From 2499540e9abb55079b5f7b7ccdac97fbc63d9ab4 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Tue, 9 May 2023 16:05:22 +0200 Subject: c++: Reject pack expansion of assume attribute [PR109756] http://eel.is/c++draft/dcl.attr#grammar-4 says "In an attribute-list, an ellipsis may appear only if that attribute's specification permits it." and doesn't explicitly permit it on any standard attribute. The https://wg21.link/p1774r8 paper which introduced assume attribute says "We could therefore hypothetically permit the assume attribute to directly support pack expansion: template void f() { [[assume(args >= 0)...]]; } However, we do not propose this. It would require substantial additional work for a very rare use case. Note that this can instead be expressed with a fold expression, which is equivalent to the above and works out of the box without any extra effort: template void f() { [[assume(((args >= 0) && ...))]]; } ", but as the testcase shows, GCC 13+ ICEs on assume attribute followed by ... if it contains packs. The following patch rejects those instead of ICE and for C++17 or later suggests using fold expressions instead (it doesn't make sense to suggest it for C++14 and earlier when we'd error on the fold expressions). 2023-05-09 Jakub Jelinek PR c++/109756 * cp-gimplify.cc (process_stmt_assume_attribute): Diagnose pack expansion of assume attribute. * g++.dg/cpp23/attr-assume11.C: New test. --- gcc/cp/cp-gimplify.cc | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'gcc/cp') diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc index 1216ef1..216a623 100644 --- a/gcc/cp/cp-gimplify.cc +++ b/gcc/cp/cp-gimplify.cc @@ -3267,6 +3267,16 @@ process_stmt_assume_attribute (tree std_attrs, tree statement, for (; attr; attr = lookup_attribute ("gnu", "assume", TREE_CHAIN (attr))) { tree args = TREE_VALUE (attr); + if (args && PACK_EXPANSION_P (args)) + { + auto_diagnostic_group d; + error_at (attrs_loc, "pack expansion of %qE attribute", + get_attribute_name (attr)); + if (cxx_dialect >= cxx17) + inform (attrs_loc, "use fold expression in the attribute " + "argument instead"); + continue; + } int nargs = list_length (args); if (nargs != 1) { -- cgit v1.1