[flang][hlfir] Inherit constant length for the result of hlfir.transpose.

[vzakhari]

Summary

Character length may be unknown for the type of Fortran::evaluate::FunctionRef
expression, but we can try to propagate it from the argument of
TRANSPOSE if it is known constant. Alternatively, we could relax
hlfir.transpose verification (i.e. allow character types mismatch
for the argument and the result).

Depends on D155912

[tblah]

Thanks for this!

flang/lib/Lower/HlfirIntrinsics.cpp

mlir::Value HlfirTransposeLowering::lowerImpl(
   mlir::Type normalisedResult =
       hlfir::getFortranElementOrSequenceType(stmtResultType);
   auto array = normalisedResult.cast<fir::SequenceType>();
   llvm::ArrayRef<int64_t> arrayShape = array.getShape();
   assert(arrayShape.size() == 2 && "arguments to transpose have a rank of 2");
   mlir::Type elementType = array.getEleTy();
   resultShape.push_back(arrayShape[0]);
   resultShape.push_back(arrayShape[1]);
+  if (auto resCharType = mlir::dyn_cast<fir::CharacterType>(elementType))
+    if (!resCharType.hasConstantLen()) {
+      // The FunctionRef expression might have imprecise character
+      // type at this point, and we can improve it by propagating
+      // the constant length from the argument.
+      auto argCharType = mlir::dyn_cast<fir::CharacterType>(
+          hlfir::getFortranElementType(operands[0].getType()));
+      if (argCharType && argCharType.hasConstantLen())
+        elementType = fir::CharacterType::get(
+            builder.getContext(), resCharType.getFKind(), argCharType.getLen());
+    }
+
   mlir::Type resultTy =
       hlfir::ExprType::get(builder.getContext(), resultShape, elementType,
                            fir::isPolymorphicType(stmtResultType));
   return createOp<hlfir::TransposeOp>(resultTy, operands[0]);
 }
 
 mlir::Value HlfirCountLowering::lowerImpl(
     const Fortran::lower::PreparedActualArguments &loweredActuals,

flang/test/Lower/HLFIR/transpose.f90

 ! CHECK:           %[[VAL_2:.*]]:2 = hlfir.declare %[[VAL_0]] {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFtest_polymorphic_resultEm"} : (!fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>) -> (!fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>, !fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>)
 ! CHECK:           %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_1]] {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFtest_polymorphic_resultEres"} : (!fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>) -> (!fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>, !fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>)
 ! CHECK:           %[[VAL_4:.*]] = fir.load %[[VAL_2]]#0 : !fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>
 ! CHECK:           %[[VAL_5:.*]] = hlfir.transpose %[[VAL_4]] : (!fir.class<!fir.heap<!fir.array<?x?xnone>>>) -> !hlfir.expr<?x?xnone?>
 ! CHECK:           hlfir.assign %[[VAL_5]] to %[[VAL_3]]#0 realloc : !hlfir.expr<?x?xnone?>, !fir.ref<!fir.class<!fir.heap<!fir.array<?x?xnone>>>>
 ! CHECK:           hlfir.destroy %[[VAL_5]] : !hlfir.expr<?x?xnone?>
 ! CHECK:           return
 ! CHECK:         }
+
+! Test that hlfir.transpose lowering inherits constant
+! character length from the argument, when the length
+! is uknown from the Fortran::evaluate expression type.
+subroutine test_unknown_char_len_result
+  character(len=3), dimension(3,3) :: w
+  character(len=2), dimension(3,3) :: w2
+  w2 = transpose(w(:,:)(1:2))
+end subroutine test_unknown_char_len_result
+! CHECK-LABEL:   func.func @_QPtest_unknown_char_len_result() {
+! CHECK:           %[[VAL_0:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_1:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_2:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_3:.*]] = fir.alloca !fir.array<3x3x!fir.char<1,3>> {bindc_name = "w", uniq_name = "_QFtest_unknown_char_len_resultEw"}
+! CHECK:           %[[VAL_4:.*]] = fir.shape %[[VAL_1]], %[[VAL_2]] : (index, index) -> !fir.shape<2>
+! CHECK:           %[[VAL_5:.*]]:2 = hlfir.declare %[[VAL_3]](%[[VAL_4]]) typeparams %[[VAL_0]] {uniq_name = "_QFtest_unknown_char_len_resultEw"} : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>, !fir.shape<2>, index) -> (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>, !fir.ref<!fir.array<3x3x!fir.char<1,3>>>)
+! CHECK:           %[[VAL_6:.*]] = arith.constant 2 : index
+! CHECK:           %[[VAL_7:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_8:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_9:.*]] = fir.alloca !fir.array<3x3x!fir.char<1,2>> {bindc_name = "w2", uniq_name = "_QFtest_unknown_char_len_resultEw2"}
+! CHECK:           %[[VAL_10:.*]] = fir.shape %[[VAL_7]], %[[VAL_8]] : (index, index) -> !fir.shape<2>
+! CHECK:           %[[VAL_11:.*]]:2 = hlfir.declare %[[VAL_9]](%[[VAL_10]]) typeparams %[[VAL_6]] {uniq_name = "_QFtest_unknown_char_len_resultEw2"} : (!fir.ref<!fir.array<3x3x!fir.char<1,2>>>, !fir.shape<2>, index) -> (!fir.ref<!fir.array<3x3x!fir.char<1,2>>>, !fir.ref<!fir.array<3x3x!fir.char<1,2>>>)
+! CHECK:           %[[VAL_12:.*]] = arith.constant 1 : index
+! CHECK:           %[[VAL_13:.*]] = arith.constant 1 : index
+! CHECK:           %[[VAL_14:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_15:.*]] = arith.constant 1 : index
+! CHECK:           %[[VAL_16:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_17:.*]] = fir.shape %[[VAL_14]], %[[VAL_16]] : (index, index) -> !fir.shape<2>
+! CHECK:           %[[VAL_18:.*]] = arith.constant 1 : index
+! CHECK:           %[[VAL_19:.*]] = arith.constant 2 : index
+! CHECK:           %[[VAL_20:.*]] = arith.constant 2 : index
+! CHECK:           %[[VAL_21:.*]] = hlfir.designate %[[VAL_5]]#0 (%[[VAL_12]]:%[[VAL_1]]:%[[VAL_13]], %[[VAL_12]]:%[[VAL_2]]:%[[VAL_15]]) substr %[[VAL_18]], %[[VAL_19]]  shape %[[VAL_17]] typeparams %[[VAL_20]] : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>, index, index, index, index, index, index, index, index, !fir.shape<2>, index) -> !fir.box<!fir.array<3x3x!fir.char<1,2>>>
+! CHECK:           %[[VAL_22:.*]] = hlfir.transpose %[[VAL_21]] : (!fir.box<!fir.array<3x3x!fir.char<1,2>>>) -> !hlfir.expr<3x3x!fir.char<1,2>>
+! CHECK:           hlfir.assign %[[VAL_22]] to %[[VAL_11]]#0 : !hlfir.expr<3x3x!fir.char<1,2>>, !fir.ref<!fir.array<3x3x!fir.char<1,2>>>
+! CHECK:           hlfir.destroy %[[VAL_22]] : !hlfir.expr<3x3x!fir.char<1,2>>
+! CHECK:           return
+! CHECK:         }