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GNU Info (gcc-295.info)MiscMiscellaneous Parameters ======================== Here are several miscellaneous parameters. `PREDICATE_CODES' Define this if you have defined special-purpose predicates in the file `MACHINE.c'. This macro is called within an initializer of an array of structures. The first field in the structure is the name of a predicate and the second field is an array of rtl codes. For each predicate, list all rtl codes that can be in expressions matched by the predicate. The list should have a trailing comma. Here is an example of two entries in the list for a typical RISC machine: #define PREDICATE_CODES \ {"gen_reg_rtx_operand", {SUBREG, REG}}, \ {"reg_or_short_cint_operand", {SUBREG, REG, CONST_INT}}, Defining this macro does not affect the generated code (however, incorrect definitions that omit an rtl code that may be matched by the predicate can cause the compiler to malfunction). Instead, it allows the table built by `genrecog' to be more compact and efficient, thus speeding up the compiler. The most important predicates to include in the list specified by this macro are those used in the most insn patterns. `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_SHORTEN_MODE (MIN_OFFSET, MAX_OFFSET, BODY)' Optional: return the preferred mode for an `addr_diff_vec' when the minimum and maximum offset are known. If you define this, it enables extra code in branch shortening to deal with `addr_diff_vec'. To make this work, you also have to define INSN_ALIGN and make the alignment for `addr_diff_vec' explicit. The BODY argument is provided so that the offset_unsigned and scale flags can be updated. `CASE_VECTOR_PC_RELATIVE' Define this macro to be a C expression to indicate when jump-tables should contain relative addresses. If jump-tables never contain relative addresses, then you need not define this macro. `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. `CASE_VALUES_THRESHOLD' Define this to be the smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. The default is four for machines with a `casesi' instruction and five otherwise. This is best for most machines. `WORD_REGISTER_OPERATIONS' Define this macro if operations between registers with integral mode smaller than a word are always performed on the entire register. Most RISC machines have this property and most CISC machines do not. `LOAD_EXTEND_OP (MODE)' Define this macro to be a C expression indicating when insns that read memory in MODE, an integral mode narrower than a word, set the bits outside of MODE to be either the sign-extension or the zero-extension of the data read. Return `SIGN_EXTEND' for values of MODE for which the insn sign-extends, `ZERO_EXTEND' for which it zero-extends, and `NIL' for other modes. This macro is not called with MODE non-integral or with a width greater than or equal to `BITS_PER_WORD', so you may return any value in this case. Do not define this macro if it would always return `NIL'. On machines where this macro is defined, you will normally define it as the constant `SIGN_EXTEND' or `ZERO_EXTEND'. `SHORT_IMMEDIATES_SIGN_EXTEND' Define this macro if loading short immediate values into registers sign extends. `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. `MOVE_MAX' The maximum number of bytes that a single instruction can move quickly between memory and registers or between two memory locations. `MAX_MOVE_MAX' The maximum number of bytes that a single instruction can move quickly between memory and registers or between two memory locations. If this is undefined, the default is `MOVE_MAX'. Otherwise, it is the constant value that is the largest value that `MOVE_MAX' can have at run-time. `SHIFT_COUNT_TRUNCATED' A C expression that is nonzero if on this machine the number of bits actually used for the count of a shift operation is equal to the number of bits needed to represent the size of the object being shifted. When this macro is non-zero, the compiler will assume that it is safe to omit a sign-extend, zero-extend, and certain bitwise `and' instructions that truncates the count of a shift operation. On machines that have instructions that act on bitfields at variable positions, which may include `bit test' instructions, a nonzero `SHIFT_COUNT_TRUNCATED' also enables deletion of truncations of the values that serve as arguments to bitfield instructions. If both types of instructions truncate the count (for shifts) and position (for bitfield operations), or if no variable-position bitfield instructions exist, you should define this macro. However, on some machines, such as the 80386 and the 680x0, truncation only applies to shift operations and not the (real or pretended) bitfield operations. Define `SHIFT_COUNT_TRUNCATED' to be zero on such machines. Instead, add patterns to the `md' file that include the implied truncation of the shift instructions. You need not define this macro if it would always have the value of zero. `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. When `TRULY_NOOP_TRUNCATION' returns 1 for a pair of sizes for modes for which `MODES_TIEABLE_P' is 0, suboptimal code can result. If this is the case, making `TRULY_NOOP_TRUNCATION' return 