[ELF][Distributed ThinLTO] Do not generate empty index when bitcode object is linked

When the same bitcode object file is given multiple times from the Command-line
as lazy object file, empty index is generated which overwrites the one from thinlink.
This could cause undefined symbols during final link.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D133740

diff --git a/lld/ELF/LTO.cpp b/lld/ELF/LTO.cpp
index d39a7ac..a8634c4 100644 (file)
--- a/lld/ELF/LTO.cpp
+++ b/lld/ELF/LTO.cpp
@@ -290,9 +290,15 @@ void BitcodeCompiler::add(BitcodeFile &f) {
 // This is needed because this is what GNU gold plugin does and we have a
 // distributed build system that depends on that behavior.
 static void thinLTOCreateEmptyIndexFiles() {
+  DenseSet<StringRef> linkedBitCodeFiles;
+  for (BitcodeFile *f : ctx->bitcodeFiles)
+    linkedBitCodeFiles.insert(f->getName());
+
   for (BitcodeFile *f : ctx->lazyBitcodeFiles) {
     if (!f->lazy)
       continue;
+    if (linkedBitCodeFiles.contains(f->getName()))
+      continue;
     std::string path = replaceThinLTOSuffix(getThinLTOOutputFile(f->getName()));
     std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
     if (!os)

diff --git a/lld/test/ELF/lto/thinlto-index-only.ll b/lld/test/ELF/lto/thinlto-index-only.ll
index 7385d66..fd95f67 100644 (file)
--- a/lld/test/ELF/lto/thinlto-index-only.ll
+++ b/lld/test/ELF/lto/thinlto-index-only.ll
@@ -42,6 +42,21 @@
 ; RUN: ld.lld --plugin-opt=thinlto-index-only -shared dummy.o --start-lib 1.o --end-lib -o /dev/null
 ; RUN: ls 1.o.thinlto.bc
 
+;; Ensure when the same bitcode object is given as both lazy and non-lazy,
+;; LLD does not generate an empty index for the lazy object.
+; RUN: rm -f 2.o.thinlto.bc
+; RUN: ld.lld --plugin-opt=thinlto-index-only -shared 1.o 2.o --start-lib 2.o --end-lib -o /dev/null
+; RUN: llvm-dis < 2.o.thinlto.bc | grep -q '\^0 = module:'
+; RUN: rm -f 2.o.thinlto.bc
+; RUN: ld.lld --plugin-opt=thinlto-index-only -shared --start-lib 2.o --end-lib 2.o 1.o -o /dev/null
+; RUN: llvm-dis < 2.o.thinlto.bc | grep -q '\^0 = module:'
+
+;; Ensure when the same lazy bitcode object is given multiple times,
+;; no empty index file is generated if one of the copies is linked.
+; RUN: rm -f 2.o.thinlto.bc
+; RUN: ld.lld --plugin-opt=thinlto-index-only -shared 1.o --start-lib 2.o --end-lib --start-lib 2.o --end-lib -o /dev/null
+; RUN: llvm-dis < 2.o.thinlto.bc | grep -q '\^0 = module:'
+
 ; NM: T f
 
 ;; The backend index for this module contains summaries from itself and