[libcxx-commits] [libcxx] [libc++][print] Includes <format>. (PR #76333)

[via libcxx-commits]

zmodem wrote:

We noticed in Chromium that this grew our preprocessed compiler input size by ca 4.3 GB (1.2%).

A small example:

```
$ cat /tmp/a.cc
#include <iostream>

int main() {
  std::cout << "Hello, world!\n";
  return 0;
}

# Before this change:
$ build2/bin/clang++ -E -stdlib=libc++ -std=c++20 /tmp/a.cc | wc --bytes
3108703
$ perf stat -r20 build2/bin/clang++ -c -stdlib=libc++ -std=c++20 /tmp/a.cc
0.879287 +- 0.000996 seconds time elapsed  ( +-  0.11% )

# After this change:
$ build2/bin/clang++ -E -stdlib=libc++ -std=c++20 /tmp/a.cc | wc --bytes
3683481
$ perf stat -r20 build2/bin/clang++ -c -stdlib=libc++ -std=c++20 /tmp/a.cc
0.98528 +- 0.00192 seconds time elapsed  ( +-  0.20% )
```

That is an 18% increase in preprocessed size and 12% increase in compile time.

I realize this kind of change is driven by the standard, but is there anything that could be done to limit the negative impact, especially for those not using std::printf in this case?

(Yes, modules is the long-term answer, but many of us are not ready yet.)

https://github.com/llvm/llvm-project/pull/76333