[DebugInfo] Make DIELocList::SizeOf() more explicit. NFCI.

[ikudrin]

Summary

DIELocList is used with a limited number of DWARF forms, see the only place where it is instantiated, DwarfCompileUnit::addLocationList().

The patch marks the unexpected execution path in DIELocList::SizeOf() as unreachable, to reduce ambiguity.

See also: D83958 and D84094.

[dblaikie]

Sounds good - thanks!

llvm/lib/CodeGen/AsmPrinter/DIE.cpp

void DIEBlock::print(raw_ostream &O) const {
   printValues(O, *this, "Blk", Size, 5);
 }
 
 //===----------------------------------------------------------------------===//
 // DIELocList Implementation
 //===----------------------------------------------------------------------===//
 
 unsigned DIELocList::SizeOf(const AsmPrinter *AP, dwarf::Form Form) const {
-  if (Form == dwarf::DW_FORM_loclistx)
+  switch (Form) {
+  case dwarf::DW_FORM_loclistx:
     return getULEB128Size(Index);
-  if (Form == dwarf::DW_FORM_data4)
+  case dwarf::DW_FORM_data4:
     return 4;
-  if (Form == dwarf::DW_FORM_sec_offset)
+  case dwarf::DW_FORM_sec_offset:
+    // FIXME: add support for DWARF64
     return 4;
-  return AP->MAI->getCodePointerSize();
+  default:
+    llvm_unreachable("DIE Value form not supported yet");
+  }
 }
 
 /// EmitValue - Emit label value.
 ///
 void DIELocList::emitValue(const AsmPrinter *AP, dwarf::Form Form) const {
   if (Form == dwarf::DW_FORM_loclistx) {
     AP->emitULEB128(Index);
     return;
   }
   DwarfDebug *DD = AP->getDwarfDebug();
   MCSymbol *Label = DD->getDebugLocs().getList(Index).Label;
   AP->emitDwarfSymbolReference(Label, /*ForceOffset*/ DD->useSplitDwarf());
 }
 
 LLVM_DUMP_METHOD
 void DIELocList::print(raw_ostream &O) const { O << "LocList: " << Index; }