[8833] | 1 | This is Info file gcc.info, produced by Makeinfo-1.55 from the input |
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| 2 | file gcc.texi. |
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| 3 | |
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| 4 | This file documents the use and the internals of the GNU compiler. |
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| 5 | |
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| 6 | Published by the Free Software Foundation 59 Temple Place - Suite 330 |
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| 7 | Boston, MA 02111-1307 USA |
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| 8 | |
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| 9 | Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 Free Software |
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| 10 | Foundation, Inc. |
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| 11 | |
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| 12 | Permission is granted to make and distribute verbatim copies of this |
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| 13 | manual provided the copyright notice and this permission notice are |
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| 14 | preserved on all copies. |
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| 15 | |
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| 16 | Permission is granted to copy and distribute modified versions of |
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| 17 | this manual under the conditions for verbatim copying, provided also |
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| 18 | that the sections entitled "GNU General Public License," "Funding for |
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| 19 | Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are |
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| 20 | included exactly as in the original, and provided that the entire |
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| 21 | resulting derived work is distributed under the terms of a permission |
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| 22 | notice identical to this one. |
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| 23 | |
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| 24 | Permission is granted to copy and distribute translations of this |
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| 25 | manual into another language, under the above conditions for modified |
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| 26 | versions, except that the sections entitled "GNU General Public |
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| 27 | License," "Funding for Free Software," and "Protect Your Freedom--Fight |
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| 28 | `Look And Feel'", and this permission notice, may be included in |
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| 29 | translations approved by the Free Software Foundation instead of in the |
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| 30 | original English. |
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| 31 | |
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| 32 | |
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| 33 | File: gcc.info, Node: VMS Misc, Prev: Global Declarations, Up: VMS |
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| 34 | |
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| 35 | Other VMS Issues |
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| 36 | ================ |
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| 37 | |
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| 38 | GNU CC automatically arranges for `main' to return 1 by default if |
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| 39 | you fail to specify an explicit return value. This will be interpreted |
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| 40 | by VMS as a status code indicating a normal successful completion. |
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| 41 | Version 1 of GNU CC did not provide this default. |
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| 42 | |
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| 43 | GNU CC on VMS works only with the GNU assembler, GAS. You need |
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| 44 | version 1.37 or later of GAS in order to produce value debugging |
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| 45 | information for the VMS debugger. Use the ordinary VMS linker with the |
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| 46 | object files produced by GAS. |
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| 47 | |
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| 48 | Under previous versions of GNU CC, the generated code would |
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| 49 | occasionally give strange results when linked to the sharable `VAXCRTL' |
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| 50 | library. Now this should work. |
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| 51 | |
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| 52 | A caveat for use of `const' global variables: the `const' modifier |
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| 53 | must be specified in every external declaration of the variable in all |
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| 54 | of the source files that use that variable. Otherwise the linker will |
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| 55 | issue warnings about conflicting attributes for the variable. Your |
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| 56 | program will still work despite the warnings, but the variable will be |
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| 57 | placed in writable storage. |
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| 58 | |
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| 59 | Although the VMS linker does distinguish between upper and lower case |
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| 60 | letters in global symbols, most VMS compilers convert all such symbols |
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| 61 | into upper case and most run-time library routines also have upper case |
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| 62 | names. To be able to reliably call such routines, GNU CC (by means of |
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| 63 | the assembler GAS) converts global symbols into upper case like other |
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| 64 | VMS compilers. However, since the usual practice in C is to distinguish |
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| 65 | case, GNU CC (via GAS) tries to preserve usual C behavior by augmenting |
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| 66 | each name that is not all lower case. This means truncating the name |
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| 67 | to at most 23 characters and then adding more characters at the end |
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| 68 | which encode the case pattern of those 23. Names which contain at |
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| 69 | least one dollar sign are an exception; they are converted directly into |
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| 70 | upper case without augmentation. |
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| 71 | |
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| 72 | Name augmentation yields bad results for programs that use |
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| 73 | precompiled libraries (such as Xlib) which were generated by another |
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| 74 | compiler. You can use the compiler option `/NOCASE_HACK' to inhibit |
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| 75 | augmentation; it makes external C functions and variables |
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| 76 | case-independent as is usual on VMS. Alternatively, you could write |
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| 77 | all references to the functions and variables in such libraries using |
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| 78 | lower case; this will work on VMS, but is not portable to other |
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| 79 | systems. The compiler option `/NAMES' also provides control over |
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| 80 | global name handling. |
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| 81 | |
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| 82 | Function and variable names are handled somewhat differently with GNU |
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| 83 | C++. The GNU C++ compiler performs "name mangling" on function names, |
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| 84 | which means that it adds information to the function name to describe |
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| 85 | the data types of the arguments that the function takes. One result of |
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| 86 | this is that the name of a function can become very long. Since the |
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| 87 | VMS linker only recognizes the first 31 characters in a name, special |
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| 88 | action is taken to ensure that each function and variable has a unique |
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| 89 | name that can be represented in 31 characters. |
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| 90 | |
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| 91 | If the name (plus a name augmentation, if required) is less than 32 |
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| 92 | characters in length, then no special action is performed. If the name |
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| 93 | is longer than 31 characters, the assembler (GAS) will generate a hash |
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| 94 | string based upon the function name, truncate the function name to 23 |
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| 95 | characters, and append the hash string to the truncated name. If the |
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| 96 | `/VERBOSE' compiler option is used, the assembler will print both the |
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| 97 | full and truncated names of each symbol that is truncated. |
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| 98 | |
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| 99 | The `/NOCASE_HACK' compiler option should not be used when you are |
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| 100 | compiling programs that use libg++. libg++ has several instances of |
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| 101 | objects (i.e. `Filebuf' and `filebuf') which become indistinguishable |
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| 102 | in a case-insensitive environment. This leads to cases where you need |
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| 103 | to inhibit augmentation selectively (if you were using libg++ and Xlib |
