Re: Clang as default compiler November 4th

On Wed, Sep 12, 2012 at 04:42:27PM -0500, Nathan Whitehorn wrote:
> On 09/11/12 09:56, Dimitry Andric wrote:
> >On 2012-09-11 16:27, Tijl Coosemans wrote:> On 11-09-2012 16:10, 
> >Dimitry Andric wrote:
> >...
> >>>Yes, maths support, specifically precision, is admittedly still one of
> >>>clang's (really llvm's) weaker points.  It is currently not really a
> >>>high priority item for upstream.
> >>>
> >>>This is obviously something that a certain part of our userbase will
> >>>care a lot about, while most of the time they won't care so much about
> >>>licensing or politics.  So those people are probably better off using
> >>>gcc for the time being.
> >>
> >>Does it affect the accuracy of libm functions?
> >
> >It seems to, at least in specific cases; Steve posted about this in an
> >earlier thread on -current:
> >
> >  http://docs.freebsd.org/cgi/mid.cgi?20120905221310.GA97847
> >_______________________________________________
> 
> If true, this is a serious problem, especially for those of us who use 
> FreeBSD in a scientific computing environment.

Just to clarify.

I do not oppose switching the default compiler to clang as long
as the proponents for the switch have shown adequate testing.
Neither clang successfully building world nor clang building a
working kernel are adequate testing (IMHO).  Neither of those
"benchmarks" use floating point, and AFAIK the libm built by
clang during a buildworld is not (extensively?) exercised.  

As far as the URL above, I've been fixing accuracy issues in
the j0f() function, and so, I have a program that allows me to
exhaustively test all possible input values in the range reported.
For my locally patched j0f(), I saw the issue as reported in the
URL, but in doing additional development on j0f() I accidentally
deletely/lost that specific version of the code.  I hope to
regenerate the code from my notes this weekend, and redo the 
tests.

In regards to my initial post in this thread, I was just trying
to assess whether any benchmarks have been performed on FreeBSD
for floating point generated by clang.  Other than the limited
testing that I've done, it appears that the answer is 'no'.

-- 
Steve