gcc-6-20180606 is now available
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Re: How to get GCC on par with ICC?
On 06/06/2018 10:22 AM, Dmitry Mikushin wrote: > The opinion you've mentioned is common in scientific community. However, in > more detail it often surfaces that the used set of GCC compiler options > simply does not correspond to that "fast" version of Intel. For instance, > when you do "-O3" for Intel it actually corresponds to (at least) "-O3 > -ffast-math -march=native" of GCC. Omitting "-ffast-math" obviously > introduces significant performance gap. > Please note that if your compute cluster uses different models of CPU, be extremely careful with -march=native. I've been bitten by it in VMs, several times. Unless you always run on the same system that did the build, you are running a risk of illegal instructions. -- Knowledge is Power -- Power Corrupts Study Hard -- Be Evil
Re: How to get GCC on par with ICC?
One case where ICC can generate much faster code sometimes is by using
the nontemporal pragma [https://software.intel.com/en-us/node/524559]
with loops.
AFAIK, there's no such equivalent pragma in gcc
[https://gcc.gnu.org/ml/gcc/2012-01/msg00028.html].
When I tried this simple example
https://github.com/rnburn/square_timing/blob/master/bench.cpp that
measures times for this loop:
void compute(const double* x, index_t N, double* y) {
#pragma vector nontemporal
for(index_t i=0; i wrote:
> Dear Paul,
>
> The opinion you've mentioned is common in scientific community. However, in
> more detail it often surfaces that the used set of GCC compiler options
> simply does not correspond to that "fast" version of Intel. For instance,
> when you do "-O3" for Intel it actually corresponds to (at least) "-O3
> -ffast-math -march=native" of GCC. Omitting "-ffast-math" obviously
> introduces significant performance gap.
>
> Kind regards,
> - Dmitry Mikushin | Applied Parallel Computing LLC |
> https://parallel-computing.pro
>
>
> 2018-06-06 18:51 GMT+03:00 Paul Menzel :
>
>> Dear GCC folks,
>>
>>
>> Some scientists in our organization still want to use the Intel compiler,
>> as they say, it produces faster code, which is then executed on clusters.
>> Some resources on the Web [1][2] confirm this. (I am aware, that it’s
>> heavily dependent on the actual program.)
>>
>> My question is, is it realistic, that GCC could catch up and that the
>> scientists will start to use it over Intel’s compiler? Or will Intel
>> developers always have the lead, because they have secret documentation and
>> direct contact with the processor designers?
>>
>> If it is realistic, how can we get there? Would first the program be
>> written, and then the compiler be optimized for that? Or are just more GCC
>> developers needed?
>>
>>
>> Kind regards,
>>
>> Paul
>>
>>
>> [1]: https://colfaxresearch.com/compiler-comparison/
>> [2]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679
>> .1280&rep=rep1&type=pdf
>>
>>
Re: How to get GCC on par with ICC?
Dear Paul, The opinion you've mentioned is common in scientific community. However, in more detail it often surfaces that the used set of GCC compiler options simply does not correspond to that "fast" version of Intel. For instance, when you do "-O3" for Intel it actually corresponds to (at least) "-O3 -ffast-math -march=native" of GCC. Omitting "-ffast-math" obviously introduces significant performance gap. Kind regards, - Dmitry Mikushin | Applied Parallel Computing LLC | https://parallel-computing.pro 2018-06-06 18:51 GMT+03:00 Paul Menzel : > Dear GCC folks, > > > Some scientists in our organization still want to use the Intel compiler, > as they say, it produces faster code, which is then executed on clusters. > Some resources on the Web [1][2] confirm this. (I am aware, that it’s > heavily dependent on the actual program.) > > My question is, is it realistic, that GCC could catch up and that the > scientists will start to use it over Intel’s compiler? Or will Intel > developers always have the lead, because they have secret documentation and > direct contact with the processor designers? > > If it is realistic, how can we get there? Would first the program be > written, and then the compiler be optimized for that? Or are just more GCC > developers needed? > > > Kind regards, > > Paul > > > [1]: https://colfaxresearch.com/compiler-comparison/ > [2]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679 > .1280&rep=rep1&type=pdf > >
Re: How to get GCC on par with ICC?
