C++: Remove unreachable IR

config/identical-files.json

@@ -1,55 +1,98 @@
 {
-    "C++ IR Instruction": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/Instruction.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/Instruction.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/Instruction.qll"
-    ],
-    "C++ IR IRBlock": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRBlock.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRBlock.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRBlock.qll"
-    ],
-    "C++ IR IRVariable": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRVariable.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRVariable.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRVariable.qll"
-    ],
-    "C++ IR FunctionIR": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/FunctionIR.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/FunctionIR.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/FunctionIR.qll"
-    ],
-    "C++ IR Operand": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/Operand.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/Operand.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/Operand.qll"
-    ],
-    "C++ IR IRImpl": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IR.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IR.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IR.qll"
-    ],
-    "C++ IR IRSanityImpl": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRSanity.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRSanity.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRSanity.qll"
-    ],
-    "C++ IR PrintIRImpl": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/PrintIR.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/PrintIR.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/PrintIR.qll"
-    ],
-    "C++ SSA AliasAnalysis": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/AliasAnalysis.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/AliasAnalysis.qll"
-    ],
-    "C++ SSA SSAConstruction": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/SSAConstruction.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SSAConstruction.qll"
-    ],
-    "C++ IR ValueNumber": [
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/gvn/ValueNumbering.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/gvn/ValueNumbering.qll",
-        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/gvn/ValueNumbering.qll"
-    ]
+  "DataFlow Java/C++": [
+    "java/ql/src/semmle/code/java/dataflow/internal/DataFlowImpl.qll",
+    "java/ql/src/semmle/code/java/dataflow/internal/DataFlowImpl2.qll",
+    "java/ql/src/semmle/code/java/dataflow/internal/DataFlowImpl3.qll",
+    "java/ql/src/semmle/code/java/dataflow/internal/DataFlowImpl4.qll",
+    "java/ql/src/semmle/code/java/dataflow/internal/DataFlowImpl5.qll",
+    "java/ql/src/semmle/code/java/dataflow/internal/DataFlowImplDepr.qll",
+    "cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl.qll",
+    "cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl2.qll",
+    "cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl3.qll",
+    "cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl4.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl2.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl3.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl4.qll"
+  ],
+  "DataFlow Java/C++ Common": [
+    "java/ql/src/semmle/code/java/dataflow/internal/DataFlowImplCommon.qll",
+    "cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImplCommon.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImplCommon.qll"
+  ],
+  "C++ IR Instruction": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/Instruction.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/Instruction.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/Instruction.qll"
+  ],
+  "C++ IR IRBlock": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRBlock.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRBlock.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRBlock.qll"
+  ],
+  "C++ IR IRVariable": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRVariable.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRVariable.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRVariable.qll"
+  ],
+  "C++ IR FunctionIR": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/FunctionIR.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/FunctionIR.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/FunctionIR.qll"
+  ],
+  "C++ IR Operand": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/Operand.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/Operand.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/Operand.qll"
+  ],
+  "C++ IR IRImpl": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IR.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IR.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IR.qll"
+  ],
+  "C++ IR IRSanityImpl": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRSanity.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRSanity.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRSanity.qll"
+  ],
+  "C++ IR PrintIRImpl": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/PrintIR.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/PrintIR.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/PrintIR.qll"
+  ],
+  "C++ SSA AliasAnalysis": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/AliasAnalysis.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/AliasAnalysis.qll"
+  ],
+  "C++ SSA SSAConstruction": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/SSAConstruction.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SSAConstruction.qll"
+  ],
+  "C++ IR ValueNumber": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/gvn/ValueNumbering.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/gvn/ValueNumbering.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/gvn/ValueNumbering.qll"
+  ],
+  "C++ IR ConstantAnalysis": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/constant/ConstantAnalysis.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/constant/ConstantAnalysis.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/constant/ConstantAnalysis.qll"
+  ],
+  "C++ IR PrintConstantAnalysis": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/constant/PrintConstantAnalysis.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/constant/PrintConstantAnalysis.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/constant/PrintConstantAnalysis.qll"
+  ],
+  "C++ IR ReachableBlock": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/reachability/ReachableBlock.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/reachability/ReachableBlock.qll"
+  ],
+  "C++ IR PrintReachableBlock": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/reachability/PrintReachableBlock.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/reachability/PrintReachableBlock.qll"
+  ],
+  "C++ IR Dominance": [
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/reachability/Dominance.qll",
+    "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/reachability/Dominance.qll"
+  ]
 }

