JonChesterfield updated this revision to Diff 247617.
JonChesterfield added a comment.
- Rename attribute, propose some documentation
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D74361/new/
https://reviews.llvm.org/D74361
Files:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/lib/AST/DeclBase.cpp
clang/lib/CodeGen/CGDecl.cpp
clang/lib/CodeGen/CodeGenModule.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/CodeGenCXX/attr-loader-uninitialized.cpp
clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/Sema/attr-loader-uninitialized.cpp
Index: clang/test/Sema/attr-loader-uninitialized.cpp
===================================================================
--- /dev/null
+++ clang/test/Sema/attr-loader-uninitialized.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only
+
+int good __attribute__((loader_uninitialized));
+const int still_cant_be_const __attribute__((loader_uninitialized)); // expected-error {{default initialization of an object of const type}}
+extern int external __attribute__((loader_uninitialized));
+
+void func() __attribute__((loader_uninitialized)) // expected-warning {{'loader_uninitialized' attribute only applies to global variables}}
+{
+ int local __attribute__((loader_uninitialized)); // expected-warning {{'loader_uninitialized' attribute only applies to global variables}}
+
+ static int sl __attribute__((loader_uninitialized));
+}
+
+struct s {
+ __attribute__((loader_uninitialized)) int field; // expected-warning {{'loader_uninitialized' attribute only applies to global variables}}
+
+ static __attribute__((loader_uninitialized)) int sfield;
+
+} __attribute__((loader_uninitialized)); // expected-warning {{'loader_uninitialized' attribute only applies to global variables}}
Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -65,6 +65,7 @@
// CHECK-NEXT: InitPriority (SubjectMatchRule_variable)
// CHECK-NEXT: InternalLinkage (SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_record)
// CHECK-NEXT: LTOVisibilityPublic (SubjectMatchRule_record)
+// CHECK-NEXT: LoaderUninitialized (SubjectMatchRule_variable_is_global)
// CHECK-NEXT: Lockable (SubjectMatchRule_record)
// CHECK-NEXT: MIGServerRoutine (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_block)
// CHECK-NEXT: MSStruct (SubjectMatchRule_record)
Index: clang/test/CodeGenCXX/attr-loader-uninitialized.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/attr-loader-uninitialized.cpp
@@ -0,0 +1,40 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -std=c++11 -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: @_ZZ4funcvE4data = internal global i32 undef
+int* func(void)
+{
+ static int data [[clang::loader_uninitialized]];
+ return &data;
+}
+
+// No code emitted
+extern int extern_unhelpful_but_harmless [[clang::loader_uninitialized]];
+
+// CHECK: @tentative = global i32 undef
+int tentative [[clang::loader_uninitialized]];
+
+// CHECK: @_ZL16tentative_static = internal global i32 undef
+static int tentative_static [[clang::loader_uninitialized]] __attribute__((used));
+
+// CHECK: @nominally_zero_init = global i32 undef
+int nominally_zero_init [[clang::loader_uninitialized]] = 0;
+
+// CHECK: @nominally_value_init = global i32 undef
+int nominally_value_init [[clang::loader_uninitialized]] = 4;
+
+class trivial
+{
+ float x;
+};
+
+// CHECK: @ut = global %class.trivial undef
+trivial ut [[clang::loader_uninitialized]];
+
+struct nontrivial
+{
+ nontrivial() : x(3.14) {}
+ double x;
+};
+
+// CHECK: @unt = global %struct.nontrivial undef
+nontrivial unt [[clang::loader_uninitialized]];
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -6505,6 +6505,11 @@
D->addAttr(::new (S.Context) UninitializedAttr(S.Context, AL));
}
+static void handleLoaderUninitializedAttr(Sema &S, Decl *D,
+ const ParsedAttr &AL) {
+ D->addAttr(::new (S.Context) LoaderUninitializedAttr(S.Context, AL));
+}
+
static bool tryMakeVariablePseudoStrong(Sema &S, VarDecl *VD,
bool DiagnoseFailure) {
QualType Ty = VD->getType();
@@ -7427,6 +7432,10 @@
handleUninitializedAttr(S, D, AL);
break;
+ case ParsedAttr::AT_LoaderUninitialized:
+ handleLoaderUninitializedAttr(S, D, AL);
+ break;
+
case ParsedAttr::AT_ObjCExternallyRetained:
handleObjCExternallyRetainedAttr(S, D, AL);
break;
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -3942,6 +3942,8 @@
if (getLangOpts().CUDA &&
(IsCUDASharedVar || IsCUDAShadowVar || IsHIPPinnedShadowVar))
Init = llvm::UndefValue::get(getTypes().ConvertType(ASTTy));
+ else if (D->hasAttr<LoaderUninitializedAttr>())
+ Init = llvm::UndefValue::get(getTypes().ConvertType(ASTTy));
else if (!InitExpr) {
// This is a tentative definition; tentative definitions are
// implicitly initialized with { 0 }.
Index: clang/lib/CodeGen/CGDecl.cpp
===================================================================
--- clang/lib/CodeGen/CGDecl.cpp
+++ clang/lib/CodeGen/CGDecl.cpp
@@ -249,7 +249,7 @@
// variables cannot have an initializer.
llvm::Constant *Init = nullptr;
if (Ty.getAddressSpace() == LangAS::opencl_local ||
- D.hasAttr<CUDASharedAttr>())
+ D.hasAttr<CUDASharedAttr>() || D.hasAttr<LoaderUninitializedAttr>())
Init = llvm::UndefValue::get(LTy);
else
Init = EmitNullConstant(Ty);
Index: clang/lib/AST/DeclBase.cpp
===================================================================
--- clang/lib/AST/DeclBase.cpp
+++ clang/lib/AST/DeclBase.cpp
@@ -454,7 +454,8 @@
}
bool Decl::hasDefiningAttr() const {
- return hasAttr<AliasAttr>() || hasAttr<IFuncAttr>();
+ return hasAttr<AliasAttr>() || hasAttr<IFuncAttr>() ||
+ hasAttr<LoaderUninitializedAttr>();
}
const Attr *Decl::getDefiningAttr() const {
@@ -462,6 +463,8 @@
return AA;
if (auto *IFA = getAttr<IFuncAttr>())
return IFA;
+ if (auto *NZA = getAttr<LoaderUninitializedAttr>())
+ return NZA;
return nullptr;
}
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -4358,6 +4358,16 @@
}];
}
+def LoaderUninitializedDocs : Documentation {
+ let Category = DocCatVariable;
+ let Content = [{
+The ``loader_uninitialized`` attribute can be placed on global variables to
+indicate that the variable does not need to be zero initialised by the loader.
+This is useful for variables that are always written to before use where the
+default zero initialization provided by the toolchain loader is expensive.
+ }];
+}
+
def CallbackDocs : Documentation {
let Category = DocCatFunction;
let Content = [{
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -3430,6 +3430,12 @@
let Documentation = [UninitializedDocs];
}
+def LoaderUninitialized : InheritableAttr {
+ let Spellings = [Clang<"loader_uninitialized">];
+ let Subjects = SubjectList<[GlobalVar]>;
+ let Documentation = [LoaderUninitializedDocs];
+}
+
def ObjCExternallyRetained : InheritableAttr {
let LangOpts = [ObjCAutoRefCount];
let Spellings = [Clang<"objc_externally_retained">];
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