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[lld-macho] Unset ExportDynamic where possible for LTO 

By unsetting this property, we are now able to internalize more symbols
during LTO. I compared the output of `-save-temps` for both LLD and
ld64, and we now match ld64's behavior as far as `lto-internalize.ll` is
concerned.

(Thanks @smeenai for working on an initial version of this diff!)

Fixes https://github.com/llvm/llvm-project/issues/50574.

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.llvm.org/D119372
This commit is contained in:
Jez Ng 2022-02-11 22:24:09 -05:00
parent af45d0fd94
commit 103e1d934a
3 changed files with 48 additions and 19 deletions
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8
lld/MachO/Driver.cpp
View File

@ -505,14 +505,6 @@ static void initLLVM() {
}
static void compileBitcodeFiles() {
// FIXME: Remove this once LTO.cpp honors config->exportDynamic.
if (config->exportDynamic)
for (InputFile *file : inputFiles)
if (isa<BitcodeFile>(file)) {
warn("the effect of -export_dynamic on LTO is not yet implemented");
break;
}
TimeTraceScope timeScope("LTO");
auto *lto = make<BitcodeCompiler>();
for (InputFile *file : inputFiles)

16
lld/MachO/LTO.cpp
View File

@ -64,6 +64,8 @@ void BitcodeCompiler::add(BitcodeFile &f) {
resols.reserve(objSyms.size());
// Provide a resolution to the LTO API for each symbol.
bool exportDynamic =
config->outputType != MH_EXECUTE || config->exportDynamic;
auto symIt = f.symbols.begin();
for (const lto::InputFile::Symbol &objSym : objSyms) {
resols.emplace_back();
@ -77,12 +79,14 @@ void BitcodeCompiler::add(BitcodeFile &f) {
// be removed.
r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
// FIXME: What about other output types? And we can probably be less
// restrictive with -flat_namespace, but it's an infrequent use case.
// FIXME: Honor config->exportDynamic.
r.VisibleToRegularObj = config->outputType != MH_EXECUTE ||
config->namespaceKind == NamespaceKind::flat ||
sym->isUsedInRegularObj;
if (const auto *defined = dyn_cast<Defined>(sym))
r.ExportDynamic =
defined->isExternal() && !defined->privateExtern && exportDynamic;
else if (const auto *common = dyn_cast<CommonSymbol>(sym))
r.ExportDynamic = !common->privateExtern && exportDynamic;
r.VisibleToRegularObj =
sym->isUsedInRegularObj || (r.Prevailing && r.ExportDynamic);
// Un-define the symbol so that we don't get duplicate symbol errors when we
// load the ObjFile emitted by LTO compilation.

43
lld/test/MachO/lto-internalize.ll
View File

@ -12,6 +12,9 @@
; RUN: llvm-dis < %t/test.0.2.internalize.bc | FileCheck %s
; RUN: llvm-objdump --macho --syms %t/test | FileCheck %s --check-prefix=SYMTAB
; CHECK: @comm = internal global
; CHECK: @comm_hide = internal global
;; Check that main is not internalized. This covers the case of bitcode symbols
;; referenced by undefined symbols that don't belong to any InputFile.
; CHECK: define void @main()
@ -28,18 +31,48 @@
;; internalized.
; CHECK: define internal void @baz()
; Check foo and bar are not emitted to the .symtab
;; Check that all internalized symbols are not emitted to the symtab
; SYMTAB-LABEL: SYMBOL TABLE:
; SYMTAB-NEXT: g F __TEXT,__text _main
; SYMTAB-NEXT: g F __TEXT,__text _used_in_regular_obj
; SYMTAB-NEXT: g F __TEXT,__text __mh_execute_header
; SYMTAB-NEXT: *UND* dyld_stub_binder
; SYMTAB-DAG: g F __TEXT,__text _main
; SYMTAB-DAG: g F __TEXT,__text _used_in_regular_obj
; SYMTAB-DAG: g F __TEXT,__text __mh_execute_header
; SYMTAB-DAG: *UND* dyld_stub_binder
; SYMTAB-EMPTY:
; RUN: %lld -lSystem -dylib %t/test.o %t/baz.o %t/regular.o -o %t/test.dylib -save-temps
; RUN: llvm-dis < %t/test.dylib.0.2.internalize.bc | FileCheck %s --check-prefix=DYN
; RUN: llvm-nm -m %t/test.dylib | FileCheck %s --check-prefix=DYN-SYMS \
; RUN: --implicit-check-not _foo
; RUN: %lld -lSystem -export_dynamic %t/test.o %t/baz.o %t/regular.o -o %t/test.extdyn -save-temps
; RUN: llvm-dis < %t/test.extdyn.0.2.internalize.bc
; RUN: llvm-nm -m %t/test.extdyn | FileCheck %s --check-prefix=DYN-SYMS \
; RUN: --implicit-check-not _foo
;; Note that only foo() gets internalized here; everything else that isn't
;; hidden must be exported.
; DYN: @comm = common global
; DYN: @comm_hide = internal global
; DYN: define void @main()
; DYN: define void @bar()
; DYN: define internal void @foo()
; DYN: define void @used_in_regular_obj()
; DYN: define void @baz()
; DYN-SYMS-DAG: (__TEXT,__text) external _bar
; DYN-SYMS-DAG: (__TEXT,__text) external _baz
; DYN-SYMS-DAG: (__DATA,__common) external _comm
; DYN-SYMS-DAG: (__TEXT,__text) external _main
; DYN-SYMS-DAG: (__TEXT,__text) external _used_in_regular_obj
;--- test.s
target triple = "x86_64-apple-macosx10.15.0"
target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
;; Common symbols are always external.
@comm = common global i8 0, align 1
@comm_hide = common hidden global i8 0, align 1
declare void @baz()
define void @main() {