0 in such cases may improve things. `STORE_FLAG_VALUE' A C expression describing the value returned by a comparison operator with an integral mode and stored by a store-flag instruction (`sCOND') when the condition is true. This description must apply to *all* the `sCOND' patterns and all the comparison operators whose results have a `MODE_INT' mode. A value of 1 or -1 means that the instruction implementing the comparison operator returns exactly 1 or -1 when the comparison is true and 0 when the comparison is false. Otherwise, the value indicates which bits of the result are guaranteed to be 1 when the comparison is true. This value is interpreted in the mode of the comparison operation, which is given by the mode of the first operand in the `sCOND' pattern. Either the low bit or the sign bit of `STORE_FLAG_VALUE' be on. Presently, only those bits are used by the compiler. If `STORE_FLAG_VALUE' is neither 1 or -1, the compiler will generate code that depends only on the specified bits. It can also replace comparison operators with equivalent operations if they cause the required bits to be set, even if the remaining bits are undefined. For example, on a machine whose comparison operators return an `SImode' value and where `STORE_FLAG_VALUE' is defined as `0x80000000', saying that just the sign bit is relevant, the expression (ne:SI (and:SI X (const_int POWER-OF-2)) (const_int 0)) can be converted to (ashift:SI X (const_int N)) where N is the appropriate shift count to move the bit being tested into the sign bit. There is no way to describe a machine that always sets the low-order bit for a true value, but does not guarantee the value of any other bits, but we do not know of any machine that has such an instruction. If you are trying to port GNU CC to such a machine, include an instruction to perform a logical-and of the result with 1 in the pattern for the comparison operators and let us know (Note: How to Report Bugs.). Often, a machine will have multiple instructions that obtain a value from a comparison (or the condition codes). Here are rules to guide the choice of value for `STORE_FLAG_VALUE', and hence the instructions to be used: * Use the shortest sequence that yields a valid definition for `STORE_FLAG_VALUE'. It is more efficient for the compiler to "normalize" the value (convert it to, e.g., 1 or 0) than for the comparison operators to do so because there may be opportunities to combine the normalization with other operations. * For equal-length sequences, use a value of 1 or -1, with -1 being slightly preferred on machines with expensive jumps and 1 preferred on other machines. * As a second choice, choose a value of `0x80000001' if instructions exist that set both the sign and low-order bits but do not define the others. * Otherwise, use a value of `0x80000000'. Many machines can produce both the value chosen for `STORE_FLAG_VALUE' and its negation in the same number of instructions. On those machines, you should also define a pattern for those cases, e.g., one matching (set A (neg:M (ne:M B C))) Some machines can also perform `and' or `plus' operations on condition code values with less instructions than the corresponding `sCOND' insn followed by `and' or `plus'. On those machines, define the appropriate patterns. Use the names `incscc' and `decscc', respectively, for the patterns which perform `plus' or `minus' operations on condition code values. See `rs6000.md' for some examples. The GNU Superoptizer can be used to find such instruction sequences on other machines. You need not define `STORE_FLAG_VALUE' if the machine has no store-flag instructions. `FLOAT_STORE_FLAG_VALUE' A C expression that gives a non-zero floating point value that is returned when comparison operators with floating-point results are true. Define this macro on machine that have comparison operations that return floating-point values. If there are no such operations, do not define this macro. `Pmode' An alias for the machine mode for pointers. On most machines, define this to be the integer mode corresponding to the width of a hardware pointer; `SImode' on 32-bit machine or `DImode' on 64-bit machines. On some machines you must define this to be one of the partial integer modes, such as `PSImode'. The width of `Pmode' must be at least as large as the value of `POINTER_SIZE'. If it is not equal, you must define the macro `POINTERS_EXTEND_UNSIGNED' to specify how pointers are extended to `Pmode'. `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'. `INTEGRATE_THRESHOLD (DECL)' A C expression for the maximum number of instructions above which the function DECL should not be inlined. DECL is a `FUNCTION_DECL' node. The default definition of this macro is 64 plus 8 times the number of arguments that the function accepts. Some people think a larger threshold should be used on RISC machines. `SCCS_DIRECTIVE' Define this if the preprocessor should ignore `#sccs' directives and print no error message. `NO_IMPLICIT_EXTERN_C' Define this macro if the system header files support C++ as well as C. This macro inhibits the usual method of using system header files in C++, which is to pretend that the file's contents are enclosed in `extern "C" {...