[cfe-dev] Implement foo in terms of __builtin_foo fails
Jon Chesterfield via cfe-dev
cfe-dev at lists.llvm.org
Mon Feb 26 08:08:50 PST 2018
I can now present this problem more clearly. I was missing flags
fno-math-errno, fno-trapping-math, but clang is also missing some
functionality.
I think that various clang builtins have the same semantics as llvm
builtins with both of these math flags set, e.g. sin, exp. There's special
handling for sqrt (including returning undef on negative inputs with
no-nans-fp-math) in CGBuiltin, but most of libm is emitted as library calls.
SelectionDAGBuilder then matches some of the library calls and emits ISD
nodes for them, e.g. it supports exp2 but misses exp. This is too late for
implementing libm but otherwise OK.
I would like to add handling to CGBuiltin to lower more of the libm derived
clang intrinsics to llvm intrinsics when appropriate fpmath flags are set.
AMDGPU duplicates the libm derived builtins, lowering them via
SelectionDAG. This would also work for me but it seems a shame to ignore
llvm.sin.f32 et al when they already exist. I can't find a way to target
them from C without changing clang.
What does the list think of extending CGBuiltin vs adding more target
specific nodes?
Cheers,
Jon
On 24 Feb 2018 05:41, "via cfe-dev" <cfe-dev at lists.llvm.org> wrote:
Send cfe-dev mailing list submissions to
cfe-dev at lists.llvm.org
To subscribe or unsubscribe via the World Wide Web, visit
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
or, via email, send a message with subject or body 'help' to
cfe-dev-request at lists.llvm.org
You can reach the person managing the list at
cfe-dev-owner at lists.llvm.org
When replying, please edit your Subject line so it is more specific
than "Re: Contents of cfe-dev digest..."
Today's Topics:
1. Re: Implement foo in terms of __builtin_foo fails
(Jon Chesterfield via cfe-dev)
2. Google Summer of Code 2018 (Réka Nikolett Kovács via cfe-dev)
3. Re: GSoC 2018 (Devin Coughlin via cfe-dev)
4. Re: Google Summer of Code 2018 (Artem Dergachev via cfe-dev)
----------------------------------------------------------------------
Message: 1
Date: Fri, 23 Feb 2018 20:45:01 +0000
From: Jon Chesterfield via cfe-dev <cfe-dev at lists.llvm.org>
To: cfe-dev at lists.llvm.org
Subject: Re: [cfe-dev] Implement foo in terms of __builtin_foo fails
Message-ID:
<CAOUYtQB2jX2YGteNifkNA1UaufCVxQeDiLmD0_v9n7rQHpaA7w at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I think this means I'm missing some compilation flags.
I'm not passing -ffast-math because treating floating point as associative
etc is unattractive, but I'm willing to violate iso c handling of errorno.
fast-math and denormal-fp-math are the only two flags I can find in the
documentation. ffreestanding and fno-builtin don't appear to change the
example. Where are the controlling flags listed?
Thanks!
Jon
On 23 Feb 2018 7:05 p.m., "Joerg Sonnenberger" <joerg at bec.de> wrote:
On Fri, Feb 23, 2018 at 05:03:46PM +0000, Jon Chesterfield via cfe-dev
wrote:
> How can I write C that generates a call to the llvm.sin.f64 intrinsic?
Why do you want to force that? The library handling already does it when
the compilation flags match them up. I.e. most of the intrinsics are a
lot more restricted than the ISO C constraints.
Joerg
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/
20180223/37d29d67/attachment-0001.html>
------------------------------
Message: 2
Date: Sat, 24 Feb 2018 01:10:34 +0100
From: Réka Nikolett Kovács via cfe-dev <cfe-dev at lists.llvm.org>
To: cfe-dev at lists.llvm.org
Subject: [cfe-dev] Google Summer of Code 2018
Message-ID:
<CAFdNtUc_hM=nHB3pUOta-HEzCGF4e-dVi6L9SeW84NBJEjr_QA at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Dear All,
I'm Réka Kovács, a final-year M.S. student from Eötvös Loránd University,
Budapest, and I would love to work on a Clang SA-related GSoC project this
summer.
