Add pass generate per block in a function a GraphViz Dot graph with ops as nodes

* Add GraphTraits that treat a block as a graph, Operation* as node and use-relationship for edges;
  - Just basic graph output;
* Add use iterator to iterate over all uses of an Operation;
* Add testing pass to generate op graph;

This does not support arbitrary operations other than function nor nested regions yet.

PiperOrigin-RevId: 268121782

mlir/include/mlir/IR/Operation.h

@@ -686,6 +686,33 @@ public:
       : llvm::mapped_iterator<ResultIterator, Type (*)(Value *)>(it, &unwrap) {}
 };
 
+/// This class implements use iterator for the Operation. This iterates over all
+/// uses of all results of an Operation.
+class UseIterator final
+    : public llvm::iterator_facade_base<UseIterator, std::forward_iterator_tag,
+                                        Operation *> {
+public:
+  /// Initialize UseIterator for op, specify end to return iterator to last use.
+  explicit UseIterator(Operation *op, bool end = false);
+
+  UseIterator &operator++();
+  Operation *operator->() { return use->getOwner(); }
+  Operation *operator*() { return use->getOwner(); }
+
+  bool operator==(const UseIterator &other) const;
+  bool operator!=(const UseIterator &other) const;
+
+private:
+  void skipOverResultsWithNoUsers();
+
+  /// The operation whose uses are being iterated over.
+  Operation *op;
+  /// The result of op whoses uses are being iterated over.
+  Operation::result_iterator res;
+  /// The use of the result.
+  Value::use_iterator use;
+};
+
 // Implement the inline result iterator methods.
 inline auto Operation::result_begin() -> result_iterator {
   return result_iterator(this, 0);

mlir/include/mlir/Transforms/ViewOpGraph.h

@@ -0,0 +1,51 @@
+//===- ViewOpGraph.h - View/write op graphviz graphs ------------*- C++ -*-===//
+//
+// Copyright 2019 The MLIR Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// =============================================================================
+//
+// Defines interface to produce Graphviz outputs of MLIR op within block.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_TRANSFORMS_VIEWOPGRAPH_H_
+#define MLIR_TRANSFORMS_VIEWOPGRAPH_H_
+
+#include "mlir/Support/LLVM.h"
+#include "llvm/Support/GraphWriter.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace mlir {
+class Block;
+class ModuleOp;
+template <typename T> class OpPassBase;
+using ModulePassBase = OpPassBase<ModuleOp>;
+
+/// Displays the graph in a window. This is for use from the debugger and
+/// depends on Graphviz to generate the graph.
+void viewGraph(Block &block, const Twine &name, bool shortNames = false,
+               const Twine &title = "",
+               llvm::GraphProgram::Name program = llvm::GraphProgram::DOT);
+
+llvm::raw_ostream &writeGraph(llvm::raw_ostream &os, Block &block,
+                              bool shortNames = false, const Twine &title = "");
+
+/// Creates a pass to print op graphs.
+std::unique_ptr<ModulePassBase>
+createPrintOpGraphPass(llvm::raw_ostream &os = llvm::errs(),
+                       bool shortNames = false, const llvm::Twine &title = "");
+
+} // end namespace mlir
+
+#endif // MLIR_TRANSFORMS_VIEWOPGRAPH_H_

mlir/lib/IR/Operation.cpp

@@ -1026,3 +1026,46 @@ void impl::ensureRegionTerminator(
 
   block.push_back(buildTerminatorOp());
 }
+
+UseIterator::UseIterator(Operation *op, bool end)
+    : op(op), res(end ? op->result_end() : op->result_begin()) {
+  // Only initialize current use if there are results/can be uses.
+  if (op->getNumResults())
+    skipOverResultsWithNoUsers();
+}
+
+UseIterator &UseIterator::operator++() {
+  // We increment over uses, if we reach the last use then move to next
+  // result.
+  if (use != (*res)->use_end())
+    ++use;
+  if (use == (*res)->use_end()) {
+    ++res;
+    skipOverResultsWithNoUsers();
+  }
+  return *this;
+}
+
+bool UseIterator::operator==(const UseIterator &other) const {
+  if (op != other.op)
+    return false;
+  if (op->getNumResults() == 0)
+    return true;
+  return res == other.res && use == other.use;
+}
+
+bool UseIterator::operator!=(const UseIterator &other) const {
+  return !(*this == other);
+}
+
+void UseIterator::skipOverResultsWithNoUsers() {
+  while (res != op->result_end() && (*res)->use_empty())
+    ++res;
+
+  // If we are at the last result, then set use to first use of
+  // first result (sentinel value used for end).
+  if (res == op->result_end())
+    use = {};
+  else
+    use = (*res)->use_begin();
+}

mlir/lib/Transforms/CMakeLists.txt

@@ -20,6 +20,7 @@ add_llvm_library(MLIRTransforms
   SimplifyAffineStructures.cpp
   StripDebugInfo.cpp
   Vectorize.cpp
+  ViewOpGraph.cpp
   ViewRegionGraph.cpp
 
