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Being able to guarantee tail calls is a useful optimization in far more cases than code replaceable by loops. I’ve used it myself where dispatch targets themsel

Being able to guarantee tail calls is a useful optimization in far more cases than code replaceable by loops. I’ve used it myself where dispatch targets themselves are dynamic (so can’t be trivially made into a loop) for significant performance gains. Some other folks who’ve done the same thing (and can post publicly) for code that’s not just “must recurse because loops are for lowly imperative serfs”: * https://blog.reverberate.org/2021/04/21/musttail-efficient-interpreters.html https://blog.reverberate.org/2021/04/21/musttail-efficient-i... * http://lua-users.org/lists/lua-l/2011-02/msg00742.html http://lua-users.org/lists/lua-l/2011-02/msg00742.html * https://cantortrading.fi/rust_decimal_str/ https://cantortrading.fi/rust_decimal_str/ Now does JavaScript really need/care about any of this? Probably not.

MrBuddyCasino 4y ago
Interesting use case, didn't occur to me that tail calls can also just be a performance optimisation technique to help out the compiler and branch predictor. I assumed hot loops could be implemented just as well using GOTOs, but maybe not?
- vgatherps 4y ago
  Tail calls are basically GOTOs, yeah. The bring a HUGE benefit of very clearly defining state flow between gotos which makes the compiler's job super easy.
- blagie 4y ago
  Everything can be implemented using IF statements and GOTOs. That's how early processors worked, and Turing completeness and all. We don't _really_ need function calls, while loops, or for loops either. That doesn't mean it's a good idea.
- chriswarbo 4y ago
  > I assumed hot loops could be implemented just as well using GOTOs, but maybe not? Tail calls are GOTOs; that's the whole argument https://apps.dtic.mil/sti/citations/ADA030751 https://apps.dtic.mil/sti/citations/ADA030751
- HALtheWise 4y ago
  In the particular linked case of protobuf parsing, a loop with goto's doesn't produce very well optimized code because of specific internal details about how modern C compilers do optimizations. You could certainly imagine a compiler that can fully optimize a go-to heavy program, in which case the code cleanliness argument would be the only reason.

MrBuddyCasino 4y ago

Interesting use case, didn't occur to me that tail calls can also just be a performance optimisation technique to help out the compiler and branch predictor. I assumed hot loops could be implemented just as well using GOTOs, but maybe not?

vgatherps 4y ago
Tail calls are basically GOTOs, yeah. The bring a HUGE benefit of very clearly defining state flow between gotos which makes the compiler's job super easy.
blagie 4y ago
Everything can be implemented using IF statements and GOTOs. That's how early processors worked, and Turing completeness and all. We don't _really_ need function calls, while loops, or for loops either. That doesn't mean it's a good idea.
chriswarbo 4y ago
> I assumed hot loops could be implemented just as well using GOTOs, but maybe not? Tail calls are GOTOs; that's the whole argument https://apps.dtic.mil/sti/citations/ADA030751 https://apps.dtic.mil/sti/citations/ADA030751
HALtheWise 4y ago
In the particular linked case of protobuf parsing, a loop with goto's doesn't produce very well optimized code because of specific internal details about how modern C compilers do optimizations. You could certainly imagine a compiler that can fully optimize a go-to heavy program, in which case the code cleanliness argument would be the only reason.