[clang] 828767f - COFF/ELF: Place llvm.global_ctors elements in llvm.used if comdat is used
Fangrui Song via cfe-commits
cfe-commits at lists.llvm.org
Wed Jul 28 11:44:24 PDT 2021
Author: Fangrui Song
Date: 2021-07-28T11:44:19-07:00
New Revision: 828767f325b5dd0356c5fd90e40a1c047010853e
URL: https://github.com/llvm/llvm-project/commit/828767f325b5dd0356c5fd90e40a1c047010853e
DIFF: https://github.com/llvm/llvm-project/commit/828767f325b5dd0356c5fd90e40a1c047010853e.diff
LOG: COFF/ELF: Place llvm.global_ctors elements in llvm.used if comdat is used
On ELF, an SHT_INIT_ARRAY outside a section group is a GC root. The current
codegen abuses SHT_INIT_ARRAY in a section group to mean a GC root.
On PE/COFF, the dynamic initialization for `__declspec(selectany)` in a comdat
can be garbage collected by `-opt:ref`.
Call `addUsedGlobal` for the two cases to fix the abuse/bug.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D106925
Added:
Modified:
clang/lib/CodeGen/CGDeclCXX.cpp
clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
clang/test/CodeGenCXX/static-member-variable-explicit-specialization.cpp
Removed:
################################################################################
diff --git a/clang/lib/CodeGen/CGDeclCXX.cpp b/clang/lib/CodeGen/CGDeclCXX.cpp
index d43fb99550a85..553fedebfe56b 100644
--- a/clang/lib/CodeGen/CGDeclCXX.cpp
+++ b/clang/lib/CodeGen/CGDeclCXX.cpp
@@ -555,7 +555,8 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
PrioritizedCXXGlobalInits.size());
PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
} else if (isTemplateInstantiation(D->getTemplateSpecializationKind()) ||
- getContext().GetGVALinkageForVariable(D) == GVA_DiscardableODR) {
+ getContext().GetGVALinkageForVariable(D) == GVA_DiscardableODR ||
+ D->hasAttr<SelectAnyAttr>()) {
// C++ [basic.start.init]p2:
// Definitions of explicitly specialized class template static data
// members have ordered initialization. Other class template static data
@@ -568,17 +569,18 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
// group with the global being initialized. On most platforms, this is a
// minor startup time optimization. In the MS C++ ABI, there are no guard
// variables, so this COMDAT key is required for correctness.
- AddGlobalCtor(Fn, 65535, COMDATKey);
- if (getTarget().getCXXABI().isMicrosoft() && COMDATKey) {
- // In The MS C++, MS add template static data member in the linker
- // drective.
- addUsedGlobal(COMDATKey);
- }
- } else if (D->hasAttr<SelectAnyAttr>()) {
+ //
// SelectAny globals will be comdat-folded. Put the initializer into a
// COMDAT group associated with the global, so the initializers get folded
// too.
+
AddGlobalCtor(Fn, 65535, COMDATKey);
+ if (COMDATKey && (getTriple().isOSBinFormatELF() ||
+ getTarget().getCXXABI().isMicrosoft())) {
+ // When COMDAT is used on ELF or in the MS C++ ABI, the key must be in
+ // llvm.used to prevent linker GC.
+ addUsedGlobal(COMDATKey);
+ }
} else {
I = DelayedCXXInitPosition.find(D); // Re-do lookup in case of re-hash.
