In this proposal, we bridge the gap between the high-level program knowledge and the speculation in multithreaded programming with the compiler's assistance. We propose a language extension to incorporate fast speculation into concurrent data structure design, and show how the language extension helps the speculation in newly emerged HTM processors. Besides, in order to improve the speculation in transaction memory systems under the circumstance with data high contention, two compiler optimization techniques are also proposed for STM and HTM, respectively.