Add a helper function to convert LogicalResult to int for return from main

At present, a lot of code contains main function bodies like "return failed(mlir::MlirOptMain(...);". This is unfortunate for two reasons: a) it uses ADL, which is maybe not what the free "failed" function was designed for; and b) it is a bit awkward to read, requring the reader to both understand the boolean nature of the value and the semantics of main's return value. (And it's also not portable, since 1 is not a portable success value.)

The replacement code, `return mlir::AsMainReturnCode(mlir::MlirOptMain(...))` is a bit more self-explanatory.

The change applies the new function to a few internal uses of MlirOptMain, too.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D102641

mlir/examples/standalone/standalone-opt/standalone-opt.cpp

@@ -33,6 +33,6 @@ int main(int argc, char **argv) {
   // will be *parsed* by the tool, not the one generated
   // registerAllDialects(registry);
 
-  return failed(
+  return mlir::asMainReturnCode(
       mlir::MlirOptMain(argc, argv, "Standalone optimizer driver\n", registry));
 }

mlir/include/mlir/Support/MlirOptMain.h

@@ -16,6 +16,7 @@
 #include "mlir/Support/LogicalResult.h"
 #include "llvm/ADT/StringRef.h"
 
+#include <cstdlib>
 #include <memory>
 
 namespace llvm {
@@ -61,6 +62,20 @@ LogicalResult MlirOptMain(int argc, char **argv, llvm::StringRef toolName,
                           DialectRegistry &registry,
                           bool preloadDialectsInContext = false);
 
+/// Helper wrapper to return the result of MlirOptMain directly from main.
+///
+/// Example:
+///
+///     int main(int argc, char **argv) {
+///       // ...
+///       return mlir::asMainReturnCode(mlir::MlirOptMain(
+///           argc, argv, /* ... */);
+///     }
+///
+inline int asMainReturnCode(LogicalResult r) {
+  return r.succeeded() ? EXIT_SUCCESS : EXIT_FAILURE;
+}
+
 } // end namespace mlir
 
 #endif // MLIR_SUPPORT_MLIROPTMAIN_H

mlir/tools/mlir-opt/mlir-opt.cpp

@@ -190,7 +190,7 @@ int main(int argc, char **argv) {
 #ifdef MLIR_INCLUDE_TESTS
   test::registerTestDialect(registry);
 #endif
-  return failed(MlirOptMain(argc, argv, "MLIR modular optimizer driver\n",
-                            registry,
-                            /*preloadDialectsInContext=*/false));
+  return mlir::asMainReturnCode(
+      mlir::MlirOptMain(argc, argv, "MLIR modular optimizer driver\n", registry,
+                        /*preloadDialectsInContext=*/false));
 }