Split getCompileUnitFor{Data,Code}Address.

[hctim]

Summary

Getting compile units for data addresses is much slower, as it often
requires a slow fallback path to walk every DWARF entry, as
data addresses don't fall into the compilation unit ranges.

Most lookups are code addresses, and don't need this logic. Split the
functionality out so that we restore the fast-path behaviour for the
code lookups.

More context at:
https://discourse.llvm.org/t/llvm-symbolizer-has-gotten-extremely-slow/67262

[dblaikie]

Yep, looks good. (interestingly, this implementation might be missing some functionality for Split DWARF - in a Split DWARF build I didn't see any perf improvement, because I think there was no perf degredation - because this feature isn't properly implemented for Split DWARF, I'd guess)

But for a non-Split DWARF build this patch does improve performance:

From: 1m16.880s
To: 0m17.188s

Thanks for doing this - also looks like we have internal use that ended up with some workarounds that can be cleaned up by this API change too.

llvm/include/llvm/DebugInfo/DWARF/DWARFContext.h

public:
   Triple::ArchType getArch() const {
     return getDWARFObj().getFile()->getArch();
   }
 
   /// Return the compile unit which contains instruction with provided
   /// address.
   /// TODO: change input parameter from "uint64_t Address"
   ///       into "SectionedAddress Address"
-  DWARFCompileUnit *getCompileUnitForAddress(uint64_t Address);
+  DWARFCompileUnit *getCompileUnitForCodeAddress(uint64_t Address);
+
+  /// Return the compile unit which contains data with the provided address.
+  /// Note: This is more expensive than `getCompileUnitForAddress`, as if
+  /// `Address` isn't found in the CU ranges (which is cheap), then it falls
+  /// back to an expensive O(n) walk of all CU's looking for data that spans the
+  /// address.
+  /// TODO: change input parameter from "uint64_t Address" into
+  ///       "SectionedAddress Address"
+  DWARFCompileUnit *getCompileUnitForDataAddress(uint64_t Address);
 
   /// Returns whether CU/TU should be populated manually. TU Index populated
   /// manually only for DWARF5.
   bool getParseCUTUIndexManually() const { return ParseCUTUIndexManually; }
 
   /// Sets whether CU/TU should be populated manually. TU Index populated
   /// manually only for DWARF5.
   void setParseCUTUIndexManually(bool PCUTU) { ParseCUTUIndexManually = PCUTU; }

llvm/lib/DebugInfo/DWARF/DWARFContext.cpp

 }
 
 DWARFCompileUnit *DWARFContext::getCompileUnitForOffset(uint64_t Offset) {
   parseNormalUnits();
   return dyn_cast_or_null<DWARFCompileUnit>(
       NormalUnits.getUnitForOffset(Offset));
 }
 
-DWARFCompileUnit *DWARFContext::getCompileUnitForAddress(uint64_t Address) {
-  // First, get the offset of the compile unit.
+DWARFCompileUnit *DWARFContext::getCompileUnitForCodeAddress(uint64_t Address) {
+  uint64_t CUOffset = getDebugAranges()->findAddress(Address);
+  return getCompileUnitForOffset(CUOffset);
+}
+
+DWARFCompileUnit *DWARFContext::getCompileUnitForDataAddress(uint64_t Address) {
   uint64_t CUOffset = getDebugAranges()->findAddress(Address);
-  // Retrieve the compile unit.
   if (DWARFCompileUnit *OffsetCU = getCompileUnitForOffset(CUOffset))
     return OffsetCU;
 
-  // Global variables are often not found by the above search, for one of two
+  // Global variables are often missed by the above search, for one of two
   // reasons:
   //   1. .debug_aranges may not include global variables. On clang, it seems we
   //      put the globals in the aranges, but this isn't true for gcc.
   //   2. Even if the global variable is in a .debug_arange, global variables
   //      may not be captured in the [start, end) addresses described by the
   //      parent compile unit.
   //
   // So, we walk the CU's and their child DI's manually, looking for the
   // specific global variable.
   for (std::unique_ptr<DWARFUnit> &CU : compile_units()) {
     if (DWARFDie Die = CU->getVariableForAddress(Address)) {
       return static_cast<DWARFCompileUnit *>(CU.get());
     }
   }
   return nullptr;
 }
 
 DWARFContext::DIEsForAddress DWARFContext::getDIEsForAddress(uint64_t Address) {
   DIEsForAddress Result;
 
