7 Dec
2015
7 Dec
'15
3:05 p.m.
adrp Xn, dest add Xn, Xn, :lo12:dest blr Xn
I don't suppose the branch predictor would like that very much, though. Can't you keep the original arrangement, and use this sequence instead? Or use the new sequence unconditionally, but nop out the add instruction and change the blr for a straight bl if the target is in range?
No, the branch predictor is fine with it. The blr Xn always goes to the same address so it is predicted. The adrp/add pair are folded into a single micro op and then dual issued with the bl, so it take exactly the same time as a straight bl.
It depends, of course, on your implementation,
Regards, Ed.