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I hope that the rust compiler team is considering to integrate BOLT by default too https://github.com/facebookincubator/BOLT https://github.com/facebookincubato

I hope that the rust compiler team is considering to integrate BOLT by default too https://github.com/facebookincubator/BOLT https://github.com/facebookincubator/BOLT (I'm aware it's being integrated into llvm but rust could integrate the external BOLT in it's toolchain in the meantime, free performance gain for everyone is nice to have right now)

ibraheemdev 6y ago
This was discussed here [1]. The conversation died off around a year ago. Not sure why... Although, it is pretty clear that BOLT's optimizations are not "free". For example: > BOLT uses enormous amount of memory (about 6GB). > Perf needs to be ran with LBR support; this is almost always unsupported with VMs (which means you don't want to run the measurement inside CI). [1] https://github.com/rust-lang/rust/issues/50655 https://github.com/rust-lang/rust/issues/50655
- The_rationalist 6y ago
  Interesting, would be nice for rustc to have a special flag that enable "maximum performance" at any compile time/ram price
  - the8472 6y ago
    At any price? You could throw something like souper at the problem[0]. It makes compilation about 20 times slower in some benchmarks in their paper. This is on the IR level, iirc similar optimizers exist for assembly generation, so you can throw that in as another pass. [0] https://github.com/google/souper https://github.com/google/souper
    - MaxBarraclough 6y ago
      > At any price? Seems to me that raising the ceiling on optimisation is good to have, even if the computational cost is very high. If it works reliably, it wouldn't be necessary to do optimised release builds very often, and they could be offloaded onto a heavyweight build server, perhaps on the cloud.
- deleted 6y ago
  [deleted]
- crb002 6y ago
  BOLT just permutes link order? The object permutation from a BOLT run should be good for months until the underlying objects have substantially drifted?
glandium 6y ago
Propeller is probably better (and should eventually be integrated in LLVM itself). http://lists.llvm.org/pipermail/llvm-dev/2019-September/135393.html http://lists.llvm.org/pipermail/llvm-dev/2019-September/1353... It's still Linux only, though.

ibraheemdev 6y ago

This was discussed here [1]. The conversation died off around a year ago. Not sure why... Although, it is pretty clear that BOLT's optimizations are not "free". For example: > BOLT uses enormous amount of memory (about 6GB). > Perf needs to be ran with LBR support; this is almost always unsupported with VMs (which means you don't want to run the measurement inside CI). [1] https://github.com/rust-lang/rust/issues/50655 https://github.com/rust-lang/rust/issues/50655

The_rationalist 6y ago
Interesting, would be nice for rustc to have a special flag that enable "maximum performance" at any compile time/ram price
- the8472 6y ago
  At any price? You could throw something like souper at the problem[0]. It makes compilation about 20 times slower in some benchmarks in their paper. This is on the IR level, iirc similar optimizers exist for assembly generation, so you can throw that in as another pass. [0] https://github.com/google/souper https://github.com/google/souper
  - MaxBarraclough 6y ago
    > At any price? Seems to me that raising the ceiling on optimisation is good to have, even if the computational cost is very high. If it works reliably, it wouldn't be necessary to do optimised release builds very often, and they could be offloaded onto a heavyweight build server, perhaps on the cloud.
deleted 6y ago
[deleted]
crb002 6y ago
BOLT just permutes link order? The object permutation from a BOLT run should be good for months until the underlying objects have substantially drifted?

glandium 6y ago

Propeller is probably better (and should eventually be integrated in LLVM itself). http://lists.llvm.org/pipermail/llvm-dev/2019-September/135393.html http://lists.llvm.org/pipermail/llvm-dev/2019-September/1353... It's still Linux only, though.