[clang] [LifetimeSafety] Cache lifetimebound macro lookup. NFC. (PR #205250)

[Zeyi Xu via cfe-commits]

zeyi2 wrote:

> Well that's a bit weird.

Yeah, that does look a bit odd.

My guess is that this is more likely benchmark noise than something caused by this change.

A few reasons:

- The two benchmark runs were not done back-to-back under the exact same machine state.
- The upstream revision also differed between the two runs. I reused the data from https://github.com/llvm/llvm-project/pull/204045#issuecomment-4744770346.
- When `-lifetime-safety-lifetimebound-macro=` is set, this path uses the spelling from `LangOpts` and skips macro lookup entirely. So a small slowdown in this row does not seem like something that would be explained by the cache lookup change.


https://github.com/llvm/llvm-project/pull/205250