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| 104 | in the same program, for example). There is no special feature for |
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| 105 | doing this, but you can get the result by defining a macro for each |
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| 106 | mixed case symbol for which you wish to inhibit augmentation. The |
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| 107 | macro should expand into the lower case equivalent of itself. For |
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| 108 | example: |
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| 109 | |
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| 110 | #define StuDlyCapS studlycaps |
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| 111 | |
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| 112 | These macro definitions can be placed in a header file to minimize |
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| 113 | the number of changes to your source code. |
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| 114 | |
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| 115 | |
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| 116 | File: gcc.info, Node: Portability, Next: Interface, Prev: VMS, Up: Top |
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| 117 | |
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| 118 | GNU CC and Portability |
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| 119 | ********************** |
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| 120 | |
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| 121 | The main goal of GNU CC was to make a good, fast compiler for |
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| 122 | machines in the class that the GNU system aims to run on: 32-bit |
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| 123 | machines that address 8-bit bytes and have several general registers. |
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| 124 | Elegance, theoretical power and simplicity are only secondary. |
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| 125 | |
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| 126 | GNU CC gets most of the information about the target machine from a |
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| 127 | machine description which gives an algebraic formula for each of the |
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| 128 | machine's instructions. This is a very clean way to describe the |
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| 129 | target. But when the compiler needs information that is difficult to |
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| 130 | express in this fashion, I have not hesitated to define an ad-hoc |
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| 131 | parameter to the machine description. The purpose of portability is to |
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| 132 | reduce the total work needed on the compiler; it was not of interest |
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| 133 | for its own sake. |
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| 134 | |
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| 135 | GNU CC does not contain machine dependent code, but it does contain |
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| 136 | code that depends on machine parameters such as endianness (whether the |
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| 137 | most significant byte has the highest or lowest address of the bytes in |
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| 138 | a word) and the availability of autoincrement addressing. In the |
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| 139 | RTL-generation pass, it is often necessary to have multiple strategies |
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| 140 | for generating code for a particular kind of syntax tree, strategies |
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| 141 | that are usable for different combinations of parameters. Often I have |
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| 142 | not tried to address all possible cases, but only the common ones or |
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| 143 | only the ones that I have encountered. As a result, a new target may |
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| 144 | require additional strategies. You will know if this happens because |
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| 145 | the compiler will call `abort'. Fortunately, the new strategies can be |
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| 146 | added in a machine-independent fashion, and will affect only the target |
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| 147 | machines that need them. |
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| 148 | |
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| 149 | |
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| 150 | File: gcc.info, Node: Interface, Next: Passes, Prev: Portability, Up: Top |
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| 151 | |
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| 152 | Interfacing to GNU CC Output |
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| 153 | **************************** |
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| 154 | |
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| 155 | GNU CC is normally configured to use the same function calling |
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| 156 | convention normally in use on the target system. This is done with the |
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| 157 | machine-description macros described (*note Target Macros::.). |
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| 158 | |
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| 159 | However, returning of structure and union values is done differently |
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| 160 | on some target machines. As a result, functions compiled with PCC |
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| 161 | returning such types cannot be called from code compiled with GNU CC, |
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| 162 | and vice versa. This does not cause trouble often because few Unix |
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| 163 | library routines return structures or unions. |
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| 164 | |
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| 165 | GNU CC code returns structures and unions that are 1, 2, 4 or 8 bytes |
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| 166 | long in the same registers used for `int' or `double' return values. |
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| 167 | (GNU CC typically allocates variables of such types in registers also.) |
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| 168 | Structures and unions of other sizes are returned by storing them into |
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| 169 | an address passed by the caller (usually in a register). The |
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| 170 | machine-description macros `STRUCT_VALUE' and `STRUCT_INCOMING_VALUE' |
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| 171 | tell GNU CC where to pass this address. |
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| 172 | |
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| 173 | By contrast, PCC on most target machines returns structures and |
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| 174 | unions of any size by copying the data into an area of static storage, |
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| 175 | and then returning the address of that storage as if it were a pointer |
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| 176 | value. The caller must copy the data from that memory area to the |
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| 177 | place where the value is wanted. This is slower than the method used |
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| 178 | by GNU CC, and fails to be reentrant. |
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| 179 | |
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| 180 | On some target machines, such as RISC machines and the 80386, the |
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| 181 | standard system convention is to pass to the subroutine the address of |
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| 182 | where to return the value. On these machines, GNU CC has been |
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| 183 | configured to be compatible with the standard compiler, when this method |
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| 184 | is used. It may not be compatible for structures of 1, 2, 4 or 8 bytes. |
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| 185 | |
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| 186 | GNU CC uses the system's standard convention for passing arguments. |
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| 187 | On some machines, the first few arguments are passed in registers; in |
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| 188 | others, all are passed on the stack. It would be possible to use |
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| 189 | registers for argument passing on any machine, and this would probably |
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| 190 | result in a significant speedup. But the result would be complete |
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| 191 | incompatibility with code that follows the standard convention. So this |
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| 192 | change is practical only if you are switching to GNU CC as the sole C |
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| 193 | compiler for the system. We may implement register argument passing on |
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| 194 | certain machines once we have a complete GNU system so that we can |
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| 195 | compile the libraries with GNU CC. |
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| 196 | |
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| 197 | On some machines (particularly the Sparc), certain types of arguments |
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| 198 | are passed "by invisible reference". This means that the value is |
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| 199 | stored in memory, and the address of the memory location is passed to |
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| 200 | the subroutine. |
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| 201 | |
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| 202 | If you use `longjmp', beware of automatic variables. ANSI C says |
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| 203 | that automatic variables that are not declared `volatile' have undefined |
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| 204 | values after a `longjmp'. And this is all GNU CC promises to do, |
