[PATCH] c++: Don't form a templated TARGET_EXPR in finish_compound_literal
Jason Merrill
jason@redhat.com
Tue Nov 24 23:12:03 GMT 2020
On 11/16/20 5:45 PM, Patrick Palka wrote:
> On Mon, 16 Nov 2020, Jason Merrill wrote:
>
>> On 11/13/20 10:43 AM, Patrick Palka wrote:
>>> 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:
>>
>> Most of these are built as part of overload resolution and then thrown away,
>> only using the result for its type. But I wonder about the build_aggr_init
>> instance.
>>
>>> 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
>>
>> This one gets discarded by build_x_conditional_expr.
>>
>>> 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
>>
>> This one looks dubious. Which testcase?
>
> IIRC many constexpr testcases trigger this one, for instance
> g++.dg/cpp0x/constexpr-initlist9.C and g++.dg/cpp0x/constexpr-static6.C:
>
> gcc/testsuite/g++.dg/cpp0x/constexpr-initlist9.C: In function ‘void generate_sudoku(T)’:
> gcc/testsuite/g++.dg/cpp0x/constexpr-initlist9.C:34:50: internal compiler error: in build_target_expr, at cp/tree.c:495
> 34 | constexpr auto positions = make_grid_positions(); // fail
> | ^
> 0x6b3c47 build_target_expr
> /home/patrick/code/gcc/gcc/cp/tree.c:495
> 0xa97248 build_cplus_new(tree_node*, tree_node*, int)
> /home/patrick/code/gcc/gcc/cp/tree.c:727
> 0x97eed5 expand_default_init
> /home/patrick/code/gcc/gcc/cp/init.c:1924
> 0x97eed5 expand_aggr_init_1
> /home/patrick/code/gcc/gcc/cp/init.c:2101
> 0x980d76 build_aggr_init(tree_node*, tree_node*, int, int)
> /home/patrick/code/gcc/gcc/cp/init.c:1835
> 0x92e5cd build_aggr_init_full_exprs
> /home/patrick/code/gcc/gcc/cp/decl.c:6696
> 0x92e5cd check_initializer
> /home/patrick/code/gcc/gcc/cp/decl.c:6857
> 0x9525c2 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int)
> /home/patrick/code/gcc/gcc/cp/decl.c:7699
> 0x9fcdf7 cp_parser_init_declarator
> /home/patrick/code/gcc/gcc/cp/parser.c:21362
>
>
> gcc/testsuite/g++.dg/cpp0x/constexpr-static6.C:17:28: internal compiler error: in build_target_expr, at cp/tree.c:495
> 17 | constexpr static B t = B();
> | ^
> 0x6b3c47 build_target_expr
> /home/patrick/code/gcc/gcc/cp/tree.c:495
> 0xa97248 build_cplus_new(tree_node*, tree_node*, int)
> /home/patrick/code/gcc/gcc/cp/tree.c:727
> 0x97eed5 expand_default_init
> /home/patrick/code/gcc/gcc/cp/init.c:1924
> 0x97eed5 expand_aggr_init_1
> /home/patrick/code/gcc/gcc/cp/init.c:2101
> 0x980d76 build_aggr_init(tree_node*, tree_node*, int, int)
> /home/patrick/code/gcc/gcc/cp/init.c:1835
> 0x92e5cd build_aggr_init_full_exprs
> /home/patrick/code/gcc/gcc/cp/decl.c:6696
> 0x92e5cd check_initializer
> /home/patrick/code/gcc/gcc/cp/decl.c:6857
> 0x9525c2 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int)
> /home/patrick/code/gcc/gcc/cp/decl.c:7699
> 0x9629ce grokfield(cp_declarator const*, cp_decl_specifier_seq*, tree_node*, bool, tree_node*, tree_node*)
> /home/patrick/code/gcc/gcc/cp/decl2.c:1000
Thanks. This is part of trying to produce a real value for a
non-dependent constexpr variable; the TARGET_EXPR gets melted down
before long, so it's OK.
>>
>>> 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
>>
>> This is discarded by finish_call_expr.
>>
>>> 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
>>
>> This is discarded by build_offset_ref_call_from_tree.
>>
>>> 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
>>
>> This is discarded by build_static_cast.
>>
>>> 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
>>
>> Discarded by build_new.
>>
>>> 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
>>
>> Discarded by build_x_modify_expr.
>>
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