Hi,
What I usually hear in gcc vs comparisons is that clang does not yet
optimize the code as good gcc
(fun fact: sometimes that's because it's more standards conformant).
Nevertheless, it's always
a good idea to compile the code with as many compilers as possible -
that way more meaningful warnings
could be found. An example - when I was compiling the patch, clang has
found this:
/builds/ceph-histograms/src/include/denc.h:1160:10: warning: binding
dereferenced null pointer to reference has undefined behavior
[-Wnull-dereference]
denc(*(bool *)nullptr, p);
^~~~~~~~~~~~~~~~
And I strongly believe we should get rid of it - dereferencing null
pointer in C++ is undefined
behavior so the compiler can do whatever he wants there. Even if it
works with current gcc,
more aggressive optimizations added to compilers in the future could
make this totally broken.
I've observed it's a common practice in many companies to develop using
clang (to get
best diagnostic and tools) but do the final release using gcc (to get
the best performance).
I also like clang for the number of tools built on top of clang - static
analyzers, sanitizers,
code formatting etc. Chandler Carruth from Goggle has given some nice
talks about this:
https://youtu.be/cX_GhJ6BuWI, https://youtu.be/E36BUcTWo50.
Regards,
Bartek
On 02/10/2017 10:31 AM, Brad Hubbard wrote:
Whilst I agree clang has some advantages I also understand from
watching recent videos that it has some disadvantages/shortcomings as
well (can't remember the specifics atm). Whilst I don't agree we
should be switching to clang I do suggest we should be compiling with
it regularly since it can pick up problems that gcc may not.
My 2c.
On Fri, Feb 10, 2017 at 12:46 PM, liuchang0812 <liuchang0812@xxxxxxxxx> wrote:
clang's compile warn is clearer than gcc
2017-02-10 2:10 GMT+08:00 Willem Jan Withagen <wjw@xxxxxxxxxxx>:
On 9-2-2017 17:18, Bassam Tabbara wrote:
Hi,
I’m curious are there specific advantages to compiling Ceph with
clang vs. gcc? I understand that clang uses less memory, compiles
faster, and has better errors/diagnostics, but as it relates to Ceph
is there any specific advantages?
Is there a plan to switching to clang?
There are a few reasons for also using Clang:
- Clang finds other types of issues in the code.
I think the speed, mem-footprint advantages you mention are not
(yet) the case.
- FreeBSD has Clang as native compiler, and I'm preparing a Ceph port
to FreeBSD.
Thanx for fixing this, I saw the PR fly by.
--WjW
Thanks! Bassam
On Feb 9, 2017, at 7:35 AM, Willem Jan Withagen <wjw@xxxxxxxxxxx>
wrote:
Hi,
I think this is a recent addition to the game? And Clang does not
really like it.
In file included from
/home/jenkins/workspace/ceph-master/src/common/perf_counters.h:21:
/home/jenkins/workspace/ceph-master/src/common/perf_histogram.h:80:9:
error: array initializer must be an initializer list
: m_axes_config(other.m_axes_config) { ^
/home/jenkins/workspace/ceph-master/src/common/perf_counters.h:98:29:
note: in instantiation of member function
'PerfHistogram<2>::PerfHistogram' requested here
histogram.reset(new PerfHistogram<>(*other.histogram)); ^ 1 error
generated.
--WjW -- To unsubscribe from this list: send the line "unsubscribe
ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
https://urldefense.proofpoint.com/v2/url?u=http-3A__vger.kernel.org_majordomo-2Dinfo.html&d=DwICaQ&c=8S5idjlO_n28Ko3lg6lskTMwneSC-WqZ5EBTEEvDlkg&r=BTMd2ANcDl5P_nTkEam5zzywWdGjHoaoXy4JMG_yHPA&m=PzCl2U7BH52mycDw3PiC7LaCbGCCTewMNBUqu8gGKIQ&s=gR4xXKHg4AFcwEccrIs-KoM7bjGw0aL9CnVF_PQE_fo&e=
--
To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
