On Thu, 12 Nov 2020, Jason Merrill wrote:
> On 11/12/20 1:27 PM, Patrick Palka wrote:
> > The atom_cache in normalize_atom relies on the assumption that two
> > equivalent (templated) trees (in the sense of cp_tree_equal) must use
> > the same template parameters (according to find_template_parameters).
> >
> > This assumption unfortunately doesn't always hold for TARGET_EXPRs,
> > because cp_tree_equal ignores an artificial target of a TARGET_EXPR, but
> > find_template_parameters walks this target (and its DECL_CONTEXT).
> >
> > Hence two TARGET_EXPRs built by force_target_expr with the same
> > initializer but under different settings of current_function_decl may
> > compare equal according to cp_tree_equal, but find_template_parameters
> > returns a different set of template parameters for them. This breaks
> > the below testcase because during normalization we build two such
> > TARGET_EXPRs (one under current_function_decl=f and another under =g),
> > and then use the same ATOMIC_CONSTR for the two corresponding atoms,
> > leading to a crash during satisfaction of g's associated constraints.
> >
> > This patch works around this assumption violation by removing the source
> > of these templated TARGET_EXPRs. The relevant call to get_target_expr was
> > added in r9-6043, but it seems it's no longer necessary (according to
> > https://gcc.gnu.org/pipermail/gcc-patches/2019-February/517323.html, the
> > call was added in order to avoid regressing on initlist109.C at the time).
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > trunk?
>
> OK. I wonder what else asserting !processing_template_decl in
> build_target_expr would find...
FWIW, testing exposed seven distinct paths that trigger such an assert,
five of which go through build_cplus_new:
0x6b3983 build_target_expr
/gcc/gcc/cp/tree.c:496
0xa94ec8 build_cplus_new(tree_node*, tree_node*, int)
/gcc/gcc/cp/tree.c:728
0x91712b force_rvalue(tree_node*, int)
/gcc/gcc/cp/cvt.c:569
0x8b8310 build_conditional_expr_1
/gcc/gcc/cp/call.c:5592
0x8ba08c build_conditional_expr(op_location_t const&, tree_node*, tree_node*,
tree_node*, int)
/gcc/gcc/cp/call.c:5777
0xaa70fb build_x_conditional_expr(unsigned int, tree_node*, tree_node*,
tree_node*, int)
/gcc/gcc/cp/typeck.c:7133
0x9cc9fa cp_parser_assignment_expression
/gcc/gcc/cp/parser.c:9964
0x6b3983 build_target_expr
/gcc/gcc/cp/tree.c:496
0xa94ec8 build_cplus_new(tree_node*, tree_node*, int)
/gcc/gcc/cp/tree.c:728
0x97d185 expand_default_init
/gcc/gcc/cp/init.c:1924
0x97d185 expand_aggr_init_1
/gcc/gcc/cp/init.c:2101
0x97f026 build_aggr_init(tree_node*, tree_node*, int, int)
/gcc/gcc/cp/init.c:1835
0x92c88d build_aggr_init_full_exprs
/gcc/gcc/cp/decl.c:6696
0x92c88d check_initializer
/gcc/gcc/cp/decl.c:6857
0x950982 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int)
/gcc/gcc/cp/decl.c:7699
0x960c7e grokfield(cp_declarator const*, cp_decl_specifier_seq*, tree_node*,
bool, tree_node*, tree_node*)
/gcc/gcc/cp/decl2.c:1000
0xa02ceb cp_parser_member_declaration
/gcc/gcc/cp/parser.c:25755
0x6b3983 build_target_expr
/gcc/gcc/cp/tree.c:496
0xa94ee8 build_cplus_new(tree_node*, tree_node*, int)
/gcc/gcc/cp/tree.c:728
0x8a0ed5 build_cxx_call(tree_node*, int, tree_node**, int, tree_node*)
/gcc/gcc/cp/call.c:9747
0xabed0b cp_build_function_call_vec(tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int, tree_node*)
/gcc/gcc/cp/typeck.c:4025
0xa75a30 finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool,
bool, int)
/gcc/gcc/cp/semantics.c:2728
0x9e9383 cp_parser_postfix_expression
/gcc/gcc/cp/parser.c:7549
0x6b3983 build_target_expr
/gcc/gcc/cp/tree.c:496
