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C#: Data-flow pruning based on call contexts #2139

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calumgrant merged 2 commits into from
Oct 21, 2019
Merged

C#: Data-flow pruning based on call contexts #2139

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C#: Add dataflow tests exhibiting missing call-context based pruning
hvitved Oct 16, 2019
c57015a
C#: Data-flow pruning based on call contexts
hvitved Oct 16, 2019
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C#: Data-flow pruning based on call contexts
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@hvitved
hvitved committed Oct 16, 2019
commit c57015af7ddf065d45979174ef361a04e2d15b29
47 changes: 46 additions & 1 deletion csharp/ql/src/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -3,10 +3,12 @@ private import cil
private import dotnet
private import DataFlowPublic
private import DataFlowDispatch
private import DataFlowImplCommon::Public
private import ControlFlowReachability
private import DelegateDataFlow
private import semmle.code.csharp.Caching
private import semmle.code.csharp.ExprOrStmtParent
private import semmle.code.csharp.controlflow.Guards
private import semmle.code.csharp.dataflow.LibraryTypeDataFlow
private import semmle.code.csharp.dispatch.Dispatch
private import semmle.code.csharp.frameworks.EntityFramework
Expand Down Expand Up @@ -439,6 +441,22 @@ private module Cached {
c.(FieldLikeContent).getField() = node2.asExpr().(FieldLikeRead).getTarget()
)
}

/**
* Holds if the node `n` is unreachable when the call context is `call`.
*/
cached
predicate isUnreachableInCall(Node n, DataFlowCall call) {
exists(
SsaDefinitionNode paramNode, Ssa::ExplicitDefinition param, Guard guard,
ControlFlow::SuccessorTypes::BooleanSuccessor bs
|
viableConstantBooleanParamArg(paramNode, bs.getValue().booleanNot(), call) and
paramNode.getDefinition() = param and
param.getARead() = guard and
guard.controlsBlock(n.getControlFlowNode().getBasicBlock(), bs)
)
}
}

import Cached
Expand Down Expand Up @@ -1358,4 +1376,31 @@ class DataFlowType = DotNet::Type;

class DataFlowLocation = Location;

predicate isUnreachableInCall(Node n, DataFlowCall call) { none() } // stub implementation
/** Holds if `e` is an expression that always has the same Boolean value `val`. */
private predicate constantBooleanExpr(Expr e, boolean val) {
e = any(AbstractValues::BooleanValue bv | val = bv.getValue()).getAnExpr()
or
exists(Ssa::ExplicitDefinition def, Expr src |
e = def.getARead() and
src = def.getADefinition().getSource() and
constantBooleanExpr(src, val)
)
}

/** An argument that always has the same Boolean value. */
private class ConstantBooleanArgumentNode extends ExprNode {
ConstantBooleanArgumentNode() { constantBooleanExpr(this.(ArgumentNode).asExpr(), _) }

/** Gets the Boolean value of this expression. */
boolean getBooleanValue() { constantBooleanExpr(this.getExpr(), result) }
}

pragma[noinline]
private predicate viableConstantBooleanParamArg(
SsaDefinitionNode paramNode, boolean b, DataFlowCall call
) {
exists(ConstantBooleanArgumentNode arg |
viableParamArg(call, paramNode, arg) and
b = arg.getBooleanValue()
)
}
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