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.. role:: raw-html(raw)
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========================
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LLVM Bitcode File Format
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========================
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This document describes the LLVM bitstream file format and the encoding of the
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What is commonly known as the LLVM bitcode file format (also, sometimes
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anachronistically known as bytecode) is actually two things: a `bitstream
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container format`_ and an `encoding of LLVM IR`_ into the container format.
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The bitstream format is an abstract encoding of structured data, very similar to
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XML in some ways. Like XML, bitstream files contain tags, and nested
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structures, and you can parse the file without having to understand the tags.
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Unlike XML, the bitstream format is a binary encoding, and unlike XML it
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provides a mechanism for the file to self-describe "abbreviations", which are
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effectively size optimizations for the content.
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LLVM IR files may be optionally embedded into a `wrapper`_ structure, or in a
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`native object file`_. Both of these mechanisms make it easy to embed extra
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data along with LLVM IR files.
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This document first describes the LLVM bitstream format, describes the wrapper
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format, then describes the record structure used by LLVM IR files.
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.. _bitstream container format:
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The bitstream format is literally a stream of bits, with a very simple
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structure. This structure consists of the following concepts:
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* A "`magic number`_" that identifies the contents of the stream.
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* Encoding `primitives`_ like variable bit-rate integers.
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* `Blocks`_, which define nested content.
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* `Data Records`_, which describe entities within the file.
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* Abbreviations, which specify compression optimizations for the file.
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Note that the :doc:`llvm-bcanalyzer <CommandGuide/llvm-bcanalyzer>` tool can be
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used to dump and inspect arbitrary bitstreams, which is very useful for
58
understanding the encoding.
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The first two bytes of a bitcode file are 'BC' (``0x42``, ``0x43``). The second
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two bytes are an application-specific magic number. Generic bitcode tools can
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look at only the first two bytes to verify the file is bitcode, while
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application-specific programs will want to look at all four.
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A bitstream literally consists of a stream of bits, which are read in order
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starting with the least significant bit of each byte. The stream is made up of
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a number of primitive values that encode a stream of unsigned integer values.
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These integers are encoded in two ways: either as `Fixed Width Integers`_ or as
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`Variable Width Integers`_.
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.. _Fixed Width Integers:
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.. _fixed-width value:
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Fixed-width integer values have their low bits emitted directly to the file.
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For example, a 3-bit integer value encodes 1 as 001. Fixed width integers are
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used when there are a well-known number of options for a field. For example,
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boolean values are usually encoded with a 1-bit wide integer.
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.. _Variable Width Integers:
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.. _Variable Width Integer:
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.. _variable-width value:
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Variable Width Integers
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^^^^^^^^^^^^^^^^^^^^^^^
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Variable-width integer (VBR) values encode values of arbitrary size, optimizing
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for the case where the values are small. Given a 4-bit VBR field, any 3-bit
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value (0 through 7) is encoded directly, with the high bit set to zero. Values
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larger than N-1 bits emit their bits in a series of N-1 bit chunks, where all
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but the last set the high bit.
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For example, the value 27 (0x1B) is encoded as 1011 0011 when emitted as a vbr4
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value. The first set of four bits indicates the value 3 (011) with a
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continuation piece (indicated by a high bit of 1). The next word indicates a
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value of 24 (011 << 3) with no continuation. The sum (3+24) yields the value
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.. _char6-encoded value:
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6-bit characters encode common characters into a fixed 6-bit field. They
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represent the following characters with the following 6-bit values:
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'a' .. 'z' --- 0 .. 25
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'A' .. 'Z' --- 26 .. 51
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'0' .. '9' --- 52 .. 61
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This encoding is only suitable for encoding characters and strings that consist
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only of the above characters. It is completely incapable of encoding characters
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Occasionally, it is useful to emit zero bits until the bitstream is a multiple
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of 32 bits. This ensures that the bit position in the stream can be represented
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as a multiple of 32-bit words.
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A bitstream is a sequential series of `Blocks`_ and `Data Records`_. Both of
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these start with an abbreviation ID encoded as a fixed-bitwidth field. The
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width is specified by the current block, as described below. The value of the
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abbreviation ID specifies either a builtin ID (which have special meanings,
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defined below) or one of the abbreviation IDs defined for the current block by
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The set of builtin abbrev IDs is:
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* 0 - `END_BLOCK`_ --- This abbrev ID marks the end of the current block.
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* 1 - `ENTER_SUBBLOCK`_ --- This abbrev ID marks the beginning of a new
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* 2 - `DEFINE_ABBREV`_ --- This defines a new abbreviation.
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* 3 - `UNABBREV_RECORD`_ --- This ID specifies the definition of an
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unabbreviated record.
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Abbreviation IDs 4 and above are defined by the stream itself, and specify an
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`abbreviated record encoding`_.
