[Bug c++/123495] [14/15/16/17 Regressio n] ICE: unexpected expression ‘(int (*)())( 0)’ of kind cast_expr in cxx_eval_constant_ expression within template during nodiscard c heck since r14-4793

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123495

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <[email protected]>:

https://gcc.gnu.org/g:0e74517b70d06105bd40c8caa6dc192b4af3ccff

commit r17-3301-g0e74517b70d06105bd40c8caa6dc192b4af3ccff
Author: Patrick Palka <[email protected]>
Date:   Fri Aug 14 14:33:46 2026 -0400

    c++: ICE w/ maybe_warn_nodiscard on non-dep call [PR123495, PR126860]

    Another latent issue uncovered by the NON_DEPENDENT_EXPR removal.
    cp_get_fndecl_from_callee, called from maybe_warn_nodiscard, tries to
    fold the templated callee via constant evaluation, but constant
    evaluation expects non-templated trees.  So use fold_non_dependent_expr
    which instantiates templated trees beforehand.  We could use f_n_d_init
    also but there should be no difference for a result that doesn't end up
    as NULL_TREE.

            PR c++/123495
            PR c++/126860

    gcc/cp/ChangeLog:

            * cvt.cc (cp_get_fndecl_from_callee): Use fold_non_dependent_expr
            instead of maybe_constant_init.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/non-dependent36.C: New test.
            * g++.dg/template/non-dependent37.C: New test.

    Reviewed-by: Jason Merrill <[email protected]>