Revert "[BPF] Fix a BTF type pruning bug"

This reverts commit 1914953.

This fix was accidentally committed.

Author: tstellar

llvm/lib/Target/BPF/BTFDebug.cpp

@@ -773,31 +773,15 @@ void BTFDebug::visitTypeEntry(const DIType *Ty, uint32_t &TypeId,
     // already defined, we should keep moving to eventually
     // bring in types for "struct t". Otherwise, the "struct s2"
     // definition won't be correct.
-    //
-    // In the above, we have following debuginfo:
-    //  {ptr, struct_member} ->  typedef -> struct
-    // and BTF type for 'typedef' is generated while 'struct' may
-    // be in FixUp. But let us generalize the above to handle
-    //  {different types} -> [various derived types]+ -> another type.
-    // For example,
-    //  {func_param, struct_member} -> const -> ptr -> volatile -> struct
-    // We will traverse const/ptr/volatile which already have corresponding
-    // BTF types and generate type for 'struct' which might be in Fixup
-    // state.
     if (Ty && (!CheckPointer || !SeenPointer)) {
       if (const auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
-        while (DTy) {
-          const DIType *BaseTy = DTy->getBaseType();
-          if (!BaseTy)
-            break;
-
-          if (DIToIdMap.find(BaseTy) != DIToIdMap.end()) {
-            DTy = dyn_cast<DIDerivedType>(BaseTy);
-          } else {
-            uint32_t TmpTypeId;
-            visitTypeEntry(BaseTy, TmpTypeId, CheckPointer, SeenPointer);
-            break;
-          }
+        unsigned 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) {
+          uint32_t TmpTypeId;
+          visitTypeEntry(DTy->getBaseType(), TmpTypeId, CheckPointer,
+                         SeenPointer);
         }
       }
     }