[clang] [clang][bytecode] Activate primitive fields before initializing them (PR #149963)
Timm Baeder via cfe-commits
cfe-commits at lists.llvm.org
Mon Jul 21 23:10:05 PDT 2025
Timm =?utf-8?q?Bäder?= <tbaeder at redhat.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/149963 at github.com>
https://github.com/tbaederr updated https://github.com/llvm/llvm-project/pull/149963
>From 7fa404e88e104eea07f26f4959cf4d6e1768dc14 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Mon, 21 Jul 2025 16:56:27 +0200
Subject: [PATCH 1/2] [clang][bytecode] Unions again
---
clang/lib/AST/ByteCode/Compiler.cpp | 9 ++++-
clang/test/AST/ByteCode/unions.cpp | 55 +++++++++++++++++++++++++++++
2 files changed, 63 insertions(+), 1 deletion(-)
diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 07efd6f852fc2..e760055a8d235 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -25,11 +25,18 @@ using APSInt = llvm::APSInt;
namespace clang {
namespace interp {
+static bool hasTrivialDefaultCtorParent(const FieldDecl *FD) {
+ assert(FD);
+ assert(FD->getParent()->isUnion());
+ const auto *CXXRD = dyn_cast<CXXRecordDecl>(FD->getParent());
+ return !CXXRD || CXXRD->hasTrivialDefaultConstructor();
+}
+
static bool refersToUnion(const Expr *E) {
for (;;) {
if (const auto *ME = dyn_cast<MemberExpr>(E)) {
if (const auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
- FD && FD->getParent()->isUnion())
+ FD && FD->getParent()->isUnion() && hasTrivialDefaultCtorParent(FD))
return true;
E = ME->getBase();
continue;
diff --git a/clang/test/AST/ByteCode/unions.cpp b/clang/test/AST/ByteCode/unions.cpp
index 7cfd0d677a7b3..ae71776353cf0 100644
--- a/clang/test/AST/ByteCode/unions.cpp
+++ b/clang/test/AST/ByteCode/unions.cpp
@@ -861,6 +861,61 @@ namespace CopyCtorMutable {
// both-note {{in call}}
}
+
+namespace NonTrivialCtor {
+ struct A { int x = 1; constexpr int f() { return 1; } };
+ struct B : A { int y = 1; constexpr int g() { return 2; } };
+ struct C {
+ int x;
+ constexpr virtual int f() = 0;
+ };
+ struct D : C {
+ int y;
+ constexpr virtual int f() override { return 3; }
+ };
+
+ union U {
+ int n;
+ B b;
+ D d;
+ };
+
+ consteval int test(int which) {
+ if (which == 0) {}
+
+ U u{.n = 5};
+ assert_active(u);
+ assert_active(u.n);
+ assert_inactive(u.b);
+
+ switch (which) {
+ case 0:
+ u.b.x = 10; // both-note {{assignment to member 'b' of union with active member 'n'}}
+ return u.b.f();
+ case 1:
+ u.b.y = 10; // both-note {{assignment to member 'b' of union with active member 'n'}}
+ return u.b.g();
+ case 2:
+ u.d.x = 10; // both-note {{assignment to member 'd' of union with active member 'n'}}
+ return u.d.f();
+ case 3:
+ u.d.y = 10; // both-note {{assignment to member 'd' of union with active member 'n'}}
+ return u.d.f();
+ }
+
+ return 1;
+ }
+ static_assert(test(0)); // both-error {{not an integral constant expression}} \
+ // both-note {{in call}}
+ static_assert(test(1)); // both-error {{not an integral constant expression}} \
+ // both-note {{in call}}
+ static_assert(test(2)); // both-error {{not an integral constant expression}} \
+ // both-note {{in call}}
+ static_assert(test(3)); // both-error {{not an integral constant expression}} \
+ // both-note {{in call}}
+
+}
+
#endif
namespace AddressComparison {
>From 67dd9f569a80ae2d3d2bb1673c86e000c9c9b900 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 22 Jul 2025 06:59:02 +0200
Subject: [PATCH 2/2] [clang][bytecode] Activate primitive fields before
initializing them
The initializer itself might need the field to be active.
