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From: Patrick Palka <ppalka@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-7802] c++: missing SFINAE for non-constant consteval calls [PR104620] Date: Thu, 24 Mar 2022 15:42:43 +0000 (GMT) [thread overview] Message-ID: <20220324154243.AA53B3858D3C@sourceware.org> (raw) https://gcc.gnu.org/g:647537adefb34041cc2d44585252fd765cc0daae commit r12-7802-g647537adefb34041cc2d44585252fd765cc0daae Author: Patrick Palka <ppalka@redhat.com> Date: Thu Mar 24 11:42:31 2022 -0400 c++: missing SFINAE for non-constant consteval calls [PR104620] Here we weren't respecting SFINAE when evaluating a call to a consteval function, which caused us to reject the new testcase below. This patch fixes this by making build_over_call use the SFINAE-friendly version of cxx_constant_value. This change causes us to no longer diagnose ahead of time a couple of non-constant non-dependent consteval calls in consteval-if2.C with -fchecking=2. These errors were apparently coming from the call to fold_non_dependent_expr in build_non_dependent_expr (for the RHS of the +=) despite complain=tf_none being passed. Now that build_over_call respects the value of complain during constant evaluation of a consteval call, the errors are gone. That the errors are also gone without -fchecking=2 is a regression caused by r12-7264-gc19f317a78c0e4 and is the subject of PR104620. As described in comment #5, I think it's basically an accident that we were diagnosing these two calls correctly before r12-7264, so perhaps we can live without these errors for GCC 12. Thus this patch just XFAILs the two tests. PR c++/104620 gcc/cp/ChangeLog: * call.cc (build_over_call): Use cxx_constant_value_sfinae instead of cxx_constant_value to evaluate a consteval call. * constexpr.cc (cxx_constant_value_sfinae): Add decl parameter and pass it to cxx_eval_outermost_constant_expr. * cp-tree.h (cxx_constant_value_sfinae): Add decl parameter. * pt.cc (fold_targs_r): Pass NULL_TREE as decl parameter to cxx_constant_value_sfinae. gcc/testsuite/ChangeLog: * g++.dg/cpp23/consteval-if2.C: XFAIL two dg-error tests where the argument to the non-constant non-dependent consteval call is wrapped by NON_DEPENDENT_EXPR. * g++.dg/cpp2a/consteval30.C: New test. Diff: --- gcc/cp/call.cc | 2 +- gcc/cp/constexpr.cc | 4 ++-- gcc/cp/cp-tree.h | 2 +- gcc/cp/pt.cc | 2 +- gcc/testsuite/g++.dg/cpp23/consteval-if2.C | 4 ++-- gcc/testsuite/g++.dg/cpp2a/consteval30.C | 12 ++++++++++++ 6 files changed, 19 insertions(+), 7 deletions(-) diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index 23d3fc496b8..ec6c5d5baa2 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -9939,7 +9939,7 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain) obj_arg = TREE_OPERAND (addr, 0); } } - call = cxx_constant_value (call, obj_arg); + call = cxx_constant_value_sfinae (call, obj_arg, complain); if (obj_arg && !error_operand_p (call)) call = build2 (INIT_EXPR, void_type_node, obj_arg, call); call = convert_from_reference (call); diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index ce4ef8edfac..778680b8270 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -7960,10 +7960,10 @@ cxx_constant_value (tree t, tree decl) /* As above, but respect SFINAE. */ tree -cxx_constant_value_sfinae (tree t, tsubst_flags_t complain) +cxx_constant_value_sfinae (tree t, tree decl, tsubst_flags_t complain) { bool sfinae = !(complain & tf_error); - tree r = cxx_eval_outermost_constant_expr (t, sfinae, true, true); + tree r = cxx_eval_outermost_constant_expr (t, sfinae, true, true, false, decl); if (sfinae && !TREE_CONSTANT (r)) r = error_mark_node; return r; diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 1bd7bc6fca2..2f718852ac1 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -8414,7 +8414,7 @@ extern bool require_constant_expression (tree); extern bool require_rvalue_constant_expression (tree); extern bool require_potential_rvalue_constant_expression (tree); extern tree cxx_constant_value (tree, tree = NULL_TREE); -extern tree cxx_constant_value_sfinae (tree, tsubst_flags_t); +extern tree cxx_constant_value_sfinae (tree, tree, tsubst_flags_t); extern void cxx_constant_dtor (tree, tree); extern tree cxx_constant_init (tree, tree = NULL_TREE); extern tree maybe_constant_value (tree, tree = NULL_TREE, bool = false); diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index 715eea27577..173bc3a8c7f 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -19811,7 +19811,7 @@ fold_targs_r (tree targs, tsubst_flags_t complain) && !glvalue_p (elt) && !TREE_CONSTANT (elt)) { - elt = cxx_constant_value_sfinae (elt, complain); + elt = cxx_constant_value_sfinae (elt, NULL_TREE, complain); if (elt == error_mark_node) return false; } diff --git a/gcc/testsuite/g++.dg/cpp23/consteval-if2.C b/gcc/testsuite/g++.dg/cpp23/consteval-if2.C index f7053b91c3c..d1845da9e58 100644 --- a/gcc/testsuite/g++.dg/cpp23/consteval-if2.C +++ b/gcc/testsuite/g++.dg/cpp23/consteval-if2.C @@ -77,11 +77,11 @@ qux (int x) } else { - r += foo (8 * x); // { dg-error "is not a constant expression" } + r += foo (8 * x); // { dg-error "is not a constant expression" "" { xfail *-*-* } } } if ! consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } } { - r += foo (32 * x);// { dg-error "is not a constant expression" } + r += foo (32 * x);// { dg-error "is not a constant expression" "" { xfail *-*-* } } } if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } } { diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval30.C b/gcc/testsuite/g++.dg/cpp2a/consteval30.C new file mode 100644 index 00000000000..035265e019c --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/consteval30.C @@ -0,0 +1,12 @@ +// Test SFINAE for a non-constant consteval call. +// { dg-do compile { target c++20 } } + +consteval int deref(const int* x) { return *x; } + +template<const int* P, int = deref(P)> // { dg-bogus "null pointer" } +constexpr int f(int) { return 0; } + +template<const int* P> +constexpr int f(...) { return 1; } + +static_assert(f<nullptr>(0) == 1);
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