[llvm] 89ddcff - [LTO] Make local linkage GlobalValue in non-prevailing COMDAT available_externally
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Mon Nov 7 10:07:16 PST 2022
Author: Fangrui Song
Date: 2022-11-07T10:07:10-08:00
New Revision: 89ddcff1d2d6e9f4de78f3a563a8b1987bf7ea8f
URL: https://github.com/llvm/llvm-project/commit/89ddcff1d2d6e9f4de78f3a563a8b1987bf7ea8f
DIFF: https://github.com/llvm/llvm-project/commit/89ddcff1d2d6e9f4de78f3a563a8b1987bf7ea8f.diff
LOG: [LTO] Make local linkage GlobalValue in non-prevailing COMDAT available_externally
For a local linkage GlobalObject in a non-prevailing COMDAT, it remains defined while its
leader has been made available_externally. This violates the COMDAT rule that
its members must be retained or discarded as a unit.
To fix this, update the regular LTO change D34803 to track local linkage
GlobalValues, and port the code to ThinLTO (GlobalAliases are not handled.)
This fixes two problems.
(a) `__cxx_global_var_init` in a non-prevailing COMDAT group used to
linger around (unreferenced, hence benign), and is now correctly discarded.
```
int foo();
inline int v = foo();
```
(b) Fix https://github.com/llvm/llvm-project/issues/58215:
as a size optimization, we place private `__profd_` in a COMDAT with a
`__profc_` key. When FuncImport.cpp makes `__profc_` available_externally due to
a non-prevailing COMDAT, `__profd_` incorrectly remains private. This change
makes the `__profd_` available_externally.
```
cat > c.h <<'eof'
extern void bar();
inline __attribute__((noinline)) void foo() {}
eof
cat > m1.cc <<'eof'
#include "c.h"
int main() {
bar();
foo();
}
eof
cat > m2.cc <<'eof'
#include "c.h"
__attribute__((noinline)) void bar() {
foo();
}
eof
clang -O2 -fprofile-generate=./t m1.cc m2.cc -flto -fuse-ld=lld -o t_gen
rm -fr t && ./t_gen && llvm-profdata show -function=foo t/default_*.profraw
clang -O2 -fprofile-generate=./t m1.cc m2.cc -flto=thin -fuse-ld=lld -o t_gen
rm -fr t && ./t_gen && llvm-profdata show -function=foo t/default_*.profraw
```
If a GlobalAlias references a GlobalValue which is just changed to
available_externally, change the GlobalAlias as well (e.g. C5/D5 comdats due to
cc1 -mconstructor-aliases). The GlobalAlias may be referenced by other
available_externally functions, so it cannot easily be removed.
Depends on D137441: we use available_externally to mark a GlobalAlias in a
non-prevailing COMDAT, similar to how we handle GlobalVariable/Function.
GlobalAlias may refer to a ConstantExpr, not changing GlobalAlias to
GlobalVariable gives flexibility for future extensions (the use case is niche.
For simplicity we don't handle it yet). In addition, available_externally
GlobalAlias is the most straightforward implementation and retains the aliasee
information to help optimizers.
Reviewed By: tejohnson
Differential Revision: https://reviews.llvm.org/D135427
Added:
llvm/test/ThinLTO/X86/constructor-alias.ll
Modified:
llvm/lib/LTO/LTO.cpp
llvm/lib/Transforms/IPO/FunctionImport.cpp
llvm/test/LTO/Resolution/X86/comdat-mixed-lto.ll
llvm/test/ThinLTO/X86/Inputs/linkonce_resolution_comdat.ll
llvm/test/ThinLTO/X86/linkonce_resolution_comdat.ll
Removed:
################################################################################
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 286d3ca3e2cc0..dc28b681a1515 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -712,11 +712,11 @@ handleNonPrevailingComdat(GlobalValue &GV,
if (!NonPrevailingComdats.count(C))
return;
- // Additionally need to drop externally visible global values from the comdat
- // to available_externally, so that there aren't multiply defined linker
- // errors.
- if (!GV.hasLocalLinkage())
- GV.setLinkage(GlobalValue::AvailableExternallyLinkage);
+ // Additionally need to drop all global values from the comdat to
+ // available_externally, to satisfy the COMDAT requirement that all members
+ // are discarded as a unit. The non-local linkage global values avoid
+ // duplicate definition linker errors.
