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| author | Peter Collingbourne <peter@pcc.me.uk> | 2014-09-18 21:28:49 +0000 |
|---|---|---|
| committer | Peter Collingbourne <peter@pcc.me.uk> | 2014-09-18 21:28:49 +0000 |
| commit | 10039c02ea1d34d39fb3b66f522c53bb50751da5 (patch) | |
| tree | d0fcaa82f000b5ef6f140be711ae02155192c4fd /llvm/docs | |
| parent | 6bf091c656f319e36721364fe50c456efca36df6 (diff) | |
| download | bcm5719-llvm-10039c02ea1d34d39fb3b66f522c53bb50751da5.tar.gz bcm5719-llvm-10039c02ea1d34d39fb3b66f522c53bb50751da5.zip | |
LTO: introduce object file-based on-disk module format.
This format is simply a regular object file with the bitcode stored in a
section named ".llvmbc", plus any number of other (non-allocated) sections.
One immediate use case for this is to accommodate compilation processes
which expect the object file to contain metadata in non-allocated sections,
such as the ".go_export" section used by some Go compilers [1], although I
imagine that in the future we could consider compiling parts of the module
(such as large non-inlinable functions) directly into the object file to
improve LTO efficiency.
[1] http://golang.org/doc/install/gccgo#Imports
Differential Revision: http://reviews.llvm.org/D4371
llvm-svn: 218078
Diffstat (limited to 'llvm/docs')
| -rw-r--r-- | llvm/docs/BitCodeFormat.rst | 18 | ||||
| -rw-r--r-- | llvm/docs/ReleaseNotes.rst | 3 |
2 files changed, 19 insertions, 2 deletions
diff --git a/llvm/docs/BitCodeFormat.rst b/llvm/docs/BitCodeFormat.rst index fce1e37cf51..2e487b32131 100644 --- a/llvm/docs/BitCodeFormat.rst +++ b/llvm/docs/BitCodeFormat.rst @@ -28,8 +28,9 @@ Unlike XML, the bitstream format is a binary encoding, and unlike XML it provides a mechanism for the file to self-describe "abbreviations", which are effectively size optimizations for the content. -LLVM IR files may be optionally embedded into a `wrapper`_ structure that makes -it easy to embed extra data along with LLVM IR files. +LLVM IR files may be optionally embedded into a `wrapper`_ structure, or in a +`native object file`_. Both of these mechanisms make it easy to embed extra +data along with LLVM IR files. This document first describes the LLVM bitstream format, describes the wrapper format, then describes the record structure used by LLVM IR files. @@ -460,6 +461,19 @@ 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. +.. _native object file: + +Native Object File Wrapper Format +================================= + +Bitcode files for LLVM IR may also be wrapped in a native object file +(i.e. ELF, COFF, Mach-O). The bitcode must be stored in a section of the +object file named ``.llvmbc``. This wrapper format is useful for accommodating +LTO in compilation pipelines where intermediate objects must be native object +files which contain metadata in other sections. + +Not all tools support this format. + .. _encoding of LLVM IR: LLVM IR Encoding diff --git a/llvm/docs/ReleaseNotes.rst b/llvm/docs/ReleaseNotes.rst index dad7e7ed842..be2954ce3c4 100644 --- a/llvm/docs/ReleaseNotes.rst +++ b/llvm/docs/ReleaseNotes.rst @@ -43,6 +43,9 @@ Non-comprehensive list of changes in this release * Support for AuroraUX has been removed. +* Added support for a `native object file-based bitcode wrapper format + <BitCodeFormat.html#native-object-file>`_. + * ... next change ... .. NOTE |
