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These linkages were introduced some time ago, but it was never very clear what exactly their semantics were or what they should be used for. Some investigation found these uses: * utf-16 strings in clang. * non-unnamed_addr strings produced by the sanitizers. It turns out they were just working around a more fundamental problem. For some sections a MachO linker needs a symbol in order to split the section into atoms, and llvm had no idea that was the case. I fixed that in r201700 and it is now safe to use the private linkage. When the object ends up in a section that requires symbols, llvm will use a 'l' prefix instead of a 'L' prefix and things just work. With that, these linkages were already dead, but there was a potential future user in the objc metadata information. I am still looking at CGObjcMac.cpp, but at this point I am convinced that linker_private and linker_private_weak are not what they need. The objc uses are currently split in * Regular symbols (no '\01' prefix). LLVM already directly provides whatever semantics they need. * Uses of a private name (start with "\01L" or "\01l") and private linkage. We can drop the "\01L" and "\01l" prefixes as soon as llvm agrees with clang on L being ok or not for a given section. I have two patches in code review for this. * Uses of private name and weak linkage. The last case is the one that one could think would fit one of these linkages. That is not the case. The semantics are * the linker will merge these symbol by *name*. * the linker will hide them in the final DSO. Given that the merging is done by name, any of the private (or internal) linkages would be a bad match. They allow llvm to rename the symbols, and that is really not what we want. From the llvm point of view, these objects should really be (linkonce|weak)(_odr)?. For now, just keeping the "\01l" prefix is probably the best for these symbols. If we one day want to have a more direct support in llvm, IMHO what we should add is not a linkage, it is just a hidden_symbol attribute. It would be applicable to multiple linkages. For example, on weak it would produce the current behavior we have for objc metadata. On internal, it would be equivalent to private (and we should then remove private). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203866 91177308-0d34-0410-b5e6-96231b3b80d8
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ReStructuredText
.. role:: raw-html(raw)
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:format: html
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========================
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LLVM Bitcode File Format
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========================
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.. contents::
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:local:
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Abstract
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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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LLVM IR into it.
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Overview
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========
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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 that makes
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it easy to embed extra 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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Bitstream Format
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================
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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
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understanding the encoding.
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.. _magic number:
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Magic Numbers
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-------------
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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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.. _primitives:
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Primitives
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----------
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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 Integers
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^^^^^^^^^^^^^^^^^^^^
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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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27.
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.. _char6-encoded value:
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6-bit characters
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^^^^^^^^^^^^^^^^
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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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::
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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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'.' --- 62
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'_' --- 63
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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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not in the set.
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Word Alignment
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^^^^^^^^^^^^^^
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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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Abbreviation IDs
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----------------
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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 stream itself.
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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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block.
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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:
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Blocks
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------
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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:
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ENTER_SUBBLOCK Encoding
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^^^^^^^^^^^^^^^^^^^^^^^
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:raw-html:`<tt>`
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[ENTER_SUBBLOCK, blockid\ :sub:`vbr8`, newabbrevlen\ :sub:`vbr4`, <align32bits>, blocklen_32]
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:raw-html:`</tt>`
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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:
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END_BLOCK Encoding
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^^^^^^^^^^^^^^^^^^
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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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multiple of 32-bits.
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.. _Data Records:
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Data Records
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------------
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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:
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UNABBREV_RECORD Encoding
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^^^^^^^^^^^^^^^^^^^^^^^^
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:raw-html:`<tt>`
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[UNABBREV_RECORD, code\ :sub:`vbr6`, numops\ :sub:`vbr6`, op0\ :sub:`vbr6`, op1\ :sub:`vbr6`, ...]
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:raw-html:`</tt>`
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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
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-------------
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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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emitted.
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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:
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DEFINE_ABBREV Encoding
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^^^^^^^^^^^^^^^^^^^^^^
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:raw-html:`<tt>`
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[DEFINE_ABBREV, numabbrevops\ :sub:`vbr5`, abbrevop0, abbrevop1, ...]
