Branch/jump target prediction

By: Peter Cordes (peter.delete@this.cordes.ca), August 12, 2016 3:23 pm
Room: Moderated Discussions
sylt (no.delete@this.thanks.com) on August 10, 2016 3:27 am wrote:
> If you have a front-end that can fetch, detect and decode a branch in something like 4 cycles or less
> (and preferably you don't consume more than one instruction per cycle, either single issue RISC thing,
> or VLIW where you consume a single bundle per cycle) then you can get good performance by having a small
> instruction buffer and scanning ahead in the stream for branches to get your target addresses.

A buffer after the early-decode stage is exactly what I was thinking of.

A jump detected this method without involving the BTB leaves that buffer empty. It can refill by being able to pre-scan more instructions per clock than the rest of the pipeline consumes. (Or on the next pipeline bubble from an execution hazard.)

I was thinking you'd still want to use the BTB for conditional branches, instead of combining this branch target detection with branch direction prediction from the branch history buffer. Did you really mean that this would be used for conditional non-indirect branches?

Thanks for the info that this kind of thing has been used in practice for simpler hardware.
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
Branch/jump target predictionTravis2016/08/09 09:44 AM
  Early decode of unconditional jumpsPeter Cordes2016/08/09 11:35 AM
    Early decode of unconditional jumpsExophase2016/08/09 12:29 PM
  pipelines are too long, noHeikki Kultala2016/08/09 11:37 AM
    pipelines are too long, nono name2016/08/09 06:17 PM
      pipelines are too long, noWilco2016/08/10 01:43 AM
        pipelines are too long, noPaul A. Clayton2016/08/10 07:44 PM
    Converged BTB/IcachePaul A. Clayton2016/08/10 07:44 PM
  Branch/jump target predictionsylt2016/08/10 02:27 AM
    Branch/jump target predictionPeter Cordes2016/08/12 03:23 PM
      Branch/jump target predictionsylt2016/08/12 10:35 PM
  Branch/jump target predictionMr. Camel2016/08/10 09:43 AM
    Branch/jump target predictionLinus Torvalds2016/08/10 11:46 AM
      Branch/jump target predictionMegol2016/08/10 02:25 PM
        Branch/jump target predictionLinus Torvalds2016/08/10 04:14 PM
          Branch/jump target predictionDavid Kanter2016/08/11 11:09 PM
            Branch/jump target predictionLinus Torvalds2016/08/12 11:25 AM
          Branch/jump target prediction2016/08/14 04:24 AM
            Branch/jump target predictionMaynard Handley2016/08/14 06:47 AM
              Branch/jump target predictionDavid Kanter2016/08/14 07:13 AM
              Branch/jump target prediction2016/08/16 05:19 AM
            Branch/jump target predictionTim McCaffrey2016/08/14 07:12 AM
              Branch/jump target predictionDavid Kanter2016/08/14 07:18 AM
                Branch/jump target predictionGabriele Svelto2016/08/14 01:09 PM
            Just a thoughtAnon2016/08/14 09:40 AM
              Just a thought2016/08/16 05:58 AM
                Just a thoughtAnon2016/08/16 07:45 AM
                  Just a thought2016/08/16 08:36 AM
            Branch/jump target predictionLinus Torvalds2016/08/14 09:40 AM
              Branch/jump target prediction2016/08/16 05:40 AM
                Branch/jump target predictionRicardo B2016/08/16 06:39 AM
                  Branch/jump target prediction -82016/08/16 08:23 AM
                    Branch/jump target prediction -8anon2016/08/16 09:09 AM
                    Branch/jump target prediction -8Ricardo B2016/08/16 09:33 AM
                      Branch/jump target prediction -8Exophase2016/08/16 10:02 AM
                        Branch/jump target prediction -8Ricardo B2016/08/16 10:31 AM
                        SPU hbr instruction (hint for branch)vvid2016/08/16 11:31 AM
                        Branch/jump target prediction -8no name2016/08/17 07:16 AM
                    Branch/jump target prediction -8Gabriele Svelto2016/08/16 10:46 AM
                      Branch/jump target prediction -8Etienne2016/08/17 12:27 AM
                        Branch/jump target prediction -8Gabriele Svelto2016/08/17 02:52 AM
                    Branch/jump target prediction -8Maynard Handley2016/08/18 09:02 AM
                      Branch/jump target prediction -82016/08/18 05:21 PM
                        Branch/jump target prediction -8Maynard Handley2016/08/18 06:27 PM
                          Branch/jump target prediction -8Megol2016/08/19 03:29 AM
                          Part 1/N - CPU-internal JIT2016/08/19 03:44 AM
                        Atom, you're such a comedian.Jim Trent2016/08/18 09:39 PM
                          Atom, you're such a comedian.2016/08/19 02:23 AM
                      Branch/jump target prediction -8Etienne2016/08/19 12:25 AM
                        Branch/jump target prediction -8Simon Farnsworth2016/08/19 03:17 AM