+ GV.setLinkage(GlobalValue::AvailableExternallyLinkage);
if (auto GO = dyn_cast<GlobalObject>(&GV))
GO->setComdat(nullptr);
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index b589ec798caa1..844ee19e1e6a5 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -1051,6 +1051,7 @@ bool llvm::convertToDeclaration(GlobalValue &GV) {
void llvm::thinLTOFinalizeInModule(Module &TheModule,
const GVSummaryMapTy &DefinedGlobals,
bool PropagateAttrs) {
+ DenseSet<Comdat *> NonPrevailingComdats;
auto FinalizeInModule = [&](GlobalValue &GV, bool Propagate = false) {
// See if the global summary analysis computed a new resolved linkage.
const auto &GS = DefinedGlobals.find(GV.getGUID());
@@ -1128,8 +1129,10 @@ void llvm::thinLTOFinalizeInModule(Module &TheModule,
// as this is a declaration for the linker, and will be dropped eventually.
// It is illegal for comdats to contain declarations.
auto *GO = dyn_cast_or_null<GlobalObject>(&GV);
- if (GO && GO->isDeclarationForLinker() && GO->hasComdat())
+ if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
+ NonPrevailingComdats.insert(GO->getComdat());
GO->setComdat(nullptr);
+ }
};
// Process functions and global now
@@ -1139,6 +1142,36 @@ void llvm::thinLTOFinalizeInModule(Module &TheModule,
FinalizeInModule(GV);
for (auto &GV : TheModule.aliases())
FinalizeInModule(GV);
+
+ // For a non-prevailing comdat, all its members must be available_externally.
+ // FinalizeInModule has handled non-local-linkage GlobalValues. Here we handle
+ // local linkage GlobalValues.
+ if (NonPrevailingComdats.empty())
+ return;
+ for (auto &GO : TheModule.global_objects()) {
+ if (auto *C = GO.getComdat(); C && NonPrevailingComdats.count(C)) {
+ GO.setComdat(nullptr);
+ GO.setLinkage(GlobalValue::AvailableExternallyLinkage);
+ }
+ }
+ bool Changed;
+ do {
+ Changed = false;
+ // If an alias references a GlobalValue in a non-prevailing comdat, change
+ // it to available_externally. For simplicity we don't handle ConstantExpr
+ // aliasee, which is unlikely used in a COMDAT.
+ for (auto &GA : TheModule.aliases()) {
+ if (GA.hasAvailableExternallyLinkage())
+ continue;
+ assert(isa<GlobalValue>(GA.getAliasee()) &&
+ "non-GlobalValue aliasee is unimplemented");
+ if (const auto *GV = dyn_cast<GlobalValue>(GA.getAliasee()))
+ if (GV->hasAvailableExternallyLinkage()) {
+ GA.setLinkage(GlobalValue::AvailableExternallyLinkage);
+ Changed = true;
+ }
+ }
+ } while (Changed);
}
/// Run internalization on \p TheModule based on symmary analysis.
diff --git a/llvm/test/LTO/Resolution/X86/comdat-mixed-lto.ll b/llvm/test/LTO/Resolution/X86/comdat-mixed-lto.ll
index d3730f4e9bcda..96d8f3157b996 100644
--- a/llvm/test/LTO/Resolution/X86/comdat-mixed-lto.ll
+++ b/llvm/test/LTO/Resolution/X86/comdat-mixed-lto.ll
@@ -8,7 +8,7 @@
; The copy of C from this module is prevailing. The copy of C from the
; regular LTO module is not prevailing, and will be dropped to
; available_externally.
-; RUN: llvm-lto2 run -r=%t1.o,C,pl -r=%t2.o,C,l -r=%t2.o,testglobfunc,lxp -r=%t1.o,testglobfunc,lx -o %t3 %t1.o %t2.o -save-temps
+; RUN: llvm-lto2 run -r=%t1.o,C,pl -r=%t2.o,C,l -r=%t1.o,testglobfunc,lxp -r=%t2.o,testglobfunc,lx -o %t3 %t1.o %t2.o -save-temps
; The Input module (regular LTO) is %t3.0. Check to make sure that we removed
; __cxx_global_var_init and testglobfunc from comdat. Also check to ensure
@@ -16,8 +16,21 @@
; have linker multiply defined errors as it is no longer in a comdat and
; would clash with the copy from this module.
; RUN: llvm-dis %t3.0.0.preopt.bc -o - | FileCheck %s
-; CHECK: define internal void @__cxx_global_var_init() section ".text.startup" {
-; CHECK: define available_externally dso_local void @testglobfunc() section ".text.startup" {
+
+; CHECK: @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @__cxx_global_var_init, ptr @C }]
+; CHECK: @C = available_externally dso_local global %"class.Test::ptr" zeroinitializer, align 4
+; CHECK-NOT: declare
+; CHECK: declare dso_local void @__cxx_global_var_init() section ".text.startup"
+; CHECK-NOT: declare
+
+; Check the behavior with the prevailing testglobfunc in %t2.o.
