Whole wave functions are functions that will run with a full EXEC mask.
They will not be invoked directly, but instead will be launched by way
of a new intrinsic, `llvm.amdgcn.call.whole.wave` (to be added in
a future patch). These functions are meant as an alternative to the
`llvm.amdgcn.init.whole.wave` or `llvm.amdgcn.strict.wwm` intrinsics.
Whole wave functions will set EXEC to -1 in the prologue and restore the
original value of EXEC in the epilogue. They must have a special first
argument, `i1 %active`, that is going to be mapped to EXEC. They may
have either the default calling convention or amdgpu_gfx. The inactive
lanes need to be preserved for all registers used, active lanes only for
the CSRs.
At the IR level, arguments to a whole wave function (other than
`%active`) contain poison in their inactive lanes. Likewise, the return
value for the inactive lanes is poison.
This patch contains the following work:
* 2 new pseudos, SI_SETUP_WHOLE_WAVE_FUNC and SI_WHOLE_WAVE_FUNC_RETURN
used for managing the EXEC mask. SI_SETUP_WHOLE_WAVE_FUNC will return
a SReg_1 representing `%active`, which needs to be passed into
SI_WHOLE_WAVE_FUNC_RETURN.
* SelectionDAG support for generating these 2 new pseudos and the
special handling of %active. Since the return may be in a different
basic block, it's difficult to add the virtual reg for %active to
SI_WHOLE_WAVE_FUNC_RETURN, so we initially generate an IMPLICIT_DEF
which is later replaced via a custom inserter.
* Expansion of the 2 pseudos during prolog/epilog insertion. PEI also
marks any used VGPRs as WWM registers, which are then spilled and
restored with the usual logic.
Future patches will include the `llvm.amdgcn.call.whole.wave` intrinsic
and a lot of optimization work (especially in order to reduce spills
around function calls).
---------
Co-authored-by: Matt Arsenault <Matthew.Arsenault@amd.com>
Co-authored-by: Shilei Tian <i@tianshilei.me>
LLVM Documentation
==================
LLVM's documentation is written in reStructuredText, a lightweight
plaintext markup language (file extension `.rst`). While the
reStructuredText documentation should be quite readable in source form, it
is mostly meant to be processed by the Sphinx documentation generation
system to create HTML pages which are hosted on <https://llvm.org/docs/> and
updated after every commit. Manpage output is also supported, see below.
If you instead would like to generate and view the HTML locally, install
Sphinx <http://sphinx-doc.org/> and then do:
cd <build-dir>
cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_HTML=true <src-dir>
make -j3 docs-llvm-html
$BROWSER <build-dir>/docs/html/index.html
The mapping between reStructuredText files and generated documentation is
`docs/Foo.rst` <-> `<build-dir>/docs//html/Foo.html` <-> `https://llvm.org/docs/Foo.html`.
If you are interested in writing new documentation, you will want to read
`SphinxQuickstartTemplate.rst` which will get you writing documentation
very fast and includes examples of the most important reStructuredText
markup syntax.
Manpage Output
===============
Building the manpages is similar to building the HTML documentation. The
primary difference is to use the `man` makefile target, instead of the
default (which is `html`). Sphinx then produces the man pages in the
directory `<build-dir>/docs/man/`.
cd <build-dir>
cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_MAN=true <src-dir>
make -j3 docs-llvm-man
man -l <build-dir>/docs/man/FileCheck.1
The correspondence between .rst files and man pages is
`docs/CommandGuide/Foo.rst` <-> `<build-dir>/docs//man/Foo.1`.
These .rst files are also included during HTML generation so they are also
viewable online (as noted above) at e.g.
`https://llvm.org/docs/CommandGuide/Foo.html`.
Checking links
==============
The reachability of external links in the documentation can be checked by
running:
cd llvm/docs/
sphinx-build -b linkcheck . _build/lintcheck/
# report will be generated in _build/lintcheck/output.txt
Doxygen page Output
==============
Install doxygen <https://www.doxygen.nl/download.html> and dot2tex <https://dot2tex.readthedocs.io/en/latest>.
cd <build-dir>
cmake -DLLVM_ENABLE_DOXYGEN=On <llvm-top-src-dir>
make doxygen-llvm # for LLVM docs
make doxygen-clang # for clang docs
It will generate html in
<build-dir>/docs/doxygen/html # for LLVM docs
<build-dir>/tools/clang/docs/doxygen/html # for clang docs
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