1.. role:: raw-html(raw) 2 :format: html 3 4======================== 5LLVM Bitcode File Format 6======================== 7 8.. contents:: 9 :local: 10 11Abstract 12======== 13 14This document describes the LLVM bitstream file format and the encoding of the 15LLVM IR into it. 16 17Overview 18======== 19 20What is commonly known as the LLVM bitcode file format (also, sometimes 21anachronistically known as bytecode) is actually two things: a `bitstream 22container format`_ and an `encoding of LLVM IR`_ into the container format. 23 24The bitstream format is an abstract encoding of structured data, very similar to 25XML in some ways. Like XML, bitstream files contain tags, and nested 26structures, and you can parse the file without having to understand the tags. 27Unlike XML, the bitstream format is a binary encoding, and unlike XML it 28provides a mechanism for the file to self-describe "abbreviations", which are 29effectively size optimizations for the content. 30 31LLVM IR files may be optionally embedded into a `wrapper`_ structure, or in a 32`native object file`_. Both of these mechanisms make it easy to embed extra 33data along with LLVM IR files. 34 35This document first describes the LLVM bitstream format, describes the wrapper 36format, then describes the record structure used by LLVM IR files. 37 38.. _bitstream container format: 39 40Bitstream Format 41================ 42 43The bitstream format is literally a stream of bits, with a very simple 44structure. This structure consists of the following concepts: 45 46* A "`magic number`_" that identifies the contents of the stream. 47 48* Encoding `primitives`_ like variable bit-rate integers. 49 50* `Blocks`_, which define nested content. 51 52* `Data Records`_, which describe entities within the file. 53 54* Abbreviations, which specify compression optimizations for the file. 55 56Note that the :doc:`llvm-bcanalyzer <CommandGuide/llvm-bcanalyzer>` tool can be 57used to dump and inspect arbitrary bitstreams, which is very useful for 58understanding the encoding. 59 60.. _magic number: 61 62Magic Numbers 63------------- 64 65The first two bytes of a bitcode file are 'BC' (``0x42``, ``0x43``). The second 66two bytes are an application-specific magic number. Generic bitcode tools can 67look at only the first two bytes to verify the file is bitcode, while 68application-specific programs will want to look at all four. 69 70.. _primitives: 71 72Primitives 73---------- 74 75A bitstream literally consists of a stream of bits, which are read in order 76starting with the least significant bit of each byte. The stream is made up of 77a number of primitive values that encode a stream of unsigned integer values. 78These integers are encoded in two ways: either as `Fixed Width Integers`_ or as 79`Variable Width Integers`_. 80 81.. _Fixed Width Integers: 82.. _fixed-width value: 83 84Fixed Width Integers 85^^^^^^^^^^^^^^^^^^^^ 86 87Fixed-width integer values have their low bits emitted directly to the file. 88For example, a 3-bit integer value encodes 1 as 001. Fixed width integers are 89used when there are a well-known number of options for a field. For example, 90boolean values are usually encoded with a 1-bit wide integer. 91 92.. _Variable Width Integers: 93.. _Variable Width Integer: 94.. _variable-width value: 95 96Variable Width Integers 97^^^^^^^^^^^^^^^^^^^^^^^ 98 99Variable-width integer (VBR) values encode values of arbitrary size, optimizing 100for the case where the values are small. Given a 4-bit VBR field, any 3-bit 101value (0 through 7) is encoded directly, with the high bit set to zero. Values 102larger than N-1 bits emit their bits in a series of N-1 bit chunks, where all 103but the last set the high bit. 104 105For example, the value 27 (0x1B) is encoded as 1011 0011 when emitted as a vbr4 106value. The first set of four bits indicates the value 3 (011) with a 107continuation piece (indicated by a high bit of 1). The next word indicates a 108value of 24 (011 << 3) with no continuation. The sum (3+24) yields the value 10927. 110 111.. _char6-encoded value: 112 1136-bit characters 114^^^^^^^^^^^^^^^^ 115 1166-bit characters encode common characters into a fixed 6-bit field. They 117represent the following characters with the following 6-bit values: 118 119:: 120 121 'a' .. 'z' --- 0 .. 25 122 'A' .. 'Z' --- 26 .. 51 123 '0' .. '9' --- 52 .. 61 124 '.' --- 62 125 '_' --- 63 126 127This encoding is only suitable for encoding characters and strings that consist 128only of the above characters. It is completely incapable of encoding characters 129not in the set. 130 131Word Alignment 132^^^^^^^^^^^^^^ 133 134Occasionally, it is useful to emit zero bits until the bitstream is a multiple 135of 32 bits. This ensures that the bit position in the stream can be represented 136as a multiple of 32-bit words. 137 138Abbreviation IDs 139---------------- 140 141A bitstream is a sequential series of `Blocks`_ and `Data Records`_. Both of 142these start with an abbreviation ID encoded as a fixed-bitwidth field. The 143width is specified by the current block, as described below. The value of the 144abbreviation ID specifies either a builtin ID (which have special meanings, 145defined below) or one of the abbreviation IDs defined for the current block by 146the stream itself. 147 148The set of builtin abbrev IDs is: 149 150* 0 - `END_BLOCK`_ --- This abbrev ID marks the end of the current block. 151 152* 1 - `ENTER_SUBBLOCK`_ --- This abbrev ID marks the beginning of a new 153 block. 154 155* 2 - `DEFINE_ABBREV`_ --- This defines a new abbreviation. 156 157* 3 - `UNABBREV_RECORD`_ --- This ID specifies the definition of an 158 unabbreviated record. 159 160Abbreviation IDs 4 and above are defined by the stream itself, and specify an 161`abbreviated record encoding`_. 162 163.. _Blocks: 164 165Blocks 166------ 167 168Blocks in a bitstream denote nested regions of the stream, and are identified by 169a content-specific id number (for example, LLVM IR uses an ID of 12 to represent 170function bodies). Block IDs 0-7 are reserved for `standard blocks`_ whose 171meaning is defined by Bitcode; block IDs 8 and greater are application 172specific. Nested blocks capture the hierarchical structure of the data encoded 173in it, and various properties are associated with blocks as the file is parsed. 