[mlir][acc] Check legality of symbols in acc regions (#167957)

This PR adds a new utility function to check whether symbols used in
OpenACC regions are legal for offloading. Functions must be marked with
`acc routine` or be built-in intrinsics. Global symbols must be marked
with `acc declare`.

The utility is designed to be extensible, and the OpenACCSupport
analysis has been updated to allow handling of additional symbols that
do not necessarily use OpenACC attributes but are marked in a way that
still guarantees the symbol will be available when offloading. For
example, in the Flang implementation, CUF attributes can be validated as
legal symbols.

Author: razvanlupusoru

mlir/include/mlir/Dialect/OpenACC/Analysis/OpenACCSupport.h

@@ -58,8 +58,10 @@
 namespace mlir {
 namespace acc {
 
-// Forward declaration for RecipeKind enum
+// Forward declarations
 enum class RecipeKind : uint32_t;
+bool isValidSymbolUse(Operation *user, SymbolRefAttr symbol,
+                      Operation **definingOpPtr);
 
 namespace detail {
 /// This class contains internal trait classes used by OpenACCSupport.
@@ -79,11 +81,27 @@ struct OpenACCSupportTraits {
 
     // Used to report a case that is not supported by the implementation.
     virtual InFlightDiagnostic emitNYI(Location loc, const Twine &message) = 0;
+
+    /// Check if a symbol use is valid for use in an OpenACC region.
+    virtual bool isValidSymbolUse(Operation *user, SymbolRefAttr symbol,
+                                  Operation **definingOpPtr) = 0;
   };
 
+  /// SFINAE helpers to detect if implementation has optional methods
+  template <typename ImplT, typename... Args>
+  using isValidSymbolUse_t =
+      decltype(std::declval<ImplT>().isValidSymbolUse(std::declval<Args>()...));
+
+  template <typename ImplT>
+  using has_isValidSymbolUse =
+      llvm::is_detected<isValidSymbolUse_t, ImplT, Operation *, SymbolRefAttr,
+                        Operation **>;
+
   /// This class wraps a concrete OpenACCSupport implementation and forwards
   /// interface calls to it. This provides type erasure, allowing different
   /// implementation types to be used interchangeably without inheritance.
+  /// Methods can be optionally implemented; if not present, default behavior
+  /// is used.
   template <typename ImplT>
   class Model final : public Concept {
   public:
@@ -102,6 +120,14 @@ struct OpenACCSupportTraits {
       return impl.emitNYI(loc, message);
     }
 
+    bool isValidSymbolUse(Operation *user, SymbolRefAttr symbol,
+                          Operation **definingOpPtr) final {
+      if constexpr (has_isValidSymbolUse<ImplT>::value)
+        return impl.isValidSymbolUse(user, symbol, definingOpPtr);
+      else
+        return acc::isValidSymbolUse(user, symbol, definingOpPtr);
+    }
+
   private:
     ImplT impl;
   };
@@ -154,6 +180,15 @@ class OpenACCSupport {
   ///         unsupported case.
   InFlightDiagnostic emitNYI(Location loc, const Twine &message);
 
+  /// Check if a symbol use is valid for use in an OpenACC region.
+  ///
+  /// \param user The operation using the symbol.
+  /// \param symbol The symbol reference being used.
+  /// \param definingOpPtr Optional output parameter to receive the defining op.
+  /// \return true if the symbol use is valid, false otherwise.
+  bool isValidSymbolUse(Operation *user, SymbolRefAttr symbol,
+                        Operation **definingOpPtr = nullptr);
+
   /// Signal that this analysis should always be preserved so that
   /// underlying implementation registration is not lost.
   bool isInvalidated(const AnalysisManager::PreservedAnalyses &pa) {

mlir/include/mlir/Dialect/OpenACC/OpenACCUtils.h

@@ -52,6 +52,16 @@ std::string getRecipeName(mlir::acc::RecipeKind kind, mlir::Type type);
 // base `array` from an operation that only accesses a subarray.
 mlir::Value getBaseEntity(mlir::Value val);
 