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:raw-html:`</tt>`
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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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type).
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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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array element type.
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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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::
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[0, Fixed, 4]
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[0, Array]
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[0, Char6]
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When emitting a record with this abbreviation, the above entry would be emitted
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as:
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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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These values are:
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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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.. _standard blocks:
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.. _standard block:
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Standard Blocks
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---------------
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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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.. _BLOCKINFO:
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#0 - BLOCKINFO Block
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^^^^^^^^^^^^^^^^^^^^
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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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::
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[SETBID (#1), blockid]
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[DEFINE_ABBREV, ...]
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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.
|
|
``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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other records.
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Standard ``DEFINE_ABBREV`` records can occur inside ``BLOCKINFO`` blocks, but
|
|
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
|
|
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.
|
|
The first operand value is a record ID number, and the rest of the elements of
|
|
the record are the bytes for the string name of the record. llvm-bcanalyzer can
|
|
use this to dump out bitcode files symbolically.
|
|
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|
Note that although the data in ``BLOCKINFO`` blocks is described as "metadata,"
|
|
the abbreviations they contain are essential for parsing records from the
|
|
corresponding blocks. It is not safe to skip them.
|
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|
.. _wrapper:
|
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|
|
Bitcode Wrapper Format
|
|
======================
|
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|
|
Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper
|
|
structure. This structure contains a simple header that indicates the offset
|
|
and size of the embedded BC file. This allows additional information to be
|
|
stored alongside the BC file. The structure of this file header is:
|
|
|
|
:raw-html:`<tt><blockquote>`
|
|
[Magic\ :sub:`32`, Version\ :sub:`32`, Offset\ :sub:`32`, Size\ :sub:`32`, CPUType\ :sub:`32`]
|
|
:raw-html:`</blockquote></tt>`
|
|
|
|
Each of the fields are 32-bit fields stored in little endian form (as with the
|
|
rest of the bitcode file fields). The Magic number is always ``0x0B17C0DE`` and
|
|
the version is currently always ``0``. The Offset field is the offset in bytes
|
|
to the start of the bitcode stream in the file, and the Size field is the size
|
|
in bytes of the stream. CPUType is a target-specific value that can be used to
|
|
encode the CPU of the target.
|
|
|
|
.. _encoding of LLVM IR:
|
|
|
|
LLVM IR Encoding
|
|
================
|
|
|
|
LLVM IR is encoded into a bitstream by defining blocks and records. It uses
|
|
blocks for things like constant pools, functions, symbol tables, etc. It uses
|
|
records for things like instructions, global variable descriptors, type
|
|
descriptions, etc. This document does not describe the set of abbreviations
|
|
that the writer uses, as these are fully self-described in the file, and the
|
|
reader is not allowed to build in any knowledge of this.
|
|
|
|
Basics
|
|
------
|
|
|
|
LLVM IR Magic Number
|
|
^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The magic number for LLVM IR files is:
|
|
|
|
:raw-html:`<tt><blockquote>`
|
|
[0x0\ :sub:`4`, 0xC\ :sub:`4`, 0xE\ :sub:`4`, 0xD\ :sub:`4`]
|
|
:raw-html:`</blockquote></tt>`
|
|
|
|
When combined with the bitcode magic number and viewed as bytes, this is
|
|
``"BC 0xC0DE"``.
|
|
|
|
.. _Signed VBRs:
|
|
|
|
Signed VBRs
|
|
^^^^^^^^^^^
|
|
|
|
`Variable Width Integer`_ encoding is an efficient way to encode arbitrary sized
|
|
unsigned values, but is an extremely inefficient for encoding signed values, as
|
|
signed values are otherwise treated as maximally large unsigned values.
|
|
|
|
As such, signed VBR values of a specific width are emitted as follows:
|
|
|
|
* Positive values are emitted as VBRs of the specified width, but with their
|
|
value shifted left by one.
