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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Therefore, to collapse stage 2, a predicate is placed on ins2 to guard against over-execution.
When the software-pipelined softwae enters the epilog the loop buffer disables the execution of instructions in the softwafe that they were inserted. The advantage of kernel-only code is that there is no code growth.
Unlike software-pipelined loop collapsing, the MLB reduces code size without requiring instruction speculation. The significant impact of the ELI project was the development of a hardware and compiler strategy at the same time.
This improves power efficiency by eliminating the fetch, decode, and execution of unused speculated instructions. For code size reduction, smaller is better, and for speed improvement, larger is better. The C62 provides a foundation of integer instructions.
Clearly, the MLB reduces code size and improves power efficiency by eliminating the overlapped copies of the instructions in the loop body.
As fetch packets are read from program memory, the instruction dispatch logic extracts execute packets from the fetch packets. Morgan Kaufmann Publishers Inc. Execution of a software-pipelined loop using the modulo loop buffer.
The register set bit bit 19 indicates which set of eight registers is used for three operand bit instructions. Other approaches to reduce the code size of software-pipelined loops employ special-purpose hardware.
Proceedings of the 25th Annual International Symposium on Microarchitecture. Only the kernel code is explicitly represented.
Therefore, the last p-bit in a fetch packet is always set toand each fetch packet starts a new execute packet. The C6X-2 processors increase the size of register file by providing an additional 32 static general-purpose registers.
Consistent with the VLIW processor philosophy, the utilization of the variable length instructions is directed by the compiler. These principles made it easier for compilers to emit fast code. The i’s VLIW mode was softwre extensively in embedded digital signal processor DSP applications since the application execution and datasets were simple, well ordered and predictable, allowing designers hardaare fully exploit the parallel execution advantages enabled by VLIW.
Forr remaining seven expansion bits bits are used to specify different variations of the bit instruction set. Kennedy, Optimizing Compilers for Modern Architectures. This is the source of most of the power reduction attributable to the MLB facility. This page was last edited on 17 Octoberat In superscalar designs, the number of execution units softwxre invisible to the instruction set. Therefore, the bit instructions occur in pairs in order to honor the bit instruction alignment.
A hardware loop buffer is a program cache specialized to hold a loop body. For example, if a VLIW wnd has five execution units, then a VLIW instruction for the device has five operation fields, each field specifying what operation should be done on that corresponding execution unit.
Code-size reduction and performance improvement on control code and other miscellaneous application benchmarks. For a bit instruction, the corresponding two p-bits in the header are not used set to 0. Therefore, the compiler implements a set of command-line options that allow users vliq control the aggressiveness of the tailoring optimizations.
The fully parallel fetch packet has one execute packet made up of eight instructions, which will execute in parallel. Average improvement factor of several parameters when using a modulo loop buffer. The operand [n] is a predicate that guards the branch.
The compressor has the responsibility vlw packing instructions into fetch packets. Softwaer Instr Fetch column shows the loop body instructions fetched from program memory and stored in the MLB. Many of these benchmarks andd complete applications. The DSP and multimedia codecs are loop-oriented applications, the control code is obviously control-oriented, and the other applications are a mixture both.
Thus, each loop iteration takes three cycles to complete. Consequently, before the loop the trip counter is incremented by one, so that the pipelined loop executes the same number of iterations produces the same number of results as the original loop. It consists of stages of II cycles each.
Each instruction in an execute packet fkr use a different functional unit. Because the C6X compiler often produces execute packets with multiple instructions, swapping instructions within an execute packet increases the conversion rate of potential bit instructions.
Torczon, Engineering a Compiler.
A similar problem occurs when the result of a parallelisable instruction is used as input for a branch. Reducing code size improves system performance hardwar allowing space for more code in on-chip memory and program caches. In this case however, ignoring loop control instructions, there are two instructions that do not execute during epilog stage 2: Having this dependency information encoded in the instruction stream allows wider implementations to issue multiple non-dependent VLIW instructions in parallel per cycle, while narrower implementations would issue a smaller number of VLIW instructions per cycle.
This is known as the modulo constraint and is the source of the term modulo scheduling.