Comment by pjmlp | Hacker News Reader

Comment by pjmlp | Hacker News Reader

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Code generated by C compilers is fast in 2018.

Code generated by C compilers for C64, Spectrum, Atari, Atari ST, Amiga, Mac, CP/M, MS-DOS, Windows 3.x, Nintendo, MegaDrive,... systems meant many times the code would be 80% like this:

    void some_func(/* params */) {
      asm {
         /* actual "C" code as inline Assembly */
      }
   }

Lots of Swift sugar also gets optimized away, and there is plenty of room to improvement.

The code that current C compilers don't generate, many times is related to taking advantage of UB.

They also generate extra code for handling stuff like floating point emulation though.

Just as an example, IBM did their whole RISC research using PL/8, including an OS and optimizing compiler using an architecture similar to what LLVM uses.

They only bothered with C, after making the business case that RISC would be a good platform for UNIX workstations.

Why bring these ancient home computer platforms into play? Those were totally different to program for. Why not compare a C compiler from 1998 to one from 2018, on x86 (no SSE of course)? C compilers have gotten better, but not spectacularly.

>> The code that current C compilers don't generate, many times is related to taking advantage of UB

Compilers are really smart in optimizing things that aren't relevant to the real world.

For example, this code would reduce to "return 32" in most modern compilers:

  int return32(){
    int x=1;
    for (int i=0; i<5; i++){
      x*=2;
    }
    return x;
  }

Does that make impact in real-world code? Almost certainly not, it's a contrived case. Most UB cases fall into the same category.

>> They also generate extra code for handling stuff like floating point emulation though.

Not necessarily.

> wWhy bring these ancient home computer platforms into play? Those were totally different to program for. Why not compare a C compiler from 1998 to one from 2018, on x86 (no SSE of course)? C compilers have gotten better, but not spectacularly.

To clear up the myth among young generations that C compilers always generated fast code, regardless of the platform.

As for something more modern, in 1998, C code quality was still at a similar level to other system's languages, before they started to fade away thanks to the increase in UNIX, Linux and BSD adoption

For example, given that Delphi and C++ Builder share the same backend, their generated code was quite similar, even if it would require disabling some of the Delphi's security checks.

> Not necessarily.

Sure, it all depends on the CPU being targeted.

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