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

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

Reviewed By: tblah

Differential Revision: https://reviews.llvm.org/D155913

2 files changed, 49 insertions, 0 deletions

diff --git a/flang/lib/Lower/HlfirIntrinsics.cpp b/flang/lib/Lower/HlfirIntrinsics.cpp
index 1b8631e..ab569ad 100644
--- a/flang/lib/Lower/HlfirIntrinsics.cpp
+++ b/flang/lib/Lower/HlfirIntrinsics.cpp
@@ -278,6 +278,18 @@ mlir::Value HlfirTransposeLowering::lowerImpl(
   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));
diff --git a/flang/test/Lower/HLFIR/transpose.f90 b/flang/test/Lower/HLFIR/transpose.f90
index 70ae372..e63e1ec 100644
--- a/flang/test/Lower/HLFIR/transpose.f90
+++ b/flang/test/Lower/HLFIR/transpose.f90
@@ -62,3 +62,40 @@ end subroutine test_polymorphic_result
 ! 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:         }