                          Branch/jump target prediction -8Michael S2016/08/19 05:39 AM
                          Branch/jump target prediction -8anon2016/08/19 06:29 AM
                            Branch/jump target prediction -8Simon Farnsworth2016/08/19 07:34 AM
                              Branch/jump target prediction -8anon2016/08/19 07:48 AM
                                Branch/jump target prediction -8Exophase2016/08/19 10:03 AM
                                Branch/jump target prediction -8Maynard Handley2016/08/19 10:34 AM
                            Branch/jump target prediction -8David Kanter2016/08/19 11:23 PM
                        Branch/jump target prediction -8Ricardo B2016/08/19 06:18 AM
                          Branch/jump target prediction -8Maynard Handley2016/08/19 07:41 AM
                            Branch/jump target prediction -8Michael S2016/08/19 08:26 AM
                              Branch/jump target prediction -8Maynard Handley2016/08/19 12:47 PM
                                Branch/jump target prediction -8Michael S2016/08/21 12:53 AM
                                  Branch/jump target prediction -8Ricardo B2016/08/22 04:17 AM
                                    Branch/jump target prediction -8Michael S2016/08/22 04:58 AM
                                      Branch/jump target prediction -8Ricardo B2016/08/22 06:50 AM
                            Branch/jump target prediction -8Simon Farnsworth2016/08/19 08:28 AM
                              Branch/jump target prediction -8Simon Farnsworth2016/08/19 08:40 AM
                            Branch/jump target prediction -8David Kanter2016/08/22 11:05 PM
                              Branch/jump target prediction -8Maynard Handley2016/08/23 06:49 AM
                      Branch/jump target prediction -8anon2016/08/26 07:00 AM
                        Branch/jump target prediction -8anon2016/08/26 07:14 AM
                Branch/jump target predictionMegol2016/08/19 03:23 AM
          Branch/jump target predictionMegol2016/08/19 06:42 AM
            Branch/jump target predictionMaynard Handley2016/08/19 10:46 AM
              Branch/jump target predictionDavid Kanter2016/08/19 11:34 PM
                Branch/jump target predictionMaynard Handley2016/08/20 06:07 AM
            Branch/jump target predictionsylt2016/08/19 10:48 AM
              Branch/jump target predictionsylt2016/08/19 11:00 AM
              Branch/jump target predictionMegol2016/08/21 09:27 AM
                The (apparent) state of trace caches on modern CPUsMaynard Handley2016/08/22 02:10 PM
                  The (apparent) state of trace caches on modern CPUsExophase2016/08/22 07:55 PM
                    The (apparent) state of trace caches on modern CPUsanon2016/08/22 11:36 PM
                      The (apparent) state of trace caches on modern CPUsExophase2016/08/23 04:08 AM
                        The (apparent) state of trace caches on modern CPUsanon2016/08/23 08:51 PM
                          The (apparent) state of trace caches on modern CPUsExophase2016/08/23 10:12 PM
                          The (apparent) state of trace caches on modern CPUsMaynard Handley2016/08/24 06:38 AM
                            The (apparent) state of trace caches on modern CPUsanon2016/08/24 07:26 PM
                    The (apparent) state of trace caches on modern CPUsMaynard Handley2016/08/23 06:48 AM
                      That's not trueDavid Kanter2016/08/23 08:39 AM
                        That's not trueMaynard Handley2016/08/23 08:56 AM
                      The (apparent) state of trace caches on modern CPUsanon2016/08/23 08:54 PM
                  The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 01:38 AM
                    The (wrong) state of trace caches on modern CPUsMichael S2016/08/25 02:28 AM
                      The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 06:12 AM
                      The (wrong) state of trace caches on modern CPUsMaynard Handley2016/08/25 08:50 AM
                        The (wrong) state of trace caches on modern CPUsMichael S2016/08/25 09:36 AM
                          The (wrong) state of trace caches on modern CPUsExophase2016/08/25 10:32 AM
                        The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 10:12 AM
                          The (wrong) state of trace caches on modern CPUsMaynard Handley2016/08/25 11:01 AM
                            The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 11:20 AM
                              The (wrong) state of trace caches on modern CPUsMaynard Handley2016/08/25 12:34 PM
        Branch/jump target predictionGabriele Svelto2016/08/11 12:15 PM
  Branch/jump target predictionGabriele Svelto2016/08/20 06:21 AM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell tangerine? 🍊