[Flang][OpenMP][MLIR] Fix common block mapping for regular and declar…

…e target link (#91829)

This PR attempts to fix common block mapping for regular mapping of
these types as well as when they have been marked as "declare target
link". This PR should allow correct mapping of both the members of a
common block and the full common block via its block symbol.

The main changes were some adjustments to the Fortran OpenMP lowering to
HLFIR/FIR, the lowering of the LLVM+OpenMP dialect to LLVM-IR and
adjustments to the way the we handle target kernel map argument
rebinding inside of the OMPIRBuilder.

For the Fortran OpenMP lowering were two changes, one to prevent the
implicit capture of common block members when the common block symbol
itself has been marked and the other creates intermediate member access
inside of the target region to be used in-place of those external to the
target region, this prevents external usages breaking the
IsolatedFromAbove pact.

In the latter case, there was an adjustment to the size calculation for
types to better handle cases where we pass an array as the type of a map
(as opposed to the bounds and the type of the element), which occurs in
the case of common blocks. There is also some adjustment to how
handleDeclareTargetMapVar handles renaming of declare target symbols in
the module to the reference pointer, now it will only apply to those
within the kernel that is currently being generated and we also perform
a modification to replace constants with instructions as necessary as we
cannot replace these with our reference pointer (non-constant and
constants do not mix nicely).

In the case of the OpenMPIRBuilder some changes were made to defer
global symbol rebinding to kernel arguments until all other arguments
have been rebound. This makes sure we do not replace uses that may refer
to the global (e.g. a GEP) but are themselves actually a separate
argument that needs bound.

Currently "declare target to" still needs some work, but this may be the
case for all types in conjunction with "declare target to" at the
moment.

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -776,6 +776,33 @@ static void genBodyOfTargetDataOp(
   }
 }
 
+// This generates intermediate common block member accesses within a region
+// and then rebinds the members symbol to the intermediate accessors we have
+// generated so that subsequent code generation will utilise these instead.
+//
+// When the scope changes, the bindings to the intermediate accessors should
+// be dropped in place of the original symbol bindings.
+//
+// This is for utilisation with TargetOp.
+static void genIntermediateCommonBlockAccessors(
+    Fortran::lower::AbstractConverter &converter,
+    const mlir::Location &currentLocation, mlir::Region &region,
+    llvm::ArrayRef<const Fortran::semantics::Symbol *> mapSyms) {
+  for (auto [argIndex, argSymbol] : llvm::enumerate(mapSyms)) {
+    if (auto *details =
+            argSymbol->detailsIf<Fortran::semantics::CommonBlockDetails>()) {
+      for (auto obj : details->objects()) {
+        auto targetCBMemberBind = Fortran::lower::genCommonBlockMember(
+            converter, currentLocation, *obj, region.getArgument(argIndex));
+        fir::ExtendedValue sexv = converter.getSymbolExtendedValue(*obj);
+        fir::ExtendedValue targetCBExv =
+            getExtendedValue(sexv, targetCBMemberBind);
+        converter.bindSymbol(*obj, targetCBExv);
+      }
+    }
+  }
+}
+
 // This functions creates a block for the body of the targetOp's region. It adds
 // all the symbols present in mapSymbols as block arguments to this block.
 static void
@@ -955,6 +982,16 @@ genBodyOfTargetOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
   // Create the insertion point after the marker.
   firOpBuilder.setInsertionPointAfter(undefMarker.getDefiningOp());
 
+  // If we map a common block using it's symbol e.g. map(tofrom: /common_block/)
+  // and accessing it's members within the target region, there is a large
+  // chance we will end up with uses external to the region accessing the common
+  // resolve these, we do so by generating new common block member accesses
+  // within the region, binding them to the member symbol for the scope of the
+  // region so that subsequent code generation within the region will utilise
+  // our new member accesses we have created.
+  genIntermediateCommonBlockAccessors(converter, currentLocation, region,
+                                      mapSyms);
+
   if (ConstructQueue::iterator next = std::next(item); next != queue.end()) {
     genOMPDispatch(converter, symTable, semaCtx, eval, currentLocation, queue,
                    next);
@@ -1670,6 +1707,13 @@ genTargetOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
     if (dsp.getAllSymbolsToPrivatize().contains(&sym))
       return;
 