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Blocks in a bitstream denote nested regions of the stream, and are identified by
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a content-specific id number (for example, LLVM IR uses an ID of 12 to represent
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function bodies). Block IDs 0-7 are reserved for `standard blocks`_ whose
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meaning is defined by Bitcode; block IDs 8 and greater are application
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specific. Nested blocks capture the hierarchical structure of the data encoded
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in it, and various properties are associated with blocks as the file is parsed.
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Block definitions allow the reader to efficiently skip blocks in constant time
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if the reader wants a summary of blocks, or if it wants to efficiently skip data
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it does not understand. The LLVM IR reader uses this mechanism to skip function
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bodies, lazily reading them on demand.
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When reading and encoding the stream, several properties are maintained for the
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block. In particular, each block maintains:
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#. A current abbrev id width. This value starts at 2 at the beginning of the
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stream, and is set every time a block record is entered. The block entry
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specifies the abbrev id width for the body of the block.
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#. A set of abbreviations. Abbreviations may be defined within a block, in
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which case they are only defined in that block (neither subblocks nor
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enclosing blocks see the abbreviation). Abbreviations can also be defined
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inside a `BLOCKINFO`_ block, in which case they are defined in all blocks
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that match the ID that the ``BLOCKINFO`` block is describing.
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As sub blocks are entered, these properties are saved and the new sub-block has
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its own set of abbreviations, and its own abbrev id width. When a sub-block is
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popped, the saved values are restored.
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ENTER_SUBBLOCK Encoding
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^^^^^^^^^^^^^^^^^^^^^^^
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[ENTER_SUBBLOCK, blockid\ :sub:`vbr8`, newabbrevlen\ :sub:`vbr4`, <align32bits>, blocklen_32]
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The ``ENTER_SUBBLOCK`` abbreviation ID specifies the start of a new block
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record. The ``blockid`` value is encoded as an 8-bit VBR identifier, and
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indicates the type of block being entered, which can be a `standard block`_ or
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an application-specific block. The ``newabbrevlen`` value is a 4-bit VBR, which
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specifies the abbrev id width for the sub-block. The ``blocklen`` value is a
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32-bit aligned value that specifies the size of the subblock in 32-bit
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words. This value allows the reader to skip over the entire block in one jump.
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``[END_BLOCK, <align32bits>]``
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The ``END_BLOCK`` abbreviation ID specifies the end of the current block record.
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Its end is aligned to 32-bits to ensure that the size of the block is an even
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Data records consist of a record code and a number of (up to) 64-bit integer
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values. The interpretation of the code and values is application specific and
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may vary between different block types. Records can be encoded either using an
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unabbrev record, or with an abbreviation. In the LLVM IR format, for example,
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there is a record which encodes the target triple of a module. The code is
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``MODULE_CODE_TRIPLE``, and the values of the record are the ASCII codes for the
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characters in the string.
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UNABBREV_RECORD Encoding
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^^^^^^^^^^^^^^^^^^^^^^^^
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[UNABBREV_RECORD, code\ :sub:`vbr6`, numops\ :sub:`vbr6`, op0\ :sub:`vbr6`, op1\ :sub:`vbr6`, ...]
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An ``UNABBREV_RECORD`` provides a default fallback encoding, which is both
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completely general and extremely inefficient. It can describe an arbitrary
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record by emitting the code and operands as VBRs.
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For example, emitting an LLVM IR target triple as an unabbreviated record
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requires emitting the ``UNABBREV_RECORD`` abbrevid, a vbr6 for the
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``MODULE_CODE_TRIPLE`` code, a vbr6 for the length of the string, which is equal
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to the number of operands, and a vbr6 for each character. Because there are no
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letters with values less than 32, each letter would need to be emitted as at
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least a two-part VBR, which means that each letter would require at least 12
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bits. This is not an efficient encoding, but it is fully general.
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.. _abbreviated record encoding:
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Abbreviated Record Encoding
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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``[<abbrevid>, fields...]``
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An abbreviated record is a abbreviation id followed by a set of fields that are
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encoded according to the `abbreviation definition`_. This allows records to be
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encoded significantly more densely than records encoded with the
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`UNABBREV_RECORD`_ type, and allows the abbreviation types to be specified in
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the stream itself, which allows the files to be completely self describing. The
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actual encoding of abbreviations is defined below.
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The record code, which is the first field of an abbreviated record, may be
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encoded in the abbreviation definition (as a literal operand) or supplied in the
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abbreviated record (as a Fixed or VBR operand value).
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.. _abbreviation definition:
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Abbreviations are an important form of compression for bitstreams. The idea is
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to specify a dense encoding for a class of records once, then use that encoding
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to emit many records. It takes space to emit the encoding into the file, but
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the space is recouped (hopefully plus some) when the records that use it are
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Abbreviations can be determined dynamically per client, per file. Because the
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abbreviations are stored in the bitstream itself, different streams of the same
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format can contain different sets of abbreviations according to the needs of the
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specific stream. As a concrete example, LLVM IR files usually emit an
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abbreviation for binary operators. If a specific LLVM module contained no or
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few binary operators, the abbreviation does not need to be emitted.
