[llvm] [SCEV] Look up uniqued nodes by using interned profile. (NFC) (PR #217571)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

@fhahn I happen to be working on speeding up `FoldingSet` with a Swiss Table-style approach as a drop-in replacement. My current patch speeds up `clang -O3` by approximately 1.8% on a wide variety of C++ source files.  I am happy to post my patch after your PR lands. Alternatively, I can post my patch now, and you might want to evaluate it to see if it meets your performance goals in SCEV?

https://github.com/llvm/llvm-project/pull/217571