1.. _bitcode_format: 2 3.. role:: raw-html(raw) 4 :format: html 5 6======================== 7LLVM Bitcode File Format 8======================== 9 10.. contents:: 11 :local: 12 13Abstract 14======== 15 16This document describes the LLVM bitstream file format and the encoding of the 17LLVM IR into it. 18 19Overview 20======== 21 22What is commonly known as the LLVM bitcode file format (also, sometimes 23anachronistically known as bytecode) is actually two things: a `bitstream 24container format`_ and an `encoding of LLVM IR`_ into the container format. 25 26The bitstream format is an abstract encoding of structured data, very similar to 27XML in some ways. Like XML, bitstream files contain tags, and nested 28structures, and you can parse the file without having to understand the tags. 29Unlike XML, the bitstream format is a binary encoding, and unlike XML it 30provides a mechanism for the file to self-describe "abbreviations", which are 31effectively size optimizations for the content. 32 33LLVM IR files may be optionally embedded into a `wrapper`_ structure that makes 34it easy to embed extra data along with LLVM IR files. 35 36This document first describes the LLVM bitstream format, describes the wrapper 37format, then describes the record structure used by LLVM IR files. 38 39.. _bitstream container format: 40 41Bitstream Format 42================ 43 44The bitstream format is literally a stream of bits, with a very simple 45structure. This structure consists of the following concepts: 46 47* A "`magic number`_" that identifies the contents of the stream. 48 49* Encoding `primitives`_ like variable bit-rate integers. 50 51* `Blocks`_, which define nested content. 52 53* `Data Records`_, which describe entities within the file. 54 55* Abbreviations, which specify compression optimizations for the file. 56 57Note that the `llvm-bcanalyzer <CommandGuide/html/llvm-bcanalyzer.html>`_ tool 58can be used to dump and inspect arbitrary bitstreams, which is very useful for 59understanding the encoding. 60 61.. _magic number: 62 63Magic Numbers 64------------- 65 66The first two bytes of a bitcode file are 'BC' (``0x42``, ``0x43``). The second 67two bytes are an application-specific magic number. Generic bitcode tools can 68look at only the first two bytes to verify the file is bitcode, while 69application-specific programs will want to look at all four. 70 71.. _primitives: 72 73Primitives 74---------- 75 76A bitstream literally consists of a stream of bits, which are read in order 77starting with the least significant bit of each byte. The stream is made up of 78a number of primitive values that encode a stream of unsigned integer values. 79These integers are encoded in two ways: either as `Fixed Width Integers`_ or as 80`Variable Width Integers`_. 81 82.. _Fixed Width Integers: 83.. _fixed-width value: 84 85Fixed Width Integers 86^^^^^^^^^^^^^^^^^^^^ 87 88Fixed-width integer values have their low bits emitted directly to the file. 89For example, a 3-bit integer value encodes 1 as 001. Fixed width integers are 90used when there are a well-known number of options for a field. For example, 91boolean values are usually encoded with a 1-bit wide integer. 92 93.. _Variable Width Integers: 94.. _Variable Width Integer: 95.. _variable-width value: 96 97Variable Width Integers 98^^^^^^^^^^^^^^^^^^^^^^^ 99 100Variable-width integer (VBR) values encode values of arbitrary size, optimizing 101for the case where the values are small. Given a 4-bit VBR field, any 3-bit 102value (0 through 7) is encoded directly, with the high bit set to zero. Values 103larger than N-1 bits emit their bits in a series of N-1 bit chunks, where all 104but the last set the high bit. 105 106For example, the value 27 (0x1B) is encoded as 1011 0011 when emitted as a vbr4 107value. The first set of four bits indicates the value 3 (011) with a 108continuation piece (indicated by a high bit of 1). The next word indicates a 109value of 24 (011 << 3) with no continuation. The sum (3+24) yields the value 11027. 111 112.. _char6-encoded value: 113 1146-bit characters 115^^^^^^^^^^^^^^^^ 116 1176-bit characters encode common characters into a fixed 6-bit field. They 118represent the following characters with the following 6-bit values: 119 120:: 121 122 'a' .. 'z' --- 0 .. 25 123 'A' .. 'Z' --- 26 .. 51 124 '0' .. '9' --- 52 .. 61 125 '.' --- 62 126 '_' --- 63 127 128This encoding is only suitable for encoding characters and strings that consist 129only of the above characters. It is completely incapable of encoding characters 130not in the set. 131 132Word Alignment 133^^^^^^^^^^^^^^ 134 135Occasionally, it is useful to emit zero bits until the bitstream is a multiple 136of 32 bits. This ensures that the bit position in the stream can be represented 137as a multiple of 32-bit words. 