--- gcc/gcc.info-11 2018/04/24 17:56:44 1.1.1.3 +++ gcc/gcc.info-11 2018/04/24 18:42:13 1.1.1.10 @@ -1,9 +1,13 @@ -This is Info file gcc.info, produced by Makeinfo-1.47 from the input -file gcc.texi. +This is Info file gcc.info, produced by Makeinfo version 1.67 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 59 Temple Place - Suite 330 +Boston, MA 02111-1307 USA + + Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 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 @@ -11,1043 +15,1130 @@ 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 +that the sections entitled "GNU General Public License," "Funding for +Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are +included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "GNU General Public -License" and "Boycott", and this permission notice, may be included in +License," "Funding for Free Software," and "Protect Your Freedom--Fight +`Look And Feel'", and this permission notice, may be included in translations approved by the Free Software Foundation instead of in the original English.  -File: gcc.info, Node: Standard Names, Next: Pattern Ordering, Prev: Constraints, Up: Machine Desc +File: gcc.info, Node: Installation Problems, Next: Cross-Compiler Problems, Prev: Actual Bugs, Up: Trouble + +Installation Problems +===================== + + This is a list of problems (and some apparent problems which don't +really mean anything is wrong) that show up during installation of GNU +CC. + + * On certain systems, defining certain environment variables such as + `CC' can interfere with the functioning of `make'. + + * If you encounter seemingly strange errors when trying to build the + compiler in a directory other than the source directory, it could + be because you have previously configured the compiler in the + source directory. Make sure you have done all the necessary + preparations. *Note Other Dir::. + + * If you build GNU CC on a BSD system using a directory stored in a + System V file system, problems may occur in running `fixincludes' + if the System V file system doesn't support symbolic links. These + problems result in a failure to fix the declaration of `size_t' in + `sys/types.h'. If you find that `size_t' is a signed type and + that type mismatches occur, this could be the cause. + + The solution is not to use such a directory for building GNU CC. + + * In previous versions of GNU CC, the `gcc' driver program looked for + `as' and `ld' in various places; for example, in files beginning + with `/usr/local/lib/gcc-'. GNU CC version 2 looks for them in + the directory `/usr/local/lib/gcc-lib/TARGET/VERSION'. + + Thus, to use a version of `as' or `ld' that is not the system + default, for example `gas' or GNU `ld', you must put them in that + directory (or make links to them from that directory). + + * Some commands executed when making the compiler may fail (return a + non-zero status) and be ignored by `make'. These failures, which + are often due to files that were not found, are expected, and can + safely be ignored. + + * It is normal to have warnings in compiling certain files about + unreachable code and about enumeration type clashes. These files' + names begin with `insn-'. Also, `real.c' may get some warnings + that you can ignore. + + * Sometimes `make' recompiles parts of the compiler when installing + the compiler. In one case, this was traced down to a bug in + `make'. Either ignore the problem or switch to GNU Make. + + * If you have installed a program known as purify, you may find that + it causes errors while linking `enquire', which is part of building + GNU CC. The fix is to get rid of the file `real-ld' which purify + installs--so that GNU CC won't try to use it. + + * On SLS 1.01, a Linux-based GNU system, there is a problem with + `libc.a': it does not contain the obstack functions. However, GNU + CC assumes that the obstack functions are in `libc.a' when it is + the GNU C library. To work around this problem, change the + `__GNU_LIBRARY__' conditional around line 31 to `#if 1'. + + * On some 386 systems, building the compiler never finishes because + `enquire' hangs due to a hardware problem in the motherboard--it + reports floating point exceptions to the kernel incorrectly. You + can install GNU CC except for `float.h' by patching out the + command to run `enquire'. You may also be able to fix the problem + for real by getting a replacement motherboard. This problem was + observed in Revision E of the Micronics motherboard, and is fixed + in Revision F. It has also been observed in the MYLEX MXA-33 + motherboard. + + If you encounter this problem, you may also want to consider + removing the FPU from the socket during the compilation. + Alternatively, if you are running SCO Unix, you can reboot and + force the FPU to be ignored. To do this, type `hd(40)unix auto + ignorefpu'. + + * On some 386 systems, GNU CC crashes trying to compile `enquire.c'. + This happens on machines that don't have a 387 FPU chip. On 386 + machines, the system kernel is supposed to emulate the 387 when you + don't have one. The crash is due to a bug in the emulator. + + One of these systems is the Unix from Interactive Systems: 386/ix. + On this system, an alternate emulator is provided, and it does + work. To use it, execute this command as super-user: + + ln /etc/emulator.rel1 /etc/emulator + + and then reboot the system. (The default emulator file remains + present under the name `emulator.dflt'.) + + Try using `/etc/emulator.att', if you have such a problem on the + SCO system. + + Another system which has this problem is Esix. We don't know + whether it has an alternate emulator that works. + + On NetBSD 0.8, a similar problem manifests itself as these error + messages: + + enquire.c: In function `fprop': + enquire.c:2328: floating overflow + + * On SCO systems, when compiling GNU CC with the system's compiler, + do not use `-O'. Some versions of the system's compiler miscompile + GNU CC with `-O'. + + * Sometimes on a Sun 4 you may observe a crash in the program + `genflags' or `genoutput' while building GNU CC. This is said to + be due to a bug in `sh'. You can probably get around it by running + `genflags' or `genoutput' manually and then retrying the `make'. + + * On Solaris 2, executables of GNU CC version 2.0.2 are commonly + available, but they have a bug that shows up when compiling current + versions of GNU CC: undefined symbol errors occur during assembly + if you use `-g'. + + The solution is to compile the current version of GNU CC without + `-g'. That makes a working compiler which you can use to recompile + with `-g'. + + * Solaris 2 comes with a number of optional OS packages. Some of + these packages are needed to use GNU CC fully. If you did not + install all optional packages when installing Solaris, you will + need to verify that the packages that GNU CC needs are installed. + + To check whether an optional package is installed, use the + `pkginfo' command. To add an optional package, use the `pkgadd' + command. For further details, see the Solaris documentation. + + For Solaris 2.0 and 2.1, GNU CC needs six packages: `SUNWarc', + `SUNWbtool', `SUNWesu', `SUNWhea', `SUNWlibm', and `SUNWtoo'. + + For Solaris 2.2, GNU CC needs an additional seventh package: + `SUNWsprot'. + + * On Solaris 2, trying to use the linker and other tools in + `/usr/ucb' to install GNU CC has been observed to cause trouble. + For example, the linker may hang indefinitely. The fix is to + remove `/usr/ucb' from your `PATH'. + + * If you use the 1.31 version of the MIPS assembler (such as was + shipped with Ultrix 3.1), you will need to use the + -fno-delayed-branch switch when optimizing floating point code. + Otherwise, the assembler will complain when the GCC compiler fills + a branch delay slot with a floating point instruction, such as + `add.d'. + + * If on a MIPS system you get an error message saying "does not have + gp sections for all it's [sic] sectons [sic]", don't worry about + it. This happens whenever you use GAS with the MIPS linker, but + there is not really anything wrong, and it is okay to use the + output file. You can stop such warnings by installing the GNU + linker. + + It would be nice to extend GAS to produce the gp tables, but they + are optional, and there should not be a warning about their + absence. + + * In Ultrix 4.0 on the MIPS machine, `stdio.h' does not work with GNU + CC at all unless it has been fixed with `fixincludes'. This causes + problems in building GNU CC. Once GNU CC is installed, the + problems go away. + + To work around this problem, when making the stage 1 compiler, + specify this option to Make: + + GCC_FOR_TARGET="./xgcc -B./ -I./include" + + When making stage 2 and stage 3, specify this option: + + CFLAGS="-g -I./include" + + * Users have reported some problems with version 2.0 of the MIPS + compiler tools that were shipped with Ultrix 4.1. Version 2.10 + which came with Ultrix 4.2 seems to work fine. + + Users have also reported some problems with version 2.20 of the + MIPS compiler tools that were shipped with RISC/os 4.x. The + earlier version 2.11 seems to work fine. + + * Some versions of the MIPS linker will issue an assertion failure + when linking code that uses `alloca' against shared libraries on + RISC-OS 5.0, and DEC's OSF/1 systems. This is a bug in the + linker, that is supposed to be fixed in future revisions. To + protect against this, GNU CC passes `-non_shared' to the linker + unless you pass an explicit `-shared' or `-call_shared' switch. + + * On System V release 3, you may get this error message while + linking: + + ld fatal: failed to write symbol name SOMETHING + in strings table for file WHATEVER + + This probably indicates that the disk is full or your ULIMIT won't + allow the file to be as large as it needs to be. + + This problem can also result because the kernel parameter `MAXUMEM' + is too small. If so, you must regenerate the kernel and make the + value much larger. The default value is reported to be 1024; a + value of 32768 is said to work. Smaller values may also work. + + * On System V, if you get an error like this, + + /usr/local/lib/bison.simple: In function `yyparse': + /usr/local/lib/bison.simple:625: virtual memory exhausted + + that too indicates a problem with disk space, ULIMIT, or `MAXUMEM'. + + * Current GNU CC versions probably do not work on version 2 of the + NeXT operating system. + + * On NeXTStep 3.0, the Objective C compiler does not work, due, + apparently, to a kernel bug that it happens to trigger. This + problem does not happen on 3.1. + + * On the Tower models 4N0 and 6N0, by default a process is not + allowed to have more than one megabyte of memory. GNU CC cannot + compile itself (or many other programs) with `-O' in that much + memory. + + To solve this problem, reconfigure the kernel adding the following + line to the configuration file: + + MAXUMEM = 4096 + + * On HP 9000 series 300 or 400 running HP-UX release 8.0, there is a + bug in the assembler that must be fixed before GNU CC can be + built. This bug manifests itself during the first stage of + compilation, while building `libgcc2.a': + + _floatdisf + cc1: warning: `-g' option not supported on this version of GCC + cc1: warning: `-g1' option not supported on this version of GCC + ./xgcc: Internal compiler error: program