Shared: Address review comments for basic block library

shared/controlflow/codeql/controlflow/BasicBlock.qll

@@ -126,18 +126,23 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     /**
      * Holds if `df` is in the dominance frontier of this basic block. That is,
      * this basic block dominates a predecessor of `df`, but does not dominate
-     * `df` itself.
+     * `df` itself. I.e., it is equivaluent to:
+     * ```
+     * this.dominates(df.getAPredecessor()) and not this.strictlyDominates(df)
+     * ```
      */
     predicate inDominanceFrontier(BasicBlock df) {
-      this.dominatesPredecessor(df) and
-      not this.strictlyDominates(df)
+      // Algorithm from Cooper et al., "A Simple, Fast Dominance Algorithm" (Figure 5),
+      // who in turn attribute it to Ferrante et al., "The program dependence graph and
+      // its use in optimization".
+      this = df.getAPredecessor() and not bbIDominates(this, df)
+      or
+      exists(BasicBlock prev | prev.inDominanceFrontier(df) |
+        bbIDominates(this, prev) and
+        not bbIDominates(this, df)
+      )
     }
 
-    /**
-     * Holds if this basic block dominates a predecessor of `df`.
-     */
-    private predicate dominatesPredecessor(BasicBlock df) { this.dominates(df.getAPredecessor()) }
-
     /**
      * Gets the basic block that immediately dominates this basic block, if any.
      *
@@ -219,7 +224,7 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     // In cases such as
     //
     // ```rb
-    // if x or y
+    // if x and y
     //     foo
     // else
     //     bar

shared/controlflow/codeql/controlflow/Cfg.qll

@@ -82,14 +82,12 @@ signature module InputSig<LocationSig Location> {
    * Gets an `id` of `node`. This is used to order the predecessors of a join
    * basic block.
    */
-  bindingset[node]
   int idOfAstNode(AstNode node);
 
   /**
    * Gets an `id` of `scope`. This is used to order the predecessors of a join
    * basic block.
    */
-  bindingset[scope]
   int idOfCfgScope(CfgScope scope);
 }
 
@@ -1008,6 +1006,41 @@ module MakeWithSplitting<
       )
     }
 
+    private module JoinBlockPredecessors {
+      predicate hasIdAndKind(BasicBlocks::JoinPredecessorBasicBlock jbp, int id, int kind) {
+        id = idOfCfgScope(jbp.(BasicBlocks::EntryBasicBlock).getScope()) and
+        kind = 0
+        or
+        not jbp instanceof BasicBlocks::EntryBasicBlock and
+        id = idOfAstNode(jbp.getFirstNode().(AstCfgNode).getAstNode()) and
+        kind = 1
+      }
+
+      string getSplitString(BasicBlocks::JoinPredecessorBasicBlock jbp) {
+        result = jbp.getFirstNode().(AstCfgNode).getSplitsString()
+        or
+        not exists(jbp.getFirstNode().(AstCfgNode).getSplitsString()) and
+        result = ""
+      }
+    }
+
+    /**
+     * Gets the `i`th predecessor of join block `jb`, with respect to some
+     * arbitrary order.
+     */
+    cached
+    BasicBlocks::JoinPredecessorBasicBlock getJoinBlockPredecessor(
+      BasicBlocks::JoinBasicBlock jb, int i
+    ) {
+      result =
+        rank[i + 1](BasicBlocks::JoinPredecessorBasicBlock jbp, int id, int kind |
+          jbp = jb.getAPredecessor() and
+          JoinBlockPredecessors::hasIdAndKind(jbp, id, kind)
+        |
+          jbp order by id, kind, JoinBlockPredecessors::getSplitString(jbp)
+        )
+    }
+
     cached
     module Public {
       /**
@@ -1570,15 +1603,13 @@ module MakeWithSplitting<
       BasicBlock getASuccessor() { result = super.getASuccessor() }
 
       /** Gets an immediate successor of this basic block of a given type, if any. */
-      BasicBlock getASuccessor(SuccessorType t) {
-        result.getFirstNode() = this.getLastNode().getASuccessor(t)
-      }
+      BasicBlock getASuccessor(SuccessorType t) { result = super.getASuccessor(t) }
 
       /** Gets an immediate predecessor of this basic block, if any. */
-      BasicBlock getAPredecessor() { result.getASuccessor() = this }
+      BasicBlock getAPredecessor() { result = super.getAPredecessor() }
 
       /** Gets an immediate predecessor of this basic block of a given type, if any. */
-      BasicBlock getAPredecessor(SuccessorType t) { result.getASuccessor(t) = this }
+      BasicBlock getAPredecessor(SuccessorType t) { result = super.getAPredecessor(t) }
 
       /**
        * Holds if this basic block immediately dominates basic block `bb`.
@@ -1673,38 +1704,6 @@ module MakeWithSplitting<
       ExitBasicBlock() { this.getLastNode() instanceof ExitNode }
     }
 
-    private module JoinBlockPredecessors {
-      predicate hasIdAndKind(JoinPredecessorBasicBlock jbp, int id, int kind) {
-        id = idOfCfgScope(jbp.(EntryBasicBlock).getScope()) and
-        kind = 0
-        or
-        not jbp instanceof EntryBasicBlock and
-        id = idOfAstNode(jbp.getFirstNode().(AstCfgNode).getAstNode()) and
-        kind = 1
-      }
-
-      string getSplitString(JoinPredecessorBasicBlock jbp) {
-        result = jbp.getFirstNode().(AstCfgNode).getSplitsString()
-        or
-        not exists(jbp.getFirstNode().(AstCfgNode).getSplitsString()) and
-        result = ""
-      }
-    }
-
-    /**
-     * Gets the `i`th predecessor of join block `jb`, with respect to some
-     * arbitrary order.
-     */
-    cached
-    JoinPredecessorBasicBlock getJoinBlockPredecessor(JoinBasicBlock jb, int i) {
-      result =
-        rank[i + 1](JoinPredecessorBasicBlock jbp, int id, int kind |
-          jbp = jb.getAPredecessor() and JoinBlockPredecessors::hasIdAndKind(jbp, id, kind)
-        |
-          jbp order by id, kind, JoinBlockPredecessors::getSplitString(jbp)
-        )
-    }
-
     /** A basic block with more than one predecessor. */
     final class JoinBasicBlock extends BasicBlock {
       JoinBasicBlock() { this.getFirstNode().isJoin() }