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Merged
merged 4 commits into from
Feb 13, 2023
Merged

Data flow: Call context virtual dispatch pruning in stage 1 #12124

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Data flow: Call context virtual dispatch pruning in stage 1
hvitved Dec 1, 2022
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Data flow: Sync files
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Address review comment
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Ruby: Add another data flow test
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108 changes: 77 additions & 31 deletions cpp/ql/lib/experimental/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -667,23 +667,78 @@ private module Stage1 implements StageSig {
)
or
// flow into a callable
exists(NodeEx arg |
fwdFlow(arg, _, config) and
viableParamArgEx(_, node, arg) and
cc = true and
not fullBarrier(node, config)
)
fwdFlowIn(_, _, _, node, config) and
cc = true
or
// flow out of a callable
fwdFlowOut(_, node, false, config) and
cc = false
or
// flow through a callable
exists(DataFlowCall call |
fwdFlowOut(call, node, false, config) and
cc = false
or
fwdFlowOutFromArg(call, node, config) and
fwdFlowIsEntered(call, cc, config)
)
}

// inline to reduce the number of iterations
pragma[inline]
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Did you compare performance of this inlining against the nomagic alternative?

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Don't remember, but it probably doesn't matter that much. The logic was previously manually inlined into fwdFlow and fwdFlowIsEntered, so I decided to keep it that way.

private predicate fwdFlowIn(
DataFlowCall call, NodeEx arg, Cc cc, ParamNodeEx p, Configuration config
) {
// call context cannot help reduce virtual dispatch
fwdFlow(arg, cc, config) and
viableParamArgEx(call, p, arg) and
not fullBarrier(p, config) and
(
cc = false
or
cc = true and
not reducedViableImplInCallContext(call, _, _)
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I think we need cc = true and here in order to not get tuple duplication in this pipeline split.

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Can't hurt.

)
or
// call context may help reduce virtual dispatch
exists(DataFlowCallable target |
fwdFlowInReducedViableImplInSomeCallContext(call, arg, p, target, config) and
target = viableImplInSomeFwdFlowCallContextExt(call, config) and
cc = true
)
}

/**
* Holds if an argument to `call` is reached in the flow covered by `fwdFlow`.
*/
pragma[nomagic]
private predicate fwdFlowIsEntered(DataFlowCall call, Cc cc, Configuration config) {
fwdFlowIn(call, _, cc, _, config)
}

pragma[nomagic]
private predicate fwdFlowInReducedViableImplInSomeCallContext(
DataFlowCall call, NodeEx arg, ParamNodeEx p, DataFlowCallable target, Configuration config
) {
fwdFlow(arg, true, config) and
viableParamArgEx(call, p, arg) and
reducedViableImplInCallContext(call, _, _) and
target = p.getEnclosingCallable() and
not fullBarrier(p, config)
}

/**
* Gets a viable dispatch target of `call` in the context `ctx`. This is
* restricted to those `call`s for which a context might make a difference,
* and to `ctx`s that are reachable in `fwdFlow`.
*/
pragma[nomagic]
private DataFlowCallable viableImplInSomeFwdFlowCallContextExt(
DataFlowCall call, Configuration config
) {
exists(DataFlowCall ctx |
fwdFlowIsEntered(ctx, _, config) and
result = viableImplInCallContextExt(call, ctx)
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I was about to say that something looked wrong here, but that was because I was thinking about prunedViableImplInCallContext rather than viableImplInCallContextExt. Could you add a flow test that fails if prunedViableImplInCallContext was mistakenly used here instead of viableImplInCallContextExt?

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Done.

)
}

private predicate fwdFlow(NodeEx node, Configuration config) { fwdFlow(node, _, config) }

pragma[nomagic]
Expand Down Expand Up @@ -726,7 +781,8 @@ private module Stage1 implements StageSig {
)
}

pragma[nomagic]
// inline to reduce the number of iterations
pragma[inline]
private predicate fwdFlowOut(DataFlowCall call, NodeEx out, Cc cc, Configuration config) {
exists(ReturnPosition pos |
fwdFlowReturnPosition(pos, cc, config) and
Expand All @@ -740,17 +796,6 @@ private module Stage1 implements StageSig {
fwdFlowOut(call, out, true, config)
}

/**
* Holds if an argument to `call` is reached in the flow covered by `fwdFlow`.
*/
pragma[nomagic]
private predicate fwdFlowIsEntered(DataFlowCall call, Cc cc, Configuration config) {
exists(ArgNodeEx arg |
fwdFlow(arg, cc, config) and
viableParamArgEx(call, _, arg)
)
}

private predicate stateStepFwd(FlowState state1, FlowState state2, Configuration config) {
exists(NodeEx node1 |
additionalLocalStateStep(node1, state1, _, state2, config) or
Expand Down Expand Up @@ -817,20 +862,21 @@ private module Stage1 implements StageSig {
)
or
// flow into a callable
exists(DataFlowCall call |
revFlowIn(call, node, false, config) and
toReturn = false
or
revFlowInToReturn(call, node, config) and
revFlowIsReturned(call, toReturn, config)
)
revFlowIn(_, node, false, config) and
toReturn = false
or
// flow out of a callable
exists(ReturnPosition pos |
revFlowOut(pos, config) and
node.(RetNodeEx).getReturnPosition() = pos and
toReturn = true
)
or
// flow through a callable
exists(DataFlowCall call |
revFlowInToReturn(call, node, config) and
revFlowIsReturned(call, toReturn, config)
)
}

