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Going deep into GCC 4.4 with Red Hat

By Sean Michael Kerner on April 29, 2009 9:10 AM

From the 'digging into GCC 4.4' files:

GCC 4.4 is a critically important component of the open source software landscape. It officially was released last week and I blogged on it briefly, but felt the need to get more insight. Fedora 11 which hit its preview release yesterday lists GCC 4.4 as one of its key features and Red Hat is a key contributor to GCC, so I asked Red Hat for their views on how GCC 4.4 will make a difference.

Tim Burke, Senior Director, RHEL Product Development told me that in his view the most significant new advancement in gcc 4.4 over gcc 4.3 is OpenMP 3.0 support (gcc 4.3 had OpenMP 2.5 support).

Burke explained that, the significant feature in OpenMP version 3.0 is the concept of tasks. One can specify whole sections of their code as separate tasks that can be run in parallel. (OpenMP 3.0 specifications can be found here: http://www.openmp.org/mp-documents/spec30.pdf and a good overview of the OpenMP standard can be found here: http://en.wikipedia.org/wiki/Openmp).

"OpenMP allows programmers to more easily create efficient multi-threaded programs in C/C++," Burke explained. "With OpenMP 3.0 the user can explicitly section off code they wish to run in parallel"

So what's next for GCC from Red Hat's point of view?

According to Burke -- Transactional Memory. He noted that Red Hat is implementing language features in C/C++ to simplify the accessing of shared memory in an atomic way within a multi-threaded program. These language features will make use of hardware features that are expected in the near future.

"Transactional Memory is very similar to Transactional SQL database access with BEGIN/COMMIT," Burke explained. "This feature in conjunction with OpenMP features greatly reduces the burdens on a C/C++ programmer when working with multi-threaded programming. Improved Debugging information."

He added that work is also ongoing to improve the debug-ability. trace-ability of optimized gcc compiled programs and that additional optimizations for register allocation and loop optimizations are ongoing. Additionally, whole program (aka link time) optimizations are coming as are continued implementation of the new C++ language/library features.

Plugins are also part of GCC's future.

"GCC plugins will allow for pluggable optimization passes in gcc," Burke said. "This will mostly make it easy for gcc developers to try new optimization passes but will also make possible for newer optimizations to be implemented in older version of gcc in the future."

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