[llvm-ar] Make llvm-lib behave more like the MSVC archiver

Summary:
Use the filepath used to open the archive member as the archive member
name instead of the file basename. This path might be absolute or
relative.  This is important because the archive member name will show
up in the PDB, and we want our PDBs to look as much like MSVC's as
possible.

This also helps avoid an issue in our PDB module descriptor writing
code, which assumes that all module names are unique. Relative paths
still aren't guaranteed to be unique, but they're much better than
basenames, which definitely aren't unique.

Reviewers: ruiu, zturner

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33575

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305223 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rnk

include/llvm/Object/ArchiveWriter.h

@@ -22,6 +22,7 @@ namespace llvm {
 
 struct NewArchiveMember {
   std::unique_ptr<MemoryBuffer> Buf;
+  StringRef MemberName;
   sys::TimePoint<std::chrono::seconds> ModTime;
   unsigned UID = 0, GID = 0, Perms = 0644;
 

lib/Object/ArchiveWriter.cpp

@@ -36,7 +36,8 @@
 using namespace llvm;
 
 NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef)
-    : Buf(MemoryBuffer::getMemBuffer(BufRef, false)) {}
+    : Buf(MemoryBuffer::getMemBuffer(BufRef, false)),
+      MemberName(BufRef.getBufferIdentifier()) {}
 
 Expected<NewArchiveMember>
 NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
@@ -48,6 +49,7 @@ NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
   NewArchiveMember M;
   assert(M.IsNew == false);
   M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false);
+  M.MemberName = M.Buf->getBufferIdentifier();
   if (!Deterministic) {
     auto ModTimeOrErr = OldMember.getLastModified();
     if (!ModTimeOrErr)
@@ -97,6 +99,7 @@ Expected<NewArchiveMember> NewArchiveMember::getFile(StringRef FileName,
   NewArchiveMember M;
   M.IsNew = true;
   M.Buf = std::move(*MemberBufferOrErr);
+  M.MemberName = M.Buf->getBufferIdentifier();
   if (!Deterministic) {
     M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>(
         Status.getLastModificationTime());
@@ -185,7 +188,7 @@ printBSDMemberHeader(raw_fd_ostream &Out, StringRef Name,
 }
 
 static bool useStringTable(bool Thin, StringRef Name) {
-  return Thin || Name.size() >= 16;
+  return Thin || Name.size() >= 16 || Name.contains('/');
 }
 
 static void
@@ -239,7 +242,7 @@ static void writeStringTable(raw_fd_ostream &Out, StringRef ArcName,
   unsigned StartOffset = 0;
   for (const NewArchiveMember &M : Members) {
     StringRef Path = M.Buf->getBufferIdentifier();
-    StringRef Name = sys::path::filename(Path);
+    StringRef Name = M.MemberName;
     if (!useStringTable(Thin, Name))
       continue;
     if (StartOffset == 0) {
@@ -423,9 +426,8 @@ llvm::writeArchive(StringRef ArcName,
     if (Kind == object::Archive::K_DARWIN)
       Padding = OffsetToAlignment(M.Buf->getBufferSize(), 8);
 
-    printMemberHeader(Out, Kind, Thin,
-                      sys::path::filename(M.Buf->getBufferIdentifier()),
-                      StringMapIndexIter, M.ModTime, M.UID, M.GID, M.Perms,
+    printMemberHeader(Out, Kind, Thin, M.MemberName, StringMapIndexIter,
+                      M.ModTime, M.UID, M.GID, M.Perms,
                       M.Buf->getBufferSize() + Padding);
 
     if (!Thin)

test/LibDriver/use-paths.test

@@ -0,0 +1,24 @@
+llvm-lib should behave like "link.exe /lib" and use relative paths to describe
+archive members.
+
+First, get in a clean working directory.
+RUN: rm -rf %t && mkdir -p %t && cd %t
+
+Make foo/a.obj and foo/b.obj.
+RUN: mkdir foo
+RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o foo/a.obj %S/Inputs/a.s
+RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o foo/b.obj %S/Inputs/b.s
+
+RUN: llvm-lib -out:foo.lib foo/a.obj foo/b.obj
+RUN: llvm-ar t foo.lib | FileCheck %s
+
+FIXME: We should probably use backslashes on Windows to better match MSVC tools.
+CHECK: foo/a.obj
+CHECK: foo/b.obj
+
+Do it again with absolute paths and see that we get something.
+RUN: llvm-lib -out:foo.lib %t/foo/a.obj %t/foo/b.obj
+RUN: llvm-ar t foo.lib | FileCheck %s --check-prefix=ABS
+
+ABS: {{.*}}/foo/a.obj
+ABS: {{.*}}/foo/b.obj

tools/llvm-ar/llvm-ar.cpp

@@ -473,6 +473,10 @@ static void addMember(std::vector<NewArchiveMember> &Members,
   Expected<NewArchiveMember> NMOrErr =
       NewArchiveMember::getFile(FileName, Deterministic);
   failIfError(NMOrErr.takeError(), FileName);
+
+  // Use the basename of the object path for the member name.
+  NMOrErr->MemberName = sys::path::filename(NMOrErr->MemberName);
+
   if (Pos == -1)
     Members.push_back(std::move(*NMOrErr));
   else