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I don't know about 2012 but in general if used correctly C++ can often be faster than C due to the widespread inlining and the use of templates. (On the other h

I don't know about 2012 but in general if used correctly C++ can often be faster than C due to the widespread inlining and the use of templates. (On the other hand, if one writes C++ as if it was Java - the code will be faster than Java's but often can be optimized further indeed.)

bitwize 7y ago
For values of "used correctly" that, by the time you have mastered them in C++x, have changed completely in C++x+3.
- ahartmetz 7y ago
  If it's about performance, that is usually not the case. In a few cases one could get a performance improvement using move semantics - most other new features are only about safety and convenience.
tpolzer 7y ago
If you write C++ like it's Java, it will be slower, mostly for two reasons: - A C++ compiler cannot do speculative devirtualization. Which hurts if you split everything into small virtual functions. - If you are churning through lots of small allocations and aren't maxing all CPU cores, a garbage collector running in parallel is nearly free - unlike the bookkeeping your C++ deallocations have to go through.
- saagarjha 7y ago
  > A C++ compiler cannot do speculative devirtualization. Yes, it can! For example: https://godbolt.org/z/-JtSiJ https://godbolt.org/z/-JtSiJ
  - quotemstr 7y ago
    A AOT compiler (almost all C++ compilers are AOT) can't do speculative devirtualization based on dynamic runtime feedback. (PGO is one-shot.) That's what the OP meant.
    - saagarjha 7y ago
      Fair enough. That's why there's the push in modern C++ for compile-time static dispatch :)
userbinator 7y ago
due to the widespread inlining and the use of templates On the other hand, this often causes a huge increase in code size, which means less code can fit in the instruction cache, and - even worse - when the system is on the verge of swapping, can make performance drop even faster. It's unfortunate that microbenchmarks often tend to favour such globally-inefficient code that's only slightly faster in isolation but bogs down the system as a whole. This article is related: https://news.ycombinator.com/item?id=18777735 https://news.ycombinator.com/item?id=18777735

bitwize 7y ago

For values of "used correctly" that, by the time you have mastered them in C++x, have changed completely in C++x+3.

ahartmetz 7y ago
If it's about performance, that is usually not the case. In a few cases one could get a performance improvement using move semantics - most other new features are only about safety and convenience.

tpolzer 7y ago

If you write C++ like it's Java, it will be slower, mostly for two reasons: - A C++ compiler cannot do speculative devirtualization. Which hurts if you split everything into small virtual functions. - If you are churning through lots of small allocations and aren't maxing all CPU cores, a garbage collector running in parallel is nearly free - unlike the bookkeeping your C++ deallocations have to go through.

saagarjha 7y ago
> A C++ compiler cannot do speculative devirtualization. Yes, it can! For example: https://godbolt.org/z/-JtSiJ https://godbolt.org/z/-JtSiJ
- quotemstr 7y ago
  A AOT compiler (almost all C++ compilers are AOT) can't do speculative devirtualization based on dynamic runtime feedback. (PGO is one-shot.) That's what the OP meant.
  - saagarjha 7y ago
    Fair enough. That's why there's the push in modern C++ for compile-time static dispatch :)

userbinator 7y ago

due to the widespread inlining and the use of templates On the other hand, this often causes a huge increase in code size, which means less code can fit in the instruction cache, and - even worse - when the system is on the verge of swapping, can make performance drop even faster. It's unfortunate that microbenchmarks often tend to favour such globally-inefficient code that's only slightly faster in isolation but bogs down the system as a whole. This article is related: https://news.ycombinator.com/item?id=18777735 https://news.ycombinator.com/item?id=18777735