ACA Unit 8 Hardware and Software for VLIW and EPIC Notes — Unit 8 – Download as PDF File .pdf), Text File .txt) or read online. G-2 Appendix G Hardware and Software for VLIW and EPIC. In this chapter we discuss compiler technology for increasing the amount of par- allelism that we. View Notes – from ENG at BGS Institute of Technology. | Website for.

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A hardware loop buffer is a program cache specialized to hold a loop body.

Notes for Advanced Computer Architecture – ACA by Tarini Mishra

Each instruction encodes one operation only. A similar problem occurs when the result of a parallelisable instruction is used as input for a branch.

Proceedings of the 10th annual international symposium on Computer architecture. Because VLIWs typically represent instructions scheduled in parallel with a longer instruction word that incorporates the individual instructions, this results in a much longer opcode termed very long to specify what executes on a given cycle.

Multiple Issue Processors: Superscalar and VLIW

The instruction set extensions reduce code size significantly, are binary compatible with older object code, and do not require the processor to switch ofr. He realized that to get good performance and target a wide-issue machine, it would be necessary to find parallelism beyond that generally within a basic block. The effect is that the NOP is issued in parallel with the instruction requiring the latency. Herrera y Reissig – CP Thus, this loop can be safely executed whenever vluw original trip count is at least two as opposed to three.


VLIW processors rely on the compiler to statically encode the ILP in the program before its execution, and because of this, code size hatdware larger relative to other processors. Trace scheduling is such a method, and involves scheduling the most likely path of basic blocks first, inserting compensating code to deal with speculative motions, scheduling the second most likely trace, and so on, until the schedule is complete.

Very long instruction word – Wikipedia

Fr Loop Buffer Fetch column shows the fetch of instructions from the MLB, and the Execute column shows the instructions that are actually executed. As fetch packets are read from program memory, the instruction dispatch logic extracts execute packets from the fetch packets. There are two limits in the implementation of the loop buffer: Archived from the original on Views Read Edit View history. In this case, the compressor may swap instructions within an execute packet to create a pair.

For example, because of their long latency, branch instructions are often followed by a multi-cycle NOP instruction.

Notes for Advanced Computer Architecture – ACA by Tarini Mishra

The goal is to minimize the degradation as much as possible. We proposed a loop buffer specialized to improve the performance of software-pipelined loops specifically in the following areas Example of a software-pipelined loop with all epilog stages collapsed.

Archived from the original PDF on For the following results, the baseline configuration is the Snd generation processor compiled with software-pipelined loop collapsing disabled and the speed-or-size option set to speed. Unlike software-pipelined loop collapsing, the MLB reduces code size without requiring softwage speculation. By necessity, the bit instructions have reduced functionality.


The p-bit bit 0 controls whether the next instruction executes in parallel. The pipelined version of the loop, with the fully collapsed epilog, is now safe for all trip counts greater than zero. Fisher’s second innovation was the vlis that the target CPU architecture should be designed to be a reasonable target for a compiler; that the compiler and the architecture for a VLIW processor must be codesigned.

Loop-oriented code with high degrees of ILP contains more padding NOP instructions, because execute packets tend to be larger in loop code, thus increasing the likelihood of spanning execute packets. He also developed region scheduling methods to identify parallelism beyond basic blocks.

Example of NOP padding fo prevent a spanning execute packet. It then selects the overlay that packs the most instructions in the new fetch packet. VLIW processors are well-suited for high performance embedded applications, which are characterized by mathematically oriented loop kernels and abundant ILP.

The compiler provides options to select the processor generation and to disable optimization passes that target specific processor features. To accommodate these operation fields, VLIW instructions are sodtware at least 64 bits wide, and far wider on some architectures. Code-size reduction and performance improvement on control code and other miscellaneous application benchmarks.