+; RUN: llvm-lto2 run -r=%t1.o,C,pl -r=%t2.o,C,l -r=%t1.o,testglobfunc,lx -r=%t2.o,testglobfunc,plx -o %t4 %t1.o %t2.o -save-temps
+; RUN: llvm-dis %t4.0.0.preopt.bc -o - | FileCheck %s --check-prefix=CHECK2
+
+; CHECK2: @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @__cxx_global_var_init, ptr @C }]
+; CHECK2: @C = available_externally dso_local global %"class.Test::ptr" zeroinitializer, align 4
+; CHECK2: declare dso_local void @__cxx_global_var_init() section ".text.startup"
+; CHECK2: define available_externally dso_local void @testglobfunc() section ".text.startup" {
; ModuleID = 'comdat-mixed-lto.o'
source_filename = "comdat-mixed-lto.cpp"
diff --git a/llvm/test/ThinLTO/X86/Inputs/linkonce_resolution_comdat.ll b/llvm/test/ThinLTO/X86/Inputs/linkonce_resolution_comdat.ll
index 92b5182315943..f5b3130fd1520 100644
--- a/llvm/test/ThinLTO/X86/Inputs/linkonce_resolution_comdat.ll
+++ b/llvm/test/ThinLTO/X86/Inputs/linkonce_resolution_comdat.ll
@@ -1,13 +1,24 @@
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
-$c2 = comdat any
+$f = comdat any
+$g = comdat any
-define linkonce_odr i32 @f(i8*) unnamed_addr comdat($c2) {
+ at g_private = private global i32 41, comdat($g)
+
+define linkonce_odr i32 @f(i8*) unnamed_addr comdat($f) {
+ ret i32 41
+}
+
+define linkonce_odr i32 @g() unnamed_addr comdat($g) {
ret i32 41
}
-define i32 @g() {
+define internal void @g_internal() unnamed_addr comdat($g) {
+ ret void
+}
+
+define i32 @h() {
%i = call i32 @f(i8* null)
ret i32 %i
}
diff --git a/llvm/test/ThinLTO/X86/constructor-alias.ll b/llvm/test/ThinLTO/X86/constructor-alias.ll
new file mode 100644
index 0000000000000..212ff7c425725
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/constructor-alias.ll
@@ -0,0 +1,44 @@
+;; The constructor alias example is reduced from
+;;
+;; template <typename T>
+;; struct A { A() {} virtual ~A() {} };
+;; template struct A<void>;
+;; void *foo() { return new A<void>; }
+;;
+;; clang -c -fpic -O1 -flto=thin a.cc && cp a.o b.o && ld.lld -shared a.o b.so
+
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: cp %t1.bc %t2.bc
+; RUN: llvm-lto2 run %t1.bc %t2.bc -r=%t1.bc,_ZTV1A,pl -r=%t1.bc,_ZN1AD0Ev,pl -r=%t1.bc,_ZN1AD1Ev,pl -r=%t1.bc,_ZN1AD2Ev,pl -r=%t1.bc,D1_a,pl -r=%t1.bc,D1_a_a,pl \
+; RUN: -r=%t2.bc,_ZTV1A,l -r=%t2.bc,_ZN1AD0Ev,l -r=%t2.bc,_ZN1AD1Ev,l -r=%t2.bc,_ZN1AD2Ev,l -r=%t2.bc,D1_a,l -r=%t2.bc,D1_a_a,l -o %t3 --save-temps
+; RUN: llvm-dis < %t3.2.1.promote.bc | FileCheck %s
+
+; CHECK: @_ZTV1A = available_externally dso_local unnamed_addr constant { [4 x ptr] } { [4 x ptr] [ptr null, ptr null, ptr @_ZN1AD1Ev, ptr @_ZN1AD0Ev] }
+; CHECK: @D1_a = available_externally dso_local unnamed_addr alias void (ptr), ptr @_ZN1AD1Ev
+; CHECK: @_ZN1AD1Ev = available_externally dso_local unnamed_addr alias void (ptr), ptr @_ZN1AD2Ev
+; CHECK: @D1_a_a = available_externally dso_local unnamed_addr alias void (ptr), ptr @D1_a
+; CHECK: define available_externally dso_local void @_ZN1AD2Ev(ptr noundef nonnull %0) unnamed_addr {
+; CHECK: define available_externally dso_local void @_ZN1AD0Ev(ptr noundef nonnull %0) unnamed_addr {
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+$_ZN1AD5Ev = comdat any
+$_ZTV1A = comdat any
+
+ at _ZTV1A = weak_odr unnamed_addr constant { [4 x ptr] } { [4 x ptr] [ptr null, ptr null, ptr @_ZN1AD1Ev, ptr @_ZN1AD0Ev] }, comdat
+
+ at D1_a = weak_odr unnamed_addr alias void (ptr), ptr @_ZN1AD1Ev
+ at _ZN1AD1Ev = weak_odr unnamed_addr alias void (ptr), ptr @_ZN1AD2Ev
+ at D1_a_a = weak_odr unnamed_addr alias void (ptr), ptr @D1_a
+
+define weak_odr void @_ZN1AD2Ev(ptr noundef nonnull %0) unnamed_addr comdat($_ZN1AD5Ev) {
+ ret void
+}
+
+define weak_odr void @_ZN1AD0Ev(ptr noundef nonnull %0) unnamed_addr comdat($_ZN1AD5Ev) {
+ call void @D1_a(ptr noundef nonnull %0)
+ call void @D1_a_a(ptr noundef nonnull %0)
+ call void @_ZN1AD1Ev(ptr noundef nonnull %0)
+ ret void
+}
diff --git a/llvm/test/ThinLTO/X86/linkonce_resolution_comdat.ll b/llvm/test/ThinLTO/X86/linkonce_resolution_comdat.ll
index 7b22180132e6a..2fb226046ea9f 100644
--- a/llvm/test/ThinLTO/X86/linkonce_resolution_comdat.ll
+++ b/llvm/test/ThinLTO/X86/linkonce_resolution_comdat.ll
@@ -1,33 +1,54 @@
-; This test ensures that we drop the preempted copy of @f from %t2.bc from its
-; comdat after making it available_externally. If not we would get a
-; verification error.
