[LLD][COFF] Make /wholearchive thin-archive member identifiers consistent (#145487)

A thin archive is an archive/library format where the archive itself
contains only references to member object files on disk, rather than
embedding the file contents.

For the non-/wholearchive case, we use the path to the archive member as
the identifier for thin-archive members (see comments in
`enqueueArchiveMember`). This patch modifies the /wholearchive path to
behave the same way.

Apart from consistency, my motivation for fixing this is DTLTO
(#126654), where having the member identifier be the path on disk allows
distribution of bitcode members during ThinLTO.

(cherry picked from commit 9f733f4)

Author: bd1976bris

lld/COFF/Driver.cpp

@@ -274,8 +274,13 @@ void LinkerDriver::addBuffer(std::unique_ptr<MemoryBuffer> mb,
       make<std::unique_ptr<Archive>>(std::move(file)); // take ownership
 
       int memberIndex = 0;
-      for (MemoryBufferRef m : getArchiveMembers(ctx, archive))
-        addArchiveBuffer(m, "<whole-archive>", filename, memberIndex++);
+      for (MemoryBufferRef m : getArchiveMembers(ctx, archive)) {
+        if (!archive->isThin())
+          addArchiveBuffer(m, "<whole-archive>", filename, memberIndex++);
+        else
+          addThinArchiveBuffer(m, "<whole-archive>");
+      }
+
       return;
     }
     addFile(make<ArchiveFile>(ctx, mbref));
@@ -386,6 +391,14 @@ void LinkerDriver::addArchiveBuffer(MemoryBufferRef mb, StringRef symName,
   Log(ctx) << "Loaded " << obj << " for " << symName;
 }
 
+void LinkerDriver::addThinArchiveBuffer(MemoryBufferRef mb, StringRef symName) {
+  // Pass an empty string as the archive name and an offset of 0 so that
+  // the original filename is used as the buffer identifier. This is
+  // useful for DTLTO, where having the member identifier be the actual
+  // path on disk enables distribution of bitcode files during ThinLTO.
+  addArchiveBuffer(mb, symName, /*parentName=*/"", /*OffsetInArchive=*/0);
+}
+
 void LinkerDriver::enqueueArchiveMember(const Archive::Child &c,
                                         const Archive::Symbol &sym,
                                         StringRef parentName) {
@@ -422,11 +435,8 @@ void LinkerDriver::enqueueArchiveMember(const Archive::Child &c,
       reportBufferError(errorCodeToError(mbOrErr.second), childName);
     llvm::TimeTraceScope timeScope("Archive: ",
                                    mbOrErr.first->getBufferIdentifier());
-    // Pass empty string as archive name so that the original filename is
-    // used as the buffer identifier.
-    ctx.driver.addArchiveBuffer(takeBuffer(std::move(mbOrErr.first)),
-                                toCOFFString(ctx, sym), "",
-                                /*OffsetInArchive=*/0);
+    ctx.driver.addThinArchiveBuffer(takeBuffer(std::move(mbOrErr.first)),
+                                    toCOFFString(ctx, sym));
   });
 }
 

lld/COFF/Driver.h

@@ -173,6 +173,7 @@ class LinkerDriver {
                  bool lazy);
   void addArchiveBuffer(MemoryBufferRef mbref, StringRef symName,
                         StringRef parentName, uint64_t offsetInArchive);
+  void addThinArchiveBuffer(MemoryBufferRef mbref, StringRef symName);
 
   void enqueueTask(std::function<void()> task);
   bool run();

lld/test/COFF/thin-archive.s

@@ -22,23 +22,34 @@
 # SYMTAB:        ?f@@YAHXZ in
 # NO-SYMTAB-NOT: ?f@@YAHXZ in
 
-# RUN: lld-link /entry:main %t.main.obj %t.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
-# RUN: lld-link /entry:main %t.main.obj %t_thin.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
-# RUN: lld-link /entry:main %t.main.obj /wholearchive:%t_thin.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
+# RUN: echo "/entry:main \"%t.main.obj\" /out:\"%t.exe\"" > %t.rsp
+
+# RUN: lld-link @%t.rsp %t.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_NON_THIN
+# RUN: lld-link @%t.rsp %t_thin.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_THIN_SYM
+# RUN: lld-link @%t.rsp /wholearchive:%t_thin.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_THIN_WHOLE
+# RUN: lld-link @%t.rsp /wholearchive %t_thin.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_THIN_WHOLE
+
+# LOAD_NON_THIN:   Loaded {{.*}}.lib({{.*}}.obj) for int __cdecl f(void)
+# LOAD_THIN_SYM:   Loaded {{.*}}.obj for int __cdecl f(void)
+# LOAD_THIN_WHOLE: Loaded {{.*}}.obj for <whole-archive>
 
 # RUN: rm %t.lib.obj
-# RUN: lld-link /entry:main %t.main.obj %t.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
-# RUN: env LLD_IN_TEST=1 not lld-link /entry:main %t.main.obj %t_thin.lib \
-# RUN:     /out:%t.exe 2>&1 | FileCheck --check-prefix=NOOBJ %s
-# RUN: env LLD_IN_TEST=1 not lld-link /entry:main %t.main.obj %t_thin.lib /out:%t.exe \
-# RUN:     /demangle:no 2>&1 | FileCheck --check-prefix=NOOBJNODEMANGLE %s
-
-# CHECK-NOT: error: could not get the buffer for the member defining
+# RUN: lld-link @%t.rsp %t.lib 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=ERR --allow-empty
+# RUN: env LLD_IN_TEST=1 not lld-link @%t.rsp %t_thin.lib 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=NOOBJ
+# RUN: env LLD_IN_TEST=1 not lld-link @%t.rsp /wholearchive:%t_thin.lib 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=NOOBJWHOLE
+# RUN: env LLD_IN_TEST=1 not lld-link @%t.rsp %t_thin.lib /demangle:no 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=NOOBJNODEMANGLE
+
+# ERR-NOT: error: could not get the buffer for the member defining
 # NOOBJ: error: could not get the buffer for the member defining symbol int __cdecl f(void): {{.*}}.lib({{.*}}.lib.obj):
+# NOOBJWHOLE: error: {{.*}}.lib: could not get the buffer for a child of the archive: '{{.*}}.obj'
 # NOOBJNODEMANGLE: error: could not get the buffer for the member defining symbol ?f@@YAHXZ: {{.*}}.lib({{.*}}.lib.obj):
 
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