+    // if the symbol is part of an already mapped common block, do not make a
+    // map for it.
+    if (const Fortran::semantics::Symbol *common =
+            Fortran::semantics::FindCommonBlockContaining(sym.GetUltimate()))
+      if (llvm::find(mapSyms, common) != mapSyms.end())
+        return;
+
     if (llvm::find(mapSyms, &sym) == mapSyms.end()) {
       mlir::Value baseOp = converter.getSymbolAddress(sym);
       if (!baseOp)

flang/test/Fir/convert-to-llvm-openmp-and-fir.fir

@@ -1006,3 +1006,77 @@ func.func @omp_map_info_nested_derived_type_explicit_member_conversion(%arg0 : !
 }
 
 // -----
+
+// CHECK-LABEL:  llvm.func @omp_map_common_block_using_common_block_symbol
+
+// CHECK: %[[ADDR_OF:.*]] = llvm.mlir.addressof @var_common_ : !llvm.ptr
+// CHECK: %[[CB_MAP:.*]] = omp.map.info var_ptr(%[[ADDR_OF]] : !llvm.ptr, !llvm.array<8 x i8>) map_clauses(tofrom) capture(ByRef) -> !llvm.ptr {name = "var_common"}
+// CHECK:    omp.target map_entries(%[[CB_MAP]] -> %[[ARG0:.*]] : !llvm.ptr) {
+// CHECK:    ^bb0(%[[ARG0]]: !llvm.ptr):
+// CHECK:      %[[VAR_2_OFFSET:.*]] = llvm.mlir.constant(4 : index) : i64
+// CHECK:      %[[VAR_1_OFFSET:.*]] = llvm.mlir.constant(0 : index) : i64
+// CHECK:      %{{.*}} = llvm.getelementptr %[[ARG0]][%[[VAR_1_OFFSET]]] : (!llvm.ptr, i64) -> !llvm.ptr, i8
+// CHECK:      %{{.*}} = llvm.getelementptr %[[ARG0]][%[[VAR_2_OFFSET]]] : (!llvm.ptr, i64) -> !llvm.ptr, i8
+
+func.func @omp_map_common_block_using_common_block_symbol() {
+  %0 = fir.address_of(@var_common_) : !fir.ref<!fir.array<8xi8>>
+  %1 = omp.map.info var_ptr(%0 : !fir.ref<!fir.array<8xi8>>, !fir.array<8xi8>) map_clauses(tofrom) capture(ByRef) -> !fir.ref<!fir.array<8xi8>> {name = "var_common"}
+  omp.target map_entries(%1 -> %arg0 : !fir.ref<!fir.array<8xi8>>) {
+  ^bb0(%arg0: !fir.ref<!fir.array<8xi8>>):
+    %c4 = arith.constant 4 : index
+    %c0 = arith.constant 0 : index
+    %c20_i32 = arith.constant 20 : i32
+    %2 = fir.convert %arg0 : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+    %3 = fir.coordinate_of %2, %c0 : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+    %4 = fir.convert %3 : (!fir.ref<i8>) -> !fir.ref<i32>
+    %5 = fir.convert %arg0 : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+    %6 = fir.coordinate_of %5, %c4 : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+    %7 = fir.convert %6 : (!fir.ref<i8>) -> !fir.ref<i32>
+    %8 = fir.load %4 : !fir.ref<i32>
+    %9 = arith.addi %8, %c20_i32 : i32
+    fir.store %9 to %7 : !fir.ref<i32>
+    omp.terminator
+  }
+  return
+}
+
+fir.global common @var_common_(dense<0> : vector<8xi8>) {alignment = 4 : i64} : !fir.array<8xi8>
+
+// -----
+
+// CHECK-LABEL:  llvm.func @omp_map_common_block_using_common_block_members
+
+// CHECK:    %[[VAR_2_OFFSET:.*]] = llvm.mlir.constant(4 : index) : i64
+// CHECK:    %[[VAR_1_OFFSET:.*]] = llvm.mlir.constant(0 : index) : i64
+// CHECK:    %[[ADDR_OF:.*]] = llvm.mlir.addressof @var_common_ : !llvm.ptr
+// CHECK:    %[[VAR_1_CB_GEP:.*]] = llvm.getelementptr %[[ADDR_OF]][%[[VAR_1_OFFSET]]] : (!llvm.ptr, i64) -> !llvm.ptr, i8
+// CHECK:    %[[VAR_2_CB_GEP:.*]] = llvm.getelementptr %[[ADDR_OF]][%[[VAR_2_OFFSET]]] : (!llvm.ptr, i64) -> !llvm.ptr, i8
+// CHECK:    %[[MAP_CB_VAR_1:.*]] = omp.map.info var_ptr(%[[VAR_1_CB_GEP]] : !llvm.ptr, i32) map_clauses(tofrom) capture(ByRef) -> !llvm.ptr {name = "var1"}
+// CHECK:    %[[MAP_CB_VAR_2:.*]] = omp.map.info var_ptr(%[[VAR_2_CB_GEP]] : !llvm.ptr, i32) map_clauses(tofrom) capture(ByRef) -> !llvm.ptr {name = "var2"}
+// CHECK:    omp.target map_entries(%[[MAP_CB_VAR_1]] -> %[[ARG0:.*]], %[[MAP_CB_VAR_2]] -> %[[ARG1:.*]] : !llvm.ptr, !llvm.ptr) {
+// CHECK:     ^bb0(%[[ARG0]]: !llvm.ptr, %[[ARG1]]: !llvm.ptr):
+
+func.func @omp_map_common_block_using_common_block_members() {
+  %c4 = arith.constant 4 : index
+  %c0 = arith.constant 0 : index
+  %0 = fir.address_of(@var_common_) : !fir.ref<!fir.array<8xi8>>
+  %1 = fir.convert %0 : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+  %2 = fir.coordinate_of %1, %c0 : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+  %3 = fir.convert %2 : (!fir.ref<i8>) -> !fir.ref<i32>
+  %4 = fir.convert %0 : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+  %5 = fir.coordinate_of %4, %c4 : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+  %6 = fir.convert %5 : (!fir.ref<i8>) -> !fir.ref<i32>
+  %7 = omp.map.info var_ptr(%3 : !fir.ref<i32>, i32) map_clauses(tofrom) capture(ByRef) -> !fir.ref<i32> {name = "var1"}
+  %8 = omp.map.info var_ptr(%6 : !fir.ref<i32>, i32) map_clauses(tofrom) capture(ByRef) -> !fir.ref<i32> {name = "var2"}
+  omp.target map_entries(%7 -> %arg0, %8 -> %arg1 : !fir.ref<i32>, !fir.ref<i32>) {
+  ^bb0(%arg0: !fir.ref<i32>, %arg1: !fir.ref<i32>):
+    %c10_i32 = arith.constant 10 : i32
+    %9 = fir.load %arg0 : !fir.ref<i32>
+    %10 = arith.muli %9, %c10_i32 : i32
+    fir.store %10 to %arg1 : !fir.ref<i32>
+    omp.terminator
+  }
+  return
+}
+
+fir.global common @var_common_(dense<0> : vector<8xi8>) {alignment = 4 : i64} : !fir.array<8xi8>

