[llvm] [DAGCombiner] Use SmallDenseMap (NFC) (PR #79681)

[Nikita Popov via llvm-commits]

nikic wrote:

Looks like this causes a regression rather than an improvement in practice: https://llvm-compile-time-tracker.com/compare.php?from=57a20d2d09bbd3cc501fc6d8b4746be2040c99b7&to=863b2c84c0fbcfb02d969fa36af4932d410a827b&stat=instructions%3Au

I think this is because SmallDenseMap (unlike SmallVector) actually incurs an extra cost because it has to always check the two representations dynamically.

https://github.com/llvm/llvm-project/pull/79681