---
clang/lib/AST/ByteCode/Compiler.cpp | 89 ++++++++++++++++-------------
clang/lib/AST/ByteCode/Compiler.h | 2 +
clang/lib/AST/ByteCode/Interp.h | 10 ++++
clang/lib/AST/ByteCode/Opcodes.td | 1 +
clang/test/AST/ByteCode/unions.cpp | 17 +++++-
5 files changed, 77 insertions(+), 42 deletions(-)
diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index e760055a8d235..63ac536c2b445 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -25,41 +25,6 @@ using APSInt = llvm::APSInt;
namespace clang {
namespace interp {
-static bool hasTrivialDefaultCtorParent(const FieldDecl *FD) {
- assert(FD);
- assert(FD->getParent()->isUnion());
- const auto *CXXRD = dyn_cast<CXXRecordDecl>(FD->getParent());
- return !CXXRD || CXXRD->hasTrivialDefaultConstructor();
-}
-
-static bool refersToUnion(const Expr *E) {
- for (;;) {
- if (const auto *ME = dyn_cast<MemberExpr>(E)) {
- if (const auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
- FD && FD->getParent()->isUnion() && hasTrivialDefaultCtorParent(FD))
- return true;
- E = ME->getBase();
- continue;
- }
-
- if (const auto *ASE = dyn_cast<ArraySubscriptExpr>(E)) {
- E = ASE->getBase()->IgnoreImplicit();
- continue;
- }
-
- if (const auto *ICE = dyn_cast<ImplicitCastExpr>(E);
- ICE && (ICE->getCastKind() == CK_NoOp ||
- ICE->getCastKind() == CK_DerivedToBase ||
- ICE->getCastKind() == CK_UncheckedDerivedToBase)) {
- E = ICE->getSubExpr();
- continue;
- }
-
- break;
- }
- return false;
-}
-
static std::optional<bool> getBoolValue(const Expr *E) {
if (const auto *CE = dyn_cast_if_present<ConstantExpr>(E);
CE && CE->hasAPValueResult() &&
@@ -5408,6 +5373,53 @@ bool Compiler<Emitter>::maybeEmitDeferredVarInit(const VarDecl *VD) {
return true;
}
+static bool hasTrivialDefaultCtorParent(const FieldDecl *FD) {
+ assert(FD);
+ assert(FD->getParent()->isUnion());
+ const auto *CXXRD = dyn_cast<CXXRecordDecl>(FD->getParent());
+ return !CXXRD || CXXRD->hasTrivialDefaultConstructor();
+}
+
+template <class Emitter> bool Compiler<Emitter>::refersToUnion(const Expr *E) {
+ for (;;) {
+ if (const auto *ME = dyn_cast<MemberExpr>(E)) {
+ if (const auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
+ FD && FD->getParent()->isUnion() && hasTrivialDefaultCtorParent(FD))
+ return true;
+ E = ME->getBase();
+ continue;
+ }
+
+ if (const auto *ASE = dyn_cast<ArraySubscriptExpr>(E)) {
+ E = ASE->getBase()->IgnoreImplicit();
+ continue;
+ }
+
+ if (const auto *ICE = dyn_cast<ImplicitCastExpr>(E);
+ ICE && (ICE->getCastKind() == CK_NoOp ||
+ ICE->getCastKind() == CK_DerivedToBase ||
+ ICE->getCastKind() == CK_UncheckedDerivedToBase)) {
+ E = ICE->getSubExpr();
+ continue;
+ }
+
+ if (const auto *This = dyn_cast<CXXThisExpr>(E)) {
+ const auto *ThisRecord =
+ This->getType()->getPointeeType()->getAsRecordDecl();
+ if (!ThisRecord->isUnion())
+ return false;
+ // Otherwise, always activate if we're in the ctor.