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| 205 | because it is very difficult to restore register variables correctly, |
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| 206 | and one of GNU CC's features is that it can put variables in registers |
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| 207 | without your asking it to. |
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| 208 | |
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| 209 | If you want a variable to be unaltered by `longjmp', and you don't |
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| 210 | want to write `volatile' because old C compilers don't accept it, just |
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| 211 | take the address of the variable. If a variable's address is ever |
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| 212 | taken, even if just to compute it and ignore it, then the variable |
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| 213 | cannot go in a register: |
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| 214 | |
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| 215 | { |
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| 216 | int careful; |
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| 217 | &careful; |
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| 218 | ... |
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| 219 | } |
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| 220 | |
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| 221 | Code compiled with GNU CC may call certain library routines. Most of |
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| 222 | them handle arithmetic for which there are no instructions. This |
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| 223 | includes multiply and divide on some machines, and floating point |
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| 224 | operations on any machine for which floating point support is disabled |
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| 225 | with `-msoft-float'. Some standard parts of the C library, such as |
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| 226 | `bcopy' or `memcpy', are also called automatically. The usual function |
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| 227 | call interface is used for calling the library routines. |
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| 228 | |
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| 229 | These library routines should be defined in the library `libgcc.a', |
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| 230 | which GNU CC automatically searches whenever it links a program. On |
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| 231 | machines that have multiply and divide instructions, if hardware |
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| 232 | floating point is in use, normally `libgcc.a' is not needed, but it is |
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| 233 | searched just in case. |
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| 234 | |
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| 235 | Each arithmetic function is defined in `libgcc1.c' to use the |
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| 236 | corresponding C arithmetic operator. As long as the file is compiled |
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| 237 | with another C compiler, which supports all the C arithmetic operators, |
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| 238 | this file will work portably. However, `libgcc1.c' does not work if |
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| 239 | compiled with GNU CC, because each arithmetic function would compile |
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| 240 | into a call to itself! |
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| 241 | |
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| 242 | |
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| 243 | File: gcc.info, Node: Passes, Next: RTL, Prev: Interface, Up: Top |
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| 244 | |
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| 245 | Passes and Files of the Compiler |
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| 246 | ******************************** |
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| 247 | |
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| 248 | The overall control structure of the compiler is in `toplev.c'. This |
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| 249 | file is responsible for initialization, decoding arguments, opening and |
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| 250 | closing files, and sequencing the passes. |
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| 251 | |
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| 252 | The parsing pass is invoked only once, to parse the entire input. |
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| 253 | The RTL intermediate code for a function is generated as the function |
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| 254 | is parsed, a statement at a time. Each statement is read in as a |
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| 255 | syntax tree and then converted to RTL; then the storage for the tree |
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| 256 | for the statement is reclaimed. Storage for types (and the expressions |
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| 257 | for their sizes), declarations, and a representation of the binding |
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| 258 | contours and how they nest, remain until the function is finished being |
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| 259 | compiled; these are all needed to output the debugging information. |
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| 260 | |
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| 261 | Each time the parsing pass reads a complete function definition or |
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| 262 | top-level declaration, it calls either the function |
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| 263 | `rest_of_compilation', or the function `rest_of_decl_compilation' in |
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| 264 | `toplev.c', which are responsible for all further processing necessary, |
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| 265 | ending with output of the assembler language. All other compiler |
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| 266 | passes run, in sequence, within `rest_of_compilation'. When that |
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| 267 | function returns from compiling a function definition, the storage used |
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| 268 | for that function definition's compilation is entirely freed, unless it |
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| 269 | is an inline function (*note An Inline Function is As Fast As a Macro: |
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| 270 | Inline.). |
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| 271 | |
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| 272 | Here is a list of all the passes of the compiler and their source |
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| 273 | files. Also included is a description of where debugging dumps can be |
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| 274 | requested with `-d' options. |
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| 275 | |
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| 276 | * Parsing. This pass reads the entire text of a function definition, |
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| 277 | constructing partial syntax trees. This and RTL generation are no |
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| 278 | longer truly separate passes (formerly they were), but it is |
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| 279 | easier to think of them as separate. |
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| 280 | |
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| 281 | The tree representation does not entirely follow C syntax, because |
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| 282 | it is intended to support other languages as well. |
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| 283 | |
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| 284 | Language-specific data type analysis is also done in this pass, |
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| 285 | and every tree node that represents an expression has a data type |
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| 286 | attached. Variables are represented as declaration nodes. |
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| 287 | |
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| 288 | Constant folding and some arithmetic simplifications are also done |
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| 289 | during this pass. |
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| 290 | |
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| 291 | The language-independent source files for parsing are |
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| 292 | `stor-layout.c', `fold-const.c', and `tree.c'. There are also |
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| 293 | header files `tree.h' and `tree.def' which define the format of |
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| 294 | the tree representation. |
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| 295 | |
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| 296 | The source files to parse C are `c-parse.in', `c-decl.c', |
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| 297 | `c-typeck.c', `c-aux-info.c', `c-convert.c', and `c-lang.c' along |
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| 298 | with header files `c-lex.h', and `c-tree.h'. |
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| 299 | |
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| 300 | The source files for parsing C++ are `cp-parse.y', `cp-class.c', |
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| 301 | `cp-cvt.c', `cp-decl.c', `cp-decl2.c', `cp-dem.c', `cp-except.c', |
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| 302 | `cp-expr.c', `cp-init.c', `cp-lex.c', `cp-method.c', `cp-ptree.c', |
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| 303 | `cp-search.c', `cp-tree.c', `cp-type2.c', and `cp-typeck.c', along |
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| 304 | with header files `cp-tree.def', `cp-tree.h', and `cp-decl.h'. |
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| 305 | |
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| 306 | The special source files for parsing Objective C are |
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| 307 | `objc-parse.y', `objc-actions.c', `objc-tree.def', and |
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| 308 | `objc-actions.h'. Certain C-specific files are used for this as |
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| 309 | well. |
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| 310 | |
