[clang] [clang][Sema] Add buffer-size checks for unistd I/O functions (PR #224979)

[Denys Fedoryshchenko via cfe-commits]

nuclearcat wrote:

Working on avoiding the per-call lookup table construction (synthetic 100,000-call benchmark was 18.7% slower with this patch).

https://github.com/llvm/llvm-project/pull/224979