[llvm] [RegAlloc] Remove default restriction on non-trivial rematerialization (PR #159211)

[Alexander Kornienko via llvm-commits]

alexfh wrote:

It turned out to be rather challenging to extract a shareable test case for this. The original input is equivalent to ~100M IR, which is already close to be a compiler stress test. And it also seems like we're only seeing the compilation time regression with memory sanitizer enabled, which likely expands the scope of what could go wrong (though register allocator seems to be sufficiently remote and independent from sanitizer instrumentation).

I wonder if a Clang profile collected while compiling the problematic file before and after this commit would be helpful to diagnose the problem?

https://github.com/llvm/llvm-project/pull/159211