MaskRay updated this revision to Diff 325336.
MaskRay marked 5 inline comments as done.
MaskRay edited the summary of this revision.
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Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D96838/new/
https://reviews.llvm.org/D96838
Files:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/lib/CodeGen/CGDecl.cpp
clang/lib/CodeGen/CodeGenModule.cpp
clang/lib/CodeGen/CodeGenModule.h
clang/lib/Sema/SemaDecl.cpp
clang/test/CodeGen/attr-retain.c
clang/test/CodeGenCXX/attr-retain.cpp
clang/test/CodeGenCXX/extern-c.cpp
clang/test/Sema/attr-retain.c
Index: clang/test/Sema/attr-retain.c
===================================================================
--- /dev/null
+++ clang/test/Sema/attr-retain.c
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+/// We allow 'retain' on non-ELF targets because 'retain' is often used together
+/// with 'used'. 'used' has GC root semantics on macOS and Windows. We want
+/// users to just write retain,used and don't need to dispatch on binary formats.
+
+extern char test1[] __attribute__((retain)); // expected-warning {{'retain' attribute ignored on a non-definition declaration}}
+extern const char test2[] __attribute__((retain)); // expected-warning {{'retain' attribute ignored on a non-definition declaration}}
+const char test3[] __attribute__((retain)) = "";
+
+struct __attribute__((retain)) s { // expected-warning {{'retain' attribute only applies to variables with non-local storage, functions, and Objective-C methods}}
+};
+
+int g0 __attribute__((retain(0))); // expected-error {{'retain' attribute takes no arguments}}
+
+void foo() {
+ static int a __attribute__((retain));
+ int b __attribute__((retain)); // expected-warning {{'retain' attribute only applies to variables with non-local storage, functions, and Objective-C methods}}
+}
+
+__attribute__((used)) static void f0();
+
+/// Test attribute merging.
+int tentative;
+int tentative __attribute__((retain));
+extern int tentative;
+int tentative = 0;
Index: clang/test/CodeGenCXX/extern-c.cpp
===================================================================
--- clang/test/CodeGenCXX/extern-c.cpp
+++ clang/test/CodeGenCXX/extern-c.cpp
@@ -70,16 +70,19 @@
__attribute__((used)) static int duplicate_internal_fn() { return 0; }
}
- // CHECK: @llvm.used = appending global {{.*}} @internal_var {{.*}} @internal_fn
+ // CHECK: @llvm.used = appending global {{.*}} @internal_var {{.*}} @internal_fn
// CHECK-NOT: @unused
// CHECK-NOT: @duplicate_internal
// CHECK: @internal_var = internal alias i32, i32* @_ZL12internal_var
+ // CHECK-NOT: !retain
// CHECK-NOT: @unused
// CHECK-NOT: @duplicate_internal
// CHECK: @internal_fn = internal alias i32 (), i32 ()* @_ZL11internal_fnv
+ // CHECK-NOT: !retain
// CHECK-NOT: @unused
// CHECK-NOT: @duplicate_internal
+ // CHECK: define internal i32 @_ZL11internal_fnv()
}
namespace PR19411 {
Index: clang/test/CodeGenCXX/attr-retain.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/attr-retain.cpp
@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -Werror %s -o - | FileCheck %s
+
+struct X0 {
+ // RETAIN: define linkonce_odr{{.*}} @_ZN2X0C1Ev({{.*}} !retain
+ __attribute__((used, retain)) X0() {}
+ // RETAIN: define linkonce_odr{{.*}} @_ZN2X0D1Ev({{.*}} !retain
+ __attribute__((used, retain)) ~X0() {}
+};
+
+struct X1 {
+ struct Nested {
+ // RETAIN-NOT: 2f0Ev
+ // RETAIN: define linkonce_odr{{.*}} @_ZN2X16Nested2f1Ev({{.*}} !retain
+ void __attribute__((retain)) f0() {}
+ void __attribute__((used, retain)) f1() {}
+ };
+};
+
+// CHECK: define internal void @_ZN10merge_declL4funcEv(){{.*}} !retain
+namespace merge_decl {
+static void func();
+void bar() { void func() __attribute__((used, retain)); }
+static void func() {}
+} // namespace merge_decl
+
+namespace instantiate_member {
+template <typename T>
+struct S {
+ void __attribute__((used, retain)) f() {}
+};
+
+void test() {
+ // CHECK: define linkonce_odr{{.*}} void @_ZN18instantiate_member1SIiE1fEv({{.*}} !retain
+ S<int> a;
+}
+} // namespace instantiate_member
Index: clang/test/CodeGen/attr-retain.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/attr-retain.c
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+
+/// Set !retain regardless of the target. The backend will lower !retain to
+/// SHF_GNU_RETAIN on ELF and ignore the metadata for other binary formats.
