Re: [AMBER-Developers] SSE2 / SSE3 settings no longer used for ifort?

From: Scott Brozell <>
Date: Mon, 26 Oct 2009 13:11:55 -0400


Please test Amber Tools with intel compilers:
./configure intel
./configure -nosse intel
./configure -altix intel
(the summary for uninterested parties).

On Mon, Oct 26, 2009 at 08:49:05AM -0700, Ross Walker wrote:
> make SSE the default and have a -nosse flag to turn it off? There can't be
> many machines left these days that don't support at least SSE2.

Ok, done -nosse is the option.
There may be a problem with -altix; should that turn sse or nosse ?
sorry cant remmeber and a quick goooogggggle didnt help.

> > > The ipo is a problem since it means all the optimization is done at
> > link
> > > stage and you lose all the benefits of parallel builds and each new
> > make is very expensive. We could specify
> >
> > IMO parallel building is irrelevant; our users will build once and
> > run often; so we should choose the options that produce the fastest
> > still-correct executables. (In addition, this quick make turnaround
> these days. The big problem with the -fast option is not actually the
> parallel build but the fact that all optimization is deferred until link
> time. This causes two things to happen. Firstly it makes the linking require
> LOTS of memory. Secondly it means that editing just one file and running
> make again takes ages at the link stage. Hence it is like you made clean
> each time. Of course this does not affect users who we assume will compile
> only once. However, anyone doing development will get very frustrated with
> this and thus we will be using different compiler flags for development as
> we use for release.

I dont get frustrated ...
In addition, if you used ipo then you might see all the great things
that compilers can do ...
Anyway lets ignore this until after at1.3.

> > Now this is where the problems arise and why i commented in my
> > advertisement that this still needs work.
> > Before 1.25 we had
> > ocflags="-O3 -ip -axN"
> > foptflags="-ip -O3 -axP"
> > which is clearly outdated and inconsistent.
> > Now we get:
> > OCFLAGS=-O3 -ip -axS ...
> > FOPTFLAGS= -O3 -ip -axS ...
> > According to my reading of the intel 10 man pages, -axS should get
> > all the possible sse vectorizations. So the next question is - are you
> I'm not sure on this. I have the following from the 10.1.018 man pages:
> Hence my read on this is that -axS only supports SSE4 which is the latest
> Nehalam chips. It does not cover SSE3 and below. Hence you need all the
> options which for ifort 10.1 would be. -axSTPW

Ok, i switched it to -axSTPW.

For future work:
> However, the warning here is that compilers older than 10.0 do not support
> the S option I believe. Additionally not all the sub options are supported
> by all compiler versions. Then to make things more complicated in ifort 11.0
> and 11.1 Intel has set the -axS... options to deprecated and now says you
> need to use the more verbose SSE4.2,SSE4.1 options etc. I assume that come
> ifort v12 they will remove the -axS... options entirely and hence things
> will no longer build. Of course SSE4.2 etc does not work with pre 11.0
> compilers and thus the -fast option has its appeal except for the fact that
> it introduces additional issues. So maybe for now we should use -axWPS which
> should work with most post 10.0 Intel compilers for the time being - maybe
> including the T option as well. Then we can issue a patch if Intel breaks
> this in 12.0.
> > There is also the compiler version wrinkle as you mentioned.
> > If someone has specific recommendations on options then make them;
> > otherwise, i suggest we make the small -axS -> -axWPS change for
> > the ambertools release and then try fast which will give us months
> > to test drive it b4 amber11.
> The only other thing is to try to detect the compiler version but this may
> get horribly complicated. Asking the user to provide the compiler version to
> configure is probably a recipe for disaster so if we do have specifics for
> specific compiler versions it should probably be selected automatically.

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Received on Mon Oct 26 2009 - 10:30:02 PDT
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