174Block definitions allow the reader to efficiently skip blocks in constant time 175if the reader wants a summary of blocks, or if it wants to efficiently skip data 176it does not understand. The LLVM IR reader uses this mechanism to skip function 177bodies, lazily reading them on demand. 178 179When reading and encoding the stream, several properties are maintained for the 180block. In particular, each block maintains: 181 182#. A current abbrev id width. This value starts at 2 at the beginning of the 183 stream, and is set every time a block record is entered. The block entry 184 specifies the abbrev id width for the body of the block. 185 186#. A set of abbreviations. Abbreviations may be defined within a block, in 187 which case they are only defined in that block (neither subblocks nor 188 enclosing blocks see the abbreviation). Abbreviations can also be defined 189 inside a `BLOCKINFO`_ block, in which case they are defined in all blocks 190 that match the ID that the ``BLOCKINFO`` block is describing. 191 192As sub blocks are entered, these properties are saved and the new sub-block has 193its own set of abbreviations, and its own abbrev id width. When a sub-block is 194popped, the saved values are restored. 195 196.. _ENTER_SUBBLOCK: 197 198ENTER_SUBBLOCK Encoding 199^^^^^^^^^^^^^^^^^^^^^^^ 200 201:raw-html:`<tt>` 202[ENTER_SUBBLOCK, blockid\ :sub:`vbr8`, newabbrevlen\ :sub:`vbr4`, <align32bits>, blocklen_32] 203:raw-html:`</tt>` 204 205The ``ENTER_SUBBLOCK`` abbreviation ID specifies the start of a new block 206record. The ``blockid`` value is encoded as an 8-bit VBR identifier, and 207indicates the type of block being entered, which can be a `standard block`_ or 208an application-specific block. The ``newabbrevlen`` value is a 4-bit VBR, which 209specifies the abbrev id width for the sub-block. The ``blocklen`` value is a 21032-bit aligned value that specifies the size of the subblock in 32-bit 211words. This value allows the reader to skip over the entire block in one jump. 212 213.. _END_BLOCK: 214 215END_BLOCK Encoding 216^^^^^^^^^^^^^^^^^^ 217 218``[END_BLOCK, <align32bits>]`` 219 220The ``END_BLOCK`` abbreviation ID specifies the end of the current block record. 221Its end is aligned to 32-bits to ensure that the size of the block is an even 222multiple of 32-bits. 223 224.. _Data Records: 225 226Data Records 227------------ 228 229Data records consist of a record code and a number of (up to) 64-bit integer 230values. The interpretation of the code and values is application specific and 231may vary between different block types. Records can be encoded either using an 232unabbrev record, or with an abbreviation. In the LLVM IR format, for example, 233there is a record which encodes the target triple of a module. The code is 234``MODULE_CODE_TRIPLE``, and the values of the record are the ASCII codes for the 235characters in the string. 236 237.. _UNABBREV_RECORD: 238 239UNABBREV_RECORD Encoding 240^^^^^^^^^^^^^^^^^^^^^^^^ 241 242:raw-html:`<tt>` 243[UNABBREV_RECORD, code\ :sub:`vbr6`, numops\ :sub:`vbr6`, op0\ :sub:`vbr6`, op1\ :sub:`vbr6`, ...] 244:raw-html:`</tt>` 245 246An ``UNABBREV_RECORD`` provides a default fallback encoding, which is both 247completely general and extremely inefficient. It can describe an arbitrary 248record by emitting the code and operands as VBRs. 249 250For example, emitting an LLVM IR target triple as an unabbreviated record 251requires emitting the ``UNABBREV_RECORD`` abbrevid, a vbr6 for the 252``MODULE_CODE_TRIPLE`` code, a vbr6 for the length of the string, which is equal 253to the number of operands, and a vbr6 for each character. Because there are no 254letters with values less than 32, each letter would need to be emitted as at 255least a two-part VBR, which means that each letter would require at least 12 256bits. This is not an efficient encoding, but it is fully general. 257 258.. _abbreviated record encoding: 259 260Abbreviated Record Encoding 261^^^^^^^^^^^^^^^^^^^^^^^^^^^ 262 263``[<abbrevid>, fields...]`` 264 265An abbreviated record is a abbreviation id followed by a set of fields that are 266encoded according to the `abbreviation definition`_. This allows records to be 267encoded significantly more densely than records encoded with the 268`UNABBREV_RECORD`_ type, and allows the abbreviation types to be specified in 269the stream itself, which allows the files to be completely self describing. The 270actual encoding of abbreviations is defined below. 271 272The record code, which is the first field of an abbreviated record, may be 273encoded in the abbreviation definition (as a literal operand) or supplied in the 274abbreviated record (as a Fixed or VBR operand value). 275 276.. _abbreviation definition: 277 278Abbreviations 279------------- 280 281Abbreviations are an important form of compression for bitstreams. The idea is 282to specify a dense encoding for a class of records once, then use that encoding 283to emit many records. It takes space to emit the encoding into the file, but 284the space is recouped (hopefully plus some) when the records that use it are 285emitted. 286 287Abbreviations can be determined dynamically per client, per file. Because the 288abbreviations are stored in the bitstream itself, different streams of the same 289format can contain different sets of abbreviations according to the needs of the 290specific stream. As a concrete example, LLVM IR files usually emit an 291abbreviation for binary operators. If a specific LLVM module contained no or 292few binary operators, the abbreviation does not need to be emitted. 293 294.. _DEFINE_ABBREV: 295 296DEFINE_ABBREV Encoding 297^^^^^^^^^^^^^^^^^^^^^^ 298 299:raw-html:`<tt>` 300[DEFINE_ABBREV, numabbrevops\ :sub:`vbr5`, abbrevop0, abbrevop1, ...] 301:raw-html:`</tt>` 302 303A ``DEFINE_ABBREV`` record adds an abbreviation to the list of currently defined 304abbreviations in the scope of this block. This definition only exists inside 305this immediate block --- it is not visible in subblocks or enclosing blocks. 306Abbreviations are implicitly assigned IDs sequentially starting from 4 (the 307first application-defined abbreviation ID). Any abbreviations defined in a 308``BLOCKINFO`` record for the particular block type receive IDs first, in order, 309followed by any abbreviations defined within the block itself. Abbreviated data 310records reference this ID to indicate what abbreviation they are invoking. 