Hi Jason,
On 3 Dec 2024, at 22:37, Jason Merrill wrote:
> On 12/3/24 12:25 PM, Simon Martin wrote:
>> 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.
>>
>> Successfully tested on x86_64-pc-linux-gnu.
>>
>> 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.
>>
>> ---
>> gcc/cp/constexpr.cc | 27
>> ++++++++++++-------
>> .../g++.dg/cpp2a/constexpr-virtual22.C | 22 +++++++++++++++
>> 2 files changed, 40 insertions(+), 9 deletions(-)
>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-virtual22.C
>>
>> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
>> index 5a87fa485c6..d9636bad683 100644
>> --- a/gcc/cp/constexpr.cc
>> +++ b/gcc/cp/constexpr.cc
>> @@ -8277,15 +8277,24 @@ cxx_eval_constant_expression (const
>> constexpr_ctx *ctx, tree t,
>> }
>> else
>> {
>> - /* This detects for example:
>> - reinterpret_cast<void*>(sizeof 0)
>> - */
>> - if (!ctx->quiet)
>> - error_at (loc, "%<reinterpret_cast<%T>(%E)%> is not "
>> - "a constant expression",
>> - type, op);
>> - *non_constant_p = true;
>> - return t;
>> + 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. */
>> + ;
>
> This could be "else if" added before the existing else so it doesn't
> need to be reindented. OK with that change.
Thanks, merged as r15-5920-g72a2380a306a1c with the suggested change.
Since this is a reject-valid, also OK for active branches?
Simon
