[llvm] [CodeGen] Reland "Use SmallMapVector for SpillPlacement::Node::Links" (PR #196270)

[Nikita Popov via llvm-commits]

nikic wrote:

First commit: https://llvm-compile-time-tracker.com/compare.php?from=ac9e437961c816896a1d7dc812e5a52bbc224b97&to=ba7bdf683c7a484e47cef7ad9024f08936ab0884&stat=instructions:u
Second commit: https://llvm-compile-time-tracker.com/compare.php?from=ba7bdf683c7a484e47cef7ad9024f08936ab0884&to=a342f64eb88c604be615cbdd3d2fdfff70f12d7e&stat=instructions:u
Original change: https://llvm-compile-time-tracker.com/compare.php?from=69c38be839913749fb34b681fe05a053f222e311&to=f217197c8d658390be97d962627a52f2cd97bd4a&stat=instructions:u

The results are better now, but it's still a significant regression.

https://github.com/llvm/llvm-project/pull/196270