4 ms·

For values with compiler-visible scoped lifetime, the compiler will automatically promote them to stack variables. There is currently no way to enforce this hap

For values with compiler-visible scoped lifetime, the compiler will automatically promote them to stack variables. There is currently no way to enforce this happening, but it would be perfectly possible to add such an annotation. Regarding preallocation, you tend to want to avoid dynamic memory allocation in high performance applications anyway, so whether you do that in C++ or in Julia, doesn't really make too much of a difference. It is true this is a little harder to control in GC'ed languages than in languages where you have to do memory management manually, but the effect is about the same. Julia provides tools to figure out where you're using dynamic memory allocation and those tools will certainly improve in the future. One thing I think is under appreciated from the performance perspective though is how easily julia lets you express data layout transformation to take better advantage of the cache hierarchy. I touched on this a bit in my JuliaCon presentation [1]. [1] https://youtu.be/uecdcADM3hY?t=32m19s https://youtu.be/uecdcADM3hY?t=32m19s

vvanders 9y ago
> Regarding preallocation, you tend to want to avoid dynamic memory allocation in high performance applications anyway, so whether you do that in C++ or in Julia, doesn't really make too much of a difference. Yes! Which is why it shouldn't take me digging through 3 different documents and still getting it partly wrong! C/C++/Rust make this easy by annotating the type modifiers(&/*/Box/etc) with how the object lives in my runtime system. Rust even gets bonus points for giving me aliasing information as well(&mut vs &).
- ChrisRackauckas 9y ago
  You just do @. and you're done?
bjourne 9y ago
> For values with compiler-visible scoped lifetime, the compiler will automatically promote them to stack variables. There is currently no way to enforce this happening, but it would be perfectly possible to add such an annotation. Other languages such as Java have that optimization too. But it is quite limited because it can only be applied to data whose size is known at compile-time. There is also the problem that if some data allocated in a procedure is passed to another procedure, it can't be allocated on the stack because it can escape. A programmer working in a low-level language can be smart and choose the best locations (stack or heap) for each piece of data. A language that does not allow explicit stack access (like C does), can never make as optimal decisions.

vvanders 9y ago

> Regarding preallocation, you tend to want to avoid dynamic memory allocation in high performance applications anyway, so whether you do that in C++ or in Julia, doesn't really make too much of a difference. Yes! Which is why it shouldn't take me digging through 3 different documents and still getting it partly wrong! C/C++/Rust make this easy by annotating the type modifiers(&/*/Box/etc) with how the object lives in my runtime system. Rust even gets bonus points for giving me aliasing information as well(&mut vs &).

ChrisRackauckas 9y ago
You just do @. and you're done?

bjourne 9y ago

> For values with compiler-visible scoped lifetime, the compiler will automatically promote them to stack variables. There is currently no way to enforce this happening, but it would be perfectly possible to add such an annotation. Other languages such as Java have that optimization too. But it is quite limited because it can only be applied to data whose size is known at compile-time. There is also the problem that if some data allocated in a procedure is passed to another procedure, it can't be allocated on the stack because it can escape. A programmer working in a low-level language can be smart and choose the best locations (stack or heap) for each piece of data. A language that does not allow explicit stack access (like C does), can never make as optimal decisions.