[llvm] [InlineCost] Disable cost-benefit when sample based PGO is used (PR #86626)

[Xiangyang Guo via llvm-commits]

helloguo wrote:

> Is it because sample PGO profile quality is worse than that of instrumentation profile or any other reasons?

The profile quality could be one of reasons. In addition, cost-benefit subtracts ColdSize based on the assumption that machine function splitting could handle the cold code later. MFS may need fine tuning for sample based pgo.  

> but it will also limit sample PGO to expose more optimization opportunities

Users can always manually turn on the cost-benefit analysis with flags. I guess the discussion here is more about if we want to turn on cost-benefit by default. Changing the default probably requires more data to support the decision. 

https://github.com/llvm/llvm-project/pull/86626