[OpenMP][MLIR] Descriptor explicit member map lowering changes

This is one of 3 PRs in a PR stack that aims to add support for explicit mapping of
allocatable members in derived types.

The primary changes in this PR are the OpenMPToLLVMIRTranslation.cpp changes,
which are small and seek to alter the current member mapping to add an
additional map insertion for pointers. Effectively, if the member is a pointer
(currently indicated by having a varPtrPtr field) we add an additional map for
the pointer and then alter the subsequent mapping of the member (the data)
to utilise the member rather than the parents base pointer. This appears to be
necessary in certain cases when mapping pointer data within record types to
avoid segfaulting on device (due to incorrect data mapping). In general this
record type mapping may be simplifiable in the future.

There are also additions of tests which should help to showcase the affect
of the changes above.

Pull Request: llvm#96265

Author: agozillon

mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp

@@ -2299,10 +2299,13 @@ static llvm::omp::OpenMPOffloadMappingFlags mapParentWithMembers(
         mlir::dyn_cast<mlir::omp::MapInfoOp>(mapData.MapClause[mapDataIndex]);
     int firstMemberIdx = getMapDataMemberIdx(
         mapData, getFirstOrLastMappedMemberPtr(mapOp, true));
-    lowAddr = builder.CreatePointerCast(mapData.Pointers[firstMemberIdx],
-                                        builder.getPtrTy());
     int lastMemberIdx = getMapDataMemberIdx(
         mapData, getFirstOrLastMappedMemberPtr(mapOp, false));
+
+    // NOTE/TODO: Should perhaps use OriginalValue here instead of Pointers to
+    // avoid offset or any manipulations interfering with the calculation.
+    lowAddr = builder.CreatePointerCast(mapData.Pointers[firstMemberIdx],
+                                        builder.getPtrTy());
     highAddr = builder.CreatePointerCast(
         builder.CreateGEP(mapData.BaseType[lastMemberIdx],
                           mapData.Pointers[lastMemberIdx], builder.getInt64(1)),
@@ -2385,6 +2388,24 @@ static void processMapMembersWithParent(
 
     assert(memberDataIdx >= 0 && "could not find mapped member of structure");
 
+    if (checkIfPointerMap(memberClause)) {
+      auto mapFlag = llvm::omp::OpenMPOffloadMappingFlags(
+          memberClause.getMapType().value());
+      mapFlag &= ~llvm::omp::OpenMPOffloadMappingFlags::OMP_MAP_TARGET_PARAM;
+      mapFlag |= llvm::omp::OpenMPOffloadMappingFlags::OMP_MAP_MEMBER_OF;
+      ompBuilder.setCorrectMemberOfFlag(mapFlag, memberOfFlag);
+      combinedInfo.Types.emplace_back(mapFlag);
+      combinedInfo.DevicePointers.emplace_back(
+          llvm::OpenMPIRBuilder::DeviceInfoTy::None);
+      combinedInfo.Names.emplace_back(
+          LLVM::createMappingInformation(memberClause.getLoc(), ompBuilder));
+      combinedInfo.BasePointers.emplace_back(
+          mapData.BasePointers[mapDataIndex]);
+      combinedInfo.Pointers.emplace_back(mapData.BasePointers[memberDataIdx]);
+      combinedInfo.Sizes.emplace_back(builder.getInt64(
+          moduleTranslation.getLLVMModule()->getDataLayout().getPointerSize()));
+    }
+
     // Same MemberOfFlag to indicate its link with parent and other members
     // of.
     auto mapFlag =
@@ -2400,7 +2421,14 @@ static void processMapMembersWithParent(
         llvm::OpenMPIRBuilder::DeviceInfoTy::None);
     combinedInfo.Names.emplace_back(
         LLVM::createMappingInformation(memberClause.getLoc(), ompBuilder));
-    combinedInfo.BasePointers.emplace_back(mapData.BasePointers[mapDataIndex]);
+
+    if (checkIfPointerMap(memberClause))
+      combinedInfo.BasePointers.emplace_back(
+          mapData.BasePointers[memberDataIdx]);
+    else
+      combinedInfo.BasePointers.emplace_back(
+          mapData.BasePointers[mapDataIndex]);
+
     combinedInfo.Pointers.emplace_back(mapData.Pointers[memberDataIdx]);
     combinedInfo.Sizes.emplace_back(mapData.Sizes[memberDataIdx]);
   }