CPP: Resolve performance issue in CastArrayPointerArithmetic.ql's 'introducesNewField' predicate.

geoffw0 · geoffw0 · commit ce29047840b3 · 2019-06-17T16:33:48.000+01:00
diff --git a/cpp/ql/src/Likely Bugs/Conversion/CastArrayPointerArithmetic.ql b/cpp/ql/src/Likely Bugs/Conversion/CastArrayPointerArithmetic.ql
@@ -43,11 +43,15 @@ class CastToPointerArithFlow extends DataFlow::Configuration {
   }
 }
 
+/**
+ * `derived` has a (possibly indirect) base class of `base`, and `derived`
+ * introduces at least one new field that isn't in a base class.
+ */
 predicate introducesNewField(Class derived, Class base) {
-  derived.getABaseClass+() = base and
   (
     exists(Field f |
-      f.getDeclaringType() = derived
+      f.getDeclaringType() = derived and
+      derived.getABaseClass+() = base
     ) or
     introducesNewField(derived.getABaseClass(), base)
   )

Original file line number	Diff line number	Diff line change
`@@ -43,11 +43,15 @@ class CastToPointerArithFlow extends DataFlow::Configuration {`
`43`	`43`	`}`
`44`	`44`	`}`
`45`	`45`
	`46`	`+/**`
	`47`	+ * `derived` has a (possibly indirect) base class of `base`, and `derived`
	`48`	`+ * introduces at least one new field that isn't in a base class.`
	`49`	`+ */`
`46`	`50`	`predicate introducesNewField(Class derived, Class base) {`
`47`		`- derived.getABaseClass+() = base and`
`48`	`51`	`(`
`49`	`52`	`exists(Field f \|`
`50`		`- f.getDeclaringType() = derived`
	`53`	`+ f.getDeclaringType() = derived and`
	`54`	`+ derived.getABaseClass+() = base`
`51`	`55`	`) or`
`52`	`56`	`introducesNewField(derived.getABaseClass(), base)`
`53`	`57`	`)`