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[clang] Fix constant evaluation of member pointer access into sibling class. #150829

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Merged
merged 2 commits into from
Aug 5, 2025
Merged

[clang] Fix constant evaluation of member pointer access into sibling class. #150829

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16b4c18
[clang] Fix constant evaluation of member pointer access to member of…
keinflue Jul 27, 2025
8478f70
Address improved documentation requests from review
keinflue Jul 29, 2025
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10 changes: 10 additions & 0 deletions clang/lib/AST/ExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5051,6 +5051,16 @@ static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
return nullptr;
}
}
// Consider member in a sibling.
const CXXRecordDecl *LastLVDecl =
(PathLengthToMember > LV.Designator.MostDerivedPathLength)
? getAsBaseClass(LV.Designator.Entries[PathLengthToMember - 1])
: LV.Designator.MostDerivedType->getAsCXXRecordDecl();
const CXXRecordDecl *LastMPDecl = MemPtr.getContainingRecord();
if (LastLVDecl->getCanonicalDecl() != LastMPDecl->getCanonicalDecl()) {
Info.FFDiag(RHS);
return nullptr;
}

// Truncate the lvalue to the appropriate derived class.
if (!CastToDerivedClass(Info, RHS, LV, MemPtr.getContainingRecord(),
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18 changes: 18 additions & 0 deletions clang/test/SemaCXX/constant-expression-cxx11.cpp
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Expand Up @@ -1210,6 +1210,24 @@ namespace MemberPointer {
return (a.*f)();
}
static_assert(apply(A(2), &A::f) == 5, "");

struct C { };
struct D : C {
constexpr int f() const { return 1; };
};
struct E : C { };
struct F : D { };
constexpr C c1, c2[2];
constexpr D d1, d2[2];
constexpr E e1, e2[2];
constexpr F f;
static_assert((c1.*(static_cast<int (C::*)() const>(&D::f)))() == 1, ""); // expected-error {{constant expression}}
static_assert((d1.*(static_cast<int (C::*)() const>(&D::f)))() == 1, "");
static_assert((e1.*(static_cast<int (C::*)() const>(&D::f)))() == 1, ""); // expected-error {{constant expression}}
static_assert((f.*(static_cast<int (C::*)() const>(&D::f)))() == 1, "");
static_assert((c2[0].*(static_cast<int (C::*)() const>(&D::f)))() == 1, ""); // expected-error {{constant expression}}
static_assert((d2[0].*(static_cast<int (C::*)() const>(&D::f)))() == 1, "");
static_assert((e2[0].*(static_cast<int (C::*)() const>(&D::f)))() == 1, ""); // expected-error {{constant expression}}
}

namespace ArrayBaseDerived {
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13 changes: 13 additions & 0 deletions clang/test/SemaCXX/constant-expression-cxx2a.cpp
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Expand Up @@ -1497,3 +1497,16 @@ namespace GH67317 {
// expected-note {{subobject of type 'const unsigned char' is not initialized}}
__builtin_bit_cast(unsigned char, *new char[3][1]);
};

namespace GH150705 {
struct A { };
struct B : A { };
struct C : A {
constexpr virtual int foo() const { return 0; }
};
constexpr auto p = &C::foo;
constexpr auto q = static_cast<int (A::*)() const>(p);
constexpr B b;
constexpr const A& a = b;
constexpr auto x = (a.*q)(); // expected-error {{constant expression}}
}