Remove thin-archive bitcode member support

This change removes the DTLTO support for thin-archive bitcode members
from this patch. This makes the patch simpler and more amenable to
review. We are also exploring how to support bitcode members in
non-thin archives. That work is progressing and may require a different
approach for thin-archive support than was originally implemented.

If that is the case, reviewing the current implementation would waste
reviewers' time.

Note that with this support removed, this patch is no longer sufficient
to allow for self-hosting an LLVM build with DTLTO. Theoretically,
--start-lib/--end-lib could be used instead. However, unlike
thin-archives, it's unclear how --start-lib/--end-lib can be easily
used with the LLVM build system.

Author: bd1976bris

cross-project-tests/CMakeLists.txt

@@ -19,12 +19,11 @@ set(CROSS_PROJECT_TEST_DEPS
   FileCheck
   check-gdb-llvm-support
   count
-  llvm-ar
-  llvm-config
   llvm-dwarfdump
+  llvm-config
   llvm-objdump
-  not
   split-file
+  not
   )
 
 if ("clang" IN_LIST LLVM_ENABLE_PROJECTS)

cross-project-tests/dtlto/archive-thin.test

@@ -19,7 +19,7 @@
 config.test_format = lit.formats.ShTest(not llvm_config.use_lit_shell)
 
 # suffixes: A list of file extensions to treat as test files.
-config.suffixes = [".c", ".cl", ".cpp", ".m", ".test"]
+config.suffixes = [".c", ".cl", ".cpp", ".m"]
 
 # excludes: A list of directories to exclude from the testsuite. The 'Inputs'
 # subdirectories contain auxiliary inputs for various tests in their parent
@@ -107,8 +107,6 @@ def get_required_attr(config, attr_name):
 if lldb_path is not None:
     config.available_features.add("lldb")
 
-if llvm_config.use_llvm_tool("llvm-ar"):
-    config.available_features.add("llvm-ar")
 
 def configure_dexter_substitutions():
     """Configure substitutions for host platform and return list of dependencies"""

cross-project-tests/lit.cfg.py

@@ -1754,33 +1754,6 @@ static uint8_t getOsAbi(const Triple &t) {
   }
 }
 
-// For DTLTO, bitcode member names must be valid paths to files on disk.
-// For thin archives, resolve `memberPath` relative to the archive's location.
-// Returns true if adjusted; false otherwise. Non-thin archives are unsupported.
-static bool dtltoAdjustMemberPathIfThinArchive(Ctx &ctx, StringRef archivePath,
-                                               std::string &memberPath) {
-  assert(!archivePath.empty() && !ctx.arg.dtltoDistributor.empty());
-
-  // Check if the archive file is a thin archive by reading its header.
-  auto bufferOrErr =
-      MemoryBuffer::getFileSlice(archivePath, sizeof(ThinArchiveMagic) - 1, 0);
-  if (std::error_code ec = bufferOrErr.getError()) {
-    ErrAlways(ctx) << "cannot open " << archivePath << ": " << ec.message();
-    return false;
-  }
-
-  if (!bufferOrErr->get()->getBuffer().starts_with(ThinArchiveMagic))
-    return false;
-
-  SmallString<64> resolvedPath;
-  if (path::is_relative(memberPath)) {
-    resolvedPath = path::parent_path(archivePath);
-    path::append(resolvedPath, memberPath);
-    memberPath = resolvedPath.str();
-  }
-  return true;
-}
-
 BitcodeFile::BitcodeFile(Ctx &ctx, MemoryBufferRef mb, StringRef archiveName,
                          uint64_t offsetInArchive, bool lazy)
     : InputFile(ctx, BitcodeKind, mb) {
@@ -1798,13 +1771,10 @@ BitcodeFile::BitcodeFile(Ctx &ctx, MemoryBufferRef mb, StringRef archiveName,
   // symbols later in the link stage). So we append file offset to make
   // filename unique.
   StringSaver &ss = ctx.saver;
-  StringRef name =
-      (archiveName.empty() ||
-       (!ctx.arg.dtltoDistributor.empty() &&
-        dtltoAdjustMemberPathIfThinArchive(ctx, archiveName, path)))
-          ? ss.save(path)
-          : ss.save(archiveName + "(" + path::filename(path) + " at " +
-                    utostr(offsetInArchive) + ")");
+  StringRef name = archiveName.empty()
+                       ? ss.save(path)
+                       : ss.save(archiveName + "(" + path::filename(path) +
+                                 " at " + utostr(offsetInArchive) + ")");
   MemoryBufferRef mbref(mb.getBuffer(), name);
 
   obj = CHECK2(lto::InputFile::create(mbref), this);