================ + +`HAVE_POST_INCREMENT' + Define this macro if the machine supports post-increment + addressing. + +`HAVE_PRE_INCREMENT' +`HAVE_POST_DECREMENT' +`HAVE_PRE_DECREMENT' + Similar for other kinds of addressing. + +`CONSTANT_ADDRESS_P (X)' + A C expression that is 1 if the RTX X is a constant whose value + is an integer. This includes integers whose values are not + explicitly known, such as `symbol_ref' and `label_ref' + expressions and `const' arithmetic expressions. + + On most machines, this can be defined as `CONSTANT_P (X)', but a + few machines are more restrictive in which constant addresses + are supported. + +`MAX_REGS_PER_ADDRESS' + A number, the maximum number of registers that can appear in a + valid memory address. Note that it is up to you to specify a + value equal to the maximum number that + `go_if_legitimate_address' would ever accept. + +`GO_IF_LEGITIMATE_ADDRESS (MODE, X, LABEL)' + A C compound statement with a conditional `goto LABEL;' executed + if X (an RTX) is a legitimate memory address on the target + machine for a memory operand of mode MODE. + + It usually pays to define several simpler macros to serve as + subroutines for this one. Otherwise it may be too complicated + to understand. + + This macro must exist in two variants: a strict variant and a + non-strict one. The strict variant is used in the reload pass. + It must be defined so that any pseudo-register that has not been + allocated a hard register is considered a memory reference. In + contexts where some kind of register is required, a + pseudo-register with no hard register must be rejected. + + The non-strict variant is used in other passes. It must be + defined to accept all pseudo-registers in every context where + some kind of register is required. + + Compiler source files that want to use the strict variant of + this macro define the macro `REG_OK_STRICT'. You should use an + `#ifdef REG_OK_STRICT' conditional to define the strict variant + in that case and the non-strict variant otherwise. + + Typically among the subroutines used to define + `GO_IF_LEGITIMATE_ADDRESS' are subroutines to check for + acceptable registers for various purposes (one for base + registers, one for index registers, and so on). Then only these + subroutine macros need have two variants; the higher levels of + macros may be the same whether strict or not. + + Normally, constant addresses which are the sum of a `symbol_ref' + and an integer are stored inside a `const' RTX to mark them as + constant. Therefore, there is no need to recognize such sums as + legitimate addresses. + + Usually `PRINT_OPERAND_ADDRESS' is not prepared to handle + constant sums that are not marked with `const'. It assumes + that a naked `plus' indicates indexing. If so, then you *must* + reject such naked constant sums as illegitimate addresses, so + that none of them will be given to `PRINT_OPERAND_ADDRESS'. + +`REG_OK_FOR_BASE_P (X)' + A C expression that is nonzero if X (assumed to be a `reg' RTX) + is valid for use as a base register. For hard registers, it + should always accept those which the hardware permits and reject + the others. Whether the macro accepts or rejects pseudo + registers must be controlled by `REG_OK_STRICT' as described + above. This usually requires two variant definitions, of which + `REG_OK_STRICT' controls the one actually used. + +`REG_OK_FOR_INDEX_P (X)' + A C expression that is nonzero if X (assumed to be a `reg' RTX) + is valid for use as an index register. + + The difference between an index register and a base register is + that the index register may be scaled. If an address involves + the sum of two registers, neither one of them scaled, then + either one may be labeled the "base" and the other the "index"; + but whichever labeling is used must fit the machine's + constraints of which registers may serve in each capacity. The + compiler will try both labelings, looking for one that is valid, + and will reload one or both registers only if neither labeling + works. + +`LEGITIMIZE_ADDRESS (X, OLDX, MODE, WIN)' + A C compound statement that attempts to replace X with a valid + memory address for an operand of mode MODE. WIN will be a C + statement label elsewhere in the code; the macro definition may + use + + GO_IF_LEGITIMATE_ADDRESS (MODE, X, WIN); + + to avoid further processing if the address has become legitimate. + + X will always be the result of a call to + `break_out_memory_refs', and OLDX will be the operand that was + given to that function to produce X. + + The code generated by this macro should not alter the + substructure of X. If it transforms X into a more legitimate + form, it should assign X (which will always be a C variable) a + new value. + + It is not necessary for this macro to come up with a legitimate + address. The compiler has standard ways of doing so in all + cases. In fact, it is safe for this macro to do nothing. But + often a machine-dependent strategy