+// CHECK: @c0 ={{.*}} constant i32 {{.*}} !retain ![[#EMPTY:]]
+// CHECK: @foo.l0 = internal global i32 {{.*}} !retain ![[#EMPTY]]
+// CHECK: @g0 ={{.*}} global i32 {{.*}} !retain ![[#EMPTY]]
+// CHECK-NEXT: @g1 ={{.*}} global i32 {{.*}} !retain ![[#EMPTY]]
+// CHECK-NEXT: @g3 = internal global i32 {{.*}} !retain ![[#EMPTY]]
+// CHECK-NEXT: @g4 = internal global i32 0, section ".data.g"{{.*}} !retain ![[#EMPTY]]
+
+const int c0 __attribute__((retain)) = 42;
+
+void foo() {
+ static int l0 __attribute__((retain)) = 2;
+}
+
+__attribute__((retain)) int g0;
+int g1 __attribute__((retain));
+__attribute__((retain)) static int g2;
+__attribute__((used, retain)) static int g3;
+__attribute__((used, retain, section(".data.g"))) static int g4;
+
+// CHECK: define dso_local void @f0(){{.*}} !retain ![[#EMPTY]]
+// CHECK-NOT: @f1
+// CHECK: define internal void @f2(){{.*}} !retain ![[#EMPTY]]
+
+void __attribute__((retain)) f0(void) {}
+static void __attribute__((retain)) f1(void) {}
+static void __attribute__((used, retain)) f2(void) {}
+
+// CHECK: [[#EMPTY]] = !{}
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -2831,6 +2831,11 @@
NewAttr->setInherited(true);
New->addAttr(NewAttr);
}
+ if (RetainAttr *OldAttr = Old->getMostRecentDecl()->getAttr<RetainAttr>()) {
+ RetainAttr *NewAttr = OldAttr->clone(Context);
+ NewAttr->setInherited(true);
+ New->addAttr(NewAttr);
+ }
if (!Old->hasAttrs() && !New->hasAttrs())
return;
@@ -2953,7 +2958,7 @@
}
// Already handled.
- if (isa<UsedAttr>(I))
+ if (isa<UsedAttr>(I) || isa<RetainAttr>(I))
continue;
if (mergeDeclAttribute(*this, New, I, LocalAMK))
@@ -13300,6 +13305,13 @@
VD->dropAttr<UsedAttr>();
}
}
+ if (RetainAttr *Attr = VD->getAttr<RetainAttr>()) {
+ if (!Attr->isInherited() && !VD->isThisDeclarationADefinition()) {
+ Diag(Attr->getLocation(), diag::warn_attribute_ignored_on_non_definition)
+ << Attr;
+ VD->dropAttr<RetainAttr>();
+ }
+ }
const DeclContext *DC = VD->getDeclContext();
// If there's a #pragma GCC visibility in scope, and this isn't a class
Index: clang/lib/CodeGen/CodeGenModule.h
===================================================================
--- clang/lib/CodeGen/CodeGenModule.h
+++ clang/lib/CodeGen/CodeGenModule.h
@@ -1048,6 +1048,9 @@
template<typename SomeDecl>
void MaybeHandleStaticInExternC(const SomeDecl *D, llvm::GlobalValue *GV);
+ /// Set the !retain metadata.
