[flang] Add IndexType support in getTypeAsString

[razvanlupusoru]

Thank you for adding this missing case.

flang/lib/Optimizer/Dialect/FIRType.cpp

std::string getTypeAsString(mlir::Type ty, const fir::KindMapping &kindMap,
                             llvm::StringRef prefix) {
   std::stringstream name;
   name << prefix.str();
   if (!prefix.empty())
     name << "_";
   ty = fir::unwrapRefType(ty);
   while (ty) {
     if (fir::isa_trivial(ty)) {
-      if (ty.isIntOrIndex()) {
+      if (mlir::isa<mlir::IndexType>(ty)) {
+        name << "idx";
+      } else if (ty.isIntOrIndex()) {
         name << 'i' << ty.getIntOrFloatBitWidth();
       } else if (ty.isa<mlir::FloatType>()) {
         name << 'f' << ty.getIntOrFloatBitWidth();
       } else if (fir::isa_complex(ty)) {
         name << 'z';
         if (auto cplxTy = mlir::dyn_cast_or_null<mlir::ComplexType>(ty)) {
           auto floatTy = cplxTy.getElementType().cast<mlir::FloatType>();
           name << floatTy.getWidth();

flang/unittests/Optimizer/FIRTypesTest.cpp

EXPECT_EQ("z32",
           mlir::ComplexType::get(mlir::FloatType::getF32(&context)), *kindMap));
   EXPECT_EQ("c8",
       fir::getTypeAsString(fir::CharacterType::get(&context, 1, 1), *kindMap));
   EXPECT_EQ("c8x10",
       fir::getTypeAsString(fir::CharacterType::get(&context, 1, 10), *kindMap));
   mlir::Type ty = mlir::IntegerType::get(&context, 64);
   mlir::Type arrTy = fir::SequenceType::get({10, 20}, ty);
   EXPECT_EQ("10x20xi64", fir::getTypeAsString(arrTy, *kindMap));
+  EXPECT_EQ(
+      "idx", fir::getTypeAsString(mlir::IndexType::get(&context), *kindMap));
 }