C#: Use Gvn comparison instead of StructuralComparisonConfiguration in MissedTernaryOpportunity.

Author: michaelnebel

csharp/ql/src/Language Abuse/MissedTernaryOpportunity.ql

@@ -12,25 +12,12 @@
 import csharp
 import semmle.code.csharp.commons.StructuralComparison
 
-class StructuralComparisonConfig extends StructuralComparisonConfiguration {
-  StructuralComparisonConfig() { this = "MissedTernaryOpportunity" }
-
-  override predicate candidate(ControlFlowElement x, ControlFlowElement y) {
-    exists(IfStmt is, AssignExpr ae1 |
-      ae1 = is.getThen().stripSingletonBlocks().(ExprStmt).getExpr()
-    |
-      x = ae1.getLValue() and
-      exists(AssignExpr ae2 | ae2 = is.getElse().stripSingletonBlocks().(ExprStmt).getExpr() |
-        y = ae2.getLValue()
-      )
-    )
-  }
+private Expr getAssignedExpr(Stmt stmt) {
+  result = stmt.stripSingletonBlocks().(ExprStmt).getExpr().(AssignExpr).getLValue()
+}
 
-  IfStmt getIfStmt() {
-    exists(AssignExpr ae | ae = result.getThen().stripSingletonBlocks().(ExprStmt).getExpr() |
-      same(ae.getLValue(), _)
-    )
-  }
+private predicate ifStmt(IfStmt is) {
+  sameGvn(getAssignedExpr(is.getThen()), getAssignedExpr(is.getElse()))
 }
 
 from IfStmt is, string what
@@ -40,10 +27,8 @@ where
     is.getElse().stripSingletonBlocks() instanceof ReturnStmt and
     what = "return"
     or
-    exists(StructuralComparisonConfig c |
-      is = c.getIfStmt() and
-      what = "write to the same variable"
-    )
+    ifStmt(is) and
+    what = "write to the same variable"
   ) and
   not exists(IfStmt other | is = other.getElse())
 select is,