[dwarfdump][dwarf] Fix parsing of tu-index

[ayermolo]

Summary

Fixed issue where {tu,cu}-index fixup code for DWARF5 that would report an error when
fixup map is empty. Which is the case when seciton(s) are not over 4GB or
--manaully-generate-unit-index is not specified

[dblaikie]

llvm/test/DebugInfo/X86/dwp-v5-tu-index.s

9

Perhaps this should be a bit less specific, otherwise it might easily be missed - maybe use an --implicit-check-not in the FileCheck command? (like --implicit-check-not=error)

[ayermolo]

addressed comments

[dblaikie]

Looks good, thanks!

llvm/lib/DebugInfo/DWARF/DWARFContext.cpp

while (Data.isValidOffset(Offset)) {
         break;
       }
       bool CU = Header.getUnitType() == DW_UT_split_compile;
       uint64_t Sig = CU ? *Header.getDWOId() : Header.getTypeHash();
       Map[Sig] = Header.getOffset();
       Offset = Header.getNextUnitOffset();
     }
   });
+  if (Map.empty())
+    return;
   for (DWARFUnitIndex::Entry &E : Index.getMutableRows()) {
     if (!E.isValid())
       continue;
     DWARFUnitIndex::Entry::SectionContribution &CUOff = E.getContribution();
     auto Iter = Map.find(E.getSignature());
     if (Iter == Map.end()) {
       logAllUnhandledErrors(
           createError("Could not find unit with signature 0x" +

llvm/test/DebugInfo/X86/dwp-v5-tu-index.s

 ## The test checks that we can parse and dump a TU index section that is
 ## compliant to the DWARFv5 standard.
 
 # RUN: llvm-mc -triple x86_64-unknown-linux %s -filetype=obj -o - | \
-# RUN:   llvm-dwarfdump -debug-tu-index - | \
-# RUN:   FileCheck %s
+# RUN:   llvm-dwarfdump -debug-tu-index - 2>&1 | \
+# RUN:   FileCheck %s --implicit-check-not "could not find unit with signature"
 
 # CHECK:      .debug_tu_index contents:
 # CHECK-NEXT: version = 5, units = 1, slots = 2
 # CHECK-EMPTY:
 # CHECK-NEXT: Index Signature          INFO                                     ABBREV                   LINE                     STR_OFFSETS
 # CHECK-NEXT: ----- ------------------ ---------------------------------------- ------------------------ ------------------------ ------------------------
 # CHECK-NEXT:     1 0x1100001122222222 [0x0000000000001000, 0x0000000000001010) [0x00002000, 0x00002020) [0x00003000, 0x00003030) [0x00004000, 0x00004040)
 
     .section .debug_tu_index, "", @progbits
 ## Header:
     .short 5            # Version