[flang] Rebox the polymorphic argument in merge intrinsic

[clementval]

Summary

When fsource or tsource is not polymorphic, the result is not
polymorphic. Rebox the polymoprhic arguement so the dynamic
type of the result is correct.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Optimizer/Builder/IntrinsicCall.cpp

IntrinsicLibrary::genMerge(mlir::Type,
   // The result is polymorphic if and only if both TSOURCE and FSOURCE are
   // polymorphic. TSOURCE and FSOURCE are required to have the same type
   // (for both declared and dynamic types) so a simple convert op can be
   // used.
   mlir::Value tsourceCast = tsource;
   mlir::Value fsourceCast = fsource;
   if (fir::isPolymorphicType(tsource.getType()) &&
       !fir::isPolymorphicType(fsource.getType())) {
-    tsourceCast = builder.createConvert(loc, fsource.getType(), tsource);
+    tsourceCast = builder.create<fir::ReboxOp>(loc, fsource.getType(), tsource,
+                                               /*shape*/ mlir::Value{},
+                                               /*slice=*/mlir::Value{});
+
+    // builder.createConvert(loc, fsource.getType(), tsource);
   } else if (!fir::isPolymorphicType(tsource.getType()) &&
              fir::isPolymorphicType(fsource.getType())) {
-    fsourceCast = builder.createConvert(loc, tsource.getType(), fsource);
+    fsourceCast = builder.create<fir::ReboxOp>(loc, tsource.getType(), fsource,
+                                               /*shape*/ mlir::Value{},
+                                               /*slice=*/mlir::Value{});
+
+    // fsourceCast = builder.createConvert(loc, tsource.getType(), fsource);
   } else {
     // FSOURCE and TSOURCE are not polymorphic.
     // FSOURCE has the same type as TSOURCE, but they may not have the same MLIR
     // types (one can have dynamic length while the other has constant lengths,
     // or one may be a fir.logical<> while the other is an i1). Insert a cast to
     // fulfill mlir::SelectOp constraint that the MLIR types must be the same.
     fsourceCast = builder.createConvert(loc, tsource.getType(), fsource);
   }

flang/test/Lower/polymorphic-temp.f90

 
 ! CHECK-LABEL: func.func @_QMpoly_tmpPtest_merge_intrinsic2(
 ! CHECK-SAME: %[[A:.*]]: !fir.ref<!fir.class<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>> {fir.bindc_name = "a"}, %[[B:.*]]: !fir.ref<!fir.box<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>> {fir.bindc_name = "b"}, %[[I:.*]]: !fir.ref<i32> {fir.bindc_name = "i"}) {
 ! CHECK: %[[LOAD_A:.*]] = fir.load %[[A]] : !fir.ref<!fir.class<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>>
 ! CHECK: %[[LOAD_B:.*]] = fir.load %[[B]] : !fir.ref<!fir.box<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>>
 ! CHECK: %[[LOAD_I:.*]] = fir.load %[[I]] : !fir.ref<i32>
 ! CHECK: %[[C1:.*]] = arith.constant 1 : i32
 ! CHECK: %[[CMPI:.*]] = arith.cmpi eq, %[[LOAD_I]], %[[C1]] : i32
-! CHECK: %[[A_CONV:.*]] = fir.convert %[[LOAD_A]] : (!fir.class<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>) -> !fir.box<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>
-! CHECK: %{{.*}} = arith.select %[[CMPI]], %[[A_CONV]], %[[LOAD_B]] : !fir.box<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>
+! CHECK: %[[A_REBOX:.*]] = fir.rebox %[[LOAD_A]] : (!fir.class<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>) -> !fir.box<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>> 
+! CHECK: %{{.*}} = arith.select %[[CMPI]], %[[A_REBOX]], %[[LOAD_B]] : !fir.box<!fir.heap<!fir.type<_QMpoly_tmpTp1{a:i32}>>>
 
 end module