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Browse Prior Art Database

Compare Branch Strategy to Reduce Unresolved-Branch Penalties

IP.com Disclosure Number: IPCOM000121490D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Barreh, JI: AUTHOR [+4]

Abstract

Disclosed is a strategy to reduce the number of idle cycles associated with unresolved branches.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Compare Branch Strategy to Reduce Unresolved-Branch Penalties

      Disclosed is a strategy to reduce the number of idle
cycles associated with unresolved branches.

      For the discussion of the compare-branch strategy, one may
assume the existence of a machine composed of three parallel
processing units.  These units could, in general, be arbitrary; but
for the discussion at hand, one can assume that they are the
following:  a fixed- point unit (fxu), a floating-point unit (fpu)
and a branch-processing unit (bpu).  In a traditional architecture,
unresolved branches may require the bpu to wait until either the fxu
or the fpu unit completes the instruction the branch is dependent on.
The compare-branch strategy seeks to eliminate these idle cycles by
providing both the sequential and target streams to the fxu and fpu
units directly.  The strategy further allows the fxu and the fpu to
decide the outcome of the unresolved branch directly.  In this
manner, the fxu and fpu units are able to resolve the branch directly
and continue executing instructions from the proper stream of
instructions without delay.

      Upon reaching an unresolved branch, the bpu issues a branch
packet to the fxu and fpu units.  This packet contains information
concerning which bit in the condition register the branch is waiting
on and the logical value required to branch.  Once either the fxu or
fpu identifies a condition register result matching the branch
packet, the respective unit decides the outcome of the branch
immedi...