reducing the cost of conditional transfers of control by using comparison specifications
A significant portion of a program's execution cycles are typically dedicated to performing conditional transfers of control. Much of the research on reducing the costs of these operations has focused on the branch, while the comparison has been largely ignored. In this paper we investigate reducing the cost of comparisons in conditional transfers of control. We decouple the specification of the values to be compared from the actual comparison itself, which now occurs as part of the branch instruction. The specification of the register or immediate values involved in the comparison is accomplished via a new instruction called a comparison specification , which is loop invariant. Decoupling the specification of the comparison from the actual comparison performed before the branch reduces the number of instructions in the loop, which provides performance benefits not possible when using conventional comparison instructions. Results from applying this technique on the ARM processor show that both the number of instructions executed and execution cycles are reduced.
comparison branch optimization compiler