+/// Check if a symbol use is valid for use in an OpenACC region.
+/// This includes looking for various attributes such as `acc.routine_info`
+/// and `acc.declare` attributes.
+/// \param user The operation using the symbol
+/// \param symbol The symbol reference being used
+/// \param definingOpPtr Optional output parameter to receive the defining op
+/// \return true if the symbol use is valid, false otherwise
+bool isValidSymbolUse(mlir::Operation *user, mlir::SymbolRefAttr symbol,
+                      mlir::Operation **definingOpPtr = nullptr);
+
 } // namespace acc
 } // namespace mlir
 

mlir/lib/Dialect/OpenACC/Analysis/OpenACCSupport.cpp

@@ -41,5 +41,12 @@ InFlightDiagnostic OpenACCSupport::emitNYI(Location loc, const Twine &message) {
   return mlir::emitError(loc, "not yet implemented: " + message);
 }
 
+bool OpenACCSupport::isValidSymbolUse(Operation *user, SymbolRefAttr symbol,
+                                      Operation **definingOpPtr) {
+  if (impl)
+    return impl->isValidSymbolUse(user, symbol, definingOpPtr);
+  return acc::isValidSymbolUse(user, symbol, definingOpPtr);
+}
+
 } // namespace acc
 } // namespace mlir

mlir/lib/Dialect/OpenACC/Utils/OpenACCUtils.cpp

@@ -9,8 +9,11 @@
 #include "mlir/Dialect/OpenACC/OpenACCUtils.h"
 
 #include "mlir/Dialect/OpenACC/OpenACC.h"
+#include "mlir/IR/SymbolTable.h"
+#include "mlir/Interfaces/FunctionInterfaces.h"
 #include "mlir/Interfaces/ViewLikeInterface.h"
 #include "llvm/ADT/TypeSwitch.h"
+#include "llvm/IR/Intrinsics.h"
 #include "llvm/Support/Casting.h"
 
 mlir::Operation *mlir::acc::getEnclosingComputeOp(mlir::Region &region) {
@@ -155,3 +158,50 @@ mlir::Value mlir::acc::getBaseEntity(mlir::Value val) {
 
   return val;
 }
+
+bool mlir::acc::isValidSymbolUse(mlir::Operation *user,
+                                 mlir::SymbolRefAttr symbol,
+                                 mlir::Operation **definingOpPtr) {
+  mlir::Operation *definingOp =
+      mlir::SymbolTable::lookupNearestSymbolFrom(user, symbol);
+
+  // If there are no defining ops, we have no way to ensure validity because
+  // we cannot check for any attributes.
+  if (!definingOp)
+    return false;
+
+  if (definingOpPtr)
+    *definingOpPtr = definingOp;
+
+  // Check if the defining op is a recipe (private, reduction, firstprivate).
+  // Recipes are valid as they get materialized before being offloaded to
+  // device. They are only instructions for how to materialize.
+  if (mlir::isa<mlir::acc::PrivateRecipeOp, mlir::acc::ReductionRecipeOp,
+                mlir::acc::FirstprivateRecipeOp>(definingOp))
+    return true;
+
+  // Check if the defining op is a function
+  if (auto func =
+          mlir::dyn_cast_if_present<mlir::FunctionOpInterface>(definingOp)) {
+    // If this symbol is actually an acc routine - then it is expected for it
+    // to be offloaded - therefore it is valid.
+    if (func->hasAttr(mlir::acc::getRoutineInfoAttrName()))
+      return true;
+
+    // If this symbol is a call to an LLVM intrinsic, then it is likely valid.
+    // Check the following:
+    // 1. The function is private
+    // 2. The function has no body
+    // 3. Name starts with "llvm."
+    // 4. The function's name is a valid LLVM intrinsic name
+    if (func.getVisibility() == mlir::SymbolTable::Visibility::Private &&
+        func.getFunctionBody().empty() && func.getName().starts_with("llvm.") &&
+        llvm::Intrinsic::lookupIntrinsicID(func.getName()) !=
+            llvm::Intrinsic::not_intrinsic)
+      return true;
+  }
+
+  // A declare attribute is needed for symbol references.
+  bool hasDeclare = definingOp->hasAttr(mlir::acc::getDeclareAttrName());
+  return hasDeclare;
+}