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

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> I think one large upfront allocation wouldn't hurt as much as repeatedly calling malloc/free to resize the underlying storage. I think things can be improved by doing a dry-run, upper-bounding the number of rows and columns, and performing the entire allocation upfront.

Another thing I noticed was a call to a copy-constructor that copies the underlying storage. Is it really necessary to copy the underlying storage?

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