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| 311 | The file `c-common.c' is also used for all of the above languages. |
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| 312 | |
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| 313 | * RTL generation. This is the conversion of syntax tree into RTL |
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| 314 | code. It is actually done statement-by-statement during parsing, |
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| 315 | but for most purposes it can be thought of as a separate pass. |
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| 316 | |
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| 317 | This is where the bulk of target-parameter-dependent code is found, |
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| 318 | since often it is necessary for strategies to apply only when |
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| 319 | certain standard kinds of instructions are available. The purpose |
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| 320 | of named instruction patterns is to provide this information to |
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| 321 | the RTL generation pass. |
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| 322 | |
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| 323 | Optimization is done in this pass for `if'-conditions that are |
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| 324 | comparisons, boolean operations or conditional expressions. Tail |
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| 325 | recursion is detected at this time also. Decisions are made about |
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| 326 | how best to arrange loops and how to output `switch' statements. |
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| 327 | |
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| 328 | The source files for RTL generation include `stmt.c', `calls.c', |
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| 329 | `expr.c', `explow.c', `expmed.c', `function.c', `optabs.c' and |
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| 330 | `emit-rtl.c'. Also, the file `insn-emit.c', generated from the |
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| 331 | machine description by the program `genemit', is used in this |
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| 332 | pass. The header file `expr.h' is used for communication within |
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| 333 | this pass. |
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| 334 | |
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| 335 | The header files `insn-flags.h' and `insn-codes.h', generated from |
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| 336 | the machine description by the programs `genflags' and `gencodes', |
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| 337 | tell this pass which standard names are available for use and |
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| 338 | which patterns correspond to them. |
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| 339 | |
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| 340 | Aside from debugging information output, none of the following |
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| 341 | passes refers to the tree structure representation of the function |
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| 342 | (only part of which is saved). |
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| 343 | |
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| 344 | The decision of whether the function can and should be expanded |
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| 345 | inline in its subsequent callers is made at the end of rtl |
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| 346 | generation. The function must meet certain criteria, currently |
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| 347 | related to the size of the function and the types and number of |
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| 348 | parameters it has. Note that this function may contain loops, |
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| 349 | recursive calls to itself (tail-recursive functions can be |
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| 350 | inlined!), gotos, in short, all constructs supported by GNU CC. |
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| 351 | The file `integrate.c' contains the code to save a function's rtl |
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| 352 | for later inlining and to inline that rtl when the function is |
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| 353 | called. The header file `integrate.h' is also used for this |
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| 354 | purpose. |
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| 355 | |
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| 356 | The option `-dr' causes a debugging dump of the RTL code after |
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| 357 | this pass. This dump file's name is made by appending `.rtl' to |
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| 358 | the input file name. |
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| 359 | |
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| 360 | * Jump optimization. This pass simplifies jumps to the following |
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| 361 | instruction, jumps across jumps, and jumps to jumps. It deletes |
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| 362 | unreferenced labels and unreachable code, except that unreachable |
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| 363 | code that contains a loop is not recognized as unreachable in this |
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| 364 | pass. (Such loops are deleted later in the basic block analysis.) |
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| 365 | It also converts some code originally written with jumps into |
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| 366 | sequences of instructions that directly set values from the |
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| 367 | results of comparisons, if the machine has such instructions. |
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| 368 | |
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| 369 | Jump optimization is performed two or three times. The first time |
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| 370 | is immediately following RTL generation. The second time is after |
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| 371 | CSE, but only if CSE says repeated jump optimization is needed. |
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| 372 | The last time is right before the final pass. That time, |
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| 373 | cross-jumping and deletion of no-op move instructions are done |
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| 374 | together with the optimizations described above. |
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| 375 | |
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| 376 | The source file of this pass is `jump.c'. |
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| 377 | |
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| 378 | The option `-dj' causes a debugging dump of the RTL code after |
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| 379 | this pass is run for the first time. This dump file's name is |
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| 380 | made by appending `.jump' to the input file name. |
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| 381 | |
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| 382 | * Register scan. This pass finds the first and last use of each |
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| 383 | register, as a guide for common subexpression elimination. Its |
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| 384 | source is in `regclass.c'. |
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| 385 | |
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| 386 | * Jump threading. This pass detects a condition jump that branches |
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| 387 | to an identical or inverse test. Such jumps can be `threaded' |
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| 388 | through the second conditional test. The source code for this |
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| 389 | pass is in `jump.c'. This optimization is only performed if |
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| 390 | `-fthread-jumps' is enabled. |
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| 391 | |
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| 392 | * Common subexpression elimination. This pass also does constant |
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| 393 | propagation. Its source file is `cse.c'. If constant propagation |
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| 394 | causes conditional jumps to become unconditional or to become |
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| 395 | no-ops, jump optimization is run again when CSE is finished. |
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| 396 | |
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| 397 | The option `-ds' causes a debugging dump of the RTL code after |
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| 398 | this pass. This dump file's name is made by appending `.cse' to |
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| 399 | the input file name. |
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| 400 | |
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| 401 | * Loop optimization. This pass moves constant expressions out of |
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| 402 | loops, and optionally does strength-reduction and loop unrolling |
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| 403 | as well. Its source files are `loop.c' and `unroll.c', plus the |
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| 404 | header `loop.h' used for communication between them. Loop |
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| 405 | unrolling uses some functions in `integrate.c' and the header |
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| 406 | `integrate.h'. |
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| 407 | |
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| 408 | The option `-dL' causes a debugging dump of the RTL code after |
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| 409 | this pass. This dump file's name is made by appending `.loop' to |
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| 410 | the input file name. |
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| 411 | |
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| 412 | * If `-frerun-cse-after-loop' was enabled, a second common |
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| 413 | subexpression elimination pass is performed after the loop |
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| 414 | optimization pass. Jump threading is also done again at this time |
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| 415 | if it was specified. |