+; This test ensures that we drop the preempted copy of @f/@g from %t2.bc from their
+; comdats after making it available_externally. If not we would get a
+; verification error. g_internal/g_private are changed to available_externally
+; as well since it is in the same comdat of g.
; RUN: opt -module-summary %s -o %t1.bc
; RUN: opt -module-summary %p/Inputs/linkonce_resolution_comdat.ll -o %t2.bc
-; RUN: llvm-lto -thinlto-action=run -disable-thinlto-funcattrs=0 %t1.bc %t2.bc -exported-symbol=f -exported-symbol=g -thinlto-save-temps=%t3.
+; RUN: llvm-lto -thinlto-action=run -disable-thinlto-funcattrs=0 %t1.bc %t2.bc -exported-symbol=f -exported-symbol=g -exported-symbol=h -thinlto-save-temps=%t3.
; RUN: llvm-dis %t3.0.3.imported.bc -o - | FileCheck %s --check-prefix=IMPORT1
; RUN: llvm-dis %t3.1.3.imported.bc -o - | FileCheck %s --check-prefix=IMPORT2
; Copy from first module is prevailing and converted to weak_odr, copy
; from second module is preempted and converted to available_externally and
; removed from comdat.
-; IMPORT1: define weak_odr i32 @f(i8* %0) unnamed_addr [[ATTR:#[0-9]+]] comdat($c1) {
+; IMPORT1: @g_private = private global i32 43, comdat($g)
+; IMPORT1: define weak_odr i32 @f(i8* %0) unnamed_addr [[ATTR:#[0-9]+]] comdat {
+; IMPORT1: define weak_odr i32 @g() unnamed_addr [[ATTR]] comdat {
+; IMPORT1: define internal void @g_internal() unnamed_addr comdat($g) {
+
+; IMPORT2: @g_private = available_externally dso_local global i32 41{{$}}
; IMPORT2: define available_externally i32 @f(i8* %0) unnamed_addr [[ATTR:#[0-9]+]] {
+; IMPORT2: define available_externally i32 @g() unnamed_addr [[ATTR]] {
+; IMPORT2: define available_externally dso_local void @g_internal() unnamed_addr {
; CHECK-DAG: attributes [[ATTR]] = { norecurse nounwind }
-; RUN: llvm-nm -o - < %t1.bc.thinlto.o | FileCheck %s --check-prefix=NM1
+; RUN: llvm-nm %t1.bc.thinlto.o | FileCheck %s --check-prefix=NM1
; NM1: W f
+; NM1: W g
-; RUN: llvm-nm -o - < %t2.bc.thinlto.o | FileCheck %s --check-prefix=NM2
+; RUN: llvm-nm %t2.bc.thinlto.o | FileCheck %s --check-prefix=NM2
; f() would have been turned into available_externally since it is preempted,
-; and inlined into g()
+; and inlined into h()
; NM2-NOT: f
+; NM2-NOT: g
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
-$c1 = comdat any
+$f = comdat any
+$g = comdat any
+
+ at g_private = private global i32 43, comdat($g)
-define linkonce_odr i32 @f(i8*) unnamed_addr comdat($c1) {
+define linkonce_odr i32 @f(i8*) unnamed_addr comdat {
ret i32 43
}
+
+define linkonce_odr i32 @g() unnamed_addr comdat {
+ ret i32 43
+}
+
+define internal void @g_internal() unnamed_addr comdat($g) {
+ ret void
+}
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