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The slowest part is LLVM. (You can pass "-Z time-passes" to rustc to get detailed timing info.)

This isn't just an "LLVM is slow" problem, though. It's also a "rustc generates extremely verbose LLVM IR" problem. Optimizing the IR before it gets to LLVM is part of the plan for solving it.

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It's also a "let's rebuild everything every time" problem. Hopefully, that will be fixed with support for building incrementally.

(Also note that compiling a C++ file with 2000 lines can take a very long time too)

You must not forget that thanks to the preprocessor, what looks like 2000 lines may in fact be around 200k lines

E.g. I have a very innocent 2000-line MainWindow.cpp that weighs 244419 lines when measured with gcc -E -o - | wc -l

Good point, it really is quite staggering what a C++ compiler has to digest to compile a standard "Hello, World!". Hopefully the much-anticipated module system will help here. Generally I find that avoiding Boost libraries (including std::regex) helps enormously ;)

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