C is a crappy NOT

Article: MAQSIP-RT: An HPC Benchmark
By: Konrad Schwarz (no.spam.delete@this.no.spam), July 8, 2010 12:29 am
Room: Moderated Discussions
Ian Ollmann (iano@apple.com) on 7/7/10 wrote:
---------------------------
>Konrad Schwarz (no.spam@no.spam) on 7/7/10 wrote:
>---------------------------
>> Well, all my RISC machines work exactly this way, and I'm sure the x86 people
>> would rather not have to deal with AH, AL, AX, EAX and RAX etc.
>
>Dunno if you think that Power still qualifies for RISC,
yes
>they use a common register format for floating point,

This is precisely the point. Sub-registers, such as AL, AH,
significantly complicate register renaming.

there is a whole set of parallel
>ISA for double and single precision ops that round differently in the 64-bit register.

Because single precision is significantly faster than
double precision, at least when the ISA was designed.

>See also AltiVec and SPE with specific ISA for each.

>Likewise, on the integer side, due to the arithmetic miracles of 2's complement,
>special instructions for smaller integer types aren't required for addition, subtraction
>and low-half multiplication. Just ignore the upper bits. In cases where they matter,
>a cheap AND or sign extend are all that are required to make full multiplication and division work.

Speed-wise, less than full-width integer addition obviously
isn't worth it. All you need, and what RISC ISAs provide,
are sub-full-width loads and stores.

This is one of the inherent benefits of a load/store
architecture.

>So, I'm not really sure that your assertion is true, in that what would be required
>to provide full support for native arithmetic in every data type is probably relatively minor.

This would clutter the instruction set for no gain at all,
occupying code space that could be more profitably used for
other things, such as vector instructions.
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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
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