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Optimise join order for varBlockReaches

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This commit is contained in:
Chris Smowton
2021-01-26 14:00:06 +00:00
committed by Owen Mansel-Chan
parent 9068315f03
commit a3eb0100a6
1 changed files with 34 additions and 5 deletions
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39
go/ql/lib/semmle/go/dataflow/SsaImpl.qll
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@@ -306,6 +306,38 @@ private module Internal {
exists(getDefReachingEndOf(b, v))
}
/**
* Holds if `v` occurs in `b1` and `b2` is one of `b1`'s successors.
*
* Factored out of `varBlockReaches` to force join order compared to the larger
* set `blockPrecedesVar(v, b2)`.
*/
pragma[noinline]
private predicate varBlockReachesBaseCand(
SsaSourceVariable v, ReachableBasicBlock b1, ReachableBasicBlock b2
) {
varOccursInBlock(v, b1) and
b2 = b1.getASuccessor()
}
/**
* Holds if `b2` is a transitive successor of `b1` and `v` occurs in `b1` and
* in `b2` or one of its transitive successors but not in any block on the path
* between `b1` and `b2`. Unlike `varBlockReaches` this may include blocks `b2`
* where `v` is dead.
*
* Factored out of `varBlockReaches` to force join order compared to the larger
* set `blockPrecedesVar(v, b2)`.
*/
pragma[noinline]
private predicate varBlockReachesRecCand(
SsaSourceVariable v, ReachableBasicBlock b1, ReachableBasicBlock mid, ReachableBasicBlock b2
) {
varBlockReaches(v, b1, mid) and
not varOccursInBlock(v, mid) and
b2 = mid.getASuccessor()
}
/**
* Holds if `b2` is a transitive successor of `b1` and `v` occurs in `b1` and
* in `b2` or one of its transitive successors but not in any block on the path
@@ -314,14 +346,11 @@ private module Internal {
private predicate varBlockReaches(
SsaSourceVariable v, ReachableBasicBlock b1, ReachableBasicBlock b2
) {
varOccursInBlock(v, b1) and
b2 = b1.getASuccessor() and
varBlockReachesBaseCand(v, b1, b2) and
blockPrecedesVar(v, b2)
or
exists(ReachableBasicBlock mid |
varBlockReaches(v, b1, mid) and
b2 = mid.getASuccessor() and
not varOccursInBlock(v, mid) and
varBlockReachesRecCand(v, b1, mid, b2) and
blockPrecedesVar(v, b2)
)
}