flang/test/Integration/OpenMP/map-types-and-sizes.f90

@@ -231,6 +231,31 @@ subroutine mapType_char
   !$omp end target
 end subroutine mapType_char
 
+!CHECK: @.offload_sizes{{.*}} = private unnamed_addr constant [1 x i64] [i64 8]
+!CHECK: @.offload_maptypes{{.*}} = private unnamed_addr constant [1 x i64] [i64 35]
+subroutine mapType_common_block
+  implicit none
+  common /var_common/ var1, var2
+  integer :: var1, var2
+!$omp target map(tofrom: /var_common/)
+  var1 = var1 + 20
+  var2 = var2 + 30
+!$omp end target
+end subroutine mapType_common_block
+
+!CHECK: @.offload_sizes{{.*}} = private unnamed_addr constant [2 x i64] [i64 4, i64 4]
+!CHECK: @.offload_maptypes{{.*}} = private unnamed_addr constant [2 x i64] [i64 35, i64 35]
+subroutine mapType_common_block_members
+  implicit none
+  common /var_common/ var1, var2
+  integer :: var1, var2
+
+!$omp target map(tofrom: var1, var2)
+  var2 = var1
+!$omp end target
+end subroutine mapType_common_block_members
+
+
 !CHECK-LABEL: define {{.*}} @{{.*}}maptype_ptr_explicit_{{.*}}
 !CHECK: %[[ALLOCA:.*]] = alloca { ptr, i64, i32, i8, i8, i8, i8 }, i64 1, align 8
 !CHECK: %[[ALLOCA_GEP:.*]] = getelementptr { ptr, i64, i32, i8, i8, i8, i8 }, ptr %[[ALLOCA]], i32 1
@@ -346,3 +371,19 @@ end subroutine mapType_char
 !CHECK: store ptr %[[ALLOCA]], ptr %[[BASE_PTR_ARR]], align 8
 !CHECK: %[[OFFLOAD_PTR_ARR:.*]] = getelementptr inbounds [1 x ptr], ptr %.offload_ptrs, i32 0, i32 0
 !CHECK: store ptr %[[ARR_OFF]], ptr %[[OFFLOAD_PTR_ARR]], align 8
+
+!CHECK-LABEL: define {{.*}} @{{.*}}maptype_common_block_{{.*}}
+!CHECK: %[[BASE_PTR_ARR:.*]] = getelementptr inbounds [1 x ptr], ptr %.offload_baseptrs, i32 0, i32 0
+!CHECK: store ptr @var_common_, ptr %[[BASE_PTR_ARR]], align 8
+!CHECK: %[[OFFLOAD_PTR_ARR:.*]] = getelementptr inbounds [1 x ptr], ptr %.offload_ptrs, i32 0, i32 0
+!CHECK: store ptr @var_common_, ptr %[[OFFLOAD_PTR_ARR]], align 8
+
+!CHECK-LABEL: define {{.*}} @{{.*}}maptype_common_block_members_{{.*}}
+!CHECK: %[[BASE_PTR_ARR:.*]] = getelementptr inbounds [2 x ptr], ptr %.offload_baseptrs, i32 0, i32 0
+!CHECK: store ptr @var_common_, ptr %[[BASE_PTR_ARR]], align 8
+!CHECK: %[[OFFLOAD_PTR_ARR:.*]] = getelementptr inbounds [2 x ptr], ptr %.offload_ptrs, i32 0, i32 0
+!CHECK: store ptr @var_common_, ptr %[[OFFLOAD_PTR_ARR]], align 8
+!CHECK: %[[BASE_PTR_ARR_1:.*]] = getelementptr inbounds [2 x ptr], ptr %.offload_baseptrs, i32 0, i32 1
+!CHECK: store ptr getelementptr (i8, ptr @var_common_, i64 4), ptr %[[BASE_PTR_ARR_1]], align 8
+!CHECK: %[[OFFLOAD_PTR_ARR_1:.*]] = getelementptr inbounds [2 x ptr], ptr %.offload_ptrs, i32 0, i32 1
+!CHECK: store ptr getelementptr (i8, ptr @var_common_, i64 4), ptr %[[OFFLOAD_PTR_ARR_1]], align 8

