Avoid creation of local derivative of const parameter (#1131)

Closes #1130.
vgvassilev · Nov 3, 2024 · a50432f · a50432f
1 parent effbb7b
commit a50432f
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diff --git a/include/clad/Differentiator/ReverseModeVisitor.h b/include/clad/Differentiator/ReverseModeVisitor.h
@@ -425,6 +425,7 @@ namespace clad {
     StmtDiff
     VisitMaterializeTemporaryExpr(const clang::MaterializeTemporaryExpr* MTE);
     StmtDiff VisitCXXStaticCastExpr(const clang::CXXStaticCastExpr* SCE);
+    StmtDiff VisitCXXConstCastExpr(const clang::CXXConstCastExpr* CCE);
     StmtDiff VisitSwitchStmt(const clang::SwitchStmt* SS);
     StmtDiff VisitCaseStmt(const clang::CaseStmt* CS);
     StmtDiff VisitDefaultStmt(const clang::DefaultStmt* DS);

diff --git a/lib/Differentiator/ReverseModeVisitor.cpp b/lib/Differentiator/ReverseModeVisitor.cpp
@@ -706,6 +706,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
           i == m_DiffReq->getNumParams() - 1)
         continue;
       auto VDDerivedType = param->getType();
+      if (VDDerivedType.isConstQualified())
+        continue;
       // We cannot initialize derived variable for pointer types because
       // we do not know the correct size.
       if (utils::isArrayOrPointerType(VDDerivedType))
@@ -4576,6 +4578,12 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     return subExprDiff;
   }
 
+  StmtDiff ReverseModeVisitor::VisitCXXConstCastExpr(
+      const clang::CXXConstCastExpr* CCE) {
+    StmtDiff subExprDiff = Visit(CCE->getSubExpr(), dfdx());
+    return {Clone(CCE), subExprDiff.getExpr_dx()};
+  }
+
   clang::QualType ReverseModeVisitor::ComputeAdjointType(clang::QualType T) {
     if (T->isReferenceType()) {
       QualType TValueType = utils::GetValueType(T);

diff --git a/test/Gradient/Assignments.C b/test/Gradient/Assignments.C
@@ -819,6 +819,62 @@ double f23(double x, double y) {
 //CHECK-NEXT:     }
 //CHECK-NEXT: }
 
+double constVal(double y, const double x) {
+  const double z = y;
+  y *= z;
+  return y * x;
+}
+
+//CHECK: void constVal_grad_0(double y, const double x, double *_d_y) {
+//CHECK-NEXT:    double _d_z = 0.;
+//CHECK-NEXT:    const double z = y;
+//CHECK-NEXT:    double _t0 = y;
+//CHECK-NEXT:    y *= z;
+//CHECK-NEXT:    *_d_y += 1 * x;
+//CHECK-NEXT:    {
+//CHECK-NEXT:        y = _t0;
+//CHECK-NEXT:        double _r_d0 = *_d_y;
+//CHECK-NEXT:        *_d_y = 0.;
+//CHECK-NEXT:        *_d_y += _r_d0 * z;
+//CHECK-NEXT:        _d_z += y * _r_d0;
+//CHECK-NEXT:    }
+//CHECK-NEXT:    *_d_y += _d_z;
+//CHECK-NEXT:}
+
+double constValConstCast(double y, const double x) {
+  double z = const_cast<double&>(x);
+  y *= z;
+  return y * x;
+}
+
+// CHECK: void constValConstCast_grad(double y, const double x, double *_d_y, double *_d_x) {
+//CHECK-NEXT:    double _d_z = 0.;
+//CHECK-NEXT:    double z = const_cast<double &>(x);
+//CHECK-NEXT:    double _t0 = y;
+//CHECK-NEXT:    y *= z;
+//CHECK-NEXT:    {
+//CHECK-NEXT:        *_d_y += 1 * x;
+//CHECK-NEXT:        *_d_x += y * 1;
+//CHECK-NEXT:    }
+//CHECK-NEXT:    {
+//CHECK-NEXT:        y = _t0;
+//CHECK-NEXT:        double _r_d0 = *_d_y;
+//CHECK-NEXT:        *_d_y = 0.;
+//CHECK-NEXT:        *_d_y += _r_d0 * z;
+//CHECK-NEXT:        _d_z += y * _r_d0;
+//CHECK-NEXT:    }
+//CHECK-NEXT:    *_d_x += _d_z;
+//CHECK-NEXT:}
+
+double constValInput(const double x) {
+  return x;
+}
+
+//CHECK: void constValInput_grad(const double x, double *_d_x) {
+//CHECK-NEXT:    *_d_x += 1;
+//CHECK-NEXT:}
+
+
 #define TEST(F, x, y)                                                          \
   {                                                                            \
     result[0] = 0;                                                             \
@@ -884,4 +940,19 @@ int main() {
   TEST(f21, 6, 4); // CHECK-EXEC: {1.00, 0.00}
   TEST(f22, 6, 4); // CHECK-EXEC: {0.00, 0.00}
   TEST(f23, 7, 5); // CHECK-EXEC: {1.00, 1.00}
+
+  auto const_test = clad::gradient(constVal, "y");
+  double const_test_result = 0;
+  const_test.execute(3, 4, &const_test_result);
+  printf("%.2f\n", const_test_result); // CHECK-EXEC: 24.00
+
+  auto const_test_const_cast = clad::gradient(constValConstCast);
+  double const_test_const_cast_result[2] = {0};
+  const_test_const_cast.execute(3, 4, &const_test_const_cast_result[0], &const_test_const_cast_result[1]);
+  printf("{%.2f, %.2f}\n", const_test_const_cast_result[0], const_test_const_cast_result[1]); // CHECK-EXEC: {16.00, 24.00}
+
+  auto const_test_input = clad::gradient(constValInput);
+  double const_test_input_result = 0;
+  const_test_input.execute(3, &const_test_input_result);
+  printf("%.2f\n", const_test_input_result); // CHECK-EXEC: 1.00
 }