[cfe-dev] Documenting Clang: question about how best to deliver the doc
Sean Silva
silvas at purdue.edu
Wed Aug 21 16:46:22 PDT 2013
On Tue, Aug 20, 2013 at 8:57 PM, Morrison, Michael <
Michael_Morrison at playstation.sony.com> wrote:
> Our main concern is picking the path forward that is most preferred by
> the community. Given the discussion thus far, it sounds like the two
> front-runners are:
>
> **
>
> ** **
>
> 1a) Maintain the documentation in Doxygen. Any other formats required
> (HTML, XML, etc) can be generated on-the-fly from the Doxygen comments as
> needed.
>
This has the advantage that -Wdocumentation will ensure that the docs and
prototypes/argument lists are in sync; I'm not sure how significant that is
since the code in these headers is mostly "write only" and not subject to
continual maintenance and evolution (at least, not to the extent of
"regular code").
Dmitri's point about formatting bears further investigation. You may want
to do a similar check for reST (although reST is quite rich already, so
hopefully nothing will be missing); however, reST is extensible from Sphinx
plugins (e.g. custom directives/roles) so there will always be a way to
work around any particular issue.
One concern for both approaches is how much code will be necessary to
translate Doxygen/Sphinx formatted text into the desired output format.
Will a simple "map this XML element to this other one" table be enough, or
will it require a lot of nasty hand-coded stuff ("for ordered lists do
this, for unordered lists do that, for italic do some other thing, for
monospace do yet another thing, etc")?
> ****
>
> ** 2) Maintain the documentation in reST/Doxygen. Any other formats
> required can be generated on-the-fly from the reST as needed. (Also, it
> seems that Sphynx has good plugins and support for converting to other
> formats.)
>
Having worked on the Sphinx docs a lot, I have a fairly good idea of the
extent of what Sphinx can do, and I can envision an easy-to-maintain way to
handle these docs. Using reST "field lists" <
http://docutils.sourceforge.net/docs/user/rst/quickref.html#field-lists>
and other reST features, you could capture it in a "highly semantic" form
like this:
:Header: x86intrin.h
:Prototype: __m256 _mm256_round_ps(__m256 v, const int m);
:Instruction: VROUNDPS
:Description:
Rounds the values stored in a packed 256-bit vector [8 x float] as
specified by the byte operand. The source values are rounded to integer
values and returned as floating point values.
:Parameters:
v
A 256-bit vector of [8 x float] values.
m
An immediate byte operand specifying how the rounding is to be
performed.
Bits [7:4] are reserved.
Bit [3] is a precision exception value:
0: A normal PE exception is used
1: The PE field is not updated
Bit [2] is a rounding control source:
0: MXCSR:RC
1: Use the RC field value
Bit [1:0] contain the rounding control definition:
00: Nearest
01: Downward (toward negative infinity)
10: Upward (toward positive infinity)
11: Truncated
:Returns:
A 256-bit vector of [8 x float] containing the rounded values.
Most of the structure in the above snippet will be represented in the
docutils XML representation. I'm not very familiar with Doxygen markup, but
my understanding is that it wouldn't be possible to semantically capture
the equivalent of the :Header: field (unless something like that is already
hardcoded into doxygen). I use the term "semantically" to indicate that
it's not just a piece of text marked up to be formatted in a specific way,
but instead associates a specific semantic intent to the text, which can
then be programmatically extracted/manipulated.
I'm not sure how important a "semantic" representation is though. What sort
of information needs to be emitted for the Microsoft tooltip format? Is it
just a blob of arbitrary formatted text, or does it actually require
separating things like "which header should be included to get this
definition"?
