Red Hat To Support PowerPC, AltiVec

Steve Cowan writes "According to an article at MacCentral, Red Hat has announced that they will produce a GNUPro toolchain and cross compiler for AltiVec-enabled PowerPC processors (such as that found in the Power Mac G4). It will be interesting to see just what kind of performance gains this will bring, because many believe that the full potential of AltiVec is far from tapped."

Comments

It will stay untapped.

[Erich]

Parallelism is really, really, really hard to do in a compiler. Intel has a hard time doing it even after spending millions for a compiler on their VLIW architecture. DLP is typically even harder than ILP for a compiler to do.

Compilers can typically do a pretty good job on sequential machines, but there is still a long way to go for getting good parallel code. Hand coding things is still the way to go for maximum performance.

That being said, the compiler can probably use it some, and having a resource available is typically better than not having the resource at all.

Re:It will stay untapped.

[RobertFisher]

I don't agree with this author's assessment. The type of "parallelism" involved in the AltiVec is SIMD -- single instruction, multiple data. It's the same kind of parallelism which Cray pioneered over 25 years ago. While in the early days, a great deal of hand-tuning was required, leading to such memorable Cray-specific replacement constructs as the vectorized Cray vector merges (CVMGT, CVMGZ, CVMGP, etc...) in place of non-vectorized If-Then's, great strides were made in Cray's compilers over the last few years. You could get very reasonable vectorized performance for most numerically intensive codes straight out of the compiler, without any modifications at all. With a bit of profiling and additional compiler directives, you could get excellent performance indeed.

The plain fact of the matter is that SIMD is MUCH, MUCH easier than doing distributed parallelization. It took Cray about 20 years to really get it right, so given how new the Altivec is, let's give Apple and company a few years to see how much they can accomplish.

Bob