[DebugInfo] Force users of DWARFDebugAbbrev to call parse before iterating

[bulbazord]

Summary

In an attempt to make it easier to catch errors when parsing the
debug_abbrev section, we should force users to call parse before
calling begin. In a follow-up change, I will change the return type of
parse from void to Error.

I also explored using the fallible_iterator pattern instead of forcing
users to parse everything up front. I think it would be a useful and
interesting pattern to implement, but it would require more extensive
changes to both DWARFDebugAbbrev and its users. Because my top priority
is improving the safety around parsing debug_abbrev, I'm opting to
preserve existing behavior until I or somebody else has time to refactor
to be able to implement a fallible_iterator.

[bulbazord]

Fix bolt test failures

[ayermolo]

bolt/lib/Core/DebugData.cpp

1301 ↗

(On Diff #538847)

Assuming my changes won't be reverted BOLT no longer uses this method.

[fdeazeve]

This LGTM. It doesn't change the amount of work we do in advance, nor does it prevent us from implementing a lazy approach if we can measure performance issues, and it enables error checking in the future.

[bulbazord]

bolt/lib/Core/DebugData.cpp

1301 ↗

(On Diff #538847)

Good to know. For now, it was causing test failures so I'm going to land this with this change. It'll just go away when we're able to delete this method.

[ayermolo]

bolt/lib/Core/DebugData.cpp

1301 ↗

(On Diff #538847)

This BOLT code is no longer in trunk...

[bulbazord]

Remove deleted BOLT code

llvm/include/llvm/DebugInfo/DWARF/DWARFDebugAbbrev.h

public:
 
   Expected<const DWARFAbbreviationDeclarationSet *>
   getAbbreviationDeclarationSet(uint64_t CUAbbrOffset) const;
 
   void dump(raw_ostream &OS) const;
   void parse() const;
 
   DWARFAbbreviationDeclarationSetMap::const_iterator begin() const {
-    parse();
+    assert(!Data && "Must call parse before iterating over DWARFDebugAbbrev");
     return AbbrDeclSets.begin();
   }
 
   DWARFAbbreviationDeclarationSetMap::const_iterator end() const {
     return AbbrDeclSets.end();
   }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_DEBUGINFO_DWARF_DWARFDEBUGABBREV_H

llvm/tools/obj2yaml/dwarf2yaml.cpp

 #include <optional>
 
 using namespace llvm;
 
 void dumpDebugAbbrev(DWARFContext &DCtx, DWARFYAML::Data &Y) {
   auto AbbrevSetPtr = DCtx.getDebugAbbrev();
   if (AbbrevSetPtr) {
     uint64_t AbbrevTableID = 0;
+    AbbrevSetPtr->parse();
     for (auto AbbrvDeclSet : *AbbrevSetPtr) {
       Y.DebugAbbrev.emplace_back();
       Y.DebugAbbrev.back().ID = AbbrevTableID++;
       for (auto AbbrvDecl : AbbrvDeclSet.second) {
         DWARFYAML::Abbrev Abbrv;
         Abbrv.Code = AbbrvDecl.getCode();
         Abbrv.Tag = AbbrvDecl.getTag();
         Abbrv.Children = AbbrvDecl.hasChildren() ? dwarf::DW_CHILDREN_yes
void dumpDebugInfo(DWARFContext &DCtx, DWARFYAML::Data &Y) {
   for (const auto &CU : DCtx.compile_units()) {
     DWARFYAML::Unit NewUnit;
     NewUnit.Format = CU->getFormat();
     NewUnit.Length = CU->getLength();
     NewUnit.Version = CU->getVersion();
     if (NewUnit.Version >= 5)
       NewUnit.Type = (dwarf::UnitType)CU->getUnitType();
     const DWARFDebugAbbrev *DebugAbbrev = DCtx.getDebugAbbrev();
+    DebugAbbrev->parse();
     NewUnit.AbbrevTableID = std::distance(
         DebugAbbrev->begin(),
         llvm::find_if(
             *DebugAbbrev,
             [&](const std::pair<uint64_t, DWARFAbbreviationDeclarationSet> &P) {
               return P.first == CU->getAbbreviations()->getOffset();
             }));
     NewUnit.AbbrOffset = CU->getAbbreviations()->getOffset();