[flang] Use box for components with non-default lower bounds (#138994)

When designating an array component that has non-default lower bounds
the bridge was producing hlfir designates yielding reference types,
which did not preserve the bounds information. Then, when creating
components, unadjusted indices were used when initializing the
structure.

We could look at the declaration to get the shape parameter, but this
would not be preserved if the component were passed as a block argument.
These results must be boxed, but we also must not lose the contiguity
information either. To address contiguity, annotate these boxes with the
`contiguous` attribute during designation.

Note that other designated entities are handled inside the
HlfirDesignatorBuilder while component designators are built in
HlfirBuilder. I am not sure if this handling should be moved into the
designator builder or left in the general builder, so feedback is
welcome.

Also, I wouldn't mind finding a test that demonstrates a box-designated
component with the contiguous attribute really is determined to be
contiguous by any passes down the line checking for that. I don't have a
test like that yet.

Author: ashermancinelli

flang/lib/Lower/ConvertExprToHLFIR.cpp

@@ -30,6 +30,7 @@
 #include "flang/Optimizer/Builder/Runtime/Derived.h"
 #include "flang/Optimizer/Builder/Runtime/Pointer.h"
 #include "flang/Optimizer/Builder/Todo.h"
+#include "flang/Optimizer/Dialect/FIRAttr.h"
 #include "flang/Optimizer/HLFIR/HLFIROps.h"
 #include "mlir/IR/IRMapping.h"
 #include "llvm/ADT/TypeSwitch.h"
@@ -125,6 +126,19 @@ class HlfirDesignatorBuilder {
   hlfir::ElementalAddrOp convertVectorSubscriptedExprToElementalAddr(
       const Fortran::lower::SomeExpr &designatorExpr);
 
+  std::tuple<mlir::Type, fir::FortranVariableFlagsEnum>
+  genComponentDesignatorTypeAndAttributes(
+      const Fortran::semantics::Symbol &componentSym, mlir::Type fieldType,
+      bool isVolatile) {
+    if (mayHaveNonDefaultLowerBounds(componentSym)) {
+      mlir::Type boxType = fir::BoxType::get(fieldType, isVolatile);
+      return std::make_tuple(boxType,
+                             fir::FortranVariableFlagsEnum::contiguous);
+    }
+    auto refType = fir::ReferenceType::get(fieldType, isVolatile);
+    return std::make_tuple(refType, fir::FortranVariableFlagsEnum{});
+  }
+
   mlir::Value genComponentShape(const Fortran::semantics::Symbol &componentSym,
                                 mlir::Type fieldType) {
     // For pointers and allocatable components, the
@@ -1863,8 +1877,9 @@ class HlfirBuilder {
           designatorBuilder.genComponentShape(sym, compType);
       const bool isDesignatorVolatile =
           fir::isa_volatile_type(baseOp.getType());
-      mlir::Type designatorType =
-          builder.getRefType(compType, isDesignatorVolatile);
+      auto [designatorType, extraAttributeFlags] =
+          designatorBuilder.genComponentDesignatorTypeAndAttributes(
+              sym, compType, isDesignatorVolatile);
 
       mlir::Type fieldElemType = hlfir::getFortranElementType(compType);
       llvm::SmallVector<mlir::Value, 1> typeParams;
@@ -1884,7 +1899,8 @@ class HlfirBuilder {
 
       // Convert component symbol attributes to variable attributes.
       fir::FortranVariableFlagsAttr attrs =
-          Fortran::lower::translateSymbolAttributes(builder.getContext(), sym);
+          Fortran::lower::translateSymbolAttributes(builder.getContext(), sym,
+                                                    extraAttributeFlags);
 
       // Get the component designator.
       auto lhs = builder.create<hlfir::DesignateOp>(

flang/test/Lower/HLFIR/designators-component-ref.f90

@@ -126,6 +126,16 @@ subroutine test_array_comp_non_contiguous_slice(a)
 ! CHECK:  %[[VAL_19:.*]] = hlfir.designate %[[VAL_1]]#0{"array_comp"} <%[[VAL_9]]> (%[[VAL_10]]:%[[VAL_11]]:%[[VAL_12]], %[[VAL_14]]:%[[VAL_15]]:%[[VAL_16]])  shape %[[VAL_18]] : (!fir.ref<!fir.type<_QMcomp_refTt_array{scalar_i:i32,array_comp:!fir.array<10x20xf32>}>>, !fir.shape<2>, index, index, index, index, index, index, !fir.shape<2>) -> !fir.box<!fir.array<6x17xf32>>
 end subroutine
 
+subroutine test_array_lbs_array_ctor()
+  use comp_ref
+  type(t_array_lbs) :: a(-1:1)
+  real :: array_comp(2:11,3:22)
+  a = (/ (t_array_lbs(i, array_comp), i=-1,1) /)
+! CHECK: hlfir.designate %{{.+}}#0{"array_comp_lbs"} <%{{.+}}> shape %{{.+}} {fortran_attrs = #fir.var_attrs<contiguous>}
+! CHECK-SAME: (!fir.ref<!fir.type<_QMcomp_refTt_array_lbs{scalar_i:i32,array_comp_lbs:!fir.array<10x20xf32>}>>, !fir.shapeshift<2>, !fir.shapeshift<2>)
+! CHECK-SAME: -> !fir.box<!fir.array<10x20xf32>>
+end subroutine
+
 subroutine test_array_lbs_comp_lbs_1(a)
   use comp_ref
   type(t_array_lbs) :: a