/**
Expand Down Expand Up @@ -886,11 +932,11 @@ private module Stage1 implements StageSig {
additional predicate viableParamArgNodeCandFwd1(
DataFlowCall call, ParamNodeEx p, ArgNodeEx arg, Configuration config
) {
viableParamArgEx(call, p, arg) and
fwdFlow(arg, config)
fwdFlowIn(call, arg, _, p, config)
}

pragma[nomagic]
// inline to reduce the number of iterations
pragma[inline]
private predicate revFlowIn(
DataFlowCall call, ArgNodeEx arg, boolean toReturn, Configuration config
) {
Expand Down
108 changes: 77 additions & 31 deletions cpp/ql/lib/experimental/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl2.qll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -667,23 +667,78 @@ private module Stage1 implements StageSig {
)
or
// flow into a callable
exists(NodeEx arg |
fwdFlow(arg, _, config) and
viableParamArgEx(_, node, arg) and
cc = true and
not fullBarrier(node, config)
)
fwdFlowIn(_, _, _, node, config) and
cc = true
or
// flow out of a callable
fwdFlowOut(_, node, false, config) and
cc = false
or
// flow through a callable
exists(DataFlowCall call |
fwdFlowOut(call, node, false, config) and
cc = false
or
fwdFlowOutFromArg(call, node, config) and
fwdFlowIsEntered(call, cc, config)
)
}

// inline to reduce the number of iterations
pragma[inline]
private predicate fwdFlowIn(
DataFlowCall call, NodeEx arg, Cc cc, ParamNodeEx p, Configuration config
) {
// call context cannot help reduce virtual dispatch
fwdFlow(arg, cc, config) and
viableParamArgEx(call, p, arg) and
not fullBarrier(p, config) and
(
cc = false
or
cc = true and
not reducedViableImplInCallContext(call, _, _)
)
or
// call context may help reduce virtual dispatch
exists(DataFlowCallable target |
fwdFlowInReducedViableImplInSomeCallContext(call, arg, p, target, config) and
target = viableImplInSomeFwdFlowCallContextExt(call, config) and
cc = true
)
}

/**
* Holds if an argument to `call` is reached in the flow covered by `fwdFlow`.
*/
pragma[nomagic]
private predicate fwdFlowIsEntered(DataFlowCall call, Cc cc, Configuration config) {
fwdFlowIn(call, _, cc, _, config)
}

pragma[nomagic]
private predicate fwdFlowInReducedViableImplInSomeCallContext(
DataFlowCall call, NodeEx arg, ParamNodeEx p, DataFlowCallable target, Configuration config
) {
fwdFlow(arg, true, config) and
viableParamArgEx(call, p, arg) and
reducedViableImplInCallContext(call, _, _) and
target = p.getEnclosingCallable() and
not fullBarrier(p, config)
}

/**
* Gets a viable dispatch target of `call` in the context `ctx`. This is
* restricted to those `call`s for which a context might make a difference,
* and to `ctx`s that are reachable in `fwdFlow`.
*/
pragma[nomagic]
private DataFlowCallable viableImplInSomeFwdFlowCallContextExt(
DataFlowCall call, Configuration config
) {
exists(DataFlowCall ctx |
fwdFlowIsEntered(ctx, _, config) and
result = viableImplInCallContextExt(call, ctx)
)
}

private predicate fwdFlow(NodeEx node, Configuration config) { fwdFlow(node, _, config) }

pragma[nomagic]
Expand Down Expand Up @@ -726,7 +781,8 @@ private module Stage1 implements StageSig {
)
}

pragma[nomagic]
// inline to reduce the number of iterations
pragma[inline]
private predicate fwdFlowOut(DataFlowCall call, NodeEx out, Cc cc, Configuration config) {
exists(ReturnPosition pos |
fwdFlowReturnPosition(pos, cc, config) and
Expand All @@ -740,17 +796,6 @@ private module Stage1 implements StageSig {
fwdFlowOut(call, out, true, config)
}

/**
* Holds if an argument to `call` is reached in the flow covered by `fwdFlow`.
*/
pragma[nomagic]
private predicate fwdFlowIsEntered(DataFlowCall call, Cc cc, Configuration config) {
exists(ArgNodeEx arg |
fwdFlow(arg, cc, config) and
viableParamArgEx(call, _, arg)
)
}

private predicate stateStepFwd(FlowState state1, FlowState state2, Configuration config) {
exists(NodeEx node1 |
additionalLocalStateStep(node1, state1, _, state2, config) or
Expand Down Expand Up @@ -817,20 +862,21 @@ private module Stage1 implements StageSig {
)
or
// flow into a callable
exists(DataFlowCall call |
revFlowIn(call, node, false, config) and
toReturn = false
or
revFlowInToReturn(call, node, config) and
revFlowIsReturned(call, toReturn, config)
)
revFlowIn(_, node, false, config) and
toReturn = false
or
// flow out of a callable
exists(ReturnPosition pos |
revFlowOut(pos, config) and
node.(RetNodeEx).getReturnPosition() = pos and
toReturn = true
)
or
// flow through a callable
exists(DataFlowCall call |
revFlowInToReturn(call, node, config) and
revFlowIsReturned(call, toReturn, config)
)
}

/**
Expand Down Expand Up @@ -886,11 +932,11 @@ private module Stage1 implements StageSig {
additional predicate viableParamArgNodeCandFwd1(
DataFlowCall call, ParamNodeEx p, ArgNodeEx arg, Configuration config
) {
viableParamArgEx(call, p, arg) and
fwdFlow(arg, config)
fwdFlowIn(call, arg, _, p, config)
}

pragma[nomagic]
// inline to reduce the number of iterations
pragma[inline]
private predicate revFlowIn(
DataFlowCall call, ArgNodeEx arg, boolean toReturn, Configuration config
) {
Expand Down
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