311 312An abbreviation definition consists of the ``DEFINE_ABBREV`` abbrevid followed 313by a VBR that specifies the number of abbrev operands, then the abbrev operands 314themselves. Abbreviation operands come in three forms. They all start with a 315single bit that indicates whether the abbrev operand is a literal operand (when 316the bit is 1) or an encoding operand (when the bit is 0). 317 318#. Literal operands --- :raw-html:`<tt>` [1\ :sub:`1`, litvalue\ 319 :sub:`vbr8`] :raw-html:`</tt>` --- Literal operands specify that the value in 320 the result is always a single specific value. This specific value is emitted 321 as a vbr8 after the bit indicating that it is a literal operand. 322 323#. Encoding info without data --- :raw-html:`<tt>` [0\ :sub:`1`, encoding\ 324 :sub:`3`] :raw-html:`</tt>` --- Operand encodings that do not have extra data 325 are just emitted as their code. 326 327#. Encoding info with data --- :raw-html:`<tt>` [0\ :sub:`1`, encoding\ 328 :sub:`3`, value\ :sub:`vbr5`] :raw-html:`</tt>` --- Operand encodings that do 329 have extra data are emitted as their code, followed by the extra data. 330 331The possible operand encodings are: 332 333* Fixed (code 1): The field should be emitted as a `fixed-width value`_, whose 334 width is specified by the operand's extra data. 335 336* VBR (code 2): The field should be emitted as a `variable-width value`_, whose 337 width is specified by the operand's extra data. 338 339* Array (code 3): This field is an array of values. The array operand has no 340 extra data, but expects another operand to follow it, indicating the element 341 type of the array. When reading an array in an abbreviated record, the first 342 integer is a vbr6 that indicates the array length, followed by the encoded 343 elements of the array. An array may only occur as the last operand of an 344 abbreviation (except for the one final operand that gives the array's 345 type). 346 347* Char6 (code 4): This field should be emitted as a `char6-encoded value`_. 348 This operand type takes no extra data. Char6 encoding is normally used as an 349 array element type. 350 351* Blob (code 5): This field is emitted as a vbr6, followed by padding to a 352 32-bit boundary (for alignment) and an array of 8-bit objects. The array of 353 bytes is further followed by tail padding to ensure that its total length is a 354 multiple of 4 bytes. This makes it very efficient for the reader to decode 355 the data without having to make a copy of it: it can use a pointer to the data 356 in the mapped in file and poke directly at it. A blob may only occur as the 357 last operand of an abbreviation. 358 359For example, target triples in LLVM modules are encoded as a record of the form 360``[TRIPLE, 'a', 'b', 'c', 'd']``. Consider if the bitstream emitted the 361following abbrev entry: 362 363:: 364 365 [0, Fixed, 4] 366 [0, Array] 367 [0, Char6] 368 369When emitting a record with this abbreviation, the above entry would be emitted 370as: 371 372:raw-html:`<tt><blockquote>` 373[4\ :sub:`abbrevwidth`, 2\ :sub:`4`, 4\ :sub:`vbr6`, 0\ :sub:`6`, 1\ :sub:`6`, 2\ :sub:`6`, 3\ :sub:`6`] 374:raw-html:`</blockquote></tt>` 375 376These values are: 377 378#. The first value, 4, is the abbreviation ID for this abbreviation. 379 380#. The second value, 2, is the record code for ``TRIPLE`` records within LLVM IR 381 file ``MODULE_BLOCK`` blocks. 382 383#. The third value, 4, is the length of the array. 384 385#. The rest of the values are the char6 encoded values for ``"abcd"``. 386 387With this abbreviation, the triple is emitted with only 37 bits (assuming a 388abbrev id width of 3). Without the abbreviation, significantly more space would 389be required to emit the target triple. Also, because the ``TRIPLE`` value is 390not emitted as a literal in the abbreviation, the abbreviation can also be used 391for any other string value. 392 393.. _standard blocks: 394.. _standard block: 395 396Standard Blocks 397--------------- 398 399In addition to the basic block structure and record encodings, the bitstream 400also defines specific built-in block types. These block types specify how the 401stream is to be decoded or other metadata. In the future, new standard blocks 402may be added. Block IDs 0-7 are reserved for standard blocks. 403 404.. _BLOCKINFO: 405 406#0 - BLOCKINFO Block 407^^^^^^^^^^^^^^^^^^^^ 408 409The ``BLOCKINFO`` block allows the description of metadata for other blocks. 410The currently specified records are: 411 412:: 413 414 [SETBID (#1), blockid] 415 [DEFINE_ABBREV, ...] 416 [BLOCKNAME, ...name...] 417 [SETRECORDNAME, RecordID, ...name...] 418 419The ``SETBID`` record (code 1) indicates which block ID is being described. 420``SETBID`` records can occur multiple times throughout the block to change which 421block ID is being described. There must be a ``SETBID`` record prior to any 422other records. 423 424Standard ``DEFINE_ABBREV`` records can occur inside ``BLOCKINFO`` blocks, but 425unlike their occurrence in normal blocks, the abbreviation is defined for blocks 426matching the block ID we are describing, *not* the ``BLOCKINFO`` block 427itself. The abbreviations defined in ``BLOCKINFO`` blocks receive abbreviation 428IDs as described in `DEFINE_ABBREV`_. 429 430The ``BLOCKNAME`` record (code 2) can optionally occur in this block. The 431elements of the record are the bytes of the string name of the block. 432llvm-bcanalyzer can use this to dump out bitcode files symbolically. 433 434The ``SETRECORDNAME`` record (code 3) can also optionally occur in this block. 435The first operand value is a record ID number, and the rest of the elements of 436the record are the bytes for the string name of the record. llvm-bcanalyzer can 437use this to dump out bitcode files symbolically. 