[fir] Add fir.select_type conversion placeholder

As for D113662, this patch just add a place holder for
the `fir.select_type` operation conversion. This operation
is part of F20xx and is not implemented yet.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D113878

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -930,6 +930,19 @@ struct LoadOpConversion : public FIROpConversion<fir::LoadOp> {
   }
 };
 
+/// Lower `fir.select_type` to LLVM IR dialect.
+struct SelectTypeOpConversion : public FIROpConversion<fir::SelectTypeOp> {
+  using FIROpConversion::FIROpConversion;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::SelectTypeOp select, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    return rewriter.notifyMatchFailure(
+        select, "fir.select_type codegen is not implemented yet");
+    return failure();
+  }
+};
+
 /// conversion of fir::SelectRankOp to an if-then-else ladder
 struct SelectRankOpConversion : public FIROpConversion<fir::SelectRankOp> {
   using FIROpConversion::FIROpConversion;
@@ -1456,9 +1469,9 @@ public:
         InsertOnRangeOpConversion, InsertValueOpConversion,
         IsPresentOpConversion, LoadOpConversion, NegcOpConversion,
         MulcOpConversion, SelectCaseOpConversion, SelectOpConversion,
-        SelectRankOpConversion, StoreOpConversion, SubcOpConversion,
-        UndefOpConversion, UnreachableOpConversion, ZeroOpConversion>(
-        typeConverter);
+        SelectRankOpConversion, SelectTypeOpConversion, StoreOpConversion,
+        SubcOpConversion, UndefOpConversion, UnreachableOpConversion,
+        ZeroOpConversion>(typeConverter);
     mlir::populateStdToLLVMConversionPatterns(typeConverter, pattern);
     mlir::arith::populateArithmeticToLLVMConversionPatterns(typeConverter,
                                                             pattern);

flang/test/Fir/convert-to-llvm-invalid.fir

@@ -50,3 +50,25 @@ func @select_case_charachter(%arg0: !fir.char<2, 10>, %arg1: !fir.char<2, 10>, %
 ^bb3:
   return
 }
+
+// -----
+
+// Test `fir.select_type` conversion failure. Not implemented yet.
+
+func @bar_select_type(%arg : !fir.box<!fir.type<derived3{f:f32}>>) -> i32 {
+  %0 = arith.constant 1 : i32
+  %2 = arith.constant 3 : i32
+
+  // expected-error@+1{{failed to legalize operation 'fir.select_type'}}
+  fir.select_type %arg : !fir.box<!fir.type<derived3{f:f32}>> [ 
+    #fir.instance<!fir.int<4>>,^bb1(%0:i32), 
+    #fir.instance<!fir.int<8>>,^bb2(%2:i32), 
+    unit,^bb5 ]
+^bb1(%a : i32) :
+  return %a : i32
+^bb2(%b : i32) :
+  return %b : i32
+^bb5 :
+  %zero = arith.constant 0 : i32
+  return %zero : i32
+}