[mlir][LLVM] Fix empty res attr import

[Dinistro]

Summary

This commit ensures that an empty list of result attributes is not
imported as an empty ArrayAttr. Instead, the attribute is just not
added to the LLVMFuncOp.

[gysit]

LGTM!

mlir/lib/Target/LLVMIR/ModuleImport.cpp

if (Attribute scalarAttr = getScalarConstantAsAttr(builder, constant))
     return scalarAttr;
 
   // Convert function references.
   if (auto *func = dyn_cast<llvm::Function>(constant))
     return SymbolRefAttr::get(builder.getContext(), func->getName());
 
   // Returns the static shape of the provided type if possible.
   auto getConstantShape = [&](llvm::Type *type) {
-    return llvm::dyn_cast_if_present<ShapedType>(getBuiltinTypeForAttr(convertType(type))
-        );
+    return llvm::dyn_cast_if_present<ShapedType>(
+        getBuiltinTypeForAttr(convertType(type)));
   };
 
   // Convert one-dimensional constant arrays or vectors that store 1/2/4/8-byte
   // integer or half/bfloat/float/double values.
   if (auto *constArray = dyn_cast<llvm::ConstantDataSequential>(constant)) {
     if (constArray->isString())
       return builder.getStringAttr(constArray->getAsString());
     auto shape = getConstantShape(constArray->getType());
while (!workList.empty()) {
       // constant expression.
       return {};
     }
     return DenseElementsAttr::get(shape, elementAttrs);
   }
 
   // Convert zero aggregates.
   if (auto *constZero = dyn_cast<llvm::ConstantAggregateZero>(constant)) {
-    auto shape = llvm::dyn_cast_if_present<ShapedType>(getBuiltinTypeForAttr(convertType(constZero->getType()))
-                     );
+    auto shape = llvm::dyn_cast_if_present<ShapedType>(
+        getBuiltinTypeForAttr(convertType(constZero->getType())));
     if (!shape)
       return {};
     // Convert zero aggregates with a static shape to splat elements attributes.
     Attribute splatAttr = builder.getZeroAttr(shape.getElementType());
     assert(splatAttr && "expected non-null zero attribute for scalar types");
     return SplatElementsAttr::get(shape, splatAttr);
   }
   return {};
void ModuleImport::convertParameterAttributes(llvm::Function *func,
   auto llvmAttrs = func->getAttributes();
   for (size_t i = 0, e = funcOp.getNumArguments(); i < e; ++i) {
     llvm::AttributeSet llvmArgAttrs = llvmAttrs.getParamAttrs(i);
     funcOp.setArgAttrs(i, convertParameterAttribute(llvmArgAttrs, builder));
   }
   // Convert the result attributes and attach them wrapped in an ArrayAttribute
   // to the funcOp.
   llvm::AttributeSet llvmResAttr = llvmAttrs.getRetAttrs();
+  if (!llvmResAttr.hasAttributes())
+    return;
   funcOp.setResAttrsAttr(
       builder.getArrayAttr(convertParameterAttribute(llvmResAttr, builder)));
 }
 
 LogicalResult ModuleImport::processFunction(llvm::Function *func) {
   clearBlockAndValueMapping();
 
   auto functionType =

mlir/test/Target/LLVMIR/Import/function-attributes-generic.ll

+; RUN: mlir-translate -import-llvm -split-input-file %s --mlir-print-op-generic | FileCheck %s
+
+; Ensure that no empty parameter attribute lists are created.
+; CHECK: "llvm.func"
+; CHECK-SAME:  <{
+; CHECK-NOT:  arg_attr
+; CHECK-NOT:  res_attrs
+; CHECK-SAME:  }>
+declare ptr @func_no_param_attrs()