as got fatal signal 11 + + A patched version of the assembler is available by anonymous ftp + from `altdorf.ai.mit.edu' as the file + `archive/cph/hpux-8.0-assembler'. If you have HP software support, + the patch can also be obtained directly from HP, as described in + the following note: + + This is the patched assembler, to patch SR#1653-010439, where + the assembler aborts on floating point constants. + + The bug is not really in the assembler, but in the shared + library version of the function "cvtnum(3c)". The bug on + "cvtnum(3c)" is SR#4701-078451. Anyway, the attached + assembler uses the archive library version of "cvtnum(3c)" + and thus does not exhibit the bug. + + This patch is also known as PHCO_4484. + + * On HP-UX version 8.05, but not on 8.07 or more recent versions, + the `fixproto' shell script triggers a bug in the system shell. + If you encounter this problem, upgrade your operating system or + use BASH (the GNU shell) to run `fixproto'. + + * Some versions of the Pyramid C compiler are reported to be unable + to compile GNU CC. You must use an older version of GNU CC for + bootstrapping. One indication of this problem is if you get a + crash when GNU CC compiles the function `muldi3' in file + `libgcc2.c'. + + You may be able to succeed by getting GNU CC version 1, installing + it, and using it to compile GNU CC version 2. The bug in the + Pyramid C compiler does not seem to affect GNU CC version 1. + + * There may be similar problems on System V Release 3.1 on 386 + systems. + + * On the Intel Paragon (an i860 machine), if you are using operating + system version 1.0, you will get warnings or errors about + redefinition of `va_arg' when you build GNU CC. + + If this happens, then you need to link most programs with the + library `iclib.a'. You must also modify `stdio.h' as follows: + before the lines + + #if defined(__i860__) && !defined(_VA_LIST) + #include + + insert the line + + #if __PGC__ + + and after the lines + + extern int vprintf(const char *, va_list ); + extern int vsprintf(char *, const char *, va_list ); + #endif + + insert the line + + #endif /* __PGC__ */ + + These problems don't exist in operating system version 1.1. + + * On the Altos 3068, programs compiled with GNU CC won't work unless + you fix a kernel bug. This happens using system versions V.2.2 + 1.0gT1 and V.2.2 1.0e and perhaps later versions as well. See the + file `README.ALTOS'. + + * You will get several sorts of compilation and linking errors on the + we32k if you don't follow the special instructions. *Note + Configurations::. + + * A bug in the HP-UX 8.05 (and earlier) shell will cause the fixproto + program to report an error of the form: + + ./fixproto: sh internal 1K buffer overflow + + To fix this, change the first line of the fixproto script to look + like: + + #!/bin/ksh + + +File: gcc.info, Node: Cross-Compiler Problems, Next: Interoperation, Prev: Installation Problems, Up: Trouble + +Cross-Compiler Problems +======================= -Standard Names for Patterns Used in Generation -============================================== + You may run into problems with cross compilation on certain machines, +for several reasons. - Here is a table of the instruction names that are meaningful in the -RTL generation pass of the compiler. Giving one of these names to an -instruction pattern tells the RTL generation pass that it can use the -pattern in to accomplish a certain task. - -`movM' - Here M stands for a two-letter machine mode name, in lower case. - This instruction pattern moves data with that machine mode from - operand 1 to operand 0. For example, `movsi' moves full-word data. - - If operand 0 is a `subreg' with mode M of a register whose own - mode is wider than M, the effect of this instruction is to store - the specified value in the part of the register that corresponds - to mode M. The effect on the rest of the register is undefined. - - This class of patterns is special in several ways. First of all, - each of these names *must* be defined, because there is no other - way to copy a datum from one place to another. - - Second, these patterns are not used solely in the RTL generation - pass. Even the reload pass can generate move insns to copy values - from stack slots into temporary registers. When it does so, one - of the operands is a hard register and the other is an operand - that can need to be reloaded into a register. - - Therefore, when given such a pair of operands, the pattern must - generate RTL which needs no reloading and needs no temporary - registers--no registers other than the operands. For example, if - you support the pattern with a `define_expand', then in such a - case the `define_expand' mustn't call `force_reg' or any other such - function which might generate new pseudo registers. - - This requirement exists even for subword modes on a RISC machine - where fetching those modes from memory normally requires several - insns and some temporary registers. Look in `spur.md' to see how - the requirement can be satisfied. - - During reload a memory reference with an invalid address may be - passed as an operand. Such an address will be replaced with a - valid address later in the reload pass. In this case, nothing may - be done with the address except to use it as it stands. If it is - copied, it will not be replaced with a valid address. No attempt - should be made to make such an address into a valid address and no - routine (such as `change_address') that will do so may be called. - Note that `general_operand' will fail when applied to such an - address. - - The global variable `reload_in_progress' (which must be explicitly - declared if required) can be used to determine whether such special - handling is required. - - The variety of operands that have reloads depends on the rest of - the machine description, but typically on a RISC machine these can - only be pseudo registers that did not get hard registers, while on - other machines explicit memory references will get optional - reloads. - - If a scratch register is required to move an object to or from - memory, it can be allocated using `gen_reg_rtx' prior to reload. - But this is impossible during and after reload. If there are - cases needing scratch registers after reload, you must define - `SECONDARY_INPUT_RELOAD_CLASS' and/or - `SECONDARY_OUTPUT_RELOAD_CLASS' to detect them, and provide - patterns `reload_inM' or `reload_outM' to handle them. *Note - Register Classes::. - - The constraints on a `moveM' must permit moving any hard register - to any other hard register provided that `HARD_REGNO_MODE_OK' - permits mode M in both registers and `REGISTER_MOVE_COST' applied - to their classes returns a value of 2. - - It is obligatory to support floating point `moveM' instructions - into and out of any registers that can hold fixed point values, - because unions and structures (which have modes `SImode' or - `DImode') can be in those registers and they may have floating - point members. - - There may also be a need to support fixed point `moveM' - instructions in and out of floating point registers. - Unfortunately, I have forgotten why this was so, and I don't know - whether it is still true. If `HARD_REGNO_MODE_OK' rejects fixed - point values in floating point registers, then the constraints of - the fixed point `moveM' instructions must be designed to avoid - ever trying to reload into a floating point register. - -`reload_inM' -`reload_outM' - Like `movM', but used when a scratch register is required to move - between operand 0 and operand 1. Operand 2 describes the scratch - register. See the discussion of the `SECONDARY_RELOAD_CLASS' - macro in *note Register Classes::.. - -`movstrictM' - Like `movM' except that if operand 0 is a `subreg' with mode M of - a register whose natural mode is wider, the `movstrictM' - instruction is guaranteed not to alter any of the register except - the part which belongs to mode M. - -`load_multiple' - Load several consecutive memory locations into consecutive - registers. Operand 0 is the first of the consecutive registers, - operand 1 is the first memory location, and operand 2 is a - constant: the number of consecutive registers. - - Define this only if the target machine really has such an - instruction; do not define this if the most efficient way of - loading consecutive registers from memory is to do them one at a - time. - - On some machines, there are restrictions as to which consecutive - registers can be stored into memory, such as particular starting or - ending register numbers or only a range of valid counts. For those - machines, use a `define_expand' (*note Expander Definitions::.) - and make the pattern fail if the restrictions are not met. - - Write the generated insn as a `parallel' with elements being a - `set' of one register from the appropriate memory location (you may - also need `use' or `clobber' elements). Use a `match_parallel' - (*note RTL Template::.) to recognize the insn. See `a29k.md' and - `rs6000.md' for examples of the use of this insn pattern. - -`store_multiple' - Similar to `load_multiple', but store several consecutive registers - into consecutive memory locations. Operand 0 is the first of the - consecutive memory locations, operand 1 is the first register, and - operand 2 is a constant: the number of consecutive registers. - -`addM3' - Add operand 2 and operand 1, storing the result in operand 0. All - operands must have mode M. This can be used even on two-address - machines, by means of constraints requiring operands 1 and 0 to be - the same location. - -`subM3', `mulM3' -`divM3', `udivM3', `modM3', `umodM3' -`sminM3', `smaxM3', `uminM3', `umaxM3' -`andM3', `iorM3', `xorM3' - Similar, for other arithmetic operations. - -`mulhisi3' - Multiply operands 1 and 2, which have mode `HImode', and store a - `SImode' product in operand 0. - -`mulqihi3', `mulsidi3' - Similar widening-multiplication instructions of other widths. - -`umulqihi3', `umulhisi3', `umulsidi3' - Similar widening-multiplication instructions that do unsigned - multiplication. - -`divmodM4' - Signed division that produces both a quotient and a remainder. - Operand 1 is divided by operand 2 to produce a quotient stored in - operand 0 and a remainder stored in operand 3. - - For machines with an instruction that produces both a quotient and - a remainder, provide a pattern for `divmodM4' but do not provide - patterns for `divM3' and `modM3'. This allows optimization in the - relatively common case when both the quotient and remainder are - computed. - - If an instruction that just produces a quotient or just a remainder - exists and is more efficient than the instruction that produces - both, write the output routine of `divmodM4' to call - `find_reg_note' and look for a `REG_UNUSED' note on the quotient - or remainder and generate the appropriate instruction. - -`udivmodM4' - Similar, but does unsigned division. - -`ashlM3' - Arithmetic-shift operand 1 left by a number of bits specified by - operand 2, and store the result in operand 0. Here M is the mode - of operand 0 and operand 1; operand 2's mode is specified by the - instruction pattern, and the compiler will convert the operand to - that mode before generating the instruction. - -`ashrM3', `lshlM3', `lshrM3', `rotlM3', `rotrM3' - Other shift and rotate instructions, analogous