Add shared basic block library

Author: paldepind

csharp/ql/lib/semmle/code/csharp/controlflow/BasicBlocks.qll

@@ -4,26 +4,20 @@
 
 import csharp
 private import ControlFlow::SuccessorTypes
+private import semmle.code.csharp.controlflow.internal.ControlFlowGraphImpl as CfgImpl
+private import CfgImpl::BasicBlocks as BasicBlocksImpl
 
 /**
  * A basic block, that is, a maximal straight-line sequence of control flow nodes
  * without branches or joins.
  */
-class BasicBlock extends TBasicBlockStart {
-  /** Gets an immediate successor of this basic block, if any. */
-  BasicBlock getASuccessor() { result.getFirstNode() = this.getLastNode().getASuccessor() }
-
+final class BasicBlock extends BasicBlocksImpl::BasicBlock {
   /** Gets an immediate successor of this basic block of a given type, if any. */
-  BasicBlock getASuccessorByType(ControlFlow::SuccessorType t) {
-    result.getFirstNode() = this.getLastNode().getASuccessorByType(t)
-  }
-
-  /** Gets an immediate predecessor of this basic block, if any. */
-  BasicBlock getAPredecessor() { result.getASuccessor() = this }
+  BasicBlock getASuccessorByType(ControlFlow::SuccessorType t) { result = this.getASuccessor(t) }
 
   /** Gets an immediate predecessor of this basic block of a given type, if any. */
   BasicBlock getAPredecessorByType(ControlFlow::SuccessorType t) {
-    result.getASuccessorByType(t) = this
+    result = this.getAPredecessor(t)
   }
 
   /**
@@ -65,23 +59,20 @@ class BasicBlock extends TBasicBlockStart {
   }
 
   /** Gets the control flow node at a specific (zero-indexed) position in this basic block. */
-  ControlFlow::Node getNode(int pos) { bbIndex(this.getFirstNode(), result, pos) }
+  ControlFlow::Node getNode(int pos) { result = super.getNode(pos) }
 
   /** Gets a control flow node in this basic block. */
-  ControlFlow::Node getANode() { result = this.getNode(_) }
+  ControlFlow::Node getANode() { result = super.getANode() }
 
   /** Gets the first control flow node in this basic block. */
-  ControlFlow::Node getFirstNode() { this = TBasicBlockStart(result) }
+  ControlFlow::Node getFirstNode() { result = super.getFirstNode() }
 
   /** Gets the last control flow node in this basic block. */
-  ControlFlow::Node getLastNode() { result = this.getNode(this.length() - 1) }
+  ControlFlow::Node getLastNode() { result = super.getLastNode() }
 
   /** Gets the callable that this basic block belongs to. */
   final Callable getCallable() { result = this.getFirstNode().getEnclosingCallable() }
 
-  /** Gets the length of this basic block. */
-  int length() { result = strictcount(this.getANode()) }
-
   /**
    * Holds if this basic block immediately dominates basic block `bb`.
    *
@@ -103,7 +94,7 @@ class BasicBlock extends TBasicBlockStart {
    * basic block on line 4 (all paths from the entry point of `M`
    * to `return s.Length;` must go through the null check).
    */
-  predicate immediatelyDominates(BasicBlock bb) { bbIDominates(this, bb) }
+  predicate immediatelyDominates(BasicBlock bb) { super.immediatelyDominates(bb) }
 
   /**
    * Holds if this basic block strictly dominates basic block `bb`.
@@ -126,7 +117,7 @@ class BasicBlock extends TBasicBlockStart {
    * basic block on line 4 (all paths from the entry point of `M`
    * to `return s.Length;` must go through the null check).
    */
-  predicate strictlyDominates(BasicBlock bb) { bbIDominates+(this, bb) }
+  predicate strictlyDominates(BasicBlock bb) { super.strictlyDominates(bb) }
 
   /**
    * Holds if this basic block dominates basic block `bb`.
@@ -178,15 +169,7 @@ class BasicBlock extends TBasicBlockStart {
    * `Console.Write(x);`. Also, the basic block starting on line 2
    * does not dominate the basic block on line 6.
    */
-  predicate inDominanceFrontier(BasicBlock df) {
-    this.dominatesPredecessor(df) and
-    not this.strictlyDominates(df)
-  }
-
-  /**
-   * Holds if this basic block dominates a predecessor of `df`.
-   */
-  private predicate dominatesPredecessor(BasicBlock df) { this.dominates(df.getAPredecessor()) }
+  predicate inDominanceFrontier(BasicBlock df) { super.inDominanceFrontier(df) }
 
