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

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

Address reviewes comments:
- Make 'tombstone' a member of 'LVDWARFReader', to eliminate the
  extra dependency on the CodeView reader.
- Rename the test case and rework some comments to make it easy
  to understand.

Author: CarlosAlbertoEnciso

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

@@ -156,9 +156,6 @@ class LLVM_ABI LVReader {
                        LVAddress LowerAddress, LVAddress UpperAddress);
   LVRange *getSectionRanges(LVSectionIndex SectionIndex);
 
-  // The value is updated for each Compile Unit that is processed.
-  std::optional<LVAddress> TombstoneAddress;
-
   // Record Compilation Unit entry.
   void addCompileUnitOffset(LVOffset Offset, LVScopeCompileUnit *CompileUnit) {
     CompileUnits.emplace(Offset, CompileUnit);
@@ -285,12 +282,6 @@ class LLVM_ABI LVReader {
     return CompileUnit->getCPUType();
   }
 
-  void setTombstoneAddress(LVAddress Address) { TombstoneAddress = Address; }
-  LVAddress getTombstoneAddress() const {
-    assert(TombstoneAddress && "Unset tombstone value");
-    return TombstoneAddress.value();
-  }
-
   // Access to the scopes root.
   LVScopeRoot *getScopesRoot() const { return Root; }
 

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

@@ -193,17 +193,11 @@ 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) {
-    // CodeView does not have the concept of 'tombstone' address.
-    setTombstoneAddress(MaxAddress);
-  }
+        Input(&Obj), ExePath(ExePath), LogicalVisitor(this, W, Input) {}
   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) {
-    // CodeView does not have the concept of 'tombstone' address.
-    setTombstoneAddress(MaxAddress);
-  }
+        Input(&Pdb), ExePath(ExePath), LogicalVisitor(this, W, Input) {}
   LVCodeViewReader(const LVCodeViewReader &) = delete;
   LVCodeViewReader &operator=(const LVCodeViewReader &) = delete;
   ~LVCodeViewReader() = default;

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

@@ -58,6 +58,9 @@ class LVDWARFReader final : public LVBinaryReader {
   bool FoundLowPC = false;
   bool FoundHighPC = false;
 
+  // The value is updated for each Compile Unit that is processed.
+  std::optional<LVAddress> TombstoneAddress;
+
   // Cross references (Elements).
   using LVElementSet = std::unordered_set<LVElement *>;
   struct LVElementEntry {
@@ -127,6 +130,12 @@ class LVDWARFReader final : public LVBinaryReader {
   LVAddress getCUHighAddress() const { return CUHighAddress; }
   void setCUHighAddress(LVAddress Address) { CUHighAddress = Address; }
 
+  void setTombstoneAddress(LVAddress Address) { TombstoneAddress = Address; }
+  LVAddress getTombstoneAddress() const {
+    assert(TombstoneAddress && "Unset tombstone value");
+    return TombstoneAddress.value();
+  }
+
   const LVSymbols &GetSymbolsWithLocations() const {
     return SymbolsWithLocations;
   }

llvm/test/tools/llvm-debuginfo-analyzer/WebAssembly/wasm-crash-tombstone.s renamed to llvm/test/tools/llvm-debuginfo-analyzer/WebAssembly/wasm-32bit-tombstone.s

@@ -1,26 +1,7 @@
 # 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
+# Test that DWARF tombstones are correctly detected/respected in wasm
+# 32 bit object files.
 
 # The test case was produced by the following steps:
 #
@@ -29,8 +10,10 @@
 # }
 #
 # 1) clang --target=wasm32 -S -g test-clang.cpp
-#                             -o Inputs/wasm-crash-tombstone.s
-# 2) Manually changing the DW_AT_low_pc for the DW_TAG_subprogram:
+#                             -o Inputs/wasm-32bit-tombstone.s
+#
+# 2) Creating a single function, tombstoning it in the assembly, by
+#    manually changing the DW_AT_low_pc for the DW_TAG_subprogram:
 #    .Lfunc_begin0 to 0xffffffff to mark the function as dead code:
 #
 #	   .int8	2                          # Abbrev [2] 0x26:0x1b DW_TAG_subprogram
@@ -42,21 +25,21 @@
 #	   .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
+# RUN:         %p/wasm-32bit-tombstone.s        \
+# RUN:         -o %t.wasm-32bit-tombstone.wasm
 
 # RUN: llvm-debuginfo-analyzer --select-elements=Discarded         \
 # RUN:                         --print=elements                    \
-# RUN:                         %t.wasm-crash-tombstone.wasm 2>&1 | \
+# RUN:                         %t.wasm-32bit-tombstone.wasm 2>&1 | \
 # RUN: FileCheck --strict-whitespace -check-prefix=ONE %s
 
 # ONE: Logical View:
-# ONE-NEXT:           {File} '{{.*}}wasm-crash-tombstone.wasm'
+# ONE-NEXT:           {File} '{{.*}}wasm-32bit-tombstone.wasm'
 # ONE-EMPTY:
 # ONE-NEXT:           {CompileUnit} 'test-clang.cpp'
 # ONE-NEXT:           {Function} not_inlined 'foo' -> 'void'
 
-# RUN: llvm-dwarfdump --debug-info %t.wasm-crash-tombstone.wasm | \
+# RUN: llvm-dwarfdump --debug-info %t.wasm-32bit-tombstone.wasm | \
 # RUN: FileCheck %s --check-prefix=TWO
 
 # TWO:      DW_TAG_subprogram