to the `ashlM3' - instructions. - - Logical and arithmetic left shift are the same. Machines that do - not allow negative shift counts often have only one instruction for - shifting left. On such machines, you should define a pattern named - `ashlM3' and leave `lshlM3' undefined. - -`negM2' - Negate operand 1 and store the result in operand 0. - -`absM2' - Store the absolute value of operand 1 into operand 0. - -`sqrtM2' - Store the square root of operand 1 into operand 0. - - The `sqrt' built-in function of C always uses the mode which - corresponds to the C data type `double'. - -`ffsM2' - Store into operand 0 one plus the index of the least significant - 1-bit of operand 1. If operand 1 is zero, store zero. M is the - mode of operand 0; operand 1's mode is specified by the instruction - pattern, and the compiler will convert the operand to that mode - before generating the instruction. - - The `ffs' built-in function of C always uses the mode which - corresponds to the C data type `int'. - -`one_cmplM2' - Store the bitwise-complement of operand 1 into operand 0. - -`cmpM' - Compare operand 0 and operand 1, and set the condition codes. The - RTL pattern should look like this: - - (set (cc0) (compare (match_operand:M 0 ...) - (match_operand:M 1 ...))) - -`tstM' - Compare operand 0 against zero, and set the condition codes. The - RTL pattern should look like this: - - (set (cc0) (match_operand:M 0 ...)) - - `tstM' patterns should not be defined for machines that do not use - `(cc0)'. Doing so would confuse the optimizer since it would no - longer be clear which `set' operations were comparisons. The - `cmpM' patterns should be used instead. - -`movstrM' - Block move instruction. The addresses of the destination and - source strings are the first two operands, and both are in mode - `Pmode'. The number of bytes to move is the third operand, in mode - M. - - The fourth operand is the known shared alignment of the source and - destination, in the form of a `const_int' rtx. Thus, if the - compiler knows that both source and destination are word-aligned, - it may provide the value 4 for this operand. - - These patterns need not give special consideration to the - possibility that the source and destination strings might overlap. - -`cmpstrM' - Block compare instruction, with five operands. Operand 0 is the - output; it has mode M. The remaining four operands are like the - operands of `movstrM'. The two memory blocks specified are - compared byte by byte in lexicographic order. The effect of the - instruction is to store a value in operand 0 whose sign indicates - the result of the comparison. - -`floatMN2' - Convert signed integer operand 1 (valid for fixed point mode M) to - floating point mode N and store in operand 0 (which has mode N). - -`floatunsMN2' - Convert unsigned integer operand 1 (valid for fixed point mode M) - to floating point mode N and store in operand 0 (which has mode N). - -`fixMN2' - Convert operand 1 (valid for floating point mode M) to fixed point - mode N as a signed number and store in operand 0 (which has mode - N). This instruction's result is defined only when the value of - operand 1 is an integer. - -`fixunsMN2' - Convert operand 1 (valid for floating point mode M) to fixed point - mode N as an unsigned number and store in operand 0 (which has - mode N). This instruction's result is defined only when the value - of operand 1 is an integer. - -`ftruncM2' - Convert operand 1 (valid for floating point mode M) to an integer - value, still represented in floating point mode M, and store it in - operand 0 (valid for floating point mode M). - -`fix_truncMN2' - Like `fixMN2' but works for any floating point value of mode M by - converting the value to an integer. - -`fixuns_truncMN2' - Like `fixunsMN2' but works for any floating point value of mode M - by converting the value to an integer. - -`truncMN' - Truncate operand 1 (valid for mode M) to mode N and store in - operand 0 (which has mode N). Both modes must be fixed point or - both floating point. - -`extendMN' - Sign-extend operand 1 (valid for mode M) to mode N and store in - operand 0 (which has mode N). Both modes must be fixed point or - both floating point. - -`zero_extendMN' - Zero-extend operand 1 (valid for mode M) to mode N and store in - operand 0 (which has mode N). Both modes must be fixed point. - -`extv' - Extract a bit field from operand 1 (a register or memory operand), - where operand 2 specifies the width in bits and operand 3 the - starting bit, and store it in operand 0. Operand 0 must have mode - `word_mode'. Operand 1 may have mode `byte_mode' or `word_mode'; - often `word_mode' is allowed only for registers. Operands 2 and 3 - must be valid for `word_mode'. - - The RTL generation pass generates this instruction only with - constants for operands 2 and 3. - - The bit-field value is sign-extended to a full word integer before - it is stored in operand 0. - -`extzv' - Like `extv' except that the bit-field value is zero-extended. - -`insv' - Store operand 3 (which must be valid for `word_mode') into a bit - field in operand 0, where operand 1 specifies the width in bits and - operand 2 the starting bit. Operand 0 may have mode `byte_mode' or - `word_mode'; often `word_mode' is allowed only for registers. - Operands 1 and 2 must be valid for `word_mode'. - - The RTL generation pass generates this instruction only with - constants for operands 1 and 2. - -`sCOND' - Store zero or nonzero in the operand according to the condition - codes. Value stored is nonzero iff the condition COND is true. - COND is the name of a comparison operation expression code, such - as `eq', `lt' or `leu'. - - You specify the mode that the operand must have when you write the - `match_operand' expression. The compiler automatically sees which - mode you have used and supplies an operand of that mode. - - The value stored for a true condition must have 1 as its low bit, - or else must be negative. Otherwise the instruction is not - suitable and you should omit it from the machine description. You - describe to the compiler exactly which value is stored by defining - the macro `STORE_FLAG_VALUE' (*note Misc::.). If a description - cannot be found that can be used for all the `sCOND' patterns, you - should omit those operations from the machine description. - - These operations may fail, but should do so only in relatively - uncommon cases; if they would fail for common cases involving - integer comparisons, it is best to omit these patterns. - - If these operations are omitted, the compiler will usually - generate code that copies the constant one to the target and - branches around an assignment of zero to the target. If this code - is more efficient than the potential instructions used for the - `sCOND' pattern followed by those required to convert the result - into a 1 or a zero in `SImode', you should omit the `sCOND' - operations from the machine description. - -`bCOND' - Conditional branch instruction. Operand 0 is a `label_ref' that - refers to the label to jump to. Jump if the condition codes meet - condition COND. - - Some machines do not follow the model assumed here where a - comparison instruction is followed by a conditional branch - instruction. In that case, the `cmpM' (and `tstM') patterns should - simply store the operands away and generate all the required insns - in a `define_expand' (*note Expander Definitions::.) for the - conditional branch operations. All calls to expand `vCOND' - patterns are immediately preceded by calls to expand either a - `cmpM' pattern or a `tstM' pattern. - - Machines that use a pseudo register for the condition code value, - or where the mode used for the comparison depends on the condition - being tested, should also use the above mechanism. *Note Jump - Patterns:: - - The above discussion also applies to `sCOND' patterns. - -`call' - Subroutine call instruction returning no value. Operand 0 is the - function to call; operand 1 is the number of bytes of arguments - pushed (in mode `SImode', except it is normally a `const_int'); - operand 2 is the number of registers used as operands. - - On most machines, operand 2 is not actually stored into the RTL - pattern. It is supplied for the sake of some RISC machines which - need to put this information into the assembler code; they can put - it in the RTL instead of operand 1. - - Operand 0 should be a `mem' RTX whose address is the address of the - function. Note, however, that this address can be a `symbol_ref' - expression even if it would not be a legitimate memory address on - the target machine. If it is also not a valid argument for a call - instruction, the pattern for this operation should be a - `define_expand' (*note Expander Definitions::.) that places the - address into a register and uses that register in the call - instruction. - -`call_value' - Subroutine call instruction returning a value. Operand 0 is the - hard register in which the value is returned. There are three more - operands, the same as the three operands of the `call' instruction - (but with numbers increased by one). - - Subroutines that return `BLKmode' objects use the `call' insn. - -`call_pop', `call_value_pop' - Similar to `call' and `call_value', except used if defined and if - `RETURN_POPS_ARGS' is non-zero. They should emit a `parallel' - that contains both the function call and a `set' to indicate the - adjustment made to the frame pointer. - - For machines where `RETURN_POPS_ARGS' can be non-zero, the use of - these patterns increases the number of functions for which the - frame pointer can be eliminated, if desired. - -`return' - Subroutine return instruction. This instruction pattern name - should be defined only if a single instruction can do all the work - of returning from a function. - - Like the `movM' patterns, this pattern is also used after the RTL - generation phase. In this case it is to support machines where - multiple instructions are usually needed to return from a - function, but some class of functions only requires one - instruction to implement a return. Normally, the applicable - functions are those which do not need to save any registers or - allocate stack space. - - For such machines, the condition specified in this pattern should - only be true when `reload_completed' is non-zero and the function's - epilogue would only be a single instruction. For machines with - register windows, the routine `leaf_function_p' may be used to - determine if a register window push is required. - - Machines that have conditional return instructions should define - patterns such as - - (define_insn "" - [(set (pc) - (if_then_else (match_operator 0 "comparison_operator" - [(cc0) (const_int 0)]) - (return) - (pc)))] - "CONDITION" - "...") - - where CONDITION would normally be the same condition specified on - the named `return' pattern. - -`nop' - No-op instruction. This instruction pattern name should always be - defined to output a no-op in assembler code. `(const_int 0)' will - do as an RTL pattern. - -`indirect_jump' - An instruction to jump to an address which is operand zero. This - pattern name is mandatory on all machines. - -`casesi' - Instruction to jump through a dispatch table, including bounds - checking. This instruction takes five operands: - - 1. The index to dispatch on, which has mode `SImode'. - - 