438 439Note that although the data in ``BLOCKINFO`` blocks is described as "metadata," 440the abbreviations they contain are essential for parsing records from the 441corresponding blocks. It is not safe to skip them. 442 443.. _wrapper: 444 445Bitcode Wrapper Format 446====================== 447 448Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper 449structure. This structure contains a simple header that indicates the offset 450and size of the embedded BC file. This allows additional information to be 451stored alongside the BC file. The structure of this file header is: 452 453:raw-html:`<tt><blockquote>` 454[Magic\ :sub:`32`, Version\ :sub:`32`, Offset\ :sub:`32`, Size\ :sub:`32`, CPUType\ :sub:`32`] 455:raw-html:`</blockquote></tt>` 456 457Each of the fields are 32-bit fields stored in little endian form (as with the 458rest of the bitcode file fields). The Magic number is always ``0x0B17C0DE`` and 459the version is currently always ``0``. The Offset field is the offset in bytes 460to the start of the bitcode stream in the file, and the Size field is the size 461in bytes of the stream. CPUType is a target-specific value that can be used to 462encode the CPU of the target. 463 464.. _native object file: 465 466Native Object File Wrapper Format 467================================= 468 469Bitcode files for LLVM IR may also be wrapped in a native object file 470(i.e. ELF, COFF, Mach-O). The bitcode must be stored in a section of the object 471file named ``__LLVM,__bitcode`` for MachO and ``.llvmbc`` for the other object 472formats. This wrapper format is useful for accommodating LTO in compilation 473pipelines where intermediate objects must be native object files which contain 474metadata in other sections. 475 476Not all tools support this format. 477 478.. _encoding of LLVM IR: 479 480LLVM IR Encoding 481================ 482 483LLVM IR is encoded into a bitstream by defining blocks and records. It uses 484blocks for things like constant pools, functions, symbol tables, etc. It uses 485records for things like instructions, global variable descriptors, type 486descriptions, etc. This document does not describe the set of abbreviations 487that the writer uses, as these are fully self-described in the file, and the 488reader is not allowed to build in any knowledge of this. 489 490Basics 491------ 492 493LLVM IR Magic Number 494^^^^^^^^^^^^^^^^^^^^ 495 496The magic number for LLVM IR files is: 497 498:raw-html:`<tt><blockquote>` 499[0x0\ :sub:`4`, 0xC\ :sub:`4`, 0xE\ :sub:`4`, 0xD\ :sub:`4`] 500:raw-html:`</blockquote></tt>` 501 502When combined with the bitcode magic number and viewed as bytes, this is 503``"BC 0xC0DE"``. 504 505.. _Signed VBRs: 506 507Signed VBRs 508^^^^^^^^^^^ 509 510`Variable Width Integer`_ encoding is an efficient way to encode arbitrary sized 511unsigned values, but is an extremely inefficient for encoding signed values, as 512signed values are otherwise treated as maximally large unsigned values. 513 514As such, signed VBR values of a specific width are emitted as follows: 515 516* Positive values are emitted as VBRs of the specified width, but with their 517 value shifted left by one. 518 519* Negative values are emitted as VBRs of the specified width, but the negated 520 value is shifted left by one, and the low bit is set. 521 522With this encoding, small positive and small negative values can both be emitted 523efficiently. Signed VBR encoding is used in ``CST_CODE_INTEGER`` and 524``CST_CODE_WIDE_INTEGER`` records within ``CONSTANTS_BLOCK`` blocks. 525It is also used for phi instruction operands in `MODULE_CODE_VERSION`_ 1. 526 527LLVM IR Blocks 528^^^^^^^^^^^^^^ 529 530LLVM IR is defined with the following blocks: 531 532* 8 --- `MODULE_BLOCK`_ --- This is the top-level block that contains the entire 533 module, and describes a variety of per-module information. 534 535* 9 --- `PARAMATTR_BLOCK`_ --- This enumerates the parameter attributes. 536 537* 10 --- `PARAMATTR_GROUP_BLOCK`_ --- This describes the attribute group table. 538 539* 11 --- `CONSTANTS_BLOCK`_ --- This describes constants for a module or 540 function. 541 542* 12 --- `FUNCTION_BLOCK`_ --- This describes a function body. 543 544* 14 --- `VALUE_SYMTAB_BLOCK`_ --- This describes a value symbol table. 545 546* 15 --- `METADATA_BLOCK`_ --- This describes metadata items. 547 548* 16 --- `METADATA_ATTACHMENT`_ --- This contains records associating metadata 549 with function instruction values. 550 551* 17 --- `TYPE_BLOCK`_ --- This describes all of the types in the module. 552 553* 23 --- `STRTAB_BLOCK`_ --- The bitcode file's string table. 554 555.. _MODULE_BLOCK: 556 557MODULE_BLOCK Contents 558--------------------- 559 560The ``MODULE_BLOCK`` block (id 8) is the top-level block for LLVM bitcode files, 561and each bitcode file must contain exactly one. In addition to records 562(described below) containing information about the module, a ``MODULE_BLOCK`` 563block may contain the following sub-blocks: 564 565* `BLOCKINFO`_ 566* `PARAMATTR_BLOCK`_ 567* `PARAMATTR_GROUP_BLOCK`_ 568* `TYPE_BLOCK`_ 569* `VALUE_SYMTAB_BLOCK`_ 570* `CONSTANTS_BLOCK`_ 571* `FUNCTION_BLOCK`_ 572* `METADATA_BLOCK`_ 573 574.. _MODULE_CODE_VERSION: 575 576MODULE_CODE_VERSION Record 577^^^^^^^^^^^^^^^^^^^^^^^^^^ 578 579``[VERSION, version#]`` 580 581The ``VERSION`` record (code 1) contains a single value indicating the format 582version. Versions 0, 1 and 2 are supported at this time. The difference between 583version 0 and 1 is in the encoding of instruction operands in 584each `FUNCTION_BLOCK`_. 585 586In version 0, each value defined by an instruction is assigned an ID 587unique to the function. Function-level value IDs are assigned starting from 588``NumModuleValues`` since they share the same namespace as module-level 589values. The value enumerator resets after each function. When a value is 590an operand of an instruction, the value ID is used to represent the operand. 591For large functions or large modules, these operand values can be large. 592 593The encoding in version 1 attempts to avoid large operand values 594in common cases. Instead of using the value ID directly, operands are 595encoded as relative to the current instruction. Thus, if an operand 596is the value defined by the previous instruction, the operand 597will be encoded as 1. 598 599For example, instead of 600 601.. code-block:: none 602 603 #n = load #n-1 604 #n+1 = icmp eq #n, #const0 605 br #n+1, label #(bb1), label #(bb2) 606 607version 1 will encode the instructions as 608 609.. code-block:: none 610 611 #n = load #1 612 #n+1 = icmp eq #1, (#n+1)-#const0 613 br #1, label #(bb1), label #(bb2) 614 615Note in the example that operands which are constants also use 616the relative encoding, while operands like basic block labels 617do not use the relative encoding. 