[flang] Rebox the polymorphic argument in merge intrinsic

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.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D146133

Author: clementval

flang/lib/Optimizer/Builder/IntrinsicCall.cpp

@@ -4035,10 +4035,18 @@ IntrinsicLibrary::genMerge(mlir::Type,
   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

flang/test/Lower/polymorphic-temp.f90

@@ -222,7 +222,7 @@ subroutine test_merge_intrinsic2(a, b, i)
 ! 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