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C++: Fix two join orders in FlowVar.qll #4146

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jbj merged 3 commits into from
Sep 2, 2020
Merged

C++: Fix two join orders in FlowVar.qll #4146

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2b720b3
C++: Fix join order in reachesWithoutAssignment
jbj Aug 27, 2020
f3e98c3
C++: Fix join order of FlowVar::definedPartiallyAt
jbj Aug 27, 2020
e949c16
C++: Add back `getSubBasicBlockStart`
jbj Aug 27, 2020
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33 changes: 24 additions & 9 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 @@ -120,15 +120,25 @@ private module PartialDefinitions {
)
}

predicate partiallyDefines(Variable v) { innerDefinedExpr = v.getAnAccess() }
deprecated predicate partiallyDefines(Variable v) { innerDefinedExpr = v.getAnAccess() }

predicate partiallyDefinesThis(ThisExpr e) { innerDefinedExpr = e }
deprecated predicate partiallyDefinesThis(ThisExpr e) { innerDefinedExpr = e }

/**
* Gets the subBasicBlock where this `PartialDefinition` is defined.
*/
ControlFlowNode getSubBasicBlockStart() { result = node }

/**
* Holds if this `PartialDefinition` defines variable `v` at control-flow
* node `cfn`.
*/
pragma[noinline]
predicate partiallyDefinesVariableAt(Variable v, ControlFlowNode cfn) {
innerDefinedExpr = v.getAnAccess() and
cfn = node
}

/**
* Holds if this partial definition may modify `inner` (or what it points
* to) through `outer`. These expressions will never be `Conversion`s.
Expand Down Expand Up @@ -188,7 +198,7 @@ module FlowVar_internal {
predicate fullySupportedSsaVariable(Variable v) {
v = any(SsaDefinition def).getAVariable() and
// A partially-defined variable is handled using the partial definitions logic.
not any(PartialDefinition p).partiallyDefines(v) and
not any(PartialDefinition p).partiallyDefinesVariableAt(v, _) and
// SSA variables do not exist before their first assignment, but one
// feature of this data flow library is to track where uninitialized data
// ends up.
Expand Down Expand Up @@ -232,7 +242,7 @@ module FlowVar_internal {
or
assignmentLikeOperation(sbb, v, _, _)
or
sbb = any(PartialDefinition p | p.partiallyDefines(v)).getSubBasicBlockStart()
exists(PartialDefinition p | p.partiallyDefinesVariableAt(v, sbb))
or
blockVarDefinedByVariable(sbb, v)
)
Expand Down Expand Up @@ -363,8 +373,7 @@ module FlowVar_internal {

override predicate definedPartiallyAt(Expr e) {
exists(PartialDefinition p |
p.partiallyDefines(v) and
sbb = p.getSubBasicBlockStart() and
p.partiallyDefinesVariableAt(v, sbb) and
p.definesExpressions(_, e)
)
}
Expand Down Expand Up @@ -427,7 +436,7 @@ module FlowVar_internal {
/**
* Gets a variable that is assigned in this loop and read outside the loop.
*/
private Variable getARelevantVariable() {
Variable getARelevantVariable() {
result = this.getAVariableAssignedInLoop() and
exists(VariableAccess va |
va.getTarget() = result and
Expand Down Expand Up @@ -472,10 +481,16 @@ module FlowVar_internal {
reachesWithoutAssignment(bb.getAPredecessor(), v) and
this.bbInLoop(bb)
) and
not assignmentLikeOperation(bb.getANode(), v, _, _)
not assignsToVar(bb, v)
}
}

pragma[noinline]
private predicate assignsToVar(BasicBlock bb, Variable v) {
assignmentLikeOperation(bb.getANode(), v, _, _) and
exists(AlwaysTrueUponEntryLoop loop | v = loop.getARelevantVariable())
}

/**
* Holds if `loop` always assigns to `v` before leaving through an edge
* from `bbInside` in its condition to `bbOutside` outside the loop. Also,
Expand Down Expand Up @@ -736,7 +751,7 @@ module FlowVar_internal {
exists(Variable v | not fullySupportedSsaVariable(v) |
assignmentLikeOperation(this, v, _, _)
or
this = any(PartialDefinition p | p.partiallyDefines(v)).getSubBasicBlockStart()
exists(PartialDefinition p | p.partiallyDefinesVariableAt(v, this))
// It is not necessary to cut the basic blocks at `Initializer` nodes
// because the affected variable can have no _other_ value before its
// initializer. It is not necessary to cut basic blocks at procedure
Expand Down