618 619Forward references will result in a negative value. 620This can be inefficient, as operands are normally encoded 621as unsigned VBRs. However, forward references are rare, except in the 622case of phi instructions. For phi instructions, operands are encoded as 623`Signed VBRs`_ to deal with forward references. 624 625In version 2, the meaning of module records ``FUNCTION``, ``GLOBALVAR``, 626``ALIAS``, ``IFUNC`` and ``COMDAT`` change such that the first two operands 627specify an offset and size of a string in a string table (see `STRTAB_BLOCK 628Contents`_), the function name is removed from the ``FNENTRY`` record in the 629value symbol table, and the top-level ``VALUE_SYMTAB_BLOCK`` may only contain 630``FNENTRY`` records. 631 632MODULE_CODE_TRIPLE Record 633^^^^^^^^^^^^^^^^^^^^^^^^^ 634 635``[TRIPLE, ...string...]`` 636 637The ``TRIPLE`` record (code 2) contains a variable number of values representing 638the bytes of the ``target triple`` specification string. 639 640MODULE_CODE_DATALAYOUT Record 641^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 642 643``[DATALAYOUT, ...string...]`` 644 645The ``DATALAYOUT`` record (code 3) contains a variable number of values 646representing the bytes of the ``target datalayout`` specification string. 647 648MODULE_CODE_ASM Record 649^^^^^^^^^^^^^^^^^^^^^^ 650 651``[ASM, ...string...]`` 652 653The ``ASM`` record (code 4) contains a variable number of values representing 654the bytes of ``module asm`` strings, with individual assembly blocks separated 655by newline (ASCII 10) characters. 656 657.. _MODULE_CODE_SECTIONNAME: 658 659MODULE_CODE_SECTIONNAME Record 660^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 661 662``[SECTIONNAME, ...string...]`` 663 664The ``SECTIONNAME`` record (code 5) contains a variable number of values 665representing the bytes of a single section name string. There should be one 666``SECTIONNAME`` record for each section name referenced (e.g., in global 667variable or function ``section`` attributes) within the module. These records 668can be referenced by the 1-based index in the *section* fields of ``GLOBALVAR`` 669or ``FUNCTION`` records. 670 671MODULE_CODE_DEPLIB Record 672^^^^^^^^^^^^^^^^^^^^^^^^^ 673 674``[DEPLIB, ...string...]`` 675 676The ``DEPLIB`` record (code 6) contains a variable number of values representing 677the bytes of a single dependent library name string, one of the libraries 678mentioned in a ``deplibs`` declaration. There should be one ``DEPLIB`` record 679for each library name referenced. 680 681MODULE_CODE_GLOBALVAR Record 682^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 683 684``[GLOBALVAR, strtab offset, strtab size, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal, unnamed_addr, externally_initialized, dllstorageclass, comdat, attributes, preemptionspecifier]`` 685 686The ``GLOBALVAR`` record (code 7) marks the declaration or definition of a 687global variable. The operand fields are: 688 689* *strtab offset*, *strtab size*: Specifies the name of the global variable. 690 See `STRTAB_BLOCK Contents`_. 691 692* *pointer type*: The type index of the pointer type used to point to this 693 global variable 694 695* *isconst*: Non-zero if the variable is treated as constant within the module, 696 or zero if it is not 697 698* *initid*: If non-zero, the value index of the initializer for this variable, 699 plus 1. 700 701.. _linkage type: 702 703* *linkage*: An encoding of the linkage type for this variable: 704 705 * ``external``: code 0 706 * ``weak``: code 1 707 * ``appending``: code 2 708 * ``internal``: code 3 709 * ``linkonce``: code 4 710 * ``dllimport``: code 5 711 * ``dllexport``: code 6 712 * ``extern_weak``: code 7 713 * ``common``: code 8 714 * ``private``: code 9 715 * ``weak_odr``: code 10 716 * ``linkonce_odr``: code 11 717 * ``available_externally``: code 12 718 * deprecated : code 13 719 * deprecated : code 14 720 721* alignment*: The logarithm base 2 of the variable's requested alignment, plus 1 722 723* *section*: If non-zero, the 1-based section index in the table of 724 `MODULE_CODE_SECTIONNAME`_ entries. 725 726.. _visibility: 727 728* *visibility*: If present, an encoding of the visibility of this variable: 729 730 * ``default``: code 0 731 * ``hidden``: code 1 732 * ``protected``: code 2 733 734.. _bcthreadlocal: 735 736* *threadlocal*: If present, an encoding of the thread local storage mode of the 737 variable: 738 739 * ``not thread local``: code 0 740 * ``thread local; default TLS model``: code 1 741 * ``localdynamic``: code 2 742 * ``initialexec``: code 3 743 * ``localexec``: code 4 744 745.. _bcunnamedaddr: 746 747* *unnamed_addr*: If present, an encoding of the ``unnamed_addr`` attribute of this 748 variable: 749 750 * not ``unnamed_addr``: code 0 751 * ``unnamed_addr``: code 1 752 * ``local_unnamed_addr``: code 2 753 754.. _bcdllstorageclass: 755 756* *dllstorageclass*: If present, an encoding of the DLL storage class of this variable: 757 758 * ``default``: code 0 759 * ``dllimport``: code 1 760 * ``dllexport``: code 2 761 762* *comdat*: An encoding of the COMDAT of this function 763 764* *attributes*: If nonzero, the 1-based index into the table of AttributeLists. 765 766.. _bcpreemptionspecifier: 767 768* *preemptionspecifier*: If present, an encoding of the runtime preemption specifier of this variable: 769 770 * ``dso_preemptable``: code 0 771 * ``dso_local``: code 1 772 773.. _FUNCTION: 774 775MODULE_CODE_FUNCTION Record 776^^^^^^^^^^^^^^^^^^^^^^^^^^^ 777 778``[FUNCTION, strtab offset, strtab size, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc, prologuedata, dllstorageclass, comdat, prefixdata, personalityfn, preemptionspecifier]`` 779 780The ``FUNCTION`` record (code 8) marks the declaration or definition of a 781function. The operand fields are: 782 783* *strtab offset*, *strtab size*: Specifies the name of the function. 784 See `STRTAB_BLOCK Contents`_. 