From: Patrick Palka Date: Wed, 1 Jun 2022 12:47:25 +0000 (-0400) Subject: c++: constexpr init of union sub-aggr w/ base [PR105491] X-Git-Tag: releases/gcc-12.2.0~252 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e30b73bad9486f11b6b0022ae4a3edfc0f9da4bb;p=thirdparty%2Fgcc.git c++: constexpr init of union sub-aggr w/ base [PR105491] Here ever since r10-7313-gb599bf9d6d1e18, reduced_constant_expression_p in C++11/14 is rejecting the marked sub-aggregate initializer (of type S) W w = {.D.2445={.s={.D.2387={.m=0}, .b=0}}}; ^ ultimately because said initializer has CONSTRUCTOR_NO_CLEARING set, hence the function must verify that all fields of S are initialized. And before C++17 it doesn't expect to see base class fields (since next_initializable_field skips over them), so the presence thereof causes r_c_e_p to return false. The reason r10-7313-gb599bf9d6d1e18 causes this is because in that commit we began using CONSTRUCTOR_NO_CLEARING to precisely track whether we're in middle of activating a union member. This ends up affecting clear_no_implicit_zero, which recurses into sub-aggregate initializers only if the outer initializer has CONSTRUCTOR_NO_CLEARING set. After that commit, the outer union initializer above no longer has the flag set at this point and so clear_no_implicit_zero no longer recurses into the marked inner initializer. But arguably r_c_e_p should be able to accept the marked initializer regardless of whether CONSTRUCTOR_NO_CLEARING is set. The primary bug therefore seems to be that r_c_e_p relies on next_initializable_field which skips over base class fields in C++11/14. To fix this, this patch introduces a new helper function next_subobject_field which is like next_initializable_field except that it never skips base class fields, and makes r_c_e_p use it. This patch then renames next_initializable_field to next_aggregate_field (and makes it skip over vptr fields again). NB: This minimal backport of r13-211-g0c7bce0ac184c0 for 12.2 just adds next_subobject_field and makes reduced_constant_expression_p use it. PR c++/105491 gcc/cp/ChangeLog: * constexpr.cc (reduced_constant_expression_p): Use next_subobject_field instead. * cp-tree.h (next_subobject_field): Declare. * decl.cc (next_subobject_field): Define. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/constexpr-union7.C: New test. * g++.dg/cpp0x/constexpr-union7a.C: New test. * g++.dg/cpp2a/constinit17.C: New test. (cherry picked from commit 0c7bce0ac184c057bacad9c8e615ce82923835fd) --- diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index 47d5113ace26..1e3342adbb99 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -3053,7 +3053,7 @@ reduced_constant_expression_p (tree t) field = NULL_TREE; } else - field = next_initializable_field (TYPE_FIELDS (TREE_TYPE (t))); + field = next_subobject_field (TYPE_FIELDS (TREE_TYPE (t))); } else field = NULL_TREE; @@ -3065,15 +3065,15 @@ reduced_constant_expression_p (tree t) return false; /* Empty class field may or may not have an initializer. */ for (; field && e.index != field; - field = next_initializable_field (DECL_CHAIN (field))) + field = next_subobject_field (DECL_CHAIN (field))) if (!is_really_empty_class (TREE_TYPE (field), /*ignore_vptr*/false)) return false; if (field) - field = next_initializable_field (DECL_CHAIN (field)); + field = next_subobject_field (DECL_CHAIN (field)); } /* There could be a non-empty field at the end. */ - for (; field; field = next_initializable_field (DECL_CHAIN (field))) + for (; field; field = next_subobject_field (DECL_CHAIN (field))) if (!is_really_empty_class (TREE_TYPE (field), /*ignore_vptr*/false)) return false; ok: diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 72177999968c..b540c2342c07 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -6885,6 +6885,7 @@ extern void initialize_artificial_var (tree, vec *); extern tree check_var_type (tree, tree, location_t); extern tree reshape_init (tree, tree, tsubst_flags_t); extern tree next_initializable_field (tree); +extern tree next_subobject_field (tree); extern tree first_field (const_tree); extern tree fndecl_declared_return_type (tree); extern bool undeduced_auto_decl (tree); diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc index d1fc7e10a523..269c6679ca26 100644 --- a/gcc/cp/decl.cc +++ b/gcc/cp/decl.cc @@ -6409,6 +6409,25 @@ next_initializable_field (tree field) return field; } +/* FIELD is an element of TYPE_FIELDS or NULL. In the former case, the value + returned is the next FIELD_DECL (possibly FIELD itself) that corresponds + to a subobject. If there are no more such fields, the return value will be + NULL. */ + +tree +next_subobject_field (tree field) +{ + while (field + && (TREE_CODE (field) != FIELD_DECL + || DECL_UNNAMED_BIT_FIELD (field) + || (DECL_ARTIFICIAL (field) + && !DECL_FIELD_IS_BASE (field) + && !DECL_VIRTUAL_P (field)))) + field = DECL_CHAIN (field); + + return field; +} + /* Return true for [dcl.init.list] direct-list-initialization from single element of enumeration with a fixed underlying type. */ diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C new file mode 100644 index 000000000000..b3147d9db502 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C @@ -0,0 +1,17 @@ +// PR c++/105491 +// { dg-do compile { target c++11 } } + +struct V { + int m = 0; +}; +struct S : V { + constexpr S(int) : b() { } + bool b; +}; +struct W { + constexpr W() : s(0) { } + union { + S s; + }; +}; +constexpr W w; diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-union7a.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7a.C new file mode 100644 index 000000000000..b676e7d17488 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7a.C @@ -0,0 +1,15 @@ +// PR c++/105491 +// { dg-do compile { target c++11 } } + +struct V { + int m = 0; +}; +struct S : V { + constexpr S(int) : b() { } + bool b; +}; +union W { + constexpr W() : s(0) { } + S s; +}; +constexpr W w; diff --git a/gcc/testsuite/g++.dg/cpp2a/constinit17.C b/gcc/testsuite/g++.dg/cpp2a/constinit17.C new file mode 100644 index 000000000000..6431654ac854 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/constinit17.C @@ -0,0 +1,24 @@ +// PR c++/105491 +// { dg-do compile { target c++11 } } + +class Message { + virtual int GetMetadata(); +}; +class ProtobufCFileOptions : Message { +public: + constexpr ProtobufCFileOptions(int); + bool no_generate_; + bool const_strings_; + bool use_oneof_field_name_; + bool gen_pack_helpers_; + bool gen_init_helpers_; +}; +constexpr ProtobufCFileOptions::ProtobufCFileOptions(int) + : no_generate_(), const_strings_(), use_oneof_field_name_(), + gen_pack_helpers_(), gen_init_helpers_() {} +struct ProtobufCFileOptionsDefaultTypeInternal { + constexpr ProtobufCFileOptionsDefaultTypeInternal() : _instance({}) {} + union { + ProtobufCFileOptions _instance; + }; +} __constinit _ProtobufCFileOptions_default_instance_;