Don't create a temporary DenseMap for each input .eh_frame

[• espindola]

Summary

These maps are small, but we are creating an destroying one for each input .eh_frame.

This patch reduces the total memory allocation from 765.54MB to 749.19MB. The peak is still the same: 563.7MB.

[ruiu]

LGTM

ELF/SyntheticSections.h

89

Please add a comment to explain that this doesn't have to be a member from the point of view of correctness, but we do this to reuse allocated buffer.

[• espindola]

331075

ELF/SyntheticSections.h

struct FdeData {
     uint32_t Pc;
     uint32_t FdeVA;
   };
 
   std::vector<FdeData> getFdeData() const;
   ArrayRef<CieRecord *> getCieRecords() const { return CieRecords; }
 
 private:
+  llvm::DenseMap<size_t, CieRecord *> OffsetToCie;
   uint64_t Size = 0;
 
   template <class ELFT, class RelTy>
   void addSectionAux(EhInputSection *S, llvm::ArrayRef<RelTy> Rels);
 
   template <class ELFT, class RelTy>
   CieRecord *addCie(EhSectionPiece &Piece, ArrayRef<RelTy> Rels);
 

ELF/SyntheticSections.cpp

 }
 
 // .eh_frame is a sequence of CIE or FDE records. In general, there
 // is one CIE record per input object file which is followed by
 // a list of FDEs. This function searches an existing CIE or create a new
 // one and associates FDEs to the CIE.
 template <class ELFT, class RelTy>
 void EhFrameSection::addSectionAux(EhInputSection *Sec, ArrayRef<RelTy> Rels) {
-  DenseMap<size_t, CieRecord *> OffsetToCie;
+  OffsetToCie.clear();
   for (EhSectionPiece &Piece : Sec->Pieces) {
     // The empty record is the end marker.
     if (Piece.Size == 4)
       return;
 
     size_t Offset = Piece.InputOff;
     uint32_t ID = read32(Piece.data().data() + 4);
     if (ID == 0) {