[llvm] [InstCombine][ValueTracking] Improve logic for shift flags. (PR #67758)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Please squash your commits before landing the pull request.
```
gh pr merge --squash --delete-branch
```
Besides, you should attach `Close #67758` at the end of the commit message to let GitHub know the commit is linked with this PR. Then GitHub will close this PR automatically.

See also https://llvm.org/docs/GitHub.html#landing-your-change.


https://github.com/llvm/llvm-project/pull/67758