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DEFINE_ABBREV Encoding
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^^^^^^^^^^^^^^^^^^^^^^
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[DEFINE_ABBREV, numabbrevops\ :sub:`vbr5`, abbrevop0, abbrevop1, ...]
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A ``DEFINE_ABBREV`` record adds an abbreviation to the list of currently defined
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abbreviations in the scope of this block. This definition only exists inside
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this immediate block --- it is not visible in subblocks or enclosing blocks.
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Abbreviations are implicitly assigned IDs sequentially starting from 4 (the
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first application-defined abbreviation ID). Any abbreviations defined in a
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``BLOCKINFO`` record for the particular block type receive IDs first, in order,
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followed by any abbreviations defined within the block itself. Abbreviated data
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records reference this ID to indicate what abbreviation they are invoking.
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An abbreviation definition consists of the ``DEFINE_ABBREV`` abbrevid followed
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by a VBR that specifies the number of abbrev operands, then the abbrev operands
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themselves. Abbreviation operands come in three forms. They all start with a
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single bit that indicates whether the abbrev operand is a literal operand (when
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the bit is 1) or an encoding operand (when the bit is 0).
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#. Literal operands --- :raw-html:`<tt>` [1\ :sub:`1`, litvalue\
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:sub:`vbr8`] :raw-html:`</tt>` --- Literal operands specify that the value in
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the result is always a single specific value. This specific value is emitted
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as a vbr8 after the bit indicating that it is a literal operand.
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#. Encoding info without data --- :raw-html:`<tt>` [0\ :sub:`1`, encoding\
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:sub:`3`] :raw-html:`</tt>` --- Operand encodings that do not have extra data
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are just emitted as their code.
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#. Encoding info with data --- :raw-html:`<tt>` [0\ :sub:`1`, encoding\
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:sub:`3`, value\ :sub:`vbr5`] :raw-html:`</tt>` --- Operand encodings that do
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have extra data are emitted as their code, followed by the extra data.
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The possible operand encodings are:
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* Fixed (code 1): The field should be emitted as a `fixed-width value`_, whose
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width is specified by the operand's extra data.
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* VBR (code 2): The field should be emitted as a `variable-width value`_, whose
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width is specified by the operand's extra data.
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* Array (code 3): This field is an array of values. The array operand has no
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extra data, but expects another operand to follow it, indicating the element
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type of the array. When reading an array in an abbreviated record, the first
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integer is a vbr6 that indicates the array length, followed by the encoded
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elements of the array. An array may only occur as the last operand of an
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abbreviation (except for the one final operand that gives the array's
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* Char6 (code 4): This field should be emitted as a `char6-encoded value`_.
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This operand type takes no extra data. Char6 encoding is normally used as an
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* Blob (code 5): This field is emitted as a vbr6, followed by padding to a
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32-bit boundary (for alignment) and an array of 8-bit objects. The array of
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bytes is further followed by tail padding to ensure that its total length is a
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multiple of 4 bytes. This makes it very efficient for the reader to decode
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the data without having to make a copy of it: it can use a pointer to the data
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in the mapped in file and poke directly at it. A blob may only occur as the
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last operand of an abbreviation.
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For example, target triples in LLVM modules are encoded as a record of the form
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``[TRIPLE, 'a', 'b', 'c', 'd']``. Consider if the bitstream emitted the
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following abbrev entry:
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When emitting a record with this abbreviation, the above entry would be emitted
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:raw-html:`<tt><blockquote>`
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[4\ :sub:`abbrevwidth`, 2\ :sub:`4`, 4\ :sub:`vbr6`, 0\ :sub:`6`, 1\ :sub:`6`, 2\ :sub:`6`, 3\ :sub:`6`]
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:raw-html:`</blockquote></tt>`
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#. The first value, 4, is the abbreviation ID for this abbreviation.
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#. The second value, 2, is the record code for ``TRIPLE`` records within LLVM IR
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file ``MODULE_BLOCK`` blocks.
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#. The third value, 4, is the length of the array.
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#. The rest of the values are the char6 encoded values for ``"abcd"``.
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With this abbreviation, the triple is emitted with only 37 bits (assuming a
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abbrev id width of 3). Without the abbreviation, significantly more space would
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be required to emit the target triple. Also, because the ``TRIPLE`` value is
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not emitted as a literal in the abbreviation, the abbreviation can also be used
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for any other string value.
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In addition to the basic block structure and record encodings, the bitstream
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also defines specific built-in block types. These block types specify how the
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stream is to be decoded or other metadata. In the future, new standard blocks
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may be added. Block IDs 0-7 are reserved for standard blocks.