-- Sean Silva
> **
>
> ** **
>
> Cheers,****
>
> Michael****
>
> ** **
>
> *From:* Sean Silva [mailto:silvas at purdue.edu]
> *Sent:* Monday, 19 August, 2013 18:35
> *To:* Morrison, Michael
> *Cc:* cfe-dev at cs.uiuc.edu; Rafael Ávila de Espíndola; me at filcab.net
> *Subject:* Re: [cfe-dev] Documenting Clang: question about how best to
> deliver the doc****
>
> ** **
>
> ** **
>
> ** **
>
> On Mon, Aug 19, 2013 at 5:39 PM, Morrison, Michael <
> Michael_Morrison at playstation.sony.com> wrote:****
>
> As some of you know, we at Sony Computer Entertainment America have been
> working on various aspects of LLVM, including Clang and its toolchain. As
> part of our work, we have created documentation for our customers about
> using Clang, and we would like to share the fruits of our work with the
> Clang and LLVM communities.****
>
> ****
>
> As our first documentation submission, we plan to provide our *CPU
> Intrinsics Guide*, which documents the Clang intrinsics for x86intrin.h,
> along with several builtin and sync types. I've included a sample of what
> we document for one of the intrinsics below.****
>
> ****
>
> Our question for the community is: what documentation format is most
> helpful and desired for this information? We currently have two main
> possibilities in mind (with three variants for the first option):****
>
> ****
>
> 1) Add the documentation for each intrinsic to the header file:****
>
> ****
>
> - 1a) Using Doxygen tagging. One benefit of this approach is that the
> documentation is available for the developer within a
> code-development/editing system. One potential difficulty with this
> approach is that the intrinsics header file becomes much larger, which
> could increase compile times.****
>
> ** **
>
> As Eli mentioned, it would be nice to get some performance numbers.****
>
> ** **
>
> ****
>
> - 1b) Using Microsoft's annotation grammar. We might be able to contain
> this annotation grammar within Doxygen tagging that deviates somewhat from
> the LLVM Doxygen style. This approach allows us to generate XML output for
> the Microsoft Visual Studio Tooltip class. The benefit of this approach is
> that the documentation is available for the developer within Visual Studio,
> without his or her having to open the specific header file. Like option
> (1a), one potential difficulty with this approach is that the intrinsics
> header file becomes much larger, which could increase compile times.****
>
> ** **
>
> Is generating MSVS Tooltip XML output a hard requirement for your use
> case? If so, can you estimate how much effort it is to convert to that
> format given each of these options? My suspicion is that keeping this info
> in reST or even just a structured XML file converted to reST with a Sphinx
> plugin for docs generation will be the easiest solution; in both cases, it
> should be a fairly straightforward Python script to slurp in the file and
> spit out XML (the `docutils` library that Sphinx is based on and that reads
> in the reST has a nice XML-based internal representation of the reST
> document).****
>
> ****
>
> ****
>
> - 1c) Using TblGen to maintain both the intrinsics definitions and their
> documentation, from which we generate the header file with both. With this
> approach, we could implement either option (1a), (1b), or both, and have a
> single point of maintenance. This option has the same benefits and
> drawbacks as (1a) and (1b).****
>
> ****
>
> 2) Add the documentation in reST and Sphynx format (to match existing
> Clang and LLVM documentation) to the Clang Web site. The main benefit of
> this approach is that the documentation is available to anyone on the Web.
> ****
>
> ****
>
> ****
>
> Thus, we come to you today to ask your opinion on which approach we should
> take. We're open to providing one or more of the formats, as desired, or
> considering a different option that one of you might make.****
>
> ** **
>
> In what format is the documentation currently?****
>
> ** **
>
> -- Sean Silva****
>
> ****
>
> ****
>
> ****
>
> Sample intrinsic documentation (ASCII formatted for forum viewing)****
>
> -------------------------------****
>
> ****
>
> _mm256_round_ps****
>
> ****
>
> SYNOPSIS****
>
> #include <x86intrin.h>****
>
> __m256 _mm256_round_ps(__m256 v, const int m);****
>
> ****
>
> INSTRUCTION****
>
> VROUNDPS****
>
> ****
>
> DESCRIPTION****
>
> Rounds the values stored in a packed 256-bit vector [8 x float] as
> specified by the byte operand. The source values are rounded to integer
> values and returned as floating point values.****
>
> ****
>
> PARAMETERS****
>
> v A 256-bit vector of [8 x float] values.****
>
> m An immediate byte operand specifying how the rounding is to
> be performed.****
>
> Bits [7:4] are reserved.****
>
> Bit [3] is a precision exception value:****
>
> 0: A normal PE exception is used****
>
> 1: The PE field is not updated****
>
> Bit [2] is a rounding control source:****
>
> 0: MXCSR:RC****
>
> 1: Use the RC field value****
>
> Bit [1:0] contain the rounding control definition:****
>
> 00: Nearest****
>
> 01: Downward (toward negative infinity)***
> *
>
> 10: Upward (toward positive infinity)****
>
> 11: Truncated****
>
> ****
>
> RETURNS****
>
> A 256-bit vector of [8 x float] containing the rounded values.****
>
> ****
>
> -------------------------------****
>
> ****
>
> ****
>
> Cheers,****
>
> Michael****
>
> △○×□ お疲れ様です****
>
> ****
>
>
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> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev****
>
> ** **
>
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