2. The lower bound for indices in the table, an integer constant. - - 3. The total range of indices in the table--the largest index - minus the smallest one (both inclusive). - - 4. A label that precedes the table itself. - - 5. A label to jump to if the index has a value outside the - bounds. (If the machine-description macro - `CASE_DROPS_THROUGH' is defined, then an out-of-bounds index - drops through to the code following the jump table instead of - jumping to this label. In that case, this label is not - actually used by the `casesi' instruction, but it is always - provided as an operand.) - - The table is a `addr_vec' or `addr_diff_vec' inside of a - `jump_insn'. The number of elements in the table is one plus the - difference between the upper bound and the lower bound. - -`tablejump' - Instruction to jump to a variable address. This is a low-level - capability which can be used to implement a dispatch table when - there is no `casesi' pattern. - - This pattern requires two operands: the address or offset, and a - label which should immediately precede the jump table. If the - macro `CASE_VECTOR_PC_RELATIVE' is defined then the first operand - is an offset which counts from the address of the table; - otherwise, it is an absolute address to jump to. In either case, - the first operand has mode `Pmode'. - - The `tablejump' insn is always the last insn before the jump table - it uses. Its assembler code normally has no need to use the - second operand, but you should incorporate it in the RTL pattern so - that the jump optimizer will not delete the table as unreachable - code. - -`save_stack_block' -`save_stack_function' -`save_stack_nonlocal' -`restore_stack_block' -`restore_stack_function' -`restore_stack_nonlocal' - Most machines save and restore the stack pointer by copying it to - or from an object of mode `Pmode'. Do not define these patterns on - such machines. - - Some machines require special handling for stack pointer saves and - restores. On those machines, define the patterns corresponding to - the non-standard cases by using a `define_expand' (*note Expander - Definitions::.) that produces the required insns. The three types - of saves and restores are: - - 1. `save_stack_block' saves the stack pointer at the start of a - block that allocates a variable-sized object and - `restore_stack_block' restores the stack pointer when the - block is exited. - - 2. `save_stack_function' and `restore_stack_function' operate - similarly for the outermost block of a function and are used - when the function allocates variable-sized objects or calls - `alloca'. Only the epilogue uses the restored stack pointer, - allowing a simpler save or restore sequence on some machines. - - 3. `save_stack_nonlocal' is used in functions that contain labels - branched to by nested functions. It saves the stack pointer - in such a way that the inner function can use - `restore_stack_nonlocal' to restore the stack pointer. The - compiler generates code to restore the frame and argument - pointer registers, but some machines require saving and - restoring additional data such as register window information - or stack backchains. Place insns in these patterns to save - and restore any such required data. - - When saving the stack pointer, operand 0 is the save area and - operand 1 is the stack pointer. The mode used to allocate the - save area is the mode of operand 0. You must specify an integral - mode, or `VOIDmode' if no save area is needed for a particular - type of save (either because no save is needed or because a - machine-specific save area can be used). Operand 0 is the stack - pointer and operand 1 is the save area for restore operations. If - `save_stack_block' is defined, operand 0 must not be `VOIDmode' - since these saves can be arbitrarily nested. - - A save area is a `mem' that is at a constant offset from - `virtual_stack_vars_rtx' when the stack pointer is saved for use by - nonlocal gotos and a `reg' in the other two cases. - -`allocate_stack' - Subtract operand 0 from the stack pointer to create space for for - dynamically allocated data. - - Do not define this pattern if all that must be done is the - subtraction. On some machines require other operations such as - stack probes or maintaining the back chain. Define this pattern - to emit those operations in addition to updating the stack pointer. + * Cross compilation can run into trouble for certain machines because + some target machines' assemblers require floating point numbers to + be written as *integer* constants in certain contexts. + + The compiler writes these integer constants by examining the + floating point value as an integer and printing that integer, + because this is simple to write and independent of the details of + the floating point representation. But this does not work if the + compiler is running on a different machine with an incompatible + floating point format, or even a different byte-ordering. + + In addition, correct constant folding of floating point values + requires representing them in the target machine's format. (The C + standard does not quite require this, but in practice it is the + only way to win.) + + It is now possible to overcome these problems by defining macros + such as `REAL_VALUE_TYPE'. But doing so is a substantial amount of + work for each target machine. *Note Cross-compilation::. + + * At present, the program `mips-tfile' which adds debug support to + object files on MIPS systems does not work in a cross compile + environment.  -File: gcc.info, Node: Pattern Ordering, Next: Dependent Patterns, Prev: Standard Names, Up: Machine Desc +File: gcc.info, Node: Interoperation, Next: External Bugs, Prev: Cross-Compiler Problems, Up: Trouble -When the Order of Patterns Matters -================================== +Interoperation +============== - Sometimes an insn can match more than one instruction pattern. Then -the pattern that appears first in the machine description is the one -used. Therefore, more specific patterns (patterns that will match fewer -things) and faster instructions (those that will produce better code -when they do match) should usually go first in the description. - - In some cases the effect of ordering the patterns can be used to hide -a pattern when it is not valid. For example, the 68000 has an -instruction for converting a fullword to floating point and another for -converting a byte to floating point. An instruction converting an -integer to floating point could match either one. We put the pattern -to convert the fullword first to make sure that one will be used rather -than the other. (Otherwise a large integer might be generated as a -single-byte immediate quantity, which would not work.) Instead of using -this pattern ordering it would be possible to make the pattern for -convert-a-byte smart enough to deal properly with any constant value. + This section lists various difficulties encountered in using GNU C or +GNU C++ together with other compilers or with the assemblers, linkers, +libraries and debuggers on certain systems. + + * Objective C does not work on the RS/6000. + + * GNU C++ does not do name mangling in the same way as other C++ + compilers. This means that object files compiled with one compiler + cannot be used with another. + + This effect is intentional, to protect you from more subtle + problems. Compilers differ as to many internal details of C++ + implementation, including: how class instances are laid out, how + multiple inheritance is implemented, and how virtual function + calls are handled. If the name encoding were made the same, your + programs would link against libraries provided from other + compilers--but the programs would then crash when run. + Incompatible libraries are then detected at link time, rather than + at run time. + + * Older GDB versions sometimes fail to read the output of GNU CC + version 2. If you have trouble, get GDB version 4.4 or later. + + * DBX rejects some files produced by GNU CC, though it accepts + similar constructs in output from PCC. Until someone can supply a + coherent description of what is valid DBX input and what is not, + there is nothing I can do about these problems. You are on your + own. + + * The GNU assembler (GAS) does not support PIC. To generate PIC + code, you must use some other assembler, such as `/bin/as'. + + * On some BSD systems, including some versions of Ultrix, use of + profiling causes static variable destructors (currently used only + in C++) not to be run. + + * Use of `-I/usr/include' may cause trouble. + + Many systems come with header files that won't work with GNU CC + unless corrected by `fixincludes'. The corrected header files go + in a new directory; GNU CC searches this directory before + `/usr/include'. If you use `-I/usr/include', this tells GNU CC to + search `/usr/include' earlier on, before the corrected headers. + The result is that you get the uncorrected header files. + + Instead, you should use these options (when compiling C programs): + + -I/usr/local/lib/gcc-lib/TARGET/VERSION/include -I/usr/include + + For C++ programs, GNU CC also uses a special directory that + defines C++ interfaces to standard C subroutines. This directory + is meant to be searched *before* other standard include + directories, so that it takes precedence. If you are compiling + C++ programs and specifying include directories explicitly, use + this option first, then the two options above: + + -I/usr/local/lib/g++-include + + * On some SGI systems, when you use `-lgl_s' as an option, it gets + translated magically to `-lgl_s -lX11_s -lc_s'. Naturally, this + does not happen when you use GNU CC. You must specify all three + options explicitly. + + * On a Sparc, GNU CC aligns all values of type `double' on an 8-byte + boundary, and it expects every `double' to be so aligned. The Sun + compiler usually gives `double' values 8-byte alignment, with one + exception: function arguments of type `double' may not be aligned. + + As a result, if a function compiled with Sun CC takes the address + of an argument of type `double' and passes this pointer of type + `double *' to a function compiled with GNU CC, dereferencing the + pointer may cause a fatal signal. + + One way to solve this problem is to compile your entire program + with GNU CC. Another solution is to modify the function that is + compiled with Sun CC to copy the argument into a local variable; + local variables are always properly aligned. A third solution is + to modify the function that uses the pointer to dereference it via + the following function `access_double' instead of directly with + `*': + + inline double + access_double (double *unaligned_ptr) + { + union d2i { double d; int i[2]; }; + + union d2i *p = (union d2i *) unaligned_ptr; + union d2i u; + + u.i[0] = p->i[0]; + u.i[1] = p->i[1]; + + return u.d; + } + + Storing into the pointer can be done likewise with the same union. + + * On Solaris, the `malloc' function in the `libmalloc.a' library may + allocate memory that is only 4 byte aligned. Since GNU CC on the + Sparc assumes that doubles are 8 byte aligned, this may result in a + fatal signal if doubles are stored in memory allocated by the + `libmalloc.a' library. + + The solution is to not use the `libmalloc.a' library. Use instead + `malloc' and related functions from `libc.a'; they