138 139Abbreviation IDs 140---------------- 141 142A bitstream is a sequential series of `Blocks`_ and `Data Records`_. Both of 143these start with an abbreviation ID encoded as a fixed-bitwidth field. The 144width is specified by the current block, as described below. The value of the 145abbreviation ID specifies either a builtin ID (which have special meanings, 146defined below) or one of the abbreviation IDs defined for the current block by 147the stream itself. 148 149The set of builtin abbrev IDs is: 150 151* 0 - `END_BLOCK`_ --- This abbrev ID marks the end of the current block. 152 153* 1 - `ENTER_SUBBLOCK`_ --- This abbrev ID marks the beginning of a new 154 block. 155 156* 2 - `DEFINE_ABBREV`_ --- This defines a new abbreviation. 157 158* 3 - `UNABBREV_RECORD`_ --- This ID specifies the definition of an 159 unabbreviated record. 160 161Abbreviation IDs 4 and above are defined by the stream itself, and specify an 162`abbreviated record encoding`_. 163 164.. _Blocks: 165 166Blocks 167------ 168 169Blocks in a bitstream denote nested regions of the stream, and are identified by 170a content-specific id number (for example, LLVM IR uses an ID of 12 to represent 171function bodies). Block IDs 0-7 are reserved for `standard blocks`_ whose 172meaning is defined by Bitcode; block IDs 8 and greater are application 173specific. Nested blocks capture the hierarchical structure of the data encoded 174in it, and various properties are associated with blocks as the file is parsed. 175Block definitions allow the reader to efficiently skip blocks in constant time 176if the reader wants a summary of blocks, or if it wants to efficiently skip data 177it does not understand. The LLVM IR reader uses this mechanism to skip function 178bodies, lazily reading them on demand. 179 180When reading and encoding the stream, several properties are maintained for the 181block. In particular, each block maintains: 182 183#. A current abbrev id width. This value starts at 2 at the beginning of the 184 stream, and is set every time a block record is entered. The block entry 185 specifies the abbrev id width for the body of the block. 186 187#. A set of abbreviations. Abbreviations may be defined within a block, in 188 which case they are only defined in that block (neither subblocks nor 189 enclosing blocks see the abbreviation). Abbreviations can also be defined 190 inside a `BLOCKINFO`_ block, in which case they are defined in all blocks 191 that match the ID that the ``BLOCKINFO`` block is describing. 192 193As sub blocks are entered, these properties are saved and the new sub-block has 194its own set of abbreviations, and its own abbrev id width. When a sub-block is 195popped, the saved values are restored. 196 197.. _ENTER_SUBBLOCK: 198 199ENTER_SUBBLOCK Encoding 200^^^^^^^^^^^^^^^^^^^^^^^ 201 202:raw-html:`<tt>` 203[ENTER_SUBBLOCK, blockid\ :sub:`vbr8`, newabbrevlen\ :sub:`vbr4`, <align32bits>, blocklen_32] 204:raw-html:`</tt>` 205 206The ``ENTER_SUBBLOCK`` abbreviation ID specifies the start of a new block 207record. The ``blockid`` value is encoded as an 8-bit VBR identifier, and 208indicates the type of block being entered, which can be a `standard block`_ or 209an application-specific block. The ``newabbrevlen`` value is a 4-bit VBR, which 210specifies the abbrev id width for the sub-block. The ``blocklen`` value is a 21132-bit aligned value that specifies the size of the subblock in 32-bit 212words. This value allows the reader to skip over the entire block in one jump. 213 214.. _END_BLOCK: 215 216END_BLOCK Encoding 217^^^^^^^^^^^^^^^^^^ 218 219``[END_BLOCK, <align32bits>]`` 220 221The ``END_BLOCK`` abbreviation ID specifies the end of the current block record. 222Its end is aligned to 32-bits to ensure that the size of the block is an even 223multiple of 32-bits. 224 225.. _Data Records: 226 227Data Records 228------------ 229 230Data records consist of a record code and a number of (up to) 64-bit integer 231values. The interpretation of the code and values is application specific and 232may vary between different block types. Records can be encoded either using an 233unabbrev record, or with an abbreviation. In the LLVM IR format, for example, 234there is a record which encodes the target triple of a module. The code is 235``MODULE_CODE_TRIPLE``, and the values of the record are the ASCII codes for the 236characters in the string. 237 238.. _UNABBREV_RECORD: 239 240UNABBREV_RECORD Encoding 241^^^^^^^^^^^^^^^^^^^^^^^^ 242 243:raw-html:`<tt>` 244[UNABBREV_RECORD, code\ :sub:`vbr6`, numops\ :sub:`vbr6`, op0\ :sub:`vbr6`, op1\ :sub:`vbr6`, ...] 