[MLIR] Krnl Dialect Definition (#357)

* a complete, roud-trippable Krnl dialect operation definition

* remove old dialect definition files, edit build files

* register dialect

* check in src for onnf_opt and dimension handler types

* re-trigger jenkins

* fix build

* clarify operation semantics

* add verifier for krnl.iterate

* refactor to make things clear

* do not hard code types

* nit and add comments

* fix rebase

* update op implementation

* fix merge

* update kernel dialect definition

* more comment on how to use the builder for krnl.iterate operation

* ammend the comment

* can parse krnl.iterate

* can parse and print if bounds are not SSA values

* address comments

* better error handling

* Update CMakeLists.txt

* update comment

* reflow comments

src/CMakeLists.txt

@@ -3,3 +3,5 @@ add_executable(onnf main.cpp)
 target_include_directories(onnf PRIVATE ${CMAKE_SOURCE_DIR})
 target_include_directories(onnf PRIVATE ${CMAKE_BINARY_DIR})
 target_link_libraries(onnf builder compiler ${Boost_LIBRARIES})
+
+install(TARGETS onnf DESTINATION bin)

src/compiler/CMakeLists.txt

@@ -1,9 +1,13 @@
 add_library(
         compiler
-        ir/knl/knl_ops.cpp
+        dialect/krnl/krnl_ops.cpp
-        ir/knl/knl_ops.hpp
+        dialect/krnl/krnl_ops.hpp
+        dialect/krnl/krnl_types.cpp
+        dialect/krnl/krnl_types.hpp
         dialect/onnx/onnx_ops.cpp
         dialect/onnx/onnx_ops.hpp
+        dialect/krnl/parser_helper.cpp
+        dialect/krnl/parser_helper.hpp
         pass/shape_inference_pass.cpp
         pass/shape_inference_interface.hpp
         pass/passes.hpp)
@@ -25,7 +29,7 @@ find_package(Boost 1.54.0
 # target_link_libraries(compiler isl inja ${Boost_LIBRARIES})
 target_link_libraries(compiler
         ${Boost_LIBRARIES}
-        )
+        ${MLIRLIBS} curses)
 
 add_executable(onnf-opt
         tool/onnf_opt/onnf_opt.cpp)
@@ -34,12 +38,6 @@ target_link_libraries(onnf-opt ${Boost_LIBRARIES} ${MLIRLIBS} curses compiler)
 target_include_directories(onnf-opt PRIVATE ../..)
 target_include_directories(onnf-opt PRIVATE ${CMAKE_BINARY_DIR})
 
-set(LLVM_TARGET_DEFINITIONS ir/knl/knl.td)
-onnf_tablegen(knl.hpp.inc -gen-op-decls)
-onnf_tablegen(knl.cpp.inc -gen-op-defs)
-add_public_tablegen_target(gen_kir)
-add_dependencies(compiler gen_kir)
-
 set(LLVM_TARGET_DEFINITIONS pass/shape_inference_interface.td)
 onnf_tablegen(shape_inference.hpp.inc -gen-op-interface-decls)
 onnf_tablegen(shape_inference.cpp.inc -gen-op-interface-defs)
@@ -51,3 +49,10 @@ onnf_tablegen(onnx.hpp.inc -gen-op-decls "-I${CMAKE_SOURCE_DIR}/compiler/pass")
 onnf_tablegen(onnx.cpp.inc -gen-op-defs "-I${CMAKE_SOURCE_DIR}/compiler/pass")
 add_public_tablegen_target(gen_onnx)
 add_dependencies(compiler gen_onnx)
+
+set(LLVM_TARGET_DEFINITIONS dialect/krnl/krnl_ops.td)
+onnf_tablegen(krnl.hpp.inc -gen-op-decls)
+onnf_tablegen(krnl.cpp.inc -gen-op-defs)
+add_public_tablegen_target(gen_krnl_ops)
+add_dependencies(compiler gen_krnl_ops)
+add_dependencies(onnf-opt gen_krnl_ops)

