FeedaMail: Comments for Sutter’s Mill

	Comments for Sutter's Mill
	(Sponsor this newsletter) Comment on Reader Q&A: When will better JITs save managed code? by Jon Harrop “This is a 199x/200x meme that's hard to kill…a JIT can never be as good as a regular optimizing compiler because a JIT compiler is in the business of being fast, not in the business of generating optimal code” In my experience, the variance between different C++ compilers is much greater than between C++ and managed languages. For example, I have found that MSVC++ usually generates poor code that runs slower than most managed languages. The Clang C++ compiler usually generates fast code but it uses the same backend (LLVM) that managed languages use. So I don’t believe your claim. Do you have any concrete examples of optimizations done by C++ compilers that are not done by JITs because compile times would be unacceptable? Read More » Comment on Reader Q&A: When will better JITs save managed code? by Ben Voigt Sure, many times there are complex expressions (perhaps including loops) performing computations which are parameterized by the parameters are known at compile-time. Numeric integration of a function that has no closed-form algebraic integral, parameterized on the limits/bounds would be an example. In C++, meta-programming (formerly with templates, now with `constexpr`) can cause those to be precomputed at compile time. JITs won’t compute those at compile time, and in fact there would be no advantage to doing so, because the compile time cost is paid for every execution. In a JITted environment, you might as well just use memoization to ensure the computation is done at most once per execution. Read More »
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