On Wed, Jun 6, 2018 at 3:51 PM, Paul Menzel wrote: > Dear GCC folks, > > > Some scientists in our organization still want to use the Intel compiler, as > they say, it produces faster code, which is then executed on clusters. Some > resources on the Web [1][2] confirm this. (I am aware, that it’s heavily > dependent on the actual program.) > > My question is, is it realistic, that GCC could catch up and that the > scientists will start to use it over Intel’s compiler? Or will Intel > developers always have the lead, because they have secret documentation and > direct contact with the processor designers? > > If it is realistic, how can we get there? Would first the program be > written, and then the compiler be optimized for that? Or are just more GCC > developers needed? There are developers actually working on performance optimization in GCC so you are not the only one :). As an opensource compiler we do lack resource so more developers is always good for the project. As Joel pointed out, typical/reduced workload showing the performance gap is very important for our developers as well as attracting new developers. We can probably open a meta-bug for tracking if you have many of these example workloads. Thanks, bin > > > Kind regards, > > Paul > > > [1]: https://colfaxresearch.com/compiler-comparison/ > [2]: > http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679.1280&rep=rep1&type=pdf >
Re: How to get GCC on par with ICC?
Dear Joel, Thank you for your quick reply. On 06/06/18 17:57, Joel Sherrill wrote: On Wed, Jun 6, 2018 at 10:51 AM, Paul Menzel wrote: Some scientists in our organization still want to use the Intel compiler, as they say, it produces faster code, which is then executed on clusters. Some resources on the Web [1][2] confirm this. (I am aware, that it’s heavily dependent on the actual program.) Do they have specific examples where icc is better for them? Or can point to specific GCC PRs which impact them? GCC versions? Are there specific CPU model variants of concern? What flags are used to compile? Some times a bit of advice can produce improvements. Without specific examples, it is hard to set goals. I could get such examples, but it will take some time, as it’s from other institutes. The clusters use exclusively Intel processors. (Hopefully, that will change.) I also found the article from the German Linux-Magazin in an English version at the ADMIN Magazin [3]. The German article had a more strong statement, that they use the Intel compilers due to performance reasons. My question is, is it realistic, that GCC could catch up and that the scientists will start to use it over Intel’s compiler? Or will Intel developers always have the lead, because they have secret documentation and direct contact with the processor designers? If it is realistic, how can we get there? Would first the program be written, and then the compiler be optimized for that? Or are just more GCC developers needed? For sure examples are needed so there are test cases to use for reference. If you want anything improved in any free software project, sponsoring developers is always a good thing. If you sponsor the right developers. :) That’s what I hoped for, but didn’t ask here. If you could point me to a list of possible contractors, that would be great. Please keep in mind, that in my organization certain decisions are made *very* slowly. I’ll try to get answers quickly, but procuring finances might take longer (half a year or much longer). Kind regards, Paul [1]: https://colfaxresearch.com/compiler-comparison/ [2]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679.1280&rep=rep1&type=pdf [3] http://www.admin-magazine.com/HPC/Articles/Selecting-Compilers-for-a-Supercomputer "HPC Compilers" smime.p7s Description: S/MIME Cryptographic Signature
Re: How to get GCC on par with ICC?
On Wed, Jun 6, 2018 at 10:51 AM, Paul Menzel < pmenzel+gcc.gnu@molgen.mpg.de> wrote: > Dear GCC folks, > > > Some scientists in our organization still want to use the Intel compiler, > as they say, it produces faster code, which is then executed on clusters. > Some resources on the Web [1][2] confirm this. (I am aware, that it’s > heavily dependent on the actual program.) > Do they have specific examples where icc is better for them? Or can point to specific GCC PRs which impact them? GCC versions? Are there specific CPU model variants of concern? What flags are used to compile? Some times a bit of advice can produce improvements. Without specific examples, it is hard to set goals. > My question is, is it realistic, that GCC could catch up and that the > scientists will start to use it over Intel’s compiler? Or will Intel > developers always have the lead, because they have secret documentation and > direct contact with the processor designers? > > If it is realistic, how can we get there? Would first the program be > written, and then the compiler be optimized for that? Or are just more GCC > developers needed? > For sure examples are needed so there are test cases to use for reference. If you want anything improved in any free software project, sponsoring developers is always a good thing. If you sponsor the right developers. :) I'm not discouraging you. I just trying to turn this into something actionable. --joel sherrill > > > Kind regards, > > Paul > > > [1]: https://colfaxresearch.com/compiler-comparison/ > [2]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679 > .1280&rep=rep1&type=pdf > >
How to get GCC on par with ICC?