   /**
    * Gets the basic block that immediately dominates this basic block, if any.
@@ -208,7 +191,7 @@ class BasicBlock extends TBasicBlockStart {
    * the basic block online 4 (all paths from the entry point of `M`
    * to `return s.Length;` must go through the null check.
    */
-  BasicBlock getImmediateDominator() { bbIDominates(result, this) }
+  BasicBlock getImmediateDominator() { result = super.getImmediateDominator() }
 
   /**
    * Holds if this basic block strictly post-dominates basic block `bb`.
@@ -234,7 +217,7 @@ class BasicBlock extends TBasicBlockStart {
    * line 3 (all paths to the exit point of `M` from `return s.Length;`
    * must go through the `WriteLine` call).
    */
-  predicate strictlyPostDominates(BasicBlock bb) { bbIPostDominates+(this, bb) }
+  predicate strictlyPostDominates(BasicBlock bb) { super.strictlyPostDominates(bb) }
 
   /**
    * Holds if this basic block post-dominates basic block `bb`.
@@ -262,10 +245,7 @@ class BasicBlock extends TBasicBlockStart {
    * This predicate is *reflexive*, so for example `Console.WriteLine("M");`
    * post-dominates itself.
    */
-  predicate postDominates(BasicBlock bb) {
-    this.strictlyPostDominates(bb) or
-    this = bb
-  }
+  predicate postDominates(BasicBlock bb) { super.postDominates(bb) }
 
   /**
    * Holds if this basic block is in a loop in the control flow graph. This
@@ -274,230 +254,44 @@ class BasicBlock extends TBasicBlockStart {
    * necessary back edges are unreachable.
    */
   predicate inLoop() { this.getASuccessor+() = this }
-
-  /** Gets a textual representation of this basic block. */
-  string toString() { result = this.getFirstNode().toString() }
-
-  /** Gets the location of this basic block. */
-  Location getLocation() { result = this.getFirstNode().getLocation() }
-}
-
-/**
- * Internal implementation details.
- */
-cached
-private module Internal {
-  /** Internal representation of basic blocks. */
-  cached
-  newtype TBasicBlock = TBasicBlockStart(ControlFlow::Node cfn) { startsBB(cfn) }
-
-  /** Holds if `cfn` starts a new basic block. */
-  private predicate startsBB(ControlFlow::Node cfn) {
-    not exists(cfn.getAPredecessor()) and exists(cfn.getASuccessor())
-    or
-    cfn.isJoin()
-    or
-    cfn.getAPredecessor().isBranch()
-    or
-    /*
-     * In cases such as
-     * ```csharp
-     * if (b)
-     *     M()
-     * ```
-     * where the `false` edge out of `b` is not present (because we can prove it
-     * impossible), we still split up the basic block in two, in order to generate
-     * a `ConditionBlock` which can be used by the guards library.
-     */
-
-    exists(cfn.getAPredecessorByType(any(ControlFlow::SuccessorTypes::ConditionalSuccessor s)))
-  }
-
-  /**
-   * Holds if `succ` is a control flow successor of `pred` within
-   * the same basic block.
-   */
-  private predicate intraBBSucc(ControlFlow::Node pred, ControlFlow::Node succ) {
-    succ = pred.getASuccessor() and
-    not startsBB(succ)
-  }
-
-  /**
-   * Holds if `cfn` is the `i`th node in basic block `bb`.
-   *
-   * In other words, `i` is the shortest distance from a node `bb`
-   * that starts a basic block to `cfn` along the `intraBBSucc` relation.
-   */
-  cached
-  predicate bbIndex(ControlFlow::Node bbStart, ControlFlow::Node cfn, int i) =
-    shortestDistances(startsBB/1, intraBBSucc/2)(bbStart, cfn, i)
-
-  /**
-   * Holds if the first node of basic block `succ` is a control flow
-   * successor of the last node of basic block `pred`.
-   */
-  private predicate succBB(BasicBlock pred, BasicBlock succ) { succ = pred.getASuccessor() }
-
-  /** Holds if `dom` is an immediate dominator of `bb`. */
-  cached
-  predicate bbIDominates(BasicBlock dom, BasicBlock bb) =
-    idominance(entryBB/1, succBB/2)(_, dom, bb)
-
-  /** Holds if `pred` is a basic block predecessor of `succ`. */
-  private predicate predBB(BasicBlock succ, BasicBlock pred) { succBB(pred, succ) }
-
-  /** Holds if `bb` is an exit basic block that represents normal exit. */
-  private predicate normalExitBB(BasicBlock bb) {
-    bb.getANode().(ControlFlow::Nodes::AnnotatedExitNode).isNormal()
-  }
-
-  /** Holds if `dom` is an immediate post-dominator of `bb`. */
-  cached
-  predicate bbIPostDominates(BasicBlock dom, BasicBlock bb) =
-    idominance(normalExitBB/1, predBB/2)(_, dom, bb)
 }
 
