Imagine the simplest “compiler” for python or perl or JavaScript that doesn’t compile anything but just interprets it. There’s a lot of advantages to not having to wait for compilation. One can write a large and useful program with reasonable speed ups just from stupid compilation as many programs don’t need to be particularly fast.

One can imagine modifying the compiler to output llvm bitcode. You now can throw plenty of optimisation at it for free (but you are now slower to compile). This may be useful for prod but I claim a lot of the time it’s still useful for dev to have a simple very very fast compiler. Think less about the time to build one file and more of the time to rebuild your entire tree (or just a file which many things depend on)

Debug builds in C++ can be slow AND generate slow code.

Like the website says, if you need performance, you do production builds, which use GCC/Clang with -O2.

In the future V will have its own optimiser.