[clang] [WIP][C++20][Modules] Lazily, but fully load 'HeaderFileInfo' table into memory. (PR #140867)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

FWIW I tried running this patch through my `clang-scan-deps` benchmark on an internal Apple project and saw 16% increase in instruction count.

https://github.com/llvm/llvm-project/pull/140867