|
|
|
|
* Negative values are emitted as VBRs of the specified width, but the negated
|
|
value is shifted left by one, and the low bit is set.
|
|
|
|
With this encoding, small positive and small negative values can both be emitted
|
|
efficiently. Signed VBR encoding is used in ``CST_CODE_INTEGER`` and
|
|
``CST_CODE_WIDE_INTEGER`` records within ``CONSTANTS_BLOCK`` blocks.
|
|
It is also used for phi instruction operands in `MODULE_CODE_VERSION`_ 1.
|
|
|
|
LLVM IR Blocks
|
|
^^^^^^^^^^^^^^
|
|
|
|
LLVM IR is defined with the following blocks:
|
|
|
|
* 8 --- `MODULE_BLOCK`_ --- This is the top-level block that contains the entire
|
|
module, and describes a variety of per-module information.
|
|
|
|
* 9 --- `PARAMATTR_BLOCK`_ --- This enumerates the parameter attributes.
|
|
|
|
* 10 --- `TYPE_BLOCK`_ --- This describes all of the types in the module.
|
|
|
|
* 11 --- `CONSTANTS_BLOCK`_ --- This describes constants for a module or
|
|
function.
|
|
|
|
* 12 --- `FUNCTION_BLOCK`_ --- This describes a function body.
|
|
|
|
* 13 --- `TYPE_SYMTAB_BLOCK`_ --- This describes the type symbol table.
|
|
|
|
* 14 --- `VALUE_SYMTAB_BLOCK`_ --- This describes a value symbol table.
|
|
|
|
* 15 --- `METADATA_BLOCK`_ --- This describes metadata items.
|
|
|
|
* 16 --- `METADATA_ATTACHMENT`_ --- This contains records associating metadata
|
|
with function instruction values.
|
|
|
|
.. _MODULE_BLOCK:
|
|
|
|
MODULE_BLOCK Contents
|
|
---------------------
|
|
|
|
The ``MODULE_BLOCK`` block (id 8) is the top-level block for LLVM bitcode files,
|
|
and each bitcode file must contain exactly one. In addition to records
|
|
(described below) containing information about the module, a ``MODULE_BLOCK``
|
|
block may contain the following sub-blocks:
|
|
|
|
* `BLOCKINFO`_
|
|
* `PARAMATTR_BLOCK`_
|
|
* `TYPE_BLOCK`_
|
|
* `TYPE_SYMTAB_BLOCK`_
|
|
* `VALUE_SYMTAB_BLOCK`_
|
|
* `CONSTANTS_BLOCK`_
|
|
* `FUNCTION_BLOCK`_
|
|
* `METADATA_BLOCK`_
|
|
|
|
.. _MODULE_CODE_VERSION:
|
|
|
|
MODULE_CODE_VERSION Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[VERSION, version#]``
|
|
|
|
The ``VERSION`` record (code 1) contains a single value indicating the format
|
|
version. Versions 0 and 1 are supported at this time. The difference between
|
|
version 0 and 1 is in the encoding of instruction operands in
|
|
each `FUNCTION_BLOCK`_.
|
|
|
|
In version 0, each value defined by an instruction is assigned an ID
|
|
unique to the function. Function-level value IDs are assigned starting from
|
|
``NumModuleValues`` since they share the same namespace as module-level
|
|
values. The value enumerator resets after each function. When a value is
|
|
an operand of an instruction, the value ID is used to represent the operand.
|
|
For large functions or large modules, these operand values can be large.
|
|
|
|
The encoding in version 1 attempts to avoid large operand values
|
|
in common cases. Instead of using the value ID directly, operands are
|
|
encoded as relative to the current instruction. Thus, if an operand
|
|
is the value defined by the previous instruction, the operand
|
|
will be encoded as 1.
