Merge pull request #212 from github/hvitved/ssa/assigns-pred

Add `Ssa::WriteDefinition::assigns/1` predicate

Author: hvitved

ql/src/codeql_ruby/controlflow/CfgNodes.qll

@@ -160,15 +160,15 @@ abstract private class ExprChildMapping extends Expr {
 /** Provides classes for control-flow nodes that wrap AST expressions. */
 module ExprNodes {
   // TODO: Add more classes
-  private class AssignmentExprChildMapping extends ExprChildMapping, Assignment {
+  private class AssignExprChildMapping extends ExprChildMapping, AssignExpr {
     override predicate relevantChild(Expr e) { e = this.getAnOperand() }
   }
 
-  /** A control-flow node that wraps an `Assignment` AST expression. */
-  class AssignmentCfgNode extends ExprCfgNode {
-    override AssignmentExprChildMapping e;
+  /** A control-flow node that wraps an `AssignExpr` AST expression. */
+  class AssignExprCfgNode extends ExprCfgNode {
+    override AssignExprChildMapping e;
 
-    final override Assignment getExpr() { result = ExprCfgNode.super.getExpr() }
+    final override AssignExpr getExpr() { result = ExprCfgNode.super.getExpr() }
 
     /** Gets the LHS of this assignment. */
     final ExprCfgNode getLhs() { e.hasCfgChild(e.getLeftOperand(), this, result) }
@@ -177,11 +177,6 @@ module ExprNodes {
     final ExprCfgNode getRhs() { e.hasCfgChild(e.getRightOperand(), this, result) }
   }
 
-  /** A control-flow node that wraps an `AssignExpr` AST expression. */
-  class AssignExprCfgNode extends AssignmentCfgNode {
-    AssignExprCfgNode() { this.getExpr() instanceof AssignExpr }
-  }
-
   private class OperationExprChildMapping extends ExprChildMapping, Operation {
     override predicate relevantChild(Expr e) { e = this.getAnOperand() }
   }

ql/src/codeql_ruby/dataflow/SSA.qll

@@ -203,6 +203,18 @@ module Ssa {
     /** Gets the underlying write access. */
     final VariableWriteAccess getWriteAccess() { result = write }
 
+    /**
+     * Holds if this SSA definition represents a direct assignment of `value`
+     * to the underlying variable.
+     */
+    predicate assigns(CfgNodes::ExprCfgNode value) {
+      exists(CfgNodes::ExprNodes::AssignExprCfgNode a, BasicBlock bb, int i |
+        this.definesAt(_, bb, i) and
+        a = bb.getNode(i) and
+        value = a.getRhs()
+      )
+    }
+
     final override string toString() { result = Definition.super.toString() }
 
     final override Location getLocation() { result = this.getControlFlowNode().getLocation() }

ql/src/codeql_ruby/dataflow/internal/DataFlowPrivate.qll

@@ -58,13 +58,8 @@ module LocalFlow {
     )
     or
     // Flow from assignment into SSA definition
-    exists(CfgNodes::ExprNodes::AssignmentCfgNode a, BasicBlock bb, int i |
-      def.definesAt(_, bb, i) and
-      a = bb.getNode(i) and
-      a.getExpr() instanceof AssignExpr and
-      nodeFrom.asExpr() = a.getRhs() and
-      nodeTo.(SsaDefinitionNode).getDefinition() = def
-    )
+    def.(Ssa::WriteDefinition).assigns(nodeFrom.asExpr()) and
+    nodeTo.(SsaDefinitionNode).getDefinition() = def
     or
     // Flow from SSA definition to first read
     def = nodeFrom.(SsaDefinitionNode).getDefinition() and