-  DWARFCompileUnit *CU = getCompileUnitForAddress(Address);
+  DWARFCompileUnit *CU = getCompileUnitForCodeAddress(Address);
   if (!CU)
     return Result;
 
   Result.CompileUnit = CU;
   Result.FunctionDIE = CU->getSubroutineForAddress(Address);
 
   std::vector<DWARFDie> Worklist;
   Worklist.push_back(Result.FunctionDIE);
void DWARFContext::addLocalsForDie(DWARFCompileUnit *CU, DWARFDie Subprogram,
 
   for (auto Child : Die)
     addLocalsForDie(CU, Subprogram, Child, Result);
 }
 
 std::vector<DILocal>
 DWARFContext::getLocalsForAddress(object::SectionedAddress Address) {
   std::vector<DILocal> Result;
-  DWARFCompileUnit *CU = getCompileUnitForAddress(Address.Address);
+  DWARFCompileUnit *CU = getCompileUnitForCodeAddress(Address.Address);
   if (!CU)
     return Result;
 
   DWARFDie Subprogram = CU->getSubroutineForAddress(Address.Address);
   if (Subprogram.isValid())
     addLocalsForDie(CU, Subprogram, Subprogram, Result);
   return Result;
 }
 
 DILineInfo DWARFContext::getLineInfoForAddress(object::SectionedAddress Address,
                                                DILineInfoSpecifier Spec) {
   DILineInfo Result;
-  DWARFCompileUnit *CU = getCompileUnitForAddress(Address.Address);
+  DWARFCompileUnit *CU = getCompileUnitForCodeAddress(Address.Address);
   if (!CU)
     return Result;
 
   getFunctionNameAndStartLineForAddress(
       CU, Address.Address, Spec.FNKind, Spec.FLIKind, Result.FunctionName,
       Result.StartFileName, Result.StartLine, Result.StartAddress);
   if (Spec.FLIKind != FileLineInfoKind::None) {
     if (const DWARFLineTable *LineTable = getLineTableForUnit(CU)) {
       LineTable->getFileLineInfoForAddress(
           {Address.Address, Address.SectionIndex}, CU->getCompilationDir(),
           Spec.FLIKind, Result);
     }
   }
 
   return Result;
 }
 
 DILineInfo
 DWARFContext::getLineInfoForDataAddress(object::SectionedAddress Address) {
   DILineInfo Result;
-  DWARFCompileUnit *CU = getCompileUnitForAddress(Address.Address);
+  DWARFCompileUnit *CU = getCompileUnitForDataAddress(Address.Address);
   if (!CU)
     return Result;
 
   if (DWARFDie Die = CU->getVariableForAddress(Address.Address)) {
     Result.FileName = Die.getDeclFile(FileLineInfoKind::AbsoluteFilePath);
     Result.Line = Die.getDeclLine();
   }
 
   return Result;
 }
 
 DILineInfoTable DWARFContext::getLineInfoForAddressRange(
     object::SectionedAddress Address, uint64_t Size, DILineInfoSpecifier Spec) {
   DILineInfoTable Lines;
-  DWARFCompileUnit *CU = getCompileUnitForAddress(Address.Address);
+  DWARFCompileUnit *CU = getCompileUnitForCodeAddress(Address.Address);
   if (!CU)
     return Lines;
 
   uint32_t StartLine = 0;
   std::string StartFileName;
   std::string FunctionName(DILineInfo::BadString);
   std::optional<uint64_t> StartAddress;
   getFunctionNameAndStartLineForAddress(CU, Address.Address, Spec.FNKind,
DILineInfoTable DWARFContext::getLineInfoForAddressRange(
   return Lines;
 }
 
 DIInliningInfo
 DWARFContext::getInliningInfoForAddress(object::SectionedAddress Address,
                                         DILineInfoSpecifier Spec) {
   DIInliningInfo InliningInfo;
 
-  DWARFCompileUnit *CU = getCompileUnitForAddress(Address.Address);
+  DWARFCompileUnit *CU = getCompileUnitForCodeAddress(Address.Address);
   if (!CU)
     return InliningInfo;
 
   const DWARFLineTable *LineTable = nullptr;
   SmallVector<DWARFDie, 4> InlinedChain;
   CU->getInlinedChainForAddress(Address.Address, InlinedChain);
   if (InlinedChain.size() == 0) {
     // If there is no DIE for address (e.g. it is in unavailable .dwo file),