# JIT style dynamic compiler **URL:** \ **Category:** language design\ **Created:** [November 7, 2020, 5:43am UTC](https://internals.rust-lang.org/t/jit-style-dynamic-compiler/13346 "2020-11-07T05:43:45Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![VaibhavDS19](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/vaibhavds19/32/7310_2.png) [@VaibhavDS19](https://internals.rust-lang.org/u/VaibhavDS19)\ **Post date:** [November 7, 2020, 5:43am UTC](https://internals.rust-lang.org/t/jit-style-dynamic-compiler/13346/1 "2020-11-07T05:43:46Z")
I have seen some stuff like Java or C# compiler running some optimizations at compile time. Can something similar be added, like a macro? Like unsafe but with dynamic compiling for purely that section? It might improve performance in some of those cases. ---
**Author:** ![bjorn3](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/bjorn3/32/2736_2.png) [@bjorn3](https://internals.rust-lang.org/u/bjorn3)\ **Post date:** [November 7, 2020, 12:56pm UTC](https://internals.rust-lang.org/t/jit-style-dynamic-compiler/13346/3 "2020-11-07T12:56:42Z")
MIRI is an interpreter, not a JIT. > [@VaibhavDS19](#): > > I have seen some stuff like Java or C# compiler running some optimizations at compile time. Running optimizations at compile time is exactly what Rust does as AOT compiler. > [@VaibhavDS19](#): > > Like unsafe but with dynamic compiling for purely that section? It might improve performance in some of those cases. What do you mean with "like unsafe"? ---
**Author:** ![bheisler](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/bheisler/32/3189_2.png) [@bheisler](https://internals.rust-lang.org/u/bheisler)\ **Post date:** [November 7, 2020, 1:37pm UTC](https://internals.rust-lang.org/t/jit-style-dynamic-compiler/13346/4 "2020-11-07T13:37:30Z")
I think what is being suggested here is a block that instructs the compiler to compile the contained code to some form of bytecode or other IR that would then be JIT-compiled at runtime. Such a thing would take a great deal of work, but there's no fundamental reason why it couldn't be done. It wouldn't even need to be built into the compiler; procedural macros could accomplish this, combined with a JIT-compiler built as a crate. If OP wants this, I would recommend building it yourself; I expect it will be very difficult to persuade others to do the large amount of work involved on a volunteer basis. ---
**Author:** ![atagunov](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/atagunov/32/5877_2.png) [@atagunov](https://internals.rust-lang.org/u/atagunov)\ **Post date:** [November 7, 2020, 1:53pm UTC](https://internals.rust-lang.org/t/jit-style-dynamic-compiler/13346/5 "2020-11-07T13:53:05Z")
Rust has been jokingly referred to as "the new C++". I guess the reasons there are no Jit compilers for Rust are similar to why there are no Jit compilers for C++ or C. ---
**Author:** ![bascule](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/bascule/32/3057_2.png) [@bascule](https://internals.rust-lang.org/u/bascule)\ **Post date:** [November 7, 2020, 3:38pm UTC](https://internals.rust-lang.org/t/jit-style-dynamic-compiler/13346/6 "2020-11-07T15:38:47Z")
For incorporating runtime information into how Rust code is optimized, check out [profile-guided optimization](https://doc.rust-lang.org/rustc/profile-guided-optimization.html). That's not a JIT, of course, but it can get you some benefits similar to ones a JIT gives you, namely runtime analysis of what optimizations should be performed. Edit: as it were, there's a new Inside Rust post on PGO: > **[Exploring PGO for the Rust compiler | Inside Rust Blog](https://blog.rust-lang.org/inside-rust/2020/11/11/exploring-pgo-for-the-rust-compiler.html)** > > Want to follow along with Rust development? Curious how you might get involved? Take a look! ---
**Author:** ![system](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/system/32/14092_2.png) [@system](https://internals.rust-lang.org/u/system)\ **Post date:** [February 5, 2021, 3:38pm UTC](https://internals.rust-lang.org/t/jit-style-dynamic-compiler/13346/7 "2021-02-05T15:38:52Z")
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