245:raw-html:`</tt>` 246 247An ``UNABBREV_RECORD`` provides a default fallback encoding, which is both 248completely general and extremely inefficient. It can describe an arbitrary 249record by emitting the code and operands as VBRs. 250 251For example, emitting an LLVM IR target triple as an unabbreviated record 252requires emitting the ``UNABBREV_RECORD`` abbrevid, a vbr6 for the 253``MODULE_CODE_TRIPLE`` code, a vbr6 for the length of the string, which is equal 254to the number of operands, and a vbr6 for each character. Because there are no 255letters with values less than 32, each letter would need to be emitted as at 256least a two-part VBR, which means that each letter would require at least 12 257bits. This is not an efficient encoding, but it is fully general. 258 259.. _abbreviated record encoding: 260 261Abbreviated Record Encoding 262^^^^^^^^^^^^^^^^^^^^^^^^^^^ 263 264``[<abbrevid>, fields...]`` 265 266An abbreviated record is a abbreviation id followed by a set of fields that are 267encoded according to the `abbreviation definition`_. This allows records to be 268encoded significantly more densely than records encoded with the 269`UNABBREV_RECORD`_ type, and allows the abbreviation types to be specified in 270the stream itself, which allows the files to be completely self describing. The 271actual encoding of abbreviations is defined below. 272 273The record code, which is the first field of an abbreviated record, may be 274encoded in the abbreviation definition (as a literal operand) or supplied in the 275abbreviated record (as a Fixed or VBR operand value). 276 277.. _abbreviation definition: 278 279Abbreviations 280------------- 281 282Abbreviations are an important form of compression for bitstreams. The idea is 283to specify a dense encoding for a class of records once, then use that encoding 284to emit many records. It takes space to emit the encoding into the file, but 285the space is recouped (hopefully plus some) when the records that use it are 286emitted. 287 288Abbreviations can be determined dynamically per client, per file. Because the 289abbreviations are stored in the bitstream itself, different streams of the same 290format can contain different sets of abbreviations according to the needs of the 291specific stream. As a concrete example, LLVM IR files usually emit an 292abbreviation for binary operators. If a specific LLVM module contained no or 293few binary operators, the abbreviation does not need to be emitted. 294 295.. _DEFINE_ABBREV: 296 297DEFINE_ABBREV Encoding 298^^^^^^^^^^^^^^^^^^^^^^ 299 300:raw-html:`<tt>` 301[DEFINE_ABBREV, numabbrevops\ :sub:`vbr5`, abbrevop0, abbrevop1, ...] 302:raw-html:`</tt>` 303 304A ``DEFINE_ABBREV`` record adds an abbreviation to the list of currently defined 305abbreviations in the scope of this block. This definition only exists inside 306this immediate block --- it is not visible in subblocks or enclosing blocks. 307Abbreviations are implicitly assigned IDs sequentially starting from 4 (the 308first application-defined abbreviation ID). Any abbreviations defined in a 309``BLOCKINFO`` record for the particular block type receive IDs first, in order, 310followed by any abbreviations defined within the block itself. Abbreviated data 311records reference this ID to indicate what abbreviation they are invoking. 312 313An abbreviation definition consists of the ``DEFINE_ABBREV`` abbrevid followed 314by a VBR that specifies the number of abbrev operands, then the abbrev operands 315themselves. Abbreviation operands come in three forms. They all start with a 316single bit that indicates whether the abbrev operand is a literal operand (when 317the bit is 1) or an encoding operand (when the bit is 0). 318 319#. Literal operands --- :raw-html:`<tt>` [1\ :sub:`1`, litvalue\ 320 :sub:`vbr8`] :raw-html:`</tt>` --- Literal operands specify that the value in 321 the result is always a single specific value. This specific value is emitted 322 as a vbr8 after the bit indicating that it is a literal operand. 323 324#. Encoding info without data --- :raw-html:`<tt>` [0\ :sub:`1`, encoding\ 325 :sub:`3`] :raw-html:`</tt>` --- Operand encodings that do not have extra data 326 are just emitted as their code. 327 328#. Encoding info with data --- :raw-html:`<tt>` [0\ :sub:`1`, encoding\ 329 :sub:`3`, value\ :sub:`vbr5`] :raw-html:`</tt>` --- Operand encodings that do 330 have extra data are emitted as their code, followed by the extra data. 331 332The possible operand encodings are: 333 334* Fixed (code 1): The field should be emitted as a `fixed-width value`_, whose 335 width is specified by the operand's extra data. 336 337* VBR (code 2): The field should be emitted as a `variable-width value`_, whose 338 width is specified by the operand's extra data. 339 340* Array (code 3): This field is an array of values. The array operand has no 341 extra data, but expects another operand to follow it, indicating the element 342 type of the array. When reading an array in an abbreviated record, the first 343 integer is a vbr6 that indicates the array length, followed by the encoded 344 elements of the array. An array may only occur as the last operand of an 345 abbreviation (except for the one final operand that gives the array's 346 type). 