[PATCH] D62188: Speed up --start-lib and --end-lib.

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

In LazyObjFile::parse():

  for (size_t I = FirstGlobal, End = ESyms.size(); I != End; ++I)
    if (ESyms[I].st_shndx != SHN_UNDEF)
      // resolveSymbol() called by addSymbol() checks if the symbol was originally undefined.
      // If that is the case, addSymbol() will transitively call SymbolTable::fetchLazy, which calls LazyObjFile::fetch().
      this->Symbols[I] = Symtab->addSymbol(
          LazyObject{*this, CHECK(ESyms[I].getName(Strtab), this)});
  return;

In LazyObjFile::parse():

  // Symbols[0,I) are inherited from LazyObjFile::parse(), other entries are nullptr.
  // This has another problem: it increases memory usage.
  // The copy assignment cannot be replaced with move assignment, because
  // parse() will continue processing Symbols[I+1] Symbols[I+2] ...
  File->Symbols = Symbols;

I think in most cases (that are not flagged by `--warn-backrefs`), this may not have a perceivable improvement in the current form. Actually,
For an (input: 4.2G; output: 1.6G) executable, I measure a performance regression, 1% or lower, but the memory usage increases by ~1.6%. Do you know if the problem can be fixed?



================
Comment at: lld/ELF/InputFiles.cpp:952
+    // Handle local symbols. Local symbols are not added to the symbol
+    // table because they are not visible from object object files. We
+    // allocate symbol instances and added their pointers to Symbols.
----------------
typo. first `object` -> `other


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D62188/new/

https://reviews.llvm.org/D62188