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C++: Performance fix for FlowVar.getAnAccess #403

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Merged
geoffw0 merged 1 commit into from
Nov 5, 2018
Merged

C++: Performance fix for FlowVar.getAnAccess #403

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13 changes: 10 additions & 3 deletions cpp/ql/src/semmle/code/cpp/dataflow/internal/FlowVar.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -221,9 +221,7 @@ module FlowVar_internal {
BlockVar() { this = TBlockVar(sbb, v) }

override VariableAccess getAnAccess() {
result.getTarget() = v and
result = getAReachedBlockVarSBB(this).getANode() and
not overwrite(result, _)
variableAccessInSBB(v, getAReachedBlockVarSBB(this), result)
}

override predicate definedByInitialValue(LocalScopeVariable lsv) {
Expand Down Expand Up @@ -373,6 +371,15 @@ module FlowVar_internal {
)
}

/** Holds if `va` is a read access to `v` in `sbb`, where `v` is modeled by `BlockVar`. */
pragma[noinline]
private predicate variableAccessInSBB(Variable v, SubBasicBlock sbb, VariableAccess va) {
exists(TBlockVar(_, v)) and
va.getTarget() = v and
va = sbb.getANode() and
not overwrite(va, _)
}

/**
* A local variable that is uninitialized immediately after its declaration.
*/
Expand Down