347 348* Char6 (code 4): This field should be emitted as a `char6-encoded value`_. 349 This operand type takes no extra data. Char6 encoding is normally used as an 350 array element type. 351 352* Blob (code 5): This field is emitted as a vbr6, followed by padding to a 353 32-bit boundary (for alignment) and an array of 8-bit objects. The array of 354 bytes is further followed by tail padding to ensure that its total length is a 355 multiple of 4 bytes. This makes it very efficient for the reader to decode 356 the data without having to make a copy of it: it can use a pointer to the data 357 in the mapped in file and poke directly at it. A blob may only occur as the 358 last operand of an abbreviation. 359 360For example, target triples in LLVM modules are encoded as a record of the form 361``[TRIPLE, 'a', 'b', 'c', 'd']``. Consider if the bitstream emitted the 362following abbrev entry: 363 364:: 365 366 [0, Fixed, 4] 367 [0, Array] 368 [0, Char6] 369 370When emitting a record with this abbreviation, the above entry would be emitted 371as: 372 373:raw-html:`<tt><blockquote>` 374[4\ :sub:`abbrevwidth`, 2\ :sub:`4`, 4\ :sub:`vbr6`, 0\ :sub:`6`, 1\ :sub:`6`, 2\ :sub:`6`, 3\ :sub:`6`] 375:raw-html:`</blockquote></tt>` 376 377These values are: 378 379#. The first value, 4, is the abbreviation ID for this abbreviation. 380 381#. The second value, 2, is the record code for ``TRIPLE`` records within LLVM IR 382 file ``MODULE_BLOCK`` blocks. 383 384#. The third value, 4, is the length of the array. 385 386#. The rest of the values are the char6 encoded values for ``"abcd"``. 387 388With this abbreviation, the triple is emitted with only 37 bits (assuming a 389abbrev id width of 3). Without the abbreviation, significantly more space would 390be required to emit the target triple. Also, because the ``TRIPLE`` value is 391not emitted as a literal in the abbreviation, the abbreviation can also be used 392for any other string value. 393 394.. _standard blocks: 395.. _standard block: 396 397Standard Blocks 398--------------- 399 400In addition to the basic block structure and record encodings, the bitstream 401also defines specific built-in block types. These block types specify how the 402stream is to be decoded or other metadata. In the future, new standard blocks 403may be added. Block IDs 0-7 are reserved for standard blocks. 404 405.. _BLOCKINFO: 406 407#0 - BLOCKINFO Block 408^^^^^^^^^^^^^^^^^^^^ 409 410The ``BLOCKINFO`` block allows the description of metadata for other blocks. 411The currently specified records are: 412 413:: 414 415 [SETBID (#1), blockid] 416 [DEFINE_ABBREV, ...] 417 [BLOCKNAME, ...name...] 418 [SETRECORDNAME, RecordID, ...name...] 419 420The ``SETBID`` record (code 1) indicates which block ID is being described. 421``SETBID`` records can occur multiple times throughout the block to change which 422block ID is being described. There must be a ``SETBID`` record prior to any 423other records. 424 425Standard ``DEFINE_ABBREV`` records can occur inside ``BLOCKINFO`` blocks, but 426unlike their occurrence in normal blocks, the abbreviation is defined for blocks 427matching the block ID we are describing, *not* the ``BLOCKINFO`` block 428itself. The abbreviations defined in ``BLOCKINFO`` blocks receive abbreviation 429IDs as described in `DEFINE_ABBREV`_. 430 431The ``BLOCKNAME`` record (code 2) can optionally occur in this block. The 432elements of the record are the bytes of the string name of the block. 433llvm-bcanalyzer can use this to dump out bitcode files symbolically. 434 435The ``SETRECORDNAME`` record (code 3) can also optionally occur in this block. 436The first operand value is a record ID number, and the rest of the elements of 437the record are the bytes for the string name of the record. llvm-bcanalyzer can 438use this to dump out bitcode files symbolically. 