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[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
This commit is contained in:
Wei Wang 2022-09-12 17:35:51 -07:00
parent 588628de3e
commit 5529a7524a
2 changed files with 21 additions and 0 deletions
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6
lld/ELF/LTO.cpp
View File

@ -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)

15
lld/test/ELF/lto/thinlto-index-only.ll
View File

@ -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