https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100102
--- Comment #23 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:f1feb74046e0feb0596b93bbb822fae02940a90e commit r11-8520-gf1feb74046e0feb0596b93bbb822fae02940a90e Author: Patrick Palka <ppa...@redhat.com> Date: Fri Jun 4 13:46:53 2021 -0400 c++: tsubst_function_decl and excess arg levels [PR100102] Here, when instantiating the dependent alias template duration::__is_harmonic with args={{T,U},{int}}, we find ourselves substituting the function decl _S_gcd. Since we have more arg levels than _S_gcd has parm levels, an old special case in tsubst_function_decl causes us to unwantedly reduce args to its innermost level, yielding args={int}, which leads to a nonsensical substitution into the decl context and eventually a crash. The comment for this special case refers to three examples for which we ought to see more arg levels than parm levels here, but none of the examples actually demonstrate this. In the first example, when defining S<int>::f(U) parms_depth is 2 and args_depth is 1, and later when instantiating say S<int>::f<char> both depths are 2. In the second example, when substituting the template friend declaration parms_depth is 2 and args_depth is 1, and later when instantiating f both depths are 1. Finally, the third example is invalid since we can't specialize a member template of an unspecialized class template like that. Given that this reduction code seems no longer relevant for its documented purpose and that it causes problems as in the PR, this patch just removes it. Note that as far as bootstrap/regtest is concerned, this code is dead; the below two tests would be the first to reach it. PR c++/100102 gcc/cp/ChangeLog: * pt.c (tsubst_function_decl): Remove old code for reducing args when it has excess levels. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/alias-decl-72.C: New test. * g++.dg/cpp0x/alias-decl-72a.C: New test. (cherry picked from commit 5357ab75dedef403b0eebf9277d61d1cbeb5898f)
