Credits

The project was leaded by David Bednárek^13.1. Following students participated in the project directly:

Zdenek Dvorák

^13.2 
Zdenek implemented the thread safe profiling code, added infrastructure for high level branch predictor algorithms.

Major part of his work is related to loop optimizations. He implemented new data structure to hold natural loop tree and modified natural loop discovery code originally contributed by Michael Hayes to produce it. On the top of it he implemented loop unswitching, loop unrolling and loop peeling algorithms, one of the most successful new optimizations in our project.

He also made numerous contributions to the control flow graph handling code, most importantly he changed the basic block representation from linearly ordered array to double linked list avoiding quadratical complexity of many important algorithms in new CFG aware code. This required many changes of code in compiler that uses basic blocks.

He also found and fixed many latent bugs in the compiler and our new improved CFG manipulation code.

Jan Hubicka

^13.3 
Jan had special role in project by being the only participant with previous knowledge of GCC internals and its development model. In early stages of project he helped other participants to familiarize with project by solving relatively simple problems and has been concentrating on adding infrastructure necessary for CFG and profile manipulation. He also added new branch prediction heuristics and a pass to estimate profile.

Predating the official start of project, he implemented first prototype of working basic block profiler, extended branch prediction pass and modified few passes to use the information. Since the information was not maintained only register allocation used the information. He also implemented bare bones of future cfg-cleanup pass.

In later stages of project he implemented few new optimization passes (tracer, webizer, register coalescing), but continued to concentrate on GCC cleanups and infrastructural changes and later on mid-level RTL implementation. He also reviewed majority of contributions of other participants before integrating to the source tree.

Pavel Nejedlý

^13.4 
Major part of Pavel's work is concentrated on the basic block profiler. He implemented new, robust and extensible file format to hold profiles. His format allows overall information to be summarized which is used to identify better hot spots in the program and to do code placement decisions as well as user errors (such as using outdated profiles) to be detected and reported. In future his work will allow more sophisticated profile merging algorithm, as new format stores each train run separately instead of merging them all at once.

Pavel has also reimplemented the interface between profile instrumentation generated by compiler and the libgcc runtime in cleaner and more extensible way.

Last his major contribution is new data structure to hold dominance information that allows fast dynamical updates and is necessary for Zdenek's new loop optimizer code.

Josef Zlomek

^13.5 
In early stages Josef has found and fixed major problem of Michael's natural loop discovery code. Later he has implemented and tuned the new basic block reordering algorithm based on software trace cache. His implementation is in many way superior to the one described by original article. He also improved and fixed the cfglayout module he used for his work.

Most important contribution is probably the new variable tracking pass fixing the aged defect of GCC debugging information output code allowing us to enable more optimizations at default level.

Josef has also reviewed lots of code done by Jan Hubicka and provided useful comments and fixed important bugs.

Following people has contributed to our project:

Andreas Jaeger

 
Andreas set up the SPEC2000 tester to do daily benchmarking of our development tree which allowed us to easily tune new optimizations on nontrivial benchmark suite. He also set up an extended weekly tester which provided feedback for our branch prediction heuristics, and kindly benchmarked results of our work that are presented in this documentation.

Richard Henderson

 
Richard, one of the most active maintainers of GCC, has reviewed and approved for inclusion to the mainline the essential parts of our work. He also provided number of important ideas. Without his help our project would not be possible at all. He also helped us to redesign scope tree maintenance code in cfglayout.c.

Jeff Law

 
Jeff pushed us to implement midRTL.

Daniel Berlin

 
Daniel implemented and tested Dwarf2 output routine based on Josef's variable tracking pass. He also tested and fixed our version of compiler on powerPC and added improvements to the loop unrolling debug output code.