flang/test/Lower/OpenMP/common-block-map.f90

@@ -0,0 +1,83 @@
+!RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
+!CHECK: fir.global common @var_common_(dense<0> : vector<8xi8>) {{.*}} : !fir.array<8xi8>
+!CHECK: fir.global common @var_common_link_(dense<0> : vector<8xi8>) {{{.*}} omp.declare_target = #omp.declaretarget<device_type = (any), capture_clause = (link)>} : !fir.array<8xi8>
+
+!CHECK-LABEL: func.func @_QPmap_full_block
+!CHECK: %[[CB_ADDR:.*]] = fir.address_of(@var_common_) : !fir.ref<!fir.array<8xi8>>
+!CHECK: %[[MAP:.*]] = omp.map.info var_ptr(%[[CB_ADDR]] : !fir.ref<!fir.array<8xi8>>, !fir.array<8xi8>) map_clauses(tofrom) capture(ByRef) -> !fir.ref<!fir.array<8xi8>> {name = "var_common"}
+!CHECK: omp.target map_entries(%[[MAP]] -> %[[MAP_ARG:.*]] : !fir.ref<!fir.array<8xi8>>) {
+!CHECK:  ^bb0(%[[MAP_ARG]]: !fir.ref<!fir.array<8xi8>>):
+!CHECK:    %[[CONV:.*]] = fir.convert %[[MAP_ARG]] : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK:    %[[INDEX:.*]] = arith.constant 0 : index
+!CHECK:    %[[COORD:.*]] = fir.coordinate_of %[[CONV]], %[[INDEX]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK:    %[[CONV2:.*]] = fir.convert %[[COORD]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK:    %[[CB_MEMBER_1:.*]]:2 = hlfir.declare %[[CONV2]] {uniq_name = "_QFmap_full_blockEvar1"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+!CHECK:    %[[CONV3:.*]] = fir.convert %[[MAP_ARG]] : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK:    %[[INDEX2:.*]] = arith.constant 4 : index
+!CHECK:    %[[COORD2:.*]] = fir.coordinate_of %[[CONV3]], %[[INDEX2]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK:    %[[CONV4:.*]] = fir.convert %[[COORD2]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK:    %[[CB_MEMBER_2:.*]]:2 = hlfir.declare %[[CONV4]] {uniq_name = "_QFmap_full_blockEvar2"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+subroutine map_full_block
+    implicit none
+    common /var_common/ var1, var2
+    integer :: var1, var2
+!$omp target map(tofrom: /var_common/)
+    var1 = var1 + 20
+    var2 = var2 + 30
+!$omp end target
+end
+
+!CHECK-LABEL: @_QPmap_mix_of_members
+!CHECK: %[[COMMON_BLOCK:.*]] = fir.address_of(@var_common_) : !fir.ref<!fir.array<8xi8>>
+!CHECK: %[[CB_CONV:.*]] = fir.convert %[[COMMON_BLOCK]] : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK: %[[INDEX:.*]] = arith.constant 0 : index
+!CHECK: %[[COORD:.*]] = fir.coordinate_of %[[CB_CONV]], %[[INDEX]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK: %[[CONV:.*]] = fir.convert %[[COORD]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK: %[[CB_MEMBER_1:.*]]:2 = hlfir.declare %[[CONV]] {uniq_name = "_QFmap_mix_of_membersEvar1"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+!CHECK: %[[CB_CONV:.*]] = fir.convert %[[COMMON_BLOCK]] : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK: %[[INDEX:.*]] = arith.constant 4 : index