I've been working on static analysis for the past half a year and started
meddling in Clang by submitting a few patches:
- 3 Clang-Tidy checks [1][2][3],
- a Clang SA check [4],
- a diagnostic flag extension [5][6], and
- a tiny tweak in the core [7].
I'm currently studying constraint solving issues in symbolic execution as
part of a university project, and plan to continue with a PhD focusing on
Clang-related stuff.
I was initially most interested in the Z3 integration project, but I've
noticed that Mikhail has applied already. Creating a checker for dangling
string pointers would also be an interesting challenge, so I'd like to
express my enthusiasm for that project.
The main goal for me would be to get more comfortable with the inner
workings of the analyzer and learn as much along the process as possible.
I'm also open to any other suggestions, so please be so kind to share your
thoughts with me.
Thanks,
Réka
[1] bugprone-suspicious-memset-usage: https://reviews.llvm.org/D32700
[2] bugprone-undefined-memory-manipulation: https://reviews.llvm.org/D35051
[3] bugprone-integer-division: https://reviews.llvm.org/D35932
[4] alpha.cplusplus.DeleteWithNonVirtualDtor: https://reviews.llvm.org/
D35796
[5] -Wenum-compare: https://reviews.llvm.org/D36407
[6] -Wenum-compare-switch: https://reviews.llvm.org/D36526
[7] model unrepresentable left shifts: https://reviews.llvm.org/D41816
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/
20180224/ee457111/attachment-0001.html>
------------------------------
Message: 3
Date: Fri, 23 Feb 2018 17:03:00 -0800
From: Devin Coughlin via cfe-dev <cfe-dev at lists.llvm.org>
To: Mikhail Ramalho <mikhail.ramalho at gmail.com>
Cc: Mikhail Ramalho via cfe-dev <cfe-dev at lists.llvm.org>
Subject: Re: [cfe-dev] GSoC 2018
Message-ID: <B33C8A2F-73E5-4D6A-A37C-FFB9F8505FB4 at apple.com>
Content-Type: text/plain; CHARSET=US-ASCII
> On Feb 23, 2018, at 9:29 AM, Mikhail Ramalho via cfe-dev <
cfe-dev at lists.llvm.org> wrote:
>
> I also have a question about the proposal. I understand that ideas about
the project will be discussed in the mailing list. However, once that's
settled and I write my first draft proposal, should I send it to the
mailing list for discussion again or should I send it only to the mentor?
Please make sure to keep email discussions on the mailing list rather than
just personal email. This is a topic that members of the community will be
interested in and will have valuable feedback on.
Devin
------------------------------
Message: 4
Date: Fri, 23 Feb 2018 21:40:32 -0800
From: Artem Dergachev via cfe-dev <cfe-dev at lists.llvm.org>
To: Réka Nikolett Kovács <rekanikolett at gmail.com>,
cfe-dev at lists.llvm.org
Subject: Re: [cfe-dev] Google Summer of Code 2018
Message-ID: <3de8dfa0-40d3-230d-aaaa-42b5dbc55a9b at gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Hey, welcome!
First of all, it's great that you let us know about your interest in the
Z3 integration project. It might be puzzling for us to come up with the
final arrangement, given how the project doesn't seem to be easy to
quantize for cooperative work, but a lot of things may change by the
time everything is settled, and your enthusiasm is an important piece of
the puzzle!
We didn't come up with other exciting project ideas so far, but the list
of projects is definitely not set in stone. I'd let you know if anything
shows up, and please feel free to share your ideas of how the analyzer
could be improved or what features you want it to have :) I guess i'd
explain the other project a little bit, for completeness.
