[mlir][nvvm]Add support for grid_constant attribute on LLVM function arguments (#78228)

Add support for attribute nvvm.grid_constant on LLVM function arguments.
The attribute can be attached only to arguments of type llvm.ptr that
have llvm.byval attribute.
Generate LLVM metadata for functions with nvvm.grid_constant arguments.
The metadata node is a list of integers, where each integer n denotes
that the nth parameter has the
grid_constant annotation (numbering from 1). The generated metadata node
will be handled by NVVM compiler. See
https://docs.nvidia.com/cuda/nvvm-ir-spec/index.html#supported-properties
for documentation on grid_constant property.

This patch also adds convertParameterAttr to
LLVMTranslationDialectInterface for supporting the translation of
derived dialect attributes on function parameters 

Author: rishisurendran

llvm/include/llvm/IR/Metadata.h

@@ -1735,7 +1735,7 @@ class NamedMDNode : public ilist_node<NamedMDNode> {
 
   explicit NamedMDNode(const Twine &N);
 
-  template <class T1, class T2> class op_iterator_impl {
+  template <class T1> class op_iterator_impl {
     friend class NamedMDNode;
 
     const NamedMDNode *Node = nullptr;
@@ -1745,10 +1745,10 @@ class NamedMDNode : public ilist_node<NamedMDNode> {
 
   public:
     using iterator_category = std::bidirectional_iterator_tag;
-    using value_type = T2;
+    using value_type = T1;
     using difference_type = std::ptrdiff_t;
     using pointer = value_type *;
-    using reference = value_type &;
+    using reference = value_type;
 
     op_iterator_impl() = default;
 
@@ -1809,12 +1809,12 @@ class NamedMDNode : public ilist_node<NamedMDNode> {
   // ---------------------------------------------------------------------------
   // Operand Iterator interface...
   //
-  using op_iterator = op_iterator_impl<MDNode *, MDNode>;
+  using op_iterator = op_iterator_impl<MDNode *>;
 
   op_iterator op_begin() { return op_iterator(this, 0); }
   op_iterator op_end()   { return op_iterator(this, getNumOperands()); }
 
-  using const_op_iterator = op_iterator_impl<const MDNode *, MDNode>;
+  using const_op_iterator = op_iterator_impl<const MDNode *>;
 
   const_op_iterator op_begin() const { return const_op_iterator(this, 0); }
   const_op_iterator op_end()   const { return const_op_iterator(this, getNumOperands()); }

mlir/include/mlir/Dialect/LLVMIR/NVVMOps.td

@@ -59,6 +59,19 @@ def NVVM_Dialect : Dialect {
     /// Get the name of the attribute used to annotate max number of
     /// registers that can be allocated per thread.
     static StringRef getMaxnregAttrName() { return "nvvm.maxnreg"; }
+
+    /// Get the name of the attribute used to annotate kernel arguments that
+    /// are grid constants.
+    static StringRef getGridConstantAttrName() { return "nvvm.grid_constant"; }
+
+    /// Verify an attribute from this dialect on the argument at 'argIndex' for
+    /// the region at 'regionIndex' on the given operation. Returns failure if
+    /// the verification failed, success otherwise. This hook may optionally be
+    /// invoked from any operation containing a region.
+    LogicalResult verifyRegionArgAttribute(Operation *op,
+                                           unsigned regionIndex,
+                                           unsigned argIndex,
+                                           NamedAttribute argAttr) override;
   }];
 
   let useDefaultAttributePrinterParser = 1;

mlir/include/mlir/Target/LLVMIR/LLVMTranslationInterface.h

@@ -13,6 +13,7 @@
 #ifndef MLIR_TARGET_LLVMIR_LLVMTRANSLATIONINTERFACE_H
 #define MLIR_TARGET_LLVMIR_LLVMTRANSLATIONINTERFACE_H
 
+#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
 #include "mlir/IR/BuiltinAttributes.h"
 #include "mlir/IR/DialectInterface.h"
 #include "mlir/Support/LogicalResult.h"
@@ -25,6 +26,7 @@ class IRBuilderBase;
 namespace mlir {
 namespace LLVM {
 class ModuleTranslation;
+class LLVMFuncOp;
 } // namespace LLVM
 
 /// Base class for dialect interfaces providing translation to LLVM IR.
@@ -58,6 +60,16 @@ class LLVMTranslationDialectInterface
                  LLVM::ModuleTranslation &moduleTranslation) const {
     return success();
   }
+
+  /// Hook for derived dialect interface to translate or act on a derived
+  /// dialect attribute that appears on a function parameter. This gets called
+  /// after the function operation has been translated.
+  virtual LogicalResult
+  convertParameterAttr(LLVM::LLVMFuncOp function, int argIdx,
+                       NamedAttribute attr,
+                       LLVM::ModuleTranslation &moduleTranslation) const {
+    return success();
+  }
 };
 
