[lld] r233128 - PECOFF: Reduce import table size.

[Rafael Espíndola]

testcase? :-)

On 24 March 2015 at 18:43, Rui Ueyama <ruiu at google.com> wrote:
> Author: ruiu
> Date: Tue Mar 24 17:43:58 2015
> New Revision: 233128
>
> URL: http://llvm.org/viewvc/llvm-project?rev=233128&view=rev
> Log:
> PECOFF: Reduce import table size.
>
> Import Lookup Table in Import Directory Table has the same contents
> as Hint/Name Table. Symbol names imported from DLLs are pointed by
> both Import Directory Table and Hint/Name Table. We had duplicate
> strings there.
>
> This patch eliminates that duplication to make the table smaller.
> This should reduce binary size by the sum of lengths of imported
> symbols.
>
> Modified:
>     lld/trunk/lib/ReaderWriter/PECOFF/IdataPass.cpp
>
> Modified: lld/trunk/lib/ReaderWriter/PECOFF/IdataPass.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/IdataPass.cpp?rev=233128&r1=233127&r2=233128&view=diff
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/PECOFF/IdataPass.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/PECOFF/IdataPass.cpp Tue Mar 24 17:43:58 2015
> @@ -69,6 +69,7 @@ static std::vector<ImportTableEntryAtom
>  createImportTableAtoms(IdataContext &context,
>                         const std::vector<COFFSharedLibraryAtom *> &sharedAtoms,
>                         bool shouldAddReference, StringRef sectionName,
> +                       std::map<StringRef, HintNameAtom *> &hintNameCache,
>                         llvm::BumpPtrAllocator &alloc) {
>    std::vector<ImportTableEntryAtom *> ret;
>    for (COFFSharedLibraryAtom *atom : sharedAtoms) {
> @@ -81,9 +82,16 @@ createImportTableAtoms(IdataContext &con
>      } else {
>        // Import by name
>        entry = new (alloc) ImportTableEntryAtom(context, 0, sectionName);
> -      HintNameAtom *hintName =
> -          new (alloc) HintNameAtom(context, atom->hint(), atom->importName());
> -      addDir32NBReloc(entry, hintName, context.ctx.getMachineType(), 0);
> +      HintNameAtom *hintNameAtom;
> +      auto it = hintNameCache.find(atom->importName());
> +      if (it == hintNameCache.end()) {
> +        hintNameAtom = new (alloc) HintNameAtom(
> +            context, atom->hint(), atom->importName());
> +        hintNameCache[atom->importName()] = hintNameAtom;
> +      } else {
> +        hintNameAtom = it->second;
> +      }
> +      addDir32NBReloc(entry, hintNameAtom, context.ctx.getMachineType(), 0);
>      }
>      ret.push_back(entry);
>      if (shouldAddReference)
> @@ -104,10 +112,13 @@ void ImportDirectoryAtom::addRelocations
>    // same. The PE/COFF loader overwrites the import address tables with the
>    // pointers to the referenced items after loading the executable into
>    // memory.
> +  std::map<StringRef, HintNameAtom *> hintNameCache;
>    std::vector<ImportTableEntryAtom *> importLookupTables =
> -      createImportTableAtoms(context, sharedAtoms, false, ".idata.t", _alloc);
> +      createImportTableAtoms(context, sharedAtoms, false, ".idata.t",
> +                             hintNameCache, _alloc);
>    std::vector<ImportTableEntryAtom *> importAddressTables =
> -      createImportTableAtoms(context, sharedAtoms, true, ".idata.a", _alloc);
> +      createImportTableAtoms(context, sharedAtoms, true, ".idata.a",
> +                             hintNameCache, _alloc);
>
>    addDir32NBReloc(this, importLookupTables[0], context.ctx.getMachineType(),
>                    offsetof(ImportDirectoryTableEntry, ImportLookupTableRVA));
> @@ -157,8 +168,10 @@ void DelayImportDirectoryAtom::addReloca
>    // as (non-delay) import table's Import Lookup Table. Contains
>    // imported function names. This is a parallel array of AddressTable
>    // field.
> +  std::map<StringRef, HintNameAtom *> hintNameCache;
>    std::vector<ImportTableEntryAtom *> nameTable =
> -      createImportTableAtoms(context, sharedAtoms, false, ".didat", _alloc);
> +      createImportTableAtoms(
> +          context, sharedAtoms, false, ".didat", hintNameCache, _alloc);
>    addDir32NBReloc(
>        this, nameTable[0], context.ctx.getMachineType(),
>        offsetof(delay_import_directory_table_entry, DelayImportNameTable));
>
>
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