}'. `HANDLE_PRAGMA (GETC, UNGETC, NAME)' Define this macro if you want to implement any pragmas. If defined, it is a C expression whose value is 1 if the pragma was handled by the macro, zero otherwise. The argument GETC is a function of type `int (*)(void)' which will return the next character in the input stream, or EOF if no characters are left. The argument UNGETC is a function of type `void (*)(int)' which will push a character back into the input stream. The argument NAME is the word following #pragma in the input stream. The input stream pointer will be pointing just beyond the end of this word. The input stream should be left undistrubed if the expression returns zero, otherwise it should be pointing at the next character after the end of the pragma. Any characters remaining on the line will be ignored. It is generally a bad idea to implement new uses of `#pragma'. The only reason to define this macro is for compatibility with other compilers that do support `#pragma' for the sake of any user programs which already use it. If the pragma can be implemented by atttributes then the macro `INSERT_ATTRIBUTES' might be a useful one to define as well. Note: older versions of this macro only had two arguments: STREAM and TOKEN. The macro was changed in order to allow it to work when gcc is built both with and without a cpp library. `HANDLE_SYSV_PRAGMA' Define this macro (to a value of 1) if you want the System V style pragmas `#pragma pack(<n>)' and `#pragma weak <name> [=<value>]' to be supported by gcc. The pack pragma specifies the maximum alignment (in bytes) of fields within a structure, in much the same way as the `__aligned__' and `__packed__' `__attribute__'s do. A pack value of zero resets the behaviour to the default. The weak pragma only works if `SUPPORTS_WEAK' and `ASM_WEAKEN_LABEL' are defined. If enabled it allows the creation of specifically named weak labels, optionally with a value. `HANDLE_PRAGMA_PACK_PUSH_POP' Define this macro (to a value of 1) if you want to support the Win32 style pragmas `#pragma pack(push,<n>)' and `#pragma pack(pop)'. The pack(push,<n>) pragma specifies the maximum alignment (in bytes) of fields within a structure, in much the same way as the `__aligned__' and `__packed__' `__attribute__'s do. A pack value of zero resets the behaviour to the default. Successive invocations of this pragma cause the previous values to be stacked, so that invocations of `#pragma pack(pop)' will return to the previous value. `VALID_MACHINE_DECL_ATTRIBUTE (DECL, ATTRIBUTES, IDENTIFIER, ARGS)' If defined, a C expression whose value is nonzero if IDENTIFIER with arguments ARGS is a valid machine specific attribute for DECL. The attributes in ATTRIBUTES have previously been assigned to DECL. `VALID_MACHINE_TYPE_ATTRIBUTE (TYPE, ATTRIBUTES, IDENTIFIER, ARGS)' If defined, a C expression whose value is nonzero if IDENTIFIER with arguments ARGS is a valid machine specific attribute for TYPE. The attributes in ATTRIBUTES have previously been assigned to TYPE. `COMP_TYPE_ATTRIBUTES (TYPE1, TYPE2)' If defined, a C expression whose value is zero if the attributes on TYPE1 and TYPE2 are incompatible, one if they are compatible, and two if they are nearly compatible (which causes a warning to be generated). `SET_DEFAULT_TYPE_ATTRIBUTES (TYPE)' If defined, a C statement that assigns default attributes to newly defined TYPE. `MERGE_MACHINE_TYPE_ATTRIBUTES (TYPE1, TYPE2)' Define this macro if the merging of type attributes needs special handling. If defined, the result is a list of the combined TYPE_ATTRIBUTES of TYPE1 and TYPE2. It is assumed that comptypes has already been called and returned 1. `MERGE_MACHINE_DECL_ATTRIBUTES (OLDDECL, NEWDECL)' Define this macro if the merging of decl attributes needs special handling. If defined, the result is a list of the combined DECL_MACHINE_ATTRIBUTES of OLDDECL and NEWDECL. NEWDECL is a duplicate declaration of OLDDECL. Examples of when this is needed are when one attribute overrides another, or when an attribute is nullified by a subsequent definition. `INSERT_ATTRIBUTES (NODE, ATTR_PTR, PREFIX_PTR)' Define this macro if you want to be able to add attributes to a decl when it is being created. This is normally useful for backends which wish to implement a pragma by using the attributes which correspond to the pragma's effect. The NODE argument is the decl which is being created. The ATTR_PTR argument is a pointer to the attribute list for this decl. The PREFIX_PTR is a pointer to the list of attributes that have appeared after the specifiers and modifiers of the declaration, but before the declaration proper. `SET_DEFAULT_DECL_ATTRIBUTES (DECL, ATTRIBUTES)' If defined, a C statement that assigns default attributes to newly defined DECL. `DOLLARS_IN_IDENTIFIERS' Define this macro to control use of the character `$' in identifier names. 0 means `$' is not allowed by default; 1 means it is allowed. 1 is the default; there is no need to define this macro in that case. This macro controls the compiler proper; it does not affect the preprocessor. `NO_DOLLAR_IN_LABEL' Define this macro if the assembler does not accept the character `$' in label names. By default constructors and destructors in G++ have `$' in the identifiers. If this macro is defined, `.' is used instead. `NO_DOT_IN_LABEL' Define this macro if the assembler does not accept the character `.' in label names. By default constructors and destructors in G++ have names that use `.'