 /// Interface collection for translation to LLVM IR, dispatches to a concrete
@@ -90,6 +102,22 @@ class LLVMTranslationInterface
     }
     return success();
   }
+
+  /// Acts on the given function operation using the interface implemented by
+  /// the dialect of one of the function parameter attributes.
+  virtual LogicalResult
+  convertParameterAttr(LLVM::LLVMFuncOp function, int argIdx,
+                       NamedAttribute attribute,
+                       LLVM::ModuleTranslation &moduleTranslation) const {
+    if (const LLVMTranslationDialectInterface *iface =
+            getInterfaceFor(attribute.getNameDialect())) {
+      return iface->convertParameterAttr(function, argIdx, attribute,
+                                         moduleTranslation);
+    }
+    function.emitWarning("Unhandled parameter attribute '" +
+                         attribute.getName().str() + "'");
+    return success();
+  }
 };
 
 } // namespace mlir

mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h

@@ -327,7 +327,9 @@ class ModuleTranslation {
                            ArrayRef<llvm::Instruction *> instructions);
 
   /// Translates parameter attributes and adds them to the returned AttrBuilder.
-  llvm::AttrBuilder convertParameterAttrs(DictionaryAttr paramAttrs);
+  /// Returns failure if any of the translations failed.
+  FailureOr<llvm::AttrBuilder>
+  convertParameterAttrs(LLVMFuncOp func, int argIdx, DictionaryAttr paramAttrs);
 
   /// Original and translated module.
   Operation *mlirModule;

mlir/lib/Dialect/LLVMIR/IR/NVVMDialect.cpp

@@ -1074,6 +1074,35 @@ LogicalResult NVVMDialect::verifyOperationAttribute(Operation *op,
   return success();
 }
 
+LogicalResult NVVMDialect::verifyRegionArgAttribute(Operation *op,
+                                                    unsigned regionIndex,
+                                                    unsigned argIndex,
+                                                    NamedAttribute argAttr) {
+  auto funcOp = dyn_cast<FunctionOpInterface>(op);
+  if (!funcOp)
+    return success();
+
+  bool isKernel = op->hasAttr(NVVMDialect::getKernelFuncAttrName());
+  StringAttr attrName = argAttr.getName();
+  if (attrName == NVVM::NVVMDialect::getGridConstantAttrName()) {
+    if (!isKernel) {
+      return op->emitError()
+             << "'" << attrName
+             << "' attribute must be present only on kernel arguments";
+    }
+    if (!isa<UnitAttr>(argAttr.getValue()))
+      return op->emitError() << "'" << attrName << "' must be a unit attribute";
+    if (!funcOp.getArgAttr(argIndex, LLVM::LLVMDialect::getByValAttrName())) {
+      return op->emitError()
+             << "'" << attrName
+             << "' attribute requires the argument to also have attribute '"
+             << LLVM::LLVMDialect::getByValAttrName() << "'";
+    }
+  }
+
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // NVVM target attribute.
 //===----------------------------------------------------------------------===//

mlir/lib/Target/LLVMIR/AttrKindDetail.h

@@ -59,6 +59,20 @@ getAttrKindToNameMapping() {
   return kindNamePairs;
 }
 
+/// Returns a dense map from LLVM attribute name to their kind in LLVM IR
+/// dialect.
+static llvm::DenseMap<llvm::StringRef, llvm::Attribute::AttrKind>
+getAttrNameToKindMapping() {
+  static auto attrNameToKindMapping = []() {
+    llvm::DenseMap<llvm::StringRef, llvm::Attribute::AttrKind> nameKindMap;
+    for (auto kindNamePair : getAttrKindToNameMapping()) {
+      nameKindMap.insert({kindNamePair.second, kindNamePair.first});
+    }
+    return nameKindMap;
+  }();
+  return attrNameToKindMapping;
+}
+
 } // namespace detail
 } // namespace LLVM
 } // namespace mlir

