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[clang] Add support for omitting only global destructors (#104899)
For mobile applications, it's common for global destructors to never be called (because the applications have their own lifecycle independent of the standard C runtime), but threads are created and destroyed as normal and so thread-local destructors are still called. -fno-static-c++-destructors omits unnecessary global destructors, which is useful for code size, but it also omits thread-local destructors, which is unsuitable. Add a ternary `-fc++-static-destructors={all,none,thread-local}` option instead to allow omitting only global destructors.
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‎clang/docs/ReleaseNotes.rst

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@@ -173,6 +173,13 @@ Non-comprehensive list of changes in this release
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New Compiler Flags
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------------------
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- The ``-fc++-static-destructors={all,thread-local,none}`` flag was
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added to control which C++ variables have static destructors
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registered: all (the default) does so for all variables, thread-local
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only for thread-local variables, and none (which corresponds to the
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existing ``-fno-c++-static-destructors`` flag) skips all static
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destructors registration.
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Deprecated Compiler Flags
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-------------------------
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‎clang/include/clang/Basic/LangOptions.def

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@@ -464,7 +464,9 @@ LANGOPT(FixedPoint, 1, 0, "fixed point types")
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LANGOPT(PaddingOnUnsignedFixedPoint, 1, 0,
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"unsigned fixed point types having one extra padding bit")
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LANGOPT(RegisterStaticDestructors, 1, 1, "Register C++ static destructors")
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ENUM_LANGOPT(RegisterStaticDestructors, RegisterStaticDestructorsKind, 2,
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RegisterStaticDestructorsKind::All,
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"Register C++ static destructors")
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LANGOPT(RegCall4, 1, 0, "Set __regcall4 as a default calling convention to respect __regcall ABI v.4")
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‎clang/include/clang/Basic/LangOptions.h

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@@ -458,6 +458,16 @@ class LangOptionsBase {
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CX_None
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};
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/// Controls which variables have static destructors registered.
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enum class RegisterStaticDestructorsKind {
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/// Register static destructors for all variables.
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All,
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/// Register static destructors only for thread-local variables.
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ThreadLocal,
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/// Don't register static destructors for any variables.
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None,
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};
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// Define simple language options (with no accessors).
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#define LANGOPT(Name, Bits, Default, Description) unsigned Name : Bits;
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#define ENUM_LANGOPT(Name, Type, Bits, Default, Description)

‎clang/include/clang/Driver/Options.td

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@@ -2302,11 +2302,18 @@ defm fixed_point : BoolFOption<"fixed-point",
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PosFlag<SetTrue, [], [ClangOption, CC1Option], "Enable">,
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NegFlag<SetFalse, [], [ClangOption], "Disable">,
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BothFlags<[], [ClangOption], " fixed point types">>;
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defm cxx_static_destructors : BoolFOption<"c++-static-destructors",
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LangOpts<"RegisterStaticDestructors">, DefaultTrue,
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NegFlag<SetFalse, [], [ClangOption, CC1Option],
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"Disable C++ static destructor registration">,
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PosFlag<SetTrue>>;
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def cxx_static_destructors_EQ : Joined<["-"], "fc++-static-destructors=">, Group<f_Group>,
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HelpText<"Controls which variables C++ static destructors are registered for">,
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Values<"all,thread-local,none">,
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NormalizedValues<["All", "ThreadLocal", "None"]>,
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NormalizedValuesScope<"LangOptions::RegisterStaticDestructorsKind">,
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MarshallingInfoEnum<LangOpts<"RegisterStaticDestructors">, "All">,
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Visibility<[ClangOption, CC1Option]>;
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def cxx_static_destructors : Flag<["-"], "fc++-static-destructors">, Group<f_Group>,
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Alias<cxx_static_destructors_EQ>, AliasArgs<["all"]>;
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def no_cxx_static_destructors : Flag<["-"], "fno-c++-static-destructors">, Group<f_Group>,
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Alias<cxx_static_destructors_EQ>, AliasArgs<["none"]>,
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HelpText<"Disable C++ static destructor registration">;
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def fsymbol_partition_EQ : Joined<["-"], "fsymbol-partition=">, Group<f_Group>,
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Visibility<[ClangOption, CC1Option]>,
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MarshallingInfoString<CodeGenOpts<"SymbolPartition">>;

