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

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

Address comments from reviewers:
- Combine test and .s file.
- Introduce the concept of a meta-tombstone value, to
  be able to check for an invalid tombstone value.

Author: CarlosAlbertoEnciso

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

@@ -84,7 +84,17 @@ using LVTypes = SmallVector<LVType *, 8>;
 
 using LVOffsets = SmallVector<LVOffset, 8>;
 
+// The following DWARF documents detail the 'tombstone' concept:
+//   https://dwarfstd.org/issues/231013.1.html
+//   https://dwarfstd.org/issues/200609.1.html
+//
+// The value of the largest representable address offset (for example,
+// 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

@@ -60,7 +60,7 @@ class LLVM_ABI LVRange final : public LVObject {
   LVAddress Upper = 0;
 
 public:
-  LVRange(LVAddress Address = MaxAddress)
+  LVRange(LVAddress Address = InvalidTombstone)
       : LVObject(), RangesTree(Allocator), TombstoneAddress(Address),
         Lower(Address) {}
   LVRange(const LVRange &) = delete;

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

@@ -156,9 +156,8 @@ 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;
+  // The value is updated for each Compile Unit that is processed.
+  LVAddress TombstoneAddress = InvalidTombstone;
 
   // Record Compilation Unit entry.
   void addCompileUnitOffset(LVOffset Offset, LVScopeCompileUnit *CompileUnit) {
@@ -287,7 +286,10 @@ class LLVM_ABI LVReader {
   }
 
   void setTombstoneAddress(LVAddress Address) { TombstoneAddress = Address; }
-  LVAddress getTombstoneAddress() const { return TombstoneAddress; }
+  LVAddress getTombstoneAddress() const {
+    assert(TombstoneAddress != InvalidTombstone && "Invalid tombstone value");
+    return TombstoneAddress;
+  }
 
   // Access to the scopes root.
   LVScopeRoot *getScopesRoot() const { return Root; }

llvm/include/llvm/DebugInfo/LogicalView/Readers/LVCodeViewReader.h

@@ -193,11 +193,17 @@ class LVCodeViewReader final : public LVBinaryReader {
                    llvm::object::COFFObjectFile &Obj, ScopedPrinter &W,
                    StringRef ExePath)
       : LVBinaryReader(Filename, FileFormatName, W, LVBinaryType::COFF),
-        Input(&Obj), ExePath(ExePath), LogicalVisitor(this, W, Input) {}
+        Input(&Obj), ExePath(ExePath), LogicalVisitor(this, W, Input) {
+    // CodeView does not have the concept of 'tombstone' address.
+    setTombstoneAddress(MaxAddress);
+  }
   LVCodeViewReader(StringRef Filename, StringRef FileFormatName,
                    llvm::pdb::PDBFile &Pdb, ScopedPrinter &W, StringRef ExePath)
       : LVBinaryReader(Filename, FileFormatName, W, LVBinaryType::COFF),
-        Input(&Pdb), ExePath(ExePath), LogicalVisitor(this, W, Input) {}
+        Input(&Pdb), ExePath(ExePath), LogicalVisitor(this, W, Input) {
+    // CodeView does not have the concept of 'tombstone' address.
+    setTombstoneAddress(MaxAddress);
+  }
   LVCodeViewReader(const LVCodeViewReader &) = delete;
   LVCodeViewReader &operator=(const LVCodeViewReader &) = delete;
   ~LVCodeViewReader() = default;

llvm/test/tools/llvm-debuginfo-analyzer/WebAssembly/Inputs/test-clang-tombstone.s renamed to llvm/test/tools/llvm-debuginfo-analyzer/WebAssembly/wasm-crash-tombstone.s

@@ -1,3 +1,66 @@
+# REQUIRES: x86-registered-target
+
+# llvm-debuginfo-analyzer crashes on dead code
+# https://github.com/llvm/llvm-project/issues/136772
+
+# For the attached reproducer:
+# llvm-dwarfdump out/lzma-lzmadec.wasm --all
+#
+# shows:
+#
+# 0x000002b3:   DW_TAG_subprogram
+#                 DW_AT_low_pc	(dead code)
+#                 DW_AT_high_pc	(0x00000362)
+#                 DW_AT_frame_base	(DW_OP_WASM_location 0x0 0x6, DW_OP_stack_value)
+
+# llvm-debuginfo-analyzer out/lzma-lzmadec.wasm --print=instructions
+#
+# crashes and shows a stack dump:
+#
+# PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/
+# and include the crash backtrace.
+# Stack dump:
+# 0. Program arguments: llvm-debuginfo-analyzer out/lzma-lzmadec.wasm --print=instructions
+
+# The test-clang-tombstone.s was produced by the following steps:
+# 1) clang --target=wasm32 -S -g Inputs/test-clang.cpp
+#                             -o Inputs/wasm-crash-tombstone.s
+# 2) Manually changing the DW_AT_low_pc for the DW_TAG_subprogram, from
+#    .Lfunc_begin0 to 0xffffffff to mark the function as dead code:
+#
+#	   .int8	2                          # Abbrev [2] 0x26:0x6a DW_TAG_subprogram
+#	   .int32	.Lfunc_begin0              # DW_AT_low_pc  <---------
+#	   .int32	.Lfunc_end0-.Lfunc_begin0  # DW_AT_high_pc
+
+#	   .int8	2                          # Abbrev [2] 0x26:0x6a DW_TAG_subprogram
+#	   .int32	0xffffffff                 # DW_AT_low_pc  <---------
+#	   .int32	.Lfunc_end0-.Lfunc_begin0  # DW_AT_high_pc
+
+# RUN: llvm-mc -arch=wasm32 -filetype=obj       \
+# RUN:         %p/wasm-crash-tombstone.s        \
+# RUN:         -o %t.wasm-crash-tombstone.wasm
+
+# llvm-debuginfo-analyzer --select-elements=Discarde          \
+#                         --print=elements                    \
+#                         %t.wasm-crash-tombstone.wasm 2>&1 | \
+# FileCheck --strict-whitespace -check-prefix=ONE %s
+
+# ONE: Logical View:
+# ONE-NEXT:           {File} '{{.*}}wasm-crash-tombstone.wasm'
+# ONE-EMPTY:
+# ONE-NEXT:           {CompileUnit} 'test.cpp'
+# ONE-NEXT:     2     {Function} extern not_inlined 'foo' -> 'int'
+
+# RUN: llvm-dwarfdump --debug-info %t.wasm-crash-tombstone.wasm | \
+# RUN: FileCheck %s --check-prefix=TWO
+
+# TWO:      DW_TAG_subprogram
+# TWO-NEXT:   DW_AT_low_pc	(dead code)
+# TWO-NEXT:   DW_AT_high_pc
+# TWO-NEXT:   DW_AT_frame_base
+# TWO-NEXT:   DW_AT_linkage_name
+# TWO-NEXT:   DW_AT_name	("foo")
+
 	.text
 	.file	"test.cpp"
 	.globaltype	__stack_pointer, i32