Exploiting dead value information

  • Authors:

  • Milo M. Martin;Amir Roth;Charles N. Fischer

  • Affiliations:

  • Computer Sciences Department, University of Wisconsin, Madison, WI;Computer Sciences Department, University of Wisconsin, Madison, WI;Computer Sciences Department, University of Wisconsin, Madison, WI

  • Venue:
  • MICRO 30 Proceedings of the 30th annual ACM/IEEE international symposium on Microarchitecture
  • Year:
  • 1997

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Abstract

We describe Dead Value Information (DVI) and introduce three new optimizations which exploit it. DVI provides assertions that certain register values are dead, meaning they will not be read before being overwritten. The processor can use DVI to track dead registers and dynamically eliminate unnecessary save and restore instructions from the execution stream at procedure calls and context switches. Our results indicate that dynamic saves and restore instances can be reduced by 46% for procedure calls and by 51% for context switches. In addition, save/restore elimination for procedure calls can improve overall performance by up to 5%. DVI also allows the processor manage physical registers to efficiently, reducing the size requirements of the physical register file. When the system clock rate is proportional to the register file cycle time, this optimization can improve performance. All of these optimizations can be supported with only a few new instructions and minimal additional hardware structures.