From 2a5ac8bd2df394366df88e128574f50c9cf6d521 Mon Sep 17 00:00:00 2001
From: Vaibhav Thakkar <vaibhav.thakkar.22.12.99@gmail.com>
Date: Thu, 18 Jul 2024 09:45:23 +0200
Subject: [PATCH] Improve fwd mode for calling fxn with zero/null derivatives

---
 include/clad/Differentiator/CladUtils.h       |  1 +
 lib/Differentiator/BaseForwardModeVisitor.cpp | 17 ++++++--------
 lib/Differentiator/CladUtils.cpp              | 16 ++++++++++++++
 test/FirstDerivative/CallArguments.C          | 22 +++++++++++++++++++
 4 files changed, 46 insertions(+), 10 deletions(-)

diff --git a/include/clad/Differentiator/CladUtils.h b/include/clad/Differentiator/CladUtils.h
index ae8b55813..05899cad7 100644
--- a/include/clad/Differentiator/CladUtils.h
+++ b/include/clad/Differentiator/CladUtils.h
@@ -317,6 +317,7 @@ namespace clad {
     void SetSwitchCaseSubStmt(clang::SwitchCase* SC, clang::Stmt* subStmt);
 
     bool IsLiteral(const clang::Expr* E);
+    bool IsZeroOrNullValue(const clang::Expr* E);
 
     bool IsMemoryFunction(const clang::FunctionDecl* FD);
     bool IsMemoryDeallocationFunction(const clang::FunctionDecl* FD);
diff --git a/lib/Differentiator/BaseForwardModeVisitor.cpp b/lib/Differentiator/BaseForwardModeVisitor.cpp
index 7853205a7..1d39622f6 100644
--- a/lib/Differentiator/BaseForwardModeVisitor.cpp
+++ b/lib/Differentiator/BaseForwardModeVisitor.cpp
@@ -1071,7 +1071,6 @@ StmtDiff BaseForwardModeVisitor::VisitCallExpr(const CallExpr* CE) {
     // Returning the function call and zero derivative
     return StmtDiff(Call, zero);
   }
-
   // Find the built-in derivatives namespace.
   std::string s = std::to_string(m_DerivativeOrder);
   if (m_DerivativeOrder == 1)
@@ -1200,19 +1199,17 @@ StmtDiff BaseForwardModeVisitor::VisitCallExpr(const CallExpr* CE) {
   // FIXME: revert this when this is integrated in the activity analysis pass.
   if (!callDiff) {
     if (!isa<CXXOperatorCallExpr>(CE) && !isa<CXXMemberCallExpr>(CE)) {
-      bool allArgsAreConstantLiterals = true;
+      bool allArgsHaveZeroDerivatives = true;
       for (unsigned i = 0, e = CE->getNumArgs(); i < e; ++i) {
-        const Expr* arg = CE->getArg(i);
-        // if it's of type MaterializeTemporaryExpr, then check its
-        // subexpression.
-        if (const auto* MTE = dyn_cast<MaterializeTemporaryExpr>(arg))
-          arg = clad_compat::GetSubExpr(MTE);
-        if (!arg->isEvaluatable(m_Context)) {
-          allArgsAreConstantLiterals = false;
+        Expr* dArg = diffArgs[i];
+        // If argDiff.expr_dx is nullptr or is a constant 0, then the derivative
+        // of the function call is 0.
+        if (!clad::utils::IsZeroOrNullValue(dArg->IgnoreParenImpCasts())) {
+          allArgsHaveZeroDerivatives = false;
           break;
         }
       }
-      if (allArgsAreConstantLiterals) {
+      if (allArgsHaveZeroDerivatives) {
         Expr* call =
             m_Sema
                 .ActOnCallExpr(getCurrentScope(), Clone(CE->getCallee()),
diff --git a/lib/Differentiator/CladUtils.cpp b/lib/Differentiator/CladUtils.cpp
index 96b35d6aa..d2784a2df 100644
--- a/lib/Differentiator/CladUtils.cpp
+++ b/lib/Differentiator/CladUtils.cpp
@@ -658,6 +658,22 @@ namespace clad {
              isa<GNUNullExpr>(E);
     }
 
+    bool IsZeroOrNullValue(const clang::Expr* E) {
+      if (!E)
+        return true;
+      if (isa<CXXNullPtrLiteralExpr>(E))
+        return true;
+      if (auto* FL = dyn_cast<FloatingLiteral>(E))
+        return FL->getValue().isZero();
+      if (auto* IL = dyn_cast<IntegerLiteral>(E))
+        return IL->getValue() == 0;
+      if (auto* CL = dyn_cast<CharacterLiteral>(E))
+        return CL->getValue() == 0;
+      if (auto* SL = dyn_cast<StringLiteral>(E))
+        return SL->getLength() == 0;
+      return false;
+    }
+
     bool IsMemoryFunction(const clang::FunctionDecl* FD) {
 
 #if CLANG_VERSION_MAJOR > 12
diff --git a/test/FirstDerivative/CallArguments.C b/test/FirstDerivative/CallArguments.C
index 9c543a655..0f2a7b49a 100644
--- a/test/FirstDerivative/CallArguments.C
+++ b/test/FirstDerivative/CallArguments.C
@@ -132,6 +132,25 @@ float f_const_args_func_8(const float x, float y) {
 // CHECK-NEXT: return _t0.pushforward + _t1.pushforward - _d_y;
 // CHECK-NEXT: }
 
+float f_literal_helper(float x, char ch, float* p, float* q) {
+  if (ch == 'a')
+    return x * x;
+  return -x * x;
+}
+
+float f_literal_args_func(float x, float y) {
+  printf("hello world ");
+  return x * f_literal_helper(0.5, 'a', nullptr, nullptr);
+}
+
+// CHECK: float f_literal_args_func_darg0(float x, float y) {
+// CHECK-NEXT: float _d_x = 1;
+// CHECK-NEXT: float _d_y = 0;
+// CHECK-NEXT: printf("hello world ");
+// CHECK-NEXT: float _t0 = f_literal_helper(0.5, 'a', nullptr, nullptr);
+// CHECK-NEXT: return _d_x * _t0 + x * 0.F;
+// CHECK-NEXT: }
+
 extern "C" int printf(const char* fmt, ...);
 int main () { // expected-no-diagnostics
   auto f = clad::differentiate(g, 0);
@@ -165,6 +184,9 @@ int main () { // expected-no-diagnostics
   const float f8x = 1.F;
   printf("f8_darg0=%f\n", f8.execute(f8x,2.F));
   //CHECK-EXEC: f8_darg0=2.000000
+  auto f9 = clad::differentiate(f_literal_args_func, 0);
+  printf("f9_darg0=%.2f\n", f9.execute(1.F,2.F));
+  //CHECK-EXEC: hello world f9_darg0=0.25
 
 // CHECK: clad::ValueAndPushforward<float, float> f_const_helper_pushforward(const float x, const float _d_x) {
 // CHECK-NEXT:     return {x * x, _d_x * x + x * _d_x};