[DWARF/AccelTable] Remove getDIESectionOffset for DWARF v5 entries

Summary:
This method was not correct for entries in DWO files as it assumed it
could just add up the CU and DIE offsets to get the absolute DIE offset.
This is not correct for the DWO files, as here the CU offset will
reference the skeleton unit, whereas the DIE offset will be the offset
in the full unit in the DWO file.

Unfortunately, this means that we are not able to determine the absolute
DIE offset using the information in the .debug_names section alone,
which means we have to offload some of this work to the users of this
class.

To demonstrate how this can be done, I've added/fixed the ability to
lookup entries using accelerator tables in DWO files in llvm-dwarfdump.
To make this happen, I've needed to make two extra changes in other
classes:
- made the DWARFContext method to lookup a CU based on the section
  offset public. I've needed this functionality to lookup a CU, and this
  seems like a useful thing in general.
- made DWARFUnit::getDWOId call extractDIEsIfNeeded. Before this, the
  DWOId was filled in only if the root DIE happened to be parsed
  before we called the accessor. Since the lazy parsing is supposed to
  happen under the hood, calling extractDIEsIfNeeded seems appropriate.

Reviewers: JDevlieghere, aprantl, dblaikie

Subscribers: mgrang, llvm-commits

Differential Revision: https://reviews.llvm.org/D48009

llvm-svn: 334578

2 files changed, 4 insertions, 11 deletions

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp b/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
index c2ba9e6027b..0ded97cabf2 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
@@ -556,14 +556,6 @@ Optional<uint64_t> DWARFDebugNames::Entry::getCUOffset() const {
   return NameIdx->getCUOffset(*Index);
 }
 
-Optional<uint64_t> DWARFDebugNames::Entry::getDIESectionOffset() const {
-  Optional<uint64_t> CUOff = getCUOffset();
-  Optional<uint64_t> DIEOff = getDIEUnitOffset();
-  if (CUOff && DIEOff)
-    return *CUOff + *DIEOff;
-  return None;
-}
-
 void DWARFDebugNames::Entry::dump(ScopedPrinter &W) const {
   W.printHex("Abbrev", Abbr->Code);
   W.startLine() << formatv("Tag: {0}\n", Abbr->Tag);
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
index fe44071d9a2..e456de5b103 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
@@ -1088,7 +1088,7 @@ unsigned DWARFVerifier::verifyNameIndexEntries(
       continue;
     }
     uint32_t CUOffset = NI.getCUOffset(CUIndex);
-    uint64_t DIEOffset = *EntryOr->getDIESectionOffset();
+    uint64_t DIEOffset = CUOffset + *EntryOr->getDIEUnitOffset();
     DWARFDie DIE = DCtx.getDIEForOffset(DIEOffset);
     if (!DIE) {
       error() << formatv("Name Index @ {0:x}: Entry @ {1:x} references a "
@@ -1261,9 +1261,10 @@ unsigned DWARFVerifier::verifyNameIndexCompleteness(
   // Now we know that our Die should be present in the Index. Let's check if
   // that's the case.
   unsigned NumErrors = 0;
+  uint64_t DieUnitOffset = Die.getOffset() - Die.getDwarfUnit()->getOffset();
   for (StringRef Name : EntryNames) {
-    if (none_of(NI.equal_range(Name), [&Die](const DWARFDebugNames::Entry &E) {
-          return E.getDIESectionOffset() == uint64_t(Die.getOffset());
+    if (none_of(NI.equal_range(Name), [&](const DWARFDebugNames::Entry &E) {
+          return E.getDIEUnitOffset() == DieUnitOffset;
         })) {
       error() << formatv("Name Index @ {0:x}: Entry for DIE @ {1:x} ({2}) with "
                          "name {3} missing.\n",