+ void setRetain(llvm::GlobalObject *GO);
+
/// Add a global to a list to be added to the llvm.used metadata.
void addUsedGlobal(llvm::GlobalValue *GV);
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -1886,6 +1886,8 @@
if (D) {
if (auto *GV = dyn_cast<llvm::GlobalVariable>(GO)) {
+ if (D->hasAttr<RetainAttr>())
+ setRetain(GV);
if (auto *SA = D->getAttr<PragmaClangBSSSectionAttr>())
GV->addAttribute("bss-section", SA->getName());
if (auto *SA = D->getAttr<PragmaClangDataSectionAttr>())
@@ -1897,6 +1899,8 @@
}
if (auto *F = dyn_cast<llvm::Function>(GO)) {
+ if (D->hasAttr<RetainAttr>())
+ setRetain(F);
if (auto *SA = D->getAttr<PragmaClangTextSectionAttr>())
if (!D->getAttr<SectionAttr>())
F->addFnAttr("implicit-section-name", SA->getName());
@@ -2065,6 +2069,11 @@
}
}
+void CodeGenModule::setRetain(llvm::GlobalObject *GO) {
+ GO->setMetadata(llvm::LLVMContext::MD_retain,
+ llvm::MDNode::get(getLLVMContext(), None));
+}
+
void CodeGenModule::addUsedGlobal(llvm::GlobalValue *GV) {
assert((isa<llvm::Function>(GV) || !GV->isDeclaration()) &&
"Only globals with definition can force usage.");
Index: clang/lib/CodeGen/CGDecl.cpp
===================================================================
--- clang/lib/CodeGen/CGDecl.cpp
+++ clang/lib/CodeGen/CGDecl.cpp
@@ -443,6 +443,8 @@
if (D.hasAttr<UsedAttr>())
CGM.addUsedGlobal(var);
+ if (D.hasAttr<RetainAttr>())
+ CGM.setRetain(var);
// We may have to cast the constant because of the initializer
// mismatch above.
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -57,6 +57,41 @@
let Heading = "section, __declspec(allocate)";
}
+def UsedDocs : Documentation {
+ let Category = DocCatFunction;
+ let Content = [{
+The attribute, when attached to a function definition, causes the function to
+be emitted even if it appears that the function is not referenced and can
+otherwise be omitted.
+
+The attribute, when attached to a variable definition with static storage,
+causes the variable to be emitted even if it appears that the variable is not
+referenced.
+
+On macOS and Windows, this attribute prevents the defining section from being
+garbage collected by the linker.
+
+On ELF targets, this attribute does not prevent garbage collection. You need to
+additionally specify the ``retain`` attribute to emit the function or variable
+in a unique section which prevents garbage collection by supported linkers.
+ }];
+}
+
+def RetainDocs : Documentation {
+ let Category = DocCatFunction;
+ let Content = [{
+This attribute only has effects on ELF targets that support SHF_GNU_RETAIN.
+The attribute, when attached to a function or variable definition, if the
+function or variable is emitted, causes the function or variable to be emitted
+in a unique section with SHF_GNU_RETAIN flag. This ELF section flag prevents
+garbage collection of the section by supported linkers (GNU ld and gold from
+binutils 2.36 onwards, LLD 13 or newer).
+
+Note: this attribute is usually used together with the ``used`` attribute
+because ``used`` is not implied.
+ }];
+}
+
def InitPriorityDocs : Documentation {
let Category = DocCatVariable;
let Content = [{
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -2648,7 +2648,14 @@
def Used : InheritableAttr {
let Spellings = [GCC<"used">];
let Subjects = SubjectList<[NonLocalVar, Function, ObjCMethod]>;
- let Documentation = [Undocumented];
+ let Documentation = [UsedDocs];
+ let SimpleHandler = 1;
+}
+
+def Retain : InheritableAttr {
+ let Spellings = [GCC<"retain">];
+ let Subjects = SubjectList<[NonLocalVar, Function, ObjCMethod]>;
+ let Documentation = [RetainDocs];
let SimpleHandler = 1;
}
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