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+title = "Speculation does not have a cost"
+date = "2022-04-29"
+author = "Yann Herklotz"
+tags = []
+categories = []
+backlinks = ["1c6d"]
+forwardlinks = []
+zettelid = "1c6e"
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+
+It is interesting to note that speculating on an instruction does not
+really incur a cost in itself. The idea is that if one is always wrong
+with the speculation, one really only reverts back to the non-pipelined
+instructions. So in the worst case one is only sequential. However, if
+one speculates, then it is highly unlikely that one is always wrong, and
+one will therefore always benefit from it.
+
+Therefore, in the speculative loop pipelining, it does not really matter
+in the end which instructions are picked to speculate on, and often the
+most efficient will be the shortest path in the pipeline. For example,
+Steven showed that even when one speculates on a binary search algorithm
+to two iterations (where one then has a 25% chance of being right), one
+still benefits from speculating going into one of the directions.