439 440Note that although the data in ``BLOCKINFO`` blocks is described as "metadata," 441the abbreviations they contain are essential for parsing records from the 442corresponding blocks. It is not safe to skip them. 443 444.. _wrapper: 445 446Bitcode Wrapper Format 447====================== 448 449Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper 450structure. This structure contains a simple header that indicates the offset 451and size of the embedded BC file. This allows additional information to be 452stored alongside the BC file. The structure of this file header is: 453 454:raw-html:`<tt><blockquote>` 455[Magic\ :sub:`32`, Version\ :sub:`32`, Offset\ :sub:`32`, Size\ :sub:`32`, CPUType\ :sub:`32`] 456:raw-html:`</blockquote></tt>` 457 458Each of the fields are 32-bit fields stored in little endian form (as with the 459rest of the bitcode file fields). The Magic number is always ``0x0B17C0DE`` and 460the version is currently always ``0``. The Offset field is the offset in bytes 461to the start of the bitcode stream in the file, and the Size field is the size 462in bytes of the stream. CPUType is a target-specific value that can be used to 463encode the CPU of the target. 464 465.. _encoding of LLVM IR: 466 467LLVM IR Encoding 468================ 469 470LLVM IR is encoded into a bitstream by defining blocks and records. It uses 471blocks for things like constant pools, functions, symbol tables, etc. It uses 472records for things like instructions, global variable descriptors, type 473descriptions, etc. This document does not describe the set of abbreviations 474that the writer uses, as these are fully self-described in the file, and the 475reader is not allowed to build in any knowledge of this. 476 477Basics 478------ 479 480LLVM IR Magic Number 481^^^^^^^^^^^^^^^^^^^^ 482 483The magic number for LLVM IR files is: 484 485:raw-html:`<tt><blockquote>` 486[0x0\ :sub:`4`, 0xC\ :sub:`4`, 0xE\ :sub:`4`, 0xD\ :sub:`4`] 487:raw-html:`</blockquote></tt>` 488 489When combined with the bitcode magic number and viewed as bytes, this is 490``"BC 0xC0DE"``. 491 492Signed VBRs 493^^^^^^^^^^^ 494 495`Variable Width Integer`_ encoding is an efficient way to encode arbitrary sized 496unsigned values, but is an extremely inefficient for encoding signed values, as 497signed values are otherwise treated as maximally large unsigned values. 498 499As such, signed VBR values of a specific width are emitted as follows: 500 501* Positive values are emitted as VBRs of the specified width, but with their 502 value shifted left by one. 503 504* Negative values are emitted as VBRs of the specified width, but the negated 505 value is shifted left by one, and the low bit is set. 506 507With this encoding, small positive and small negative values can both be emitted 508efficiently. Signed VBR encoding is used in ``CST_CODE_INTEGER`` and 509``CST_CODE_WIDE_INTEGER`` records within ``CONSTANTS_BLOCK`` blocks. 510 511LLVM IR Blocks 512^^^^^^^^^^^^^^ 513 514LLVM IR is defined with the following blocks: 515 516* 8 --- `MODULE_BLOCK`_ --- This is the top-level block that contains the entire 517 module, and describes a variety of per-module information. 518 519* 9 --- `PARAMATTR_BLOCK`_ --- This enumerates the parameter attributes. 520 521* 10 --- `TYPE_BLOCK`_ --- This describes all of the types in the module. 522 523* 11 --- `CONSTANTS_BLOCK`_ --- This describes constants for a module or 524 function. 525 526* 12 --- `FUNCTION_BLOCK`_ --- This describes a function body. 527 528* 13 --- `TYPE_SYMTAB_BLOCK`_ --- This describes the type symbol table. 529 530* 14 --- `VALUE_SYMTAB_BLOCK`_ --- This describes a value symbol table. 531 532* 15 --- `METADATA_BLOCK`_ --- This describes metadata items. 533 534* 16 --- `METADATA_ATTACHMENT`_ --- This contains records associating metadata 535 with function instruction values. 536 537.. _MODULE_BLOCK: 538 539MODULE_BLOCK Contents 540--------------------- 541 542The ``MODULE_BLOCK`` block (id 8) is the top-level block for LLVM bitcode files, 543and each bitcode file must contain exactly one. In addition to records 544(described below) containing information about the module, a ``MODULE_BLOCK`` 545block may contain the following sub-blocks: 546 547* `BLOCKINFO`_ 548* `PARAMATTR_BLOCK`_ 549* `TYPE_BLOCK`_ 550* `TYPE_SYMTAB_BLOCK`_ 551* `VALUE_SYMTAB_BLOCK`_ 552* `CONSTANTS_BLOCK`_ 553* `FUNCTION_BLOCK`_ 554* `METADATA_BLOCK`_ 555 556MODULE_CODE_VERSION Record 557^^^^^^^^^^^^^^^^^^^^^^^^^^ 558 559``[VERSION, version#]`` 560 561The ``VERSION`` record (code 1) contains a single value indicating the format 562version. Only version 0 is supported at this time. 563 564MODULE_CODE_TRIPLE Record 565^^^^^^^^^^^^^^^^^^^^^^^^^ 566 567``[TRIPLE, ...string...]`` 568 569The ``TRIPLE`` record (code 2) contains a variable number of values representing 570the bytes of the ``target triple`` specification string. 571 572MODULE_CODE_DATALAYOUT Record 573^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 574 575``[DATALAYOUT, ...string...]`` 576 577The ``DATALAYOUT`` record (code 3) contains a variable number of values 578representing the bytes of the ``target datalayout`` specification string. 579 580MODULE_CODE_ASM Record 581^^^^^^^^^^^^^^^^^^^^^^ 582 583``[ASM, ...string...]