[flang][HLFIR] lower hlfir.declare of assumed-ranks (#93468)

hlfir.declare is in charge of ensuring that the lower bounds of its
"hlfir entity" output are the ones of the source program. For
non-allocatable/non-pointer assumed-ranks where the input descriptor
lower bounds may not be ones, the hlfir.declare needs to be lowered to
an hlfir.rebox_assumed_rank to set the lower bounds to ones.

Author: jeanPerier

flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp

@@ -348,7 +348,17 @@ class DeclareOpConversion : public mlir::OpRewritePattern<hlfir::DeclareOp> {
       // Helper to generate the hlfir fir.box with the local lower bounds and
       // type parameters.
       auto genHlfirBox = [&]() -> mlir::Value {
-        if (!mlir::isa<fir::BaseBoxType>(firBase.getType())) {
+        if (auto baseBoxType =
+                mlir::dyn_cast<fir::BaseBoxType>(firBase.getType())) {
+          // Rebox so that lower bounds are correct.
+          if (baseBoxType.isAssumedRank())
+            return builder.create<fir::ReboxAssumedRankOp>(
+                loc, hlfirBaseType, firBase,
+                fir::LowerBoundModifierAttribute::SetToOnes);
+          return builder.create<fir::ReboxOp>(loc, hlfirBaseType, firBase,
+                                              declareOp.getShape(),
+                                              /*slice=*/mlir::Value{});
+        } else {
           llvm::SmallVector<mlir::Value> typeParams;
           auto maybeCharType = mlir::dyn_cast<fir::CharacterType>(
               fir::unwrapSequenceType(fir::unwrapPassByRefType(hlfirBaseType)));
@@ -358,11 +368,6 @@ class DeclareOpConversion : public mlir::OpRewritePattern<hlfir::DeclareOp> {
           return builder.create<fir::EmboxOp>(
               loc, hlfirBaseType, firBase, declareOp.getShape(),
               /*slice=*/mlir::Value{}, typeParams);
-        } else {
-          // Rebox so that lower bounds are correct.
-          return builder.create<fir::ReboxOp>(loc, hlfirBaseType, firBase,
-                                              declareOp.getShape(),
-                                              /*slice=*/mlir::Value{});
         }
       };
       if (!mlir::cast<fir::FortranVariableOpInterface>(declareOp.getOperation())

flang/test/HLFIR/declare-codegen.fir

@@ -210,3 +210,12 @@ func.func @dummy_scope(%arg0: !fir.ref<f32>) {
 // CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<f32>) {
 // CHECK:         %[[SCOPE:.*]] = fir.dummy_scope : !fir.dscope
 // CHECK:         %[[VAL_1:.*]] = fir.declare %[[VAL_0]] dummy_scope %[[SCOPE]] {uniq_name = "x"} : (!fir.ref<f32>, !fir.dscope) -> !fir.ref<f32>
+
+func.func @assumed_rank_declare(%arg0: !fir.box<!fir.array<*:f32>>) {
+  %0:2 = hlfir.declare %arg0 {uniq_name = "x"} : (!fir.box<!fir.array<*:f32>>) -> (!fir.box<!fir.array<*:f32>>, !fir.box<!fir.array<*:f32>>)
+  return
+}
+// CHECK-LABEL:  func.func @assumed_rank_declare(
+// CHECK-SAME: %[[VAL_0:.*]]: !fir.box<!fir.array<*:f32>>) {
+// CHECK:    %[[VAL_1:.*]] = fir.declare %[[VAL_0]] {uniq_name = "x"} : (!fir.box<!fir.array<*:f32>>) -> !fir.box<!fir.array<*:f32>>
+// CHECK:    %[[VAL_2:.*]] = fir.rebox_assumed_rank %[[VAL_1]] lbs ones : (!fir.box<!fir.array<*:f32>>) -> !fir.box<!fir.array<*:f32>>