[libcxx-commits] [clang] [libcxx] [Clang] Normalize constraints before checking for satisfaction (PR #161671)

[Reid Kleckner via libcxx-commits]

rnk wrote:

I discussed this with Hans today, and we think one way to evaluate the performance impact would be to bootstrap clang itself *with C++20 enabled*. I think Chromium, and probably most C++ code in the wild, isn't using C++20 concepts heavily, and is mostly picking them up through libc++.

I really would not want to eat a 16% C++ compile time regression on normal C++ code. As a point of comparison, we're using 32-bit source locations to avoid a 4% peak memory usage increase with 0% measurable regression, which is very conservative.

It's hard, though, since it's a performance vs conformance (arguably correctness) tradeoff, it's just not a correctness *regression*, which we usually weight very highly when making tradeoff decisions. :)

https://github.com/llvm/llvm-project/pull/161671