5 ms·

Can use any compiler. (GCC sometimes optimizes better than LLVM, GCC has more platform support, TCC can be used for faster compilation). LLVM interface is unst

Can use any compiler. (GCC sometimes optimizes better than LLVM, GCC has more platform support, TCC can be used for faster compilation). LLVM interface is unstable. That said there are things you can't properly implement by compiling to C.

posix_me_less 6y ago
> there are things you can't properly implement by compiling to C Very interesting claim, any examples?
- thysultan 6y ago
  It's not only interesting, it's blatantly false.
- aweinstock 6y ago
  If your source language has some construct that you want to express as state machines (e.g. async, CPS, pattern match compilation), and you want to compile the state machine as direct threaded code[0] (which involves fewer branches than a while-switch), then if you're compiling to C, you need computed gotos[1], which are non-standard. [0]: https://en.wikipedia.org/wiki/Threaded_code#Direct_threading https://en.wikipedia.org/wiki/Threaded_code#Direct_threading [1]: https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html
  - mratsim 6y ago
    GCC, Clang, ICC do support computed gotos and you can fallback to ``while true`` loop + switch dispatch for others. This is what Nim does: https://nim-lang.org/docs/manual.html#pragmas-computedgoto-pragma https://nim-lang.org/docs/manual.html#pragmas-computedgoto-p...
- pornel 6y ago
  • You don't control your ABI. For example, you can't reserve a register for error object return like Swift does. • You don't control your stack and stack frames. You can't implement a segmented stack, for example. • You have very limited options for unwinding. setjmp doesn't really cut it. You could leverage C++ exceptions or platform-specific things like SEH, but you can't design anything radically different. • You can't have debug information fancier than #line and maybe reusing C++ name mangling. You can't make debuggers see your higher-level constructs and data as anything other than their lowering. • You have very limited options for specifying pointer aliasing. • If you don't want to inherit UB from C, you'll have to be very clever about using alternative constructs that don't cause UB while still compile to efficient code you wanted. • If you mean standard C, not C with compiler extensions, then look at the whole list of non-standard intrinsics and built-ins for things C can't do.

posix_me_less 6y ago

> there are things you can't properly implement by compiling to C Very interesting claim, any examples?

thysultan 6y ago
It's not only interesting, it's blatantly false.
aweinstock 6y ago
If your source language has some construct that you want to express as state machines (e.g. async, CPS, pattern match compilation), and you want to compile the state machine as direct threaded code[0] (which involves fewer branches than a while-switch), then if you're compiling to C, you need computed gotos[1], which are non-standard. [0]: https://en.wikipedia.org/wiki/Threaded_code#Direct_threading https://en.wikipedia.org/wiki/Threaded_code#Direct_threading [1]: https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html
- mratsim 6y ago
  GCC, Clang, ICC do support computed gotos and you can fallback to ``while true`` loop + switch dispatch for others. This is what Nim does: https://nim-lang.org/docs/manual.html#pragmas-computedgoto-pragma https://nim-lang.org/docs/manual.html#pragmas-computedgoto-p...
pornel 6y ago
• You don't control your ABI. For example, you can't reserve a register for error object return like Swift does. • You don't control your stack and stack frames. You can't implement a segmented stack, for example. • You have very limited options for unwinding. setjmp doesn't really cut it. You could leverage C++ exceptions or platform-specific things like SEH, but you can't design anything radically different. • You can't have debug information fancier than #line and maybe reusing C++ name mangling. You can't make debuggers see your higher-level constructs and data as anything other than their lowering. • You have very limited options for specifying pointer aliasing. • If you don't want to inherit UB from C, you'll have to be very clever about using alternative constructs that don't cause UB while still compile to efficient code you wanted. • If you mean standard C, not C with compiler extensions, then look at the whole list of non-standard intrinsics and built-ins for things C can't do.