Files
clang-p2996/llvm/docs
Hans 3bb39690d7 [coro] Lower llvm.coro.await.suspend.handle to resume with tail call (#89751)
The C++ standard requires that symmetric transfer from one coroutine to
another is performed via a tail call. Failure to do so is a miscompile
and often breaks programs by quickly overflowing the stack.

Until now, the coro split pass tried to ensure this in the
`addMustTailToCoroResumes()` function by searching for
`llvm.coro.resume` calls to lower as tail calls if the conditions were
right: the right function arguments, attributes, calling convention
etc., and if a `ret void` was sure to be reached after traversal with
some ad-hoc constant folding following the call.

This was brittle, as the kind of implicit variants required for a tail
call to happen could easily be broken by other passes (e.g. if some
instruction got in between the `resume` and `ret`), see for example
9d1cb18d19 and
284da049f5.

Also the logic seemed backwards: instead of searching for possible tail
call candidates and doing them if the circumstances are right, it seems
better to start with the intention of making the tail calls we need, and
forcing the circumstances to be right.

Now that we have the `llvm.coro.await.suspend.handle` intrinsic (since
f786881340) which corresponds exactly to
symmetric transfer, change the lowering of that to also include the
`resume` part, always lowered as a tail call.
2024-05-15 15:29:08 +02:00
..
2024-05-15 13:10:16 +01:00
2023-12-17 15:36:44 -08:00
2024-01-09 11:06:33 +08:00
2023-10-18 08:36:18 +08:00

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