[Bug c++/97975] [8/9/10 Regression] ICE unexpected expression '(int)A< <template-parameter-1-1> >::b' of kind implicit_conv_expr

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97975

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Marek Polacek
<mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:d0684e49ee8d859fc527b22aaaaed206930371a3

commit r10-9207-gd0684e49ee8d859fc527b22aaaaed206930371a3
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Dec 1 10:39:08 2020 -0500

    c++: Fix ICE with inline variable in template [PR97975]

    In this test, we have

      static inline const int c = b;

    in a class template, and we call store_init_value as usual.  There, the
    value is

      IMPLICIT_CONV_EXPR<const float>(b)

    which is is_nondependent_static_init_expression but isn't
    is_nondependent_constant_expression (they only differ in STRICT).
    We call fold_non_dependent_expr, but that just returns the expression
    because it only instantiates is_nondependent_constant_expression
    expressions.  Since we're not checking the initializer of a constexpr
    variable, we go on to call maybe_constant_init, whereupon we crash
    because it tries to evaluate all is_nondependent_static_init_expression
    expressions, which our value is, but it still contains a template code.

    I think the fix is to call fold_non_dependent_init instead of
    maybe_constant_init, and only call fold_non_dependent_expr on the
    "this is a constexpr variable" path so as to avoid instantiating twice
    in a row.  Outside a template this should also avoid evaluating the
    value twice.

    gcc/cp/ChangeLog:

            PR c++/97975
            * constexpr.c (fold_non_dependent_init): Add a tree parameter.
            Use it.
            * cp-tree.h (fold_non_dependent_init): Add a tree parameter with
            a default value.
            * typeck2.c (store_init_value): Call fold_non_dependent_expr
            only when checking the initializer for constexpr variables.
            Call fold_non_dependent_init instead of maybe_constant_init.

    gcc/testsuite/ChangeLog:

            PR c++/97975
            * g++.dg/cpp1z/inline-var8.C: New test.

    (cherry picked from commit 69bf1c7d5ee21392334f1982d1b40c38e103bbd4)