`` 584 585The ``ASM`` record (code 4) contains a variable number of values representing 586the bytes of ``module asm`` strings, with individual assembly blocks separated 587by newline (ASCII 10) characters. 588 589.. _MODULE_CODE_SECTIONNAME: 590 591MODULE_CODE_SECTIONNAME Record 592^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 593 594``[SECTIONNAME, ...string...]`` 595 596The ``SECTIONNAME`` record (code 5) contains a variable number of values 597representing the bytes of a single section name string. There should be one 598``SECTIONNAME`` record for each section name referenced (e.g., in global 599variable or function ``section`` attributes) within the module. These records 600can be referenced by the 1-based index in the *section* fields of ``GLOBALVAR`` 601or ``FUNCTION`` records. 602 603MODULE_CODE_DEPLIB Record 604^^^^^^^^^^^^^^^^^^^^^^^^^ 605 606``[DEPLIB, ...string...]`` 607 608The ``DEPLIB`` record (code 6) contains a variable number of values representing 609the bytes of a single dependent library name string, one of the libraries 610mentioned in a ``deplibs`` declaration. There should be one ``DEPLIB`` record 611for each library name referenced. 612 613MODULE_CODE_GLOBALVAR Record 614^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 615 616``[GLOBALVAR, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal, unnamed_addr]`` 617 618The ``GLOBALVAR`` record (code 7) marks the declaration or definition of a 619global variable. The operand fields are: 620 621* *pointer type*: The type index of the pointer type used to point to this 622 global variable 623 624* *isconst*: Non-zero if the variable is treated as constant within the module, 625 or zero if it is not 626 627* *initid*: If non-zero, the value index of the initializer for this variable, 628 plus 1. 629 630.. _linkage type: 631 632* *linkage*: An encoding of the linkage type for this variable: 633 * ``external``: code 0 634 * ``weak``: code 1 635 * ``appending``: code 2 636 * ``internal``: code 3 637 * ``linkonce``: code 4 638 * ``dllimport``: code 5 639 * ``dllexport``: code 6 640 * ``extern_weak``: code 7 641 * ``common``: code 8 642 * ``private``: code 9 643 * ``weak_odr``: code 10 644 * ``linkonce_odr``: code 11 645 * ``available_externally``: code 12 646 * ``linker_private``: code 13 647 648* alignment*: The logarithm base 2 of the variable's requested alignment, plus 1 649 650* *section*: If non-zero, the 1-based section index in the table of 651 `MODULE_CODE_SECTIONNAME`_ entries. 652 653.. _visibility: 654 655* *visibility*: If present, an encoding of the visibility of this variable: 656 * ``default``: code 0 657 * ``hidden``: code 1 658 * ``protected``: code 2 659 660* *threadlocal*: If present, an encoding of the thread local storage mode of the 661 variable: 662 * ``not thread local``: code 0 663 * ``thread local; default TLS model``: code 1 664 * ``localdynamic``: code 2 665 * ``initialexec``: code 3 666 * ``localexec``: code 4 667 668* *unnamed_addr*: If present and non-zero, indicates that the variable has 669 ``unnamed_addr`` 670 671.. _FUNCTION: 672 673MODULE_CODE_FUNCTION Record 674^^^^^^^^^^^^^^^^^^^^^^^^^^^ 675 676``[FUNCTION, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc]`` 677 678The ``FUNCTION`` record (code 8) marks the declaration or definition of a 679function. The operand fields are: 680 681* *type*: The type index of the function type describing this function 682 683* *callingconv*: The calling convention number: 684 * ``ccc``: code 0 685 * ``fastcc``: code 8 686 * ``coldcc``: code 9 687 * ``x86_stdcallcc``: code 64 688 * ``x86_fastcallcc``: code 65 689 * ``arm_apcscc``: code 66 690 * ``arm_aapcscc``: code 67 691 * ``arm_aapcs_vfpcc``: code 68 692 693* isproto*: Non-zero if this entry represents a declaration rather than a 694 definition 695 696* *linkage*: An encoding of the `linkage type`_ for this function 697 698* *paramattr*: If nonzero, the 1-based parameter attribute index into the table 699 of `PARAMATTR_CODE_ENTRY`_ entries. 700 701* *alignment*: The logarithm base 2 of the function's requested alignment, plus 702 1 703 704* *section*: If non-zero, the 1-based section index in the table of 705 `MODULE_CODE_SECTIONNAME`_ entries. 706 707* *visibility*: An encoding of the `visibility`_ of this function 708 709* *gc*: If present and nonzero, the 1-based garbage collector index in the table 710 of `MODULE_CODE_GCNAME`_ entries. 