src/compiler/dialect/krnl/krnl_ops.cpp

@@ -0,0 +1,398 @@
+//===--------------------- krnl_ops.cpp - MLIR Operations -----------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
+#include <iostream>
+#include <queue>
+
+#include "src/compiler/dialect/krnl/parser_helper.hpp"
+
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallBitVector.h"
+#include "mlir/IR/Block.h"
+#include "mlir/IR/Builders.h"
+#include "mlir/IR/Function.h"
+#include "mlir/IR/IntegerSet.h"
+#include "mlir/IR/Matchers.h"
+#include "mlir/IR/Module.h"
+#include "mlir/IR/OpImplementation.h"
+#include "mlir/IR/Operation.h"
+#include "mlir/IR/PatternMatch.h"
+#include "mlir/Transforms/DialectConversion.h"
+
+#include "krnl_ops.hpp"
+
+using namespace mlir;
+
+namespace mlir {
+KrnlOpsDialect::KrnlOpsDialect(MLIRContext* context)
+    : Dialect(getDialectNamespace(), context) {
+  addOperations<
+#define GET_OP_LIST
+#include "src/compiler/krnl.cpp.inc"
+      >();
+  addTypes<LoopType>();
+}
+
+//===----------------------------------------------------------------------===//
+// KrnlDefineLoopsOp
+//===----------------------------------------------------------------------===//
+
+void KrnlDefineLoopsOp::build(
+    Builder* builder, OperationState& result, int64_t num_loops) {
+  // Create the same number of dimension handlers as the number of
+  // dimensions in the associated integer set.
+  result.types.append(num_loops, LoopType::get(builder->getContext()));
+  result.addAttribute(
+      getNumLoopsAttrName(), builder->getI32IntegerAttr(num_loops));
+}
+
+void print(OpAsmPrinter& p, KrnlDefineLoopsOp& op) {
+  auto num_loop_attr = op.getAttrOfType<IntegerAttr>(op.getNumLoopsAttrName());
+  p << "krnl.define_loops " << num_loop_attr.getValue().getSExtValue();
+}
+
+ParseResult parseKrnlDefineLoopsOp(
+    OpAsmParser& parser, OperationState& result) {
+  // Parse the attribute indicating number of loops defined.
+  IntegerAttr num_loops;
+  auto& builder = parser.getBuilder();
+  auto int32_type = builder.getIntegerType(64);
+  if (parser.parseAttribute(num_loops, int32_type,
+          KrnlDefineLoopsOp::getNumLoopsAttrName(), result.attributes))
+    return failure();
+
+  auto loop_types = llvm::SmallVector<Type, 4>(
+      num_loops.getValue().getSExtValue(), LoopType::get(builder.getContext()));
+  if (parser.addTypesToList(loop_types, result.types))
+    return failure();
+
+  return success();
+}
+
+//===----------------------------------------------------------------------===//
+// KrnlOptimizeLoopsOp
+//===----------------------------------------------------------------------===//
+
+void KrnlOptimizeLoopsOp::build(
+    Builder* builder, OperationState& result, int num_optimized_loops) {
+  result.types.append(
+      num_optimized_loops, LoopType::get(builder->getContext()));
+  // Create a region and a block for the body.
+  // Schedule intrinsics will be placed into this region.
+  Region* region = result.addRegion();
+  auto* body = new Block();
+  region->push_back(body);
+}
+
+void print(OpAsmPrinter& p, KrnlOptimizeLoopsOp& op) {
+  p << "krnl.optimize_loops ";
+  p.printRegion(op.region(), /*printEntryBlockArgs=*/false,
+      /*printBlockTerminators=*/true);
+  p << " : ";
+  p.printFunctionalType(op);
+}
+
+ParseResult parseKrnlOptimizeLoopsOp(
+    OpAsmParser& parser, OperationState& result) {
+  // Parse the schedule body region.
+  Region* region = result.addRegion();
+  if (parser.parseRegion(*region, llvm::None, llvm::None))
+    return failure();
+
+  // Parse the function type for the schedule operation.
+  // Then following the hint of this parsed function type, parse the
+  // returned timestamp space dimension handlers.
+  FunctionType schedule_func_type;
+  if (parser.parseColonType(schedule_func_type) ||
+      parser.addTypesToList(schedule_func_type.getResults(), result.types)) {
+    failure();
+  }
+
+  return success();
+}
+
+//===----------------------------------------------------------------------===//
+// KrnlIterateOp
+//===----------------------------------------------------------------------===//
+
+/*!
+ * Build a Krnl Dialect iterate operation.
+ * input_loops: a collection of input krnl.loops being optimized.
+ * optimized_loops: a collection of optimized (scheduled) krnl.loops.
+ * operand_bounds: a collection of SSA value bounds.
+ * const_bounds: a collection of constant bounds.
+ * bound_types: a collection of integer values indicating how bounds are given.
+ *   0 : bound is given as an integer in const_bounds.
+ *   1 : bound is given as an operand in operand_bounds.
+ *   2 : bound is given as an affine map. (TODO).
+ *
+ * The following example illustrates how induction variable bounds are parsed
+ * from builder function inputs:
+ *
+ * - operand_bounds = [N, M]
+ * - const_bounds = [10, 20]
+ * - bound_types = [0, 1, 1, 0]
+ *
+ * Then the bounds will be parsed as:
+ *   %i0 = 10 to N : %i1 = M to 20
+ */
