ASF GitHub Bot commented on QUICKSTEP-59:

Github user cramja commented on the issue:

    +1 cool trick, and the comments were easy to follow!

> Improve performance of BitVector in Quickstep by eliminating branches
> ---------------------------------------------------------------------
>                 Key: QUICKSTEP-59
>                 URL: https://issues.apache.org/jira/browse/QUICKSTEP-59
>             Project: Apache Quickstep
>          Issue Type: Improvement
>          Components: Query Execution, Utility
>            Reporter: Saket Saurabh
>         Attachments: QUICKSTEP-59.01.patch
> The {{setBitRegularVersion()}} of {{BitVector.hpp}} is a critical function 
> that is called in various tight loop iterations over storage blocks 
> throughout the Quickstep code. This function has a simple purpose of setting 
> a bit value in a BitVector to true/false given a boolean argument. However, 
> it has an expensive if-else branch that can add a significant penalty at 
> runtime due to branch mis-predictions. 
> This short PR completely removes branching from the 
> {{setBitRegularVersion()}} by replacing the same functionality with a set of 
> bitwise arithmetic operations. Given that a branch mis-prediction costs about 
> 10 cycles, the branchless code is expected to save those precious 10 cycles 
> at the slight expense of 4 additional bitwise operations (an additional 2-4 
> cycles only, given hyper-threading).
> *Tests:*
> The existing unit tests should already cover the changes introduced by this 
> PR. Correctness also verified by comparing TPC-H query output results.

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