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This attribute would then affect all stack variables of that type, when the
type has been evaluated as ok wrt. initialisation, or a for performance /
security trade-offs.
An example of use could be container with preallocated storage like
SmallVector, if we consider that it is too costly to initialize that storage.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D156337
Files:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/lib/CodeGen/CGDecl.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/CodeGenCXX/trivial-auto-var-init-attribute.cpp
clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/Sema/attr-uninitialized.c
Index: clang/test/Sema/attr-uninitialized.c
===================================================================
--- clang/test/Sema/attr-uninitialized.c
+++ clang/test/Sema/attr-uninitialized.c
@@ -18,4 +18,4 @@
struct TheWordIsOut {
__attribute((uninitialized)) int youre_doin_wrong; // expected-warning {{'uninitialized' attribute only applies to local variables}}
-} __attribute((uninitialized)); // expected-warning {{'uninitialized' attribute only applies to local variables}}
+} __attribute((uninitialized));
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
@@ -188,7 +188,7 @@
// CHECK-NEXT: TargetVersion (SubjectMatchRule_function)
// CHECK-NEXT: TestTypestate (SubjectMatchRule_function_is_member)
// CHECK-NEXT: TrivialABI (SubjectMatchRule_record)
-// CHECK-NEXT: Uninitialized (SubjectMatchRule_variable_is_local)
+// CHECK-NEXT: Uninitialized (SubjectMatchRule_variable_is_local, SubjectMatchRule_record)
// CHECK-NEXT: UnsafeBufferUsage (SubjectMatchRule_function)
// CHECK-NEXT: UseHandle (SubjectMatchRule_variable_is_parameter)
// CHECK-NEXT: VecReturn (SubjectMatchRule_record)
Index: clang/test/CodeGenCXX/trivial-auto-var-init-attribute.cpp
===================================================================
--- clang/test/CodeGenCXX/trivial-auto-var-init-attribute.cpp
+++ clang/test/CodeGenCXX/trivial-auto-var-init-attribute.cpp
@@ -38,4 +38,24 @@
}
#pragma clang attribute pop
+struct [[clang::uninitialized]] uninitialized_record {
+ int i;
+};
+
+// UNINIT-LABEL: test_record_attribute_uninitialized(
+// UNINIT: alloca
+// UNINIT-NEXT: call void
+// ZERO-LABEL: test_record_attribute_uninitialized(
+// ZERO: alloca
+// ZERO-NOT: !annotation
+// ZERO-NEXT: call void
+// PATTERN-LABEL: test_record_attribute_uninitialized(
+// PATTERN: alloca
+// PATTERN-NOT: !annotation
+// PATTERN-NEXT: call void
+void test_record_attribute_uninitialized() {
+ uninitialized_record some;
+ used(some);
+}
+
} // extern "C"
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -8438,8 +8438,11 @@
}
static void handleUninitializedAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
- assert(cast<VarDecl>(D)->getStorageDuration() == SD_Automatic &&
- "uninitialized is only valid on automatic duration variables");
+ assert(((isa<VarDecl>(D) &&
+ cast<VarDecl>(D)->getStorageDuration() == SD_Automatic) ||
+ isa<RecordDecl>(D)) &&
+ "uninitialized is only valid on automatic duration variables and "
+ "record type");
D->addAttr(::new (S.Context) UninitializedAttr(S.Context, AL));
}
Index: clang/lib/CodeGen/CGDecl.cpp
===================================================================
--- clang/lib/CodeGen/CGDecl.cpp
+++ clang/lib/CodeGen/CGDecl.cpp
@@ -1902,13 +1902,17 @@
const Address Loc =
locIsByrefHeader ? emission.getObjectAddress(*this) : emission.Addr;
- // Note: constexpr already initializes everything correctly.
- LangOptions::TrivialAutoVarInitKind trivialAutoVarInit =
- (D.isConstexpr()
- ? LangOptions::TrivialAutoVarInitKind::Uninitialized
- : (D.getAttr<UninitializedAttr>()
- ? LangOptions::TrivialAutoVarInitKind::Uninitialized
- : getContext().getLangOpts().getTrivialAutoVarInit()));
+ LangOptions::TrivialAutoVarInitKind trivialAutoVarInit;
+ if (D.isConstexpr())
+ // Note: constexpr already initializes everything correctly.
+ trivialAutoVarInit = LangOptions::TrivialAutoVarInitKind::Uninitialized;
+ else if (D.getAttr<UninitializedAttr>())
+ trivialAutoVarInit = LangOptions::TrivialAutoVarInitKind::Uninitialized;
+ else if (const auto *RecordTy = D.getType()->getAsRecordDecl();
+ RecordTy && RecordTy->hasAttr<UnusedAttr>())
+ trivialAutoVarInit = LangOptions::TrivialAutoVarInitKind::Uninitialized;
+ else
+ trivialAutoVarInit = getContext().getLangOpts().getTrivialAutoVarInit();
auto initializeWhatIsTechnicallyUninitialized = [&](Address Loc) {
if (trivialAutoVarInit ==
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -5782,8 +5782,10 @@
The command-line parameter ``-ftrivial-auto-var-init=*`` can be used to
initialize trivial automatic stack variables. By default, trivial automatic
stack variables are uninitialized. This attribute is used to override the
-command-line parameter, forcing variables to remain uninitialized. It has no
-semantic meaning in that using uninitialized values is undefined behavior,
+command-line parameter, forcing variables to remain uninitialized.
+When set on a struct or class, all stack variables of this type are affected.
+
+It has no semantic meaning in that using uninitialized values is undefined behavior,
it rather documents the programmer's intent.
}];
}
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -3960,7 +3960,7 @@
def Uninitialized : InheritableAttr {
let Spellings = [Clang<"uninitialized", 0>];
- let Subjects = SubjectList<[LocalVar]>;
+ let Subjects = SubjectList<[LocalVar, Record]>;
let PragmaAttributeSupport = 1;
let Documentation = [UninitializedDocs];
}
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