+!CHECK: %[[COORD:.*]] = fir.coordinate_of %[[CB_CONV]], %[[INDEX]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK: %[[CONV:.*]] = fir.convert %[[COORD]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK: %[[CB_MEMBER_2:.*]]:2 = hlfir.declare %[[CONV]] {uniq_name = "_QFmap_mix_of_membersEvar2"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+!CHECK: %[[MAP_EXP:.*]] = omp.map.info var_ptr(%[[CB_MEMBER_2]]#0 : !fir.ref<i32>, i32) map_clauses(tofrom) capture(ByRef) -> !fir.ref<i32> {name = "var2"}
+!CHECK: %[[MAP_IMP:.*]] = omp.map.info var_ptr(%[[CB_MEMBER_1]]#1 : !fir.ref<i32>, i32) map_clauses(implicit, exit_release_or_enter_alloc) capture(ByCopy) -> !fir.ref<i32> {name = "var1"}
+!CHECK: omp.target map_entries(%[[MAP_EXP]] -> %[[ARG_EXP:.*]], %[[MAP_IMP]] -> %[[ARG_IMP:.*]] : !fir.ref<i32>, !fir.ref<i32>) {
+!CHECK: ^bb0(%[[ARG_EXP]]: !fir.ref<i32>, %[[ARG_IMP]]: !fir.ref<i32>):
+!CHECK:  %[[EXP_MEMBER:.*]]:2 = hlfir.declare %[[ARG_EXP]] {uniq_name = "_QFmap_mix_of_membersEvar2"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+!CHECK:  %[[IMP_MEMBER:.*]]:2 = hlfir.declare %[[ARG_IMP]] {uniq_name = "_QFmap_mix_of_membersEvar1"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+subroutine map_mix_of_members
+    implicit none
+    common /var_common/ var1, var2
+    integer :: var1, var2
+
+!$omp target map(tofrom: var2)
+  var2 = var1
+!$omp end target
+end
+
+!CHECK-LABEL: @_QQmain
+!CHECK: %[[DECL_TAR_CB:.*]] = fir.address_of(@var_common_link_) : !fir.ref<!fir.array<8xi8>>
+!CHECK: %[[MAP_DECL_TAR_CB:.*]] = omp.map.info var_ptr(%[[DECL_TAR_CB]] : !fir.ref<!fir.array<8xi8>>, !fir.array<8xi8>) map_clauses(tofrom) capture(ByRef) -> !fir.ref<!fir.array<8xi8>> {name = "var_common_link"}
+!CHECK: omp.target map_entries(%[[MAP_DECL_TAR_CB]] -> %[[MAP_DECL_TAR_ARG:.*]] : !fir.ref<!fir.array<8xi8>>) {
+!CHECK: ^bb0(%[[MAP_DECL_TAR_ARG]]: !fir.ref<!fir.array<8xi8>>):
+!CHECK:  %[[CONV:.*]] = fir.convert %[[MAP_DECL_TAR_ARG]] : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK:  %[[INDEX:.*]] = arith.constant 0 : index
+!CHECK:  %[[COORD:.*]] = fir.coordinate_of %[[CONV]], %[[INDEX]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK:  %[[CONV:.*]] = fir.convert %[[COORD]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK:  %[[MEMBER_ONE:.*]]:2 = hlfir.declare %[[CONV]] {uniq_name = "_QFElink1"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+!CHECK:  %[[CONV:.*]] = fir.convert %[[MAP_DECL_TAR_ARG]] : (!fir.ref<!fir.array<8xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK:  %[[INDEX:.*]] = arith.constant 4 : index
+!CHECK:  %[[COORD:.*]] = fir.coordinate_of %[[CONV]], %[[INDEX]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK:  %[[CONV:.*]] = fir.convert %[[COORD]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK:  %[[MEMBER_TWO:.*]]:2 = hlfir.declare %[[CONV]] {uniq_name = "_QFElink2"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+program main
+    implicit none
+    common /var_common_link/ link1, link2
+    integer :: link1, link2
+    !$omp declare target link(/var_common_link/)
+
+!$omp target map(tofrom: /var_common_link/)
+    link1 = link2 + 20
+!$omp end target
+end program

