Add support for C-style memory alloc and free in reverse mode AD

include/clad/Differentiator/CladUtils.h

@@ -328,6 +328,9 @@ namespace clad {
     void SetSwitchCaseSubStmt(clang::SwitchCase* SC, clang::Stmt* subStmt);
 
     bool IsLiteral(const clang::Expr* E);
+
+    bool IsMemoryAllocationFunction(const clang::FunctionDecl* FD);
+    bool IsMemoryDeallocationFunction(const clang::FunctionDecl* FD);
     } // namespace utils
     } // namespace clad
 

lib/Differentiator/CladUtils.cpp

@@ -641,5 +641,21 @@ namespace clad {
              isa<ObjCBoolLiteralExpr>(E) || isa<CXXBoolLiteralExpr>(E) ||
              isa<GNUNullExpr>(E);
     }
+
+    bool IsMemoryAllocationFunction(const clang::FunctionDecl* FD) {
+      if (FD->getNameAsString() == "malloc")
+        return true;
+      if (FD->getNameAsString() == "calloc")
+        return true;
+      if (FD->getNameAsString() == "realloc")
+        return true;
+      return false;
+    }
+
+    bool IsMemoryDeallocationFunction(const clang::FunctionDecl* FD) {
+      if (FD->getNameAsString() == "free")
+        return true;
+      return false;
+    }
   } // namespace utils
 } // namespace clad

lib/Differentiator/ReverseModeVisitor.cpp

@@ -1441,6 +1441,48 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     // Stores tape decl and pushes for multiarg numerically differentiated
     // calls.
     llvm::SmallVector<Stmt*, 16> NumericalDiffMultiArg{};
+
+    // For calls to C-style memory allocation functions, we do not need to
+    // differentiate the call. We just need to visit the arguments to the
+    // function.
+    if (utils::IsMemoryAllocationFunction(FD)) {
+      for (const Expr* Arg : CE->arguments()) {
+        StmtDiff ArgDiff = Visit(Arg, dfdx());
+        CallArgs.push_back(ArgDiff.getExpr());
+      }
+      Expr* call =
+          m_Sema
+              .ActOnCallExpr(getCurrentScope(), Clone(CE->getCallee()), noLoc,
+                             llvm::MutableArrayRef<Expr*>(CallArgs), noLoc)
+              .get();
+      return StmtDiff(call, call);
+    }
+    // For calls to C-style memory deallocation functions, we do not need to
+    // differentiate the call. We just need to visit the arguments to the
+    // function. Also, don't add any statements either in forward or reverse
+    // pass. Instead, add it in m_DeallocExprs.
+    if (utils::IsMemoryDeallocationFunction(FD)) {
+      for (const Expr* Arg : CE->arguments()) {
+        StmtDiff ArgDiff = Visit(Arg, dfdx());
+        CallArgs.push_back(ArgDiff.getExpr());
+        DerivedCallArgs.push_back(ArgDiff.getExpr_dx());
+      }
+      Expr* call =
+          m_Sema
+              .ActOnCallExpr(getCurrentScope(), Clone(CE->getCallee()), noLoc,
+                             llvm::MutableArrayRef<Expr*>(CallArgs), noLoc)
+              .get();
+      Expr* call_dx =
+          m_Sema
+              .ActOnCallExpr(getCurrentScope(), Clone(CE->getCallee()), noLoc,
+                             llvm::MutableArrayRef<Expr*>(DerivedCallArgs),
+                             noLoc)
+              .get();
+      m_DeallocExprs.push_back(call);
+      m_DeallocExprs.push_back(call_dx);
+      return StmtDiff();
+    }
+
     // If the result does not depend on the result of the call, just clone
     // the call and visit arguments (since they may contain side-effects like
     // f(x = y))

test/Gradient/Pointers.C

@@ -430,6 +430,38 @@ double structPointer (double x) {
 // CHECK-NEXT:     delete _d_t;
 // CHECK-NEXT: }
 
+double cStyleMemoryAlloc(double x, size_t n) {
+  T* t = (T*)malloc(n * sizeof(T));
+  t->x = x;
+  double res = t->x;
+  free(t);
+  return res;
+}
+
+// CHECK: void cStyleMemoryAlloc_grad_0(double x, size_t n, clad::array_ref<double> _d_x) {
+// CHECK-NEXT:     size_t _d_n = 0;
+// CHECK-NEXT:     T *_d_t = 0;
+// CHECK-NEXT:     double _t0;
+// CHECK-NEXT:     double _d_res = 0;
+// CHECK-NEXT:     _d_t = (T *)malloc(n * sizeof(T));
+// CHECK-NEXT:     T *t = (T *)malloc(n * sizeof(T));
+// CHECK-NEXT:     _t0 = t->x;
+// CHECK-NEXT:     t->x = x;
+// CHECK-NEXT:     double res = t->x;
+// CHECK-NEXT:     goto _label0;
+// CHECK-NEXT:   _label0:
+// CHECK-NEXT:     _d_res += 1;
+// CHECK-NEXT:     _d_t->x += _d_res;
+// CHECK-NEXT:     {
+// CHECK-NEXT:         t->x = _t0;
+// CHECK-NEXT:         double _r_d0 = _d_t->x;
+// CHECK-NEXT:         _d_t->x -= _r_d0;
+// CHECK-NEXT:         * _d_x += _r_d0;
+// CHECK-NEXT:     }
+// CHECK-NEXT:     free(t);
+// CHECK-NEXT:     free(_d_t);
+// CHECK-NEXT: }
+
 #define NON_MEM_FN_TEST(var)\
 res[0]=0;\
 var.execute(5,res);\
@@ -533,4 +565,10 @@ int main() {
   auto d_structPointer = clad::gradient(structPointer);
   double d_x = 0;
   d_structPointer.execute(5, &d_x);
+  printf("%.2f\n", d_x); // CHECK-EXEC: 1.00
+
+  auto d_cStyleMemoryAlloc = clad::gradient(cStyleMemoryAlloc, "x");
+  d_x = 0;
+  d_cStyleMemoryAlloc.execute(5, 7, &d_x);
+  printf("%.2f\n", d_x); // CHECK-EXEC: 1.00
 }