[BPF] Reorganize BTFDebug::visitMapDefType for better readability

Kernel BPF selftests passing. No change in BTF generated for kernel
selftests, modulo some reorderings.

Signed-off-by: Mahe Tardy <[email protected]>

Author: eddyz87

llvm/lib/Target/BPF/BTFDebug.cpp

@@ -957,38 +957,26 @@ void BTFDebug::visitMapDefType(const DIType *Ty, uint32_t &TypeId) {
     return;
   }
 
-  // MapDef type may be a struct type or a derived type
-  const DIType *OrigTy = Ty;
-  while (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
-    auto Tag = DTy->getTag();
-    if (Tag != dwarf::DW_TAG_typedef && Tag != dwarf::DW_TAG_const_type &&
-        Tag != dwarf::DW_TAG_volatile_type &&
-        Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_pointer_type)
-      break;
-    Ty = DTy->getBaseType();
-  }
-
-  const auto *CTy = dyn_cast<DICompositeType>(Ty);
-  if (!CTy)
-    return;
-
-  auto Tag = CTy->getTag();
-  if ((Tag != dwarf::DW_TAG_structure_type &&
-       Tag != dwarf::DW_TAG_array_type) ||
-      CTy->isForwardDecl())
-    return;
-
-  // Visit potential nested map array
-  if (CTy->getTag() == dwarf::DW_TAG_array_type) {
-    // Jump to the element type of the array
-    visitMapDefType(CTy->getBaseType(), TypeId);
-  } else {
+  uint32_t TmpId;
+  switch (Ty->getTag()) {
+  case dwarf::DW_TAG_typedef:
+  case dwarf::DW_TAG_const_type:
+  case dwarf::DW_TAG_volatile_type:
+  case dwarf::DW_TAG_restrict_type:
+  case dwarf::DW_TAG_pointer_type:
+    visitMapDefType(dyn_cast<DIDerivedType>(Ty)->getBaseType(), TmpId);
+    break;
+  case dwarf::DW_TAG_array_type:
+    // Visit nested map array and jump to the element type
+    visitMapDefType(dyn_cast<DICompositeType>(Ty)->getBaseType(), TmpId);
+    break;
+  case dwarf::DW_TAG_structure_type: {
     // Visit all struct members to ensure their types are visited.
+    const auto *CTy = cast<DICompositeType>(Ty);
     const DINodeArray Elements = CTy->getElements();
     for (const auto *Element : Elements) {
       const auto *MemberType = cast<DIDerivedType>(Element);
       const DIType *MemberBaseType = MemberType->getBaseType();
-
       // If the member is a composite type, that may indicate the currently
       // visited composite type is a wrapper, and the member represents the
       // actual map definition.
@@ -997,15 +985,19 @@ void BTFDebug::visitMapDefType(const DIType *Ty, uint32_t &TypeId) {
       // than as a regular composite type.
       const auto *MemberCTy = dyn_cast<DICompositeType>(MemberBaseType);
       if (MemberCTy) {
-        visitMapDefType(MemberBaseType, TypeId);
+        visitMapDefType(MemberBaseType, TmpId);
       } else {
         visitTypeEntry(MemberBaseType);
       }
     }
+    break;
+  }
+  default:
+    break;
   }
 
   // Visit this type, struct or a const/typedef/volatile/restrict type
-  visitTypeEntry(OrigTy, TypeId, false, false);
+  visitTypeEntry(Ty, TypeId, false, false);
 }
 
 /// Read file contents from the actual file or from the source