-private import Internal
-
 /**
  * An entry basic block, that is, a basic block whose first node is
- * the entry node of a callable.
+ * an entry node.
  */
-class EntryBasicBlock extends BasicBlock {
-  EntryBasicBlock() { entryBB(this) }
-}
-
-/** Holds if `bb` is an entry basic block. */
-private predicate entryBB(BasicBlock bb) {
-  bb.getFirstNode() instanceof ControlFlow::Nodes::EntryNode
-}
+final class EntryBasicBlock extends BasicBlock, BasicBlocksImpl::EntryBasicBlock { }
 
 /**
- * An annotated exit basic block, that is, a basic block that contains
- * an annotated exit node.
+ * An annotated exit basic block, that is, a basic block that contains an
+ * annotated exit node.
  */
-class AnnotatedExitBasicBlock extends BasicBlock {
-  private boolean isNormal;
-
-  AnnotatedExitBasicBlock() {
-    this.getANode() =
-      any(ControlFlow::Nodes::AnnotatedExitNode n |
-        if n.isNormal() then isNormal = true else isNormal = false
-      )
-  }
-
-  /** Holds if this block represents a normal exit. */
-  predicate isNormal() { isNormal = true }
-}
+final class AnnotatedExitBasicBlock extends BasicBlock, BasicBlocksImpl::AnnotatedExitBasicBlock { }
 
 /**
  * An exit basic block, that is, a basic block whose last node is
- * the exit node of a callable.
+ * an exit node.
  */
-class ExitBasicBlock extends BasicBlock {
-  ExitBasicBlock() { this.getLastNode() instanceof ControlFlow::Nodes::ExitNode }
-}
-
-private module JoinBlockPredecessors {
-  private import ControlFlow::Nodes
-  private import semmle.code.csharp.controlflow.internal.ControlFlowGraphImpl as Impl
-
-  int getId(JoinBlockPredecessor jbp) {
-    exists(Impl::AstNode n | result = n.getId() |
-      n = jbp.getFirstNode().getAstNode()
-      or
-      n = jbp.(EntryBasicBlock).getCallable()
-    )
-  }
-
-  string getSplitString(JoinBlockPredecessor jbp) {
-    result = jbp.getFirstNode().(ElementNode).getSplitsString()
-    or
-    not exists(jbp.getFirstNode().(ElementNode).getSplitsString()) and
-    result = ""
-  }
-}
+final class ExitBasicBlock extends BasicBlock, BasicBlocksImpl::ExitBasicBlock { }
 
 /** A basic block with more than one predecessor. */
-class JoinBlock extends BasicBlock {
-  JoinBlock() { this.getFirstNode().isJoin() }
-
-  /**
-   * Gets the `i`th predecessor of this join block, with respect to some
-   * arbitrary order.
-   */
-  cached
-  JoinBlockPredecessor getJoinBlockPredecessor(int i) {
-    result =
-      rank[i + 1](JoinBlockPredecessor jbp |
-        jbp = this.getAPredecessor()
-      |
-        jbp order by JoinBlockPredecessors::getId(jbp), JoinBlockPredecessors::getSplitString(jbp)
-      )
-  }
+final class JoinBlock extends BasicBlock, BasicBlocksImpl::JoinBasicBlock {
+  JoinBlockPredecessor getJoinBlockPredecessor(int i) { result = super.getJoinBlockPredecessor(i) }
 }
 