|
|
|
|
For example, instead of
|
|
|
|
.. code-block:: llvm
|
|
|
|
#n = load #n-1
|
|
#n+1 = icmp eq #n, #const0
|
|
br #n+1, label #(bb1), label #(bb2)
|
|
|
|
version 1 will encode the instructions as
|
|
|
|
.. code-block:: llvm
|
|
|
|
#n = load #1
|
|
#n+1 = icmp eq #1, (#n+1)-#const0
|
|
br #1, label #(bb1), label #(bb2)
|
|
|
|
Note in the example that operands which are constants also use
|
|
the relative encoding, while operands like basic block labels
|
|
do not use the relative encoding.
|
|
|
|
Forward references will result in a negative value.
|
|
This can be inefficient, as operands are normally encoded
|
|
as unsigned VBRs. However, forward references are rare, except in the
|
|
case of phi instructions. For phi instructions, operands are encoded as
|
|
`Signed VBRs`_ to deal with forward references.
|
|
|
|
|
|
MODULE_CODE_TRIPLE Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[TRIPLE, ...string...]``
|
|
|
|
The ``TRIPLE`` record (code 2) contains a variable number of values representing
|
|
the bytes of the ``target triple`` specification string.
|
|
|
|
MODULE_CODE_DATALAYOUT Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[DATALAYOUT, ...string...]``
|
|
|
|
The ``DATALAYOUT`` record (code 3) contains a variable number of values
|
|
representing the bytes of the ``target datalayout`` specification string.
|
|
|
|
MODULE_CODE_ASM Record
|
|
^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[ASM, ...string...]``
|
|
|
|
The ``ASM`` record (code 4) contains a variable number of values representing
|
|
the bytes of ``module asm`` strings, with individual assembly blocks separated
|
|
by newline (ASCII 10) characters.
|
|
|
|
.. _MODULE_CODE_SECTIONNAME:
|
|
|
|
MODULE_CODE_SECTIONNAME Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[SECTIONNAME, ...string...]``
|
|
|
|
The ``SECTIONNAME`` record (code 5) contains a variable number of values
|
|
representing the bytes of a single section name string. There should be one
|
|
``SECTIONNAME`` record for each section name referenced (e.g., in global
|
|
variable or function ``section`` attributes) within the module. These records
|
|
can be referenced by the 1-based index in the *section* fields of ``GLOBALVAR``
|
|
or ``FUNCTION`` records.
|
|
|
|
MODULE_CODE_DEPLIB Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[DEPLIB, ...string...]``
|
|
|
|
The ``DEPLIB`` record (code 6) contains a variable number of values representing
|
|
the bytes of a single dependent library name string, one of the libraries
|
|
mentioned in a ``deplibs`` declaration. There should be one ``DEPLIB`` record
|
|
for each library name referenced.
|
|
|
|
MODULE_CODE_GLOBALVAR Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[GLOBALVAR, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal, unnamed_addr, dllstorageclass]``
|
|
|
|
The ``GLOBALVAR`` record (code 7) marks the declaration or definition of a
|
|
global variable. The operand fields are:
|
|
|
|
* *pointer type*: The type index of the pointer type used to point to this
|
|
global variable
|
|
|
|
* *isconst*: Non-zero if the variable is treated as constant within the module,
|
|
or zero if it is not
|
|
|
|
* *initid*: If non-zero, the value index of the initializer for this variable,
|
|
plus 1.
|
|
|
|
.. _linkage type:
|
|
|
|
* *linkage*: An encoding of the linkage type for this variable:
|
|
* ``external``: code 0
|
|
* ``weak``: code 1
|
|
* ``appending``: code 2
|
|
* ``internal``: code 3
|
|
* ``linkonce``: code 4
|
|
* ``dllimport``: code 5
|
|
* ``dllexport``: code 6
|
|
* ``extern_weak``: code 7
|
|
* ``common``: code 8
|
|
* ``private``: code 9
|
|
* ``weak_odr``: code 10
|
|
* ``linkonce_odr``: code 11
|
|
* ``available_externally``: code 12
|
|
* deprecated : code 13
|
|
* deprecated : code 14
|
|
|
|
* alignment*: The logarithm base 2 of the variable's requested alignment, plus 1
|
|
|
|
* *section*: If non-zero, the 1-based section index in the table of
|
|
`MODULE_CODE_SECTIONNAME`_ entries.