0xa94ee8 build_cplus_new(tree_node*, tree_node*, int)
/gcc/gcc/cp/tree.c:728
0x8a0ed5 build_cxx_call(tree_node*, int, tree_node**, int, tree_node*)
/gcc/gcc/cp/call.c:9747
0xabed0b cp_build_function_call_vec(tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int, tree_node*)
/gcc/gcc/cp/typeck.c:4025
0x95eb40 build_offset_ref_call_from_tree(tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int)
/gcc/gcc/cp/decl2.c:5292
0x9e9b1f cp_parser_postfix_expression
/gcc/gcc/cp/parser.c:7534
0x6b3983 build_target_expr
/gcc/gcc/cp/tree.c:496
0xa94ec8 build_cplus_new(tree_node*, tree_node*, int)
/gcc/gcc/cp/tree.c:728
0x8b67c2 perform_direct_initialization_if_possible(tree_node*, tree_node*,
bool, int)
/gcc/gcc/cp/call.c:12038
0xaba6a9 build_static_cast_1
/gcc/gcc/cp/typeck.c:7607
0xabb500 build_static_cast(unsigned int, tree_node*, tree_node*, int)
/gcc/gcc/cp/typeck.c:7813
0x9e9f9e cp_parser_postfix_expression
/gcc/gcc/cp/parser.c:7049
0x6b3983 build_target_expr
/gcc/gcc/cp/tree.c:496
0x97fb53 build_new_1
/gcc/gcc/cp/init.c:3281
0x982382 build_new(unsigned int, vec<tree_node*, va_gc, vl_embed>**,
tree_node*, tree_node*, vec<tree_node*, va_gc, vl_embed>**, int, int)
/gcc/gcc/cp/init.c:3817
0x9f2107 cp_parser_new_expression
/gcc/gcc/cp/parser.c:8919
0x6b3983 build_target_expr
/gcc/gcc/cp/tree.c:496
0xaa2b0f get_target_expr(tree_node*)
/gcc/gcc/cp/tree.c:899
0xaa2b0f stabilize_expr(tree_node*, tree_node**)
/gcc/gcc/cp/tree.c:5509
0xabfa2a cp_build_modify_expr(unsigned int, tree_node*, tree_code, tree_node*,
int)
/gcc/gcc/cp/typeck.c:8736
0x8b7c91 build_new_op_1
/gcc/gcc/cp/call.c:6537
0x8b809d build_new_op(op_location_t const&, tree_code, int, tree_node*,
tree_node*, tree_node*, tree_node**, int)
/gcc/gcc/cp/call.c:6623
0xac0b04 build_x_modify_expr(unsigned int, tree_node*, tree_code, tree_node*,
int)
/gcc/gcc/cp/typeck.c:8936
0x9ccafe cp_parser_assignment_expression
/gcc/gcc/cp/parser.c:10002
>
> > gcc/cp/ChangeLog:
> >
> > * semantics.c (finish_compound_literal): Don't wrap the original
> > compound literal in a TARGET_EXPR when inside a template.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp2a/concepts-decltype3.C: New test.
> > ---
> > gcc/cp/semantics.c | 7 +------
> > gcc/testsuite/g++.dg/cpp2a/concepts-decltype3.C | 15 +++++++++++++++
> > 2 files changed, 16 insertions(+), 6 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-decltype3.C
> >
> > diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
> > index 33d715edaec..172286922e7 100644
> > --- a/gcc/cp/semantics.c
> > +++ b/gcc/cp/semantics.c
> > @@ -3006,12 +3006,7 @@ finish_compound_literal (tree type, tree
> > compound_literal,
> > /* If we're in a template, return the original compound literal. */
> > if (orig_cl)
> > - {
> > - if (!VECTOR_TYPE_P (type))
> > - return get_target_expr_sfinae (orig_cl, complain);
> > - else
> > - return orig_cl;
> > - }
> > + return orig_cl;
> > if (TREE_CODE (compound_literal) == CONSTRUCTOR)
> > {
> > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-decltype3.C
> > b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype3.C
> > new file mode 100644
> > index 00000000000..837855ce8ac
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype3.C
> > @@ -0,0 +1,15 @@
> > +// { dg-do compile { target c++20 } }
> > +
> > +template <class T> concept C = requires(T t) { t; };
> > +
> > +template <class T> using A = decltype((T{}, int{}));
> > +
> > +template <class T> concept D = C<A<T>>;
> > +
> > +template <class T, class U> void f() requires D<T>;
> > +template <class T> void g() requires D<T>;
> > +
> > +void h() {
> > + f<int, int>();
> > + g<int>();
> > +}
> >
>
>