‎clang/lib/AST/Decl.cpp

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@@ -2799,9 +2799,17 @@ bool VarDecl::isKnownToBeDefined() const {
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}
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bool VarDecl::isNoDestroy(const ASTContext &Ctx) const {
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return hasGlobalStorage() && (hasAttr<NoDestroyAttr>() ||
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(!Ctx.getLangOpts().RegisterStaticDestructors &&
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!hasAttr<AlwaysDestroyAttr>()));
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if (!hasGlobalStorage())
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return false;
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if (hasAttr<NoDestroyAttr>())
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return true;
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if (hasAttr<AlwaysDestroyAttr>())
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return false;
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using RSDKind = LangOptions::RegisterStaticDestructorsKind;
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RSDKind K = Ctx.getLangOpts().getRegisterStaticDestructors();
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return K == RSDKind::None ||
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(K == RSDKind::ThreadLocal && getTLSKind() == TLS_None);
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}
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QualType::DestructionKind

‎clang/lib/Driver/ToolChains/Clang.cpp

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@@ -7972,8 +7972,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
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options::OPT_fno_keep_persistent_storage_variables);
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Args.addOptInFlag(CmdArgs, options::OPT_fcomplete_member_pointers,
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options::OPT_fno_complete_member_pointers);
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Args.addOptOutFlag(CmdArgs, options::OPT_fcxx_static_destructors,
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options::OPT_fno_cxx_static_destructors);
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if (Arg *A = Args.getLastArg(options::OPT_cxx_static_destructors_EQ))
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A->render(Args, CmdArgs);
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addMachineOutlinerArgs(D, Args, CmdArgs, Triple, /*IsLTO=*/false);
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‎clang/test/CodeGenCXX/always_destroy.cpp

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@@ -1,12 +1,16 @@
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// RUN: %clang_cc1 %s -fno-c++-static-destructors -emit-llvm -triple x86_64-apple-macosx10.13.0 -o - | FileCheck %s
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// RUN: %clang_cc1 %s -fc++-static-destructors=none -emit-llvm -triple x86_64-apple-macosx10.13.0 -o - | \
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// RUN: FileCheck --check-prefixes=CHECK,NO-DTORS %s
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// RUN: %clang_cc1 %s -fc++-static-destructors=thread-local -emit-llvm -triple x86_64-apple-macosx10.13.0 -o - | \
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// RUN: FileCheck --check-prefixes=CHECK,THREAD-LOCAL-DTORS %s
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struct NonTrivial {
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~NonTrivial();
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};
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// CHECK-NOT: __cxa_atexit{{.*}}_ZN10NonTrivialD1Ev
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NonTrivial nt1;
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// CHECK-NOT: _tlv_atexit{{.*}}_ZN10NonTrivialD1Ev
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// NO-DTORS-NOT: _tlv_atexit{{.*}}_ZN10NonTrivialD1Ev
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// THREAD-LOCAL-DTORS: _tlv_atexit{{.*}}_ZN10NonTrivialD1Ev
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thread_local NonTrivial nt2;
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struct NonTrivial2 {

‎clang/test/CodeGenCXX/attr-no-destroy-d54344.cpp

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@@ -1,6 +1,7 @@
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// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR %s -o - | FileCheck %s
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// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu %s -o - | FileCheck %s --check-prefix=CHECK-ATTR
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// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR -fno-c++-static-destructors %s -o - | FileCheck %s --check-prefix=CHECK-FLAG
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// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR -fc++-static-destructors=none %s -o - | FileCheck %s --check-prefix=CHECK-FLAG
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// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR -fc++-static-destructors=thread-local %s -o - | FileCheck %s --check-prefix=CHECK-FLAG
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// Regression test for D54344. Class with no user-defined destructor
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// that has an inherited member that has a non-trivial destructor

