The paper demonstrates how an Instruction Path Coprocessor (I-COP) can be efficiently implemented using the PipeRench reconfigurable architecture. An I-COP is a programmable on-chip coprocessor that operates on the core processor's instructions to transform them into a new format that can be more efficiently executed. The I-COP can be used to implement many sophisticated hardware code modification techniques. We show how four specific techniques can be mapped to the PipeRench pipelined computation model. The experimental results show that a PipeRench I-COP used to perform trace construction and trace optimizations for a trace cache fill unit not only achieves good performance gains but can potentially be implemented in less than 10 mm/sup 2/ (assuming 0.18 micron technology) or approximately 3% of the die area of a current high-end microprocessor. We believe these results demonstrate the usefulness and feasibility of the I-COP concept.

This paper presents the concept of dynamic control independence (DCl) and shows how it can be detected and exploited in an out-of-order superscalar processor to reduce the performance penalties of branch mispredictions.We show how DCI can be leveraged during branch misprediction recovery to reduce the number of instructions squashed on a misprediction as well as how it can be used to avoid predicting unpredictable branches by fetching instructions out-of-order A realistic implementation is described and evaluated using six SPECint95 benchmarks.We show that exploiting DCI during branch misprediction recovety improves pe$ormance by 0.9-9.9% on a I-wide processol; by I&11.2% on an b-wide processor and by 1.9-15.3%on a 12-wideprocessol: We also show that using DCI information to fetch instructions out-of-order when an unpredictable branch is encountered potentially improves performance by 0.9-15.2% on a I-wide processol: by 2.0-14.8% on an 8-wide processor and by 2.6-16.2% on a 12wide processor: Some of the largest performance gains are observed on go and gee, which have traditionally posed the most d@cult challenge to aggressive branch prediction techniques.h-mission LO make digital or hard copies ol'all or par1 of this work for personal or classroom use is granrcd without fee provided that topics are not made or distributed for profit or commercial advantage and that copies bear this notice and lhe full citation on the tirst page.To copy otherwise, to republish, IO post on servers or to redistribute lo lisls.requires prior specific permission and/or a fee.ICS ")') Rhodes Greccc