C++: Speed up primitive basic block calculation #285
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The existing implementation of `primitive_basic_block_entry_node` was "cleverly" computing two properties about `node` with a single `strictcount`: whether `node` had multiple predecessors and whether any of those predecessors had more than once successor. This was fast enough on most snapshots, but on the snapshot of our own code it took 37 seconds to compute `primitive_basic_block_entry_node` and its auxiliary predicates. This is likely to have affected other large snapshots too. With this change, the property is computed like in our other languages, and it brings the run time down to 4 seconds.
This predicate looked like a join of two already-computed predicates, but it was a bit more complicated because the `*` operator expands into two cases: the reflexive case and the transitive case. The join order for the transitive case placed the `PrimitiveBasicBlock` charpred call _after_ the `member_step+` call, which means that all the tuples of `member_step+` passed through the pipeline. This commit changes the implementation by fully writing out the expansion of `*` into two cases, where the base case is manually specialised to make sure the join orderer doesn't get tempted into reusing the same strategy for both cases. This speeds up the predicate from 2m38s to 1s on a snapshot of our own C/C++ code.
geoffw0
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Oct 6, 2018
smowton
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Apr 16, 2022
Switch to expanding property initializers and init blocks in-place
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This is an attempt to fix the timeouts we've seen in Dashboards/Internal in the last few days. I'm aiming this at 1.18.1 because the second commit fixes a regression introduced in #123 that might affect customers -- see the discussion in CPP-279.
The first commit is not a regression fix but should be Nice To Have. I've tested it for correctness by comparing the output of
select strictcount(PrimitiveBasicBlock b)before and after. The implementation is ported from the Java basic-blocks library.