+void KrnlIterateOp::build(Builder* builder, OperationState& result,
+    ArrayRef<Value*> input_loops, ArrayRef<Value*> optimized_loops,
+    ArrayRef<Value*> operand_bounds, ArrayRef<int64_t> const_bounds,
+    ArrayRef<int> bound_types) {
+  // Record optimized loops and the number of such loops.
+  result.addOperands(optimized_loops);
+  result.addAttribute(getNumOptimizedLoopsAttrName(),
+      builder->getI64IntegerAttr(optimized_loops.size()));
+
+  // Record input loops and the number of such loops.
+  result.addOperands(input_loops);
+  result.addAttribute(getNumInputLoopsAttrName(),
+      builder->getI64IntegerAttr(input_loops.size()));
+
+  // Record bound either as attribute or from operand list.
+  auto next_operand_bound = operand_bounds.begin();
+  auto next_const_bound = const_bounds.begin();
+  for (size_t i = 0; i < bound_types.size(); i++) {
+    auto bound_type = bound_types[i];
+    if (bound_type == 0) {
+      // Constant bound.
+      result.addAttribute(getBoundAttrName(i / 2, i % 2),
+          builder->getI64IntegerAttr(*next_const_bound));
+      next_const_bound = std::next(next_const_bound);
+    } else {
+      // Operand bound.
+      result.addOperands(*next_operand_bound);
+      next_operand_bound = std::next(next_operand_bound);
+    }
+  }
+
+  // Record bound types as attribute:
+  result.addAttribute(KrnlIterateOp::getBoundTypesAttrName(),
+      builder->getI32ArrayAttr(bound_types));
+
+  // Create a region and a block for the body. The arguments of the region is
+  // the loop induction variables; there can be multiple induction variables
+  // associated with the same krnl.iterate operation.
+  Region* bodyRegion = result.addRegion();
+  auto* body = new Block();
+  auto body_args = llvm::SmallVector<Type, 4>(
+      input_loops.size(), IndexType::get(builder->getContext()));
+  body->addArguments(body_args);
+  bodyRegion->push_back(body);
+
+  ensureTerminator(*bodyRegion, *builder, result.location);
+}
+
+void print(OpAsmPrinter& p, KrnlIterateOp& op) {
+  p << "krnl.iterate(";
+  // Print optimized loops:
+  auto num_optimized_loops = op.getNumOptimizedLoops();
+  p.printOperands(op.operand_begin(), op.operand_begin() + num_optimized_loops);
+  p << ") with (";
+
+  // Set up iterator to input loops:
+  auto num_input_loops = op.getNumInputLoops();
+  auto input_loop_begin = op.operand_begin() + num_optimized_loops;
+
+  // Set up iterators to operand bounds.
+  auto next_operand_bound = input_loop_begin + num_input_loops;
+
+  // Function to print a lower or upper bound.
+  auto print_bound = [&](ArrayRef<Attribute> bound_types, size_t idx) {
+    IntegerAttr type = bound_types[idx].dyn_cast<IntegerAttr>();
+    if (type.getValue().getSExtValue() == 0) {
+      // Bound is an operand.
+      p.printOperand(*next_operand_bound);
+      next_operand_bound = std::next(next_operand_bound);
+    } else {
+      // Bound is an integer attribute.
+      auto bound_idx = idx / 2;
+      auto is_ub = idx % 2;
+      IntegerAttr bound = op.getAttrOfType<IntegerAttr>(
+          KrnlIterateOp::getBoundAttrName(bound_idx, is_ub));
+      p << bound.getValue().getSExtValue();
+    }
+  };
+
+  auto induction_variables = op.bodyRegion().front().getArguments();
+  ArrayRef<Attribute> bound_types =
+      op.getAttrOfType<ArrayAttr>(KrnlIterateOp::getBoundTypesAttrName())
+          .getValue();
+
+  // Print input loop operands, induction variables and their ranges.
+  for (size_t i = 0; i < num_input_loops; i++) {
+    if (i != 0)
+      p << ", ";
+
+    p.printOperand(*std::next(input_loop_begin, i));
+    p << " -> ";
+
+    // Print induction variable block argument.
+    p.printOperand(induction_variables[i]);
+    p << " = ";
+
+    print_bound(bound_types, 2 * i);  // Print lower bound.
+    p << " to ";
+    print_bound(bound_types, 2 * i + 1);  // Print upper bound.
+  }
+  p << ")";
+
+  p.printRegion(op.bodyRegion(), /*printEntryBlockArgs=*/false,
+      /*printBlockTerminators=*/false);
+}
+
+ParseResult parseKrnlIterateOp(OpAsmParser& parser, OperationState& result) {
+  auto builder = parser.getBuilder();
+  auto context = builder.getContext();
+  onnf::KrnlDialectOperandParser operand_parser(parser);
+
+  // Parse optimized loops:
+  SmallVector<OpAsmParser::OperandType, 4> num_optimized_loops;
+  if (parser.parseOperandList(
+          num_optimized_loops, OpAsmParser::Delimiter::Paren) ||
+      parser.resolveOperands(num_optimized_loops,
+          LoopType::get(result.getContext()), result.operands))
+    return failure();
+
+  // Record how many optimized loops did we parse.
+  result.addAttribute(KrnlIterateOp::getNumOptimizedLoopsAttrName(),
+      builder.getI64IntegerAttr(num_optimized_loops.size()));
+
+  // Parse input loops and their lower and upper bounds.
+  SmallVector<OpAsmParser::OperandType, 4> in_loop_refs, induction_var_refs;
+  SmallVector<Value*, 4> in_loop_operands, operand_bounds;
+  SmallVector<Attribute, 4> bound_types;