785 786* *type*: The type index of the function type describing this function 787 788* *callingconv*: The calling convention number: 789 * ``ccc``: code 0 790 * ``fastcc``: code 8 791 * ``coldcc``: code 9 792 * ``webkit_jscc``: code 12 793 * ``anyregcc``: code 13 794 * ``preserve_mostcc``: code 14 795 * ``preserve_allcc``: code 15 796 * ``swiftcc`` : code 16 797 * ``cxx_fast_tlscc``: code 17 798 * ``x86_stdcallcc``: code 64 799 * ``x86_fastcallcc``: code 65 800 * ``arm_apcscc``: code 66 801 * ``arm_aapcscc``: code 67 802 * ``arm_aapcs_vfpcc``: code 68 803 804* isproto*: Non-zero if this entry represents a declaration rather than a 805 definition 806 807* *linkage*: An encoding of the `linkage type`_ for this function 808 809* *paramattr*: If nonzero, the 1-based parameter attribute index into the table 810 of `PARAMATTR_CODE_ENTRY`_ entries. 811 812* *alignment*: The logarithm base 2 of the function's requested alignment, plus 813 1 814 815* *section*: If non-zero, the 1-based section index in the table of 816 `MODULE_CODE_SECTIONNAME`_ entries. 817 818* *visibility*: An encoding of the `visibility`_ of this function 819 820* *gc*: If present and nonzero, the 1-based garbage collector index in the table 821 of `MODULE_CODE_GCNAME`_ entries. 822 823* *unnamed_addr*: If present, an encoding of the 824 :ref:`unnamed_addr<bcunnamedaddr>` attribute of this function 825 826* *prologuedata*: If non-zero, the value index of the prologue data for this function, 827 plus 1. 828 829* *dllstorageclass*: An encoding of the 830 :ref:`dllstorageclass<bcdllstorageclass>` of this function 831 832* *comdat*: An encoding of the COMDAT of this function 833 834* *prefixdata*: If non-zero, the value index of the prefix data for this function, 835 plus 1. 836 837* *personalityfn*: If non-zero, the value index of the personality function for this function, 838 plus 1. 839 840* *preemptionspecifier*: If present, an encoding of the :ref:`runtime preemption specifier<bcpreemptionspecifier>` of this function. 841 842MODULE_CODE_ALIAS Record 843^^^^^^^^^^^^^^^^^^^^^^^^ 844 845``[ALIAS, strtab offset, strtab size, alias type, aliasee val#, linkage, visibility, dllstorageclass, threadlocal, unnamed_addr, preemptionspecifier]`` 846 847The ``ALIAS`` record (code 9) marks the definition of an alias. The operand 848fields are 849 850* *strtab offset*, *strtab size*: Specifies the name of the alias. 851 See `STRTAB_BLOCK Contents`_. 852 853* *alias type*: The type index of the alias 854 855* *aliasee val#*: The value index of the aliased value 856 857* *linkage*: An encoding of the `linkage type`_ for this alias 858 859* *visibility*: If present, an encoding of the `visibility`_ of the alias 860 861* *dllstorageclass*: If present, an encoding of the 862 :ref:`dllstorageclass<bcdllstorageclass>` of the alias 863 864* *threadlocal*: If present, an encoding of the 865 :ref:`thread local property<bcthreadlocal>` of the alias 866 867* *unnamed_addr*: If present, an encoding of the 868 :ref:`unnamed_addr<bcunnamedaddr>` attribute of this alias 869 870* *preemptionspecifier*: If present, an encoding of the :ref:`runtime preemption specifier<bcpreemptionspecifier>` of this alias. 871 872.. _MODULE_CODE_GCNAME: 873 874MODULE_CODE_GCNAME Record 875^^^^^^^^^^^^^^^^^^^^^^^^^ 876 877``[GCNAME, ...string...]`` 878 879The ``GCNAME`` record (code 11) contains a variable number of values 880representing the bytes of a single garbage collector name string. There should 881be one ``GCNAME`` record for each garbage collector name referenced in function 882``gc`` attributes within the module. These records can be referenced by 1-based 883index in the *gc* fields of ``FUNCTION`` records. 884 885.. _PARAMATTR_BLOCK: 886 887PARAMATTR_BLOCK Contents 888------------------------ 889 890The ``PARAMATTR_BLOCK`` block (id 9) contains a table of entries describing the 891attributes of function parameters. These entries are referenced by 1-based index 892in the *paramattr* field of module block `FUNCTION`_ records, or within the 893*attr* field of function block ``INST_INVOKE`` and ``INST_CALL`` records. 894 895Entries within ``PARAMATTR_BLOCK`` are constructed to ensure that each is unique 896(i.e., no two indices represent equivalent attribute lists). 897 898.. _PARAMATTR_CODE_ENTRY: 899 900PARAMATTR_CODE_ENTRY Record 901^^^^^^^^^^^^^^^^^^^^^^^^^^^ 902 903``[ENTRY, attrgrp0, attrgrp1, ...]`` 904 905The ``ENTRY`` record (code 2) contains a variable number of values describing a 906unique set of function parameter attributes. Each *attrgrp* value is used as a 907key with which to look up an entry in the the attribute group table described 908in the ``PARAMATTR_GROUP_BLOCK`` block. 909 910.. _PARAMATTR_CODE_ENTRY_OLD: 911 912PARAMATTR_CODE_ENTRY_OLD Record 913^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 914 915.. note:: 916 This is a legacy encoding for attributes, produced by LLVM versions 3.2 and 917 earlier. It is guaranteed to be understood by the current LLVM version, as 918 specified in the :ref:`IR backwards compatibility` policy. 919 920``[ENTRY, paramidx0, attr0, paramidx1, attr1...]`` 921 922The ``ENTRY`` record (code 1) contains an even number of values describing a 923unique set of function parameter attributes. Each *paramidx* value indicates 924which set of attributes is represented, with 0 representing the return value 925attributes, 0xFFFFFFFF representing function attributes, and other values 926representing 1-based function parameters. Each *attr* value is a bitmap with the 927following interpretation: 928 929* bit 0: ``zeroext`` 930* bit 1: ``signext`` 931* bit 2: ``noreturn`` 932* bit 3: ``inreg`` 933* bit 4: ``sret`` 934* bit 5: ``nounwind`` 935* bit 6: ``noalias`` 936* bit 7: ``byval`` 937* bit 8: ``nest`` 938* bit 9: ``readnone`` 939* bit 10: ``readonly`` 940* bit 11: ``noinline`` 941* bit 12: ``alwaysinline`` 942* bit 13: ``optsize`` 943* bit 14: ``ssp`` 944* bit 15: ``sspreq`` 945* bits 16-31: ``align n`` 946* bit 32: ``nocapture`` 947* bit 33: ``noredzone`` 948* bit 34: ``noimplicitfloat`` 949* bit 35: ``naked`` 950* bit 36: ``inlinehint`` 951* bits 37-39: ``alignstack n``, represented as the logarithm 952 base 2 of the requested alignment, plus 1 953 954.. _PARAMATTR_GROUP_BLOCK: 955 956PARAMATTR_GROUP_BLOCK Contents 957------------------------------ 958 959The ``PARAMATTR_GROUP_BLOCK`` block (id 10) contains a table of entries 960describing the attribute groups present in the module. These entries can be 961referenced within ``PARAMATTR_CODE_ENTRY`` entries. 