can generate better code. + +`GO_IF_MODE_DEPENDENT_ADDRESS (ADDR, LABEL)' + A C statement or compound statement with a conditional `goto + LABEL;' executed if memory address X (an RTX) can have different + meanings depending on the machine mode of the memory reference + it is used for. + + Autoincrement and autodecrement addresses typically have + mode-dependent effects because the amount of the increment or + decrement is the size of the operand being addressed. Some + machines have other mode-dependent addresses. Many RISC + machines have no mode-dependent addresses. + + You may assume that ADDR is a valid address for the machine. + +`LEGITIMATE_CONSTANT_P (X)' + A C expression that is nonzero if X is a legitimate constant for + an immediate operand on the target machine. You can assume that + either X is a `const_double' or it satisfies `CONSTANT_P', so + you need not check these things. In fact, `1' is a suitable + definition for this macro on machines where any `const_double' + is valid and anything `CONSTANT_P' is valid. + + +File: gcc.info, Node: Delayed Branch, Next: Condition Code, Prev: Addressing Modes, Up: Machine Macros + +Parameters for Delayed Branch Optimization +========================================== + +`HAVE_DELAYED_BRANCH' + Define this macro if the target machine has delayed branches, + that is, a branch does not take effect immediately, and the + actual branch instruction may be followed by one or more + instructions that will be issued before the PC is actually + changed. + + If defined, this allows a special scheduling pass to be run + after the second jump optimization to attempt to reorder + instructions to exploit this. Defining this macro also requires + the definition of certain other macros described below. + +`DBR_SLOTS_AFTER (INSN)' + This macro must be defined if `HAVE_DELAYED_BRANCH' is defined. + Its definition should be a C expression returning the number of + available delay slots following the instruction(s) output by the + pattern for INSN. The definition of "slot" is + machine-dependent, and may denote instructions, bytes, or + whatever. + +`DBR_INSN_SLOTS (INSN)' + This macro must be defined if `HAVE_DELAYED_BRANCH' is defined. + It should be a C expression returning the number of slots + (typically the number of machine instructions) consumed by INSN. + + You may assume that INSN is truly an insn, not a note, label, + barrier, dispatch table, `use', or `clobber'. + +`DBR_INSN_ELIGIBLE_P (INSN, DINSN)' + A C expression whose value is non-zero if it is legitimate to + put INSN in the delay slot following DINSN. + + You do not need to take account of data flow considerations in + the definition of this macro, because the delayed branch + optimizer always does that. This macro is needed only when + certain insns may not be placed in certain delay slots for + reasons not evident from the RTL expressions themselves. If + there are no such problems, you don't need to define this macro. + + You may assume that INSN is truly an insn, not a note, label, + barrier, dispatch table, `use', or `clobber'. You may assume + that DINSN is a jump insn with a delay slot. + +`DBR_OUTPUT_SEQEND(FILE)' + A C statement, to be executed after all slot-filler instructions + have been output. If necessary, call `dbr_sequence_length' to + determine the number of slots filled in a sequence (zero if not + currently outputting a sequence), to decide how many no-ops to + output, or whatever. + + Don't define this macro if it has nothing to do, but it is + helpful in reading assembly output if the extent of the delay + sequence is made explicit (e.g. with white space). + + Note that output routines for instructions with delay slots must + be prepared to deal with not being output as part of a sequence + (i.e. when the scheduling pass is not run, or when no slot + fillers could be found.) The variable `final_sequence' is null + when not processing a sequence, otherwise it contains the + `sequence' rtx being output. + + +File: gcc.info, Node: Condition Code, Next: Cross-compilation, Prev: Delayed Branch, Up: Machine Macros + +Condition Code Information +========================== + + The file `conditions.h' defines a variable `cc_status' to describe +how the condition code was computed (in case the interpretation of +the condition code depends on the instruction that it was set by). +This variable contains the RTL expressions on which the condition +code is currently based, and several standard flags. + + Sometimes additional machine-specific flags must be defined in the +machine description header file. It can also add additional +machine-specific information by defining `CC_STATUS_MDEP'. + +`CC_STATUS_MDEP' + C code for a data type which is used for declaring the `mdep' + component of `cc_status'. It defaults to `int'. + +`CC_STATUS_MDEP_INIT' + A C expression to initialize the `mdep' field to "empty". The + default definition does nothing, since most machines don't