|
|
|
|
.. _visibility:
|
|
|
|
* *visibility*: If present, an encoding of the visibility of this variable:
|
|
* ``default``: code 0
|
|
* ``hidden``: code 1
|
|
* ``protected``: code 2
|
|
|
|
* *threadlocal*: If present, an encoding of the thread local storage mode of the
|
|
variable:
|
|
* ``not thread local``: code 0
|
|
* ``thread local; default TLS model``: code 1
|
|
* ``localdynamic``: code 2
|
|
* ``initialexec``: code 3
|
|
* ``localexec``: code 4
|
|
|
|
* *unnamed_addr*: If present and non-zero, indicates that the variable has
|
|
``unnamed_addr``
|
|
|
|
.. _dllstorageclass:
|
|
|
|
* *dllstorageclass*: If present, an encoding of the DLL storage class of this variable:
|
|
|
|
* ``default``: code 0
|
|
* ``dllimport``: code 1
|
|
* ``dllexport``: code 2
|
|
|
|
.. _FUNCTION:
|
|
|
|
MODULE_CODE_FUNCTION Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[FUNCTION, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc, prefix, dllstorageclass]``
|
|
|
|
The ``FUNCTION`` record (code 8) marks the declaration or definition of a
|
|
function. The operand fields are:
|
|
|
|
* *type*: The type index of the function type describing this function
|
|
|
|
* *callingconv*: The calling convention number:
|
|
* ``ccc``: code 0
|
|
* ``fastcc``: code 8
|
|
* ``coldcc``: code 9
|
|
* ``webkit_jscc``: code 12
|
|
* ``anyregcc``: code 13
|
|
* ``preserve_mostcc``: code 14
|
|
* ``preserve_allcc``: code 15
|
|
* ``x86_stdcallcc``: code 64
|
|
* ``x86_fastcallcc``: code 65
|
|
* ``arm_apcscc``: code 66
|
|
* ``arm_aapcscc``: code 67
|
|
* ``arm_aapcs_vfpcc``: code 68
|
|
* ``x86_thiscallcc``: code 70
|
|
* ``x86_cdeclmethodcc``: code 80
|
|
|
|
* isproto*: Non-zero if this entry represents a declaration rather than a
|
|
definition
|
|
|
|
* *linkage*: An encoding of the `linkage type`_ for this function
|
|
|
|
* *paramattr*: If nonzero, the 1-based parameter attribute index into the table
|
|
of `PARAMATTR_CODE_ENTRY`_ entries.
|
|
|
|
* *alignment*: The logarithm base 2 of the function's requested alignment, plus
|
|
1
|
|
|
|
* *section*: If non-zero, the 1-based section index in the table of
|
|
`MODULE_CODE_SECTIONNAME`_ entries.
|
|
|
|
* *visibility*: An encoding of the `visibility`_ of this function
|
|
|
|
* *gc*: If present and nonzero, the 1-based garbage collector index in the table
|
|
of `MODULE_CODE_GCNAME`_ entries.
|
|
|
|
* *unnamed_addr*: If present and non-zero, indicates that the function has
|
|
``unnamed_addr``
|
|
|
|
* *prefix*: If non-zero, the value index of the prefix data for this function,
|
|
plus 1.
