From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 5921 invoked by alias); 17 Jan 2004 19:01:06 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 5912 invoked from network); 17 Jan 2004 19:01:05 -0000 Received: from unknown (HELO mail.codesourcery.com) (65.74.133.9) by sources.redhat.com with SMTP; 17 Jan 2004 19:01:05 -0000 Received: (qmail 14268 invoked from network); 17 Jan 2004 19:00:59 -0000 Received: from 227.148-60-66-fuji-dsl.static.surewest.net (HELO minax.codesourcery.com) (mitchell@66.60.148.227) by mail.codesourcery.com with SMTP; 17 Jan 2004 19:00:59 -0000 Subject: Re: [RFC] Contributing tree-ssa to mainline From: Mark Mitchell To: Diego Novillo Cc: "gcc@gcc.gnu.org" In-Reply-To: <1074298740.3147.79.camel@frodo.toronto.redhat.com> References: <1074298740.3147.79.camel@frodo.toronto.redhat.com> Content-Type: text/plain Organization: CodeSourcery, LLC Message-Id: <1074366070.3537.36.camel@minax.codesourcery.com> Mime-Version: 1.0 Date: Sat, 17 Jan 2004 19:01:00 -0000 Content-Transfer-Encoding: 7bit X-SW-Source: 2004-01/txt/msg01097.txt.bz2 On Fri, 2004-01-16 at 16:19, Diego Novillo wrote: > Now that we are about to enter Stage 1 of 3.5, I wanted to solicit > feedback regarding the merge of the tree-ssa branch into mainline. I've now read the messages in this thread. Diego, first, I would like to thank you for bringing up this issue and presenting in such a balanced fashion. Here are my thoughts on several of the key issues raised: (1) Ada does not work with tree-ssa. ACT does not see this as a blocking issue. When the time comes, I think that it's reasonable to ask that Ada people provide effort to do this work, and I think it's also reasonable to ask tree-ssa people to commit to helping them. I have every confidence that will happen. (2) G77 does not work with tree-ssa. I do not see this as a blocking issue either, but it concerns me more, in that nobody has come forward to say "I don't care about G77 working with tree-ssa yet" in the same way that Dewar/Kenner have said that about Ada. (3) Coding standards, documentation issues, etc. Clearly, these must be fixed before we merge the branch. But Diego is not asking to merge the branch *right now*; he is asking whether to merge it for GCC 3.5. Diego clearly understands that these issues must be fixed before the merge occurs. I'm sure that with concentrated effort these issues could be fixed in the next few weeks on the branch. (4) Mergin piecemeal vs. merging wholesale. I think that if we decide to merge tree-ssa into the mainline for 3.5, then it should be done wholesale. If we do not decide to do that, it might make sense to merge some of the changes in piecemeal. But, I do not think we should revisit the entire design space at this point. I have a very high confidence in the key tree-ssa architects to make good decisions about the architecture, and all the evidence is that they have. (5) If we don't merge tree-ssa into 3.5, what will be in 3.5? I'm not sure -- but I am sure there will be good things. Apple is working on compile-time performance improvements, and maybe Objective-C++. There will be new targets and other back-end improvements. Now, here are a few thoughts not relating so directly to particular issues already raised. (A) Ultimately, we want tree-ssa not because it is modern, but because it provides user-visible improvements. It's the better performance of generated code, better compile-time performance, better language support, and fewer bugs that our users are after. To me, at this point, it sounds like tree-ssa has the potential to help with all of those things, except better language support. But, it doesn't sound to me like it has *realized* that potential in a sufficiently monotonic way. There are improvements in some areas, regressions in others. (B) The new C++ parser is a fair analogy, although clearly the new C++ parser was a much smaller piece of work. It is only about 15,000 lines of code. It only affects C++. It's not nearly as risky to the overall project as tree-ssa. Therefore, my feeling is that tree-ssa is probably not ready for GCC 3.5. My instinct is that we should try to get a GCC 3.5 release out on something much more like our stated devlopment schedule, while tree-ssa matures. At the rate that has been happening, I would be astonished if it weren't ready for GCC 3.6, especially if effort is invested in dealing with the documentation issues and existing regressions. I would suggest that we focus less on adding new stuff and more on getting the bugs out, improving the compile-time performance, and doing what can be done to remove the RTL optimizers. Waiting for GCC 3.6 gives gfortran time to become a stronger replacement for G77, and for Ada to port to tree-ssa; doing those things are benefits, even if not essential. However, this is my preliminary opinion. -- Mark Mitchell CodeSourcery, LLC