 /** A basic block that is an immediate predecessor of a join block. */
-class JoinBlockPredecessor extends BasicBlock {
-  JoinBlockPredecessor() { this.getASuccessor() instanceof JoinBlock }
-}
-
-/** A basic block that terminates in a condition, splitting the subsequent control flow. */
-class ConditionBlock extends BasicBlock {
-  ConditionBlock() { this.getLastNode().isCondition() }
+final class JoinBlockPredecessor extends BasicBlock, BasicBlocksImpl::JoinPredecessorBasicBlock { }
 
-  /**
-   * Holds if basic block `succ` is immediately controlled by this basic
-   * block with conditional value `s`. That is, `succ` is an immediate
-   * successor of this block, and `succ` can only be reached from
-   * the callable entry point by going via the `s` edge out of this basic block.
-   */
-  pragma[nomagic]
+/**
+ * A basic block that terminates in a condition, splitting the subsequent
+ * control flow.
+ */
+final class ConditionBlock extends BasicBlock, BasicBlocksImpl::ConditionBasicBlock {
   predicate immediatelyControls(BasicBlock succ, ConditionalSuccessor s) {
-    succ = this.getASuccessorByType(s) and
-    forall(BasicBlock pred | pred = succ.getAPredecessor() and pred != this | succ.dominates(pred))
+    super.immediatelyControls(succ, s)
   }
 
-  /**
-   * Holds if basic block `controlled` is controlled by this basic block with
-   * conditional value `s`. That is, `controlled` can only be reached from
-   * the callable entry point by going via the `s` edge out of this basic block.
-   */
   predicate controls(BasicBlock controlled, ConditionalSuccessor s) {
-    /*
-     * For this block to control the block `controlled` with `testIsTrue` the following must be true:
-     * Execution must have passed through the test i.e. `this` must strictly dominate `controlled`.
-     * Execution must have passed through the `testIsTrue` edge leaving `this`.
-     *
-     * Although "passed through the true edge" implies that `this.getATrueSuccessor()` dominates `controlled`,
-     * the reverse is not true, as flow may have passed through another edge to get to `this.getATrueSuccessor()`
-     * so we need to assert that `this.getATrueSuccessor()` dominates `controlled` *and* that
-     * all predecessors of `this.getATrueSuccessor()` are either `this` or dominated by `this.getATrueSuccessor()`.
-     *
-     * For example, in the following C# snippet:
-     * ```csharp
-     * if (x)
-     *   controlled;
-     * false_successor;
-     * uncontrolled;
-     * ```
-     * `false_successor` dominates `uncontrolled`, but not all of its predecessors are `this` (`if (x)`)
-     *  or dominated by itself. Whereas in the following code:
-     * ```csharp
-     * if (x)
-     *   while (controlled)
-     *     also_controlled;
-     * false_successor;
-     * uncontrolled;
-     * ```
-     * the block `while controlled` is controlled because all of its predecessors are `this` (`if (x)`)
-     * or (in the case of `also_controlled`) dominated by itself.
-     *
-     * The additional constraint on the predecessors of the test successor implies
-     * that `this` strictly dominates `controlled` so that isn't necessary to check
-     * directly.
-     */
-
-    exists(BasicBlock succ | this.immediatelyControls(succ, s) | succ.dominates(controlled))
+    super.controls(controlled, s)
   }
 }

csharp/ql/lib/semmle/code/csharp/controlflow/internal/ControlFlowGraphImpl.qll

@@ -95,6 +95,10 @@ private module CfgInput implements CfgShared::InputSig<Location> {
     t instanceof ST::SuccessorTypes::ExceptionSuccessor or
     t instanceof ST::SuccessorTypes::ExitSuccessor
   }
+
+  predicate idOfAstNode(AstNode node, int id) { node.getId() = id }
+
+  predicate idOfCfgScope(CfgScope node, int id) { idOfAstNode(node, id) }
 }
 
 private module CfgSplittingInput implements CfgShared::SplittingInputSig<Location, CfgInput> {