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

[Alexander Kornienko via llvm-commits]

alexfh wrote:

Hi @lukel97, is this change expected to affect compilation time a lot? We see quite significant regressions on some protobuf-generated files:
- before
```
   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
  130.3845 ( 61.6%)   0.6329 (  3.6%)  131.0175 ( 57.1%)  131.0921 ( 57.1%)  Greedy Register Allocator #2
```
- after
```
   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
  399.9995 ( 79.2%)   0.8087 (  4.4%)  400.8082 ( 76.5%)  401.0294 ( 76.5%)  Greedy Register Allocator #2
```

This results in around 2x end-to-end compilation slowdown.

Do you see any opportunities for optimization? Is there a way to mitigate this using compiler flags?

I can try preparing a reduced test case, but it's going to take some time.

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