cpp/ql/src/filters/ImportAdditionalLibraries.ql

@@ -14,6 +14,10 @@ import semmle.code.cpp.dataflow.DataFlow2
 import semmle.code.cpp.dataflow.DataFlow3
 import semmle.code.cpp.dataflow.DataFlow4
 import semmle.code.cpp.dataflow.TaintTracking
+import semmle.code.cpp.ir.dataflow.DataFlow
+import semmle.code.cpp.ir.dataflow.DataFlow2
+import semmle.code.cpp.ir.dataflow.DataFlow3
+import semmle.code.cpp.ir.dataflow.DataFlow4
 import semmle.code.cpp.valuenumbering.HashCons
 
 from File f, string tag

cpp/ql/src/semmle/code/cpp/ir/dataflow/DataFlow.qll

@@ -0,0 +1,23 @@
+/**
+ * Provides a library for local (intra-procedural) and global (inter-procedural)
+ * data flow analysis: deciding whether data can flow from a _source_ to a
+ * _sink_. This library differs from the one in `semmle.code.cpp.dataflow` in that
+ * this library uses the IR (Intermediate Representation) library, which provides
+ * a more precise semantic representation of the program, whereas the other dataflow
+ * library uses the more syntax-oriented ASTs. This library should provide more accurate
+ * results than the AST-based library in most scenarios.
+ *
+ * Unless configured otherwise, _flow_ means that the exact value of
+ * the source may reach the sink. We do not track flow across pointer
+ * dereferences or array indexing.
+ *
+ * To use global (interprocedural) data flow, extend the class
+ * `DataFlow::Configuration` as documented on that class. To use local
+ * (intraprocedural) data flow, invoke `DataFlow::localFlow` or
+ * `DataFlow::LocalFlowStep` with arguments of type `DataFlow::Node`.
+ */
+import cpp
+
+module DataFlow {
+  import semmle.code.cpp.ir.dataflow.internal.DataFlowImpl
+}

cpp/ql/src/semmle/code/cpp/ir/dataflow/DataFlow2.qll

@@ -0,0 +1,38 @@
+/**
+ * Provides a `DataFlow2` module, which is a copy of the `DataFlow` module. Use
+ * this class when data-flow configurations must depend on each other. Two
+ * classes extending `DataFlow::Configuration` should never depend on each
+ * other, but one of them should instead depend on a
+ * `DataFlow2::Configuration`, a `DataFlow3::Configuration`, or a
+ * `DataFlow4::Configuration`.
+ *
+ * See `semmle.code.cpp.dataflow.DataFlow` for the full documentation.
+ */
+import cpp
+
+module DataFlow2 {
+  import semmle.code.cpp.ir.dataflow.internal.DataFlowImpl2
+
+  /**
+   * This class exists to prevent mutual recursion between the user-overridden
+   * member predicates of `Configuration` and the rest of the data-flow library.
+   * Good performance cannot be guaranteed in the presence of such recursion, so
+   * it should be replaced by using more than one copy of the data flow library.
+   * Four copies are available: `DataFlow` through `DataFlow4`.
+   */
+  private abstract
+  class ConfigurationRecursionPrevention extends Configuration {
+    bindingset[this]
+    ConfigurationRecursionPrevention() { any() }
+
+    override predicate hasFlow(Node source, Node sink) {
+      strictcount(Node n | this.isSource(n)) < 0
+      or
+      strictcount(Node n | this.isSink(n)) < 0
+      or
+      strictcount(Node n1, Node n2 | this.isAdditionalFlowStep(n1, n2)) < 0
+      or
+      super.hasFlow(source, sink)
+    }
+  }
+}

cpp/ql/src/semmle/code/cpp/ir/dataflow/DataFlow3.qll

@@ -0,0 +1,38 @@
+/**
+ * Provides a `DataFlow3` module, which is a copy of the `DataFlow` module. Use
+ * this class when data-flow configurations must depend on each other. Two
+ * classes extending `DataFlow::Configuration` should never depend on each
+ * other, but one of them should instead depend on a
+ * `DataFlow2::Configuration`, a `DataFlow3::Configuration`, or a
+ * `DataFlow4::Configuration`.
+ *
+ * See `semmle.code.cpp.dataflow.DataFlow` for the full documentation.
+ */
+import cpp
+
+module DataFlow3 {
+  import semmle.code.cpp.ir.dataflow.internal.DataFlowImpl3
+
+  /**
+   * This class exists to prevent mutual recursion between the user-overridden
+   * member predicates of `Configuration` and the rest of the data-flow library.
+   * Good performance cannot be guaranteed in the presence of such recursion, so
+   * it should be replaced by using more than one copy of the data flow library.
+   * Four copies are available: `DataFlow` through `DataFlow4`.
+   */
+  private abstract
+  class ConfigurationRecursionPrevention extends Configuration {
+    bindingset[this]
+    ConfigurationRecursionPrevention() { any() }
+
+    override predicate hasFlow(Node source, Node sink) {
+      strictcount(Node n | this.isSource(n)) < 0
+      or
+      strictcount(Node n | this.isSink(n)) < 0
+      or
+      strictcount(Node n1, Node n2 | this.isAdditionalFlowStep(n1, n2)) < 0
+      or
+      super.hasFlow(source, sink)
+    }
+  }
+}