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The ``BLOCKINFO`` block allows the description of metadata for other blocks.
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The currently specified records are:
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[SETBID (#1), blockid]
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[BLOCKNAME, ...name...]
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[SETRECORDNAME, RecordID, ...name...]
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The ``SETBID`` record (code 1) indicates which block ID is being described.
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``SETBID`` records can occur multiple times throughout the block to change which
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block ID is being described. There must be a ``SETBID`` record prior to any
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Standard ``DEFINE_ABBREV`` records can occur inside ``BLOCKINFO`` blocks, but
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unlike their occurrence in normal blocks, the abbreviation is defined for blocks
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matching the block ID we are describing, *not* the ``BLOCKINFO`` block
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itself. The abbreviations defined in ``BLOCKINFO`` blocks receive abbreviation
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IDs as described in `DEFINE_ABBREV`_.
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The ``BLOCKNAME`` record (code 2) can optionally occur in this block. The
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elements of the record are the bytes of the string name of the block.
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llvm-bcanalyzer can use this to dump out bitcode files symbolically.
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The ``SETRECORDNAME`` record (code 3) can also optionally occur in this block.
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The first operand value is a record ID number, and the rest of the elements of
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the record are the bytes for the string name of the record. llvm-bcanalyzer can
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use this to dump out bitcode files symbolically.
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Note that although the data in ``BLOCKINFO`` blocks is described as "metadata,"
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the abbreviations they contain are essential for parsing records from the
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corresponding blocks. It is not safe to skip them.
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Bitcode Wrapper Format
446
======================
448
Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper
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structure. This structure contains a simple header that indicates the offset
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and size of the embedded BC file. This allows additional information to be
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stored alongside the BC file. The structure of this file header is:
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:raw-html:`<tt><blockquote>`
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[Magic\ :sub:`32`, Version\ :sub:`32`, Offset\ :sub:`32`, Size\ :sub:`32`, CPUType\ :sub:`32`]
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:raw-html:`</blockquote></tt>`
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Each of the fields are 32-bit fields stored in little endian form (as with the
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rest of the bitcode file fields). The Magic number is always ``0x0B17C0DE`` and
459
the version is currently always ``0``. The Offset field is the offset in bytes
460
to the start of the bitcode stream in the file, and the Size field is the size
461
in bytes of the stream. CPUType is a target-specific value that can be used to
462
encode the CPU of the target.
464
.. _native object file:
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Native Object File Wrapper Format
467
=================================
469
Bitcode files for LLVM IR may also be wrapped in a native object file
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(i.e. ELF, COFF, Mach-O). The bitcode must be stored in a section of the
471
object file named ``.llvmbc``. This wrapper format is useful for accommodating
472
LTO in compilation pipelines where intermediate objects must be native object
473
files which contain metadata in other sections.
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Not all tools support this format.
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.. _encoding of LLVM IR:
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LLVM IR is encoded into a bitstream by defining blocks and records. It uses
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blocks for things like constant pools, functions, symbol tables, etc. It uses
484
records for things like instructions, global variable descriptors, type
485
descriptions, etc. This document does not describe the set of abbreviations
486
that the writer uses, as these are fully self-described in the file, and the
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reader is not allowed to build in any knowledge of this.
495
The magic number for LLVM IR files is:
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:raw-html:`<tt><blockquote>`
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[0x0\ :sub:`4`, 0xC\ :sub:`4`, 0xE\ :sub:`4`, 0xD\ :sub:`4`]
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:raw-html:`</blockquote></tt>`
501
When combined with the bitcode magic number and viewed as bytes, this is
509
`Variable Width Integer`_ encoding is an efficient way to encode arbitrary sized
510
unsigned values, but is an extremely inefficient for encoding signed values, as
511
signed values are otherwise treated as maximally large unsigned values.
513
As such, signed VBR values of a specific width are emitted as follows:
515
* Positive values are emitted as VBRs of the specified width, but with their
516
value shifted left by one.
518
* Negative values are emitted as VBRs of the specified width, but the negated
519
value is shifted left by one, and the low bit is set.
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With this encoding, small positive and small negative values can both be emitted
522
efficiently. Signed VBR encoding is used in ``CST_CODE_INTEGER`` and
523
``CST_CODE_WIDE_INTEGER`` records within ``CONSTANTS_BLOCK`` blocks.
524
It is also used for phi instruction operands in `MODULE_CODE_VERSION`_ 1.
529
LLVM IR is defined with the following blocks:
531
* 8 --- `MODULE_BLOCK`_ --- This is the top-level block that contains the entire
532
module, and describes a variety of per-module information.
534
* 9 --- `PARAMATTR_BLOCK`_ --- This enumerates the parameter attributes.
536
* 10 --- `TYPE_BLOCK`_ --- This describes all of the types in the module.