mlir/lib/Target/LLVMIR/Dialect/NVVM/NVVMToLLVMIRTranslation.cpp

@@ -201,6 +201,62 @@ class NVVMDialectLLVMIRTranslationInterface
     }
     return success();
   }
+
+  LogicalResult
+  convertParameterAttr(LLVMFuncOp funcOp, int argIdx, NamedAttribute attribute,
+                       LLVM::ModuleTranslation &moduleTranslation) const final {
+
+    llvm::LLVMContext &llvmContext = moduleTranslation.getLLVMContext();
+    llvm::Function *llvmFunc =
+        moduleTranslation.lookupFunction(funcOp.getName());
+    llvm::NamedMDNode *nvvmAnnotations =
+        moduleTranslation.getOrInsertNamedModuleMetadata("nvvm.annotations");
+
+    if (attribute.getName() == NVVM::NVVMDialect::getGridConstantAttrName()) {
+      llvm::MDNode *gridConstantMetaData = nullptr;
+
+      // Check if a 'grid_constant' metadata node exists for the given function
+      for (llvm::MDNode *opnd : llvm::reverse(nvvmAnnotations->operands())) {
+        if (opnd->getNumOperands() == 3 &&
+            opnd->getOperand(0) == llvm::ValueAsMetadata::get(llvmFunc) &&
+            opnd->getOperand(1) ==
+                llvm::MDString::get(llvmContext, "grid_constant")) {
+          gridConstantMetaData = opnd;
+          break;
+        }
+      }
+
+      // 'grid_constant' is a function-level meta data node with a list of
+      // integers, where each integer n denotes that the nth parameter has the
+      // grid_constant annotation (numbering from 1). This requires aggregating
+      // the indices of the individual parameters that have this attribute.
+      llvm::Type *i32 = llvm::IntegerType::get(llvmContext, 32);
+      if (gridConstantMetaData == nullptr) {
+        // Create a new 'grid_constant' metadata node
+        SmallVector<llvm::Metadata *> gridConstMetadata = {
+            llvm::ValueAsMetadata::getConstant(
+                llvm::ConstantInt::get(i32, argIdx + 1))};
+        llvm::Metadata *llvmMetadata[] = {
+            llvm::ValueAsMetadata::get(llvmFunc),
+            llvm::MDString::get(llvmContext, "grid_constant"),
+            llvm::MDNode::get(llvmContext, gridConstMetadata)};
+        llvm::MDNode *llvmMetadataNode =
+            llvm::MDNode::get(llvmContext, llvmMetadata);
+        nvvmAnnotations->addOperand(llvmMetadataNode);
+      } else {
+        // Append argIdx + 1 to the 'grid_constant' argument list
+        if (auto argList =
+                dyn_cast<llvm::MDTuple>(gridConstantMetaData->getOperand(2))) {
+          llvm::TempMDTuple clonedArgList = argList->clone();
+          clonedArgList->push_back((llvm::ValueAsMetadata::getConstant(
+              llvm::ConstantInt::get(i32, argIdx + 1))));
+          gridConstantMetaData->replaceOperandWith(
+              2, llvm::MDNode::replaceWithUniqued(std::move(clonedArgList)));
+        }
+      }
+    }
+    return success();
+  }
 };
 } // namespace
 

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -1298,28 +1298,29 @@ static void convertFunctionAttributes(LLVMFuncOp func,
   llvmFunc->setMemoryEffects(newMemEffects);
 }
 
-llvm::AttrBuilder
-ModuleTranslation::convertParameterAttrs(DictionaryAttr paramAttrs) {
+FailureOr<llvm::AttrBuilder>
+ModuleTranslation::convertParameterAttrs(LLVMFuncOp func, int argIdx,
+                                         DictionaryAttr paramAttrs) {
   llvm::AttrBuilder attrBuilder(llvmModule->getContext());
-
-  for (auto [llvmKind, mlirName] : getAttrKindToNameMapping()) {
-    Attribute attr = paramAttrs.get(mlirName);
-    // Skip attributes that are not present.
-    if (!attr)
-      continue;
-
-    // NOTE: C++17 does not support capturing structured bindings.
-    llvm::Attribute::AttrKind llvmKindCap = llvmKind;
-
-    llvm::TypeSwitch<Attribute>(attr)
-        .Case<TypeAttr>([&](auto typeAttr) {
-          attrBuilder.addTypeAttr(llvmKindCap,
-                                  convertType(typeAttr.getValue()));
-        })
-        .Case<IntegerAttr>([&](auto intAttr) {
-          attrBuilder.addRawIntAttr(llvmKindCap, intAttr.getInt());
-        })
-        .Case<UnitAttr>([&](auto) { attrBuilder.addAttribute(llvmKindCap); });
+  auto attrNameToKindMapping = getAttrNameToKindMapping();
+
+  for (auto namedAttr : paramAttrs) {
+    auto it = attrNameToKindMapping.find(namedAttr.getName());
+    if (it != attrNameToKindMapping.end()) {
+      llvm::Attribute::AttrKind llvmKind = it->second;
+
+      llvm::TypeSwitch<Attribute>(namedAttr.getValue())
+          .Case<TypeAttr>([&](auto typeAttr) {
+            attrBuilder.addTypeAttr(llvmKind, convertType(typeAttr.getValue()));
+          })
+          .Case<IntegerAttr>([&](auto intAttr) {
+            attrBuilder.addRawIntAttr(llvmKind, intAttr.getInt());
+          })
+          .Case<UnitAttr>([&](auto) { attrBuilder.addAttribute(llvmKind); });
+    } else if (namedAttr.getNameDialect()) {
+      if (failed(iface.convertParameterAttr(func, argIdx, namedAttr, *this)))
+        return failure();
+    }
   }
 