do not have + this problem. + + * Sun forgot to include a static version of `libdl.a' with some + versions of SunOS (mainly 4.1). This results in undefined symbols + when linking static binaries (that is, if you use `-static'). If + you see undefined symbols `_dlclose', `_dlsym' or `_dlopen' when + linking, compile and link against the file `mit/util/misc/dlsym.c' + from the MIT version of X windows. + + * The 128-bit long double format that the Sparc port supports + currently works by using the architecturally defined quad-word + floating point instructions. Since there is no hardware that + supports these instructions they must be emulated by the operating + system. Long doubles do not work in Sun OS versions 4.0.3 and + earlier, because the kernel emulator uses an obsolete and + incompatible format. Long doubles do not work in Sun OS version + 4.1.1 due to a problem in a Sun library. Long doubles do work on + Sun OS versions 4.1.2 and higher, but GNU CC does not enable them + by default. Long doubles appear to work in Sun OS 5.x (Solaris + 2.x). + + * On HP-UX version 9.01 on the HP PA, the HP compiler `cc' does not + compile GNU CC correctly. We do not yet know why. However, GNU CC + compiled on earlier HP-UX versions works properly on HP-UX 9.01 + and can compile itself properly on 9.01. + + * On the HP PA machine, ADB sometimes fails to work on functions + compiled with GNU CC. Specifically, it fails to work on functions + that use `alloca' or variable-size arrays. This is because GNU CC + doesn't generate HP-UX unwind descriptors for such functions. It + may even be impossible to generate them. + + * Debugging (`-g') is not supported on the HP PA machine, unless you + use the preliminary GNU tools (*note Installation::.). + + * Taking the address of a label may generate errors from the HP-UX + PA assembler. GAS for the PA does not have this problem. + + * Using floating point parameters for indirect calls to static + functions will not work when using the HP assembler. There simply + is no way for GCC to specify what registers hold arguments for + static functions when using the HP assembler. GAS for the PA does + not have this problem. + + * In extremely rare cases involving some very large functions you may + receive errors from the HP linker complaining about an out of + bounds unconditional branch offset. This used to occur more often + in previous versions of GNU CC, but is now exceptionally rare. If + you should run into it, you can work around by making your + function smaller. + + * GNU CC compiled code sometimes emits warnings from the HP-UX + assembler of the form: + + (warning) Use of GR3 when + frame >= 8192 may cause conflict. + + These warnings are harmless and can be safely ignored. + + * The current version of the assembler (`/bin/as') for the RS/6000 + has certain problems that prevent the `-g' option in GCC from + working. Note that `Makefile.in' uses `-g' by default when + compiling `libgcc2.c'. + + IBM has produced a fixed version of the assembler. The upgraded + assembler unfortunately was not included in any of the AIX 3.2 + update PTF releases (3.2.2, 3.2.3, or 3.2.3e). Users of AIX 3.1 + should request PTF U403044 from IBM and users of AIX 3.2 should + request PTF U416277. See the file `README.RS6000' for more + details on these updates. + + You can test for the presense of a fixed assembler by using the + command + + as -u < /dev/null + + If the command exits normally, the assembler fix already is + installed. If the assembler complains that "-u" is an unknown + flag, you need to order the fix. + + * On the IBM RS/6000, compiling code of the form + + extern int foo; + + ... foo ... + + static int foo; + + will cause the linker to report an undefined symbol `foo'. + Although this behavior differs from most other systems, it is not a + bug because redefining an `extern' variable as `static' is + undefined in ANSI C. + + * AIX on the RS/6000 provides support (NLS) for environments outside + of the United States. Compilers and assemblers use NLS to support + locale-specific representations of various objects including + floating-point numbers ("." vs "," for separating decimal + fractions). There have been problems reported where the library + linked with GCC does not produce the same floating-point formats + that the assembler accepts. If you have this problem, set the + LANG environment variable to "C" or "En_US". + + * Even if you specify `-fdollars-in-identifiers', you cannot + successfully use `$' in identifiers on the RS/6000 due to a + restriction in the IBM assembler. GAS supports these identifiers. + + * On the RS/6000, XLC version 1.3.0.0 will miscompile `jump.c'. XLC + version 1.3.0.1 or later fixes this problem. You can obtain + XLC-1.3.0.2 by requesting PTF 421749 from IBM. + + * There is an assembler bug in versions of DG/UX prior to 5.4.2.01 + that occurs when the `fldcr' instruction is used. GNU CC uses + `fldcr' on the 88100 to serialize volatile memory references. Use + the option `-mno-serialize-volatile' if your version of the + assembler has this bug. + + * On VMS, GAS versions 1.38.1 and earlier may cause spurious warning + messages from the linker. These warning messages complain of + mismatched psect attributes. You can ignore them. *Note VMS + Install::. + + * On NewsOS version 3, if you include both of the files `stddef.h' + and `sys/types.h', you get an error because there are two typedefs + of `size_t'. You should change `sys/types.h' by adding these + lines around the definition of `size_t': + + #ifndef _SIZE_T + #define _SIZE_T + ACTUAL TYPEDEF HERE + #endif + + * On the Alliant, the system's own convention for returning + structures and unions is unusual, and is not compatible with GNU + CC no matter what options are used. + + * On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different + convention for structure and union returning. Use the option + `-mhc-struct-return' to tell GNU CC to use a convention compatible + with it. + + * On Ultrix, the Fortran compiler expects registers 2 through 5 to + be saved by function calls. However, the C compiler uses + conventions compatible with BSD Unix: registers 2 through 5 may be + clobbered by function calls. + + GNU CC uses the same convention as the Ultrix C compiler. You can + use these options to produce code compatible with the Fortran + compiler: + + -fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5 + + * On the WE32k, you may find that programs compiled with GNU CC do + not work with the standard shared C library. You may need to link + with the ordinary C compiler. If you do so, you must specify the + following options: + + -L/usr/local/lib/gcc-lib/we32k-att-sysv/2.7.1 -lgcc -lc_s + + The first specifies where to find the library `libgcc.a' specified + with the `-lgcc' option. + + GNU CC does linking by invoking `ld', just as `cc' does, and there + is no reason why it *should* matter which compilation program you + use to invoke `ld'. If someone tracks this problem down, it can + probably be fixed easily. + + * On the Alpha, you may get assembler errors about invalid syntax as + a result of floating point constants. This is due to a bug in the + C library functions `ecvt', `fcvt' and `gcvt'. Given valid + floating point numbers, they sometimes print `NaN'. + + * On Irix 4.0.5F (and perhaps in some other versions), an assembler + bug sometimes reorders instructions incorrectly when optimization + is turned on. If you think this may be happening to you, try + using the GNU assembler; GAS version 2.1 supports ECOFF on Irix. + + Or use the `-noasmopt' option when you compile GNU CC with itself, + and then again when you compile your program. (This is a temporary + kludge to turn off assembler optimization on Irix.) If this + proves to be what you need, edit the assembler spec in the file + `specs' so that it unconditionally passes `-O0' to the assembler, + and never passes `-O2' or `-O3'.  -File: gcc.info, Node: Dependent Patterns, Next: Jump Patterns, Prev: Pattern Ordering, Up: Machine Desc +File: gcc.info, Node: External Bugs, Next: Incompatibilities, Prev: Interoperation, Up: Trouble + +Problems Compiling Certain Programs +=================================== + + Certain programs have problems compiling. + + * Parse errors may occur compiling X11 on a Decstation running + Ultrix 4.2 because of problems in DEC's versions of the X11 header + files `X11/Xlib.h' and `X11/Xutil.h'. People recommend adding + `-I/usr/include/mit' to use the MIT versions of the header files, + using the `-traditional' switch to turn off ANSI C, or fixing the + header files by adding this: + + #ifdef __STDC__ + #define NeedFunctionPrototypes 0 + #endif + + * If you have trouble compiling Perl on a SunOS 4 system, it may be + because Perl specifies `-I/usr/ucbinclude'. This accesses the + unfixed header files. Perl specifies the options + + -traditional -Dvolatile=__volatile__ + -I/usr/include/sun -I/usr/ucbinclude + -fpcc-struct-return + + most of which are unnecessary with GCC 2.4.5 and newer versions. + You can make a properly working Perl by setting `ccflags' to + `-fwritable-strings' (implied by the `-traditional' in the + original options) and `cppflags' to empty in `config.sh', then + typing `./doSH; make depend; make'. + + * On various 386 Unix systems derived from System V, including SCO, + ISC, and ESIX, you may get error messages about running out of + virtual memory while compiling certain programs. + + You can prevent this problem by linking GNU CC with the GNU malloc + (which thus replaces the malloc that comes with the system). GNU + malloc is available as a separate package, and also in the file + `src/gmalloc.c' in the GNU Emacs 19 distribution. + + If you have installed GNU malloc as a separate library package, + use this option when you relink GNU CC: + + MALLOC=/usr/local/lib/libgmalloc.a + + Alternatively, if you have compiled `gmalloc.c' from Emacs 19, copy + the object file to `gmalloc.o' and use this option when you relink + GNU CC: -Interdependence of Patterns + MALLOC=gmalloc.o + + +File: gcc.info, Node: Incompatibilities, Next: Fixed Headers, Prev: External Bugs, Up: Trouble + +Incompatibilities of GNU CC =========================== - Every machine description must have a named pattern for each of the -conditional branch names `bCOND'. The recognition template must always -have the form - - (set (pc) - (if_then_else (COND (cc0) (const_int 0)) - (label_ref (match_operand 0 "" "")) - (pc))) - -In addition, every machine description must have an anonymous pattern -for each of the possible reverse-conditional branches. Their templates -look like - - (set (pc) - (if_then_else (COND (cc0) (const_int 0)) - (pc) - (label_ref (match_operand 0 "" "")))) - -They are necessary because jump optimization can turn direct-conditional -branches into reverse-conditional branches. - - It is often convenient to use the `match_operator' construct to -reduce the number of patterns that must be specified for branches. For -example, - - (define_insn "" - [(set (pc) - (if_then_else (match_operator 0 "comparison_operator" - [(cc0) (const_int 0)]) - (pc) - (label_ref (match_operand 1 "" ""))))] - "CONDITION" - "...") - - In some cases machines support instructions identical except for the -machine mode of one or more operands. For example, there may be -"sign-extend