[llvm-debuginfo-analyzer] Fix crash with WebAssembly dead code

#136772
Incorrect handling of 'tombstone' value for WebAssembly.

Address reviewes comments:
- Reduce the test case.
- Use std::optional to illustrate the set/unset state.
- Rebase with main branch.

Author: CarlosAlbertoEnciso

llvm/include/llvm/DebugInfo/LogicalView/Core/LVObject.h

@@ -92,9 +92,7 @@ using LVOffsets = SmallVector<LVOffset, 8>;
 // 0xffffffff when the size of an address is 32 bits).
 //
 // -1 (0xffffffff) => Valid tombstone
-// -2 (0xfffffffe) => Undefined tomstone
 const LVAddress MaxAddress = std::numeric_limits<uint64_t>::max();
-const LVAddress InvalidTombstone = MaxAddress - 1;
 
 enum class LVBinaryType { NONE, ELF, COFF };
 enum class LVComparePass { Missing, Added };

llvm/include/llvm/DebugInfo/LogicalView/Core/LVRange.h

@@ -55,14 +55,14 @@ class LLVM_ABI LVRange final : public LVObject {
   LVAllocator Allocator;
   LVRangesTree RangesTree;
   LVRangeEntries RangeEntries;
-  LVAddress TombstoneAddress;
-  LVAddress Lower;
+  std::optional<LVAddress> TombstoneAddress;
+  LVAddress Lower = 0;
   LVAddress Upper = 0;
 
 public:
-  LVRange(LVAddress Address = InvalidTombstone)
+  LVRange(std::optional<LVAddress> Address = std::nullopt)
       : LVObject(), RangesTree(Allocator), TombstoneAddress(Address),
-        Lower(Address) {}
+        Lower(Address ? Address.value() : MaxAddress) {}
   LVRange(const LVRange &) = delete;
   LVRange &operator=(const LVRange &) = delete;
   ~LVRange() = default;
@@ -79,7 +79,7 @@ class LLVM_ABI LVRange final : public LVObject {
 
   void clear() {
     RangeEntries.clear();
-    Lower = TombstoneAddress;
+    Lower = TombstoneAddress ? TombstoneAddress.value() : MaxAddress;
     Upper = 0;
   }
   bool empty() const { return RangeEntries.empty(); }

llvm/include/llvm/DebugInfo/LogicalView/Core/LVReader.h

@@ -157,7 +157,7 @@ class LLVM_ABI LVReader {
   LVRange *getSectionRanges(LVSectionIndex SectionIndex);
 
   // The value is updated for each Compile Unit that is processed.
-  LVAddress TombstoneAddress = InvalidTombstone;
+  std::optional<LVAddress> TombstoneAddress;
 
   // Record Compilation Unit entry.
   void addCompileUnitOffset(LVOffset Offset, LVScopeCompileUnit *CompileUnit) {
@@ -287,8 +287,8 @@ class LLVM_ABI LVReader {
 
   void setTombstoneAddress(LVAddress Address) { TombstoneAddress = Address; }
   LVAddress getTombstoneAddress() const {
-    assert(TombstoneAddress != InvalidTombstone && "Invalid tombstone value");
-    return TombstoneAddress;
+    assert(TombstoneAddress && "Unset tombstone value");
+    return TombstoneAddress.value();
   }
 
   // Access to the scopes root.