‎clang/test/Driver/cxx-static-destructors.cpp

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@@ -0,0 +1,11 @@
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// RUN: %clang -### -c -fc++-static-destructors=all %s 2>&1 | FileCheck --check-prefix ALL %s
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// RUN: %clang -### -c -fc++-static-destructors %s 2>&1 | FileCheck --check-prefix ALL %s
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// RUN: %clang -### -c -fno-c++-static-destructors -fc++-static-destructors %s 2>&1 | FileCheck --check-prefix ALL %s
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// RUN: %clang -### -c -fc++-static-destructors=none %s 2>&1 | FileCheck --check-prefix NONE %s
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// RUN: %clang -### -c -fno-c++-static-destructors %s 2>&1 | FileCheck --check-prefix NONE %s
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// RUN: %clang -### -c -fc++-static-destructors -fno-c++-static-destructors %s 2>&1 | FileCheck --check-prefix NONE %s
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// RUN: %clang -### -c -fc++-static-destructors=thread-local %s 2>&1 | FileCheck --check-prefix THREAD-LOCAL %s
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// ALL: -fc++-static-destructors=all
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// NONE: -fc++-static-destructors=none
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// THREAD-LOCAL: -fc++-static-destructors=thread-local

‎clang/test/SemaCXX/no_destroy.cpp

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@@ -1,31 +1,21 @@
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// RUN: %clang_cc1 -DNO_DTORS -DNO_EXCEPTIONS -fno-c++-static-destructors -verify %s
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// RUN: %clang_cc1 -DNO_EXCEPTIONS -verify %s
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// RUN: %clang_cc1 -DNO_DTORS -fexceptions -fno-c++-static-destructors -verify %s
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// RUN: %clang_cc1 -fexceptions -verify %s
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// RUN: %clang_cc1 -fc++-static-destructors=none -verify %s
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// RUN: %clang_cc1 -fc++-static-destructors=thread-local -verify=expected,thread-local-dtors %s
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// RUN: %clang_cc1 -verify=expected,thread-local-dtors,all-dtors %s
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// RUN: %clang_cc1 -fexceptions -fc++-static-destructors=none -verify %s
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// RUN: %clang_cc1 -fexceptions -fc++-static-destructors=thread-local -verify=expected,thread-local-dtors %s
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// RUN: %clang_cc1 -fexceptions -verify=expected,thread-local-dtors,all-dtors %s
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struct SecretDestructor {
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#ifndef NO_DTORS
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// expected-note@+2 4 {{private}}
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#endif
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private: ~SecretDestructor(); // expected-note + {{private}}
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};
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SecretDestructor sd1;
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thread_local SecretDestructor sd2;
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SecretDestructor sd1; // all-dtors-error{{private}}
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thread_local SecretDestructor sd2; // thread-local-dtors-error{{private}}
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void locals() {
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static SecretDestructor sd3;
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thread_local SecretDestructor sd4;
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static SecretDestructor sd3; // all-dtors-error{{private}}
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thread_local SecretDestructor sd4; // thread-local-dtors-error{{private}}
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}
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#ifndef NO_DTORS
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// SecretDestructor sd1; // expected-error@-8 {{private}}
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// thread_local SecretDestructor sd2; // expected-error@-8 {{private}}
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// void locals() {
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// static SecretDestructor sd3; // expected-error@-8 {{private}}
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// thread_local SecretDestructor sd4; // expected-error@-8 {{private}}
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// }
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#endif
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[[clang::always_destroy]] SecretDestructor sd6; // expected-error{{private}}
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[[clang::always_destroy]] thread_local SecretDestructor sd7; // expected-error{{private}}
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