The current peephole mechanism has several drawbacks:
- Can only match and remove adjacent instructions.
- Cannot match machine ideal nodes (e.g MachSpillCopyNode).
- Can only replace 1 instruction, the position of insertion is limited to the position at which the matched nodes reside.

The author proposes to enhance the peephole mechanism by allowing a peep rule to call into a dedicated function, which takes the responsibility to perform all required transformations on the basic block. This allows the peephole mechanism to perform several transformations effectively in a more fine-grain manner.