Factor out translation registry.

The mlir-translate tool is expected to discover individual translations at link
time.  These translations must register themselves and may need the utilities
that are currently defined in mlir-translate.cpp for their entry point
functions.  Since mlir-translate is linking against individual translations,
the translations cannot link against mlir-translate themselves.  Extract out
the utilities into a separate "Translation" library to avoid the potential
dependency cycle.  Individual translations link to that library to access
TranslateRegistration. The mlir-translate tool links to individual translations
and to the "Translation" library because it needs the utilities as well.

The main header of the new library is located in include/mlir/Translation.h to
make it easily accessible by translators.  The rationale for putting it to
include/mlir rather than to one of its subdirectories is that its purpose is
similar to that of include/mlir/Pass.h so it makes sense to put them at the
same level.

PiperOrigin-RevId: 222398617

mlir/include/mlir/Translation.h

@@ -0,0 +1,54 @@
+//===- Translation.h - Translation registry ---------------------*- 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.
+// =============================================================================
+//
+// Registry for user-provided translations.
+//
+//===----------------------------------------------------------------------===//
+#ifndef MLIR_TRANSLATION_H
+#define MLIR_TRANSLATION_H
+
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+
+namespace mlir {
+class MLIRContext;
+class Module;
+
+using TranslateFunction =
+    std::function<bool(llvm::StringRef inputFilename,
+                       llvm::StringRef oututFilename, MLIRContext *)>;
+
+// Use TranslateRegistration as a global initialiser that registers a function
+// and associates it with name. This requires that a translation has not been
+// registered to a given name.
+//
+// Usage:
+//
+//   // At namespace scope.
+//   static TranslateRegistration Unused(&MySubCommand, [] { ... });
+//
+struct TranslateRegistration {
+  TranslateRegistration(llvm::StringRef name,
+                        const TranslateFunction &function);
+};
+
+/// Get a read-only reference to the translator registry.
+const llvm::StringMap<TranslateFunction> &getTranslationRegistry();
+
+} // namespace mlir
+
+#endif // MLIR_TRANSLATION_H

mlir/lib/Translation/Translation.cpp

@@ -0,0 +1,48 @@
+//===- Translation.cpp - Translation registry -------------------*- 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.
+// =============================================================================
+//
+// Definitions of the translation registry.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Translation.h"
+#include "mlir/Support/LLVM.h"
+#include "llvm/Support/ManagedStatic.h"
+
+using namespace mlir;
+
+// Get the mutable static map between translations registered and the
+// TranslateFunctions that perform those translations.
+static llvm::StringMap<TranslateFunction> &getMutableTranslationRegistry() {
+  static llvm::StringMap<TranslateFunction> translationRegistry;
+  return translationRegistry;
+}
+
+TranslateRegistration::TranslateRegistration(
+    StringRef name, const TranslateFunction &function) {
+  auto &translationRegistry = getMutableTranslationRegistry();
+  if (translationRegistry.find(name) != translationRegistry.end())
+    llvm::report_fatal_error("Attempting to overwrite an existing function");
+  assert(function && "Attempting to register an empty translate function");
+  translationRegistry[name] = function;
+}
+
+// Merely add the const qualifier to the mutable registry so that external users
+// cannot modify it.
+const llvm::StringMap<TranslateFunction> &mlir::getTranslationRegistry() {
+  return getMutableTranslationRegistry();
+}

mlir/tools/mlir-translate/mlir-translate.cpp

@@ -24,11 +24,11 @@
 #include "mlir/IR/MLIRContext.h"
 #include "mlir/IR/Module.h"
 #include "mlir/Parser.h"
+#include "mlir/Translation.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileUtilities.h"
 #include "llvm/Support/InitLLVM.h"
-#include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/ToolOutputFile.h"
@@ -57,17 +57,26 @@ Module *mlir::parseMLIRInput(StringRef inputFilename, MLIRContext *context) {
   return parseSourceFile(sourceMgr, context);
 }
 
-bool mlir::printMLIROutput(const Module &module,
-                           llvm::StringRef outputFilename) {
+std::unique_ptr<llvm::ToolOutputFile>
+mlir::openOutputFile(llvm::StringRef outputFilename) {
   std::error_code error;
   auto result = llvm::make_unique<llvm::ToolOutputFile>(outputFilename, error,
                                                         llvm::sys::fs::F_None);
   if (error) {
     llvm::errs() << error.message();
-    return true;
+    return nullptr;
   }
-  module.print(result->os());
-  result->keep();
+
+  return result;
+}
+
+bool mlir::printMLIROutput(const Module &module,
+                           llvm::StringRef outputFilename) {
+  auto file = openOutputFile(outputFilename);
+  if (!file)
+    return true;
+  module.print(file->os());
+  file->keep();
   return false;
 }
 
@@ -83,24 +92,11 @@ static TranslateRegistration MLIRToMLIRTranslate(
       return printMLIROutput(*module, outputFilename);
     });
 
-// Static map between translations registered and the TranslateFunctions that
-// perform those translations.
-static llvm::ManagedStatic<llvm::StringMap<TranslateFunction>>
-    translationRegistry;
-
-TranslateRegistration::TranslateRegistration(
-    llvm::StringRef name, const TranslateFunction &function) {
-  if (translationRegistry->find(name) != translationRegistry->end())
-    llvm::report_fatal_error("Attempting to overwrite an existing function");
-  assert(function && "Attempting to register an empty translate function");
-  (*translationRegistry)[name] = function;
-}
-
 // Custom parser for TranslateFunction.
 struct TranslationParser : public llvm::cl::parser<const TranslateFunction *> {
   TranslationParser(llvm::cl::Option &opt)
       : llvm::cl::parser<const TranslateFunction *>(opt) {
-    for (const auto &kv : *translationRegistry) {
+    for (const auto &kv : getTranslationRegistry()) {
       addLiteralOption(kv.first(), &kv.second, kv.first());
     }
   }

mlir/tools/mlir-translate/mlir-translate.h

@@ -1,4 +1,4 @@
-//===- mlir-translate.h - Registry & utility functions for translations ---===//
+//===- mlir-translate.h - Translation driver -----------------*- C++ -*----===//
 //
 // Copyright 2019 The MLIR Authors.
 //
@@ -22,29 +22,20 @@
 #ifndef TOOLS_MLIR_TRANSLATE_H
 #define TOOLS_MLIR_TRANSLATE_H
 
-#include "llvm/ADT/StringRef.h"
+#include "mlir/Support/LLVM.h"
+#include <memory>
+
+namespace llvm {
+class ToolOutputFile;
+}
 
 namespace mlir {
 class MLIRContext;
 class Module;
 
-using TranslateFunction =
-    std::function<bool(llvm::StringRef inputFilename,
-                       llvm::StringRef oututFilename, MLIRContext *)>;
-
-// Use TranslateRegistration as a global initialiser that registers a function
-// and associates it with name. This requires that a translation has not been
-// registered to a given name.
-//
-// Usage:
-//
-//   // At namespace scope.
-//   static TranslateRegistration Unused(&MySubCommand, [] { ... });
-//
-struct TranslateRegistration {
-  TranslateRegistration(llvm::StringRef name,
-                        const TranslateFunction &function);
-};
+/// Open a file to be used as raw_ostream.
+std::unique_ptr<llvm::ToolOutputFile>
+openOutputFile(llvm::StringRef outputFilename);
 
 // Returns module parsed from input filename or null in case of error.
 Module *parseMLIRInput(llvm::StringRef inputFilename, MLIRContext *context);