+  SmallVector<IntegerAttr, 4> const_bounds;
+
+  if (parser.parseKeyword("with") || parser.parseLParen())
+    return failure();
+
+  // A function to parse a lower or upper bound.
+  auto parse_bound = [&result, &builder, &operand_parser, &parser, &bound_types,
+                         &operand_bounds, &const_bounds](
+                         bool is_ub, size_t bound_pair_count) -> ParseResult {
+    // Try parse an SSA operand.
+    Value* bound;
+    operand_parser.ParseOptionalOperand(builder.getIndexType(), bound);
+
+    if (bound != nullptr) {
+      // Parsed an SSA id as bound.
+      operand_bounds.emplace_back(bound);
+      // Record bound_type as an operand type.
+      bound_types.emplace_back(builder.getI32IntegerAttr(0));
+    } else {
+      // Bound is not an SSA id, then it must be an integer.
+      // Parse an integer constant attribute.
+      IntegerAttr boundAttr;
+      if (parser.parseAttribute(boundAttr, builder.getIndexType(),
+              KrnlIterateOp::getBoundAttrName(bound_pair_count, is_ub),
+              result.attributes))
+        return failure();
+      const_bounds.emplace_back(
+          builder.getIntegerAttr(builder.getIndexType(), boundAttr.getValue()));
+
+      // Record that the bound_type is a constant integer attribute.
+      bound_types.emplace_back(builder.getI32IntegerAttr(1));
+    }
+  };
+
+  bool keep_parsing;            // Do we keep parsing loops/bounds?
+  size_t bound_pair_count = 0;  // Record the number of bound pairs parsed.
+  do {
+    // Parse an input loop operand;
+    Value* in_loop_operand;
+    operand_parser.ParseOperand(LoopType::get(context), in_loop_operand);
+    in_loop_operands.emplace_back(in_loop_operand);
+
+    parser.parseArrow();
+
+    // Parse induction variable.
+    OpAsmParser::OperandType induction_var;
+    if (parser.parseRegionArgument(induction_var) || parser.parseEqual())
+      return failure();
+    induction_var_refs.emplace_back(induction_var);
+
+    // Parse bound par (min to max).
+    if (parse_bound(false, bound_pair_count) || parser.parseKeyword("to") ||
+        parse_bound(true, bound_pair_count))
+      return failure();
+
+    bound_pair_count++;
+    // We may fail to parse a comma if an operand bound is followed by
+    // a comma and the next input loop operand, in which case
+    // the entire "{operand bound}, {input_loop_operand}" sequence will
+    // be parsed as an operand list.
+    parser.parseOptionalComma();
+
+    // If we don't see a RParen token, we keep parsing.
+    keep_parsing = failed(parser.parseOptionalRParen());
+  } while (keep_parsing);
+
+  // At this point, there shouldn't be any operands left to parse.
+  if (operand_parser.has_operand_left())
+    return parser.emitError(parser.getCurrentLocation());
+
+  // Record how many input loops did we parse.
+  result.addOperands(in_loop_operands);
+  result.addAttribute(KrnlIterateOp::getNumInputLoopsAttrName(),
+      builder.getI64IntegerAttr(in_loop_operands.size()));
+
+  // Add operand bounds to the list of operands of current operation.
+  result.addOperands(operand_bounds);
+
+  // A list of 2N elements where the (2n) and (2n+1) th element specifies
+  // whether the lower and upper bound of the n'th induction variable is stored
+  // as an operand or as an attribute. N being the number of input loops
+  // specified in this krnl.iterate operation.
+  result.addAttribute(KrnlIterateOp::getBoundTypesAttrName(),
+      builder.getArrayAttr(bound_types));
+
+  // Parse the schedule body region.
+  Region* region = result.addRegion();
+  SmallVector<Type, 4> induction_var_types(
+      induction_var_refs.size(), builder.getIndexType());
+  if (parser.parseRegion(*region, induction_var_refs, induction_var_types))
+    return failure();
+
+  // Ensure iterate region is closed off with krnl.terminate.
+  KrnlIterateOp::ensureTerminator(
+      *region, parser.getBuilder(), result.location);
+
+  return success();
+}
+
+static LogicalResult verify(KrnlIterateOp op) {
+  // TODO: Verify number of induction variable bounds matches the number of
+  // input loops.
+}
+
+//===----------------------------------------------------------------------===//
+// KrnlReturnLoopsOp
+//===----------------------------------------------------------------------===//
+
+void print(OpAsmPrinter& p, KrnlReturnLoopsOp& op) {
+  p << "krnl.return_loops ";
+  p.printOperands(op.operand_begin(), op.operand_end());
+}
+
+ParseResult parseKrnlReturnLoopsOp(
+    OpAsmParser& parser, OperationState& result) {
+  // Parse the loops to return.
+  SmallVector<OpAsmParser::OperandType, 4> timestamp_dim_handlers;
+  if (parser.parseOperandList(timestamp_dim_handlers) ||
+      parser.resolveOperands(timestamp_dim_handlers,
+          LoopType::get(result.getContext()), result.operands))
+    return failure();
+
+  return success();
+}
+
+#define GET_OP_CLASSES
+#include "src/compiler/krnl.cpp.inc"
+}  // namespace mlir

