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C++: Fix join order in def-by-reference data flow #1070

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Merged
geoffw0 merged 1 commit into from
Mar 12, 2019
Merged

C++: Fix join order in def-by-reference data flow #1070

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15 changes: 7 additions & 8 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 @@ -237,15 +237,8 @@ module FlowVar_internal {

override VariableAccess getAnAccess() {
exists(SubBasicBlock reached |
reached = getAReachedBlockVarSBB(this)
|
reached = getAReachedBlockVarSBB(this) and
variableAccessInSBB(v, reached, result)
or
// Allow flow into a `VariableAccess` that is used as definition by
// reference. This flow is blocked by `getAReachedBlockVarSBB` because
// flow should not propagate past that.
result = reached.getASuccessor().(VariableAccess) and
blockVarDefinedByReference(result, v, _)
)
}

Expand Down Expand Up @@ -420,6 +413,12 @@ module FlowVar_internal {
va.getTarget() = v and
va = sbb.getANode() and
not overwrite(va, _)
or
// Allow flow into a `VariableAccess` that is used as definition by
// reference. This flow is blocked by `getAReachedBlockVarSBB` because
// flow should not propagate past that.
va = sbb.getASuccessor().(VariableAccess) and
blockVarDefinedByReference(va, v, _)
}

/**
Expand Down