Sentence:  However, <WSD>aggressive</WSD> compiler techniques such as loop unrolling, promoting of subscripted array variables into registers (especially in of subscripted array variables into registers (especially in loops) and interprocedural optimizations create heavy register pressure and it is still quite important to do a good job of register allocation. 
Meaning of the word marked with <WSD> tags:  Of heuristics, source code optimization techniques, etc.: exploiting every opportunity to be applied.