711 712* *unnamed_addr*: If present and non-zero, indicates that the function has 713 ``unnamed_addr`` 714 715MODULE_CODE_ALIAS Record 716^^^^^^^^^^^^^^^^^^^^^^^^ 717 718``[ALIAS, alias type, aliasee val#, linkage, visibility]`` 719 720The ``ALIAS`` record (code 9) marks the definition of an alias. The operand 721fields are 722 723* *alias type*: The type index of the alias 724 725* *aliasee val#*: The value index of the aliased value 726 727* *linkage*: An encoding of the `linkage type`_ for this alias 728 729* *visibility*: If present, an encoding of the `visibility`_ of the alias 730 731MODULE_CODE_PURGEVALS Record 732^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 733 734``[PURGEVALS, numvals]`` 735 736The ``PURGEVALS`` record (code 10) resets the module-level value list to the 737size given by the single operand value. Module-level value list items are added 738by ``GLOBALVAR``, ``FUNCTION``, and ``ALIAS`` records. After a ``PURGEVALS`` 739record is seen, new value indices will start from the given *numvals* value. 740 741.. _MODULE_CODE_GCNAME: 742 743MODULE_CODE_GCNAME Record 744^^^^^^^^^^^^^^^^^^^^^^^^^ 745 746``[GCNAME, ...string...]`` 747 748The ``GCNAME`` record (code 11) contains a variable number of values 749representing the bytes of a single garbage collector name string. There should 750be one ``GCNAME`` record for each garbage collector name referenced in function 751``gc`` attributes within the module. These records can be referenced by 1-based 752index in the *gc* fields of ``FUNCTION`` records. 753 754.. _PARAMATTR_BLOCK: 755 756PARAMATTR_BLOCK Contents 757------------------------ 758 759The ``PARAMATTR_BLOCK`` block (id 9) contains a table of entries describing the 760attributes of function parameters. These entries are referenced by 1-based index 761in the *paramattr* field of module block `FUNCTION`_ records, or within the 762*attr* field of function block ``INST_INVOKE`` and ``INST_CALL`` records. 763 764Entries within ``PARAMATTR_BLOCK`` are constructed to ensure that each is unique 765(i.e., no two indicies represent equivalent attribute lists). 766 767.. _PARAMATTR_CODE_ENTRY: 768 769PARAMATTR_CODE_ENTRY Record 770^^^^^^^^^^^^^^^^^^^^^^^^^^^ 771 772``[ENTRY, paramidx0, attr0, paramidx1, attr1...]`` 773 774The ``ENTRY`` record (code 1) contains an even number of values describing a 775unique set of function parameter attributes. Each *paramidx* value indicates 776which set of attributes is represented, with 0 representing the return value 777attributes, 0xFFFFFFFF representing function attributes, and other values 778representing 1-based function parameters. Each *attr* value is a bitmap with the 779following interpretation: 780 781* bit 0: ``zeroext`` 782* bit 1: ``signext`` 783* bit 2: ``noreturn`` 784* bit 3: ``inreg`` 785* bit 4: ``sret`` 786* bit 5: ``nounwind`` 787* bit 6: ``noalias`` 788* bit 7: ``byval`` 789* bit 8: ``nest`` 790* bit 9: ``readnone`` 791* bit 10: ``readonly`` 792* bit 11: ``noinline`` 793* bit 12: ``alwaysinline`` 794* bit 13: ``optsize`` 795* bit 14: ``ssp`` 796* bit 15: ``sspreq`` 797* bits 16-31: ``align n`` 798* bit 32: ``nocapture`` 799* bit 33: ``noredzone`` 800* bit 34: ``noimplicitfloat`` 801* bit 35: ``naked`` 802* bit 36: ``inlinehint`` 803* bits 37-39: ``alignstack n``, represented as the logarithm 804 base 2 of the requested alignment, plus 1 805 806.. _TYPE_BLOCK: 807 808TYPE_BLOCK Contents 809------------------- 810 811The ``TYPE_BLOCK`` block (id 10) contains records which constitute a table of 812type operator entries used to represent types referenced within an LLVM 813module. Each record (with the exception of `NUMENTRY`_) generates a single type 814table entry, which may be referenced by 0-based index from instructions, 815constants, metadata, type symbol table entries, or other type operator records. 816 817Entries within ``TYPE_BLOCK`` are constructed to ensure that each entry is 818unique (i.e., no two indicies represent structurally equivalent types). 819 820.. _TYPE_CODE_NUMENTRY: 821.. _NUMENTRY: 822 823TYPE_CODE_NUMENTRY Record 824^^^^^^^^^^^^^^^^^^^^^^^^^ 825 826``[NUMENTRY, numentries]`` 827 828The ``NUMENTRY`` record (code 1) contains a single value which indicates the 829total number of type code entries in the type table of the module. If present, 830``NUMENTRY`` should be the first record in the block. 831 832TYPE_CODE_VOID Record 833^^^^^^^^^^^^^^^^^^^^^ 834 835``[VOID]`` 836 837The ``VOID`` record (code 2) adds a ``void`` type to the type table. 838 839TYPE_CODE_HALF Record 840^^^^^^^^^^^^^^^^^^^^^ 841 842``[HALF]`` 843 844The ``HALF`` record (code 10) adds a ``half`` (16-bit floating point) type to 845the type table. 846 847TYPE_CODE_FLOAT Record 848^^^^^^^^^^^^^^^^^^^^^^ 849 850``[FLOAT]`` 851 852The ``FLOAT`` record (code 3) adds a ``float`` (32-bit floating point) type to 853the type table. 854 855TYPE_CODE_DOUBLE Record 856^^^^^^^^^^^^^^^^^^^^^^^ 857 858``[DOUBLE]`` 859 860The ``DOUBLE`` record (code 4) adds a ``double`` (64-bit floating point) type to 861the type table. 862 863TYPE_CODE_LABEL Record 864^^^^^^^^^^^^^^^^^^^^^^ 865 866``[LABEL]`` 867 868The ``LABEL`` record (code 5) adds a ``label`` type to the type table. 