From ac24906f915addd882c47b52635e334dc7e68ba7 Mon Sep 17 00:00:00 2001
From: Rohan Julka <rohanjulka19@gmail.com>
Date: Wed, 19 Jun 2024 22:58:04 +0100
Subject: [PATCH] Add validation to prevent error on empty if block

---
 .../clad/Differentiator/ReverseModeVisitor.h  |  4 +-
 test/Gradient/Gradients.C                     | 94 +++++++++++++++++--
 2 files changed, 89 insertions(+), 9 deletions(-)

diff --git a/include/clad/Differentiator/ReverseModeVisitor.h b/include/clad/Differentiator/ReverseModeVisitor.h
index 7475a383b..11673bb63 100644
--- a/include/clad/Differentiator/ReverseModeVisitor.h
+++ b/include/clad/Differentiator/ReverseModeVisitor.h
@@ -405,7 +405,9 @@ namespace clad {
         const clang::SubstNonTypeTemplateParmExpr* NTTP);
     StmtDiff
     VisitCXXNullPtrLiteralExpr(const clang::CXXNullPtrLiteralExpr* NPE);
-    StmtDiff VisitNullStmt(const clang::NullStmt* NS) { return StmtDiff{}; };
+    StmtDiff VisitNullStmt(const clang::NullStmt* NS) {
+      return StmtDiff{Clone(NS), Clone(NS)};
+    };
     static DeclDiff<clang::StaticAssertDecl>
     DifferentiateStaticAssertDecl(const clang::StaticAssertDecl* SAD);
 
diff --git a/test/Gradient/Gradients.C b/test/Gradient/Gradients.C
index 1362b268a..6c09c4038 100644
--- a/test/Gradient/Gradients.C
+++ b/test/Gradient/Gradients.C
@@ -832,16 +832,20 @@ double fn_cond_init(double x) {
 //CHECK-NEXT:          }
 
 double fn_null_stmts(double x) {
-    ;;;;;;;;;;;;;;;;;
-    ;;;;;return x;;;;
-    ;;;;;;;;;;;;;;;;;
+  return x;
+  ;
+  ;
 } // = x
 
-//CHECK:               void fn_null_stmts_grad(double x, double *_d_x) {
-//CHECK-NEXT:              goto _label0;
-//CHECK-NEXT:            _label0:
-//CHECK-NEXT:              *_d_x += 1;
-//CHECK-NEXT:          }
+//CHECK: void fn_null_stmts_grad(double x, double *_d_x) {
+//CHECK-NEXT:    goto _label0;
+//CHECK-NEXT:    ;
+//CHECK-NEXT:    ;
+//CHECK-NEXT:    ;
+//CHECK-NEXT:    ;
+//CHECK-NEXT:  _label0:
+//CHECK-NEXT:    *_d_x += 1;
+//CHECK-NEXT:}
 
 double fn_const_cond_op(double x) {
   return x + (x > 0 ? 1.0 : 0.0);
@@ -853,6 +857,73 @@ double fn_const_cond_op(double x) {
 //CHECK-NEXT:              *_d_x += 1;
 //CHECK-NEXT:          }
 
+
+double fn_empty_if_block(double x) {
+  double res = 0;
+  if (x > 0)
+    ;
+  return res;
+}
+
+//CHECK:void fn_empty_if_block_grad(double x, double *_d_x) {
+//CHECK-NEXT:    double _d_res = 0;
+//CHECK-NEXT:    bool _cond0;
+//CHECK-NEXT:    double res = 0;
+//CHECK-NEXT:    {
+//CHECK-NEXT:        _cond0 = x > 0;
+//CHECK-NEXT:        if (_cond0)
+//CHECK-NEXT:            ;
+//CHECK-NEXT:    }
+//CHECK-NEXT:    _d_res += 1;
+//CHECK-NEXT:    if (_cond0)
+//CHECK-NEXT:        ;
+//CHECK-NEXT:}
+
+double fn_empty_if_else(double x) {
+  double res = 0;
+  if ((res = 0))
+    ; else {
+    res = 5 * x;
+    }
+  return res;
+}
+
+//CHECK: void fn_empty_if_else_grad(double x, double *_d_x) {
+//CHECK-NEXT:    double _d_res = 0;
+//CHECK-NEXT:    double _t0;
+//CHECK-NEXT:    bool _cond0;
+//CHECK-NEXT:    double _t1;
+//CHECK-NEXT:    double res = 0;
+//CHECK-NEXT:    {
+//CHECK-NEXT:        _t0 = res;
+//CHECK-NEXT:        _cond0 = (res = 0);
+//CHECK-NEXT:        if (_cond0)
+//CHECK-NEXT:            ;
+//CHECK-NEXT:        else {
+//CHECK-NEXT:            _t1 = res;
+//CHECK-NEXT:            res = 5 * x;
+//CHECK-NEXT:        }
+//CHECK-NEXT:    }
+//CHECK-NEXT:    _d_res += 1;
+//CHECK-NEXT:    {
+//CHECK-NEXT:        if (_cond0)
+//CHECK-NEXT:            ;
+//CHECK-NEXT:        else {
+//CHECK-NEXT:            {
+//CHECK-NEXT:                res = _t1;
+//CHECK-NEXT:                double _r_d1 = _d_res;
+//CHECK-NEXT:                _d_res -= _r_d1;
+//CHECK-NEXT:                *_d_x += 5 * _r_d1;
+//CHECK-NEXT:            }
+//CHECK-NEXT:        }
+//CHECK-NEXT:        {
+//CHECK-NEXT:            res = _t0;
+//CHECK-NEXT:            double _r_d0 = _d_res;
+//CHECK-NEXT:            _d_res -= _r_d0;
+//CHECK-NEXT:        }
+//CHECK-NEXT:    }
+//CHECK-NEXT:}
+
 #define TEST(F, x, y)                                                          \
   {                                                                            \
     result[0] = 0;                                                             \
@@ -928,4 +999,11 @@ int main() {
 
   INIT_GRADIENT(fn_const_cond_op);
   TEST_GRADIENT(fn_const_cond_op, /*numOfDerivativeArgs=*/1, 0, &dx); // CHECK-EXEC: 1.00
+
+  INIT_GRADIENT(fn_empty_if_block);
+  TEST_GRADIENT(fn_empty_if_block, /*numOfDerivativeArgs=*/1, 0, &dx); // CHECK-EXEC: 0.00
+
+  INIT_GRADIENT(fn_empty_if_else);
+  TEST_GRADIENT(fn_empty_if_else, /*numOfDerivativeArgs=*/1, 1, &dx); // CHECK-EXEC: 5.00
+
 }