HP's broad objective is to seed research that will result in heavy-hitting IA-64 software. "To really make the new architecture work, compilers are key," said Jim Carlson, HP's director of marketing for IA-64. "Compilers have been crucial in RISC. But as we move into the Epic (Explicitly Parallel Instruction Computing) architecture, compilers become 10 times more important. Four or five years in the future, this will really pay off."

Trimaran is based in large part on the Impact compiler, which was developed by Wen-mei Hwu, a computer-science professor at the University of Illinois at Urbana-Champaign. The compiler also encompasses work done at the React-ILP Lab at New York University.

Trimaran currently runs on workstations equipped with the HP-UX operating system. Future ports to Windows NT and Sun OS are expected.

Trimaran doesn't actually execute Merced instructions, but it does implement speculation and predication, which are the processor's key software features. (Predication removes unnecessary branches from a program; speculation masks memory latency by executing load instructions as early as possible.)

Hwu said Trimaran includes a source-level environment, a code generator and "an emulator from NYU that takes the code and executes it so that people can do fairly detailed simulations."

There is full support for predication and speculation. "There's also some support for cache management," Hwu added. "These are the kinds of things that will be relevant to IA-64."

Tom Christian, a scientist at HP Labs, Palo Alto, said Trimaran has a mechanism that allows users to specify an Epic architecture. "You can vary all kinds of parameters, such as the instruction width."

"Once you have specified an architecture, you have a compiler that can create code," Christian explained. "Then there's a simulator and measurement tools that can execute the code and monitor its execution."

Trimaran also includes a suite of optimization modules, which can perform tasks ranging from loop unrolling to global scheduling.

Most important, working with the compiler will enable developers to understand some of the quirks at work in IA-64. "Epic is an architecture that doesn't like surprises," Christian explained. "Things like branches that go the wrong way or loads that miss the cache are really bad news. You can stall the processor or have to completely unload the stack and start over again.

"With the capabilities in Trimaran, you are able to go in an aggregate large chunks of code, and kind of undo the modularity that we've all been told in computer science is a good thing," Christian continued. "That gives you a broader base from which to compile, so that you can understand and put more code together."

Christian noted that the sophisticated analysis process performed by a compiler—both in existing superscalar architectures and with IA-64—is almost like tearing apart a program. "You're undoing all the modularity and putting lots of functions in line," he said. "By the time you have finished this process, there is little or no resemblance to the original, elegant linear code."

Such complexity is a big reason developers will want to study Trimaran. Indeed, IA-64 will usher in a new kind of cooperation between the hardware and the compiler. Merced itself will contain a large number of execution units. The compiler will organize instructions into streams that can be simultaneously executed.

Those hoping for shipping software, however, will be disappointed: Trimaran won't be Merced's production compiler.

"There's a lot of technology we didn't put in Trimaran," Christian said. "We are not in any way showing our latest and greatest stuff."

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