[DebugInfo] Fix initialization of DwarfCompileUnit::LabelBegin.

[ikudrin]

Summary

This also fixes the condition in the assertion in DwarfCompileUnit::getLabelBegin() because it checked something unrelated to the returned value.

[aprantl]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

302

can you add an && "some meaningful message" to hint at what went wrong?

[dblaikie]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

60

Is this used before its initialization - generally nice not to prematurely initiliaze things, because it thwarts checking like msan that might find bugs if this isn't intended to be used until after some other initialization.

[ikudrin]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

60

LabelBegin is initialized under a condition, not in the constructor, thus, it can be left uninitialized. If we rely on MSan, the assert in getLabelBegin() is useless and vice versa.

302

Nothing more meaningful than "LabelBegin is not initialized" comes to me, but that would be a tautology. Any suggestions?

[dblaikie]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

60

Fair enough - thanks for the explanation!

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

class DwarfCompileUnit final : public DwarfUnit {
   /// The start of the unit line section, this is also
   /// reused in appyStmtList.
   MCSymbol *LineTableStartSym;
 
   /// Skeleton unit associated with this unit.
   DwarfCompileUnit *Skeleton = nullptr;
 
   /// The start of the unit within its section.
-  MCSymbol *LabelBegin;
+  MCSymbol *LabelBegin = nullptr;
 
   /// The start of the unit macro info within macro section.
   MCSymbol *MacroLabelBegin;
 
   using ImportedEntityList = SmallVector<const MDNode *, 8>;
   using ImportedEntityMap = DenseMap<const MDNode *, ImportedEntityList>;
 
   ImportedEntityMap ImportedEntities;
public:
   }
 
   void emitHeader(bool UseOffsets) override;
 
   /// Add the DW_AT_addr_base attribute to the unit DIE.
   void addAddrTableBase();
 
   MCSymbol *getLabelBegin() const {
-    assert(getSection());
+    assert(LabelBegin && "LabelBegin is not initialized");
     return LabelBegin;
   }
 
   MCSymbol *getMacroLabelBegin() const {
     return MacroLabelBegin;
   }
 
   /// Add a new global name to the compile unit.