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* 11 --- `CONSTANTS_BLOCK`_ --- This describes constants for a module or
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* 12 --- `FUNCTION_BLOCK`_ --- This describes a function body.
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* 13 --- `TYPE_SYMTAB_BLOCK`_ --- This describes the type symbol table.
545
* 14 --- `VALUE_SYMTAB_BLOCK`_ --- This describes a value symbol table.
547
* 15 --- `METADATA_BLOCK`_ --- This describes metadata items.
549
* 16 --- `METADATA_ATTACHMENT`_ --- This contains records associating metadata
550
with function instruction values.
554
MODULE_BLOCK Contents
555
---------------------
557
The ``MODULE_BLOCK`` block (id 8) is the top-level block for LLVM bitcode files,
558
and each bitcode file must contain exactly one. In addition to records
559
(described below) containing information about the module, a ``MODULE_BLOCK``
560
block may contain the following sub-blocks:
565
* `TYPE_SYMTAB_BLOCK`_
566
* `VALUE_SYMTAB_BLOCK`_
571
.. _MODULE_CODE_VERSION:
573
MODULE_CODE_VERSION Record
574
^^^^^^^^^^^^^^^^^^^^^^^^^^
576
``[VERSION, version#]``
578
The ``VERSION`` record (code 1) contains a single value indicating the format
579
version. Versions 0 and 1 are supported at this time. The difference between
580
version 0 and 1 is in the encoding of instruction operands in
581
each `FUNCTION_BLOCK`_.
583
In version 0, each value defined by an instruction is assigned an ID
584
unique to the function. Function-level value IDs are assigned starting from
585
``NumModuleValues`` since they share the same namespace as module-level
586
values. The value enumerator resets after each function. When a value is
587
an operand of an instruction, the value ID is used to represent the operand.
588
For large functions or large modules, these operand values can be large.
590
The encoding in version 1 attempts to avoid large operand values
591
in common cases. Instead of using the value ID directly, operands are
592
encoded as relative to the current instruction. Thus, if an operand
593
is the value defined by the previous instruction, the operand
594
will be encoded as 1.
596
For example, instead of
601
#n+1 = icmp eq #n, #const0
602
br #n+1, label #(bb1), label #(bb2)
604
version 1 will encode the instructions as
609
#n+1 = icmp eq #1, (#n+1)-#const0
610
br #1, label #(bb1), label #(bb2)
612
Note in the example that operands which are constants also use
613
the relative encoding, while operands like basic block labels
614
do not use the relative encoding.
616
Forward references will result in a negative value.
617
This can be inefficient, as operands are normally encoded
618
as unsigned VBRs. However, forward references are rare, except in the
619
case of phi instructions. For phi instructions, operands are encoded as
620
`Signed VBRs`_ to deal with forward references.
623
MODULE_CODE_TRIPLE Record
624
^^^^^^^^^^^^^^^^^^^^^^^^^
626
``[TRIPLE, ...string...]``
628
The ``TRIPLE`` record (code 2) contains a variable number of values representing
629
the bytes of the ``target triple`` specification string.
631
MODULE_CODE_DATALAYOUT Record
632
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
634
``[DATALAYOUT, ...string...]``
636
The ``DATALAYOUT`` record (code 3) contains a variable number of values
637
representing the bytes of the ``target datalayout`` specification string.
639
MODULE_CODE_ASM Record
640
^^^^^^^^^^^^^^^^^^^^^^
642
``[ASM, ...string...]``
644
The ``ASM`` record (code 4) contains a variable number of values representing
645
the bytes of ``module asm`` strings, with individual assembly blocks separated
646
by newline (ASCII 10) characters.
648
.. _MODULE_CODE_SECTIONNAME:
650
MODULE_CODE_SECTIONNAME Record
651
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
653
``[SECTIONNAME, ...string...]``
655
The ``SECTIONNAME`` record (code 5) contains a variable number of values
656
representing the bytes of a single section name string. There should be one
657
``SECTIONNAME`` record for each section name referenced (e.g., in global
658
variable or function ``section`` attributes) within the module. These records
659
can be referenced by the 1-based index in the *section* fields of ``GLOBALVAR``
660
or ``FUNCTION`` records.
662
MODULE_CODE_DEPLIB Record
663
^^^^^^^^^^^^^^^^^^^^^^^^^
665
``[DEPLIB, ...string...]``
667
The ``DEPLIB`` record (code 6) contains a variable number of values representing
668
the bytes of a single dependent library name string, one of the libraries
669
mentioned in a ``deplibs`` declaration. There should be one ``DEPLIB`` record
670
for each library name referenced.