|
|
|
|
* *dllstorageclass*: An encoding of the `dllstorageclass`_ of this function
|
|
|
|
MODULE_CODE_ALIAS Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[ALIAS, alias type, aliasee val#, linkage, visibility, dllstorageclass]``
|
|
|
|
The ``ALIAS`` record (code 9) marks the definition of an alias. The operand
|
|
fields are
|
|
|
|
* *alias type*: The type index of the alias
|
|
|
|
* *aliasee val#*: The value index of the aliased value
|
|
|
|
* *linkage*: An encoding of the `linkage type`_ for this alias
|
|
|
|
* *visibility*: If present, an encoding of the `visibility`_ of the alias
|
|
|
|
* *dllstorageclass*: If present, an encoding of the `dllstorageclass`_ of the alias
|
|
|
|
MODULE_CODE_PURGEVALS Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[PURGEVALS, numvals]``
|
|
|
|
The ``PURGEVALS`` record (code 10) resets the module-level value list to the
|
|
size given by the single operand value. Module-level value list items are added
|
|
by ``GLOBALVAR``, ``FUNCTION``, and ``ALIAS`` records. After a ``PURGEVALS``
|
|
record is seen, new value indices will start from the given *numvals* value.
|
|
|
|
.. _MODULE_CODE_GCNAME:
|
|
|
|
MODULE_CODE_GCNAME Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[GCNAME, ...string...]``
|
|
|
|
The ``GCNAME`` record (code 11) contains a variable number of values
|
|
representing the bytes of a single garbage collector name string. There should
|
|
be one ``GCNAME`` record for each garbage collector name referenced in function
|
|
``gc`` attributes within the module. These records can be referenced by 1-based
|
|
index in the *gc* fields of ``FUNCTION`` records.
|
|
|
|
.. _PARAMATTR_BLOCK:
|
|
|
|
PARAMATTR_BLOCK Contents
|
|
------------------------
|
|
|
|
The ``PARAMATTR_BLOCK`` block (id 9) contains a table of entries describing the
|
|
attributes of function parameters. These entries are referenced by 1-based index
|
|
in the *paramattr* field of module block `FUNCTION`_ records, or within the
|
|
*attr* field of function block ``INST_INVOKE`` and ``INST_CALL`` records.
|
|
|
|
Entries within ``PARAMATTR_BLOCK`` are constructed to ensure that each is unique
|
|
(i.e., no two indicies represent equivalent attribute lists).
|
|
|
|
.. _PARAMATTR_CODE_ENTRY:
|
|
|
|
PARAMATTR_CODE_ENTRY Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[ENTRY, paramidx0, attr0, paramidx1, attr1...]``
|
|
|
|
The ``ENTRY`` record (code 1) contains an even number of values describing a
|
|
unique set of function parameter attributes. Each *paramidx* value indicates
|
|
which set of attributes is represented, with 0 representing the return value
|
|
attributes, 0xFFFFFFFF representing function attributes, and other values
|
|
representing 1-based function parameters. Each *attr* value is a bitmap with the
|
|
following interpretation:
|
|
|
|
* bit 0: ``zeroext``
|
|
* bit 1: ``signext``
|
|
* bit 2: ``noreturn``
|
|
* bit 3: ``inreg``
|
|
* bit 4: ``sret``
|
|
* bit 5: ``nounwind``
|
|
* bit 6: ``noalias``
|
|
* bit 7: ``byval``
|
|
* bit 8: ``nest``
|
|
* bit 9: ``readnone``
|
|
* bit 10: ``readonly``
|
|
* bit 11: ``noinline``
|
|
* bit 12: ``alwaysinline``
|
|
* bit 13: ``optsize``
|
|
* bit 14: ``ssp``
|
|
* bit 15: ``sspreq``
|
|
* bits 16-31: ``align n``
|
|
* bit 32: ``nocapture``
|
|
* bit 33: ``noredzone``
|
|
* bit 34: ``noimplicitfloat``
|
|
* bit 35: ``naked``
|
|
* bit 36: ``inlinehint``
|
|
* bits 37-39: ``alignstack n``, represented as the logarithm
|
|
base 2 of the requested alignment, plus 1
|
|
|
|
.. _TYPE_BLOCK:
|
|
|
|
TYPE_BLOCK Contents
|
|
-------------------
|
|
|
|
The ``TYPE_BLOCK`` block (id 10) contains records which constitute a table of
|
|
type operator entries used to represent types referenced within an LLVM
|
|
module. Each record (with the exception of `NUMENTRY`_) generates a single type
|
|
table entry, which may be referenced by 0-based index from instructions,
|
|
constants, metadata, type symbol table entries, or other type operator records.
