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Compilers spend a lot of time with hashtables, which exist on the heap. Rust isn't some magical language that makes the heap some unnecessary entity. One still

by __s 10y ago

Compilers spend a lot of time with hashtables, which exist on the heap. Rust isn't some magical language that makes the heap some unnecessary entity. One still has objects whose lifetime do not fit the stack model or whose size is dynamic Their comment went on to claim that given their hypothesis, allocation optimization shouldn't be impactful. Yet this post demonstrates otherwise, perhaps showing that therefore their hypothesis is false (if a then b, b is false, therefore a is false) One of the post's optimizations was to use Cow<str> over String tho, which is an example of reducing allocations with borrows Additionally it's oft mentioned that a weak point in Rust's compile time is LLVM. This has to do with various things, some of which are Rust's fault (it could generate less IR), but it points out that there's a lot of time being spent in C++ code. LLVM's great, but it's guidelines essentially suggest 'if you want to make llvm play nice, generate IR like clang'

acqq 10y ago
> Their comment went on to claim that given their hypothesis, allocation optimization shouldn't be impactful. And what was the hypothesis? That the code for the compiler itself should use the features imagined to be used by the language, just like your example: > One of the post's optimizations was to use Cow<str> over String Then: > allocation optimization shouldn't be impactful. Yet this post demonstrates otherwise "not impactful": It looks to me like that: 36.526s vs 32.373s for the longest compile tested. It is measurable, but not something that I as the programmer will be able to notice. My definition of impactful for the compilation times is "at least a factor of 2" not 1.1. And the claim is, once the language possibilities are actually used. If the code is written differently, of course not much is expected. The result of a moderate speedup exactly shows that the language possibilities weren't always used in a way to minimize allocations, but the difference is still not, for my perception, significant (10% is hard to recognize unless measured or the actual compilations last hours and not seconds). But I still claim that much bigger potential gains are the actual changes in the algorithms and the data structures. The data structures especially can hugely change the result if they are made to be really cache friendly, and together with the changes in algorithms such modifications have the potential to make an order of magnitude speedups, if they are actually possible.

by __s 10y ago

acqq 10y ago

> Their comment went on to claim that given their hypothesis, allocation optimization shouldn't be impactful. And what was the hypothesis? That the code for the compiler itself should use the features imagined to be used by the language, just like your example: > One of the post's optimizations was to use Cow<str> over String Then: > allocation optimization shouldn't be impactful. Yet this post demonstrates otherwise "not impactful": It looks to me like that: 36.526s vs 32.373s for the longest compile tested. It is measurable, but not something that I as the programmer will be able to notice. My definition of impactful for the compilation times is "at least a factor of 2" not 1.1. And the claim is, once the language possibilities are actually used. If the code is written differently, of course not much is expected. The result of a moderate speedup exactly shows that the language possibilities weren't always used in a way to minimize allocations, but the difference is still not, for my perception, significant (10% is hard to recognize unless measured or the actual compilations last hours and not seconds). But I still claim that much bigger potential gains are the actual changes in the algorithms and the data structures. The data structures especially can hugely change the result if they are made to be really cache friendly, and together with the changes in algorithms such modifications have the potential to make an order of magnitude speedups, if they are actually possible.