src/compiler/dialect/krnl/krnl_ops.hpp

@@ -0,0 +1,51 @@
+//===--------------------- krnl_ops.hpp - MLIR Operations -----------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include "mlir/IR/Builders.h"
+#include "mlir/IR/Dialect.h"
+#include "mlir/IR/OpDefinition.h"
+#include "mlir/IR/StandardTypes.h"
+
+#include "src/compiler/dialect/krnl/krnl_types.hpp"
+
+namespace mlir {
+class KrnlOpsDialect : public Dialect {
+ public:
+  KrnlOpsDialect(MLIRContext* context);
+  static StringRef getDialectNamespace() { return "krnl"; }
+
+  /// Parse a type registered to this dialect. Overriding this method is
+  /// required for dialects that have custom types.
+  /// Technically this is only needed to be able to round-trip to textual IR.
+  mlir::Type parseType(
+      llvm::StringRef tyData, mlir::Location loc) const override {
+    MLIRContext* context = getContext();
+
+    if (tyData.consume_front("loop"))
+      return LoopType::get(context);
+    else
+      return (emitError(loc, "Unexpected type: " + tyData), Type());
+  }
+
+  /// Print a type registered to this dialect. Overriding this method is
+  /// only required for dialects that have custom types.
+  /// Technically this is only needed to be able to round-trip to textual IR.
+  void printType(mlir::Type type, llvm::raw_ostream& os) const override {
+    switch (type.getKind()) {
+      case KrnlTypes::Loop:
+        os << "loop";
+        return;
+    }
+  }
+};
+
+#define GET_OP_CLASSES
+#include "src/compiler/krnl.hpp.inc"
+}  // namespace mlir

