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Comment by m_mueller

7 years ago

As someone who likes Fortran90+ for numerics in HPC, I'd put it this way:

* Pointers are required mainly so you can do pointer swaps and be sure there is no unnecessary allocation (in simulations this often means being sure there's no 10-100GB allocation each timestep, which is where it really matters).

* Pointer math is unnecessary and only there because C has no/poor support of multidimensional arrays. Use a reasonable language like Julia or Fortran instead. In fact, the potential for pointer math has a big negative impact on performance since compilers have to assume aliasing. The __restrict solution is clunky in C and completely non-standard in C++, Fortran does not require this at all (no aliasing allowed except where explicitly stated).

* For almost all usecases (except swaps) a semi-managed approach like Fortran's allocatables or Objective-C's ARC or even retain/release seems to me the most straight-forward.

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m_mueller

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saagarjha  7 years ago

> Pointers are required mainly so you can do pointer swaps and be sure there is no unnecessary allocation

Many languages are getting around this issue by hiding pointers in their type system, performing copy-on-write, and taking the decision of whether allocations are performed on the stack or heap out of the hands of the programmer.

  • m_mueller  7 years ago

    > out of the hands of the programmer

    see, and that's where these languages become really clunky for HPC purposes. A compiler/runtime with HPC support (and I think also systems programming) should provide (a) performant defaults with safety as a second (but still high) priority and (b) the ability for programmers to go and set things a certain way when it is clear to them how things should be implemented on the machine.

    Otherwise, in large applications, there's just too many moving parts that the compiler (optimization) can mess up. As long as we have no AGI baked into compilers it's an illusion to think that compilers will do the job of HPC engineers, so if you take away these tools we just have to look elsewhere.