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If you think AWK is hard to parse then try C++. The latter is so hard to parse thus very slow compile time that most probably inspired a funny programmer skit l

If you think AWK is hard to parse then try C++. The latter is so hard to parse thus very slow compile time that most probably inspired a funny programmer skit like this, one of the most popular XKCDs of all time [1]. Then come along fast compilation modern languages like Go and D. The latter is such a fresh air is that even though it's a complex language like C++ and Rust but it managed to compile very fast. Heck it even has RDMD facility that can perform compiled REPL as you interacting with the prompt similar to interpreted programming languages like Python and Matlab. According to its author, the main reason D has very fast compile time (as long as you avoid the CTFE) is because of the language design decisions avoid the notorious symbols that can complicated symbol table just like happened in C++ and the popular << and >> overloading for I/O and shifting. But the fact that Rust come much later than C++ and D but still slow to compile is bewildering to say the least. [1] Compiling: https://xkcd.com/303/ https://xkcd.com/303/

moomin 2y ago
Pretty sure Rust's compile times are a function of the complex type system and generic instantiation. Everything's a trade-off.
- dotancohen 2y ago
  Which are damn more important (to me) than is the compile time metric.
- masklinn 2y ago
  Except in some rare edge cases, it’s mostly the latter, indirectly: in the average crate the vast majority of the time is spent in LLVM optimization passes and linking. Sometimes IR generation gets a pretty high score, but that’s somewhat inconsistent.
- deleted 2y ago
  [deleted]
- fnord77 2y ago
  IIRC, rust's long compile times are because it is basically doing static analysis, looking for potential errors
- pornel 2y ago
  `cargo check` that does all the parsing, type system checks, and lifetime analysis is pretty fast compared to builds. Rust compilation time spends most time in LLVM, due to verbosity of the IR it outputs, and during linking, due to absurd amount of debug info and objects to link. When cargo check isn't fast, it's usually due to build scripts and procedural macros, which are slow due to being compiled binaries, so LLVM, linking, and running of an unoptimized ton of code blocks type checking.
keybored 2y ago
> According to its author, the main reason D has very fast compile time (as long as you avoid the CTFE) is because of the language design decisions avoid the notorious symbols that can complicated symbol table just like happened in C++ and the popular << and >> overloading for I/O and shifting. But the fact that Rust come much later than C++ and D but still slow to compile is bewildering to say the least. The reasons why Rust (rustc) is slow to compile are well-known. Not bewildering.
- orwin 2y ago
  Rust isn't particulary slow to compile as long as you keep opt-level to 1 and the number of external library minimal. But even them it isn't as slow as C++ (but i write shit C++ code, i've heard that modern C++ is way better, i learned with C++98 and never really improved my style despite using C++11).
  - kragen 2y ago
    http://canonical.org/~kragen/sw/dev3/gcd.rs http://canonical.org/~kragen/sw/dev3/gcd.rs, which uses no external libraries, takes 400–450ms to compile with rustc -C opt-level=1 gcd.rs (buggy program, i know). gcc 12, which is not anyone's idea of a fast c compiler, compiles the c equivalent http://canonical.org/~kragen/sw/dev3/gcd.c http://canonical.org/~kragen/sw/dev3/gcd.c in 70–90ms, so the rust compiler is 300–500% slower tcc, which is most people's idea of a fast c compiler, compiles gcd.c in 8–9ms, so the rust compiler is 4300–5500% slower so from my point of view 'rust isn't particularly slow to compile' is off by about an order of magnitude is it as slow as c++? well, g++ compiles the c++ version of the same code http://canonical.org/~kragen/sw/dev3/gcd.cc http://canonical.org/~kragen/sw/dev3/gcd.cc in 460–490ms. so in this case compiling rust is, yeah, on the order of 10% faster than compiling c++? i feel like that's basically the same of course you can make compiling c++ arbitrarily slow with templates
    - orwin 2y ago
      > of course you can make compiling c++ arbitrarily slow with templates This might be my problem :/ (template are the closest to metaprogramming I can find outside of Lisps) Tbf I was mostly comparing my experience with Rust, SBCL and C++, to me it was a given that C was an order of magnitude faster (3 order of magnitude seems a bit much). I found opt-level=1 quite early and managed to feel way better about rust and let C++ go (i was toying with polynomial regressions) (I rolled my own matrix library :D never do that!) Thank you for the informations.
mardifoufs 2y ago
How much time does the parsing step take when compiling c++, relatively speaking? Is it actually significant compared to everything else that happens?