use + the field anyway. If you want to use the field, you should + probably define this macro to initialize it. + +`NOTICE_UPDATE_CC (EXP, INSN)' + A C compound statement to set the components of `cc_status' + appropriately for an insn INSN whose body is EXP. It is this + macro's responsibility to recognize insns that set the condition + code as a byproduct of other activity as well as those that + explicitly set `(cc0)'. + + If there are insn that do not set the condition code but do + alter other machine registers, this macro must check to see + whether they invalidate the expressions that the condition code + is recorded as reflecting. For example, on the 68000, insns + that store in address registers do not set the condition code, + which means that usually `NOTICE_UPDATE_CC' can leave + `cc_status' unaltered for such insns. But suppose that the + previous insn set the condition code based on location + `a4@(102)' and the current insn stores a new value in `a4'. + Although the condition code is not changed by this, it will no + longer be true that it reflects the contents of `a4@(102)'. + Therefore, `NOTICE_UPDATE_CC' must alter `cc_status' in this + case to say that nothing is known about the condition code value. + + The definition of `NOTICE_UPDATE_CC' must be prepared to deal + with the results of peephole optimization: insns whose patterns + are `parallel' RTXs containing various `reg', `mem' or constants + which are just the operands. The RTL structure of these insns + is not sufficient to indicate what the insns actually do. What + `NOTICE_UPDATE_CC' should do when it sees one is just to run + `CC_STATUS_INIT'. + + +File: gcc.info, Node: Cross-compilation, Next: Misc, Prev: Condition Code, Up: Machine Macros + +Cross Compilation and Floating-Point Format +=========================================== + + While all modern machines use 2's complement representation for +integers, there are a variety of representations for floating point +numbers. This means that in a cross-compiler the representation of +floating point numbers in the compiled program may be different from +that used in the machine doing the compilation. + + Because different representation systems may offer different +amounts of range and precision, the cross compiler cannot safely use +the host machine's floating point arithmetic. Therefore, floating +point constants must be represented in the target machine's format. +This means that the cross compiler cannot use `atof' to parse a +floating point constant; it must have its own special routine to use +instead. Also, constant folding must emulate the target machine's +arithmetic (or must not be done at all). + + The macros in the following table should be defined only if you +are cross compiling between different floating point formats. + + Otherwise, don't define them. Then default definitions will be set +up which use `double' as the data type, `==' to test for equality, etc. + + You don't need to worry about how many times you use an operand of +any of these macros. The compiler never uses operands which have +side effects. + +`REAL_VALUE_TYPE' + A macro for the C data type to be used to hold a floating point + value in the target machine's format. Typically this would be a + `struct' containing an array of `int'. + +`REAL_VALUES_EQUAL (X, Y)' + A macro for a C expression which compares for equality the two + values, X and Y, both of type `REAL_VALUE_TYPE'. + +`REAL_VALUES_LESS (X, Y)' + A macro for a C expression which tests whether X is less than Y, + both values being of type `REAL_VALUE_TYPE' and interpreted as + floating point numbers in the target machine's representation. + +`REAL_VALUE_LDEXP (X, SCALE)' + A macro for a C expression which performs the standard library + function `ldexp', but using the target machine's floating point + representation. Both X and the value of the expression have + type `REAL_VALUE_TYPE'. The second argument, SCALE, is an + integer. + +`REAL_VALUE_ATOF (STRING)' + A macro for a C expression which converts STRING, an expression + of type `char *', into a floating point number in the target + machine's representation. The value has type `REAL_VALUE_TYPE'. + + Define the following additional macros if you want to make +floating point constant folding work while cross compiling. If you +don't define them, cross compilation is still possible, but constant +folding will not happen for floating point values. + +`REAL_ARITHMETIC (OUTPUT, CODE, X, Y)' + A macro for a C statement which calculates an arithmetic + operation of the two floating point values X and Y, both of type + `REAL_VALUE_TYPE' in the target machine's representation, to + produce a result of the same type and representation which is + stored in OUTPUT (which will be a variable). + + The operation to be performed is specified by CODE, a tree code + which will always be one of the following: `PLUS_EXPR', + `MINUS_EXPR', `MULT_EXPR', `RDIV_EXPR', `MAX_EXPR', `MIN_EXPR'. + + The