. If this macro is defined, these names are rewritten to avoid `.'. `DEFAULT_MAIN_RETURN' Define this macro if the target system expects every program's `main' function to return a standard "success" value by default (if no other value is explicitly returned). The definition should be a C statement (sans semicolon) to generate the appropriate rtl instructions. It is used only when compiling the end of `main'. `HAVE_ATEXIT' Define this if the target system supports the function `atexit' from the ANSI C standard. If this is not defined, and `INIT_SECTION_ASM_OP' is not defined, a default `exit' function will be provided to support C++. `EXIT_BODY' Define this if your `exit' function needs to do something besides calling an external function `_cleanup' before terminating with `_exit'. The `EXIT_BODY' macro is only needed if neither `HAVE_ATEXIT' nor `INIT_SECTION_ASM_OP' are defined. `INSN_SETS_ARE_DELAYED (INSN)' Define this macro as a C expression that is nonzero if it is safe for the delay slot scheduler to place instructions in the delay slot of INSN, even if they appear to use a resource set or clobbered in INSN. INSN is always a `jump_insn' or an `insn'; GNU CC knows that every `call_insn' has this behavior. On machines where some `insn' or `jump_insn' is really a function call and hence has this behavior, you should define this macro. You need not define this macro if it would always return zero. `INSN_REFERENCES_ARE_DELAYED (INSN)' Define this macro as a C expression that is nonzero if it is safe for the delay slot scheduler to place instructions in the delay slot of INSN, even if they appear to set or clobber a resource referenced in INSN. INSN is always a `jump_insn' or an `insn'. On machines where some `insn' or `jump_insn' is really a function call and its operands are registers whose use is actually in the subroutine it calls, you should define this macro. Doing so allows the delay slot scheduler to move instructions which copy arguments into the argument registers into the delay slot of INSN. You need not define this macro if it would always return zero. `MACHINE_DEPENDENT_REORG (INSN)' In rare cases, correct code generation requires extra machine dependent processing between the second jump optimization pass and delayed branch scheduling. On those machines, define this macro as a C statement to act on the code starting at INSN. `MULTIPLE_SYMBOL_SPACES' Define this macro if in some cases global symbols from one translation unit may not be bound to undefined symbols in another translation unit without user intervention. For instance, under Microsoft Windows symbols must be explicitly imported from shared libraries (DLLs). `ISSUE_RATE' A C expression that returns how many instructions can be issued at the same time if the machine is a superscalar machine. This is only used by the `Haifa' scheduler, and not the traditional scheduler. `MD_SCHED_INIT (FILE, VERBOSE)' A C statement which is executed by the `Haifa' scheduler at the beginning of each block of instructions that are to be scheduled. FILE is either a null pointer, or a stdio stream to write any debug output to. VERBOSE is the verbose level provided by `-fsched-verbose-'N. `MD_SCHED_REORDER (FILE, VERBOSE, READY, N_READY)' A C statement which is executed by the `Haifa' scheduler after it has scheduled the ready list to allow the machine description to reorder it (for example to combine two small instructions together on `VLIW' machines). FILE is either a null pointer, or a stdio stream to write any debug output to. VERBOSE is the verbose level provided by `-fsched-verbose-'N. READY is a pointer to the ready list of instructions that are ready to be scheduled. N_READY is the number of elements in the ready list. The scheduler reads the ready list in reverse order, starting with READY[N_READY-1] and going to READY[0]. `MD_SCHED_VARIABLE_ISSUE (FILE, VERBOSE, INSN, MORE)' A C statement which is executed by the `Haifa' scheduler after it has scheduled an insn from the ready list. FILE is either a null pointer, or a stdio stream to write any debug output to. VERBOSE is the verbose level provided by `-fsched-verbose-'N. INSN is the instruction that was scheduled. MORE is the number of instructions that can be issued in the current cycle. The `MD_SCHED_VARIABLE_ISSUE' macro is responsible for updating the value of MORE (typically by MORE-). `MAX_INTEGER_COMPUTATION_MODE' Define this to the largest integer machine mode which can be used for operations other than load, store and copy operations. You need only define this macro if the target holds values larger than `word_mode' in general purpose registers. Most targets should not define this macro. `MATH_LIBRARY' Define this macro as a C string constant for the linker argument to link in the system math library, or `""' if the target does not have a separate math library. You need only define this macro if the default of `"-lm"' is wrong. automatically generated by info2www version 1.2.2.9 |