autovectorization in gcc

autovectorization in gcc

[Xin Tong]

One of the research projects I am working on at the University of
Toronto is the speculative vectorization. Nowadays, many processors
come with vector instructions.

In order to make use of its vectorization capability, one will need
autovectorization compilers (hand written assembly is not scabale).
One of the most difficult part about autovectorization is dependence
test. Very commonly, dependence test will need to rely on alias
analysis. However, alias analysis needs to be very conservative for
weakly typed languages, i.e. C, C++, etc. This could sometimes result
in the inability to fully take advantage of the vector capability of
the processor. Therefore,Say I have a processor that have a set of
speculative vector instructions,  these instructions behave just like
the regular vector instructions in case of no data dependencies, but
act as a NOP in case aliasing is detected when the instructions are
about to be issued to the functional units of the processor. If
aliasing happens, one needs to make the processor fall back to the
scalar approach of doing the computation.

In order to implement this project, I will need a state-of-art
autovectorizing compiler. Considering the open-source compilers in the
field, gcc looks like a good choice.  Unfortunately, while I do have
much experience working llvm, I have no experience with gcc.

Can any of you give me some suggestions on where to start, I think I
need to learn the gcc framework as a whole first, then I need to focus
on the autovectorization pass. Also, any comments on the project idea
are appreciated as well.


Thanks

Xin

Re: autovectorization in gcc

[Ian Lance Taylor]

Xin Tong <xerox.time.tech@gmail.com> writes:

> In order to implement this project, I will need a state-of-art
> autovectorizing compiler. Considering the open-source compilers in the
> field, gcc looks like a good choice.  Unfortunately, while I do have
> much experience working llvm, I have no experience with gcc.
>
> Can any of you give me some suggestions on where to start, I think I
> need to learn the gcc framework as a whole first, then I need to focus
> on the autovectorization pass. Also, any comments on the project idea
> are appreciated as well.

I think you have pretty much summed up the situation.  Since you will
want to focus on the vectorization passes, I would start by reading
gcc/tree-vect*.[ch].  As you find areas that you don't understand, refer
to the gcc internal's manual (http://gcc.gnu.org/onlinedocs/gccint/) and
the wiki (http://gcc.gnu.org/wiki/).  Also feel free to ask questions
here.

Ian

Re: autovectorization in gcc

[Ira Rosen]

gcc-help-owner@gcc.gnu.org wrote on 07/12/2011 01:56:54 AM:

> Xin Tong <xerox.time.tech@gmail.com> writes:
>
> > In order to implement this project, I will need a state-of-art
> > autovectorizing compiler. Considering the open-source compilers in the
> > field, gcc looks like a good choice.  Unfortunately, while I do have
> > much experience working llvm, I have no experience with gcc.
> >
> > Can any of you give me some suggestions on where to start, I think I
> > need to learn the gcc framework as a whole first, then I need to focus
> > on the autovectorization pass. Also, any comments on the project idea
> > are appreciated as well.
>
> I think you have pretty much summed up the situation.  Since you will
> want to focus on the vectorization passes, I would start by reading
> gcc/tree-vect*.[ch].  As you find areas that you don't understand, refer
> to the gcc internal's manual (http://gcc.gnu.org/onlinedocs/gccint/) and
> the wiki (http://gcc.gnu.org/wiki/).

Here is vectorizer's page
http://gcc.gnu.org/projects/tree-ssa/vectorization.html.

Ira

> Also feel free to ask questions
> here.
>
> Ian
>

Re: autovectorization in gcc

[陳韋任]

> Can any of you give me some suggestions on where to start, I think I
> need to learn the gcc framework as a whole first, then I need to focus
> on the autovectorization pass. Also, any comments on the project idea
> are appreciated as well.

  http://www.cse.iitb.ac.in/grc/

  :)

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj

autovectorization in gcc

[ranjith kumar]

Can gcc 4.1.2 do "cycle shrinking" to vectorize more
loops?????



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