[llvm] r349637 - [Object] Deduplicate long archive member names

[Peter Wu via llvm-commits]

Author: lekensteyn
Date: Wed Dec 19 08:15:05 2018
New Revision: 349637

URL: http://llvm.org/viewvc/llvm-project?rev=349637&view=rev
Log:
[Object] Deduplicate long archive member names

Summary:
Import libraries as created by llvm-dlltool always use the same archive
member name for every object file (namely, the DLL library name). Ensure
that long names are not repeatedly stored in the string table.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D55860

Modified:
    llvm/trunk/lib/Object/ArchiveWriter.cpp
    llvm/trunk/test/Object/archive-format.test

Modified: llvm/trunk/lib/Object/ArchiveWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Object/ArchiveWriter.cpp?rev=349637&r1=349636&r2=349637&view=diff
==============================================================================
--- llvm/trunk/lib/Object/ArchiveWriter.cpp (original)
+++ llvm/trunk/lib/Object/ArchiveWriter.cpp Wed Dec 19 08:15:05 2018
@@ -250,6 +250,7 @@ static void addToStringTable(raw_ostream
 
 static void printMemberHeader(raw_ostream &Out, uint64_t Pos,
                               raw_ostream &StringTable,
+                              StringMap<uint64_t> &MemberNames,
                               object::Archive::Kind Kind, bool Thin,
                               StringRef ArcName, const NewArchiveMember &M,
                               sys::TimePoint<std::chrono::seconds> ModTime,
@@ -262,8 +263,20 @@ static void printMemberHeader(raw_ostrea
     return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
                                      M.Perms, Size);
   Out << '/';
-  uint64_t NamePos = StringTable.tell();
-  addToStringTable(StringTable, ArcName, M, Thin);
+  uint64_t NamePos;
+  if (Thin) {
+    NamePos = StringTable.tell();
+    addToStringTable(StringTable, ArcName, M, Thin);
+  } else {
+    StringMap<uint64_t>::const_iterator it = MemberNames.find(M.MemberName);
+    if (it == MemberNames.end()) {
+      NamePos = StringTable.tell();
+      addToStringTable(StringTable, ArcName, M, Thin);
+      MemberNames[M.MemberName] = NamePos;
+    } else {
+      NamePos = it->second;
+    }
+  }
   printWithSpacePadding(Out, NamePos, 15);
   printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size);
 }
@@ -433,6 +446,11 @@ computeMemberData(raw_ostream &StringTab
   std::vector<MemberData> Ret;
   bool HasObject = false;
 
+  // Deduplicate long member names in the string table and reuse earlier name
+  // offsets. This especially saves space for COFF Import libraries where all
+  // members have the same name.
+  StringMap<uint64_t> MemberNames;
+
   // UniqueTimestamps is a special case to improve debugging on Darwin:
   //
   // The Darwin linker does not link debug info into the final
@@ -505,8 +523,8 @@ computeMemberData(raw_ostream &StringTab
       ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++);
     else
       ModTime = M.ModTime;
-    printMemberHeader(Out, Pos, StringTable, Kind, Thin, ArcName, M, ModTime,
-                      Buf.getBufferSize() + MemberPadding);
+    printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, ArcName,
+                      M, ModTime, Buf.getBufferSize() + MemberPadding);
     Out.flush();
 
     Expected<std::vector<unsigned>> Symbols =

Modified: llvm/trunk/test/Object/archive-format.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Object/archive-format.test?rev=349637&r1=349636&r2=349637&view=diff
==============================================================================
--- llvm/trunk/test/Object/archive-format.test (original)
+++ llvm/trunk/test/Object/archive-format.test Wed Dec 19 08:15:05 2018
@@ -15,8 +15,7 @@ RUN: llvm-ar --format=gnu rc %t.a 012345
 RUN: cat %t.a | FileCheck -strict-whitespace %s
 
 CHECK:      !<arch>
-CHECK-NEXT: //                                              36        `
-CHECK-NEXT: 0123456789abcdef/
+CHECK-NEXT: //                                              18        `
 CHECK-NEXT: 0123456789abcdef/
 CHECK-NEXT: 0123456789abcde/0           0     0     644     4         `
 CHECK-NEXT: bar.
@@ -24,7 +23,7 @@ CHECK-SAME: /0              0
 CHECK-NEXT: zed.
 CHECK-SAME: 0123456789abcde/0           0     0     644     4         `
 CHECK-NEXT: bar2
-CHECK-SAME: /18             0           0     0     644     4         `
+CHECK-SAME: /0              0           0     0     644     4         `
 CHECK-NEXT: zed2
 
 RUN: rm -f %t.a