Unified Parallel C (UPC) Comes To LLVM/Clang
Written by Michael Larabel in Compiler on 30 November 2012 at 10:19 AM EST. 2 Comments
Clang UPC has been announced, which is a Unified Parallel C implementation targeting the LLVM/Clang compiler stack. Unified Parallel C is a C99 extension targeting high-performance computing on parallel machines.

Unified Parallel C is coming to GCC after its support was living separately from mainline GCC for some time. Now, developers have announced an initial implementation of Unified Parallel C for LLVM's Clang compiler. Clang UPC is this initial implementation.

Aside from needing the separate Clang UPC code-base, for now a special version of LLVM is required. This branched version of LLVM has a few minor changes necessary for supporting Unified Parallel C that aren't yet in the mainline code-base.

UPC is described as "an extension of the C programming language designed for high-performance computing on large-scale parallel machines, including those with a common global address space (SMP and NUMA) and those with distributed memory (e.g. clusters). The programmer is presented with a single shared, partitioned address space, where variables may be directly read and written by any processor, but each variable is physically associated with a single processor. UPC uses a Single Program Multiple Data (SPMD) model of computation in which the amount of parallelism is fixed at program startup time, typically with a single thread of execution per processor."

Eventually there is a plan to merge Clang UPC into the main Clang/LLVM code-base. In addition, there is a desire to develop a UPC-to-C source translator based upon Clang UPC. This work though is too late for the LLVM/Clang 3.2 release that will happen in December.

For more details on the Clang UPC announcement, see the Clang mailing list.

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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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