|
|
|
|
Entries within ``TYPE_BLOCK`` are constructed to ensure that each entry is
|
|
unique (i.e., no two indicies represent structurally equivalent types).
|
|
|
|
.. _TYPE_CODE_NUMENTRY:
|
|
.. _NUMENTRY:
|
|
|
|
TYPE_CODE_NUMENTRY Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[NUMENTRY, numentries]``
|
|
|
|
The ``NUMENTRY`` record (code 1) contains a single value which indicates the
|
|
total number of type code entries in the type table of the module. If present,
|
|
``NUMENTRY`` should be the first record in the block.
|
|
|
|
TYPE_CODE_VOID Record
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[VOID]``
|
|
|
|
The ``VOID`` record (code 2) adds a ``void`` type to the type table.
|
|
|
|
TYPE_CODE_HALF Record
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[HALF]``
|
|
|
|
The ``HALF`` record (code 10) adds a ``half`` (16-bit floating point) type to
|
|
the type table.
|
|
|
|
TYPE_CODE_FLOAT Record
|
|
^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[FLOAT]``
|
|
|
|
The ``FLOAT`` record (code 3) adds a ``float`` (32-bit floating point) type to
|
|
the type table.
|
|
|
|
TYPE_CODE_DOUBLE Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[DOUBLE]``
|
|
|
|
The ``DOUBLE`` record (code 4) adds a ``double`` (64-bit floating point) type to
|
|
the type table.
|
|
|
|
TYPE_CODE_LABEL Record
|
|
^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[LABEL]``
|
|
|
|
The ``LABEL`` record (code 5) adds a ``label`` type to the type table.
|
|
|
|
TYPE_CODE_OPAQUE Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[OPAQUE]``
|
|
|
|
The ``OPAQUE`` record (code 6) adds an ``opaque`` type to the type table. Note
|
|
that distinct ``opaque`` types are not unified.
|
|
|
|
TYPE_CODE_INTEGER Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[INTEGER, width]``
|
|
|
|
The ``INTEGER`` record (code 7) adds an integer type to the type table. The
|
|
single *width* field indicates the width of the integer type.
|
|
|
|
TYPE_CODE_POINTER Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[POINTER, pointee type, address space]``
|
|
|
|
The ``POINTER`` record (code 8) adds a pointer type to the type table. The
|
|
operand fields are
|
|
|
|
* *pointee type*: The type index of the pointed-to type
|
|
|
|
* *address space*: If supplied, the target-specific numbered address space where
|
|
the pointed-to object resides. Otherwise, the default address space is zero.