src/compiler/dialect/krnl/krnl_ops.td

@@ -0,0 +1,209 @@
+//===--------------------- krnl_ops.td - MLIR Operations ------------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
+include "mlir/IR/OpBase.td"
+
+def Krnl_Dialect : Dialect {
+  let name = "krnl";
+  let cppNamespace = "";
+}
+
+// Require regions to have krnl.terminate terminator operation.
+def ImplicitKrnlTerminator
+    : SingleBlockImplicitTerminator<"KrnlTerminatorOp">;
+
+def KrnlDefineLoopsOp : Op<Krnl_Dialect, "define_loops"> {
+  let summary = "define_loops operation";
+  let description = [{
+
+    The "krnl.define_loops" operation is used to define input loops,
+    those are the for loops appearing in the input program that we
+    intend to optimize.
+
+  }];
+
+  let arguments = (ins);
+  let results = (outs Variadic<AnyType>);
+
+  let skipDefaultBuilders = 1;
+
+  let builders = [
+    OpBuilder<"Builder *builder, OperationState &result,"
+              "int64_t num_loops">
+  ];
+
+  let printer = [{ return ::print(p, *this); }];
+  let parser = [{ return ::parse$cppClass(parser, result); }];
+
+  let extraClassDeclaration = [{
+    static StringRef getNumLoopsAttrName() { return "num_loops"; }
+
+    // Helper function to extract the number of loops being defined.
+    int64_t getNumLoops() {
+        auto num_loops =
+        getAttrOfType<IntegerAttr>(
+            getNumLoopsAttrName())
+                .getValue()
+                .getSExtValue();
+        return num_loops;
+    }
+  }];
+
+
+}
+
+def KrnlOptimizeLoopsOp : Op<Krnl_Dialect, "optimize_loops"> {
+  let summary = "optimize_loops operation";
+  let description = [{
+
+    The "krnl.optimize_loops" operation is essentially a cosmetic operation
+    which exists to encapsulate a region where loops are being scheduled/optimized.
+
+    The optimized loops are returned at the end of the
+    region associated with the krnl.optimize_loops operation.
+
+    For example:
+      TBD once we have actual schedule intrinsics.
+
+  }];
+
+  let arguments = (ins Variadic<AnyType>);
+  let results = (outs Variadic<AnyType>);
+  let regions = (region SizedRegion<1>:$region);
+
+  let skipDefaultBuilders = 1;
+
+  let builders = [
+    OpBuilder<"Builder *builder, OperationState &result, "
+              "int timestamp_space_rank">
+  ];
+
+  let printer = [{ return ::print(p, *this); }];
+  let parser = [{ return ::parse$cppClass(parser, result); }];
+}
+
+def KrnlIterateOp : Op<Krnl_Dialect, "iterate", [ImplicitKrnlTerminator]> {
+  let summary = "iterate operation";
+  let description = [{
+
+    The "krnl.iterate" operation is conceptually equivalent to a nested for loops.
+
+    For instance, say we have the following two
+    %l0, %l1 = krnl.define_loops 2
+    %o0, %o1 = krnl.optimize_loops  {
+        // Identity schedule.
+        krnl.return_loops %l0, %l1
+    }
+
+    Then, consider the following krnl.iterate operation:
+    krnl.iterate (%o0, %o1) with (%l0 -> %i0 = 0 to 10, %l1 -> %i1 = 0 to 10) {
+        // Some operations.
+    }
+
+    It is equivalent to:
+    for (i0=0; i0<10; i0++)
+      for (i1=0; i1<10; i1++)
+        // Some operations.
+  }];
+
+  let arguments = (ins Variadic<AnyType>);
+
+  let regions = (region SizedRegion<1>:$bodyRegion);
+
+  let skipDefaultBuilders = 1;
+
+  let builders = [
+    OpBuilder<"Builder *builder, OperationState &result, "
+              "ArrayRef<Value*> input_loops, ArrayRef<Value*> optimized_loops, "
+              "ArrayRef<Value*> operand_bounds, ArrayRef<int64_t> const_bounds, "
+              "ArrayRef<int> bound_types">
+  ];
+
+  let extraClassDeclaration = [{
+
+    // In krnl.iterate operation, three types of SSA values are stored:
+    // - Optimized krnl.loops.
+    // - Input krnl.loops.
+    // - SSA value based induction variable bound (parametric bound).
+    // We record the number of optimized and input loops to separate these three
+    // group of operands out.
+    static StringRef getNumOptimizedLoopsAttrName() { return "num_optimized_loops"; }
+
+    int64_t getNumOptimizedLoops() {
+      auto num_optimized_loops =
+        getAttrOfType<IntegerAttr>(
+                getNumOptimizedLoopsAttrName())
+              .getValue()
+              .getSExtValue();
+      return num_optimized_loops;
+    }
+
+    static StringRef getNumInputLoopsAttrName() { return "num_input_loops"; }
+
+    int64_t getNumInputLoops() {
+      auto num_loops =
+        getAttrOfType<IntegerAttr>(
+                getNumInputLoopsAttrName())
+              .getValue()
+              .getSExtValue();
+      return num_loops;
+    }
+
+    // Constant bounds are stored here as a list attribute.
+    static StringRef getConstantBoundsAttrName() { return "constant_bounds"; }
+
+    // Store type of each bound as three types:
+    // - 0 = constant attribute.
+    // - 1 = operand type.
+    // - 2 = affine maps (TODO).
+    static StringRef getBoundTypesAttrName() { return "bound_types"; }
+
+    // Get dynamic attribute name for the i-th lower and upper bound.
+    static std::string getBoundAttrName(int64_t i, bool is_ub) {
+      std::string bound_type = is_ub ? "_ub" : "_lb";
+      std::string bound_idx = std::to_string(i);
+      return "__bound_" + bound_idx + bound_type;
+    }
+    }];
+
+  let printer = [{ return ::print(p, *this); }];
+  let parser = [{ return ::parse$cppClass(parser, result); }];
+  let verifier = [{ return ::verify(*this); }];
+}
+
+def KrnlReturnLoopsOp : Op<Krnl_Dialect, "return_loops", [Terminator]> {
+  let summary = "Krnl return handler operation";
+  let description = [{
+    Krnl return_loops operation is a terminator operation for returning
+    scheduled dimension handlers in the krnl.optimize_loops region.
+  }];
+
+  let arguments = (ins Variadic<AnyType>);
+
+  let printer = [{ return ::print(p, *this); }];
+  let parser = [{ return ::parse$cppClass(parser, result); }];
+}
+
+def KrnlTerminatorOp : Op<Krnl_Dialect, "terminate", [Terminator]> {
+  let summary = "Krnl terminator operation";
+  let description = [{
+    Krnl terminator is a special terminator operation for blocks inside krnl
+    iterate operations. It unconditionally transmits the control flow to the
+    successor of the operation enclosing the region.
+
+    This operation does _not_ have a custom syntax. However, krnl control
+    operations omit the terminator in their custom syntax for brevity.
+  }];
+
+  // No custom parsing/printing form.
+  let parser = ?;
+  let printer = ?;
+
+  // Fully specified by traits.
+  let verifier = ?;
+}

