[mlir] Use x.empty() instead of llvm::empty(x) (NFC)

I'm planning to deprecate and eventually remove llvm::empty.

Note that no use of llvm::empty requires the ability of llvm::empty to
determine the emptiness from begin/end only.

mlir/lib/Conversion/AffineToStandard/AffineToStandard.cpp

@@ -46,7 +46,7 @@ using namespace mlir::vector;
 static Value buildMinMaxReductionSeq(Location loc,
                                      arith::CmpIPredicate predicate,
                                      ValueRange values, OpBuilder &builder) {
-  assert(!llvm::empty(values) && "empty min/max chain");
+  assert(!values.empty() && "empty min/max chain");
 
   auto valueIt = values.begin();
   Value value = *valueIt++;

mlir/lib/IR/Block.cpp

@@ -173,7 +173,7 @@ BlockArgument Block::insertArgument(unsigned index, Type type, Location loc) {
 /// Insert one value to the given position of the argument list. The existing
 /// arguments are shifted. The block is expected not to have predecessors.
 BlockArgument Block::insertArgument(args_iterator it, Type type, Location loc) {
-  assert(llvm::empty(getPredecessors()) &&
+  assert(getPredecessors().empty() &&
          "cannot insert arguments to blocks with predecessors");
   return insertArgument(it->getArgNumber(), type, loc);
 }

mlir/lib/IR/Operation.cpp

@@ -1154,14 +1154,14 @@ impl::foldCastInterfaceOp(Operation *op, ArrayRef<Attribute> attrOperands,
 LogicalResult impl::verifyCastInterfaceOp(
     Operation *op, function_ref<bool(TypeRange, TypeRange)> areCastCompatible) {
   auto resultTypes = op->getResultTypes();
-  if (llvm::empty(resultTypes))
+  if (resultTypes.empty())
     return op->emitOpError()
            << "expected at least one result for cast operation";
 
   auto operandTypes = op->getOperandTypes();
   if (!areCastCompatible(operandTypes, resultTypes)) {
     InFlightDiagnostic diag = op->emitOpError("operand type");
-    if (llvm::empty(operandTypes))
+    if (operandTypes.empty())
       diag << "s []";
     else if (llvm::size(operandTypes) == 1)
       diag << " " << *operandTypes.begin();

mlir/lib/Rewrite/FrozenRewritePatternSet.cpp

@@ -18,7 +18,7 @@ using namespace mlir;
 
 static LogicalResult convertPDLToPDLInterp(ModuleOp pdlModule) {
   // Skip the conversion if the module doesn't contain pdl.
-  if (llvm::empty(pdlModule.getOps<pdl::PatternOp>()))
+  if (pdlModule.getOps<pdl::PatternOp>().empty())
     return success();
 
   // Simplify the provided PDL module. Note that we can't use the canonicalizer

mlir/lib/Tools/PDLL/AST/NodePrinter.cpp

@@ -37,7 +37,7 @@ private:
             std::enable_if_t<!std::is_convertible<RangeT, const Node *>::value>
                 * = nullptr>
   void printChildren(RangeT &&range) {
-    if (llvm::empty(range))
+    if (range.empty())
       return;
 
     // Print the first N-1 elements with a prefix of "|-".
@@ -59,7 +59,7 @@ private:
   /// the given label.
   template <typename RangeT>
   void printChildren(StringRef label, RangeT &&range) {
-    if (llvm::empty(range))
+    if (range.empty())
       return;
     elementIndentStack.reserve(elementIndentStack.size() + 1);
     llvm::SaveAndRestore<bool> lastElement(elementIndentStack.back(), true);

mlir/lib/Transforms/Utils/DialectConversion.cpp

@@ -34,7 +34,7 @@ computeConversionSet(iterator_range<Region::iterator> region,
                      Location regionLoc,
                      SmallVectorImpl<Operation *> &toConvert,
                      ConversionTarget *target = nullptr) {
-  if (llvm::empty(region))
+  if (region.empty())
     return success();
 
   // Traverse starting from the entry block.

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

@@ -2839,7 +2839,7 @@ void OpEmitter::genOpAsmInterface() {
   auto &body = method->body();
   for (int i = 0; i != numResults; ++i) {
     body << "  auto resultGroup" << i << " = getODSResults(" << i << ");\n"
-         << "  if (!llvm::empty(resultGroup" << i << "))\n"
+         << "  if (!resultGroup" << i << ".empty())\n"
          << "    setNameFn(*resultGroup" << i << ".begin(), \""
          << resultNames[i] << "\");\n";
   }