Adding check for name collisions in DifferentiateVarDecl

lib/Differentiator/BaseForwardModeVisitor.cpp

@@ -1499,6 +1499,27 @@ BaseForwardModeVisitor::DifferentiateVarDecl(const VarDecl* VD,
       VD->getType(), "_d_" + VD->getNameAsString(), initDiff.getExpr_dx(),
       VD->isDirectInit(), nullptr, VD->getInitStyle());
   m_Variables.emplace(VDClone, BuildDeclRef(VDDerived));
+  // Check if decl's name is the same as before. The name may be changed
+  // if decl name collides with something in the derivative body.
+  // This can happen in rare cases, e.g. when the original function
+  // has both y and _d_y (here _d_y collides with the name produced by
+  // the derivation process), e.g.
+  // double f(double x) {
+  //   double y = x;
+  //   double _d_y = x;
+  // }
+  // ->
+  // double f_darg0(double x) {
+  //   double _d_x = 1;
+  //   double _d_y = _d_x; // produced as a derivative for y
+  //   double y = x;
+  //   double _d__d_y = _d_x;
+  //   double _d_y = x; // copied from original funcion, collides with
+  //   _d_y
+  // }
+
+  if (VDClone->getDeclName() != VD->getDeclName())
+    m_DeclReplacements[VD] = VDClone;
   return DeclDiff<VarDecl>(VDClone, VDDerived);
 }
 
@@ -1544,26 +1565,6 @@ StmtDiff BaseForwardModeVisitor::VisitDeclStmt(const DeclStmt* DS) {
   for (auto D : DS->decls()) {
     if (auto VD = dyn_cast<VarDecl>(D)) {
       DeclDiff<VarDecl> VDDiff = DifferentiateVarDecl(VD);
-      // Check if decl's name is the same as before. The name may be changed
-      // if decl name collides with something in the derivative body.
-      // This can happen in rare cases, e.g. when the original function
-      // has both y and _d_y (here _d_y collides with the name produced by
-      // the derivation process), e.g.
-      // double f(double x) {
-      //   double y = x;
-      //   double _d_y = x;
-      // }
-      // ->
-      // double f_darg0(double x) {
-      //   double _d_x = 1;
-      //   double _d_y = _d_x; // produced as a derivative for y
-      //   double y = x;
-      //   double _d__d_y = _d_x;
-      //   double _d_y = x; // copied from original funcion, collides with
-      //   _d_y
-      // }
-      if (VDDiff.getDecl()->getDeclName() != VD->getDeclName())
-        m_DeclReplacements[VD] = VDDiff.getDecl();
       decls.push_back(VDDiff.getDecl());
       declsDiff.push_back(VDDiff.getDecl_dx());
     } else if (auto* SAD = dyn_cast<StaticAssertDecl>(D)) {