[fir] Add fir.select_type conversion placeholder

[clementval]

Summary

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.

[kiranchandramohan]

LGTM.

[clementval]

Rebase

flang/lib/Optimizer/CodeGen/CodeGen.cpp

if (load.getType().isa<fir::BoxType>()) {
       ArrayRef<NamedAttribute> at = load->getAttrs();
       rewriter.replaceOpWithNewOp<mlir::LLVM::LoadOp>(
           load, ty, adaptor.getOperands(), at);
     }
     return success();
   }
 };
 
+/// 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;
 
   mlir::LogicalResult
   matchAndRewrite(fir::SelectRankOp op, OpAdaptor adaptor,
                   mlir::ConversionPatternRewriter &rewriter) const override {
     selectMatchAndRewrite<fir::SelectRankOp>(lowerTy(), op, adaptor, rewriter);
pattern.insert<
         BoxEleSizeOpConversion, BoxIsAllocOpConversion, BoxIsArrayOpConversion,
         BoxIsPtrOpConversion, BoxRankOpConversion, CallOpConversion,
         ConvertOpConversion, DispatchOpConversion, DispatchTableOpConversion,
         DTEntryOpConversion, DivcOpConversion, EmboxCharOpConversion,
         ExtractValueOpConversion, HasValueOpConversion, GlobalOpConversion,
         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);
     mlir::ConversionTarget target{*context};
     target.addLegalDialect<mlir::LLVM::LLVMDialect>();
 
     // required NOPs for applying a full conversion
     target.addLegalOp<mlir::ModuleOp>();

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

^bb1:
   %c1_i32 = arith.constant 1 : i32
   br ^bb3
 ^bb2:
   %c2_i32 = arith.constant 2 : i32
   br ^bb3
 ^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
+}