[mlir] Add --list-passes option to mlir-opt (#100420)

Currently, the only way to see the passes that were registered is by
calling “mlir-opt --help”. However, for compilers with 500+ passes, the
help message becomes too long and sometimes hard to understand. In this
PR I add a new "--list-passes" option to mlir-opt, which can be used for
printing only the registered passes, a feature that would be extremely
useful.

Author: Natan-GabrielTiutiuIntel

mlir/include/mlir/Pass/PassRegistry.h

@@ -44,6 +44,9 @@ using PassAllocatorFunction = std::function<std::unique_ptr<Pass>()>;
 // PassRegistry
 //===----------------------------------------------------------------------===//
 
+/// Prints the passes that were previously registered and stored in passRegistry
+void printRegisteredPasses();
+
 /// Structure to group information about a passes and pass pipelines (argument
 /// to invoke via mlir-opt, description, pass pipeline builder).
 class PassRegistryEntry {

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

@@ -119,6 +119,13 @@ class MlirOptMainConfig {
     return success();
   }
 
+  /// List the registered passes and return.
+  MlirOptMainConfig &listPasses(bool list) {
+    listPassesFlag = list;
+    return *this;
+  }
+  bool shouldListPasses() const { return listPassesFlag; }
+
   /// Enable running the reproducer information stored in resources (if
   /// present).
   MlirOptMainConfig &runReproducer(bool enableReproducer) {
@@ -219,6 +226,9 @@ class MlirOptMainConfig {
   /// The callback to populate the pass manager.
   std::function<LogicalResult(PassManager &)> passPipelineCallback;
 
+  /// List the registered passes and return.
+  bool listPassesFlag = false;
+
   /// Enable running the reproducer.
   bool runReproducerFlag = false;
 

mlir/lib/Pass/PassRegistry.cpp

@@ -68,6 +68,32 @@ static void printOptionHelp(StringRef arg, StringRef desc, size_t indent,
 // PassRegistry
 //===----------------------------------------------------------------------===//
 
+/// Prints the passes that were previously registered and stored in passRegistry
+void mlir::printRegisteredPasses() {
+  size_t maxWidth = 0;
+  for (auto &entry : *passRegistry)
+    maxWidth = std::max(maxWidth, entry.second.getOptionWidth() + 4);
+
+  // Functor used to print the ordered entries of a registration map.
+  auto printOrderedEntries = [&](StringRef header, auto &map) {
+    llvm::SmallVector<PassRegistryEntry *, 32> orderedEntries;
+    for (auto &kv : map)
+      orderedEntries.push_back(&kv.second);
+    llvm::array_pod_sort(
+        orderedEntries.begin(), orderedEntries.end(),
+        [](PassRegistryEntry *const *lhs, PassRegistryEntry *const *rhs) {
+          return (*lhs)->getPassArgument().compare((*rhs)->getPassArgument());
+        });
+
+    llvm::outs().indent(0) << header << ":\n";
+    for (PassRegistryEntry *entry : orderedEntries)
+      entry->printHelpStr(/*indent=*/2, maxWidth);
+  };
+
+  // Print the available passes.
+  printOrderedEntries("Passes", *passRegistry);
+}
+
 /// Print the help information for this pass. This includes the argument,
 /// description, and any pass options. `descIndent` is the indent that the
 /// descriptions should be aligned.

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

@@ -30,6 +30,7 @@
 #include "mlir/Parser/Parser.h"
 #include "mlir/Pass/Pass.h"
 #include "mlir/Pass/PassManager.h"
+#include "mlir/Pass/PassRegistry.h"
 #include "mlir/Support/FileUtilities.h"
 #include "mlir/Support/Timing.h"
 #include "mlir/Support/ToolUtilities.h"
@@ -118,6 +119,10 @@ struct MlirOptMainConfigCLOptions : public MlirOptMainConfig {
                  "parsing"),
         cl::location(useExplicitModuleFlag), cl::init(false));
 
+    static cl::opt<bool, /*ExternalStorage=*/true> listPasses(
+        "list-passes", cl::desc("Print the list of registered passes and exit"),
+        cl::location(listPassesFlag), cl::init(false));
+
     static cl::opt<bool, /*ExternalStorage=*/true> runReproducer(
         "run-reproducer", cl::desc("Run the pipeline stored in the reproducer"),
         cl::location(runReproducerFlag), cl::init(false));
@@ -522,13 +527,21 @@ static LogicalResult printRegisteredDialects(DialectRegistry &registry) {
   return success();
 }
 
+static LogicalResult printRegisteredPassesAndReturn() {
+  mlir::printRegisteredPasses();
+  return success();
+}
+
 LogicalResult mlir::MlirOptMain(llvm::raw_ostream &outputStream,
                                 std::unique_ptr<llvm::MemoryBuffer> buffer,
                                 DialectRegistry &registry,
                                 const MlirOptMainConfig &config) {
   if (config.shouldShowDialects())
     return printRegisteredDialects(registry);
 
+  if (config.shouldListPasses())
+    return printRegisteredPassesAndReturn();
+
   // The split-input-file mode is a very specific mode that slices the file
   // up into small pieces and checks each independently.
   // We use an explicit threadpool to avoid creating and joining/destroying
@@ -565,6 +578,9 @@ LogicalResult mlir::MlirOptMain(int argc, char **argv,
   if (config.shouldShowDialects())
     return printRegisteredDialects(registry);
 
+  if (config.shouldListPasses())
+    return printRegisteredPassesAndReturn();
+
   // When reading from stdin and the input is a tty, it is often a user mistake
   // and the process "appears to be stuck". Print a message to let the user know
   // about it!