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| 416 | |
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| 417 | The option `-dt' causes a debugging dump of the RTL code after |
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| 418 | this pass. This dump file's name is made by appending `.cse2' to |
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| 419 | the input file name. |
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| 420 | |
---|
| 421 | * Stupid register allocation is performed at this point in a |
---|
| 422 | nonoptimizing compilation. It does a little data flow analysis as |
---|
| 423 | well. When stupid register allocation is in use, the next pass |
---|
| 424 | executed is the reloading pass; the others in between are skipped. |
---|
| 425 | The source file is `stupid.c'. |
---|
| 426 | |
---|
| 427 | * Data flow analysis (`flow.c'). This pass divides the program into |
---|
| 428 | basic blocks (and in the process deletes unreachable loops); then |
---|
| 429 | it computes which pseudo-registers are live at each point in the |
---|
| 430 | program, and makes the first instruction that uses a value point at |
---|
| 431 | the instruction that computed the value. |
---|
| 432 | |
---|
| 433 | This pass also deletes computations whose results are never used, |
---|
| 434 | and combines memory references with add or subtract instructions |
---|
| 435 | to make autoincrement or autodecrement addressing. |
---|
| 436 | |
---|
| 437 | The option `-df' causes a debugging dump of the RTL code after |
---|
| 438 | this pass. This dump file's name is made by appending `.flow' to |
---|
| 439 | the input file name. If stupid register allocation is in use, this |
---|
| 440 | dump file reflects the full results of such allocation. |
---|
| 441 | |
---|
| 442 | * Instruction combination (`combine.c'). This pass attempts to |
---|
| 443 | combine groups of two or three instructions that are related by |
---|
| 444 | data flow into single instructions. It combines the RTL |
---|
| 445 | expressions for the instructions by substitution, simplifies the |
---|
| 446 | result using algebra, and then attempts to match the result |
---|
| 447 | against the machine description. |
---|
| 448 | |
---|
| 449 | The option `-dc' causes a debugging dump of the RTL code after |
---|
| 450 | this pass. This dump file's name is made by appending `.combine' |
---|
| 451 | to the input file name. |
---|
| 452 | |
---|
| 453 | * Instruction scheduling (`sched.c'). This pass looks for |
---|
| 454 | instructions whose output will not be available by the time that |
---|
| 455 | it is used in subsequent instructions. (Memory loads and floating |
---|
| 456 | point instructions often have this behavior on RISC machines). It |
---|
| 457 | re-orders instructions within a basic block to try to separate the |
---|
| 458 | definition and use of items that otherwise would cause pipeline |
---|
| 459 | stalls. |
---|
| 460 | |
---|
| 461 | Instruction scheduling is performed twice. The first time is |
---|
| 462 | immediately after instruction combination and the second is |
---|
| 463 | immediately after reload. |
---|
| 464 | |
---|
| 465 | The option `-dS' causes a debugging dump of the RTL code after this |
---|
| 466 | pass is run for the first time. The dump file's name is made by |
---|
| 467 | appending `.sched' to the input file name. |
---|
| 468 | |
---|
| 469 | * Register class preferencing. The RTL code is scanned to find out |
---|
| 470 | which register class is best for each pseudo register. The source |
---|
| 471 | file is `regclass.c'. |
---|
| 472 | |
---|
| 473 | * Local register allocation (`local-alloc.c'). This pass allocates |
---|
| 474 | hard registers to pseudo registers that are used only within one |
---|
| 475 | basic block. Because the basic block is linear, it can use fast |
---|
| 476 | and powerful techniques to do a very good job. |
---|
| 477 | |
---|
| 478 | The option `-dl' causes a debugging dump of the RTL code after |
---|
| 479 | this pass. This dump file's name is made by appending `.lreg' to |
---|
| 480 | the input file name. |
---|
| 481 | |
---|
| 482 | * Global register allocation (`global.c'). This pass allocates hard |
---|
| 483 | registers for the remaining pseudo registers (those whose life |
---|
| 484 | spans are not contained in one basic block). |
---|
| 485 | |
---|
| 486 | * Reloading. This pass renumbers pseudo registers with the hardware |
---|
| 487 | registers numbers they were allocated. Pseudo registers that did |
---|
| 488 | not get hard registers are replaced with stack slots. Then it |
---|
| 489 | finds instructions that are invalid because a value has failed to |
---|
| 490 | end up in a register, or has ended up in a register of the wrong |
---|
| 491 | kind. It fixes up these instructions by reloading the |
---|
| 492 | problematical values temporarily into registers. Additional |
---|
| 493 | instructions are generated to do the copying. |
---|
| 494 | |
---|
| 495 | The reload pass also optionally eliminates the frame pointer and |
---|
| 496 | inserts instructions to save and restore call-clobbered registers |
---|
| 497 | around calls. |
---|
| 498 | |
---|
| 499 | Source files are `reload.c' and `reload1.c', plus the header |
---|
| 500 | `reload.h' used for communication between them. |
---|
| 501 | |
---|
| 502 | The option `-dg' causes a debugging dump of the RTL code after |
---|
| 503 | this pass. This dump file's name is made by appending `.greg' to |
---|
| 504 | the input file name. |
---|
| 505 | |
---|
| 506 | * Instruction scheduling is repeated here to try to avoid pipeline |
---|
| 507 | stalls due to memory loads generated for spilled pseudo registers. |
---|
| 508 | |
---|
| 509 | The option `-dR' causes a debugging dump of the RTL code after |
---|
| 510 | this pass. This dump file's name is made by appending `.sched2' |
---|
| 511 | to the input file name. |
---|
| 512 | |
---|
| 513 | * Jump optimization is repeated, this time including cross-jumping |
---|
| 514 | and deletion of no-op move instructions. |
---|
| 515 | |
---|
| 516 | The option `-dJ' causes a debugging dump of the RTL code after |
---|
| 517 | this pass. This dump file's name is made by appending `.jump2' to |
---|
| 518 | the input file name. |
---|
| 519 | |
---|
| 520 | * Delayed branch scheduling. This optional pass attempts to find |
---|
| 521 | instructions that can go into the delay slots of other |
---|
| 522 | instructions, usually jumps and calls. The source file name is |
---|
| 523 | `reorg.c'. |
---|
| 524 | |
---|
| 525 | The option `-dd' causes a debugging dump of the RTL code after |
---|
| 526 | this pass. This dump file's name is made by appending `.dbr' to |
---|
| 527 | the input file name. |
---|
| 528 | |
---|
| 529 | * Conversion from usage of some hard registers to usage of a register |
---|
| 530 | stack may be done at this point. Currently, this is supported only |
---|
| 531 | for the floating-point registers of the Intel 80387 coprocessor. |
---|
| 532 | The source file name is `reg-stack.c'. |
---|
| 533 | |
---|
| 534 | The options `-dk' causes a debugging dump of the RTL code after |
---|
| 535 | this pass. This dump file's name is made by appending `.stack' to |
---|
| 536 | the input file name. |
---|
| 537 | |
---|
| 538 | * Final. This pass outputs the assembler code for the function. It |
---|
| 539 | is also responsible for identifying spurious test and compare |
---|
| 540 | instructions. Machine-specific peephole optimizations are |
---|
| 541 | performed at the same time. The function entry and exit sequences |
---|
| 542 | are generated directly as assembler code in this pass; they never |
---|
| 543 | exist as RTL. |
---|
| 544 | |
---|
| 545 | The source files are `final.c' plus `insn-output.c'; the latter is |
---|
| 546 | generated automatically from the machine description by the tool |
---|
| 547 | `genoutput'. The header file `conditions.h' is used for |
---|
| 548 | communication between these files. |
---|
| 549 | |
---|
| 550 | * Debugging information output. This is run after final because it |
---|
| 551 | must output the stack slot offsets for pseudo registers that did |
---|
| 552 | not get hard registers. Source files are `dbxout.c' for DBX |
---|
| 553 | symbol table format, `sdbout.c' for SDB symbol table format, and |
---|
| 554 | `dwarfout.c' for DWARF symbol table format. |
---|
| 555 | |
---|
| 556 | Some additional files are used by all or many passes: |
---|
| 557 | |
---|
| 558 | * Every pass uses `machmode.def' and `machmode.h' which define the |
---|
| 559 | machine modes. |
---|
| 560 | |
---|
| 561 | * Several passes use `real.h', which defines the default |
---|
| 562 | representation of floating point constants and how to operate on |
---|
| 563 | them. |
---|
| 564 | |
---|
| 565 | * All the passes that work with RTL use the header files `rtl.h' and |
---|
| 566 | `rtl.def', and subroutines in file `rtl.c'. The tools `gen*' also |
---|
| 567 | use these files to read and work with the machine description RTL. |
---|
| 568 | |
---|
| 569 | * Several passes refer to the header file `insn-config.h' which |
---|
| 570 | contains a few parameters (C macro definitions) generated |
---|
| 571 | automatically from the machine description RTL by the tool |
---|
| 572 | `genconfig'. |
---|
| 573 | |
---|
| 574 | * Several passes use the instruction recognizer, which consists of |
---|
| 575 | `recog.c' and `recog.h', plus the files `insn-recog.c' and |
---|
| 576 | `insn-extract.c' that are generated automatically from the machine |
---|
| 577 | description by the tools `genrecog' and `genextract'. |
---|
| 578 | |
---|
| 579 | * Several passes use the header files `regs.h' which defines the |
---|
| 580 | information recorded about pseudo register usage, and |
---|
| 581 | `basic-block.h' which defines the information recorded about basic |
---|
| 582 | blocks. |
---|
| 583 | |
---|
| 584 | * `hard-reg-set.h' defines the type `HARD_REG_SET', a bit-vector |
---|
| 585 | with a bit for each hard register, and some macros to manipulate |
---|
| 586 | it. This type is just `int' if the machine has few enough hard |
---|
| 587 | registers; otherwise it is an array of `int' and some of the |
---|
| 588 | macros expand into loops. |
---|
| 589 | |
---|
| 590 | * Several passes use instruction attributes. A definition of the |
---|
| 591 | attributes defined for a particular machine is in file |
---|
| 592 | `insn-attr.h', which is generated from the machine description by |
---|
| 593 | the program `genattr'. The file `insn-attrtab.c' contains |
---|
| 594 | subroutines to obtain the attribute values for insns. It is |
---|
| 595 | generated from the machine description by the program `genattrtab'. |
---|
| 596 | |
---|
| 597 | |
---|
| 598 | File: gcc.info, Node: RTL, Next: Machine Desc, Prev: Passes, Up: Top |
---|
| 599 | |
---|
| 600 | RTL Representation |
---|
| 601 | ****************** |
---|
| 602 | |
---|
| 603 | Most of the work of the compiler is done on an intermediate |
---|
| 604 | representation called register transfer language. In this language, |
---|
| 605 | the instructions to be output are described, pretty much one by one, in |
---|
| 606 | an algebraic form that describes what the instruction does. |
---|
| 607 | |
---|
| 608 | RTL is inspired by Lisp lists. It has both an internal form, made |
