ON THE CALL: Shin-ming Liu (HP), Vladimir Makarov (Red Hat), Diego Novillo (Red Hat), Mark Smith (Gelato), Bob Kidd (UIUC), Mark Davis (Intel)
A fair amount of time was spent discussing the pros and cons of LLVM vs. LTO. Keep in mind that the next Gelato conference is coming up in April 06. If you would like to speak in the GCC track, please contact Mark Smith. Comments from each participant on the call can be found below. NEXT MEETING: January 12th, 2006. Details will be emailed out prior to the call. Bob Kidd: --------- The ia64-improvements branch is up. I haven't had time to do much with it, but I've checked it out and bootstrapped. I applied Steven Bosscher's revised superblock patch, bootstrapped and tested it. I'm looking at updating the branch to either 4.2 or CVS head and will check in the superblock patch. Shin-ming Liu: -------------- * HP has posted the GCC 4.0.2 source and binary package on HP site for HP-UX in November * HP is working toward the similar posting for Linux in the near future * HP is actively participating in the LTO activity in GCC community * HP has started the alternative backend effort based on Open64 with several universities Vladimir Makarov: ----------------- I asked Bob to tell more details about superblock scheduling he made. Because the current version does not take predication into account, I told that to get better results it is good to combine predication and superblock forming in future. Also superblock scheduling could work without profile information as it does currently according to Bob's review. Gcc has decent evaluation of branch probabilities. It would be reasonable to try how superblock scheduling will work with the branch probabilities evaluation. As for work status of ISP RAS team, they work on infrastructure for another insn scheduling. It is a big project. They sent patch for improvement of aliasing analysis for ia64. Diego Novillo and Daniel Berlin are reviewing the patch. They'll send patch for speculation support for review soon. It is control and data speculation support with recovering code. Now it is necessary only for ia64 but it will be useful for future Intel x86 and x86_64 processors which as I heard will have speculation support too. As for LLVM, I told it is a very interesting research project. In any case it will help to gcc finally and itself. We will see will it be finally adopted in gcc. At least, it have more chances for that than OpenRC with its WHIRL because transition of copyrights to FSF of LLVM is more probable than one of OpenRC from SGI. But adoption of LLVM should not stop other project therefore LTO is a right thing to do. The competition is good and there will be more chance to have intermodule optimizations finally. Additionally to the obstacles to adopt LLVM mentioned by Diego, I named usage of C++ (although it has advantages too) and patents. LLVM should be checked for usage of compiler patents. Gcc people avoided many patents especially from Microsoft. We can not be sure right now about LLVM. Diego Novillo: -------------- I talked about the new developments in GCC for doing link-time optimizations. We discussed both the LTO proposal and LLVM. Although it's not clear at the moment which proposal will end up being adopted, we all agreed this is an excellent sign that GCC will start evolving in that direction. I also talked about the new ia64-improvements branch and Dmitry's alias patch. The ia64-improvements branch is ready for people to use. I have started reviewing Dmitry's patch and will try to send feedback in the next few days. Mark Smith: ----------- I will continue to work with Intel to secure a Montecito SDV to use for GCC builds. Itanium Solutions Alliance has funded Bob Kidd's GCC superblock work. I also talked about the upcoming Gelato conference in April 2006. We want to have a strong GCC track at the meeting. Please consider attending. Shin-ming and I will work together on designing the track. If you would like to speak, please contact one of us.