962 963.. _PARAMATTR_GRP_CODE_ENTRY: 964 965PARAMATTR_GRP_CODE_ENTRY Record 966^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 967 968``[ENTRY, grpid, paramidx, attr0, attr1, ...]`` 969 970The ``ENTRY`` record (code 3) contains *grpid* and *paramidx* values, followed 971by a variable number of values describing a unique group of attributes. The 972*grpid* value is a unique key for the attribute group, which can be referenced 973within ``PARAMATTR_CODE_ENTRY`` entries. The *paramidx* value indicates which 974set of attributes is represented, with 0 representing the return value 975attributes, 0xFFFFFFFF representing function attributes, and other values 976representing 1-based function parameters. 977 978Each *attr* is itself represented as a variable number of values: 979 980``kind, key [, ...], [value [, ...]]`` 981 982Each attribute is either a well-known LLVM attribute (possibly with an integer 983value associated with it), or an arbitrary string (possibly with an arbitrary 984string value associated with it). The *kind* value is an integer code 985distinguishing between these possibilities: 986 987* code 0: well-known attribute 988* code 1: well-known attribute with an integer value 989* code 3: string attribute 990* code 4: string attribute with a string value 991 992For well-known attributes (code 0 or 1), the *key* value is an integer code 993identifying the attribute. For attributes with an integer argument (code 1), 994the *value* value indicates the argument. 995 996For string attributes (code 3 or 4), the *key* value is actually a variable 997number of values representing the bytes of a null-terminated string. For 998attributes with a string argument (code 4), the *value* value is similarly a 999variable number of values representing the bytes of a null-terminated string. 1000 1001The integer codes are mapped to well-known attributes as follows. 1002 1003* code 1: ``align(<n>)`` 1004* code 2: ``alwaysinline`` 1005* code 3: ``byval`` 1006* code 4: ``inlinehint`` 1007* code 5: ``inreg`` 1008* code 6: ``minsize`` 1009* code 7: ``naked`` 1010* code 8: ``nest`` 1011* code 9: ``noalias`` 1012* code 10: ``nobuiltin`` 1013* code 11: ``nocapture`` 1014* code 12: ``noduplicates`` 1015* code 13: ``noimplicitfloat`` 1016* code 14: ``noinline`` 1017* code 15: ``nonlazybind`` 1018* code 16: ``noredzone`` 1019* code 17: ``noreturn`` 1020* code 18: ``nounwind`` 1021* code 19: ``optsize`` 1022* code 20: ``readnone`` 1023* code 21: ``readonly`` 1024* code 22: ``returned`` 1025* code 23: ``returns_twice`` 1026* code 24: ``signext`` 1027* code 25: ``alignstack(<n>)`` 1028* code 26: ``ssp`` 1029* code 27: ``sspreq`` 1030* code 28: ``sspstrong`` 1031* code 29: ``sret`` 1032* code 30: ``sanitize_address`` 1033* code 31: ``sanitize_thread`` 1034* code 32: ``sanitize_memory`` 1035* code 33: ``uwtable`` 1036* code 34: ``zeroext`` 1037* code 35: ``builtin`` 1038* code 36: ``cold`` 1039* code 37: ``optnone`` 1040* code 38: ``inalloca`` 1041* code 39: ``nonnull`` 1042* code 40: ``jumptable`` 1043* code 41: ``dereferenceable(<n>)`` 1044* code 42: ``dereferenceable_or_null(<n>)`` 1045* code 43: ``convergent`` 1046* code 44: ``safestack`` 1047* code 45: ``argmemonly`` 1048* code 46: ``swiftself`` 1049* code 47: ``swifterror`` 1050* code 48: ``norecurse`` 1051* code 49: ``inaccessiblememonly`` 1052* code 50: ``inaccessiblememonly_or_argmemonly`` 1053* code 51: ``allocsize(<EltSizeParam>[, <NumEltsParam>])`` 1054* code 52: ``writeonly`` 1055 1056.. note:: 1057 The ``allocsize`` attribute has a special encoding for its arguments. Its two 1058 arguments, which are 32-bit integers, are packed into one 64-bit integer value 1059 (i.e. ``(EltSizeParam << 32) | NumEltsParam``), with ``NumEltsParam`` taking on 1060 the sentinel value -1 if it is not specified. 1061 1062.. _TYPE_BLOCK: 1063 1064TYPE_BLOCK Contents 1065------------------- 1066 1067The ``TYPE_BLOCK`` block (id 17) contains records which constitute a table of 1068type operator entries used to represent types referenced within an LLVM 1069module. Each record (with the exception of `NUMENTRY`_) generates a single type 1070table entry, which may be referenced by 0-based index from instructions, 1071constants, metadata, type symbol table entries, or other type operator records. 1072 1073Entries within ``TYPE_BLOCK`` are constructed to ensure that each entry is 1074unique (i.e., no two indices represent structurally equivalent types). 1075 1076.. _TYPE_CODE_NUMENTRY: 1077.. _NUMENTRY: 1078 1079TYPE_CODE_NUMENTRY Record 1080^^^^^^^^^^^^^^^^^^^^^^^^^ 1081 1082``[NUMENTRY, numentries]`` 1083 1084The ``NUMENTRY`` record (code 1) contains a single value which indicates the 1085total number of type code entries in the type table of the module. If present, 1086``NUMENTRY`` should be the first record in the block. 1087 1088TYPE_CODE_VOID Record 1089^^^^^^^^^^^^^^^^^^^^^ 1090 1091``[VOID]`` 1092 1093The ``VOID`` record (code 2) adds a ``void`` type to the type table. 1094 1095TYPE_CODE_HALF Record 1096^^^^^^^^^^^^^^^^^^^^^ 1097 1098``[HALF]`` 1099 1100The ``HALF`` record (code 10) adds a ``half`` (16-bit floating point) type to 1101the type table. 1102 1103TYPE_CODE_FLOAT Record 1104^^^^^^^^^^^^^^^^^^^^^^ 1105 1106``[FLOAT]`` 1107 1108The ``FLOAT`` record (code 3) adds a ``float`` (32-bit floating point) type to 1109the type table. 1110 1111TYPE_CODE_DOUBLE Record 1112^^^^^^^^^^^^^^^^^^^^^^^ 1113 1114``[DOUBLE]`` 1115 1116The ``DOUBLE`` record (code 4) adds a ``double`` (64-bit floating point) type to 1117the type table. 1118 1119TYPE_CODE_LABEL Record 1120^^^^^^^^^^^^^^^^^^^^^^ 1121 1122``[LABEL]`` 1123 1124The ``LABEL`` record (code 5) adds a ``label`` type to the type table. 1125 1126TYPE_CODE_OPAQUE Record 1127^^^^^^^^^^^^^^^^^^^^^^^ 1128 1129``[OPAQUE]`` 1130 1131The ``OPAQUE`` record (code 6) adds an ``opaque`` type to the type table, with 1132a name defined by a previously encountered ``STRUCT_NAME`` record. Note that 1133distinct ``opaque`` types are not unified. 