fix performance

Author: erik-krogh

javascript/ql/lib/semmle/javascript/GlobalAccessPaths.qll

@@ -275,9 +275,12 @@ module AccessPath {
      * Either the definition or a use of the SSA variable
      */
     private VarRef getAVariableRef(SsaVariable variable) {
-      result = variable.getAUse()
-      or
-      result = variable.getDefinition().(SsaExplicitDefinition).getDef().getTarget()
+      (
+        result = variable.getAUse()
+        or
+        result = variable.getDefinition().(SsaExplicitDefinition).getDef().getTarget()
+      ) and
+      variable = getARelevantVariableSimple()
     }
 
     /**
@@ -341,13 +344,24 @@ module AccessPath {
       if result = getBaseVar(_) then usedInWrite = true else usedInWrite = false
     }
 
-    /** Gets a variable that is relevant for the computations in the `GetLaterAccess` module. */
-    private SsaVariable getARelevantVariable() {
+    /**
+     * Gets a variable that is relevant for the computations in the `GetLaterAccess` module.
+     * This predicate restricts as much as it can, but without depending on `getAVariableRef`.
+     */
+    pragma[inline]
+    private SsaVariable getARelevantVariableSimple() {
       // The variable might be used where `getLaterBaseAccess()` is called.
       exists(DataFlow::Node node |
         exists(fromRhs(node, _)) and
-        node.asExpr() = getAVariableRef(result)
-      ) and
+        node.asExpr() = result.getAUse()
+      )
+    }
+
+    /**
+     * Gets a variable that is relevant for the computations in the `GetLaterAccess` module.
+     * This predicate depends on `getAVariableRef`, which in turn depends on `getARelevantVariableSimple`.
+     */
+    private SsaVariable getARelevantVariable() {
       // There is a write that writes to the variable.
       getBaseVar(_) = getAVariableRef(result) and
       // There is both a "write" and "read" in the same container of the variable.
@@ -364,7 +378,7 @@ module AccessPath {
         getAVariableRef(var) = baseExpr and
         var = getARelevantVariable() and
         writeNode = write.getWriteNode() and
-        writeNode.getBasicBlock().(ReachableBasicBlock).strictlyDominates(result) and
+        result.getImmediateDominator+() = writeNode.getBasicBlock() and
         // manual magic.
         result = getAnAccessInContainer(getARelevantVariable(), _, false).getBasicBlock()
       )