   return attrBuilder;
@@ -1348,14 +1349,21 @@ LogicalResult ModuleTranslation::convertFunctionSignatures() {
     // Convert result attributes.
     if (ArrayAttr allResultAttrs = function.getAllResultAttrs()) {
       DictionaryAttr resultAttrs = cast<DictionaryAttr>(allResultAttrs[0]);
-      llvmFunc->addRetAttrs(convertParameterAttrs(resultAttrs));
+      FailureOr<llvm::AttrBuilder> attrBuilder =
+          convertParameterAttrs(function, -1, resultAttrs);
+      if (failed(attrBuilder))
+        return failure();
+      llvmFunc->addRetAttrs(*attrBuilder);
     }
 
     // Convert argument attributes.
     for (auto [argIdx, llvmArg] : llvm::enumerate(llvmFunc->args())) {
       if (DictionaryAttr argAttrs = function.getArgAttrDict(argIdx)) {
-        llvm::AttrBuilder attrBuilder = convertParameterAttrs(argAttrs);
-        llvmArg.addAttrs(attrBuilder);
+        FailureOr<llvm::AttrBuilder> attrBuilder =
+            convertParameterAttrs(function, argIdx, argAttrs);
+        if (failed(attrBuilder))
+          return failure();
+        llvmArg.addAttrs(*attrBuilder);
       }
     }
 

mlir/test/Dialect/LLVMIR/nvvm.mlir

@@ -472,3 +472,29 @@ gpu.module @module_1 [#nvvm.target<chip = "sm_90", features = "+ptx70", link = [
 
 gpu.module @module_2 [#nvvm.target<chip = "sm_90">, #nvvm.target<chip = "sm_80">, #nvvm.target<chip = "sm_70">] {
 }
+
+// CHECK-LABEL : nvvm.grid_constant
+llvm.func @kernel_func(%arg0: !llvm.ptr {llvm.byval = i32, nvvm.grid_constant}) attributes {nvvm.kernel} {
+  llvm.return
+}
+
+// -----
+
+// expected-error @below {{'"nvvm.grid_constant"' attribute must be present only on kernel arguments}}
+llvm.func @kernel_func(%arg0: !llvm.ptr {llvm.byval = i32, nvvm.grid_constant}) {
+  llvm.return
+}
+
+// -----
+
+// expected-error @below {{'"nvvm.grid_constant"' attribute requires the argument to also have attribute 'llvm.byval'}}
+llvm.func @kernel_func(%arg0: !llvm.ptr {nvvm.grid_constant}) attributes {nvvm.kernel} {
+  llvm.return
+}
+
+// -----
+
+// expected-error @below {{'"nvvm.grid_constant"' must be a unit attribute}}
+llvm.func @kernel_func(%arg0: !llvm.ptr {llvm.byval = i32, nvvm.grid_constant = true}) attributes {nvvm.kernel} {
+  llvm.return
+}

mlir/test/Target/LLVMIR/nvvmir.mlir

@@ -538,3 +538,20 @@ llvm.func @kernel_func() attributes {nvvm.kernel, nvvm.maxntid = array<i32: 3, 4
   llvm.return
 }
 
+// -----
+// CHECK: !nvvm.annotations =
+// CHECK: !1 = !{ptr @kernel_func, !"grid_constant", !2}
+// CHECK: !2 = !{i32 1}
+// CHECK: !3 = !{ptr @kernel_func, !"kernel", i32 1}
+llvm.func @kernel_func(%arg0: !llvm.ptr {llvm.byval = i32, nvvm.grid_constant}) attributes {nvvm.kernel} {
+  llvm.return
+}
+
+// -----
+// CHECK: !nvvm.annotations =
+// CHECK: !1 = !{ptr @kernel_func, !"grid_constant", !2}
+// CHECK: !2 = !{i32 1, i32 3}
+// CHECK: !3 = !{ptr @kernel_func, !"kernel", i32 1}
+llvm.func @kernel_func(%arg0: !llvm.ptr {llvm.byval = i32, nvvm.grid_constant}, %arg1: f32, %arg2: !llvm.ptr {llvm.byval = f32, nvvm.grid_constant}) attributes {nvvm.kernel} {
+  llvm.return
+}