expansion of this macro is responsible for checking for + overflow. If overflow happens, the macro expansion should + execute the statement `return 0;', which indicates the inability + to perform the arithmetic operation requested. + +`REAL_VALUE_NEGATE (X)' + A macro for a C expression which returns the negative of the + floating point value X. Both X and the value of the expression + have type `REAL_VALUE_TYPE' and are in the target machine's + floating point representation. + + There is no way for this macro to report overflow, since + overflow can't happen in the negation operation. + +`REAL_VALUE_TO_INT (LOW, HIGH, X)' + A macro for a C expression which converts a floating point value + X into a double-precision integer which is then stored into LOW + and HIGH, two variables of type INT. + +`REAL_VALUE_FROM_INT (X, LOW, HIGH)' + A macro for a C expression which converts a double-precision + integer found in LOW and HIGH, two variables of type INT, into a + floating point value which is then stored into X. + + +File: gcc.info, Node: Misc, Next: Assembler Format, Prev: Cross-compilation, Up: Machine Macros + +Miscellaneous Parameters +======================== + +`CASE_VECTOR_MODE' + An alias for a machine mode name. This is the machine mode that + elements of a jump-table should have. + +`CASE_VECTOR_PC_RELATIVE' + Define this macro if jump-tables should contain relative + addresses. + +`CASE_DROPS_THROUGH' + Define this if control falls through a `case' insn when the + index value is out of range. This means the specified + default-label is actually ignored by the `case' insn proper. + +`IMPLICIT_FIX_EXPR' + An alias for a tree code that should be used by default for + conversion of floating point values to fixed point. Normally, + `FIX_ROUND_EXPR' is used. + +`FIXUNS_TRUNC_LIKE_FIX_TRUNC' + Define this macro if the same instructions that convert a + floating point number to a signed fixed point number also + convert validly to an unsigned one. + +`EASY_DIV_EXPR' + An alias for a tree code that is the easiest kind of division to + compile code for in the general case. It may be + `TRUNC_DIV_EXPR', `FLOOR_DIV_EXPR', `CEIL_DIV_EXPR' or + `ROUND_DIV_EXPR'. These four division operators differ in how + they round the result to an integer. `EASY_DIV_EXPR' is used + when it is permissible to use any of those kinds of division and + the choice should be made on the basis of efficiency. + +`DEFAULT_SIGNED_CHAR' + An expression whose value is 1 or 0, according to whether the + type `char' should be signed or unsigned by default. The user + can always override this default with the options + `-fsigned-char' and `-funsigned-char'. + +`SCCS_DIRECTIVE' + Define this if the preprocessor should ignore `#sccs' directives + and print no error message. + +`HAVE_VPRINTF' + Define this if the library function `vprintf' is available on + your system. + +`MOVE_MAX' + The maximum number of bytes that a single instruction can move + quickly from memory to memory. + +`INT_TYPE_SIZE' + A C expression for the size in bits of the type `int' on the + target machine. If you don't define this, the default is one + word. + +`SHORT_TYPE_SIZE' + A C expression for the size in bits of the type `short' on the + target machine. If you don't define this, the default is half a + word. (If this would be less than one storage unit, it is + rounded up to one unit.) + +`LONG_TYPE_SIZE' + A C expression for the size in bits of the type `long' on the + target machine. If you don't define this, the default is one + word. + +`LONG_LONG_TYPE_SIZE' + A C expression for the size in bits of the type `long long' on + the target machine. If you don't define this, the default is + two words. + +`CHAR_TYPE_SIZE' + A C expression for the size in bits of the type `char' on the + target machine. If you don't define this, the default is one + quarter of a word. (If this would be less than one storage + unit, it is rounded up to one unit.) + +`FLOAT_TYPE_SIZE' + A C expression for the size in bits of the type `float' on the + target machine. If you don't define this, the default is one + word. + +`DOUBLE_TYPE_SIZE' + A C expression for the size in bits of the type `double' on the + target machine. If you don't define this, the default is two + words. + +`LONG_DOUBLE_TYPE_SIZE' + A C expression for the size in bits of the type `long double' on + the target machine. If you don't define this, the default is + two words. + +`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 slow (requires more than one instruction). + +`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'. + +`SHIFT_COUNT_TRUNCATED' + Define this macro if shift instructions ignore all but the + lowest few bits of the shift count. It implies that a + sign-extend or zero-extend instruction for the shift count can + be omitted. + +`TRULY_NOOP_TRUNCATION (OUTPREC, INPREC)' + A C expression which is nonzero if on this machine it is safe to + "convert" an