+ if (const auto *Ctor =
+ dyn_cast_if_present<CXXConstructorDecl>(CompilingFunction))
+ return Ctor->getParent() == ThisRecord;
+ return false;
+ }
+
+ break;
+ }
+ return false;
+}
+
template <class Emitter>
bool Compiler<Emitter>::visitDeclStmt(const DeclStmt *DS,
bool EvaluateConditionDecl) {
@@ -5940,16 +5952,15 @@ bool Compiler<Emitter>::compileConstructor(const CXXConstructorDecl *Ctor) {
return false;
if (OptPrimType T = this->classify(InitExpr)) {
+ if (Activate && !this->emitActivateThisField(FieldOffset, InitExpr))
+ return false;
+
if (!this->visit(InitExpr))
return false;
bool BitField = F->isBitField();
- if (BitField && Activate)
- return this->emitInitThisBitFieldActivate(*T, F, FieldOffset, InitExpr);
if (BitField)
return this->emitInitThisBitField(*T, F, FieldOffset, InitExpr);
- if (Activate)
- return this->emitInitThisFieldActivate(*T, FieldOffset, InitExpr);
return this->emitInitThisField(*T, FieldOffset, InitExpr);
}
// Non-primitive case. Get a pointer to the field-to-initialize
diff --git a/clang/lib/AST/ByteCode/Compiler.h b/clang/lib/AST/ByteCode/Compiler.h
index 503269399c757..3a263429a0e15 100644
--- a/clang/lib/AST/ByteCode/Compiler.h
+++ b/clang/lib/AST/ByteCode/Compiler.h
@@ -401,6 +401,8 @@ class Compiler : public ConstStmtVisitor<Compiler<Emitter>, bool>,
bool checkLiteralType(const Expr *E);
bool maybeEmitDeferredVarInit(const VarDecl *VD);
+ bool refersToUnion(const Expr *E);
+
protected:
/// Variable to storage mapping.
llvm::DenseMap<const ValueDecl *, Scope::Local> Locals;
diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 7f29200f8617f..a234f8ebf0c82 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -1983,6 +1983,16 @@ static inline bool Activate(InterpState &S, CodePtr OpPC) {
return true;
}
+static inline bool ActivateThisField(InterpState &S, CodePtr OpPC, uint32_t I) {
+ if (S.checkingPotentialConstantExpression())
+ return false;
+
+ const Pointer &Ptr = S.Current->getThis();
+ assert(Ptr.atField(I).canBeInitialized());
+ Ptr.atField(I).activate();
+ return true;
+}
+
template <PrimType Name, class T = typename PrimConv<Name>::T>
bool StoreActivate(InterpState &S, CodePtr OpPC) {
const T &Value = S.Stk.pop<T>();
diff --git a/clang/lib/AST/ByteCode/Opcodes.td b/clang/lib/AST/ByteCode/Opcodes.td
index 80703ad72d954..abfed77750f87 100644
--- a/clang/lib/AST/ByteCode/Opcodes.td
+++ b/clang/lib/AST/ByteCode/Opcodes.td
@@ -510,6 +510,7 @@ def StoreBitFieldActivate : StoreBitFieldOpcode {}
def StoreBitFieldActivatePop : StoreBitFieldOpcode {}
def Activate : Opcode {}
+def ActivateThisField : Opcode { let Args = [ArgUint32]; }
// [Pointer, Value] -> []
def Init : StoreOpcode {}
diff --git a/clang/test/AST/ByteCode/unions.cpp b/clang/test/AST/ByteCode/unions.cpp
index ae71776353cf0..139e318e1ba68 100644
--- a/clang/test/AST/ByteCode/unions.cpp
+++ b/clang/test/AST/ByteCode/unions.cpp
@@ -79,10 +79,9 @@ namespace DefaultInit {
constexpr U1 u1; /// OK.
- constexpr int foo() { // expected-error {{never produces a constant expression}}
+ constexpr int foo() {
U1 u;
- return u.a; // both-note {{read of member 'a' of union with active member 'b'}} \
- // expected-note {{read of member 'a' of union with active member 'b'}}
+ return u.a; // both-note {{read of member 'a' of union with active member 'b'}}
}
static_assert(foo() == 42); // both-error {{not an integral constant expression}} \
// both-note {{in call to}}
@@ -916,6 +915,18 @@ namespace NonTrivialCtor {
}
+namespace PrimitiveFieldInitActivates {
+ /// The initializer of a needs the field to be active _before_ it's visited.
+ template<int> struct X {};
+ union V {
+ int a, b;
+ constexpr V(X<0>) : a(a = 1) {} // ok
+ constexpr V(X<2>) : a() { b = 1; } // ok
+ };
+ constinit V v0 = X<0>();
+ constinit V v2 = X<2>();
+}
+
#endif
namespace AddressComparison {
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