672
MODULE_CODE_GLOBALVAR Record
673
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
675
``[GLOBALVAR, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal, unnamed_addr, externally_initialized, dllstorageclass, comdat]``
677
The ``GLOBALVAR`` record (code 7) marks the declaration or definition of a
678
global variable. The operand fields are:
680
* *pointer type*: The type index of the pointer type used to point to this
683
* *isconst*: Non-zero if the variable is treated as constant within the module,
686
* *initid*: If non-zero, the value index of the initializer for this variable,
691
* *linkage*: An encoding of the linkage type for this variable:
692
* ``external``: code 0
694
* ``appending``: code 2
695
* ``internal``: code 3
696
* ``linkonce``: code 4
697
* ``dllimport``: code 5
698
* ``dllexport``: code 6
699
* ``extern_weak``: code 7
701
* ``private``: code 9
702
* ``weak_odr``: code 10
703
* ``linkonce_odr``: code 11
704
* ``available_externally``: code 12
705
* deprecated : code 13
706
* deprecated : code 14
708
* alignment*: The logarithm base 2 of the variable's requested alignment, plus 1
710
* *section*: If non-zero, the 1-based section index in the table of
711
`MODULE_CODE_SECTIONNAME`_ entries.
715
* *visibility*: If present, an encoding of the visibility of this variable:
716
* ``default``: code 0
718
* ``protected``: code 2
720
* *threadlocal*: If present, an encoding of the thread local storage mode of the
722
* ``not thread local``: code 0
723
* ``thread local; default TLS model``: code 1
724
* ``localdynamic``: code 2
725
* ``initialexec``: code 3
726
* ``localexec``: code 4
728
* *unnamed_addr*: If present and non-zero, indicates that the variable has
731
.. _bcdllstorageclass:
733
* *dllstorageclass*: If present, an encoding of the DLL storage class of this variable:
735
* ``default``: code 0
736
* ``dllimport``: code 1
737
* ``dllexport``: code 2
741
MODULE_CODE_FUNCTION Record
742
^^^^^^^^^^^^^^^^^^^^^^^^^^^
744
``[FUNCTION, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc, prologuedata, dllstorageclass, comdat, prefixdata, personalityfn]``
746
The ``FUNCTION`` record (code 8) marks the declaration or definition of a
747
function. The operand fields are:
749
* *type*: The type index of the function type describing this function
751
* *callingconv*: The calling convention number:
755
* ``webkit_jscc``: code 12
756
* ``anyregcc``: code 13
757
* ``preserve_mostcc``: code 14
758
* ``preserve_allcc``: code 15
759
* ``x86_stdcallcc``: code 64
760
* ``x86_fastcallcc``: code 65
761
* ``arm_apcscc``: code 66
762
* ``arm_aapcscc``: code 67
763
* ``arm_aapcs_vfpcc``: code 68
765
* isproto*: Non-zero if this entry represents a declaration rather than a
768
* *linkage*: An encoding of the `linkage type`_ for this function
770
* *paramattr*: If nonzero, the 1-based parameter attribute index into the table
771
of `PARAMATTR_CODE_ENTRY`_ entries.
773
* *alignment*: The logarithm base 2 of the function's requested alignment, plus
776
* *section*: If non-zero, the 1-based section index in the table of
777
`MODULE_CODE_SECTIONNAME`_ entries.
779
* *visibility*: An encoding of the `visibility`_ of this function
781
* *gc*: If present and nonzero, the 1-based garbage collector index in the table
782
of `MODULE_CODE_GCNAME`_ entries.
784
* *unnamed_addr*: If present and non-zero, indicates that the function has
787
* *prologuedata*: If non-zero, the value index of the prologue data for this function,
790
* *dllstorageclass*: An encoding of the
791
:ref:`dllstorageclass<bcdllstorageclass>` of this function
793
* *comdat*: An encoding of the COMDAT of this function
795
* *prefixdata*: If non-zero, the value index of the prefix data for this function,
798
* *personalityfn*: If non-zero, the value index of the personality function for this function,
801
MODULE_CODE_ALIAS Record
802
^^^^^^^^^^^^^^^^^^^^^^^^
804
``[ALIAS, alias type, aliasee val#, linkage, visibility, dllstorageclass]``
806
The ``ALIAS`` record (code 9) marks the definition of an alias. The operand
809
* *alias type*: The type index of the alias
811
* *aliasee val#*: The value index of the aliased value
813
* *linkage*: An encoding of the `linkage type`_ for this alias
815
* *visibility*: If present, an encoding of the `visibility`_ of the alias
817
* *dllstorageclass*: If present, an encoding of the
818
:ref:`dllstorageclass<bcdllstorageclass>` of the alias
820
MODULE_CODE_PURGEVALS Record
821
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
823
``[PURGEVALS, numvals]``
825
The ``PURGEVALS`` record (code 10) resets the module-level value list to the
826
size given by the single operand value. Module-level value list items are added
827
by ``GLOBALVAR``, ``FUNCTION``, and ``ALIAS`` records. After a ``PURGEVALS``
828
record is seen, new value indices will start from the given *numvals* value.