moomin 2y ago

Pretty sure Rust's compile times are a function of the complex type system and generic instantiation. Everything's a trade-off.

dotancohen 2y ago
Which are damn more important (to me) than is the compile time metric.
masklinn 2y ago
Except in some rare edge cases, it’s mostly the latter, indirectly: in the average crate the vast majority of the time is spent in LLVM optimization passes and linking. Sometimes IR generation gets a pretty high score, but that’s somewhat inconsistent.
deleted 2y ago
[deleted]
fnord77 2y ago
IIRC, rust's long compile times are because it is basically doing static analysis, looking for potential errors
pornel 2y ago
`cargo check` that does all the parsing, type system checks, and lifetime analysis is pretty fast compared to builds. Rust compilation time spends most time in LLVM, due to verbosity of the IR it outputs, and during linking, due to absurd amount of debug info and objects to link. When cargo check isn't fast, it's usually due to build scripts and procedural macros, which are slow due to being compiled binaries, so LLVM, linking, and running of an unoptimized ton of code blocks type checking.

keybored 2y ago

> According to its author, the main reason D has very fast compile time (as long as you avoid the CTFE) is because of the language design decisions avoid the notorious symbols that can complicated symbol table just like happened in C++ and the popular << and >> overloading for I/O and shifting. But the fact that Rust come much later than C++ and D but still slow to compile is bewildering to say the least. The reasons why Rust (rustc) is slow to compile are well-known. Not bewildering.

orwin 2y ago
Rust isn't particulary slow to compile as long as you keep opt-level to 1 and the number of external library minimal. But even them it isn't as slow as C++ (but i write shit C++ code, i've heard that modern C++ is way better, i learned with C++98 and never really improved my style despite using C++11).
- kragen 2y ago
  http://canonical.org/~kragen/sw/dev3/gcd.rs http://canonical.org/~kragen/sw/dev3/gcd.rs, which uses no external libraries, takes 400–450ms to compile with rustc -C opt-level=1 gcd.rs (buggy program, i know). gcc 12, which is not anyone's idea of a fast c compiler, compiles the c equivalent http://canonical.org/~kragen/sw/dev3/gcd.c http://canonical.org/~kragen/sw/dev3/gcd.c in 70–90ms, so the rust compiler is 300–500% slower tcc, which is most people's idea of a fast c compiler, compiles gcd.c in 8–9ms, so the rust compiler is 4300–5500% slower so from my point of view 'rust isn't particularly slow to compile' is off by about an order of magnitude is it as slow as c++? well, g++ compiles the c++ version of the same code http://canonical.org/~kragen/sw/dev3/gcd.cc http://canonical.org/~kragen/sw/dev3/gcd.cc in 460–490ms. so in this case compiling rust is, yeah, on the order of 10% faster than compiling c++? i feel like that's basically the same of course you can make compiling c++ arbitrarily slow with templates
  - orwin 2y ago
    > of course you can make compiling c++ arbitrarily slow with templates This might be my problem :/ (template are the closest to metaprogramming I can find outside of Lisps) Tbf I was mostly comparing my experience with Rust, SBCL and C++, to me it was a given that C was an order of magnitude faster (3 order of magnitude seems a bit much). I found opt-level=1 quite early and managed to feel way better about rust and let C++ go (i was toying with polynomial regressions) (I rolled my own matrix library :D never do that!) Thank you for the informations.

mardifoufs 2y ago

How much time does the parsing step take when compiling c++, relatively speaking? Is it actually significant compared to everything else that happens?