gcc-4.4-crunch

[Martin Guy]

[Bcc to 15 developers]

Hi!
I've been looking at the old EP93xx MaverickCrunch FPU patches for
GCC again and almost have a working set for gcc-4.4. It "seems to
work" for most programs but one FP-math-intensive testsuite is
failing.(*)
The good news is that FFTW's speed test reports an increase from
6.13 to 7.65 MFlops and I think I now know what was wrong with the
64-bit integer arithmetic(**): fixing that should bring a speed
increase to OpenSSL and others. It also integrates better with the new
Debian release "wheezy", whose minimum GCC version is now 4.4.
I'm writing as a fundraiser to prod me into finding and applying the
bug fix, and finish, package and publish it, to then compile the
Debian repository of crunch-acelerated packages for wheezy.
So if anyone happens to work for a company that gains form my work,
do feel free to campaign with the accountants on my behalf :)

In any case, I'll write again when the new compiler and repositories
are available.

Cheers

M

*) In fftw. It looks like another variant of a known silicon bug: when
one instruction modifies an ARM register ina a way that induces a wait
state, and the next instruction is a crunch double load/store whose
address indirects through that register, the result is garbage or RAM
is corrupted at random.

**) By default, its 64-bit arithmetic operations do saturating
arithmetic instead of "going round the clock", maxing out at 0x7F* and
-0x80*. The only place that notices is openssl's 64-bit-optimized
bignum div/rem function.