On Thu, Mar 10, 2022 at 05:04:59PM -0500, Marek Polacek via Gcc-patches wrote:
> Since r9-6073 cxx_eval_store_expression preevaluates the value to
> be stored, and that revealed a crash where a template code (here,
> code=IMPLICIT_CONV_EXPR) leaks into cxx_eval*.
>
> It happens because we're performing build_vec_init while processing
> a template, which calls get_temp_regvar which creates an INIT_EXPR.
> This INIT_EXPR's RHS contains an rvalue conversion so we create an
> IMPLICIT_CONV_EXPR. Its operand is not type-dependent and the whole
> INIT_EXPR is not type-dependent. So we call build_non_dependent_expr
> which, with -fchecking=2, calls fold_non_dependent_expr. At this
> point the expression still has an IMPLICIT_CONV_EXPR, which ought to
> be handled in instantiate_non_dependent_expr_internal. However,
> tsubst_copy_and_build doesn't handle INIT_EXPR; it will just call
> tsubst_copy which does nothing when args is null. So we fail to
> replace the IMPLICIT_CONV_EXPR and ICE.
Forgot to mention: without -fchecking=2 there's no problem because
digest_init will subst the IMPLICIT_CONV_EXPR:
#0 tsubst_copy_and_build (t=<implicit_conv_expr 0x7fffea4a9f20>, args=<tree
0x0>, complain=3,
in_decl=<tree 0x0>, function_p=false, integral_constant_expression_p=true)
at /home/mpolacek/src/gcc/gcc/cp/pt.cc:20063
#1 0x0000000000de1ae1 in instantiate_non_dependent_expr_internal
(expr=<implicit_conv_expr 0x7fffea4a9f20>,
complain=3) at /home/mpolacek/src/gcc/gcc/cp/pt.cc:6358
#2 0x0000000000b702d4 in fold_non_dependent_expr_template
(t=<implicit_conv_expr 0x7fffea4a9f20>,
complain=3, manifestly_const_eval=false, object=<tree 0x0>)
at /home/mpolacek/src/gcc/gcc/cp/constexpr.cc:8050
#3 0x0000000000b706f0 in fold_non_dependent_init (t=<implicit_conv_expr
0x7fffea4a9f20>, complain=3,
manifestly_const_eval=false, object=<tree 0x0>) at
/home/mpolacek/src/gcc/gcc/cp/constexpr.cc:8143
#4 0x0000000000f08f4f in massage_init_elt (type=<record_type 0x7fffea4b29d8
S>,
init=<implicit_conv_expr 0x7fffea4a9f20>, nested=0, flags=257, complain=3)
at /home/mpolacek/src/gcc/gcc/cp/typeck2.cc:1437
#5 0x0000000000f0949c in process_init_constructor_array (type=<array_type
0x7fffea4c9348>,
init=<constructor 0x7fffea4bfb10>, nested=0, flags=257, complain=3)
at /home/mpolacek/src/gcc/gcc/cp/typeck2.cc:1502
#6 0x0000000000f0aec1 in process_init_constructor (type=<array_type
0x7fffea4c9348>,
init=<constructor 0x7fffea4bfb10>, nested=0, flags=257, complain=3)
at /home/mpolacek/src/gcc/gcc/cp/typeck2.cc:1917
#7 0x0000000000f0890c in digest_init_r (type=<array_type 0x7fffea4c9348>,
init=<constructor 0x7fffea4bfb10>, nested=0, flags=257, complain=3)
at /home/mpolacek/src/gcc/gcc/cp/typeck2.cc:1324
#8 0x0000000000f08b1b in digest_init_flags (type=<array_type 0x7fffea4c9348>,
init=<constructor 0x7fffea4bfb10>, flags=257, complain=3)
at /home/mpolacek/src/gcc/gcc/cp/typeck2.cc:1370
#9 0x0000000000f06815 in store_init_value (decl=<var_decl 0x7fffea357cf0 s>,
init=<constructor 0x7fffea4bfb10>, cleanups=0x7fffffffba68, flags=257)
at /home/mpolacek/src/gcc/gcc/cp/typeck2.cc:842
#10 0x0000000000bf56cc in check_initializer (decl=<var_decl 0x7fffea357cf0 s>,
init=<constructor 0x7fffea4bfb10>, flags=257, cleanups=0x7fffffffba68)
at /home/mpolacek/src/gcc/gcc/cp/decl.cc:7337
#11 0x0000000000bfa8df in cp_finish_decl (decl=<var_decl 0x7fffea357cf0 s>,
init=<constructor 0x7fffea4bfac8>, init_const_expr_p=true,
asmspec_tree=<tree 0x0>, flags=1)
at /home/mpolacek/src/gcc/gcc/cp/decl.cc:8174
> Eliding the IMPLICIT_CONV_EXPR in this particular case would be too
> risky, so we could do
>
> if (TREE_CODE (t) == INIT_EXPR)
> t = TREE_OPERAND (t, 1);
>
> in fold_non_dependent_expr, but that feels too ad hoc. So it might
> make sense to actually take care of INIT_EXPR in tsubst_c_and_b.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11?
>
> PR c++/104284
>
> gcc/cp/ChangeLog:
>
> * pt.cc (tsubst_copy_and_build): Handle INIT_EXPR.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp1y/constexpr-104284.C: New test.
> ---
> gcc/cp/pt.cc | 8 ++++++++
> gcc/testsuite/g++.dg/cpp1y/constexpr-104284.C | 17 +++++++++++++++++
> 2 files changed, 25 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-104284.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index f7ee33a6dfd..e8920f98e4d 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -21289,6 +21289,14 @@ tsubst_copy_and_build (tree t,
> with constant operands. */
> RETURN (t);
>
> + case INIT_EXPR:
> + {
> + tree op0 = RECUR (TREE_OPERAND (t, 0));
> + tree op1 = RECUR (TREE_OPERAND (t, 1));
> + RETURN (build2_loc (input_location, INIT_EXPR, TREE_TYPE (op0),
> + op0, op1));
> + }
> +
> case NON_LVALUE_EXPR:
> case VIEW_CONVERT_EXPR:
> if (location_wrapper_p (t))
> diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284.C
> b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284.C
> new file mode 100644
> index 00000000000..f60033069e4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284.C
> @@ -0,0 +1,17 @@
> +// PR c++/104284
> +// { dg-do compile { target c++14 } }
> +// { dg-additional-options "-fchecking=2" }
> +
> +struct S {
> + char c{};
> +};
> +
> +auto x = [](auto) { constexpr S s[]{{}}; };
> +
> +template<class>
> +constexpr void gn ()
> +{
> + constexpr S s[]{{}};
> +}
> +
> +static_assert ((gn<int>(), true), "");
>
> base-commit: b5417a0ba7e26bec2abf05cad6c6ef840a9be41c
> --
> 2.35.1
>
Marek