halfword" and "sign-extend byte" instructions whose -patterns are - - (set (match_operand:SI 0 ...) - (extend:SI (match_operand:HI 1 ...))) - - (set (match_operand:SI 0 ...) - (extend:SI (match_operand:QI 1 ...))) - -Constant integers do not specify a machine mode, so an instruction to -extend a constant value could match either pattern. The pattern it -actually will match is the one that appears first in the file. For -correct results, this must be the one for the widest possible mode -(`HImode', here). If the pattern matches the `QImode' instruction, the -results will be incorrect if the constant value does not actually fit -that mode. - - Such instructions to extend constants are rarely generated because -they are optimized away, but they do occasionally happen in nonoptimized -compilations. - - If a constraint in a pattern allows a constant, the reload pass may -replace a register with a constant permitted by the constraint in some -cases. Similarly for memory references. You must ensure that the -predicate permits all objects allowed by the constraints to prevent the -compiler from crashing. - - Because of this substitution, you should not provide separate -patterns for increment and decrement instructions. Instead, they -should be generated from the same pattern that supports -register-register add insns by examining the operands and generating -the appropriate machine instruction. + There are several noteworthy incompatibilities between GNU C and most +existing (non-ANSI) versions of C. The `-traditional' option +eliminates many of these incompatibilities, *but not all*, by telling +GNU C to behave like the other C compilers. + + * GNU CC normally makes string constants read-only. If several + identical-looking string constants are used, GNU CC stores only one + copy of the string. + + One consequence is that you cannot call `mktemp' with a string + constant argument. The function `mktemp' always alters the string + its argument points to. + + Another consequence is that `sscanf' does not work on some systems + when passed a string constant as its format control string or + input. This is because `sscanf' incorrectly tries to write into + the string constant. Likewise `fscanf' and `scanf'. + + The best solution to these problems is to change the program to use + `char'-array variables with initialization strings for these + purposes instead of string constants. But if this is not possible, + you can use the `-fwritable-strings' flag, which directs GNU CC to + handle string constants the same way most C compilers do. + `-traditional' also has this effect, among others. + + * `-2147483648' is positive. + + This is because 2147483648 cannot fit in the type `int', so + (following the ANSI C rules) its data type is `unsigned long int'. + Negating this value yields 2147483648 again. + + * GNU CC does not substitute macro arguments when they appear inside + of string constants. For example, the following macro in GNU CC + + #define foo(a) "a" + + will produce output `"a"' regardless of what the argument A is. + + The `-traditional' option directs GNU CC to handle such cases + (among others) in the old-fashioned (non-ANSI) fashion. + + * When you use `setjmp' and `longjmp', the only automatic variables + guaranteed to remain valid are those declared `volatile'. This is + a consequence of automatic register allocation. Consider this + function: + + jmp_buf j; + + foo () + { + int a, b; + + a = fun1 (); + if (setjmp (j)) + return a; + + a = fun2 (); + /* `longjmp (j)' may occur in `fun3'. */ + return a + fun3 (); + } + + Here `a' may or may not be restored to its first value when the + `longjmp' occurs. If `a' is allocated in a register, then its + first value is restored; otherwise, it keeps the last value stored + in it. + + If you use the `-W' option with the `-O' option, you will get a + warning when GNU CC thinks such a problem might be possible. + + The `-traditional' option directs GNU C to put variables in the + stack by default, rather than in registers, in functions that call + `setjmp'. This results in the behavior found in traditional C + compilers. + + * Programs that use preprocessing directives in the middle of macro + arguments do not work with GNU CC. For example, a program like + this will not work: + + foobar ( + #define luser + hack) + + ANSI C does not permit such a construct. It would make sense to + support it when `-traditional' is used, but it is too much work to + implement. + + * Declarations of external variables and functions within a block + apply only to the block containing the declaration. In other + words, they have the same scope as any other declaration in the + same place. + + In some other C compilers, a `extern' declaration affects all the + rest of the file even if it happens within a block. + + The `-traditional' option directs GNU C to treat all `extern' + declarations as global, like traditional compilers. + + * In traditional C, you can combine `long', etc., with a typedef + name, as shown here: + + typedef int foo; + typedef long foo bar; + + In ANSI C, this is not allowed: `long' and other type modifiers + require an explicit `int'. Because this criterion is expressed by + Bison grammar rules rather than C code, the `-traditional' flag + cannot alter it. + + * PCC allows typedef names to be used as function parameters. The + difficulty described immediately above applies here too. + + * PCC allows whitespace in the middle of compound assignment + operators such as `+='. GNU CC, following the ANSI standard, does + not allow this. The difficulty described immediately above + applies here too. + + * GNU CC complains about unterminated character constants inside of + preprocessing conditionals that fail. Some programs have English + comments enclosed in conditionals that are guaranteed to fail; if + these comments contain apostrophes, GNU CC will probably report an + error. For example, this code would produce an error: + + #if 0 + You can't expect this to work. + #endif + + The best solution to such a problem is to put the text into an + actual C comment delimited by `/*...*/'. However, `-traditional' + suppresses these error messages. + + * Many user programs contain the declaration `long time ();'. In the + past, the system header files on many systems did not actually + declare `time', so it did not matter what type your program + declared it to return. But in systems with ANSI C headers, `time' + is declared to return `time_t', and if that is not the same as + `long', then `long time ();' is erroneous. + + The solution is to change your program to use `time_t' as the + return type of `time'. + + * When compiling functions that return `float', PCC converts it to a + double. GNU CC actually returns a `float'. If you are concerned + with PCC compatibility, you should declare your functions to return + `double'; you might as well say what you mean. + + * When compiling functions that return structures or unions, GNU CC + output code normally uses a method different from that used on most + versions of Unix. As a result, code compiled with GNU CC cannot + call a structure-returning function compiled with PCC, and vice + versa. + + The method used by GNU CC is as follows: a structure or union + which is 1, 2, 4 or 8 bytes long is returned like a scalar. A + structure or union with any other size is stored into an address + supplied by the caller (usually in a special, fixed register, but + on some machines it is passed on the stack). The + machine-description macros `STRUCT_VALUE' and + `STRUCT_INCOMING_VALUE' tell GNU CC where to pass this address. + + By contrast, PCC on most target machines returns structures and + unions of any size by copying the data into an area of static + storage, and then returning the address of that storage as if it + were a pointer value. The caller must copy the data from that + memory area to the place where the value is wanted. GNU CC does + not use this method because it is slower and nonreentrant. + + On some newer machines, PCC uses a reentrant convention for all + structure and union returning. GNU CC on most of these machines + uses a compatible convention when returning structures and unions + in memory, but still returns small structures and unions in + registers. + + You can tell GNU CC to use a compatible convention for all + structure and union returning with the option + `-fpcc-struct-return'. + + * GNU C complains about program fragments such as `0x74ae-0x4000' + which appear to be two hexadecimal constants separated by the minus + operator. Actually, this string is a single "preprocessing token". + Each such token must correspond to one token in C. Since this + does not, GNU C prints an error message. Although it may appear + obvious that what is meant is an operator and two values, the ANSI + C standard specifically requires that this be treated as erroneous. + + A "preprocessing token" is a "preprocessing number" if it begins + with a digit and is followed by letters, underscores, digits, + periods and `e+', `e-', `E+', or `E-' character sequences. + + To make the above program fragment valid, place whitespace in + front of the minus sign. This whitespace will end the + preprocessing number.  -File: gcc.info, Node: Jump Patterns, Next: Insn Canonicalizations, Prev: Dependent Patterns, Up: Machine Desc +File: gcc.info, Node: Fixed Headers, Next: Standard Libraries, Prev: Incompatibilities, Up: Trouble -Defining Jump Instruction Patterns -================================== +Fixed Header Files +================== - For most machines, GNU CC assumes that the machine has a condition -code. A comparison insn sets the condition code, recording the results -of both signed and unsigned comparison of the given operands. A -separate branch insn tests the condition code and branches or not -according its value. The branch insns come in distinct signed and -unsigned flavors. Many common machines, such as the Vax, the 68000 and -the 32000, work this way. - - Some machines have distinct signed and unsigned compare -instructions, and only one set of conditional branch instructions. The -easiest way to handle these machines is to treat them just like the -others until the final stage where assembly code is written. At this -time, when outputting code for the compare instruction, peek ahead at -the following branch using `next_cc0_user (insn)'. (The variable -`insn' refers to the insn being output, in the output-writing code in -an instruction pattern.) If the RTL says that is an unsigned branch, -output an unsigned compare; otherwise output a signed compare. When -the branch itself is output, you can treat signed and unsigned branches -identically. - - The reason you can do this is that GNU CC always generates a pair of -consecutive RTL insns, possibly separated by `note' insns, one to set -the condition code and one to test it, and keeps the pair inviolate -until the end. - - To go with this technique, you must define the machine-description -macro `NOTICE_UPDATE_CC' to do `CC_STATUS_INIT'; in other words, no -compare instruction is superfluous. - - Some machines have compare-and-branch instructions and no condition -code. A similar technique works for them. When it is time to "output" a -compare instruction, record its operands in two static variables. When -outputting the branch-on-condition-code