Why GCC is big and complicated (my guess)

Article: MAQSIP-RT: An HPC Benchmark
By: Mark Roulo (nothanks.delete@this.xxx.com), June 24, 2010 12:17 pm
Room: Moderated Discussions
ajensen (@.) on 6/24/10 wrote:
---------------------------
>Gabriele Svelto (gabriele.svelto@gmail.com) on 6/24/10 wrote:
>What's wrong with it?
>
>Well as far as I can gather, the problem is not the feature richness, but the monolithic
>architecture. A large project buildt more modular would be easier to maintain and
>move forward as some parts gets outdated and new ones are added. Am I wrong? Its
>not like I'm trying to force feed this into capabilities like mr. Schmidt here,
>but I'd really like to know why it is often seen as convoluted and unmaintainable.

I suspect that one of the issues making GCC larger/more-complicated/harder-to-maintain is that the architectures that it supports are much more varied (weirder) as a group than any one is individually. The compiler internals have to handle the collective strangeness.

A few examples:

*) Some of the older RISC architectures (I'm thinking SPARC) have these things called "branch delay slots." If GCC wants to support SPARC, then some parts of GCC need to be aware of this concept. My guess is that this concept impacts internal data structures over large parts of GCC and code that needs to deal with this concept is also all over GCC. The concept of "branch delay slot" isn't (and can't be) neatly encapsulated in a small, modular part of GCC.

*) Itanium EPIC is substantially odder than many of the RISC architectures we had in the 1990s and 2000s (explicit instruction bundles that *logically* execute together, predication [yes, ARM has this to a degree]). Again, as with "branch delay slots", these oddities probably spread throughout GCC.

*) Unless you want a totally different instruction scheduler for each target architecture (and maybe you do ... maybe this is what GCC already does?), then you need some sort of super-set of all the constraints one can have when building instruction sequences (the branch-delay-slot is one example of this sort of constraint). The super-set is going to be more complicated than any one constraint set.

The only obvious way to simplify things is to either:

a) Cut down on the architectures supported, not because of number but because of differences, or
b) Maybe (but I doubt it), totally re-architect the whole thing with the idea that we have a better idea of the range of capabilities/limitations and can do a better job designing the internals with this knowledge (my opinion is that this approach won't work).