---|
| 609 | up of structures that point at other structures, and a textual form |
---|
| 610 | that is used in the machine description and in printed debugging dumps. |
---|
| 611 | The textual form uses nested parentheses to indicate the pointers in |
---|
| 612 | the internal form. |
---|
| 613 | |
---|
| 614 | * Menu: |
---|
| 615 | |
---|
| 616 | * RTL Objects:: Expressions vs vectors vs strings vs integers. |
---|
| 617 | * Accessors:: Macros to access expression operands or vector elts. |
---|
| 618 | * Flags:: Other flags in an RTL expression. |
---|
| 619 | * Machine Modes:: Describing the size and format of a datum. |
---|
| 620 | * Constants:: Expressions with constant values. |
---|
| 621 | * Regs and Memory:: Expressions representing register contents or memory. |
---|
| 622 | * Arithmetic:: Expressions representing arithmetic on other expressions. |
---|
| 623 | * Comparisons:: Expressions representing comparison of expressions. |
---|
| 624 | * Bit Fields:: Expressions representing bitfields in memory or reg. |
---|
| 625 | * Conversions:: Extending, truncating, floating or fixing. |
---|
| 626 | * RTL Declarations:: Declaring volatility, constancy, etc. |
---|
| 627 | * Side Effects:: Expressions for storing in registers, etc. |
---|
| 628 | * Incdec:: Embedded side-effects for autoincrement addressing. |
---|
| 629 | * Assembler:: Representing `asm' with operands. |
---|
| 630 | * Insns:: Expression types for entire insns. |
---|
| 631 | * Calls:: RTL representation of function call insns. |
---|
| 632 | * Sharing:: Some expressions are unique; others *must* be copied. |
---|
| 633 | * Reading RTL:: Reading textual RTL from a file. |
---|
| 634 | |
---|
| 635 | |
---|
| 636 | File: gcc.info, Node: RTL Objects, Next: Accessors, Prev: RTL, Up: RTL |
---|
| 637 | |
---|
| 638 | RTL Object Types |
---|
| 639 | ================ |
---|
| 640 | |
---|
| 641 | RTL uses five kinds of objects: expressions, integers, wide integers, |
---|
| 642 | strings and vectors. Expressions are the most important ones. An RTL |
---|
| 643 | expression ("RTX", for short) is a C structure, but it is usually |
---|
| 644 | referred to with a pointer; a type that is given the typedef name `rtx'. |
---|
| 645 | |
---|
| 646 | An integer is simply an `int'; their written form uses decimal |
---|
| 647 | digits. A wide integer is an integral object whose type is |
---|
| 648 | `HOST_WIDE_INT' (*note Config::.); their written form uses decimal |
---|
| 649 | digits. |
---|
| 650 | |
---|
| 651 | A string is a sequence of characters. In core it is represented as a |
---|
| 652 | `char *' in usual C fashion, and it is written in C syntax as well. |
---|
| 653 | However, strings in RTL may never be null. If you write an empty |
---|
| 654 | string in a machine description, it is represented in core as a null |
---|
| 655 | pointer rather than as a pointer to a null character. In certain |
---|
| 656 | contexts, these null pointers instead of strings are valid. Within RTL |
---|
| 657 | code, strings are most commonly found inside `symbol_ref' expressions, |
---|
| 658 | but they appear in other contexts in the RTL expressions that make up |
---|
| 659 | machine descriptions. |
---|
| 660 | |
---|
| 661 | A vector contains an arbitrary number of pointers to expressions. |
---|
| 662 | The number of elements in the vector is explicitly present in the |
---|
| 663 | vector. The written form of a vector consists of square brackets |
---|
| 664 | (`[...]') surrounding the elements, in sequence and with whitespace |
---|
| 665 | separating them. Vectors of length zero are not created; null pointers |
---|
| 666 | are used instead. |
---|
| 667 | |
---|
| 668 | Expressions are classified by "expression codes" (also called RTX |
---|
| 669 | codes). The expression code is a name defined in `rtl.def', which is |
---|
| 670 | also (in upper case) a C enumeration constant. The possible expression |
---|
| 671 | codes and their meanings are machine-independent. The code of an RTX |
---|
| 672 | can be extracted with the macro `GET_CODE (X)' and altered with |
---|
| 673 | `PUT_CODE (X, NEWCODE)'. |
---|
| 674 | |
---|
| 675 | The expression code determines how many operands the expression |
---|
| 676 | contains, and what kinds of objects they are. In RTL, unlike Lisp, you |
---|
| 677 | cannot tell by looking at an operand what kind of object it is. |
---|
| 678 | Instead, you must know from its context--from the expression code of |
---|
| 679 | the containing expression. For example, in an expression of code |
---|
| 680 | `subreg', the first operand is to be regarded as an expression and the |
---|
| 681 | second operand as an integer. In an expression of code `plus', there |
---|
| 682 | are two operands, both of which are to be regarded as expressions. In |
---|
| 683 | a `symbol_ref' expression, there is one operand, which is to be |
---|
| 684 | regarded as a string. |
---|
| 685 | |
---|
| 686 | Expressions are written as parentheses containing the name of the |
---|
| 687 | expression type, its flags and machine mode if any, and then the |
---|
| 688 | operands of the expression (separated by spaces). |
---|
| 689 | |
---|
| 690 | Expression code names in the `md' file are written in lower case, |
---|
| 691 | but when they appear in C code they are written in upper case. In this |
---|
| 692 | manual, they are shown as follows: `const_int'. |
---|
| 693 | |
---|
| 694 | In a few contexts a null pointer is valid where an expression is |
---|
| 695 | normally wanted. The written form of this is `(nil)'. |
---|
| 696 | |
---|
| 697 | |
---|
| 698 | File: gcc.info, Node: Accessors, Next: Flags, Prev: RTL Objects, Up: RTL |
---|
| 699 | |
---|
| 700 | Access to Operands |
---|
| 701 | ================== |
---|
| 702 | |
---|
| 703 | For each expression type `rtl.def' specifies the number of contained |
---|
| 704 | objects and their kinds, with four possibilities: `e' for expression |
---|
| 705 | (actually a pointer to an expression), `i' for integer, `w' for wide |
---|
| 706 | integer, `s' for string, and `E' for vector of expressions. The |
---|
| 707 | sequence of letters for an expression code is called its "format". |
---|
| 708 | Thus, the format of `subreg' is `ei'. |
---|
| 709 | |
---|
| 710 | A few other format characters are used occasionally: |
---|
| 711 | |
---|
| 712 | `u' |
---|
| 713 | `u' is equivalent to `e' except that it is printed differently in |
---|
| 714 | debugging dumps. It is used for pointers to insns. |
---|
| 715 | |
---|
| 716 | `n' |
---|
| 717 | `n' is equivalent to `i' except that it is printed differently in |
---|
| 718 | debugging dumps. It is used for the line number or code number of |
---|
| 719 | a `note' insn. |
---|
| 720 | |
---|
| 721 | `S' |
---|
| 722 | `S' indicates a string which is optional. In the RTL objects in |
---|
| 723 | core, `S' is equivalent to `s', but when the object is read, from |
---|
| 724 | an `md' file, the string value of this operand may be omitted. An |
---|
| 725 | omitted string is taken to be the null string. |
---|
| 726 | |
---|
| 727 | `V' |
---|
| 728 | `V' indicates a vector which is optional. In the RTL objects in |
---|
| 729 | core, `V' is equivalent to `E', but when the object is read from |
---|
| 730 | an `md' file, the vector value of this operand may be omitted. An |
---|
| 731 | omitted vector is effectively the same as a vector of no elements. |
---|
| 732 | |
---|
| 733 | `0' |
---|
| 734 | `0' means a slot whose contents do not fit any normal category. |
---|
| 735 | `0' slots are not printed at all in dumps, and are often used in |
---|
| 736 | special ways by small parts of the compiler. |
---|
| 737 | |
---|
| 738 | There are macros to get the number of operands, the format, and the |
---|
| 739 | class of an expression code: |
---|
| 740 | |
---|
| 741 | `GET_RTX_LENGTH (CODE)' |
---|
| 742 | Number of operands of an RTX of code CODE. |
---|
| 743 | |
---|
| 744 | `GET_RTX_FORMAT (CODE)' |
---|
| 745 | The format of an RTX of code CODE, as a C string. |
---|
| 746 | |
---|
| 747 | `GET_RTX_CLASS (CODE)' |
---|
| 748 | A single character representing the type of RTX operation that code |
---|
| 749 | CODE performs. |
---|
| 750 | |
---|
| 751 | The following classes are defined: |
---|
| 752 | |
---|
| 753 | `o' |
---|
| 754 | An RTX code that represents an actual object, such as `reg' or |
---|
| 755 | `mem'. `subreg' is not in this class. |
---|
| 756 | |
---|
| 757 | `<' |
---|
| 758 | An RTX code for a comparison. The codes in this class are |
---|
| 759 | `NE', `EQ', `LE', `LT', `GE', `GT', `LEU', `LTU', `GEU', |
---|
| 760 | `GTU'. |
---|
| 761 | |
---|
| 762 | `1' |
---|
| 763 | An RTX code for a unary arithmetic operation, such as `neg'. |
---|
| 764 | |
---|
| 765 | `c' |
---|
| 766 | An RTX code for a commutative binary operation, other than |
---|
| 767 | `NE' and `EQ' (which have class `<'). |
---|
| 768 | |
---|
| 769 | `2' |
---|
| 770 | An RTX code for a noncommutative binary operation, such as |
---|
| 771 | `MINUS'. |
---|
| 772 | |
---|
| 773 | `b' |
---|
| 774 | An RTX code for a bitfield operation, either `ZERO_EXTRACT' or |
---|
| 775 | `SIGN_EXTRACT'. |
---|
| 776 | |
---|
| 777 | `3' |
---|
| 778 | An RTX code for other three input operations, such as |
---|
| 779 | `IF_THEN_ELSE'. |
---|
| 780 | |
---|
| 781 | `i' |
---|
| 782 | An RTX code for a machine insn (`INSN', `JUMP_INSN', and |
---|
| 783 | `CALL_INSN'). |
---|
| 784 | |
---|
| 785 | `m' |
---|
| 786 | An RTX code for something that matches in insns, such as |
---|
| 787 | `MATCH_DUP'. |
---|
| 788 | |
---|
| 789 | `x' |
---|
| 790 | All other RTX codes. |
---|
| 791 | |
---|
| 792 | Operands of expressions are accessed using the macros `XEXP', |
---|
| 793 | `XINT', `XWINT' and `XSTR'. Each of these macros takes two arguments: |
---|
| 794 | an expression-pointer (RTX) and an operand number (counting from zero). |
---|
| 795 | Thus, |
---|
| 796 | |
---|
| 797 | XEXP (X, 2) |
---|
| 798 | |
---|
| 799 | accesses operand 2 of expression X, as an expression. |
---|
| 800 | |
---|
| 801 | XINT (X, 2) |
---|
| 802 | |
---|
| 803 | accesses the same operand as an integer. `XSTR', used in the same |
---|
| 804 | fashion, would access it as a string. |
---|
| 805 | |
---|
| 806 | Any operand can be accessed as an integer, as an expression or as a |
---|
| 807 | string. You must choose the correct method of access for the kind of |
---|
| 808 | value actually stored in the operand. You would do this based on the |
---|
| 809 | expression code of the containing expression. That is also how you |
---|
| 810 | would know how many operands there are. |
---|
| 811 | |
---|
| 812 | For example, if X is a `subreg' expression, you know that it has two |
---|
| 813 | operands which can be correctly accessed as `XEXP (X, 0)' and `XINT (X, |
---|
| 814 | 1)'. If you did `XINT (X, 0)', you would get the address of the |
---|
| 815 | expression operand but cast as an integer; that might occasionally be |
---|
| 816 | useful, but it would be cleaner to write `(int) XEXP (X, 0)'. `XEXP |
---|
| 817 | (X, 1)' would also compile without error, and would return the second, |
---|
| 818 | integer operand cast as an expression pointer, which would probably |
---|
| 819 | result in a crash when accessed. Nothing stops you from writing `XEXP |
---|
| 820 | (X, 28)' either, but this will access memory past the end of the |