instruction that follows, -actually output a compare-and-branch instruction that uses the -remembered operands. - - It also works to define patterns for compare-and-branch instructions. -In optimizing compilation, the pair of compare and branch instructions -will be combined according to these patterns. But this does not happen -if optimization is not requested. So you must use one of the solutions -above in addition to any special patterns you define. - - In many RISC machines, most instructions do not affect the condition -code and there may not even be a separate condition code register. On -these machines, the restriction that the definition and use of the -condition code be adjacent insns is not necessary and can prevent -important optimizations. For example, on the IBM RS/6000, there is a -delay for taken branches unless the condition code register is set three -instructions earlier than the conditional branch. The instruction -scheduler cannot perform this optimization if it is not permitted to -separate the definition and use of the condition code register. - - On these machines, do not use `(cc0)', but instead use a register to -represent the condition code. If there is a specific condition code -register in the machine, use a hard register. If the condition code or -comparison result can be placed in any general register, or if there are -multiple condition registers, use a pseudo register. - - On some machines, the type of branch instruction generated may -depend on the way the condition code was produced; for example, on the -68k and Sparc, setting the condition code directly from an add or -subtract instruction does not clear the overflow bit the way that a test -instruction does, so a different branch instruction must be used for -some conditional branches. For machines that use `(cc0)', the set and -use of the condition code must be adjacent (separated only by `note' -insns) allowing flags in `cc_status' to be used. (*Note Condition -Code::.) Also, the comparison and branch insns can be located from -each other by using the functions `prev_cc0_setter' and `next_cc0_user'. - - However, this is not true on machines that do not use `(cc0)'. On -those machines, no assumptions can be made about the adjacency of the -compare and branch insns and the above methods cannot be used. Instead, -we use the machine mode of the condition code register to record -different formats of the condition code register. - - Registers used to store the condition code value should have a mode -that is in class `MODE_CC'. Normally, it will be `CCmode'. If -additional modes are required (as for the add example mentioned above in -the Sparc), define the macro `EXTRA_CC_MODES' to list the additional -modes required (*note Condition Code::.). Also define `EXTRA_CC_NAMES' -to list the names of those modes and `SELECT_CC_MODE' to choose a mode -given an operand of a compare. - - If it is known during RTL generation that a different mode will be -required (for example, if the machine has separate compare instructions -for signed and unsigned quantities, like most IBM processors), they can -be specified at that time. - - If the cases that require different modes would be made by -instruction combination, the macro `SELECT_CC_MODE' determines which -machine mode should be used for the comparison result. The patterns -should be written using that mode. To support the case of the add on -the Sparc discussed above, we have the pattern - - (define_insn "" - [(set (reg:CC_NOOV 0) - (compare:CC_NOOV (plus:SI (match_operand:SI 0 "register_operand" "%r") - (match_operand:SI 1 "arith_operand" "rI")) - (const_int 0)))] - "" - "...") + GNU CC needs to install corrected versions of some system header +files. This is because most target systems have some header files that +won't work with GNU CC unless they are changed. Some have bugs, some +are incompatible with ANSI C, and some depend on special features of +other compilers. + + Installing GNU CC automatically creates and installs the fixed header +files, by running a program called `fixincludes' (or for certain +targets an alternative such as `fixinc.svr4'). Normally, you don't +need to pay attention to this. But there are cases where it doesn't do +the right thing automatically. + + * If you update the system's header files, such as by installing a + new system version, the fixed header files of GNU CC are not + automatically updated. The easiest way to update them is to + reinstall GNU CC. (If you want to be clever, look in the makefile + and you can find a shortcut.) + + * On some systems, in particular SunOS 4, header file directories + contain machine-specific symbolic links in certain places. This + makes it possible to share most of the header files among hosts + running the same version of SunOS 4 on different machine models. + + The programs that fix the header files do not understand this + special way of using symbolic links; therefore, the directory of + fixed header files is good only for the machine model used to + build it. + + In SunOS 4, only programs that look inside the kernel will notice + the difference between machine models. Therefore, for most + purposes, you need not be concerned about this. + + It is possible to make separate sets of fixed header files for the + different machine models, and arrange a structure of symbolic + links so as to use the proper set, but you'll have to do this by + hand. + + * On Lynxos, GNU CC by default does not fix the header files. This + is because bugs in the shell cause the `fixincludes' script to + fail. + + This means you will encounter problems due to bugs in the system + header files. It may be no comfort that they aren't GNU CC's + fault, but it does mean that there's nothing for us to do about + them. - The `SELECT_CC_MODE' macro on the Sparc returns `CC_NOOVmode' for -comparisons whose argument is a `plus'. + +File: gcc.info, Node: Standard Libraries, Next: Disappointments, Prev: Fixed Headers, Up: Trouble + +Standard Libraries +================== + + GNU CC by itself attempts to be what the ISO/ANSI C standard calls a +"conforming freestanding implementation". This means all ANSI C +language features are available, as well as the contents of `float.h', +`limits.h', `stdarg.h', and `stddef.h'. The rest of the C library is +supplied by the vendor of the operating system. If that C library +doesn't conform to the C standards, then your programs might get +warnings (especially when using `-Wall') that you don't expect. + + For example, the `sprintf' function on SunOS 4.1.3 returns `char *' +while the C standard says that `sprintf' returns an `int'. The +`fixincludes' program could make the prototype for this function match +the Standard, but that would be wrong, since the function will still +return `char *'. + + If you need a Standard compliant library, then you need to find one, +as GNU CC does not provide one. The GNU C library (called `glibc') has +been ported to a number of operating systems, and provides ANSI/ISO, +POSIX, BSD and SystemV compatibility. You could also ask your operating +system vendor if newer libraries are available.  -File: gcc.info, Node: Insn Canonicalizations, Next: Peephole Definitions, Prev: Jump Patterns, Up: Machine Desc +File: gcc.info, Node: Disappointments, Next: C++ Misunderstandings, Prev: Standard Libraries, Up: Trouble + +Disappointments and Misunderstandings +===================================== + + These problems are perhaps regrettable, but we don't know any +practical way around them. + + * Certain local variables aren't recognized by debuggers when you + compile with optimization. + + This occurs because sometimes GNU CC optimizes the variable out of + existence. There is no way to tell the debugger how to compute the + value such a variable "would have had", and it is not clear that + would be desirable anyway. So GNU CC simply does not mention the + eliminated variable when it writes debugging information. + + You have to expect a certain amount of disagreement between the + executable and your source code, when you use optimization. + + * Users often think it is a bug when GNU CC reports an error for code + like this: + + int foo (struct mumble *); + + struct mumble { ... }; + + int foo (struct mumble *x) + { ... } + + This code really is erroneous, because the scope of `struct + mumble' in the prototype is limited to the argument list + containing it. It does not refer to the `struct mumble' defined + with file scope immediately below--they are two unrelated types + with similar names in different scopes. + + But in the definition of `foo', the file-scope type is used + because that is available to be inherited. Thus, the definition + and the prototype do not match, and you get an error. + + This behavior may seem silly, but it's what the ANSI standard + specifies. It is easy enough for you to make your code work by + moving the definition of `struct mumble' above the prototype. + It's not worth being incompatible with ANSI C just to avoid an + error for the example shown above. + + * Accesses to bitfields even in volatile objects works by accessing + larger objects, such as a byte or a word. You cannot rely on what + size of object is accessed in order to read or write the bitfield; + it may even vary for a given bitfield according to the precise + usage. + + If you care about controlling the amount of memory that is + accessed, use volatile but do not use bitfields. + + * GNU CC comes with shell scripts to fix certain known problems in + system header files. They install corrected copies of various + header files in a special directory where only GNU CC will + normally look for them. The scripts adapt to various systems by + searching all the system header files for the problem cases that + we know about. + + If new system header files are installed, nothing automatically + arranges to update the corrected header files. You will have to + reinstall GNU CC to fix the new header files. More specifically, + go to the build directory and delete the files `stmp-fixinc' and + `stmp-headers', and the subdirectory `include'; then do `make + install' again. + + * On 68000 systems, you can get paradoxical results if you test the + precise values of floating point numbers. For example, you can + find that a floating point value which is not a NaN is not equal + to itself. This results from the fact that the the floating point + registers hold a few more bits of precision than fit in a `double' + in memory. Compiled code moves values between memory and floating + point registers at its convenience, and moving them into memory + truncates them. + + You can partially avoid this problem by using the `-ffloat-store' + option (*note Optimize Options::.). + + * On the MIPS, variable argument functions using `varargs.h' cannot + have a floating point value for the first argument. The reason + for this is that in the absence of a prototype in scope, if the + first argument is a floating point, it is passed in a floating + point register, rather than an integer register. + + If the code is rewritten to use the ANSI standard `stdarg.h' + method of variable arguments, and the prototype is in scope at the + time of the call, everything will work fine. + + +File: gcc.info, Node: C++ Misunderstandings, Next: Protoize Caveats, Prev: Disappointments, Up: