[mlir][NFC] Split registerAndParseCLIOptions() in mlir-opt

mlir-opt's registerAndParseCLIOptions() forces users to both register
default MLIR options and parse the command line string. Custom mlir-opt
implementations, however, may need to provide own options or own
parsing. It seems that separating the two functions makes it easier to
achieve necessary customizations.

For example, one can register "default" options, then register custom
options (not available in standard mlir-opt), then parse all of them.
Other cases include two-stage parsing where some additional options
become available based on parsed information (e.g. compilation target
can allow additional options to be present).

Author: andrey-golubev

mlir/include/mlir/Tools/mlir-opt/MlirOptMain.h

@@ -359,6 +359,20 @@ class MlirOptMainConfig {
 /// the loaded IR.
 using PassPipelineFn = llvm::function_ref<LogicalResult(PassManager &pm)>;
 
+/// Register basic command line options.
+/// - toolName is used for the header displayed by `--help`.
+/// - registry should contain all the dialects that can be parsed in the source.
+/// - return std::string for help header
+std::string registerCLIOptions(llvm::StringRef toolName,
+                               DialectRegistry &registry);
+
+/// Parse command line options.
+/// - helpHeader is used for the header displayed by `--help`.
+/// - return std::pair<std::string, std::string> for
+///   inputFilename and outputFilename command line option values.
+std::pair<std::string, std::string> parseCLIOptions(int argc, char **argv,
+                                                    llvm::StringRef helpHeader);
+
 /// Register and parse command line options.
 /// - toolName is used for the header displayed by `--help`.
 /// - registry should contain all the dialects that can be parsed in the source.

mlir/lib/Tools/mlir-opt/MlirOptMain.cpp

@@ -681,17 +681,8 @@ processBuffer(raw_ostream &os, std::unique_ptr<MemoryBuffer> ownedBuffer,
   return success();
 }
 
-std::pair<std::string, std::string>
-mlir::registerAndParseCLIOptions(int argc, char **argv,
-                                 llvm::StringRef toolName,
-                                 DialectRegistry &registry) {
-  static cl::opt<std::string> inputFilename(
-      cl::Positional, cl::desc("<input file>"), cl::init("-"));
-
-  static cl::opt<std::string> outputFilename("o", cl::desc("Output filename"),
-                                             cl::value_desc("filename"),
-                                             cl::init("-"));
-  // Register any command line options.
+std::string mlir::registerCLIOptions(llvm::StringRef toolName,
+                                     DialectRegistry &registry) {
   MlirOptMainConfig::registerCLOptions(registry);
   registerAsmPrinterCLOptions();
   registerMLIRContextCLOptions();
@@ -706,11 +697,29 @@ mlir::registerAndParseCLIOptions(int argc, char **argv,
     interleaveComma(registry.getDialectNames(), os,
                     [&](auto name) { os << name; });
   }
-  // Parse pass names in main to ensure static initialization completed.
+  return helpHeader;
+}
+
+std::pair<std::string, std::string>
+mlir::parseCLIOptions(int argc, char **argv, llvm::StringRef helpHeader) {
+  static cl::opt<std::string> inputFilename(
+      cl::Positional, cl::desc("<input file>"), cl::init("-"));
+
+  static cl::opt<std::string> outputFilename("o", cl::desc("Output filename"),
+                                             cl::value_desc("filename"),
+                                             cl::init("-"));
   cl::ParseCommandLineOptions(argc, argv, helpHeader);
   return std::make_pair(inputFilename.getValue(), outputFilename.getValue());
 }
 
+std::pair<std::string, std::string>
+mlir::registerAndParseCLIOptions(int argc, char **argv,
+                                 llvm::StringRef toolName,
+                                 DialectRegistry &registry) {
+  auto helpHeader = registerCLIOptions(toolName, registry);
+  return parseCLIOptions(argc, argv, helpHeader);
+}
+
 static LogicalResult printRegisteredDialects(DialectRegistry &registry) {
   llvm::outs() << "Available Dialects: ";
   interleave(registry.getDialectNames(), llvm::outs(), ",");