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[69.125.73.58]) by smtp.gmail.com with ESMTPSA id h13sm641822qtu.23.2020.02.10.11.21.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Feb 2020 11:21:46 -0800 (PST) From: Patrick Palka Date: Mon, 10 Feb 2020 19:22:00 -0000 To: Jason Merrill cc: Patrick Palka , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++: Fix return type deduction with an abbreviated function template In-Reply-To: Message-ID: References: <20200210132032.586931-1-ppalka@redhat.com> User-Agent: Alpine 2.22 (DEB 395 2020-01-19) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable X-IsSubscribed: yes X-SW-Source: 2020-02/txt/msg00580.txt.bz2 On Mon, 10 Feb 2020, Jason Merrill wrote: > On 2/10/20 2:20 PM, Patrick Palka wrote: > > This patch fixes two issues with return type deduction in the presence = of an > > abbreviated function template. > >=20 > > The first issue (PR 69448) is that if a placeholder auto return type > > contains > > any modifiers such as & or *, then the abbreviated-function-template > > compensation in splice_late_return_type does not get performed for the > > underlying auto node, leading to incorrect return type deduction. This > > happens > > because splice_late_return_type checks for a placeholder auto with is_a= uto, > > which does not look through modifiers. This patch replaces the use of > > is_auto > > with find_type_usage, but it first refactors find_type_usage to return a > > pointer > > to the matched tree so that we next subsequently replace it. > >=20 > > The second issue (PR 80471) is that the AUTO_IS_DECLTYPE flag is not be= ing > > preserved in splice_late_return_type when compensating for an abbreviat= ed > > function template, leading to us treating a decltype(auto) return type = as if > > it > > was an auto return type. Fixed by propagating AUTO_IS_DECLTYPE. The t= est > > for > > PR 80471 is adjusted to expect the correct behavior. >=20 > The comment in make_constrained_decltype_auto suggests that we should set > AUTO_IS_DECLTYPE in make_auto_1 if name =3D=3D decltype_auto_identifier; = then > callers won't need to worry about it. Updated the patch to make_auto_1 to set AUTO_IS_DECLTYPE when appropriate, and adjusted callers accordingly. Now make_auto_1 is the only place where we set AUTO_IS_DECLTYPE. >=20 > > Bootstrapped and regtested on x86_64-pc-linux-gnu, is this OK to commit? > >=20 > > gcc/cp/ChangeLog: > >=20 > > PR c++/69448 > > PR c++/80471 > > * type-utils.h (find_type_usage): Refactor to take a tree * and to > > return a tree *, and update documentation accordingly. > > * pt.c (splice_late_return_type): Use find_type_usage to find and > > replace a possibly nested auto node. Preserve the AUTO_IS_DECLTYPE > > flag when replacing the node. > > (type_uses_auto): Adjust the call to find_type_usage. > >=20 > > gcc/testsuite/ChangeLog: > >=20 > > PR c++/69448 > > PR c++/80471 > > * g++.dg/concepts/abbrev3.C: New test. > > * g++.dg/cpp2a/concepts-pr80471.C: Adjust a static_assert to expect > > the > > correct behavior. > > --- > > gcc/cp/pt.c | 26 ++++++++++++------- > > gcc/cp/type-utils.h | 26 +++++++++---------- > > gcc/testsuite/g++.dg/concepts/abbrev3.C | 11 ++++++++ > > gcc/testsuite/g++.dg/cpp2a/concepts-pr80471.C | 2 +- > > 4 files changed, 41 insertions(+), 24 deletions(-) > > create mode 100644 gcc/testsuite/g++.dg/concepts/abbrev3.C > >=20 > > diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c > > index 