[polly] [polly] Add profitability check for expanded region. (PR #96548)

[Huihui Zhang via llvm-commits]

huihzhang wrote:

Thanks a lot @Meinersbur for the review feedbacks!

I have updated the region expansion heuristic, and addressed the following issues:
1) Check exactly for memory accesses that are not used in any loop of the expanded region;
2) Accept region expansion if unprofitable blocks added are followed by another loop, to encourage loop fusion.
A similar test with unrelated memory accesses in between loops is added into test/CodeGen/region_expansion_profitability_check_loopfusion_2.ll
The updated heuristic is accepting such case, and fusion is successful.

Please help take a look of my update, let me know what you think ? Thanks a lot!

https://github.com/llvm/llvm-project/pull/96548