cpp/ql/src/semmle/code/cpp/ir/dataflow/DataFlow4.qll

@@ -0,0 +1,38 @@
+/**
+ * Provides a `DataFlow4` module, which is a copy of the `DataFlow` module. Use
+ * this class when data-flow configurations must depend on each other. Two
+ * classes extending `DataFlow::Configuration` should never depend on each
+ * other, but one of them should instead depend on a
+ * `DataFlow2::Configuration`, a `DataFlow3::Configuration`, or a
+ * `DataFlow4::Configuration`.
+ *
+ * See `semmle.code.cpp.dataflow.DataFlow` for the full documentation.
+ */
+import cpp
+
+module DataFlow4 {
+  import semmle.code.cpp.ir.dataflow.internal.DataFlowImpl4
+
+  /**
+   * This class exists to prevent mutual recursion between the user-overridden
+   * member predicates of `Configuration` and the rest of the data-flow library.
+   * Good performance cannot be guaranteed in the presence of such recursion, so
+   * it should be replaced by using more than one copy of the data flow library.
+   * Four copies are available: `DataFlow` through `DataFlow4`.
+   */
+  private abstract
+  class ConfigurationRecursionPrevention extends Configuration {
+    bindingset[this]
+    ConfigurationRecursionPrevention() { any() }
+
+    override predicate hasFlow(Node source, Node sink) {
+      strictcount(Node n | this.isSource(n)) < 0
+      or
+      strictcount(Node n | this.isSink(n)) < 0
+      or
+      strictcount(Node n1, Node n2 | this.isAdditionalFlowStep(n1, n2)) < 0
+      or
+      super.hasFlow(source, sink)
+    }
+  }
+}

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowDispatch.qll

@@ -0,0 +1,73 @@
+private import cpp
+private import DataFlowPrivate
+
+Function viableImpl(MethodAccess ma) {
+  result = ma.getTarget()
+}
+
+Function viableCallable(Call call) {
+  result = call.getTarget()
+}
+
+/**
+ * Holds if the call context `ctx` reduces the set of viable dispatch
+ * targets of `ma` in `c`.
+ */
+predicate reducedViableImplInCallContext(MethodAccess ma, Callable c, Call ctx) {
+  none()
+}
+
+/**
+ * Gets a viable dispatch target of `ma` in the context `ctx`. This is
+ * restricted to those `ma`s for which a context might make a difference.
+ */
+private Method viableImplInCallContext(MethodAccess ma, Call ctx) {
+  // stub implementation
+  result = viableImpl(ma) and
+  viableCallable(ctx) = ma.getEnclosingFunction()
+}
+
+/**
+ * Gets a viable dispatch target of `ma` in the context `ctx`. This is
+ * restricted to those `ma`s for which the context makes a difference.
+ */
+Method prunedViableImplInCallContext(MethodAccess ma, Call ctx) {
+  result = viableImplInCallContext(ma, ctx) and
+  reducedViableImplInCallContext(ma, _, ctx)
+}
+
+/**
+ * Holds if data might flow from `ma` to a return statement in some
+ * configuration.
+ */
+private predicate maybeChainedReturn(MethodAccess ma) {
+  exists(ReturnStmt ret |
+    exists(ret.getExpr()) and
+    ret.getEnclosingFunction() = ma.getEnclosingFunction() and
+    not ma.getParent() instanceof ExprStmt
+  )
+}
+
+/**
+ * Holds if flow returning from `m` to `ma` might return further and if
+ * this path restricts the set of call sites that can be returned to.
+ */
+predicate reducedViableImplInReturn(Method m, MethodAccess ma) {
+  exists(int tgts, int ctxtgts |
+    m = viableImpl(ma) and
+    ctxtgts = count(Call ctx | m = viableImplInCallContext(ma, ctx)) and
+    tgts = strictcount(Call ctx | viableCallable(ctx) = ma.getEnclosingFunction()) and
+    ctxtgts < tgts
+  ) and
+  maybeChainedReturn(ma)
+}
+
+/**
+ * Gets a viable dispatch target of `ma` in the context `ctx`. This is
+ * restricted to those `ma`s and results for which the return flow from the
+ * result to `ma` restricts the possible context `ctx`.
+ */
+Method prunedViableImplInCallContextReverse(MethodAccess ma, Call ctx) {
+  result = viableImplInCallContext(ma, ctx) and
+  reducedViableImplInReturn(result, ma)
+}