From 71ca82a3383cbef1fc6e6edeaee1e61632c225ce Mon Sep 17 00:00:00 2001
From: Atell Krasnopolski <delta_atell@protonmail.com>
Date: Sat, 21 Sep 2024 22:32:27 +0200
Subject: [PATCH] Fix some cases of `std::vector::push_back` in the rvs mode

Fixes: #1071
---
 include/clad/Differentiator/STLBuiltins.h | 16 +++++++++-
 test/Gradient/STLCustomDerivatives.C      | 39 +++++++++++++++++++++++
 2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/include/clad/Differentiator/STLBuiltins.h b/include/clad/Differentiator/STLBuiltins.h
index 744bdff38..40b562dc4 100644
--- a/include/clad/Differentiator/STLBuiltins.h
+++ b/include/clad/Differentiator/STLBuiltins.h
@@ -392,13 +392,27 @@ size_pushforward(const ::std::array<T, N>* a,
 // vector reverse mode
 // more can be found in tests: test/Gradient/STLCustomDerivatives.C
 
+template <typename T, typename U, typename pU>
+void push_back_reverse_forw(::std::vector<T>* v, U val, ::std::vector<T>* d_v,
+                            pU /*d_val*/) {
+  v->push_back(val);
+  d_v->push_back(0);
+}
+
 template <typename T, typename U>
 void push_back_reverse_forw(::std::vector<T>* v, U val, ::std::vector<T>* d_v,
-                            U d_val) {
+                            U /*d_val*/) {
   v->push_back(val);
   d_v->push_back(0);
 }
 
+template <typename T, typename U, typename pU>
+void push_back_pullback(::std::vector<T>* v, U val, ::std::vector<T>* d_v,
+                        pU* d_val) {
+  *d_val += d_v->back();
+  d_v->pop_back();
+}
+
 template <typename T, typename U>
 void push_back_pullback(::std::vector<T>* v, U val, ::std::vector<T>* d_v,
                         U* d_val) {
diff --git a/test/Gradient/STLCustomDerivatives.C b/test/Gradient/STLCustomDerivatives.C
index f5739109f..adb1981cd 100644
--- a/test/Gradient/STLCustomDerivatives.C
+++ b/test/Gradient/STLCustomDerivatives.C
@@ -177,6 +177,13 @@ double fn20(double x, double y) {
     return res; // 11x+y
 }
 
+double fn21(double x, double y) {
+  std::vector<double> a;
+  a.push_back(0);
+  a[0] = x*x;
+  return a[0];
+}
+
 int main() {
     double d_i, d_j;
     INIT_GRADIENT(fn10);
@@ -190,6 +197,7 @@ int main() {
     INIT_GRADIENT(fn18);
     INIT_GRADIENT(fn19);
     INIT_GRADIENT(fn20);
+    INIT_GRADIENT(fn21);
 
     TEST_GRADIENT(fn10, /*numOfDerivativeArgs=*/2, 3, 5, &d_i, &d_j);  // CHECK-EXEC: {1.00, 1.00}
     TEST_GRADIENT(fn11, /*numOfDerivativeArgs=*/2, 3, 5, &d_i, &d_j);  // CHECK-EXEC: {2.00, 1.00}
@@ -202,6 +210,7 @@ int main() {
     TEST_GRADIENT(fn18, /*numOfDerivativeArgs=*/2, 3, 4, &d_i, &d_j);  // CHECK-EXEC: {2.00, 0.00}
     TEST_GRADIENT(fn19, /*numOfDerivativeArgs=*/2, 3, 4, &d_i, &d_j);  // CHECK-EXEC: {3.00, 2.00}
     TEST_GRADIENT(fn20, /*numOfDerivativeArgs=*/2, 3, 4, &d_i, &d_j);  // CHECK-EXEC: {11.00, 1.00}
+    TEST_GRADIENT(fn21, /*numOfDerivativeArgs=*/2, 3, 4, &d_i, &d_j);  // CHECK-EXEC: {6.00, 0.00}
 }
 
 // CHECK: void fn10_grad(double u, double v, double *_d_u, double *_d_v) {
@@ -841,3 +850,33 @@ int main() {
 // CHECK-NEXT:              {{.*}}reserve_pullback(&_t0, 10, &_d_v, &_r0);
 // CHECK-NEXT:          }
 // CHECK-NEXT:      }
+
+// CHECK:      void fn21_grad(double x, double y, double *_d_x, double *_d_y) {
+// CHECK-NEXT:          std::vector<double> _d_a({});
+// CHECK-NEXT:          std::vector<double> a;
+// CHECK-NEXT:          std::vector<double> _t0 = a;
+// CHECK-NEXT:          {{.*}}push_back_reverse_forw(&a, 0{{.*}}, &_d_a, _r0);
+// CHECK-NEXT:          std::vector<double> _t1 = a;
+// CHECK-NEXT:          {{.*}}ValueAndAdjoint<double &, double &> _t2 = {{.*}}operator_subscript_reverse_forw(&a, 0, &_d_a, _r1);
+// CHECK-NEXT:          double _t3 = _t2.value;
+// CHECK-NEXT:          _t2.value = x * x;
+// CHECK-NEXT:          std::vector<double> _t4 = a;
+// CHECK-NEXT:          {{.*}}ValueAndAdjoint<double &, double &> _t5 = {{.*}}operator_subscript_reverse_forw(&a, 0, &_d_a, _r2);
+// CHECK-NEXT:          {
+// CHECK-NEXT:              {{.*}}size_type _r2 = 0{{.*}};
+// CHECK-NEXT:              {{.*}}operator_subscript_pullback(&_t4, 0, 1, &_d_a, &_r2);
+// CHECK-NEXT:          }
+// CHECK-NEXT:          {
+// CHECK-NEXT:              _t2.value = _t3;
+// CHECK-NEXT:              double _r_d0 = _t2.adjoint;
+// CHECK-NEXT:              _t2.adjoint = 0{{.*}};
+// CHECK-NEXT:              *_d_x += _r_d0 * x;
+// CHECK-NEXT:              *_d_x += x * _r_d0;
+// CHECK-NEXT:              {{.*}}size_type _r1 = 0{{.*}};
+// CHECK-NEXT:              {{.*}}operator_subscript_pullback(&_t1, 0, 0{{.*}}, &_d_a, &_r1);
+// CHECK-NEXT:          }
+// CHECK-NEXT:          {
+// CHECK-NEXT:              {{.*}}value_type _r0 = 0.;
+// CHECK-NEXT:              {{.*}}push_back_pullback(&_t0, 0{{.*}}, &_d_a, &_r0);
+// CHECK-NEXT:          }
+// CHECK-NEXT:      }