src/compiler/dialect/krnl/krnl_types.cpp

@@ -0,0 +1,9 @@
+//===--------------------- krnl_types.cpp - MLIR Operations ---------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
+#include "krnl_types.hpp"

src/compiler/dialect/krnl/krnl_types.hpp

@@ -0,0 +1,36 @@
+//===--------------------- krnl_types.hpp - MLIR Operations ---------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include <mlir/IR/Types.h>
+
+namespace mlir {
+
+namespace KrnlTypes {
+enum Kinds {
+  // A krnl.loop is simply a reference to a for loop and will be used to:
+  // - Indicate the presence of a for loop in krnl.iterate.
+  // - Identify the loop in optimization intrinsics.
+  Loop = mlir::Type::Kind::FIRST_PRIVATE_EXPERIMENTAL_0_TYPE,
+};
+}
+
+class LoopType : public mlir::Type::TypeBase<LoopType, mlir::Type> {
+ public:
+  using Base::Base;
+
+  // Support type inquiry through isa, cast and dyn_cast.
+  static bool kindof(unsigned kind) { return kind == KrnlTypes::Loop; }
+
+  // Get a unique instance of Loop type.
+  static LoopType get(mlir::MLIRContext* context) {
+    return Base::get(context, KrnlTypes::Loop);
+  }
+};
+}  // namespace mlir

src/compiler/dialect/krnl/parser_helper.cpp

@@ -0,0 +1,52 @@
+//===------------------ parser_helper.cpp - MLIR Operations ---------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
+#include "parser_helper.hpp"
+
+#include "src/compiler/dialect/krnl/krnl_ops.hpp"
+
+namespace onnf {
+
+mlir::ParseResult KrnlDialectOperandParser::ParseOptionalOperand(
+    mlir::Type operand_type, mlir::Value*& operand) {
+  // If operand queue is empty, parse more operands and cache them.
+  if (_operand_ref_queue.empty()) {
+    // Parse operand types:
+    llvm::SmallVector<mlir::OpAsmParser::OperandType, 2> operand_refs;
+    _parser.parseOperandList(operand_refs);
+
+    // Record operands:
+    for (auto& operand_ref : operand_refs)
+      _operand_ref_queue.emplace(operand_ref);
+  }
+
+  // If we parsed some operand reference(s), resolve the ref to an operand:
+  if (!_operand_ref_queue.empty()) {
+    auto operand_ref = _operand_ref_queue.front();
+    _operand_ref_queue.pop();
+
+    llvm::SmallVector<mlir::Value*, 1> operands;
+    _parser.resolveOperand(operand_ref, operand_type, operands);
+    operand = operands.front();
+    return mlir::success();
+  } else {
+    operand = nullptr;
+    return mlir::failure();
+  }
+}
+
+mlir::ParseResult KrnlDialectOperandParser::ParseOperand(
+    mlir::Type operand_type, mlir::Value*& operand) {
+  ParseOptionalOperand(operand_type, operand);
+  if (operand == nullptr)
+    return _parser.emitError(
+        _parser.getCurrentLocation(), "Expecting an operand.");
+  return mlir::success();
+}
+
+}  // namespace onnf

src/compiler/dialect/krnl/parser_helper.hpp

@@ -0,0 +1,46 @@
+//===------------------ parser_helper.hpp - MLIR Operations ---------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include <queue>
+
+#include "mlir/IR/Builders.h"
+#include "mlir/IR/Dialect.h"
+#include "mlir/IR/OpDefinition.h"
+#include "mlir/IR/OpImplementation.h"
+#include "mlir/IR/StandardTypes.h"
+
+namespace onnf {
+
+class KrnlDialectOperandParser {
+ public:
+  KrnlDialectOperandParser(mlir::OpAsmParser& parser)
+      : _parser(parser), _builder(parser.getBuilder()){};
+
+  // Parse an optional operand.
+  mlir::ParseResult ParseOptionalOperand(
+      mlir::Type operand_type, mlir::Value*& operand);
+
+  // Parse a required operand.
+  mlir::ParseResult ParseOperand(
+      mlir::Type operand_type, mlir::Value*& operand);
+
+  // Do we have more operands to parse?
+  bool has_operand_left() { return !_operand_ref_queue.empty(); }
+
+ private:
+  mlir::OpAsmParser& _parser;
+
+  mlir::Builder& _builder;
+
+  // A queue storing the parsed SSA id references.
+  std::queue<mlir::OpAsmParser::OperandType> _operand_ref_queue;
+};
+
+}  // namespace onnf