-Mark Roulo
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
New article online: MAQSIP RTDavid Kanter2010/06/21 11:57 AM
  Why no GCC?Rohit2010/06/22 09:25 PM
    Why no GCC?David Kanter2010/06/23 12:45 AM
      sun 's cc better than GCC?Rohit2010/06/23 05:04 AM
        sun 's cc better than GCC?anon2010/06/23 07:49 AM
          Where is the GCC optimization effort directed?Mark Roulo2010/06/23 10:42 AM
            GCC is very ugly bad everywhere in 64 bitsVincent Diepeveen2010/06/23 02:49 PM
              even for 64-bit arch?anon2010/06/23 02:59 PM
              GCC is very ugly bad everywhere in 64 bitsajensen2010/06/23 11:03 PM
                GCC is very ugly bad everywhere in 64 bitsGabriele Svelto2010/06/24 02:33 AM
                  GCC is very ugly bad everywhere in 64 bitsajensen2010/06/24 05:32 AM
                    GCC is very ugly bad everywhere in 64 bitsGabriele Svelto2010/06/24 07:18 AM
                      GCC is very ugly bad everywhere in 64 bitsajensen2010/06/24 09:50 AM
                        Why GCC is big and complicated (my guess)Mark Roulo2010/06/24 12:17 PM
                          Why GCC is big and complicated (my guess)Gabriele Svelto2010/06/28 04:00 AM
                GCC is very ugly bad everywhere in 64 bitsBernd Schmidt2010/06/24 05:46 AM
                  GCC is very ugly bad everywhere in 64 bitsajensen2010/06/24 09:43 AM
                  GCC is very ugly bad everywhere in 64 bitsVincent Diepeveen2010/06/26 02:12 PM
                GCC is very ugly bad everywhere in 64 bitsRob Thorpe2010/06/24 07:47 AM
                  GCC is very ugly bad everywhere in 64 bitsAnon2010/06/24 05:23 PM
            Where is the GCC optimization effort directed?Gabriele Svelto2010/06/23 10:45 PM
              Where is the GCC optimization effort directed??2010/06/24 01:48 AM
                Where is the GCC optimization effort directed?Gabriele Svelto2010/06/24 02:29 AM
                  Where is the GCC optimization effort directed??2010/06/24 03:13 AM
                    Where is the GCC optimization effort directed?Andi Kleen2010/06/24 03:15 AM
                      Where is the GCC optimization effort directed??2010/06/24 04:08 AM
                    Where is the GCC optimization effort directed?Gabriele Svelto2010/06/24 03:54 AM
                      Where is the GCC optimization effort directed??2010/06/24 04:15 AM
                        Where is the GCC optimization effort directed?Gabriele Svelto2010/06/24 07:22 AM
                Where is the GCC optimization effort directed?Rohit2010/06/24 03:04 AM
                  Placebo effect?2010/06/24 06:37 AM
                    Placebo effectRohit2010/06/24 08:45 AM
                    Placebo effectVincent Diepeveen2010/06/26 02:50 PM
                      Compile timeMark Roulo2010/06/26 05:28 PM
                        Compile timeRichard Cownie2010/06/27 04:44 AM
                          Compile timeMark Roulo2010/06/27 10:12 AM
                          Compile timeMark Roulo2010/06/27 10:21 AM
                            Compile timeEduardoS2010/06/27 11:37 AM
                            Compile timeRichard Cownie2010/06/27 04:07 PM
                              Compile time & efficiency?2010/06/28 12:03 AM
                                Compile time & efficiencyMark Christiansen2010/06/28 06:08 AM
                                Compile time & efficiencyLinus Torvalds2010/06/28 07:48 AM
                                  kernel programming languageJohn Simon2010/06/29 06:46 PM
                                Compile time & efficiencyRichard Cownie2010/06/28 09:29 AM
                                  Compile time & efficiencyLinus Torvalds2010/06/28 11:17 AM
                                    Compile time & efficiencyRichard Cownie2010/06/28 02:16 PM
                                      Compile time & efficiencyRichard Cownie2010/06/28 06:23 PM
                                        Compile time & efficiencyMark Roulo2010/06/29 08:31 AM
                                          Compile time & efficiencyRichard Cownie2010/06/29 11:48 AM
                                          Compile time & efficiencyrwessel2010/06/29 12:28 PM
                                            C is a crappydev2010/06/29 07:12 PM
                                              C is a crappy, but only when you push it out of it's nicheRohit2010/06/30 02:11 AM
                                              C is a crappyanon2010/06/30 02:17 AM
                                                C is a crappydev2010/06/30 07:59 AM
                                                  C is a crappyMax2010/07/01 04:30 AM
                                                    C is a crappyMichael S2010/07/01 07:00 AM
                                                      C is a crappyKonrad Schwarz2010/07/01 08:02 AM
                                                        C is a crappyMichael S2010/07/01 08:50 AM
                                                          C isn't so crappyanon2010/07/01 10:11 AM
                                                            C isn't so crappyMikael Tillenius2010/07/01 11:39 AM
                                                          C is a crappyKonrad Schwarz2010/07/01 11:22 AM
                                                          C is a crappyMax2010/07/02 08:44 AM
                                                            C is a crappyrwessel2010/07/02 12:33 PM
                                                              C is a crappyanon2010/07/02 01:17 PM
                                                              C is a crappyMax2010/07/02 02:56 PM
                                                                C is a crappyMax2010/07/02 03:13 PM
                                                                  C is a crappyrwessel2010/07/02 03:32 PM
                                                                    C is a crappyMax2010/07/02 04:19 PM
                                                                    C is a crappyGabriele Svelto2010/07/05 05:25 AM
                                                      C is a crappygallier22010/07/02 12:14 AM
                                                    C is a crappyIan Ollmann2010/07/06 03:07 PM
                                                      PortabilityMax2010/07/06 03:37 PM
                                                      C is a crappyhobold2010/07/07 02:31 AM
                                                        C is a crappyIan Ollmann2010/07/07 05:18 PM
                                                      failure to standardize typesCarlie Coats2010/07/07 04:11 AM
                                                      C is a crappyKonrad Schwarz2010/07/07 08:34 AM
                                                        C is a crappyIan Ollmann2010/07/07 05:29 PM
                                                          C is a crappy NOTKonrad Schwarz2010/07/08 12:29 AM
                                                  C is a crappyanon2010/07/01 10:40 PM
                                                    C type safety?2010/07/02 01:10 AM
                                                      C type safetyanon2010/07/02 11:02 PM
                                                    C is a crappydev2010/07/03 04:51 PM
                                                      C is a crappyanon2010/07/03 07:02 PM
                                                        C is a crappydev2010/07/05 07:27 AM
                                                          C is a crappy?2010/07/05 09:05 AM
                                                            C is a crappyanonymous2010/07/07 08:32 AM
                                                              C is a crappy?2010/07/07 10:48 PM
                                                              C is a crappyAnon2010/07/08 12:53 AM
                                                      C is a crappy and a crappie is a fishanonymous2010/07/03 07:24 PM
                                      Compile time & efficiencyMichael S2010/06/29 03:18 AM
                                        Compile time & efficiencyrwessel2010/06/29 12:20 PM
                                        Compile time & efficiencysomeone2010/06/30 11:03 AM
                                        Compile time & efficiencyJouni Osmala2010/07/02 05:29 AM
                                  Compile time & efficiencyMax2010/06/28 05:05 PM
                                    Compile time & efficiencyEduardoS2010/06/28 05:11 PM
                                    Compile time & efficiencyMichael S2010/06/29 03:33 AM
                              Compile timeFoo_2010/06/28 09:03 AM
          sun 's cc better than GCC?Silent2010/06/23 06:19 PM
            sun 's cc better than GCC?Foo_2010/06/23 07:06 PM
          sun 's cc better than GCC?Andi Kleen2010/06/24 02:49 AM
        sun 's versus gccVincent Diepeveen2010/06/23 03:07 PM
    Why no GCC?Carlie Coats2010/06/23 05:11 AM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell avocado?