---|
| 821 | expression with unpredictable results. |
---|
| 822 | |
---|
| 823 | Access to operands which are vectors is more complicated. You can |
---|
| 824 | use the macro `XVEC' to get the vector-pointer itself, or the macros |
---|
| 825 | `XVECEXP' and `XVECLEN' to access the elements and length of a vector. |
---|
| 826 | |
---|
| 827 | `XVEC (EXP, IDX)' |
---|
| 828 | Access the vector-pointer which is operand number IDX in EXP. |
---|
| 829 | |
---|
| 830 | `XVECLEN (EXP, IDX)' |
---|
| 831 | Access the length (number of elements) in the vector which is in |
---|
| 832 | operand number IDX in EXP. This value is an `int'. |
---|
| 833 | |
---|
| 834 | `XVECEXP (EXP, IDX, ELTNUM)' |
---|
| 835 | Access element number ELTNUM in the vector which is in operand |
---|
| 836 | number IDX in EXP. This value is an RTX. |
---|
| 837 | |
---|
| 838 | It is up to you to make sure that ELTNUM is not negative and is |
---|
| 839 | less than `XVECLEN (EXP, IDX)'. |
---|
| 840 | |
---|
| 841 | All the macros defined in this section expand into lvalues and |
---|
| 842 | therefore can be used to assign the operands, lengths and vector |
---|
| 843 | elements as well as to access them. |
---|
| 844 | |
---|
| 845 | |
---|
| 846 | File: gcc.info, Node: Flags, Next: Machine Modes, Prev: Accessors, Up: RTL |
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| 847 | |
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| 848 | Flags in an RTL Expression |
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| 849 | ========================== |
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| 850 | |
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| 851 | RTL expressions contain several flags (one-bit bitfields) that are |
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| 852 | used in certain types of expression. Most often they are accessed with |
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| 853 | the following macros: |
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| 854 | |
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| 855 | `MEM_VOLATILE_P (X)' |
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| 856 | In `mem' expressions, nonzero for volatile memory references. |
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| 857 | Stored in the `volatil' field and printed as `/v'. |
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| 858 | |
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| 859 | `MEM_IN_STRUCT_P (X)' |
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| 860 | In `mem' expressions, nonzero for reference to an entire |
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| 861 | structure, union or array, or to a component of one. Zero for |
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| 862 | references to a scalar variable or through a pointer to a scalar. |
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| 863 | Stored in the `in_struct' field and printed as `/s'. |
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| 864 | |
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| 865 | `REG_LOOP_TEST_P' |
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| 866 | In `reg' expressions, nonzero if this register's entire life is |
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| 867 | contained in the exit test code for some loop. Stored in the |
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| 868 | `in_struct' field and printed as `/s'. |
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| 869 | |
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| 870 | `REG_USERVAR_P (X)' |
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| 871 | In a `reg', nonzero if it corresponds to a variable present in the |
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| 872 | user's source code. Zero for temporaries generated internally by |
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| 873 | the compiler. Stored in the `volatil' field and printed as `/v'. |
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| 874 | |
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| 875 | `REG_FUNCTION_VALUE_P (X)' |
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| 876 | Nonzero in a `reg' if it is the place in which this function's |
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| 877 | value is going to be returned. (This happens only in a hard |
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| 878 | register.) Stored in the `integrated' field and printed as `/i'. |
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| 879 | |
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| 880 | The same hard register may be used also for collecting the values |
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| 881 | of functions called by this one, but `REG_FUNCTION_VALUE_P' is zero |
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| 882 | in this kind of use. |
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| 883 | |
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| 884 | `SUBREG_PROMOTED_VAR_P' |
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| 885 | Nonzero in a `subreg' if it was made when accessing an object that |
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| 886 | was promoted to a wider mode in accord with the `PROMOTED_MODE' |
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| 887 | machine description macro (*note Storage Layout::.). In this |
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| 888 | case, the mode of the `subreg' is the declared mode of the object |
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| 889 | and the mode of `SUBREG_REG' is the mode of the register that |
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| 890 | holds the object. Promoted variables are always either sign- or |
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| 891 | zero-extended to the wider mode on every assignment. Stored in |
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| 892 | the `in_struct' field and printed as `/s'. |
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| 893 | |
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| 894 | `SUBREG_PROMOTED_UNSIGNED_P' |
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| 895 | Nonzero in a `subreg' that has `SUBREG_PROMOTED_VAR_P' nonzero if |
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| 896 | the object being referenced is kept zero-extended and zero if it |
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| 897 | is kept sign-extended. Stored in the `unchanging' field and |
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| 898 | printed as `/u'. |
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| 899 | |
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| 900 | `RTX_UNCHANGING_P (X)' |
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| 901 | Nonzero in a `reg' or `mem' if the value is not changed. (This |
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| 902 | flag is not set for memory references via pointers to constants. |
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| 903 | Such pointers only guarantee that the object will not be changed |
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| 904 | explicitly by the current function. The object might be changed by |
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| 905 | other functions or by aliasing.) Stored in the `unchanging' field |
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| 906 | and printed as `/u'. |
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| 907 | |
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| 908 | `RTX_INTEGRATED_P (INSN)' |
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| 909 | Nonzero in an insn if it resulted from an in-line function call. |
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| 910 | Stored in the `integrated' field and printed as `/i'. This may be |
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| 911 | deleted; nothing currently depends on it. |
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| 912 | |
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| 913 | `SYMBOL_REF_USED (X)' |
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| 914 | In a `symbol_ref', indicates that X has been used. This is |
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| 915 | normally only used to ensure that X is only declared external |
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| 916 | once. Stored in the `used' field. |
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| 917 | |
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| 918 | `SYMBOL_REF_FLAG (X)' |
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| 919 | In a `symbol_ref', this is used as a flag for machine-specific |
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| 920 | purposes. Stored in the `volatil' field and printed as `/v'. |
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| 921 | |
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| 922 | `LABEL_OUTSIDE_LOOP_P' |
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| 923 | In `label_ref' expressions, nonzero if this is a reference to a |
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| 924 | label that is outside the innermost loop containing the reference |
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| 925 | to the label. Stored in the `in_struct' field and printed as `/s'. |
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| 926 | |
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| 927 | `INSN_DELETED_P (INSN)' |
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| 928 | In an insn, nonzero if the insn has been deleted. Stored in the |
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| 929 | `volatil' field and printed as `/v'. |
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| 930 | |
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| 931 | `INSN_ANNULLED_BRANCH_P (INSN)' |
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| 932 | In an `insn' in the delay slot of a branch insn, indicates that an |
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| 933 | annulling branch should be used. See the discussion under |
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| 934 | `sequence' below. Stored in the `unchanging' field and printed as |
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| 935 | `/u'. |
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| 936 | |
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| 937 | `INSN_FROM_TARGET_P (INSN)' |
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| 938 | In an `insn' in a delay slot of a branch, indicates that the insn |
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| 939 | is from the target of the branch. If the branch insn has |
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| 940 | `INSN_ANNULLED_BRANCH_P' set, this insn should only be executed if |
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| 941 | the branch is taken. For annulled branches with this bit clear, |
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| 942 | the insn should be executed only if the branch is not taken. |
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| 943 | Stored in the `in_struct' field and printed as `/s'. |
