[llvm] ConstraintSystem: replace data structure with Matrix (PR #98895)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

Okay, the final results from LLVM Compile Time Tracker are back, and it looks like this change has a significant impact on one benchmark, and negligible regressions in ReleaseLTO: http://llvm-compile-time-tracker.com/compare.php?from=c5ee3c05ca61f3fae11337c5853aee7b450a9dc6&to=15dd68506d479cc50349de1cf1e70bd896b9c82e&stat=instructions%3Au.

@fhahn Could you check it on some more programs, when you have the time?

https://github.com/llvm/llvm-project/pull/98895