   ADDITIONAL_HEADER_DIRS

mlir/lib/Transforms/ViewOpGraph.cpp

@@ -0,0 +1,163 @@
+//===- ViewOpGraph.cpp - View/write op graphviz graphs --------------------===//
+//
+// Copyright 2019 The MLIR Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// =============================================================================
+
+#include "mlir/Transforms/ViewOpGraph.h"
+#include "mlir/IR/Block.h"
+#include "mlir/IR/Operation.h"
+#include "mlir/Pass/Pass.h"
+#include "llvm/Support/CommandLine.h"
+
+// NOLINTNEXTLINE
+static llvm::cl::opt<int> elideIfLarger(
+    "print-op-graph-elide-if-larger",
+    llvm::cl::desc("Upper limit to emit elements attribute rather than elide"),
+    llvm::cl::init(16));
+
+namespace llvm {
+
+// Specialize GraphTraits to treat Block as a graph of Operations as nodes and
+// uses as edges.
+template <> struct llvm::GraphTraits<mlir::Block *> {
+  using GraphType = mlir::Block *;
+  using NodeRef = mlir::Operation *;
+
+  using ChildIteratorType = mlir::UseIterator;
+  static ChildIteratorType child_begin(NodeRef n) {
+    return ChildIteratorType(n);
+  }
+  static ChildIteratorType child_end(NodeRef n) {
+    return ChildIteratorType(n, /*end=*/true);
+  }
+
+  // Operation's destructor is private so use Operation* instead and use
+  // mapped iterator.
+  static mlir::Operation *AddressOf(mlir::Operation &op) { return &op; }
+  using nodes_iterator =
+      mapped_iterator<mlir::Block::iterator, decltype(&AddressOf)>;
+  static nodes_iterator nodes_begin(mlir::Block *b) {
+    return nodes_iterator(b->begin(), &AddressOf);
+  }
+  static nodes_iterator nodes_end(mlir::Block *b) {
+    return nodes_iterator(b->end(), &AddressOf);
+  }
+};
+
+// Specialize DOTGraphTraits to produce more readable output.
+template <>
+struct DOTGraphTraits<mlir::Block *> : public DefaultDOTGraphTraits {
+  using DefaultDOTGraphTraits::DefaultDOTGraphTraits;
+  static std::string getNodeLabel(mlir::Operation *op, mlir::Block *);
+};
+
+std::string DOTGraphTraits<mlir::Block *>::getNodeLabel(mlir::Operation *op,
+                                                        mlir::Block *b) {
+  // Reuse the print output for the node labels.
+  std::string ostr;
+  raw_string_ostream os(ostr);
+  os << op->getName() << "\n";
+  for (auto attr : op->getAttrs()) {
+    os << '\n' << attr.first << ": ";
+    // Always emit splat attributes.
+    if (attr.second.isa<mlir::SplatElementsAttr>()) {
+      attr.second.print(os);
+      continue;
+    }
+
+    // Elide "big" elements attributes.
+    auto elements = attr.second.dyn_cast<mlir::ElementsAttr>();
+    if (elements && elements.getNumElements() > elideIfLarger) {
+      os << "...";
+      continue;
+    }
+
+    // Print all other attributes.
+    attr.second.print(os);
+  }
+  return os.str();
+}
+
+} // end namespace llvm
+
+namespace {
+// PrintOpPass is simple pass to write graph per function.
+// Note: this is a module pass only to avoid interleaving on the same ostream
+// due to multi-threading over functions.
+struct PrintOpPass : public mlir::ModulePass<PrintOpPass> {
+  explicit PrintOpPass(llvm::raw_ostream &os = llvm::errs(),
+                       bool short_names = false, const llvm::Twine &title = "")
+      : os(os), title(title.str()), short_names(short_names) {}
+
+  std::string getOpName(mlir::Operation &op) {
+    auto symbolAttr = op.getAttrOfType<mlir::StringAttr>(
+        mlir::SymbolTable::getSymbolAttrName());
+    if (symbolAttr)
+      return symbolAttr.getValue();
+    ++unnamedOpCtr;
+    return (op.getName().getStringRef() + llvm::utostr(unnamedOpCtr)).str();
+  }
+
+  // Print all the ops in a module.
+  void processModule(mlir::ModuleOp module) {
+    for (mlir::Operation &op : module) {
+      // Modules may actually be nested, recurse on nesting.
+      if (auto nestedModule = llvm::dyn_cast<mlir::ModuleOp>(op)) {
+        processModule(nestedModule);
+        continue;
+      }
+      auto opName = getOpName(op);
+      for (mlir::Region &region : op.getRegions()) {
+        for (auto indexed_block : llvm::enumerate(region)) {
+          // Suffix block number if there are more than 1 block.
+          auto blockName = region.getBlocks().size() == 1
+                               ? ""
+                               : ("__" + llvm::utostr(indexed_block.index()));
+          llvm::WriteGraph(os, &indexed_block.value(), short_names,
+                           llvm::Twine(title) + opName + blockName);
+        }
+      }
+    }
+  }
+
+  void runOnModule() override { processModule(getModule()); }
+
+private:
+  llvm::raw_ostream &os;
+  std::string title;
+  int unnamedOpCtr = 0;
+  bool short_names;
+};
+} // namespace
+
+void mlir::viewGraph(mlir::Block &block, const llvm::Twine &name,
+                     bool shortNames, const llvm::Twine &title,
+                     llvm::GraphProgram::Name program) {
+  llvm::ViewGraph(&block, name, shortNames, title, program);
+}
+
+llvm::raw_ostream &mlir::writeGraph(llvm::raw_ostream &os, mlir::Block &block,
+                                    bool shortNames, const llvm::Twine &title) {
+  return llvm::WriteGraph(os, &block, shortNames, title);
+}
+
+std::unique_ptr<mlir::ModulePassBase>
+mlir::createPrintOpGraphPass(llvm::raw_ostream &os, bool shortNames,
+                             const llvm::Twine &title) {
+  return std::make_unique<PrintOpPass>(os, shortNames, title);
+}
+
+static mlir::PassRegistration<PrintOpPass> pass("print-op-graph",
+                                                "Print op graph per region");