830
.. _MODULE_CODE_GCNAME:
832
MODULE_CODE_GCNAME Record
833
^^^^^^^^^^^^^^^^^^^^^^^^^
835
``[GCNAME, ...string...]``
837
The ``GCNAME`` record (code 11) contains a variable number of values
838
representing the bytes of a single garbage collector name string. There should
839
be one ``GCNAME`` record for each garbage collector name referenced in function
840
``gc`` attributes within the module. These records can be referenced by 1-based
841
index in the *gc* fields of ``FUNCTION`` records.
845
PARAMATTR_BLOCK Contents
846
------------------------
848
The ``PARAMATTR_BLOCK`` block (id 9) contains a table of entries describing the
849
attributes of function parameters. These entries are referenced by 1-based index
850
in the *paramattr* field of module block `FUNCTION`_ records, or within the
851
*attr* field of function block ``INST_INVOKE`` and ``INST_CALL`` records.
853
Entries within ``PARAMATTR_BLOCK`` are constructed to ensure that each is unique
854
(i.e., no two indicies represent equivalent attribute lists).
856
.. _PARAMATTR_CODE_ENTRY:
858
PARAMATTR_CODE_ENTRY Record
859
^^^^^^^^^^^^^^^^^^^^^^^^^^^
861
``[ENTRY, paramidx0, attr0, paramidx1, attr1...]``
863
The ``ENTRY`` record (code 1) contains an even number of values describing a
864
unique set of function parameter attributes. Each *paramidx* value indicates
865
which set of attributes is represented, with 0 representing the return value
866
attributes, 0xFFFFFFFF representing function attributes, and other values
867
representing 1-based function parameters. Each *attr* value is a bitmap with the
868
following interpretation:
872
* bit 2: ``noreturn``
875
* bit 5: ``nounwind``
879
* bit 9: ``readnone``
880
* bit 10: ``readonly``
881
* bit 11: ``noinline``
882
* bit 12: ``alwaysinline``
883
* bit 13: ``optsize``
886
* bits 16-31: ``align n``
887
* bit 32: ``nocapture``
888
* bit 33: ``noredzone``
889
* bit 34: ``noimplicitfloat``
891
* bit 36: ``inlinehint``
892
* bits 37-39: ``alignstack n``, represented as the logarithm
893
base 2 of the requested alignment, plus 1
900
The ``TYPE_BLOCK`` block (id 10) contains records which constitute a table of
901
type operator entries used to represent types referenced within an LLVM
902
module. Each record (with the exception of `NUMENTRY`_) generates a single type
903
table entry, which may be referenced by 0-based index from instructions,
904
constants, metadata, type symbol table entries, or other type operator records.
906
Entries within ``TYPE_BLOCK`` are constructed to ensure that each entry is
907
unique (i.e., no two indicies represent structurally equivalent types).
909
.. _TYPE_CODE_NUMENTRY:
912
TYPE_CODE_NUMENTRY Record
913
^^^^^^^^^^^^^^^^^^^^^^^^^
915
``[NUMENTRY, numentries]``
917
The ``NUMENTRY`` record (code 1) contains a single value which indicates the
918
total number of type code entries in the type table of the module. If present,
919
``NUMENTRY`` should be the first record in the block.
921
TYPE_CODE_VOID Record
922
^^^^^^^^^^^^^^^^^^^^^
926
The ``VOID`` record (code 2) adds a ``void`` type to the type table.
928
TYPE_CODE_HALF Record
929
^^^^^^^^^^^^^^^^^^^^^
933
The ``HALF`` record (code 10) adds a ``half`` (16-bit floating point) type to
936
TYPE_CODE_FLOAT Record
937
^^^^^^^^^^^^^^^^^^^^^^
941
The ``FLOAT`` record (code 3) adds a ``float`` (32-bit floating point) type to
944
TYPE_CODE_DOUBLE Record
945
^^^^^^^^^^^^^^^^^^^^^^^
949
The ``DOUBLE`` record (code 4) adds a ``double`` (64-bit floating point) type to
952
TYPE_CODE_LABEL Record
953
^^^^^^^^^^^^^^^^^^^^^^
957
The ``LABEL`` record (code 5) adds a ``label`` type to the type table.
959
TYPE_CODE_OPAQUE Record
960
^^^^^^^^^^^^^^^^^^^^^^^
964
The ``OPAQUE`` record (code 6) adds an ``opaque`` type to the type table. Note
965
that distinct ``opaque`` types are not unified.
967
TYPE_CODE_INTEGER Record
968
^^^^^^^^^^^^^^^^^^^^^^^^
972
The ``INTEGER`` record (code 7) adds an integer type to the type table. The
973
single *width* field indicates the width of the integer type.
