Case block table for predicting the outcome of blocks of conditi

Details Case block table for predicting the outcome of blocks of conditi Case block table for predicting the outcome of blocks of conditi

1991-10-29

1994-07-26

Lall, Parshotam S.

Boots, shoes, and leggings

395700, 364DIG1, 3642613, 3642631, 364938, G06F 938, G06F 9345

Patent

active

053332830

ABSTRACT:
A method and apparatus is disclosed for folding the execution of a multi-way branch or switch based upon an operand (e.g.,the block of instructions normally associated with a case statement) into a single instruction. This insulates branch prediction mechanisms from making incorrect predictions that are normally associated with a multi-way branch. A table saves the past history of multi-way branch execution. This table contains three fields: the starting address of a multi-way branch; a value of the operand used to execute that multi-way branch in the past; and the larger target address generated by that multi-way branch in the past when that particular operand value was used. In accordance with one embodiment of this invention, other branch prediction mechanisms (such as a Branch History Table or Decode History Table) are disabled from redirecting instruction fetching during execution of a multi-way branch in an instruction stream.

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