[clang] [clang] Add support for `__declspec(no_init_all)` (PR #116847)
Daniel Paoliello via cfe-commits
cfe-commits at lists.llvm.org
Tue Nov 19 09:40:40 PST 2024
https://github.com/dpaoliello created https://github.com/llvm/llvm-project/pull/116847
In MSVC, when `/d1initall` is enabled, `__declspec(no_init_all)` can be applied to a type to suppress auto-initialization for all instances of that type or to a function to suppress auto-initialization for all locals within that function.
This change does the same for Clang, except that it applies to the `-ftrivial-auto-var-init` flag instead.
NOTE:
* I did not add a Clang-specific spelling for this but would be happy to make a followup PR if folks are interested in that.
* Since this is implementing a `__declspec` only, I chose to leave it undocumented.
>From c1392cf51ae96bafbe02fdf3d32a8a5a554b6575 Mon Sep 17 00:00:00 2001
From: "Daniel Paoliello (HE/HIM)" <danpao at microsoft.com>
Date: Tue, 19 Nov 2024 09:34:51 -0800
Subject: [PATCH] [clang] Add support for __declspec(no_init_all)
---
clang/include/clang/Basic/Attr.td | 7 +++
clang/lib/CodeGen/CGDecl.cpp | 19 ++++---
clang/test/CodeGenCXX/auto-var-init-attr.cpp | 59 ++++++++++++++++++++
3 files changed, 78 insertions(+), 7 deletions(-)
create mode 100644 clang/test/CodeGenCXX/auto-var-init-attr.cpp
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 6035a563d5fce7..5d3270280c17f6 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -4888,3 +4888,10 @@ def ClspvLibclcBuiltin: InheritableAttr {
let Documentation = [ClspvLibclcBuiltinDoc];
let SimpleHandler = 1;
}
+
+def NoTrivialAutoVarInit: InheritableAttr {
+ let Spellings = [Declspec<"no_init_all">];
+ let Subjects = SubjectList<[Function, Tag]>;
+ let Documentation = [Undocumented];
+ let SimpleHandler = 1;
+}
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 6e9d28cea28e79..ff53ffae4459af 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1900,10 +1900,16 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
locIsByrefHeader ? emission.getObjectAddress(*this) : emission.Addr;
// Note: constexpr already initializes everything correctly.
+ auto typeHasNoTrivialAutoVarInitAttr = [&]() {
+ auto *TD = type->getAsTagDecl();
+ return TD && TD->hasAttr<NoTrivialAutoVarInitAttr>();
+ };
LangOptions::TrivialAutoVarInitKind trivialAutoVarInit =
(D.isConstexpr()
? LangOptions::TrivialAutoVarInitKind::Uninitialized
- : (D.getAttr<UninitializedAttr>()
+ : ((D.getAttr<UninitializedAttr>() ||
+ typeHasNoTrivialAutoVarInitAttr() ||
+ CurFuncDecl->hasAttr<NoTrivialAutoVarInitAttr>())
? LangOptions::TrivialAutoVarInitKind::Uninitialized
: getContext().getLangOpts().getTrivialAutoVarInit()));
@@ -1944,13 +1950,13 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
replaceUndef(CGM, isPattern, constant));
}
- if (constant && D.getType()->isBitIntType() &&
- CGM.getTypes().typeRequiresSplitIntoByteArray(D.getType())) {
+ if (constant && type->isBitIntType() &&
+ CGM.getTypes().typeRequiresSplitIntoByteArray(type)) {
// Constants for long _BitInt types are split into individual bytes.
// Try to fold these back into an integer constant so it can be stored
// properly.
- llvm::Type *LoadType = CGM.getTypes().convertTypeForLoadStore(
- D.getType(), constant->getType());
+ llvm::Type *LoadType =
+ CGM.getTypes().convertTypeForLoadStore(type, constant->getType());
constant = llvm::ConstantFoldLoadFromConst(
constant, LoadType, llvm::APInt::getZero(32), CGM.getDataLayout());
}
@@ -1967,8 +1973,7 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
// It may be that the Init expression uses other uninitialized memory,
// but auto-var-init here would not help, as auto-init would get
// overwritten by Init.
- if (!D.getType()->isScalarType() || capturedByInit ||
- isAccessedBy(D, Init)) {
+ if (!type->isScalarType() || capturedByInit || isAccessedBy(D, Init)) {
initializeWhatIsTechnicallyUninitialized(Loc);
}
}
diff --git a/clang/test/CodeGenCXX/auto-var-init-attr.cpp b/clang/test/CodeGenCXX/auto-var-init-attr.cpp
new file mode 100644
index 00000000000000..5481c6e8613c56
--- /dev/null
+++ b/clang/test/CodeGenCXX/auto-var-init-attr.cpp
@@ -0,0 +1,59 @@
+// RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown -fblocks -fdeclspec -ftrivial-auto-var-init=zero %s -emit-llvm -o - | FileCheck %s
+
+struct S { char c; };
+class C { char c; };
+enum class E { ZERO };
+union U { char c; int i; };
+
+struct __declspec(no_init_all) NoInitS { char c; };
+class __declspec(no_init_all) NoInitC { char c; };
+enum class __declspec(no_init_all) NoInitE { ZERO };
+union __declspec(no_init_all) NoInitU { char c; int i; };
+
+extern "C" {
+ void test_no_attr() {
+ // CHECK-LABEL: @test_no_attr()
+ // CHECK-NEXT: entry:
+ // CHECK-NEXT: %s = alloca %struct.S, align 1
+ // CHECK-NEXT: %c = alloca %class.C, align 1
+ // CHECK-NEXT: %e = alloca i32, align 4
+ // CHECK-NEXT: %u = alloca %union.U, align 4
+ // CHECK-NEXT: call void @llvm.memset.p0.i64(ptr align 1 %s, i8 0, i64 1, i1 false)
+ // CHECK-NEXT: call void @llvm.memset.p0.i64(ptr align 1 %c, i8 0, i64 1, i1 false)
+ // CHECK-NEXT: store i32 0, ptr %e, align 4
+ // CHECK-NEXT: call void @llvm.memset.p0.i64(ptr align 4 %u, i8 0, i64 4, i1 false)
+ // CHECK-NEXT ret void
+ S s;
+ C c;
+ E e;
+ U u;
+ }
+
+ void __declspec(no_init_all) test_attr_on_function() {
+ // CHECK-LABEL: @test_attr_on_function()
+ // CHECK-NEXT: entry:
+ // CHECK-NEXT: %s = alloca %struct.S, align 1
+ // CHECK-NEXT: %c = alloca %class.C, align 1
+ // CHECK-NEXT: %e = alloca i32, align 4
+ // CHECK-NEXT: %u = alloca %union.U, align 4
+ // CHECK-NEXT: ret void
+ S s;
+ C c;
+ E e;
+ U u;
+ }
+
+ void test_attr_on_decl() {
+ // CHECK-LABEL: @test_attr_on_decl()
+ // CHECK-NEXT: entry:
+ // CHECK-NEXT: %s = alloca %struct.NoInitS, align 1
+ // CHECK-NEXT: %c = alloca %class.NoInitC, align 1
+ // CHECK-NEXT: %e = alloca i32, align 4
+ // CHECK-NEXT: %u = alloca %union.NoInitU, align 4
+ // CHECK-NEXT: ret void
+ NoInitS s;
+ NoInitC c;
+ NoInitE e;
+ NoInitU u;
+ }
+}
\ No newline at end of file
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