The use-after-free-like checker for values managed by temporary objects
should be an easier and more straightforward project than Z3, but there
are quite a lot of unknowns here as well. Because internals of
std::string and other similar classes are too hard for the analyzer's
generic use-after-free checker to understand (partially because of the
lack of a good solver, but mostly due to how hard it is to track STL's
internal invariants, and how not all of the code is necessarily present
in the header), an API-specific checker seems to be necessary. The
original plan we've had in mind was to keep track of dangerous values
like str.c_str() in the program state (similarly to how
SimpleStreamChecker tracks file descriptors) and then see if any of them
are still present in memory at the end of the original value's lifetime
(similarly to how StackAddrEscape checker finds stack pointers at the
end of a function's stack frame).
With this description and your knowledge, you'd probably be able to
think of how the checker might be implemented (and if it's of interest
to you) - though also feel free to ask if you have any questions! The
unknowns here include how easy would it be to track scopes (for now we
only track function scopes, but if fairly old but recently reincarnated
patches [1] and [2] land any time soon, we may get a much better
granularity), how easy would it be to track objects when they are moved
or lifetime-extended by binding to references, which was a large problem
for other C++ object checkers, but we may work our way around it to some
extent (or do it properly, depending on my current work outlined in [3]
and in follow-up mails in February), and also how helpful inlining would
be (eg. would we be able to automagically support string_view-like
classes by inlining their methods?). So the checker would need an almost
indefinite amount of incremental improvements once the initial prototype
is done, some of which must be fairly curious and would certainly expose
you to some of the analyzer's internals.
[1] https://reviews.llvm.org/D16403
[2] https://reviews.llvm.org/D19979
[3] http://lists.llvm.org/pipermail/cfe-dev/2018-January/056691.html
On 23/02/2018 4:10 PM, Réka Nikolett Kovács via cfe-dev wrote:
> Dear All,
>
> I'm Réka Kovács, a final-year M.S. student from Eötvös Loránd
> University, Budapest, and I would love to work on a Clang SA-related
> GSoC project this summer.
>
> I've been working on static analysis for the past half a year and
> started meddling in Clang by submitting a few patches:
> - 3 Clang-Tidy checks [1][2][3],
> - a Clang SA check [4],
> - a diagnostic flag extension [5][6], and
> - a tiny tweak in the core [7].
>
> I'm currently studying constraint solving issues in symbolic execution
> as part of a university project, and plan to continue with a PhD
> focusing on Clang-related stuff.
>
> I was initially most interested in the Z3 integration project, but
> I've noticed that Mikhail has applied already. Creating a checker for
> dangling string pointers would also be an interesting challenge, so
> I'd like to express my enthusiasm for that project.
>
> The main goal for me would be to get more comfortable with the inner
> workings of the analyzer and learn as much along the process as possible.
>
> I'm also open to any other suggestions, so please be so kind to share
> your thoughts with me.
>
> Thanks,
> Réka
>
>
> [1] bugprone-suspicious-memset-usage:https://reviews.llvm.org/D32700
> <https://reviews.llvm.org/D32700>
> [2]
> bugprone-undefined-memory-manipulation:https://reviews.llvm.org/D35051
> <https://reviews.llvm.org/D35051>
> [3] bugprone-integer-division:https://reviews.llvm.org/D35932
> <https://reviews.llvm.org/D35932>
> [4]
> alpha.cplusplus.DeleteWithNonVirtualDtor:https://reviews.llvm.org/D35796
> <https://reviews.llvm.org/D35796>
> [5] -Wenum-compare:https://reviews.llvm.org/D36407
> <https://reviews.llvm.org/D36407>
> [6] -Wenum-compare-switch:https://reviews.llvm.org/D36526
> <https://reviews.llvm.org/D36526>
> [7] model unrepresentable left shifts:https://reviews.llvm.org/D41816
> <https://reviews.llvm.org/D41816>
>
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
------------------------------
Subject: Digest Footer
_______________________________________________
cfe-dev mailing list
cfe-dev at lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
------------------------------
End of cfe-dev Digest, Vol 128, Issue 71
****************************************
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20180226/eb8988d0/attachment.html>
More information about the cfe-dev
mailing list