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| 944 | |
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| 945 | `CONSTANT_POOL_ADDRESS_P (X)' |
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| 946 | Nonzero in a `symbol_ref' if it refers to part of the current |
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| 947 | function's "constants pool". These are addresses close to the |
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| 948 | beginning of the function, and GNU CC assumes they can be addressed |
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| 949 | directly (perhaps with the help of base registers). Stored in the |
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| 950 | `unchanging' field and printed as `/u'. |
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| 951 | |
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| 952 | `CONST_CALL_P (X)' |
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| 953 | In a `call_insn', indicates that the insn represents a call to a |
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| 954 | const function. Stored in the `unchanging' field and printed as |
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| 955 | `/u'. |
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| 956 | |
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| 957 | `LABEL_PRESERVE_P (X)' |
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| 958 | In a `code_label', indicates that the label can never be deleted. |
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| 959 | Labels referenced by a non-local goto will have this bit set. |
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| 960 | Stored in the `in_struct' field and printed as `/s'. |
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| 961 | |
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| 962 | `SCHED_GROUP_P (INSN)' |
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| 963 | During instruction scheduling, in an insn, indicates that the |
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| 964 | previous insn must be scheduled together with this insn. This is |
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| 965 | used to ensure that certain groups of instructions will not be |
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| 966 | split up by the instruction scheduling pass, for example, `use' |
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| 967 | insns before a `call_insn' may not be separated from the |
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| 968 | `call_insn'. Stored in the `in_struct' field and printed as `/s'. |
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| 969 | |
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| 970 | These are the fields which the above macros refer to: |
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| 971 | |
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| 972 | `used' |
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| 973 | Normally, this flag is used only momentarily, at the end of RTL |
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| 974 | generation for a function, to count the number of times an |
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| 975 | expression appears in insns. Expressions that appear more than |
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| 976 | once are copied, according to the rules for shared structure |
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| 977 | (*note Sharing::.). |
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| 978 | |
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| 979 | In a `symbol_ref', it indicates that an external declaration for |
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| 980 | the symbol has already been written. |
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| 981 | |
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| 982 | In a `reg', it is used by the leaf register renumbering code to |
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| 983 | ensure that each register is only renumbered once. |
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| 984 | |
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| 985 | `volatil' |
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| 986 | This flag is used in `mem', `symbol_ref' and `reg' expressions and |
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| 987 | in insns. In RTL dump files, it is printed as `/v'. |
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| 988 | |
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| 989 | In a `mem' expression, it is 1 if the memory reference is volatile. |
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| 990 | Volatile memory references may not be deleted, reordered or |
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| 991 | combined. |
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| 992 | |
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| 993 | In a `symbol_ref' expression, it is used for machine-specific |
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| 994 | purposes. |
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| 995 | |
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| 996 | In a `reg' expression, it is 1 if the value is a user-level |
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| 997 | variable. 0 indicates an internal compiler temporary. |
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| 998 | |
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| 999 | In an insn, 1 means the insn has been deleted. |
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| 1000 | |
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| 1001 | `in_struct' |
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| 1002 | In `mem' expressions, it is 1 if the memory datum referred to is |
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| 1003 | all or part of a structure or array; 0 if it is (or might be) a |
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| 1004 | scalar variable. A reference through a C pointer has 0 because |
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| 1005 | the pointer might point to a scalar variable. This information |
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| 1006 | allows the compiler to determine something about possible cases of |
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| 1007 | aliasing. |
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| 1008 | |
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| 1009 | In an insn in the delay slot of a branch, 1 means that this insn |
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| 1010 | is from the target of the branch. |
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| 1011 | |
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| 1012 | During instruction scheduling, in an insn, 1 means that this insn |
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| 1013 | must be scheduled as part of a group together with the previous |
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| 1014 | insn. |
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| 1015 | |
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| 1016 | In `reg' expressions, it is 1 if the register has its entire life |
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| 1017 | contained within the test expression of some loop. |
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| 1018 | |
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| 1019 | In `subreg' expressions, 1 means that the `subreg' is accessing an |
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| 1020 | object that has had its mode promoted from a wider mode. |
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| 1021 | |
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| 1022 | In `label_ref' expressions, 1 means that the referenced label is |
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| 1023 | outside the innermost loop containing the insn in which the |
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| 1024 | `label_ref' was found. |
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| 1025 | |
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| 1026 | In `code_label' expressions, it is 1 if the label may never be |
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| 1027 | deleted. This is used for labels which are the target of |
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| 1028 | non-local gotos. |
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| 1029 | |
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| 1030 | In an RTL dump, this flag is represented as `/s'. |
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| 1031 | |
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| 1032 | `unchanging' |
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| 1033 | In `reg' and `mem' expressions, 1 means that the value of the |
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| 1034 | expression never changes. |
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| 1035 | |
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| 1036 | In `subreg' expressions, it is 1 if the `subreg' references an |
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| 1037 | unsigned object whose mode has been promoted to a wider mode. |
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| 1038 | |
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| 1039 | In an insn, 1 means that this is an annulling branch. |
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| 1040 | |
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| 1041 | In a `symbol_ref' expression, 1 means that this symbol addresses |
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| 1042 | something in the per-function constants pool. |
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| 1043 | |
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| 1044 | In a `call_insn', 1 means that this instruction is a call to a |
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| 1045 | const function. |
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| 1046 | |
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| 1047 | In an RTL dump, this flag is represented as `/u'. |
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| 1048 | |
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| 1049 | `integrated' |
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| 1050 | In some kinds of expressions, including insns, this flag means the |
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| 1051 | rtl was produced by procedure integration. |
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| 1052 | |
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| 1053 | In a `reg' expression, this flag indicates the register containing |
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| 1054 | the value to be returned by the current function. On machines |
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| 1055 | that pass parameters in registers, the same register number may be |
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| 1056 | used for parameters as well, but this flag is not set on such uses. |
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| 1057 | |
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