3 ms·

I agree it shouldn't really matter if there's no C++ features in play, but I suppose third party headers could bite you if they use #ifdef __cplusplus to guard

by jsheard 8mo ago

I agree it shouldn't really matter if there's no C++ features in play, but I suppose third party headers could bite you if they use #ifdef __cplusplus to guard optional C++ extensions on top of their basic C interface. In that case the compiler could be dealing with dramatically more complex code when you build in C++ mode.

uecker 8mo ago
Maybe it is similar for the same compiler (but one should check, I suspect C could still be faster), but then there are much more C compilers. For example, TCC is a lot faster than GCC.
- levodelellis 8mo ago
  tcc is 8x faster, twice as fast isn't doing it justice. As for the header thing, that'd could potentially be true if the compile time was something like 450ms -> 220ms, but why bother saying it when you're only saving a few hundred milliseconds
  - petters 8mo ago
    Going from 220 to 450 ms would be a disaster in my project. It has many thousands of files. Recompilation of almost everything happens from time to time. If those made-up numbers were true, they would be very significant and an argument in favor of keeping the code in C
    - levodelellis 8mo ago
      A 200ms difference is adding or removing 200lines lines of implementation, and spliting it up into a file can make it slower because of include overhead. You completely made up C being twice as fast as C++.
- pjmlp 8mo ago
  The question is the performance optimisations on top. 1990's compilers were also super fast, they only did optimisation for size, speed, constant propagation, and little else. Zero code motion, loop unroling, code elision, heap via stack replacement, inlining,...
  - uecker 8mo ago
    Of course, but gcc with -O0 is still slower and there is no TCC for C++.
    - pjmlp 8mo ago
      There are other C++ compilers to benchmark against, using the same common C subset for comparison, though.
      - uecker 8mo ago
        Is there still any non-LLVM C++ compiler left besides GCC? LLVM is not exactly known for its speed.
        not_a9 8mo ago
        MSVC?
        pjmlp 8mo ago
        Many embedded vendors still haven't made the jump, and Microsoft.

by jsheard 8mo ago

uecker 8mo ago

Maybe it is similar for the same compiler (but one should check, I suspect C could still be faster), but then there are much more C compilers. For example, TCC is a lot faster than GCC.

levodelellis 8mo ago
tcc is 8x faster, twice as fast isn't doing it justice. As for the header thing, that'd could potentially be true if the compile time was something like 450ms -> 220ms, but why bother saying it when you're only saving a few hundred milliseconds
- petters 8mo ago
  Going from 220 to 450 ms would be a disaster in my project. It has many thousands of files. Recompilation of almost everything happens from time to time. If those made-up numbers were true, they would be very significant and an argument in favor of keeping the code in C
  - levodelellis 8mo ago
    A 200ms difference is adding or removing 200lines lines of implementation, and spliting it up into a file can make it slower because of include overhead. You completely made up C being twice as fast as C++.
pjmlp 8mo ago
The question is the performance optimisations on top. 1990's compilers were also super fast, they only did optimisation for size, speed, constant propagation, and little else. Zero code motion, loop unroling, code elision, heap via stack replacement, inlining,...
- uecker 8mo ago
  Of course, but gcc with -O0 is still slower and there is no TCC for C++.
  - pjmlp 8mo ago
    There are other C++ compilers to benchmark against, using the same common C subset for comparison, though.
    - uecker 8mo ago
      Is there still any non-LLVM C++ compiler left besides GCC? LLVM is not exactly known for its speed.
      - not_a9 8mo ago
        MSVC?
      - pjmlp 8mo ago
        Many embedded vendors still haven't made the jump, and Microsoft.