Re: version of gcc and auto-vectorization

[ranjith kumar <ranjit_kumar_b4u at yahoo dot co dot uk>]

--- Ian Lance Taylor <iant@google.com> wrote:

> ranjith kumar <ranjit_kumar_b4u@yahoo.co.uk> writes:
> 
> > 1) In my P.C. gcc version 4.1.2 has been
> installed.
> > I have a look at http://gcc.gnu.org/.
> >    In that it is said that 4.1.2 is the "current
> > release series", "Next release series:  GCC 4.2.0"
> and
> > "Active development:  GCC 4.3.0"
> > 
> > What does it mean? Has gcc 4.2.0/4.3.0 been
> > released???
> 
> No.  It means that 4.2 is the next release.  4.3 is
> under active
> development.
> > 
> > 2)From which version "auto-vectorization" has been
> > included?
> > In  
> >
>
http://gcc.gnu.org/projects/tree-ssa/vectorization.html#status4.0
> >  it is said that gcc 4.0 also does
> > "auto-vectorization".
> > Deos it mean auto-vectorization cababilities of
> gcc4.0
> > and gcc4.1/4.2 are same??
> 
> No, it is under active development and is enhanced
> in each release.
> 
> > 3)-ftree-vectorize is the flag that enables
> > autovectorization. isn't it??
> 
> Yes.
> 
> > 4) where can I get C programs for which gcc can do
> > autovectorization and for which it cant?
> 
> There are test cases in gcc/testsuite/gcc.dg/vect.
What does auto-vectorization mean??
I think it must be converting 'for' loops which does
not exploit SIMD features of a processor(say Pentium
4) to 'for' loops which exploit SIMD features(of
course, it could be at any intermediate
representation).

I have taken vect-40.c in that directory and compiled
as "gcc -march=pentium4 -S -O3 -ftree-vectorize
vect-40.c". I looked at the assembly code. No
MMX/SSE/SSE2 instructions were there.
(I have gcc-4.1.2 installed in my P.C. and my
processor is Pentium4.)

What can gcc do? Can it produce MMX/SSE/SSE2
instructions even if the source file(.c) does not use
any functions defined in 
mmintrin.h/xmmintrin.h/emmintrin.h????
If so, did I miss any other option while compiling?
Thanks in advance.
> 
> > 4) I know all languages are internallay converted
> to
> > same representation(in the context of gcc
> compiler).
> > So what is said in gcc manuals about
> > auto-vectorization is applicable to all languages
> gcc
> > supports. Isn't it?
> 
> Yes.  But some languages are more amenable to
> vectorization than
> others.
> 
> Ian
> 



		
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