Trouble + +Common Misunderstandings with GNU C++ +===================================== + + C++ is a complex language and an evolving one, and its standard +definition (the ANSI C++ draft standard) is also evolving. As a result, +your C++ compiler may occasionally surprise you, even when its behavior +is correct. This section discusses some areas that frequently give +rise to questions of this sort. -Canonicalization of Instructions -================================ +* Menu: - There are often cases where multiple RTL expressions could represent -an operation performed by a single machine instruction. This situation -is most commonly encountered with logical, branch, and -multiply-accumulate instructions. In such cases, the compiler attempts -to convert these multiple RTL expressions into a single canonical form -to reduce the number of insn patterns required. - - In addition to algebraic simplifications, following canonicalizations -are performed: - - * For commutative and comparison operators, a constant is always - made the second operand. If a machine only supports a constant as - the second operand, only patterns that match a constant in the - second operand need be supplied. - - For these operators, if only one operand is a `neg', `not', - `mult', `plus', or `minus' expression, it will be the first - operand. - - * For the `compare' operator, a constant is always the second operand - on machines where `cc0' is used (*note Jump Patterns::.). On other - machines, there are rare cases where the compiler might want to - construct a `compare' with a constant as the first operand. - However, these cases are not common enough for it to be worthwhile - to provide a pattern matching a constant as the first operand - unless the machine actually has such an instruction. - - An operand of `neg', `not', `mult', `plus', or `minus' is made the - first operand under the same conditions as above. - - * `(minus X (const_int N))' is converted to `(plus X (const_int - -N))'. - - * Within address computations (i.e., inside `mem'), a left shift is - converted into the appropriate multiplication by a power of two. - - De`Morgan's Law is used to move bitwise negation inside a bitwise - logical-and or logical-or operation. If this results in only one - operand being a `not' expression, it will be the first one. - - A machine that has an instruction that performs a bitwise - logical-and of one operand with the bitwise negation of the other - should specify the pattern for that instruction as - - (define_insn "" - [(set (match_operand:M 0 ...) - (and:M (not:M (match_operand:M 1 ...)) - (match_operand:M 2 ...)))] - "..." - "...") - - Similarly, a pattern for a "NAND" instruction should be written - - (define_insn "" - [(set (match_operand:M 0 ...) - (ior:M (not:M (match_operand:M 1 ...)) - (not:M (match_operand:M 2 ...))))] - "..." - "...") - - In both cases, it is not necessary to include patterns for the many - logically equivalent RTL expressions. - - * The only possible RTL expressions involving both bitwise - exclusive-or and bitwise negation are `(xor:M X) Y)' and `(not:M - (xor:M X Y))'. - - * The sum of three items, one of which is a constant, will only - appear in the form - - (plus:M (plus:M X Y) CONSTANT) - - * On machines that do not use `cc0', `(compare X (const_int 0))' - will be converted to X. - - * Equality comparisons of a group of bits (usually a single bit) - with zero will be written using `zero_extract' rather than the - equivalent `and' or `sign_extract' operations. +* Static Definitions:: Static member declarations are not definitions +* Temporaries:: Temporaries may vanish before you expect  -File: gcc.info, Node: Peephole Definitions, Next: Expander Definitions, Prev: Insn Canonicalizations, Up: Machine Desc +File: gcc.info, Node: Static Definitions, Next: Temporaries, Up: C++ Misunderstandings -Defining Machine-Specific Peephole Optimizers -============================================= +Declare *and* Define Static Members +----------------------------------- - In addition to instruction patterns the `md' file may contain -definitions of machine-specific peephole optimizations. + When a class has static data members, it is not enough to *declare* +the static member; you must also *define* it. For example: - The combiner does not notice certain peephole optimizations when the -data flow in the program does not suggest that it should try them. For -example, sometimes two consecutive insns related in purpose can be -combined even though the second one does not appear to use a register -computed in the first one. A machine-specific peephole optimizer can -detect such opportunities. - - A definition looks like this: - - (define_peephole - [INSN-PATTERN-1 - INSN-PATTERN-2 - ...] - "CONDITION" - "TEMPLATE" - "OPTIONAL INSN-ATTRIBUTES") - -The last string operand may be omitted if you are not using any -machine-specific information in this machine description. If present, -it must obey the same rules as in a `define_insn'. - - In this skeleton, INSN-PATTERN-1 and so on are patterns to match -consecutive insns. The optimization applies to a sequence of insns when -INSN-PATTERN-1 matches the first one, INSN-PATTERN-2 matches the next, -and so on. - - Each of the insns matched by a peephole must also match a -`define_insn'. Peepholes are checked only at the last stage just -before code generation, and only optionally. Therefore, any insn which -would match a peephole but no `define_insn' will cause a crash in code -generation in an unoptimized compilation, or at various optimization -stages. - - The operands of the insns are matched with `match_operands', -`match_operator', and `match_dup', as usual. What is not usual is that -the operand numbers apply to all the insn patterns in the definition. -So, you can check for identical operands in two insns by using -`match_operand' in one insn and `match_dup' in the other. - - The operand constraints used in `match_operand' patterns do not have -any direct effect on the applicability of the peephole, but they will -be validated afterward, so make sure your constraints are general enough -to apply whenever the peephole matches. If the peephole matches but -the constraints are not satisfied, the compiler will crash. - - It is safe to omit constraints in all the operands of the peephole; -or you can write constraints which serve as a double-check on the -criteria previously tested. - - Once a sequence of insns matches the patterns, the CONDITION is -checked. This is a C expression which makes the final decision whether -to perform the optimization (we do so if the expression is nonzero). If -CONDITION is omitted (in other words, the string is empty) then the -optimization is applied to every sequence of insns that matches the -patterns. - - The defined peephole optimizations are applied after register -allocation is complete. Therefore, the peephole definition can check -which operands have ended up in which kinds of registers, just by -looking at the operands. - - The way to refer to the operands in CONDITION is to write -`operands[I]' for operand number I (as matched by `(match_operand I -...)'). Use the variable `insn' to refer to the last of the insns -being matched; use `prev_nonnote_insn' to find the preceding insns. - - When optimizing computations with intermediate results, you can use -CONDITION to match only when the intermediate results are not used -elsewhere. Use the C expression `dead_or_set_p (INSN, OP)', where INSN -is the insn in which you expect the value to be used for the last time -(from the value of `insn', together with use of `prev_nonnote_insn'), -and OP is the intermediate value (from `operands[I]'). - - Applying the optimization means replacing the sequence of insns with -one new insn. The TEMPLATE controls ultimate output of assembler code -for this combined insn. It works exactly like the template of a -`define_insn'. Operand numbers in this template are the same ones used -in matching the original sequence of insns. - - The result of a defined peephole optimizer does not need to match -any of the insn patterns in the machine description; it does not even -have an opportunity to match them. The peephole optimizer definition -itself serves as the insn pattern to control how the insn is output. - - Defined peephole optimizers are run as assembler code is being -output, so the insns they produce are never combined or rearranged in -any way. - - Here is an example, taken from the 68000 machine description: - - (define_peephole - [(set (reg:SI 15) (plus:SI (reg:SI 15) (const_int 4))) - (set (match_operand:DF 0 "register_operand" "=f") - (match_operand:DF 1 "register_operand" "ad"))] - "FP_REG_P (operands[0]) && ! FP_REG_P (operands[1])" - "* + class Foo { - rtx xoperands[2]; - xoperands[1] = gen_rtx (REG, SImode, REGNO (operands[1]) + 1); - #ifdef MOTOROLA - output_asm_insn (\"move.l %1,(sp)\", xoperands); - output_asm_insn (\"move.l %1,-(sp)\", operands); - return \"fmove.d (sp)+,%0\"; - #else - output_asm_insn (\"movel %1,sp@\", xoperands); - output_asm_insn (\"movel %1,sp@-\", operands); - return \"fmoved sp@+,%0\"; - #endif - } - ") - - The effect of this optimization is to change - - jbsr _foobar - addql #4,sp - movel d1,sp@- - movel d0,sp@- - fmoved sp@+,fp0 - -into - - jbsr _foobar - movel d1,sp@ - movel d0,sp@- - fmoved sp@+,fp0 - - INSN-PATTERN-1 and so on look *almost* like the second operand of -`define_insn'. There is one important difference: the second operand -of `define_insn' consists of one or more RTX's enclosed in square -brackets. Usually, there is only one: then the same action can be -written as an element of a `define_peephole'. But when there are -multiple actions in a `define_insn', they are implicitly enclosed in a -`parallel'. Then you must explicitly write the `parallel', and the -square brackets within it, in the `define_peephole'. Thus, if an insn -pattern looks like this, - - (define_insn "divmodsi4" - [(set (match_operand:SI 0 "general_operand" "=d") - (div:SI (match_operand:SI 1 "general_operand" "0") - (match_operand:SI 2 "general_operand" "dmsK"))) - (set (match_operand:SI 3 "general_operand" "=d") - (mod:SI (match_dup 1) (match_dup 2)))] - "TARGET_68020" - "divsl%.l %2,%3:%0") - -then the way to mention this insn in a peephole is as follows: - - (define_peephole - [... - (parallel - [(set (match_operand:SI 0 "general_operand" "=d") - (div:SI (match_operand:SI 1 "general_operand" "0") - (match_operand:SI 2 "general_operand" "dmsK"))) - (set (match_operand:SI 3 "general_operand" "=d") - (mod:SI (match_dup 1) (match_dup 2)))]) - ...] - ...) + ... + void method(); + static int bar; + }; + + This declaration only establishes that the class `Foo' has an `int' +named `Foo::bar', and a member function named `Foo::method'. But you +still need to define *both* `method' and `bar' elsewhere. According to +the draft ANSI standard, you must supply an initializer in one (and +only one) source file, such as: + + int Foo::bar = 0; + + Other C++ compilers may not correctly implement the standard +behavior. As a result, when you switch to `g++' from one of these +compilers, you may discover that a program that appeared to work +correctly in fact does not conform to the standard: `g++' reports as +undefined symbols any static data members that lack definitions. - \ No newline at end of file