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -5164,15 +5164,7 @@ static Function *createOutlinedFunction(
           ? make_range(Func->arg_begin() + 1, Func->arg_end())
           : Func->args();
 
-  // Rewrite uses of input valus to parameters.
-  for (auto InArg : zip(Inputs, ArgRange)) {
-    Value *Input = std::get<0>(InArg);
-    Argument &Arg = std::get<1>(InArg);
-    Value *InputCopy = nullptr;
-
-    Builder.restoreIP(
-        ArgAccessorFuncCB(Arg, Input, InputCopy, AllocaIP, Builder.saveIP()));
-
+  auto ReplaceValue = [](Value *Input, Value *InputCopy, Function *Func) {
     // Things like GEP's can come in the form of Constants. Constants and
     // ConstantExpr's do not have access to the knowledge of what they're
     // contained in, so we must dig a little to find an instruction so we
@@ -5198,8 +5190,49 @@ static Function *createOutlinedFunction(
       if (auto *Instr = dyn_cast<Instruction>(User))
         if (Instr->getFunction() == Func)
           Instr->replaceUsesOfWith(Input, InputCopy);
+  };
+
+  SmallVector<std::pair<Value *, Value *>> DeferredReplacement;
+
+  // Rewrite uses of input valus to parameters.
+  for (auto InArg : zip(Inputs, ArgRange)) {
+    Value *Input = std::get<0>(InArg);
+    Argument &Arg = std::get<1>(InArg);
+    Value *InputCopy = nullptr;
+
+    Builder.restoreIP(
+        ArgAccessorFuncCB(Arg, Input, InputCopy, AllocaIP, Builder.saveIP()));
+
+    // In certain cases a Global may be set up for replacement, however, this
+    // Global may be used in multiple arguments to the kernel, just segmented
+    // apart, for example, if we have a global array, that is sectioned into
+    // multiple mappings (technically not legal in OpenMP, but there is a case
+    // in Fortran for Common Blocks where this is neccesary), we will end up
+    // with GEP's into this array inside the kernel, that refer to the Global
+    // but are technically seperate arguments to the kernel for all intents and
+    // purposes. If we have mapped a segment that requires a GEP into the 0-th
+    // index, it will fold into an referal to the Global, if we then encounter
+    // this folded GEP during replacement all of the references to the
+    // Global in the kernel will be replaced with the argument we have generated
+    // that corresponds to it, including any other GEP's that refer to the
+    // Global that may be other arguments. This will invalidate all of the other
+    // preceding mapped arguments that refer to the same global that may be
+    // seperate segments. To prevent this, we defer global processing until all
+    // other processing has been performed.
+    if (llvm::isa<llvm::GlobalValue>(std::get<0>(InArg)) ||
+        llvm::isa<llvm::GlobalObject>(std::get<0>(InArg)) ||
+        llvm::isa<llvm::GlobalVariable>(std::get<0>(InArg))) {
+      DeferredReplacement.push_back(std::make_pair(Input, InputCopy));
+      continue;
+    }
+
+    ReplaceValue(Input, InputCopy, Func);
   }
 
+  // Replace all of our deferred Input values, currently just Globals.
+  for (auto Deferred : DeferredReplacement)
+    ReplaceValue(std::get<0>(Deferred), std::get<1>(Deferred), Func);
+
   // Restore insert point.
   Builder.restoreIP(OldInsertPoint);