integer of INPREC bits to one of OUTPREC bits + (where OUTPREC is smaller than INPREC) by merely operating on it + as if it had only OUTPREC bits. + + On many machines, this expression can be 1. + +`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. + +`PROMOTE_PROTOTYPES' + Define this macro if an argument declared as `char' or `short' + in a prototype should actually be passed as an `int'. In + addition to avoiding errors in certain cases of mismatch, it + also makes for better code on certain machines. + +`STORE_FLAG_VALUE' + A C expression for the value stored by a store-flag instruction + (`sCOND') when the condition is true. This is usually 1 or -1; + it is required to be an odd number or a negative number. + + Do not define `STORE_FLAG_VALUE' if the machine has no + store-flag instructions. + +`Pmode' + An alias for the machine mode for pointers. Normally the + definition can be + + #define Pmode SImode + +`FUNCTION_MODE' + An alias for the machine mode used for memory references to + functions being called, in `call' RTL expressions. On most + machines this should be `QImode'. + +`INSN_MACHINE_INFO' + This macro should expand into a C structure type to use for the + machine-dependent info field specified with the optional last + argument in `define_insn' and `define_peephole' patterns. For + example, it might expand into `struct machine_info'; then it + would be up to you to define this structure in the `tm.h' file. + + You do not need to define this macro if you do not write the + optional last argument in any of the patterns in the machine + description. + +`DEFAULT_MACHINE_INFO' + This macro should expand into a C initializer to use to + initialize the machine-dependent info for one insn pattern. It + is used for patterns that do not specify the machine-dependent + info. + + If you do not define this macro, zero is used. + +`CONST_COSTS (X, CODE)' + A part of a C `switch' statement that describes the relative + costs of constant RTL expressions. It must contain `case' + labels for expression codes `const_int', `const', `symbol_ref', + `label_ref' and `const_double'. Each case must ultimately reach + a `return' statement to return the relative cost of the use of + that kind of constant value in an expression. The cost may + depend on the precise value of the constant, which is available + for examination in X. + + CODE is the expression code--redundant, since it can be obtained + with `GET_CODE (X)'. + +`DOLLARS_IN_IDENTIFIERS' + Define this to be nonzero if the character `$' should be allowed + by default in identifier names.  File: gcc.info, Node: Assembler Format, Prev: Misc, Up: Machine Macros @@ -55,6 +610,14 @@ Output of Assembler Code If this macro is not defined, a default is provided that loads the standard C library from the usual place. See `gcc.c'. +`LIBG_SPEC' + Another C string constant used much like `LINK_SPEC'. This + controls whether to link `libg.a' when debugging. Some systems + expect this; others do not have any `libg.a'. + + If this macro is not defined, a default is provided that loads + the `libg.a' provided `-g' is specified. See `gcc.c'. + `STARTFILE_SPEC' Another C string constant used much like `LINK_SPEC'. The difference between the two is that `STARTFILE_SPEC' is used at @@ -407,8 +970,8 @@ Output of Assembler Code instruction to assemble a `int', `short' or `char' constant whose value is VALUE. The argument EXP will be an RTL expression which represents a constant value. Use - `output_addr_const (EXP)' to output this value as an assembler - expression. + `output_addr_const (STREAM, EXP)' to output this value as an + assembler expression. `ASM_OUTPUT_DOUBLE_INT (STREAM, EXP)' A C statement to output to the stdio stream STREAM an assembler @@ -512,11 +1075,11 @@ Output of Assembler Code 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. + 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 @@ -595,29 +1158,4 @@ Output of Assembler Code #define ASM_OPEN_PAREN "(" #define ASM_CLOSE_PAREN ")" - - -File: gcc.info, Node: Config, Prev: Machine Macros, Up: Top - -The Configuration File -********************** - -The configuration file `xm-MACHINE.h' contains macro definitions that -describe the machine and system on which the compiler is running. -Most of the values in it are actually the same on all machines that -GNU CC runs on, so large parts of all configuration files are -identical. But there are some macros that vary: - -`FAILURE_EXIT_CODE' - A C expression for the status code to be returned when the - compiler exits after serious errors. - -`SUCCESS_EXIT_CODE' - A C expression for the status code to be returned when the - compiler exits without serious errors. - -In addition, configuration files for system V define `bcopy', `bzero' -and `bcmp' as aliases. Some files define `alloca' as a macro when -compiled with GNU CC, in order to take advantage of the benefit of -GNU CC's built-in `alloca'. - + \ No newline at end of file