869 870TYPE_CODE_OPAQUE Record 871^^^^^^^^^^^^^^^^^^^^^^^ 872 873``[OPAQUE]`` 874 875The ``OPAQUE`` record (code 6) adds an ``opaque`` type to the type table. Note 876that distinct ``opaque`` types are not unified. 877 878TYPE_CODE_INTEGER Record 879^^^^^^^^^^^^^^^^^^^^^^^^ 880 881``[INTEGER, width]`` 882 883The ``INTEGER`` record (code 7) adds an integer type to the type table. The 884single *width* field indicates the width of the integer type. 885 886TYPE_CODE_POINTER Record 887^^^^^^^^^^^^^^^^^^^^^^^^ 888 889``[POINTER, pointee type, address space]`` 890 891The ``POINTER`` record (code 8) adds a pointer type to the type table. The 892operand fields are 893 894* *pointee type*: The type index of the pointed-to type 895 896* *address space*: If supplied, the target-specific numbered address space where 897 the pointed-to object resides. Otherwise, the default address space is zero. 898 899TYPE_CODE_FUNCTION Record 900^^^^^^^^^^^^^^^^^^^^^^^^^ 901 902``[FUNCTION, vararg, ignored, retty, ...paramty... ]`` 903 904The ``FUNCTION`` record (code 9) adds a function type to the type table. The 905operand fields are 906 907* *vararg*: Non-zero if the type represents a varargs function 908 909* *ignored*: This value field is present for backward compatibility only, and is 910 ignored 911 912* *retty*: The type index of the function's return type 913 914* *paramty*: Zero or more type indices representing the parameter types of the 915 function 916 917TYPE_CODE_STRUCT Record 918^^^^^^^^^^^^^^^^^^^^^^^ 919 920``[STRUCT, ispacked, ...eltty...]`` 921 922The ``STRUCT`` record (code 10) adds a struct type to the type table. The 923operand fields are 924 925* *ispacked*: Non-zero if the type represents a packed structure 926 927* *eltty*: Zero or more type indices representing the element types of the 928 structure 929 930TYPE_CODE_ARRAY Record 931^^^^^^^^^^^^^^^^^^^^^^ 932 933``[ARRAY, numelts, eltty]`` 934 935The ``ARRAY`` record (code 11) adds an array type to the type table. The 936operand fields are 937 938* *numelts*: The number of elements in arrays of this type 939 940* *eltty*: The type index of the array element type 941 942TYPE_CODE_VECTOR Record 943^^^^^^^^^^^^^^^^^^^^^^^ 944 945``[VECTOR, numelts, eltty]`` 946 947The ``VECTOR`` record (code 12) adds a vector type to the type table. The 948operand fields are 949 950* *numelts*: The number of elements in vectors of this type 951 952* *eltty*: The type index of the vector element type 953 954TYPE_CODE_X86_FP80 Record 955^^^^^^^^^^^^^^^^^^^^^^^^^ 956 957``[X86_FP80]`` 958 959The ``X86_FP80`` record (code 13) adds an ``x86_fp80`` (80-bit floating point) 960type to the type table. 961 962TYPE_CODE_FP128 Record 963^^^^^^^^^^^^^^^^^^^^^^ 964 965``[FP128]`` 966 967The ``FP128`` record (code 14) adds an ``fp128`` (128-bit floating point) type 968to the type table. 969 970TYPE_CODE_PPC_FP128 Record 971^^^^^^^^^^^^^^^^^^^^^^^^^^ 972 973``[PPC_FP128]`` 974 975The ``PPC_FP128`` record (code 15) adds a ``ppc_fp128`` (128-bit floating point) 976type to the type table. 977 978TYPE_CODE_METADATA Record 979^^^^^^^^^^^^^^^^^^^^^^^^^ 980 981``[METADATA]`` 982 983The ``METADATA`` record (code 16) adds a ``metadata`` type to the type table. 984 985.. _CONSTANTS_BLOCK: 986 987CONSTANTS_BLOCK Contents 988------------------------ 989 990The ``CONSTANTS_BLOCK`` block (id 11) ... 991 992.. _FUNCTION_BLOCK: 993 994FUNCTION_BLOCK Contents 995----------------------- 996 997The ``FUNCTION_BLOCK`` block (id 12) ... 998 999In addition to the record types described below, a ``FUNCTION_BLOCK`` block may 1000contain the following sub-blocks: 1001 1002* `CONSTANTS_BLOCK`_ 1003* `VALUE_SYMTAB_BLOCK`_ 1004* `METADATA_ATTACHMENT`_ 1005 1006.. _TYPE_SYMTAB_BLOCK: 1007 1008TYPE_SYMTAB_BLOCK Contents 1009-------------------------- 1010 1011The ``TYPE_SYMTAB_BLOCK`` block (id 13) contains entries which map between 1012module-level named types and their corresponding type indices. 1013 1014.. _TST_CODE_ENTRY: 1015 1016TST_CODE_ENTRY Record 1017^^^^^^^^^^^^^^^^^^^^^ 1018 1019``[ENTRY, typeid, ...string...]`` 1020 1021The ``ENTRY`` record (code 1) contains a variable number of values, with the 1022first giving the type index of the designated type, and the remaining values 1023giving the character codes of the type name. Each entry corresponds to a single 1024named type. 1025 1026.. _VALUE_SYMTAB_BLOCK: 1027 1028VALUE_SYMTAB_BLOCK Contents 1029--------------------------- 1030 1031The ``VALUE_SYMTAB_BLOCK`` block (id 14) ... 1032 1033.. _METADATA_BLOCK: 1034 1035METADATA_BLOCK Contents 1036----------------------- 1037 1038The ``METADATA_BLOCK`` block (id 15) ... 1039 1040.. _METADATA_ATTACHMENT: 1041 1042METADATA_ATTACHMENT Contents 1043---------------------------- 1044 1045The ``METADATA_ATTACHMENT`` block (id 16) ... 1046