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Branch predictor



Branch predictor - Wikipedia, the free encyclopedia

In computer architecture, a branch predictor is the part of a processor that determines whether a conditional branch in the instruction flow of a program is likely to be taken or not.
Branch target prediction attempts to guess the target of the branch or unconditional jump before it is computed from parsing the instruction itself.
Static prediction is used as a fall-back technique (when there isn't any information for dynamic predictors to use) in most processors with dynamic branch prediction.

http://en.wikipedia.org/wiki/Branch_predictor (2205 words)



December 94 - Balance of Power: PowerPC Branch Prediction

The branch is handled early, and the new instructions are fetched from the cache immediately.
Prediction of guessed branches are based on two things: the direction of the branch and a software "hint" bit.
Typically about one-seventh of the instructions in your code are branches, either to call subroutines or to make logical decisions in your program.

http://developer.apple.com/dev/techsupport/develop.mactech/issue_20/20balance.html (1767 words)



Evaluation of branch-prediction methods on traces from commercial applications

Instructions which in fact are not even branches may be predicted as branching instructions because of mapping to a BTB entry from the previous task.
Dynamic branches are all branches which occur as a result of running the program and thus are found in the trace.
A static branch may have many occurrences as a dynamic branch; e.g., when the program performs a loop, the static branch at the end of the loop will occur as many times dynamically as the loop does.

http://www.research.ibm.com/journal/rd/434/hilgendorf.html (7186 words)



Untitled Document

In other computers however, if the address of the branch target was computed earlier in the pipeline, then there would be some gain in using the predict-taken strategy.
If after the branch is finished executing, it is found that we really wanted to take the branch, then the (possible) next instruction that we had been executing is thrown out by the hardware, and we being executing the correct instruction, the branch target.
When a RISC machine encounters a branch instruction, there are only two possible outcomes, either the branch is taken, or the branch is not taken.

http://www.cs.umd.edu/class/fall2001/cmsc411/projects/branches/prediction.html (970 words)



Branch prediction in the Pentium family

A branch instruction is the implementation of an if-then-else construct.
Apparently, somebody at the design labs has done a lot of research to find a good branch prediction scheme, and then somebody else has messed it all up by letting state 0 mean vacant BTB entry without realizing the consequence.
However, since mispredictions are expensive in terms of execution time, I found it important to know how the prediction works in order to optimize my programs.

http://x86.ddj.com/articles/branch/branchprediction.htm (1921 words)



CBP_CFP

The goal of the Championship Branch Prediction competition is to evaluate and compare branch prediction algorithms in a common framework.
Contestants will be given a fixed storage budget to implement their best branch prediction algorithms on a common evaluation framework distributed by the CBP steering committee.
of the prediction algorithm including references to published work directly relevant to the implemented algorithm.

http://www.jilp.org/cbp (522 words)



[No title]

Branch history, whose length is usually fixed in most branch prediction schemes, is employed by branch predictors to represent the interdependence between branch instructions which are executed consecutively.
Their idea is to allow each branch instruction to have its own path length, which is computed either statically by compilers or dynamically by hardware through profiling.
For this reason, the first task to be done is to implement an existing branch predictor and a framework of the same predictor with per-branch history length fitting.

http://www.cs.cmu.edu/~gla/740/proposal.html (1015 words)



Branch prediction (EP0381444B1)

If the cache includes associated information predicting that the branch will be taken, the target address from cache is used so long as the associated length and displacement match the length and displacement for the branch instruction; otherwise, the target address must be computed.
A branch prediction is made by searching a cache memory (79) for branch history information associated with a branch instruction.
If associated information is not found in the cache, then the branch is predicted based on a predetermined branch bias for the branch instruction's opcode; otherwise, the branch is predicted based upon the associated information from the cache.

http://www.delphion.com/details?pn=EP00381444B1 (380 words)



Branch Prediction Schemes

In a cancelling branch the instruction includes the direction that the branch was predicted.
In a delayed branch, the execution cycle with a branch delay of length n is
As soon as the branch is decoded and the target address is computed, we assume the branch to be taken and

http://www.cs.iastate.edu/~prabhu/Tutorial/PIPELINE/branchPred.html (665 words)



