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On RISC-V, there are a few ways to control whether the PostMachineScheduler is enabled. If `-enable-post-misched` is passed or passed with a value of true, then the PostMachineScheduler is enabled. If it is passed with a value of false then the PostMachineScheduler is disabled. If the option is not passed at all, then `RISCVSubtarget::enablePostRAMachineScheduler` decides whether the pass should be enabled or not. `TargetSubtargetInfo::enablePostRAScheduler` and `TargetSubtargetInfo::enablePostRAMachineScheduler` who check the SchedModel value are not called by RISC-V backend. `RISCVSubtarget::enablePostRAMachineScheduler` currently checks if the active scheduler model sets `PostRAScheduler`. If it is set to true by the scheduler model, then the pass is enabled. If it is not set to true by the scheduler model, then the value of `UsePostRAScheduler` subtarget feature is used. I argue that the RISC-V backend should not use `PostRAScheduler` field of the scheduler model to control whether the PostMachineScheduler is enabled for the following reasons: 1. No other targets use this value to control whether PostMachineScheduler is enabled. They only use it to check whether the legacy PostRASchedulerList scheduler is enabled. 2. We can add the `UsePostRAScheduler` feature to the processor definition in RISCVProcessors.td to tie a processor to whether the pass should be enabled by default. This makes the feature and the sched model field redundant. 3. Since these options are redundant, we should prefer the feature, since we can set `+` and `-` on the feature, but the value of the scheduler cannot be controlled on the command line. 4. Keeping both options allows us to set the feature and the scheduler model value to conflicting values. Although the scheduler model value will win out, it feels awkward to allow it.
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