975
TYPE_CODE_POINTER Record
976
^^^^^^^^^^^^^^^^^^^^^^^^
978
``[POINTER, pointee type, address space]``
980
The ``POINTER`` record (code 8) adds a pointer type to the type table. The
983
* *pointee type*: The type index of the pointed-to type
985
* *address space*: If supplied, the target-specific numbered address space where
986
the pointed-to object resides. Otherwise, the default address space is zero.
988
TYPE_CODE_FUNCTION Record
989
^^^^^^^^^^^^^^^^^^^^^^^^^
991
``[FUNCTION, vararg, ignored, retty, ...paramty... ]``
993
The ``FUNCTION`` record (code 9) adds a function type to the type table. The
996
* *vararg*: Non-zero if the type represents a varargs function
998
* *ignored*: This value field is present for backward compatibility only, and is
1001
* *retty*: The type index of the function's return type
1003
* *paramty*: Zero or more type indices representing the parameter types of the
1006
TYPE_CODE_STRUCT Record
1007
^^^^^^^^^^^^^^^^^^^^^^^
1009
``[STRUCT, ispacked, ...eltty...]``
1011
The ``STRUCT`` record (code 10) adds a struct type to the type table. The
1014
* *ispacked*: Non-zero if the type represents a packed structure
1016
* *eltty*: Zero or more type indices representing the element types of the
1019
TYPE_CODE_ARRAY Record
1020
^^^^^^^^^^^^^^^^^^^^^^
1022
``[ARRAY, numelts, eltty]``
1024
The ``ARRAY`` record (code 11) adds an array type to the type table. The
1027
* *numelts*: The number of elements in arrays of this type
1029
* *eltty*: The type index of the array element type
1031
TYPE_CODE_VECTOR Record
1032
^^^^^^^^^^^^^^^^^^^^^^^
1034
``[VECTOR, numelts, eltty]``
1036
The ``VECTOR`` record (code 12) adds a vector type to the type table. The
1039
* *numelts*: The number of elements in vectors of this type
1041
* *eltty*: The type index of the vector element type
1043
TYPE_CODE_X86_FP80 Record
1044
^^^^^^^^^^^^^^^^^^^^^^^^^
1048
The ``X86_FP80`` record (code 13) adds an ``x86_fp80`` (80-bit floating point)
1049
type to the type table.
1051
TYPE_CODE_FP128 Record
1052
^^^^^^^^^^^^^^^^^^^^^^
1056
The ``FP128`` record (code 14) adds an ``fp128`` (128-bit floating point) type
1059
TYPE_CODE_PPC_FP128 Record
1060
^^^^^^^^^^^^^^^^^^^^^^^^^^
1064
The ``PPC_FP128`` record (code 15) adds a ``ppc_fp128`` (128-bit floating point)
1065
type to the type table.
1067
TYPE_CODE_METADATA Record
1068
^^^^^^^^^^^^^^^^^^^^^^^^^
1072
The ``METADATA`` record (code 16) adds a ``metadata`` type to the type table.
1074
.. _CONSTANTS_BLOCK:
1076
CONSTANTS_BLOCK Contents
1077
------------------------
1079
The ``CONSTANTS_BLOCK`` block (id 11) ...
1083
FUNCTION_BLOCK Contents
1084
-----------------------
1086
The ``FUNCTION_BLOCK`` block (id 12) ...
1088
In addition to the record types described below, a ``FUNCTION_BLOCK`` block may
1089
contain the following sub-blocks:
1091
* `CONSTANTS_BLOCK`_
1092
* `VALUE_SYMTAB_BLOCK`_
1093
* `METADATA_ATTACHMENT`_
1095
.. _TYPE_SYMTAB_BLOCK:
1097
TYPE_SYMTAB_BLOCK Contents
1098
--------------------------
1100
The ``TYPE_SYMTAB_BLOCK`` block (id 13) contains entries which map between
1101
module-level named types and their corresponding type indices.
1105
TST_CODE_ENTRY Record
1106
^^^^^^^^^^^^^^^^^^^^^
1108
``[ENTRY, typeid, ...string...]``
1110
The ``ENTRY`` record (code 1) contains a variable number of values, with the
1111
first giving the type index of the designated type, and the remaining values
1112
giving the character codes of the type name. Each entry corresponds to a single
1115
.. _VALUE_SYMTAB_BLOCK:
1117
VALUE_SYMTAB_BLOCK Contents
1118
---------------------------
1120
The ``VALUE_SYMTAB_BLOCK`` block (id 14) ...
1124
METADATA_BLOCK Contents
1125
-----------------------
1127
The ``METADATA_BLOCK`` block (id 15) ...
1129
.. _METADATA_ATTACHMENT:
1131
METADATA_ATTACHMENT Contents
1132
----------------------------
1134
The ``METADATA_ATTACHMENT`` block (id 16) ...