Add the ability to get attribute values as Optional<T>

When getting attributes it is sometimes nicer to use Optional<T> some of the time instead of magic values. I tried to cut over to only using the Optional values but it made many of the call sites very messy, so it makes sense the leave in the calls that can return a default value. Otherwise code that looks like this:

uint64_t CallColumn = Die.getAttributeValueAsAddress(DW_AT_call_line, 0);

Has to be turned into:

uint64_t CallColumn = 0;
if (auto CallColumnValue = Die.getAttributeValueAsAddress(DW_AT_call_line))
    CallColumn = *CallColumnValue;

The first snippet of code looks much better. But in cases where you want an offset that may or may not be there, the following code looks better:

if (auto StmtOffset = Die.getAttributeValueAsSectionOffset(DW_AT_stmt_list)) {
  // Use StmtOffset
}

Differential Revision: https://reviews.llvm.org/D27772

llvm-svn: 289731

1 files changed, 21 insertions, 23 deletions

diff --git a/llvm/tools/dsymutil/DwarfLinker.cpp b/llvm/tools/dsymutil/DwarfLinker.cpp
index 068bf22cc89..803f7f98cc5 100644
--- a/llvm/tools/dsymutil/DwarfLinker.cpp
+++ b/llvm/tools/dsymutil/DwarfLinker.cpp
@@ -841,10 +841,9 @@ void DwarfStreamer::emitLocationsForUnit(const CompileUnit &Unit,
   DWARFUnit &OrigUnit = Unit.getOrigUnit();
   auto OrigUnitDie = OrigUnit.getUnitDIE(false);
   int64_t UnitPcOffset = 0;
-  uint64_t OrigLowPc = OrigUnitDie.getAttributeValueAsAddress(
-      dwarf::DW_AT_low_pc, -1ULL);
-  if (OrigLowPc != -1ULL)
-    UnitPcOffset = int64_t(OrigLowPc) - Unit.getLowPc();
+  auto OrigLowPc = OrigUnitDie.getAttributeValueAsAddress(dwarf::DW_AT_low_pc);
+  if (OrigLowPc)
+    UnitPcOffset = int64_t(*OrigLowPc) - Unit.getLowPc();
 
   for (const auto &Attr : Attributes) {
     uint32_t Offset = Attr.first.get();
@@ -2124,10 +2123,9 @@ unsigned DwarfLinker::shouldKeepSubprogramDIE(
   std::tie(LowPcOffset, LowPcEndOffset) =
       getAttributeOffsets(Abbrev, *LowPcIdx, Offset, OrigUnit);
 
-  uint64_t LowPc =
-      DIE.getAttributeValueAsAddress(dwarf::DW_AT_low_pc, -1ULL);
-  assert(LowPc != -1ULL && "low_pc attribute is not an address.");
-  if (LowPc == -1ULL ||
+  auto LowPc = DIE.getAttributeValueAsAddress(dwarf::DW_AT_low_pc);
+  assert(LowPc.hasValue() && "low_pc attribute is not an address.");
+  if (!LowPc ||
       !RelocMgr.hasValidRelocation(LowPcOffset, LowPcEndOffset, MyInfo))
     return Flags;
 
@@ -2148,12 +2146,12 @@ unsigned DwarfLinker::shouldKeepSubprogramDIE(
     HighPc = *HighPcValue->getAsAddress();
   } else {
     assert(HighPcValue->isFormClass(DWARFFormValue::FC_Constant));
-    HighPc = LowPc + *HighPcValue->getAsUnsignedConstant();
+    HighPc = *LowPc + *HighPcValue->getAsUnsignedConstant();
   }
 
   // Replace the debug map range with a more accurate one.
-  Ranges[LowPc] = std::make_pair(HighPc, MyInfo.AddrAdjust);
-  Unit.addFunctionRange(LowPc, HighPc, MyInfo.AddrAdjust);
+  Ranges[*LowPc] = std::make_pair(HighPc, MyInfo.AddrAdjust);
+  Unit.addFunctionRange(*LowPc, HighPc, MyInfo.AddrAdjust);
   return Flags;
 }
 
@@ -2974,9 +2972,8 @@ static void patchStmtList(DIE &Die, DIEInteger Offset) {
 void DwarfLinker::patchLineTableForUnit(CompileUnit &Unit,
                                         DWARFContext &OrigDwarf) {
   DWARFDie CUDie = Unit.getOrigUnit().getUnitDIE();
-  uint64_t StmtList = CUDie.getAttributeValueAsSectionOffset(
-      dwarf::DW_AT_stmt_list, -1ULL);
-  if (StmtList == -1ULL)
+  auto StmtList = CUDie.getAttributeValueAsSectionOffset(dwarf::DW_AT_stmt_list);
+  if (!StmtList)
     return;
 
   // Update the cloned DW_AT_stmt_list with the correct debug_line offset.
@@ -2985,7 +2982,7 @@ void DwarfLinker::patchLineTableForUnit(CompileUnit &Unit,
 
   // Parse the original line info for the unit.
   DWARFDebugLine::LineTable LineTable;
-  uint32_t StmtOffset = StmtList;
+  uint32_t StmtOffset = *StmtList;
   StringRef LineData = OrigDwarf.getLineSection().Data;
   DataExtractor LineExtractor(LineData, OrigDwarf.isLittleEndian(),
                               Unit.getOrigUnit().getAddressByteSize());
@@ -3079,7 +3076,7 @@ void DwarfLinker::patchLineTableForUnit(CompileUnit &Unit,
   }
 
   // Finished extracting, now emit the line tables.
-  uint32_t PrologueEnd = StmtList + 10 + LineTable.Prologue.PrologueLength;
+  uint32_t PrologueEnd = *StmtList + 10 + LineTable.Prologue.PrologueLength;
   // FIXME: LLVM hardcodes it's prologue values. We just copy the
   // prologue over and that works because we act as both producer and
   // consumer. It would be nicer to have a real configurable line
@@ -3094,7 +3091,7 @@ void DwarfLinker::patchLineTableForUnit(CompileUnit &Unit,
     Params.DWARF2LineBase = LineTable.Prologue.LineBase;
     Params.DWARF2LineRange = LineTable.Prologue.LineRange;
     Streamer->emitLineTableForUnit(Params,
-                                   LineData.slice(StmtList + 4, PrologueEnd),
+                                   LineData.slice(*StmtList + 4, PrologueEnd),
                                    LineTable.Prologue.MinInstLength, NewRows,
                                    Unit.getOrigUnit().getAddressByteSize());
   }
@@ -3207,12 +3204,13 @@ void DwarfLinker::DIECloner::copyAbbrev(
 
 static uint64_t getDwoId(const DWARFDie &CUDie,
                          const DWARFUnit &Unit) {
-  uint64_t DwoId =
-      CUDie.getAttributeValueAsUnsignedConstant(dwarf::DW_AT_dwo_id, 0);
-  if (!DwoId)
-    DwoId = CUDie.getAttributeValueAsUnsignedConstant(dwarf::DW_AT_GNU_dwo_id,
-                                                      0);
-  return DwoId;
+  auto DwoId = CUDie.getAttributeValueAsUnsignedConstant(dwarf::DW_AT_dwo_id);
+  if (DwoId)
+    return *DwoId;
+  DwoId = CUDie.getAttributeValueAsUnsignedConstant(dwarf::DW_AT_GNU_dwo_id);
+  if (DwoId)
+    return *DwoId;
+  return 0;
 }
 
 bool DwarfLinker::registerModuleReference(