|
|
|
|
TYPE_CODE_FUNCTION Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[FUNCTION, vararg, ignored, retty, ...paramty... ]``
|
|
|
|
The ``FUNCTION`` record (code 9) adds a function type to the type table. The
|
|
operand fields are
|
|
|
|
* *vararg*: Non-zero if the type represents a varargs function
|
|
|
|
* *ignored*: This value field is present for backward compatibility only, and is
|
|
ignored
|
|
|
|
* *retty*: The type index of the function's return type
|
|
|
|
* *paramty*: Zero or more type indices representing the parameter types of the
|
|
function
|
|
|
|
TYPE_CODE_STRUCT Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[STRUCT, ispacked, ...eltty...]``
|
|
|
|
The ``STRUCT`` record (code 10) adds a struct type to the type table. The
|
|
operand fields are
|
|
|
|
* *ispacked*: Non-zero if the type represents a packed structure
|
|
|
|
* *eltty*: Zero or more type indices representing the element types of the
|
|
structure
|
|
|
|
TYPE_CODE_ARRAY Record
|
|
^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[ARRAY, numelts, eltty]``
|
|
|
|
The ``ARRAY`` record (code 11) adds an array type to the type table. The
|
|
operand fields are
|
|
|
|
* *numelts*: The number of elements in arrays of this type
|
|
|
|
* *eltty*: The type index of the array element type
|
|
|
|
TYPE_CODE_VECTOR Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[VECTOR, numelts, eltty]``
|
|
|
|
The ``VECTOR`` record (code 12) adds a vector type to the type table. The
|
|
operand fields are
|
|
|
|
* *numelts*: The number of elements in vectors of this type
|
|
|
|
* *eltty*: The type index of the vector element type
|
|
|
|
TYPE_CODE_X86_FP80 Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[X86_FP80]``
|
|
|
|
The ``X86_FP80`` record (code 13) adds an ``x86_fp80`` (80-bit floating point)
|
|
type to the type table.
|
|
|
|
TYPE_CODE_FP128 Record
|
|
^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[FP128]``
|
|
|
|
The ``FP128`` record (code 14) adds an ``fp128`` (128-bit floating point) type
|
|
to the type table.
|
|
|
|
TYPE_CODE_PPC_FP128 Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[PPC_FP128]``
|
|
|
|
The ``PPC_FP128`` record (code 15) adds a ``ppc_fp128`` (128-bit floating point)
|
|
type to the type table.
|
|
|
|
TYPE_CODE_METADATA Record
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[METADATA]``
|
|
|
|
The ``METADATA`` record (code 16) adds a ``metadata`` type to the type table.
|
|
|
|
.. _CONSTANTS_BLOCK:
|
|
|
|
CONSTANTS_BLOCK Contents
|
|
------------------------
|
|
|
|
The ``CONSTANTS_BLOCK`` block (id 11) ...
|
|
|
|
.. _FUNCTION_BLOCK:
|
|
|
|
FUNCTION_BLOCK Contents
|
|
-----------------------
|
|
|
|
The ``FUNCTION_BLOCK`` block (id 12) ...
|
|
|
|
In addition to the record types described below, a ``FUNCTION_BLOCK`` block may
|
|
contain the following sub-blocks:
|
|
|
|
* `CONSTANTS_BLOCK`_
|
|
* `VALUE_SYMTAB_BLOCK`_
|
|
* `METADATA_ATTACHMENT`_
|
|
|
|
.. _TYPE_SYMTAB_BLOCK:
|
|
|
|
TYPE_SYMTAB_BLOCK Contents
|
|
--------------------------
|
|
|
|
The ``TYPE_SYMTAB_BLOCK`` block (id 13) contains entries which map between
|
|
module-level named types and their corresponding type indices.
|
|
|
|
.. _TST_CODE_ENTRY:
|
|
|
|
TST_CODE_ENTRY Record
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
``[ENTRY, typeid, ...string...]``
|
|
|
|
The ``ENTRY`` record (code 1) contains a variable number of values, with the
|
|
first giving the type index of the designated type, and the remaining values
|
|
giving the character codes of the type name. Each entry corresponds to a single
|
|
named type.
|
|
|
|
.. _VALUE_SYMTAB_BLOCK:
|
|
|
|
VALUE_SYMTAB_BLOCK Contents
|
|
---------------------------
|
|
|
|
The ``VALUE_SYMTAB_BLOCK`` block (id 14) ...
|
|
|
|
.. _METADATA_BLOCK:
|
|
|
|
METADATA_BLOCK Contents
|
|
-----------------------
|
|
|
|
The ``METADATA_BLOCK`` block (id 15) ...
|
|
|
|
.. _METADATA_ATTACHMENT:
|
|
|
|
METADATA_ATTACHMENT Contents
|
|
----------------------------
|
|
|
|
The ``METADATA_ATTACHMENT`` block (id 16) ...
|