Dear GCC folks, Some scientists in our organization still want to use the Intel compiler, as they say, it produces faster code, which is then executed on clusters. Some resources on the Web [1][2] confirm this. (I am aware, that it’s heavily dependent on the actual program.) My question is, is it realistic, that GCC could catch up and that the scientists will start to use it over Intel’s compiler? Or will Intel developers always have the lead, because they have secret documentation and direct contact with the processor designers? If it is realistic, how can we get there? Would first the program be written, and then the compiler be optimized for that? Or are just more GCC developers needed? Kind regards, Paul [1]: https://colfaxresearch.com/compiler-comparison/ [2]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679.1280&rep=rep1&type=pdf smime.p7s Description: S/MIME Cryptographic Signature
Re: I want to know the information about the function arguments
On Wed, 2018-06-06 at 13:04 +0200, Martin Jambor wrote:
> Hi,
>
> On Wed, Jun 06 2018, 冠人 王 via gcc wrote:
> > When I modify the gcc source code, sometimes I do not know what
> > parameters does the function call.
> > For example,
> > bool warn_if_unused_value(const tree exp,location_t locus){
> > function declaration ...
> > }
> > I want to know what "exp" and "locus" are by using fprintf such as
> > fprintf(stderr,"%s\n%s\n",exp,locus) --> I know it does not work
> > since exp and locus is not strings
> > How should I do to know the content of variable "exp" and "locus" ?
>
> For trees, look for example at:
>
> - debug_tree (tree);
> - print_node (FILE *, const char *, tree, int);
> - print_node_brief (FILE *, const char *, const_tree, int);
>
> For location_t, I *think* you need to expand it yourself first. Look
> at
> how it is being done for example in tree-dump.c.
>
> Generally speaking, for any given type, try searching for functions
> with
> "debug" or "dump" in their names that dump any particular type.
For a location_t, you can try adding a call to "inform" e.g.
inform (locus, "some message");
This will emit a "note" diagnostic at the source location that "locus"
represents.
Alternatively, if you're already debugging the compiler in gdb, you can
call "inform" directly:
(gdb) call inform (locus, "")
and it will emit a "note" diagnostic describing "locus".
FWIW, I've written some notes on debugging GCC here:
https://dmalcolm.fedorapeople.org/gcc/newbies-guide/debugging.html
Hope this is helpful; good luck!
Dave
Re: I want to know the information about the function arguments
Hi,
On Wed, Jun 06 2018, 冠人 王 via gcc wrote:
> When I modify the gcc source code, sometimes I do not know what parameters
> does the function call.
> For example,
> bool warn_if_unused_value(const tree exp,location_t locus){ function
> declaration ...
> }
> I want to know what "exp" and "locus" are by using fprintf such as
> fprintf(stderr,"%s\n%s\n",exp,locus) --> I know it does not work since exp
> and locus is not strings
> How should I do to know the content of variable "exp" and "locus" ?
For trees, look for example at:
- debug_tree (tree);
- print_node (FILE *, const char *, tree, int);
- print_node_brief (FILE *, const char *, const_tree, int);
For location_t, I *think* you need to expand it yourself first. Look at
how it is being done for example in tree-dump.c.
Generally speaking, for any given type, try searching for functions with
"debug" or "dump" in their names that dump any particular type.
HTH
Martin
RE: What is dump_file in gcc ?
> Subject: What is dump_file in gcc ? > > I have ever seen "fprintf(dump_file,"something writes into dump_file") many > times. > I want to know what dump_file is and how can I check its content ? I'm not 100% sure, but my best guess is that this is related to GCC dumps, e.g. related to passes. You can do -fdump-- where type can be e.g. rtl and pass the pass for which you want to gather information. I suppose there is more to those dumps, but this should get you started. Sebastian > >
What is dump_file in gcc ?
I have ever seen "fprintf(dump_file,"something writes into dump_file") many times. I want to know what dump_file is and how can I check its content ?
I want to know the information about the function arguments
When I modify the gcc source code, sometimes I do not know what parameters does
the function call.
For example,
bool warn_if_unused_value(const tree exp,location_t locus){ function
declaration ...
}
I want to know what "exp" and "locus" are by using fprintf such as
fprintf(stderr,"%s\n%s\n",exp,locus) --> I know it does not work since exp and
locus is not strings
How should I do to know the content of variable "exp" and "locus" ?