src/compiler/ir/knl/knl.td

@@ -1,27 +0,0 @@
-include "mlir/IR/OpBase.td"
-
-def Knl_Dialect : Dialect {
-  let name = "knl";
-  let cppNamespace = "";
-}
-
-def KnlIterate : Op<Knl_Dialect, "iterate"> {
-  let summary = "iterate operation";
-  let description = [{
-
-    The "knl.iterate" operation is conceptually equivalent to a nested for loop
-    in that it represents ordered interation of integer coordinates within an
-    affine integer set.
-
-  }];
-
-  let arguments = (ins Variadic<AnyType>);
-  let regions = (region SizedRegion<1>:$region);
-
-  let skipDefaultBuilders = 1;
-
-  let builders = [
-    OpBuilder<"Builder *builder, OperationState &result, "
-              "IntegerSet set, ArrayRef<Value *> args">
-  ];
-}

src/compiler/ir/knl/knl_ops.cpp

@@ -1,23 +0,0 @@
-#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/SmallBitVector.h"
-#include "mlir/IR/Block.h"
-#include "mlir/IR/Builders.h"
-#include "mlir/IR/Function.h"
-#include "mlir/IR/IntegerSet.h"
-#include "mlir/IR/Matchers.h"
-#include "mlir/IR/OpImplementation.h"
-#include "mlir/IR/PatternMatch.h"
-
-#include "knl_ops.hpp"
-
-namespace mlir {
-KnlOpsDialect::KnlOpsDialect(MLIRContext* context)
-    : Dialect(getDialectNamespace(), context) {
-  addOperations<
-#define GET_OP_LIST
-#include "src/compiler/knl.cpp.inc"
-      >();
-}
-}  // namespace mlir
-
-namespace onnf {}

src/compiler/ir/knl/knl_ops.hpp

@@ -1,19 +0,0 @@
-#pragma once
-
-#include "mlir/IR/Builders.h"
-#include "mlir/IR/Dialect.h"
-#include "mlir/IR/OpDefinition.h"
-#include "mlir/IR/StandardTypes.h"
-
-namespace mlir {
-class KnlOpsDialect : public Dialect {
- public:
-  KnlOpsDialect(MLIRContext* context);
-  static StringRef getDialectNamespace() { return "knl"; }
-};
-
-#define GET_OP_CLASSES
-#include "src/compiler/knl.hpp.inc"
-}  // namespace mlir
-
-namespace onnf {}

src/compiler/tool/onnf_opt/onnf_opt.cpp

@@ -16,6 +16,11 @@
 #include <mlir/Support/MlirOptMain.h>
 #include <mlir/Dialect/StandardOps/Ops.h>
 
+#include "src/compiler/dialect/krnl/krnl_ops.hpp"
+#include "src/compiler/helper.hpp"
+
+using namespace onnf;
+
 static llvm::cl::opt<std::string> input_filename(
     llvm::cl::Positional, llvm::cl::desc("<input file>"), llvm::cl::init("-"));
 
@@ -52,6 +57,7 @@ int main(int argc, char** argv) {
 
   auto output = mlir::openOutputFile(output_filename, &error_message);
 
+  mlir::registerDialect<mlir::KrnlOpsDialect>();
   mlir::registerDialect<mlir::StandardOpsDialect>();
 
   return failed(mlir::MlirOptMain(output->os(), std::move(file), passPipeline,

src/main.cpp

@@ -1,3 +1,11 @@
+//===--------------------------- main.cpp ---------------------------------===//
+//
+// Copyright 2019 The IBM Research Authors.
+//
+// =============================================================================
+//
+//===----------------------------------------------------------------------===//
+
 #include <cmath>
 #include <cstdlib>
 #include <iostream>
@@ -21,6 +29,7 @@
 #include <boost/program_options.hpp>
 
 #include "src/builder/frontend_dialect_transformer.hpp"
+#include "src/compiler/dialect/krnl/krnl_ops.hpp"
 #include "src/compiler/dialect/onnx/onnx_ops.hpp"
 #include "src/compiler/pass/passes.hpp"
 
@@ -57,6 +66,7 @@ int main(int ac, char* av[]) {
   }
 
   mlir::registerDialect<mlir::ONNXOpsDialect>();
+  mlir::registerDialect<mlir::KrnlOpsDialect>();
 
   mlir::MLIRContext context;
   mlir::OwningModuleRef module;