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

[Asher Mancinelli via flang-commits]

https://github.com/ashermancinelli created https://github.com/llvm/llvm-project/pull/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.

>From cfcafcf57776beaab75c1c69095c8639b37644aa Mon Sep 17 00:00:00 2001
From: Asher Mancinelli <ashermancinelli at gmail.com>
Date: Wed, 7 May 2025 16:43:12 -0700
Subject: [PATCH] [flang] Use box for components with non-default lower bounds

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,
the correct indices were not used when initializing a 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 desgnated 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.
---
 flang/lib/Lower/ConvertExprToHLFIR.cpp        | 22 ++++++++++++++++---
 .../Lower/HLFIR/designators-component-ref.f90 | 10 +++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/flang/lib/Lower/ConvertExprToHLFIR.cpp b/flang/lib/Lower/ConvertExprToHLFIR.cpp
index 04b63f92a1fb4..da21d407e927d 100644
--- a/flang/lib/Lower/ConvertExprToHLFIR.cpp
+++ b/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>(
diff --git a/flang/test/Lower/HLFIR/designators-component-ref.f90 b/flang/test/Lower/HLFIR/designators-component-ref.f90
index 653e28e0a6018..935176becac75 100644
--- a/flang/test/Lower/HLFIR/designators-component-ref.f90
+++ b/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