serge-sans-paille updated this revision to Diff 541475.
serge-sans-paille added a comment.
switch from cascading ternary operator to cascading if for readability.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D155580/new/
https://reviews.llvm.org/D155580
Files:
clang/lib/CodeGen/CGDecl.cpp
clang/test/CodeGenCXX/auto-var-init-empty-class.cpp
clang/test/CodeGenCXX/auto-var-init.cpp
Index: clang/test/CodeGenCXX/auto-var-init.cpp
===================================================================
--- clang/test/CodeGenCXX/auto-var-init.cpp
+++ clang/test/CodeGenCXX/auto-var-init.cpp
@@ -43,9 +43,6 @@
// PATTERN-NOT: undef
// ZERO-NOT: undef
-// PATTERN-O0: @__const.test_empty_uninit.uninit = private unnamed_addr constant %struct.empty { i8 [[I8]] }, align 1
-// PATTERN-O1-NOT: @__const.test_empty_uninit.uninit
-struct empty {};
// PATTERN-O0: @__const.test_small_uninit.uninit = private unnamed_addr constant %struct.small { i8 [[I8]] }, align 1
// PATTERN-O0: @__const.test_small_custom.custom = private unnamed_addr constant %struct.small { i8 42 }, align 1
// ZERO-O0: @__const.test_small_custom.custom = private unnamed_addr constant %struct.small { i8 42 }, align 1
@@ -586,24 +583,6 @@
// CHECK-NOT: !annotation
// CHECK-NEXT: call void @{{.*}}used{{.*}}%braces)
-TEST_UNINIT(empty, empty);
-// CHECK-LABEL: @test_empty_uninit()
-// CHECK: %uninit = alloca %struct.empty, align
-// CHECK-NEXT: call void @{{.*}}used{{.*}}%uninit)
-// PATTERN-LABEL: @test_empty_uninit()
-// PATTERN-O0: call void @llvm.memcpy{{.*}} @__const.test_empty_uninit.uninit{{.+}}), !annotation [[AUTO_INIT]]
-// PATTERN-O1: store i8 [[I8]], {{.*}} align 1, !annotation [[AUTO_INIT]]
-// ZERO-LABEL: @test_empty_uninit()
-// ZERO-O0: call void @llvm.memset{{.*}}, i8 0,{{.+}}), !annotation [[AUTO_INIT]]
-// ZERO-O1: store i8 0, {{.*}} align 1, !annotation [[AUTO_INIT]]
-
-TEST_BRACES(empty, empty);
-// CHECK-LABEL: @test_empty_braces()
-// CHECK: %braces = alloca %struct.empty, align
-// CHECK-NEXT: call void @llvm.memcpy
-// CHECK-NOT: !annotation
-// CHECK-NEXT: call void @{{.*}}used{{.*}}%braces)
-
TEST_UNINIT(small, small);
// CHECK-LABEL: @test_small_uninit()
// CHECK: %uninit = alloca %struct.small, align
Index: clang/test/CodeGenCXX/auto-var-init-empty-class.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/auto-var-init-empty-class.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=pattern %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=zero %s -emit-llvm -o - | FileCheck %s
+
+// C++ empty classes still take some memory, but there is no need to initialize
+// it has it cannot be accessed. This matches GCC behavior.
+
+struct S {
+};
+
+extern "C" void use(struct S*);
+
+// CHECK-LABEL: @empty_class(
+// CHECK: %s = alloca
+// CHECK-NEXT: call void @use(ptr noundef %s)
+extern "C" void empty_class(void) {
+ S s;
+ return use(&s);
+}
Index: clang/lib/CodeGen/CGDecl.cpp
===================================================================
--- clang/lib/CodeGen/CGDecl.cpp
+++ clang/lib/CodeGen/CGDecl.cpp
@@ -1855,6 +1855,13 @@
}
}
+static bool isEmptyClass(VarDecl const &D) {
+ const Type *Ty = D.getType().getTypePtr();
+ if (const auto *CxxRecordTy = Ty->getAsCXXRecordDecl())
+ return CxxRecordTy->isEmpty();
+ return false;
+}
+
void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
assert(emission.Variable && "emission was not valid!");
@@ -1902,13 +1909,18 @@
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())
+ // Constexpr already initializes everything correctly.
+ trivialAutoVarInit = LangOptions::TrivialAutoVarInitKind::Uninitialized;
+ else if (D.getAttr<UninitializedAttr>())
+ trivialAutoVarInit = LangOptions::TrivialAutoVarInitKind::Uninitialized;
+ else if (isEmptyClass(D))
+ // Empty classes still use a byte, but it's ok not to initialize it as
+ // it cannot be legitimately accessed.
+ trivialAutoVarInit = LangOptions::TrivialAutoVarInitKind::Uninitialized;
+ else
+ trivialAutoVarInit = getContext().getLangOpts().getTrivialAutoVarInit();
auto initializeWhatIsTechnicallyUninitialized = [&](Address Loc) {
if (trivialAutoVarInit ==
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