[llvm] [LSR] Provide TTI hook to enable dropping solutions deemed to be unprofitable (PR #89924)

[Philip Reames via llvm-commits]

preames wrote:

LGTM - but note that if the following RISCV patch ends up not landing, you should probably revert this to avoid complexity in tree with no purpose.  

https://github.com/llvm/llvm-project/pull/89924