1134 1135TYPE_CODE_INTEGER Record 1136^^^^^^^^^^^^^^^^^^^^^^^^ 1137 1138``[INTEGER, width]`` 1139 1140The ``INTEGER`` record (code 7) adds an integer type to the type table. The 1141single *width* field indicates the width of the integer type. 1142 1143TYPE_CODE_POINTER Record 1144^^^^^^^^^^^^^^^^^^^^^^^^ 1145 1146``[POINTER, pointee type, address space]`` 1147 1148The ``POINTER`` record (code 8) adds a pointer type to the type table. The 1149operand fields are 1150 1151* *pointee type*: The type index of the pointed-to type 1152 1153* *address space*: If supplied, the target-specific numbered address space where 1154 the pointed-to object resides. Otherwise, the default address space is zero. 1155 1156TYPE_CODE_FUNCTION_OLD Record 1157^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1158 1159.. note:: 1160 This is a legacy encoding for functions, produced by LLVM versions 3.0 and 1161 earlier. It is guaranteed to be understood by the current LLVM version, as 1162 specified in the :ref:`IR backwards compatibility` policy. 1163 1164``[FUNCTION_OLD, vararg, ignored, retty, ...paramty... ]`` 1165 1166The ``FUNCTION_OLD`` record (code 9) adds a function type to the type table. 1167The operand fields are 1168 1169* *vararg*: Non-zero if the type represents a varargs function 1170 1171* *ignored*: This value field is present for backward compatibility only, and is 1172 ignored 1173 1174* *retty*: The type index of the function's return type 1175 1176* *paramty*: Zero or more type indices representing the parameter types of the 1177 function 1178 1179TYPE_CODE_ARRAY Record 1180^^^^^^^^^^^^^^^^^^^^^^ 1181 1182``[ARRAY, numelts, eltty]`` 1183 1184The ``ARRAY`` record (code 11) adds an array type to the type table. The 1185operand fields are 1186 1187* *numelts*: The number of elements in arrays of this type 1188 1189* *eltty*: The type index of the array element type 1190 1191TYPE_CODE_VECTOR Record 1192^^^^^^^^^^^^^^^^^^^^^^^ 1193 1194``[VECTOR, numelts, eltty]`` 1195 1196The ``VECTOR`` record (code 12) adds a vector type to the type table. The 1197operand fields are 1198 1199* *numelts*: The number of elements in vectors of this type 1200 1201* *eltty*: The type index of the vector element type 1202 1203TYPE_CODE_X86_FP80 Record 1204^^^^^^^^^^^^^^^^^^^^^^^^^ 1205 1206``[X86_FP80]`` 1207 1208The ``X86_FP80`` record (code 13) adds an ``x86_fp80`` (80-bit floating point) 1209type to the type table. 1210 1211TYPE_CODE_FP128 Record 1212^^^^^^^^^^^^^^^^^^^^^^ 1213 1214``[FP128]`` 1215 1216The ``FP128`` record (code 14) adds an ``fp128`` (128-bit floating point) type 1217to the type table. 1218 1219TYPE_CODE_PPC_FP128 Record 1220^^^^^^^^^^^^^^^^^^^^^^^^^^ 1221 1222``[PPC_FP128]`` 1223 1224The ``PPC_FP128`` record (code 15) adds a ``ppc_fp128`` (128-bit floating point) 1225type to the type table. 1226 1227TYPE_CODE_METADATA Record 1228^^^^^^^^^^^^^^^^^^^^^^^^^ 1229 1230``[METADATA]`` 1231 1232The ``METADATA`` record (code 16) adds a ``metadata`` type to the type table. 1233 1234TYPE_CODE_X86_MMX Record 1235^^^^^^^^^^^^^^^^^^^^^^^^ 1236 1237``[X86_MMX]`` 1238 1239The ``X86_MMX`` record (code 17) adds an ``x86_mmx`` type to the type table. 1240 1241TYPE_CODE_STRUCT_ANON Record 1242^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1243 1244``[STRUCT_ANON, ispacked, ...eltty...]`` 1245 1246The ``STRUCT_ANON`` record (code 18) adds a literal struct type to the type 1247table. The operand fields are 1248 1249* *ispacked*: Non-zero if the type represents a packed structure 1250 1251* *eltty*: Zero or more type indices representing the element types of the 1252 structure 1253 1254TYPE_CODE_STRUCT_NAME Record 1255^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1256 1257``[STRUCT_NAME, ...string...]`` 1258 1259The ``STRUCT_NAME`` record (code 19) contains a variable number of values 1260representing the bytes of a struct name. The next ``OPAQUE`` or 1261``STRUCT_NAMED`` record will use this name. 1262 1263TYPE_CODE_STRUCT_NAMED Record 1264^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1265 1266``[STRUCT_NAMED, ispacked, ...eltty...]`` 1267 1268The ``STRUCT_NAMED`` record (code 20) adds an identified struct type to the 1269type table, with a name defined by a previously encountered ``STRUCT_NAME`` 1270record. The operand fields are 1271 1272* *ispacked*: Non-zero if the type represents a packed structure 1273 1274* *eltty*: Zero or more type indices representing the element types of the 1275 structure 1276 1277TYPE_CODE_FUNCTION Record 1278^^^^^^^^^^^^^^^^^^^^^^^^^ 1279 1280``[FUNCTION, vararg, retty, ...paramty... ]`` 1281 1282The ``FUNCTION`` record (code 21) adds a function type to the type table. The 1283operand fields are 1284 1285* *vararg*: Non-zero if the type represents a varargs function 1286 1287* *retty*: The type index of the function's return type 1288 1289* *paramty*: Zero or more type indices representing the parameter types of the 1290 function 1291 1292.. _CONSTANTS_BLOCK: 1293 1294CONSTANTS_BLOCK Contents 1295------------------------ 1296 1297The ``CONSTANTS_BLOCK`` block (id 11) ... 1298 1299.. _FUNCTION_BLOCK: 1300 1301FUNCTION_BLOCK Contents 1302----------------------- 1303 1304The ``FUNCTION_BLOCK`` block (id 12) ... 1305 1306In addition to the record types described below, a ``FUNCTION_BLOCK`` block may 1307contain the following sub-blocks: 1308 1309* `CONSTANTS_BLOCK`_ 1310* `VALUE_SYMTAB_BLOCK`_ 1311* `METADATA_ATTACHMENT`_ 1312 1313.. _VALUE_SYMTAB_BLOCK: 1314 1315VALUE_SYMTAB_BLOCK Contents 1316--------------------------- 1317 1318The ``VALUE_SYMTAB_BLOCK`` block (id 14) ... 1319 1320.. _METADATA_BLOCK: 1321 1322METADATA_BLOCK Contents 1323----------------------- 1324 1325The ``METADATA_BLOCK`` block (id 15) ... 1326 1327.. _METADATA_ATTACHMENT: 1328 1329METADATA_ATTACHMENT Contents 1330---------------------------- 1331 1332The ``METADATA_ATTACHMENT`` block (id 16) ... 1333 1334.. _STRTAB_BLOCK: 1335 1336STRTAB_BLOCK Contents 1337--------------------- 1338 1339The ``STRTAB`` block (id 23) contains a single record (``STRTAB_BLOB``, id 1) 1340with a single blob operand containing the bitcode file's string table. 1341 1342Strings in the string table are not null terminated. A record's *strtab 1343offset* and *strtab size* operands specify the byte offset and size of a 1344string within the string table. 1345 1346The string table is used by all preceding blocks in the bitcode file that are 1347not succeeded by another intervening ``STRTAB`` block. Normally a bitcode 1348file will have a single string table, but it may have more than one if it 1349was created by binary concatenation of multiple bitcode files. 1350