Dynamic Branch Prediction

The latency of resolving a branch does not decrease, so the CPI is more significantly affected than it is for a single-issue machine.
In this way, the branch "disappears" since it is replaced with the instruction given by its target address.
Since the branch decision and target PC are computed in ID, assuming there is no hazard on the register tested.

http://www.cs.umbc.edu/~plusquel/611/slides/chap4_5.html (960 words)



branch prediction Computer Encyclopedia Enterprise Resource Directory Complete Guide to Internet

This information is used to predict which way the instruction will branch the next time it is executed so that instruction prefetch can continue.
When a branch instruction is executed, its address and that of the next instruction executed (the chosen destination of the branch) are stored in the {Branch Target Buffer}.
branch prediction Computer Encyclopedia Enterprise Resource Directory Complete Guide to Internet

http://jaysir.com/computer-encyclopedia/b/branch-prediction-computer-terms.htm (151 words)



Static Methods in Hybrid Branch Prediction

All the results we present are based on a cross-validation methodology, in which the profile data used for static selection are based on training inputs that are entirely different from the inputs used to evaluate the performance of the technique.
We show that the combination function is better performed statically, using prediction hints in the branch instructions.
An important advantage of our approach is that a branch site only causes interference within a single component predictor, reducing capacity demands.

http://systems.cs.colorado.edu/Papers/Architecture/PACT98-StaticHybrid (219 words)



Programmable branch prediction system and method for inserting prediction operation which is independent of execution ...

Branch prediction mechanism in which a branch history table is updated using an operand sensitive branch table
A system for predicting branches in a computer system, comprising:
Andreas Krall, "Improving Semi-static Branch Prediction by Code Replication," Association for Computing Machinery, vol.

http://www.delphion.com/details?&pn=US05949995__ (688 words)



Senior Thesis: Juang, "Classification-based Hybrid Branch Prediction"

Current branch predictors invest quite a bit of logic in sophisticated, general purpose constructs designed to handle all branches in the instruction stream.
Conditional branches disrupt the normal control flow of a program by introducing irregularities; instead of a natural, steady progression, conditional branches order the processor to "jump" to different places in the instruction stream.
One of the largest limiting factors in microprocessor instruction execution throughput is the existence of conditional branches in the instruction stream.

http://www.cs.virginia.edu/~skadron/Papers/juang_thesis.abstract.html (383 words)



Analysis of Branch Prediction Strategies and Branch Target Buffer Design

Branches which change the expected order of instruction execution require that the pipeline be reloaded, resulting in several lost machine cycles per such branch.
For further information concerning use of UC Berkeley documents for other than research or instructional purposes, contact the Computer Science Division at the University of California at Berkeley, tr-cs@cs.berkeley.edu.
We also consider issues relating to the implementation of real branch target buffers.

http://sunsite.berkeley.edu/TechRepPages/CSD-83-121 (354 words)



Dynamic Branch Prediction with Perceptrons - Jimenez, Lin (ResearchIndex)

The key idea is to use one of the simplest possible neural networks, the perceptron, as an alternative to the commonly used two-bit counters.
For example, the locality in Figure 2 can be expressed as (ignoring the non value producing stores and branches) 1 = N N x x, and...
30 Evidencebased static branch prediction using machine learnin..

http://citeseer.ist.psu.edu/379813.html (653 words)



Branch Prediction Research in the LAVA Lab (including hybrid predictors, speculative update, return address stack, and ...

Improving branch prediction, although already a well-studied subject, remains critical because delivering very high branch-prediction rates is crucial to further performance gains in high-performance computing.
We are also looking for new benchmarks that exhibit interesting branch-prediction behavior, especially programs with poor predictability and/or a large branch footprint.
"Branch Prediction, Instruction-Window Size, and Cache Size: Performance Tradeoffs and Simulation Techniques." IEEE Transactions on Computers, 48(11):1260-81, Nov. 1999.

http://lava.cs.virginia.edu/bpred.html (819 words)



The PC Guide Discussion Forums - Pentium Branch Prediction

To increase performance CPUs have branch prediction that enables them to "guess" what the result of a conditional branch statement will be and fetch the data or run the code that's after the branch before the branch returns a result.
A branch is alot like an "If..then..else statment" (a conditional branch) or a "goto" statement (a unconditional branch)
03-01-2002 08:46 PM Most programs are made of branches.

