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Improve reachability sets computation #84204

Merged
merged 2 commits into from
Apr 1, 2023
Merged

Improve reachability sets computation #84204

merged 2 commits into from
Apr 1, 2023

Commits on Apr 1, 2023

  1. Improve reachability sets computation 

    Two changes to improve the throughput of computing `bbReach` sets:
1. In `fgComputeReachabilitySets()`, iterate over the blocks in reverse
post-order. This leads to fewer outer `do ... while(change)` iterations.
To do this, the `fgDfsReversePostorder()` function which creates the
reverse post-order numbers and ordering was hoisted out of dominator
creation and above reachability computation.
2. Create a `BlockSetOps::UnionDChanged()` function that does a `UnionD`
operation but also returns `true` if the target bitset changed value.

Some additional stats were added under `COUNT_BASIC_BLOCKS` regarding
how many iterations dominators and reachability computations take to
converge.
    @BruceForstall
    BruceForstall committed Apr 1, 2023
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  2. Code review feedback

    @BruceForstall
    BruceForstall committed Apr 1, 2023
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