computer architecture branch delay slot branch - best-online-slots efficient use of branch delay slots Navigating the Nuances of Computer Architecture: Understanding the Branch Delay Slot

coushatta-casino-resort In the intricate world of computer architecture, optimizing instruction execution is paramount作者：TR Gross·1982·被引用次数：137—Delayed branchesare commonly found in micro-architectures. A compiler or assembler can exploitdelayed branches. This is achieved by moving code from one  One fascinating, albeit historically significant, concept that addresses this is the branch delay slotFor longerbranch delays, hardware-basedbranchprediction is usually used. ○ Thedelayed branchalways executes the next sequential instruction, with the  This mechanism, particularly prevalent in RISC (Reduced Instruction Set Computing) and DSP (Digital Signal Processing) architectures, fundamentally alters how branch instructions are handled within a pipelined processorLecture 20 Pipelining Reference Appendix C, Hennessy & Essentially, a branch delay slot is an instruction slot being executed without the effects of a preceding instruction, creating a predictable one-cycle delay after a branch instruction• Compiler effectiveness for single branch delay slot –Fills about 60% of branch delay slots. – About 80% of instructions executed in branch delay slots.

The purpose of the branch delay slot is to mitigate performance penalties inherently associated with branches in pipelined systemsWhere to get instructions to fillbranch delay slot? – Before branch instruction. – From the target address only valuable when branch taken. – From fall  When a branch instruction is encountered, the pipeline typically needs to stall until the outcome of the branch (whether it's taken or not) is determined and the correct instruction fetch address is knownLecture 3 This stall represents wasted processing cyclesIn (b), thebranch delay slotis scheduled from the target of the branch; usually the target instruction will need to be copied because it can be reached by  The branch delay slot introduces an instruction that is *always* executed in the cycle immediately following the branch instruction, regardless of whether the branch is ultimately taken or notThe instruction after the branch is said to be in thebranch delay slot. ▫ For between 60% and 85% of branches, compilers find an instruction for the branch  This means that a single cycle delay that comes after a conditional branch instruction has begun execution is filled, preventing a full pipeline stall• Compiler effectiveness for single branch delay slot –Fills about 60% of branch delay slots. – About 80% of instructions executed in branch delay slots.

Scheduling branch delay slots is a critical task for compilers and assemblersComputer Architecture TDTS10 Their effectiveness directly impacts processor performanceIn computer architecture, a delay slot isan instruction slot being executed without the effects of a preceding instruction. The most common form is a single arbitrary instruction located immediately after a branch instruction on a RISC or DSP architecture; this instruction will execute even if the preceding branch  The goal is to find an instruction that can be safely moved into the branch delay slot without altering the program's intended logicComputer Architecture TDTS10 According to research and common observations in computer architecture education, compilers typically manage to fill about 60% of branch delay slotsFor longerbranch delays, hardware-basedbranchprediction is usually used. ○ Thedelayed branchalways executes the next sequential instruction, with the  This implies that for approximately 60% to 85% of branches, compilers can discover a useful instruction to place in the delay slotThis paper describes the generaliseddelayed branchmechanism that we have developed for the HSAarchitecture, including a recent simplification of our  When a suitable instruction *can* be found, it's often referred to as a delayed branchIn (b), thebranch delay slotis scheduled from the target of the branch; usually the target instruction will need to be copied because it can be reached by 

Where do these instructions for the branch delay slot originate? There are a few primary sources:

* Instructions that appear *before* the branch instruction in the original code sequence(10 pts)Scheduling branch delay slots(see Figure A.14) can improve performance. Assume a single branch delay slot and an instruction execution pipeline that 

* Instructions from the *target address* of the branch(PDF) Delayed branches versus dynamic branch prediction This is particularly valuable if the branch is likely to be taken, as it avoids fetching a new instruction from the fall-through pathIn DLX 5-stage pipeline,one delay slot is enough to avoid branch delay. • In more aggressively pipelined machine (eg. MIPS R4000) more delay slots would be.

* Instructions from the *fall-through path* (the instruction immediately following the branch)In DLX 5-stage pipeline,one delay slot is enough to avoid branch delay. • In more aggressively pipelined machine (eg. MIPS R4000) more delay slots would be.

The effectiveness of this strategy is evident in architectures like DLX, where one delay slot is enough to avoid branch delayUS9535701B2 - Efficient use of branch delay slots and However, in more aggressively pipelined machines, such as the MIPS R4000 architecture, more delay slots might be employed to maintain performanceWhat is a delayed branch in a pipeline? The MIPS R4000 processor, for instance, explicitly addresses the behavior of branches within branch delay slots, stating that the result of putting a branch in a branch delay slot is unpredictableFor longerbranch delays, hardware-basedbranchprediction is usually used. ○ Thedelayed branchalways executes the next sequential instruction, with the  This highlights the careful management required for efficient use of branch delay slotsCSE 4201 Computer Architecture Outline

While the concept of delayed branches was a significant innovation, modern computer architecture has largely moved towards more sophisticated branch prediction techniques to handle branch delaysHaving Fun with Branch Delay Slots For longer branch delays, hardware-based branch prediction is generally preferred(10 pts)Scheduling branch delay slots(see Figure A.14) can improve performance. Assume a single branch delay slot and an instruction execution pipeline that  Nevertheless, understanding the branch delay slot and branch with exposed delay slots provides valuable insight into the historical evolution of pipelined processing and the ongoing quest for performance optimization in computer architectureThe one-cyclebranch delay slotmean that one needs to add an extra cycle in addition to thebranchlatency. The complexities surrounding the branch delay slot, including its implementation and the compiler's role in scheduling branch delay slots, offer a rich area of study for anyone interested in the foundational principles of how computers execute instructionsBranch delay slot