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c++: Don't reject pointer to virtual method during constant evaluation [PR117615]

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We currently reject the following valid code:

=== cut here ===
struct Base {
    virtual void doit (int v) const {}
};
struct Derived : Base {
    void doit (int v) const {}
};
using fn_t = void (Base::*)(int) const;
struct Helper {
    fn_t mFn;
    constexpr Helper (auto && fn) : mFn(static_cast<fn_t>(fn)) {}
};
void foo () {
    constexpr Helper h (&Derived::doit);
}
=== cut here ===

The problem is that since r6-4014-gdcdbc004d531b4, &Derived::doit is
represented with an expression with type pointer to method and using an
INTEGER_CST (here 1), and that cxx_eval_constant_expression rejects any
such expression with a non-null INTEGER_CST.

This patch uses the same strategy as r12-4491-gf45610a45236e9 (fix for
PR c++/102786), and simply lets such expressions go through.

	PR c++/117615

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_constant_expression): Don't reject
	INTEGER_CSTs with type POINTER_TYPE to METHOD_TYPE.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/constexpr-virtual22.C: New test.
This commit is contained in:
Simon Martin 2024-12-03 14:30:43 +01:00
parent 2055919192
commit 72a2380a30
2 changed files with 28 additions and 0 deletions
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6
gcc/cp/constexpr.cc
View file

@ -8275,6 +8275,12 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
return t;
}
}
else if (TYPE_PTR_P (type)
&& TREE_CODE (TREE_TYPE (type)) == METHOD_TYPE)
/* INTEGER_CST with pointer-to-method type is only used
for a virtual method in a pointer to member function.
Don't reject those. */
;
else
{
/* This detects for example:

22
gcc/testsuite/g++.dg/cpp2a/constexpr-virtual22.C Normal file
View file

@ -0,0 +1,22 @@
// PR c++/117615
// { dg-do "compile" { target c++20 } }
struct Base {
virtual void doit (int v) const {}
};
struct Derived : Base {
void doit (int v) const {}
};
using fn_t = void (Base::*)(int) const;
struct Helper {
fn_t mFn;
constexpr Helper (auto && fn) : mFn(static_cast<fn_t>(fn)) {}
};
void foo () {
constexpr Helper h (&Derived::doit);
constexpr Helper h2 (&Base::doit);
}