http://www.pcguide.com/vb/printthread.php?t=6504 (284 words)



Branch Prediction

Dynamic Branch Prediction uses Yeh’s Prediction Algorithm, which recognize behavior patterns such as taken and not taken.
At the Instruction Fetch pipeline stage, the address of any conditional branch instruction is submitted to the BTB for lookup.
Static branch unlike Dynamic uses the static branch predictor.

http://carbon.cudenver.edu/~jcha/5593pres/tsld018.htm (108 words)



Pattern History Table based Branch Prediction Techniques

In this technique, the prediction information are kept on the pattern history table which is consist of 2-bit saturated up-down counters.
Second, for taken branches, the instruction from the target must be available for execution with minimal delay.
For example, Branch address scheme works well when each branch is strongly biased in a particular direction.

http://www.umiacs.umd.edu/~hismail/818K/node2.html (263 words)



Control-Flow Speculation through Value Prediction

In this paper, we introduce a new branch predictor that predicts the outcome of branches by predicting the value of their inputs and performing an early computation of their results according to the predicted values.
This selector is based on the path followed to reach the branch.
Evers, P.-Y. Chang, and Y.N. Patt, "Using Hybrid Branch Predictors to Improve Branch Prediction Accuracy in the Presence of Context Switches," Proc.

http://csdl2.computer.org/persagen/DLAbsToc.jsp?resourcePath=/dl/trans/tc/&toc=comp/trans/tc/2001/12/tztoc.xml&DOI=10.1109/TC.2001.970574 (690 words)



Comp.compilers: Re: Branch prediction hints in an ISA

Re: Branch prediction hints in an ISA david.thompson1@worldnet.att.net (David Thompson) (2000-10-18)
Re: Branch prediction hints in an ISA dietrich@216.26.55.26 (Dietrich Epp) (2000-10-19)
Branch prediction hints in an ISA timgleason@my-deja.com (2000-10-10)

http://compilers.iecc.com/comparch/article/00-10-133 (313 words)



NRL 7320: Ocean Dynamics and Prediction Branch

NRL's Ocean Dynamics and Prediction Branch (NRL 7320) performs basic and applied research in computer modeling of ocean hydro/thermodynamics (i.e., ocean circulation and density structure), modeling of ice dynamics, computational numerical techniques, data assimilation, and the analysis of satellite oceanographic data as related to the development of modeling and data assimilation capabilities.
This branch translates the results of basic and applied research into accurate, scientifically valid, environmentel models and analyses and streamlines these models into operational, data assimilative, nowcast/forecast systems.
Research in computational techniques includes the study of efficient solution to partial differential equations arising in oceanography with a special focus on efficient utilitization of massively parallel processing technology.

http://www7320.nrlssc.navy.mil/html/7320-home.html (314 words)



Static Methods in Branch Prediction

The prediction combining hardware --- the selection mechanism --- has costs that I eliminate by controlling selection from software, in what I call a static hybrid predictor.
An important advantage of static selection is that each branch site is assigned to a single component predictor.
This class can be efficiently implemented by Programmed Logic Arrays and are trained by growing decision trees over sets of branch history patterns.

http://systems.cs.colorado.edu/Papers/Thesis/Thesis-lindsay (326 words)



Branch Prediction For Free - Ball, Larus (ResearchIndex)

In addition to using natural loop analysis to predict branches that control the...
In Proceedings of the SIGPLAN '93 Conference on Programming Language Design and Implementation (PLDI), pages 300--313, June 1993.
0.1: Source Level Static Branch Prediction - Wong (1999)

http://citeseer.ist.psu.edu/ball93branch.html (517 words)



Geneseo CSci 380 Branch Prediction

(buffer = table with one entry per branch instruction, entries record what this branch did last time, predict branch will do the same this time)
load i31, #1000 cycles 101 - X (instruction aborted when branch turns out to be taken)

http://www.cs.geneseo.edu/~baldwin/csci380/fall2003/bpred1022.html (126 words)