if (I == DelayedCXXInitPosition.end()) {
diff --git a/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp b/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
index 3b419c18c0e23..d8d0ed3950803 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
@@ -88,5 +88,4 @@ int foo();
inline int zoo = foo();
inline static int boo = foo();
-
-// CHECK: @llvm.used = appending global [7 x i8*] [i8* bitcast (i32* @"?x1 at selectany_init@@3HA" to i8*), i8* bitcast (i32* @"?x@?$A at H@explicit_template_instantiation@@2HA" to i8*), i8* bitcast (i32* @"?ioo@?$X_ at H@@2HA" to i8*), i8* getelementptr inbounds (%struct.A, %struct.A* @"?aoo at S1@@2UA@@A", i32 0, i32 0), i8* bitcast (i32* @"?zoo@@3HA" to i8*), i8* getelementptr inbounds (%struct.S, %struct.S* @"?s@?$ExportedTemplate at H@@2US@@A", i32 0, i32 0), i8* bitcast (i32* @"?x@?$A at H@implicit_template_instantiation@@2HA" to i8*)], section "llvm.metadata"
+// CHECK: @llvm.used = appending global [8 x i8*] [i8* bitcast (i32* @"?x at selectany_init@@3HA" to i8*), i8* bitcast (i32* @"?x1 at selectany_init@@3HA" to i8*), i8* bitcast (i32* @"?x@?$A at H@explicit_template_instantiation@@2HA" to i8*), i8* bitcast (i32* @"?ioo@?$X_ at H@@2HA" to i8*), i8* getelementptr inbounds (%struct.A, %struct.A* @"?aoo at S1@@2UA@@A", i32 0, i32 0), i8* bitcast (i32* @"?zoo@@3HA" to i8*), i8* getelementptr inbounds (%struct.S, %struct.S* @"?s@?$ExportedTemplate at H@@2US@@A", i32 0, i32 0), i8* bitcast (i32* @"?x@?$A at H@implicit_template_instantiation@@2HA" to i8*)], section "llvm.metadata"
diff --git a/clang/test/CodeGenCXX/static-member-variable-explicit-specialization.cpp b/clang/test/CodeGenCXX/static-member-variable-explicit-specialization.cpp
index 2bd01b301e522..13323e7efe79c 100644
--- a/clang/test/CodeGenCXX/static-member-variable-explicit-specialization.cpp
+++ b/clang/test/CodeGenCXX/static-member-variable-explicit-specialization.cpp
@@ -1,5 +1,20 @@
// RUN: %clang_cc1 %s -std=c++1y -triple=x86_64-pc-linux -emit-llvm -o - | FileCheck --check-prefix=ELF --check-prefix=ALL %s
// RUN: %clang_cc1 %s -std=c++1y -triple=x86_64-apple-darwin -emit-llvm -o - | FileCheck --check-prefix=MACHO --check-prefix=ALL %s
+// RUN: %clang_cc1 %s -std=c++1y -triple=x86_64-pc-linux -emit-llvm -fdeclspec -DSELECTANY -o - | FileCheck --check-prefix=ELF-SELECTANY %s
+
+#ifdef SELECTANY
+struct S {
+ S();
+ ~S();
+};
+
+int f();
+
+// ELF-SELECTANY: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @__cxx_global_var_init, i8* bitcast (i32* @selectany to i8*) }]
+// ELF-SELECTANY: @llvm.used = appending global [1 x i8*] [i8* bitcast (i32* @selectany to i8*)]
+int __declspec(selectany) selectany = f();
+
+#else
// ALL: ; ModuleID
@@ -38,6 +53,9 @@ template<> int A<bool>::a = 10;
// ALL: { i32, void ()*, i8* } { i32 65535, void ()* @_GLOBAL__sub_I_static_member_variable_explicit_specialization.cpp, i8* null }]
+/// llvm.used ensures SHT_INIT_ARRAY in a section group cannot be GCed.
+// ELF: @llvm.used = appending global [6 x i8*] [i8* bitcast (i32* @_ZN1AIsE1aE to i8*), i8* bitcast (i16* @_Z1xIsE to i8*), i8* bitcast (i32* @_ZN2ns1aIiE1iE to i8*), i8* bitcast (i32* @_ZN2ns1b1iIiEE to i8*), i8* bitcast (i32* @_ZN1AIvE1aE to i8*), i8* @_Z1xIcE]
+
template int A<short>::a; // Unordered
int b = foo();
int c = foo();
@@ -76,6 +94,8 @@ template<typename T> int Internal<T>::a = foo();
}
int *use_internal_a = &Internal<int>::a;
+#endif
+
// ALL: define internal void @[[unordered1]](
// ALL: call i32 @foo()
// ALL: store {{.*}} @_ZN1AIsE1aE
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