Summary:
* Investigate conditional compare.

Details:
1. Expand conditional compare as TRUTH_AND_EXPR/TRUTH_IOR_EXPR for tests.
2. Test tree-level changes for conditional compare.
  * Fix/workaround most ICE issues in regression tests.
  * Still some fails which expected VRP can optimize the cases.
3. Try to build Coremark and find that conditional compare does block optimizations, which leads to worse performance.

Plan:
* Investigate VRP and other optimizations to handle conditional compare.
* Raise the propose for upstream discussion.

Planned leaves:
* April 4-8: Chinese Ching Ming Festival and annual leaves.
* April 12: Internal team event.
* April 16-17: Internal training.

Best Regards!
-Zhenqiang