NASA - Life Prediction Branch

With organizational experience in delivering products for high-visibility aerospace industry projects, the Life Prediction Branch is well positioned to meet the challenges to develop and demonstrate revolutionary aerospace propulsion and power systems that encounter severe, long-term environmental and operating conditions.
Please browse through our website to learn more about our current research and technology development efforts in each of the three core research diciplines below or contact us for additional information on any of our technologies.
We pioneer interdisciplinary approaches to enable the best utilization of advanced materials through innovative structural concepts and integrated design methodologies.

http://www.grc.nasa.gov/WWW/LPB (216 words)



NOAA/OAR/ESRL/FRB/LAPS

The Local Analysis and Prediction Section performs high resolution analyses and forecasts of the weather using both locally and centrally available meteorological observations.
Local implementations include our branch machine (toro) and the AWIPS/ WFO-Advanced workstation.
The prediction component is being configured using the RAMS, MM5, WRF, and ETA models.

http://laps.fsl.noaa.gov (498 words)



Comp.compilers: Re: Branch prediction

The branch prediction problem can be viewed as a general problem,
not per se related to a static prediction, encoded or
Grok it or not, prediction has barriers, they are regretaly

http://compilers.iecc.com/comparch/article/00-06-072 (294 words)



Branch Predictor Prediction: A Power-Aware Branch Predictor for High-Performance Processors

We show that on the average and for an 8-way processor, BPP can reduce branch prediction power dissipation by 28% and 14% compared to non-banked and banked 32k predictors respectively.
Later we refer to this buffer to decide if any of the sub-predictors and the selector could be gated without harming performance.
We introduce Branch Predictor Prediction (BPP) as a power-aware branch prediction technique for high performance processors.

http://csdl2.computer.org/persagen/DLAbsToc.jsp?resourcePath=/dl/proceedings/&toc=comp/proceedings/iccd/2002/1700/00/1700toc.xml&DOI=10.1109/ICCD.2002.1106813 (263 words)



[No title]

Indirection predictionó¨Some Approaches¨'Netrual Approach Data Compression PPM ¡:#ª!ó¨ Conclusion¨êBranch prediction techniques have a dramatically important effect on the computer performance.

http://www.cs.uakron.edu/~dang/CS665/Fall03/BranchSurvey.ppt (846 words)



[No title]

What is the improvement of storing target instructions over storing targetPCs?
What is the penalty in clock cycles when an unconditional branch is found in the buffer?ó—¨Example 2(cont)¨`90% hit rate b.

http://www.csc.calpoly.edu/~franklin/520/Fall03/Lec11BranchPred.ppt (140 words)



Branch Prediction

Try to guess ahead of time which way a branch instruction will go.
If this were the case, then these two instructions would take only 5 cycles.
It is possible to get 90% of the guesses correct using branch prediction.

http://www.cs.fiu.edu/~downeyt/cop3402/prediction.html (346 words)



Integration Corp.

Early Branch Prediction circuit for application in DSP

http://www.integration-corp.com/publication2.html (598 words)



[No title]

10-bit history allows patterns 10 branches to be discovered and predicted.
Next level Selected entry from the local history table is used to index a table of 1K entries consisting a 3-bit saturating counters, which provide the local prediction Total size: 4K*2 + 4K*2 + 1K*10 + 1K*3 = 29K bits!

http://ece-www.colorado.edu/~ecen5593/notes/bp_stats.ppt (262 words)



[No title]

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http://www.cs.unc.edu/~montek/teaching/fall-02/lectures/lecture-12.ppt (398 words)



[No title]

0²P ð8¨NT¡ðá2 ð1P ãðT é ¿Ììÿ¿ÀËoÿ?¿ÿð°´à ðU¨State 0 Predict Not Taken¡ðá2 ð2P ãðTé ¿Ììÿ¿ÀËoÿ?¿ÿðT °à ðU¨State 1 Predict Not Taken¡ð¹ðN ðÐÀP ð3Pððð ´pðB ð4P óðZ¿D¿ÀËÔ”Ðÿ?¿ÿðÐÀÐðÉ¢ ð5P óðZt é ¿¿ÀË1ÿ?¿ÿð´0P ð7¨T¡ðlðN ð¯Â ôr ð6Pðð¯Â ôr ð
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http://www.cs.unc.edu/~montek/teaching/fall-03/lectures/lecture-12.ppt (417 words)

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