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

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

llvm-debuginfo-analyzer already uses the tombstone approach
to identify dead code. Currently, the tombstone value is
evaluated as std::numeric_limits<uint64_t>::max(). Which is
wrong as it does not take into account the 'Address Byte Size'
from the Compile Unit header.

Author: CarlosAlbertoEnciso

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

@@ -55,11 +55,14 @@ class LLVM_ABI LVRange final : public LVObject {
   LVAllocator Allocator;
   LVRangesTree RangesTree;
   LVRangeEntries RangeEntries;
-  LVAddress Lower = MaxAddress;
+  LVAddress TombstoneAddress;
+  LVAddress Lower;
   LVAddress Upper = 0;
 
 public:
-  LVRange() : LVObject(), RangesTree(Allocator) {}
+  LVRange(LVAddress Address = MaxAddress)
+      : LVObject(),
+        RangesTree(Allocator), TombstoneAddress(Address), Lower(Address) {}
   LVRange(const LVRange &) = delete;
   LVRange &operator=(const LVRange &) = delete;
   ~LVRange() = default;
@@ -76,7 +79,7 @@ class LLVM_ABI LVRange final : public LVObject {
 
   void clear() {
     RangeEntries.clear();
-    Lower = MaxAddress;
+    Lower = TombstoneAddress;
     Upper = 0;
   }
   bool empty() const { return RangeEntries.empty(); }

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

@@ -156,6 +156,10 @@ class LLVM_ABI LVReader {
                        LVAddress LowerAddress, LVAddress UpperAddress);
   LVRange *getSectionRanges(LVSectionIndex SectionIndex);
 
+  // Tombstone value. Assume 64 bits. The value is updated for each
+  // Compile Unit that is processed.
+  LVAddress TombstoneAddress = MaxAddress;
+
   // Record Compilation Unit entry.
   void addCompileUnitOffset(LVOffset Offset, LVScopeCompileUnit *CompileUnit) {
     CompileUnits.emplace(Offset, CompileUnit);
@@ -282,6 +286,9 @@ class LLVM_ABI LVReader {
     return CompileUnit->getCPUType();
   }
 
+  void setTombstoneAddress(LVAddress Address) { TombstoneAddress = Address; }
+  LVAddress getTombstoneAddress() const { return TombstoneAddress; }
+
   // Access to the scopes root.
   LVScopeRoot *getScopesRoot() const { return Root; }
 

llvm/lib/DebugInfo/LogicalView/Readers/LVDWARFReader.cpp

@@ -214,10 +214,11 @@ void LVDWARFReader::processOneAttribute(const DWARFDie &Die,
         }
       }
       if (FoundLowPC) {
-        if (CurrentLowPC == MaxAddress)
+        if (CurrentLowPC == getTombstoneAddress())
           CurrentElement->setIsDiscarded();
-        // Consider the case of WebAssembly.
-        CurrentLowPC += WasmCodeSectionOffset;
+        else
+          // Consider the case of WebAssembly.
+          CurrentLowPC += WasmCodeSectionOffset;
         if (CurrentElement->isCompileUnit())
           setCUBaseAddress(CurrentLowPC);
       }
@@ -271,7 +272,8 @@ void LVDWARFReader::processOneAttribute(const DWARFDie &Die,
       DWARFAddressRangesVector Ranges = RangesOrError.get();
       for (DWARFAddressRange &Range : Ranges) {
         // This seems to be a tombstone for empty ranges.
-        if (Range.LowPC == Range.HighPC)
+        if ((Range.LowPC == Range.HighPC) ||
+            (Range.LowPC = getTombstoneAddress()))
           continue;
         // Store the real upper limit for the address range.
         if (UpdateHighAddress && Range.HighPC > 0)
@@ -629,6 +631,11 @@ Error LVDWARFReader::createScopes() {
                                          : DwarfContext->dwo_compile_units();
   for (const std::unique_ptr<DWARFUnit> &CU : CompileUnits) {
 
+    // Take into account the address byte size for a correct 'tombstone'
+    // value identification.
+    setTombstoneAddress(
+        dwarf::computeTombstoneAddress(CU->getAddressByteSize()));
+
     // Deduction of index used for the line records.
     //
     // For the following test case: test.cpp