From f45610a45236e97616726ca042898d6ac46a082e Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Tue, 19 Oct 2021 09:24:57 +0200 Subject: [PATCH] c++: Don't reject calls through PMF during constant evaluation [PR102786] The following testcase incorrectly rejects the c initializer, while in the s.*a case cxx_eval_* sees .__pfn reads etc., in the s.*&S::foo case get_member_function_from_ptrfunc creates expressions which use INTEGER_CSTs with type of pointer to METHOD_TYPE. And cxx_eval_constant_expression rejects any INTEGER_CSTs with pointer type if they aren't 0. Either we'd need to make sure we defer such folding till cp_fold but the function and pfn_from_ptrmemfunc is used from lots of places, or the following patch just tries to reject only non-zero INTEGER_CSTs with pointer types if they don't point to METHOD_TYPE in the hope that all such INTEGER_CSTs with POINTER_TYPE to METHOD_TYPE are result of folding valid pointer-to-member function expressions. I don't immediately see how one could create such INTEGER_CSTs otherwise, cast of integers to PMF is rejected and would have the PMF RECORD_TYPE anyway, etc. 2021-10-19 Jakub Jelinek PR c++/102786 * constexpr.c (cxx_eval_constant_expression): Don't reject INTEGER_CSTs with type POINTER_TYPE to METHOD_TYPE. * g++.dg/cpp2a/constexpr-virtual19.C: New test. --- gcc/cp/constexpr.c | 4 ++++ gcc/testsuite/g++.dg/cpp2a/constexpr-virtual19.C | 11 +++++++++++ 2 files changed, 15 insertions(+) create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-virtual19.C diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index c5f01b954703..6f83d303cdd7 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -6191,6 +6191,10 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t, if (TREE_CODE (t) == INTEGER_CST && TYPE_PTR_P (TREE_TYPE (t)) + /* INTEGER_CST with pointer-to-method type is only used + for a virtual method in a pointer to member function. + Don't reject those. */ + && TREE_CODE (TREE_TYPE (TREE_TYPE (t))) != METHOD_TYPE && !integer_zerop (t)) { if (!ctx->quiet) diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual19.C b/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual19.C new file mode 100644 index 000000000000..cb0d1bed0b12 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual19.C @@ -0,0 +1,11 @@ +// PR c++/102786 +// { dg-do compile { target c++20 } } + +struct S { + virtual constexpr int foo () const { return 42; } +}; + +constexpr S s; +constexpr auto a = &S::foo; +constexpr auto b = (s.*a) (); +constexpr auto c = (s.*&S::foo) ();