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include/clad/Differentiator/DiffPlanner.h

@@ -46,7 +46,7 @@ struct DiffRequest {
   clang::CallExpr* CallContext = nullptr;
   /// Args provided to the call to clad::gradient/differentiate.
   const clang::Expr* Args = nullptr;
-  /// Indexes of global args of function as a subset of Args.
+  /// Indexes of global GPU args of function as a subset of Args.
   std::unordered_set<size_t> GlobalArgsIndexes;
   /// Requested differentiation mode, forward or reverse.
   DiffMode Mode = DiffMode::unknown;

include/clad/Differentiator/ReverseModeVisitor.h

@@ -56,7 +56,7 @@ namespace clad {
     /// that will be put immediately in the beginning of derivative function
     /// block.
     Stmts m_Globals;
-    /// Global args of the function.
+    /// Global GPU args of the function.
     std::unordered_set<const clang::ParmVarDecl*> m_GlobalArgs;
     //// A reference to the output parameter of the gradient function.
     clang::Expr* m_Result;

lib/Differentiator/ReverseModeVisitor.cpp

@@ -109,7 +109,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     if (!m_GlobalArgs.empty())
       if (const auto* DRE = dyn_cast<DeclRefExpr>(E))
         if (const auto* PVD = dyn_cast<ParmVarDecl>(DRE->getDecl()))
-          // we need to check whether this param is in global memory of the GPU
+          // we need to check whether this param is in the global memory of the
+          // GPU
           return m_GlobalArgs.find(PVD) != m_GlobalArgs.end();
 
     return false;
@@ -450,6 +451,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     if (m_ExternalSource)
       m_ExternalSource->ActAfterCreatingDerivedFnParams(params);
 
+    // if the function is a global kernel, all its parameters reside in the
+    // global memory of the GPU
     if (m_DiffReq->hasAttr<clang::CUDAGlobalAttr>())
       for (auto param : params)
         m_GlobalArgs.emplace(param);
@@ -601,9 +604,13 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
       m_ExternalSource->ActAfterCreatingDerivedFnParams(params);
 
     m_Derivative->setParams(params);
+    // Match the global arguments of the call to the device function to the
+    // pullback function's parameters.
     if (!m_DiffReq.GlobalArgsIndexes.empty())
       for (auto index : m_DiffReq.GlobalArgsIndexes)
         m_GlobalArgs.emplace(m_Derivative->getParamDecl(index));
+    // If the function is a global kernel, all its parameters reside in the
+    // global memory of the GPU
     else if (m_DiffReq->hasAttr<clang::CUDAGlobalAttr>())
       for (auto param : params)
         m_GlobalArgs.emplace(param);
@@ -1753,6 +1760,9 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
         StmtDiff ArgDiff = Visit(Arg, dfdx());
         CallArgs.push_back(ArgDiff.getExpr());
         if (auto* DRE = dyn_cast<DeclRefExpr>(ArgDiff.getExpr())) {
+          // If the arg is used for differentiation of the function, then we
+          // cannot free it in the end as it's the result to be returned to the
+          // user.
           if (m_ParamVarsWithDiff.find(DRE->getDecl()) ==
               m_ParamVarsWithDiff.end())
             DerivedCallArgs.push_back(ArgDiff.getExpr_dx());
@@ -2024,7 +2034,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
         pullbackRequest.Function = FD;
 
         // Mark the indexes of the global args. Necessary if the argument of the
-        // call has a different name than the function's signature argument.
+        // call has a different name than the function's signature parameter.
         if (!m_GlobalArgs.empty())
           for (size_t i = 0; i < pullbackCallArgs.size(); i++)
             if (auto* DRE = dyn_cast<DeclRefExpr>(pullbackCallArgs[i]))