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Fix Darwin 'constinit thread_local' variables. #1412

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Merged
merged 1 commit into from
Jul 3, 2020
Merged

Fix Darwin 'constinit thread_local' variables. #1412

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27 changes: 17 additions & 10 deletions clang/lib/CodeGen/CodeGenModule.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4065,17 +4065,24 @@ void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D,

GV->setAlignment(getContext().getDeclAlign(D).getAsAlign());

// On Darwin, if the normal linkage of a C++ thread_local variable is
// LinkOnce or Weak, we keep the normal linkage to prevent multiple
// copies within a linkage unit; otherwise, the backing variable has
// internal linkage and all accesses should just be calls to the
// Itanium-specified entry point, which has the normal linkage of the
// variable. This is to preserve the ability to change the implementation
// behind the scenes.
if (!D->isStaticLocal() && D->getTLSKind() == VarDecl::TLS_Dynamic &&
// On Darwin, unlike other Itanium C++ ABI platforms, the thread-wrapper
// function is only defined alongside the variable, not also alongside
// callers. Normally, all accesses to a thread_local go through the
// thread-wrapper in order to ensure initialization has occurred, underlying
// variable will never be used other than the thread-wrapper, so it can be
// converted to internal linkage.
//
// However, if the variable has the 'constinit' attribute, it _can_ be
// referenced directly, without calling the thread-wrapper, so the linkage
// must not be changed.
//
// Additionally, if the variable isn't plain external linkage, e.g. if it's
// weak or linkonce, the de-duplication semantics are important to preserve,
// so we don't change the linkage.
if (D->getTLSKind() == VarDecl::TLS_Dynamic &&
Linkage == llvm::GlobalValue::ExternalLinkage &&
Context.getTargetInfo().getTriple().isOSDarwin() &&
!llvm::GlobalVariable::isLinkOnceLinkage(Linkage) &&
!llvm::GlobalVariable::isWeakLinkage(Linkage))
!D->hasAttr<ConstInitAttr>())
Linkage = llvm::GlobalValue::InternalLinkage;

GV->setLinkage(Linkage);
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57 changes: 37 additions & 20 deletions clang/test/CodeGenCXX/cxx2a-thread-local-constinit.cpp
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@@ -1,41 +1,55 @@
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++2a %s -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++2a %s -emit-llvm -o - | FileCheck --check-prefix=CHECK --check-prefix=LINUX %s
// RUN: %clang_cc1 -triple x86_64-apple-darwin12 -std=c++2a %s -emit-llvm -o - | FileCheck --check-prefix=CHECK --check-prefix=DARWIN %s

// Check variable definitions/declarations. Note that on Darwin, typically the
// variable's symbol is marked internal, and only the _ZTW function is
// exported. Except: constinit variables do get exported, even on darwin.

// CHECK-DAG: @a = external thread_local global i32
// CHECK-DAG: @b = external thread_local global i32
// LINUX-DAG: @c = thread_local global i32 0, align 4
// DARWIN-DAG: @c = internal thread_local global i32 0, align 4
// LINUX-DAG: @d = thread_local global i32 0, align 4
// DARWIN-DAG: @d = internal thread_local global i32 0, align 4
// CHECK-DAG: @e = external thread_local global %struct.Destructed, align 4
// CHECK-DAG: @e2 = thread_local global %struct.Destructed zeroinitializer, align 4
// CHECK-DAG: @f = thread_local global i32 4, align 4

// CHECK-DAG: @a = external thread_local global i32
extern thread_local int a;

// CHECK-DAG: @b = external thread_local global i32
extern thread_local constinit int b;

// CHECK-LABEL: define i32 @_Z1fv()
// CHECK: call i32* @_ZTW1a()
// CHECK-LABEL: define i32 @_Z5get_av()
// CHECK: call {{(cxx_fast_tlscc )?}}i32* @_ZTW1a()
// CHECK: }
int f() { return a; }
int get_a() { return a; }

// CHECK-LABEL: define linkonce_odr {{.*}} @_ZTW1a()
// CHECK: br i1
// CHECK: call void @_ZTH1a()
// CHECK: }
// LINUX-LABEL: define linkonce_odr {{.*}} @_ZTW1a()
// LINUX: br i1
// LINUX: call void @_ZTH1a()
// LINUX: }
// DARWIN-NOT: define {{.*}}@_ZTW1a()

// CHECK-LABEL: define i32 @_Z1gv()
// CHECK-LABEL: define i32 @_Z5get_bv()
// CHECK-NOT: call
// CHECK: load i32, i32* @b
// CHECK-NOT: call
// CHECK: }
int g() { return b; }
int get_b() { return b; }

// CHECK-NOT: define {{.*}} @_ZTW1b()

extern thread_local int c;

// CHECK-LABEL: define i32 @_Z1hv()
// CHECK: call i32* @_ZTW1c()
// CHECK-LABEL: define i32 @_Z5get_cv()
// LINUX: call {{(cxx_fast_tlscc )?}}i32* @_ZTW1c()
// CHECK: load i32, i32* %
// CHECK: }
int h() { return c; }
int get_c() { return c; }

// Note: use of 'c' does not trigger initialization of 'd', because 'c' has a
// constant initializer.
// CHECK-LABEL: define weak_odr {{.*}} @_ZTW1c()
// DARWIN-LABEL: define cxx_fast_tlscc {{.*}} @_ZTW1c()
// LINUX-LABEL: define weak_odr {{.*}} @_ZTW1c()
// CHECK-NOT: br i1
// CHECK-NOT: call
// CHECK: ret i32* @c
Expand All @@ -55,15 +69,18 @@ struct Destructed {
};

extern thread_local constinit Destructed e;
// CHECK-LABEL: define i32 @_Z1iv()
// CHECK-LABEL: define i32 @_Z5get_ev()
// CHECK: call {{.*}}* @_ZTW1e()
// CHECK: }
int i() { return e.n; }
int get_e() { return e.n; }

// CHECK: define {{.*}}[[E2_INIT:@__cxx_global_var_init[^(]*]](
// CHECK: call {{.*}} @__cxa_thread_atexit({{.*}} @_ZN10DestructedD1Ev {{.*}} @e2
// LINUX: call {{.*}} @__cxa_thread_atexit({{.*}} @_ZN10DestructedD1Ev {{.*}} @e2
// DARWIN: call {{.*}} @_tlv_atexit({{.*}} @_ZN10DestructedD1Ev {{.*}} @e2
thread_local constinit Destructed e2;

thread_local constinit int f = 4;

// CHECK-LABEL: define {{.*}}__tls_init
// CHECK: call {{.*}} [[D_INIT]]
// CHECK: call {{.*}} [[E2_INIT]]