[PATCH] D33183: [ELF] - Simplify readAddressArea() implementation.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
Herald added a subscriber: aprantl.

This patch depends on a change for LLVM DWARF parsers, I'll post it in a few minutes as
a separate patch.

Approach significantly simplifies LLD .gdb_index code and makes it much faster.
Also it should resolve issues, like https://reviews.llvm.org/D33176 tries to address once and forever in a clean way.

LLC binary linking without patch and without --gdb-index: 1,599241063
LLC binary linking without patch and with --gdb-index: 6,064316262
LLC binary linking with patch and with --gdb-index: 4,116792104

Time spent for building gdbindex changes from (6,064316262 - 1,599241063 == 4,465075199)
to (4,116792104- 1,599241063 == 2,517551041).
That is 2,517551041/4,465075199 = 0,564 or about 44% speedup.


https://reviews.llvm.org/D33183

Files:
  ELF/SyntheticSections.cpp


Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -1701,16 +1701,6 @@
   return Ret;
 }
 
-static InputSectionBase *findSection(ArrayRef<InputSectionBase *> Arr,
-                                     uint64_t Offset) {
-  for (InputSectionBase *S : Arr)
-    if (S && S != &InputSection::Discarded)
-      if (Offset >= S->getOffsetInFile() &&
-          Offset < S->getOffsetInFile() + S->getSize())
-        return S;
-  return nullptr;
-}
-
 static std::vector<AddressEntry>
 readAddressArea(DWARFContext &Dwarf, InputSection *Sec, size_t CurrentCU) {
   std::vector<AddressEntry> Ret;
@@ -1720,10 +1710,12 @@
     CU->collectAddressRanges(Ranges);
 
     ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
-    for (std::pair<uint64_t, uint64_t> &R : Ranges)
-      if (InputSectionBase *S = findSection(Sections, R.first))
-        Ret.push_back({S, R.first - S->getOffsetInFile(),
-                       R.second - S->getOffsetInFile(), CurrentCU});
+    for (DWARFAddress &R : Ranges) {
+      InputSectionBase *S = Sections[R.SecNdx];
+      if (!S || S == &InputSection::Discarded)
+        continue;
+      Ret.push_back({S, R.LowPC, R.HighPC, CurrentCU});
+    }
     ++CurrentCU;
   }
   return Ret;
@@ -1744,27 +1736,15 @@
   return Ret;
 }
 
-class ObjInfoTy : public llvm::LoadedObjectInfo {
-  uint64_t getSectionLoadAddress(const object::SectionRef &Sec) const override {
-    auto &S = static_cast<const object::ELFSectionRef &>(Sec);
-    if (S.getFlags() & ELF::SHF_ALLOC)
-      return S.getOffset();
-    return 0;
-  }
-
-  std::unique_ptr<llvm::LoadedObjectInfo> clone() const override { return {}; }
-};
-
 void GdbIndexSection::readDwarf(InputSection *Sec) {
   Expected<std::unique_ptr<object::ObjectFile>> Obj =
       object::ObjectFile::createObjectFile(Sec->File->MB);
   if (!Obj) {
     error(toString(Sec->File) + ": error creating DWARF context");
     return;
   }
 
-  ObjInfoTy ObjInfo;
-  DWARFContextInMemory Dwarf(*Obj.get(), &ObjInfo);
+  DWARFContextInMemory Dwarf(*Obj.get());
 
   size_t CuId = CompilationUnits.size();
   for (std::pair<uint64_t, uint64_t> &P : readCuList(Dwarf, Sec))


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