2fb52caa5d4..c83aaa7c7e1 100644 > > --- a/gcc/cp/pt.c > > +++ b/gcc/cp/pt.c > > @@ -28904,17 +28904,21 @@ do_auto_deduction (tree type, tree init, tree > > auto_node, > > tree > > splice_late_return_type (tree type, tree late_return_type) > > { > > - if (is_auto (type)) > > - { > > - if (late_return_type) > > - return late_return_type; > > + if (is_auto (type) && late_return_type) > > + return late_return_type; >=20 > It occurs to me that we could just check late_return_type here, maybe cha= nge > the is_auto test to an assert. Done -- I had to add a seen_error test to the assert to accomodate error recovery and also adjust a dg-error directive in g++.dg/cpp0x/auto9.C. Does this version look OK after testing? -- >8 -- gcc/cp/ChangeLog: PR c++/69448 PR c++/80471 * type-utils.h (find_type_usage): Refactor to take a tree * and to return a tree *, and update documentation accordingly. * pt.c (make_auto_1): Set AUTO_IS_DECLTYPE when building a decltype(auto) node. (make_constrained_decltype_auto): No need to explicitly set AUTO_IS_DECLTYPE anymore. (splice_late_return_type): Use find_type_usage to find and replace a possibly nested auto node instead of using is_auto. Check test for is_auto into an assert when deciding whether to late_return_type. (type_uses_auto): Adjust the call to find_type_usage. * parser.c (cp_parser_decltype): No need to explicitly set AUTO_IS_DECLTYPE anymore. gcc/libcc1/ChangeLog: * libcp1plugin.cc (plugin_get_expr_type): No need to explicitly set AUTO_IS_DECLTYPE anymore. gcc/testsuite/ChangeLog: PR c++/69448 PR c++/80471 * g++.dg/concepts/abbrev3.C: New test. * g++.dg/cpp2a/concepts-pr80471.C: Adjust a static_assert to expect the correct behavior. * g++.dg/cpp0x/auto9.C: Adjust a dg-error directive. --- gcc/cp/parser.c | 7 ++--- gcc/cp/pt.c | 21 +++++++++------ gcc/cp/type-utils.h | 26 +++++++++---------- gcc/testsuite/g++.dg/concepts/abbrev3.C | 11 ++++++++ gcc/testsuite/g++.dg/cpp0x/auto9.C | 2 +- gcc/testsuite/g++.dg/cpp2a/concepts-pr80471.C | 2 +- libcc1/libcp1plugin.cc | 5 +--- 7 files changed, 42 insertions(+), 32 deletions(-) create mode 100644 gcc/testsuite/g++.dg/concepts/abbrev3.C diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c index d4c9523289f..640affd8368 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -14901,11 +14901,8 @@ cp_parser_decltype (cp_parser *parser) } =20 if (!expr) - { - /* Build auto. */ - expr =3D make_decltype_auto (); - AUTO_IS_DECLTYPE (expr) =3D true; - } + /* Build auto. */ + expr =3D make_decltype_auto (); else expr =3D finish_decltype_type (expr, id_expression_or_member_access_p, tf_warning_or_error); diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 01bade85cdf..e1c832c7035 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -27539,6 +27539,8 @@ make_auto_1 (tree name, bool set_canonical) TYPE_CANONICAL (au) =3D canonical_type_parameter (au); DECL_ARTIFICIAL (TYPE_NAME (au)) =3D 1; SET_DECL_TEMPLATE_PARM_P (TYPE_NAME (au)); + if (name =3D=3D decltype_auto_identifier) + AUTO_IS_DECLTYPE (au) =3D true; =20 return au; } @@ -27616,8 +27618,6 @@ tree make_constrained_decltype_auto (tree con, tree args) { tree type =3D make_auto_1 (decltype_auto_identifier, false); - /* FIXME: I don't know why this isn't done in make_auto_1. */ - AUTO_IS_DECLTYPE (type) =3D true; return make_constrained_placeholder_type (type, con, args); } =20 @@ -28930,17 +28930,20 @@ do_auto_deduction (tree type, tree init, tree aut= o_node, tree splice_late_return_type (tree type, tree late_return_type) { - if (is_auto (type)) + if (late_return_type) { - if (late_return_type) - return late_return_type; + gcc_assert (is_auto (type) || seen_error ()); + return late_return_type; + } =20 - tree idx =3D get_template_parm_index (type); + if (tree *auto_node =3D find_type_usage (&type, is_auto)) + { + tree idx =3D get_template_parm_index (*auto_node); if (TEMPLATE_PARM_LEVEL (idx) <=3D processing_template_decl) /* In an abbreviated function template we didn't know we were dealing with a function template when we saw the auto return type, so update it to have the correct level. */ - return make_auto_1 (TYPE_IDENTIFIER (type), true); + *auto_node =3D make_auto_1 (TYPE_IDENTIFIER (*auto_node), true); } return type; } @@ -28986,8 +28989,10 @@ type_uses_auto (tree type) else return NULL_TREE; } + else if (tree *tp =3D find_type_usage (&type, is_auto)) + return *tp; else - return find_type_usage (type, is_auto); + return NULL_TREE; } =20 /* Report ill-formed occurrences of auto types in ARGUMENTS. If diff --git a/gcc/cp/type-utils.h b/gcc/cp/type-utils.h index 680b2497a36..4ad0d822119 100644 --- a/gcc/cp/type-utils.h +++ b/gcc/cp/type-utils.h @@ -20,36 +20,36 @@ along with GCC; see the file COPYING3. If not see #ifndef GCC_CP_TYPE_UTILS_H #define GCC_CP_TYPE_UTILS_H =20 -/* Returns the first tree within T that is directly matched by PRED. T ma= y be a - type or PARM_DECL and is incrementally decomposed toward its type-speci= fier - until a match is found. NULL_TREE is returned if PRED does not match a= ny - part of T. +/* Returns a pointer to the first tree within *TP that is directly matched= by + PRED. *TP may be a type or PARM_DECL and is incrementally decomposed t= oward + its type-specifier until a match is found. NULL is returned if PRED do= es not + match any part of *TP. =20 - This is primarily intended for detecting whether T uses `auto' or a con= cept + This is primarily intended for detecting whether *TP uses `auto' or a c= oncept identifier. Since either of these can only appear as a type-specifier = for the declaration in question, only top-level qualifications are traverse= d; find_type_usage does not look through the whole type. */ =20 -inline tree -find_type_usage (tree t, bool (*pred) (const_tree)) +inline tree * +find_type_usage (tree *tp, bool (*pred) (const_tree)) { - enum tree_code code; + tree t =3D *tp; if (pred (t)) - return t; + return tp; =20 - code =3D TREE_CODE (t); + enum tree_code code =3D TREE_CODE (t); =20 if (code =3D=3D POINTER_TYPE || code =3D=3D REFERENCE_TYPE || code =3D=3D PARM_DECL || code =3D=3D OFFSET_TYPE || code =3D=3D FUNCTION_TYPE || code =3D=3D METHOD_TYPE || code =3D=3D ARRAY_TYPE) - return find_type_usage (TREE_TYPE (t), pred); + return find_type_usage (&TREE_TYPE (t), pred); =20 if (TYPE_PTRMEMFUNC_P (t)) return find_type_usage - (TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (t)), pred); + (&TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (t)), pred); =20 - return NULL_TREE; + return NULL; } =20 #endif // GCC_CP_TYPE_UTILS_H diff --git a/gcc/testsuite/g++.dg/concepts/abbrev3.C b/gcc/testsuite/g++.dg= /concepts/abbrev3.C new file mode 100644 index 00000000000..ba2a648156e --- /dev/null +++ b/gcc/testsuite/g++.dg/concepts/abbrev3.C @@ -0,0 +1,11 @@ +// PR c++/69448 +// { dg-do compile { target c++14 } } +// { dg-additional-options "-fconcepts" } + +long x; + +auto& f(auto) { return x; } +auto* g(auto) { return &x; } + +long& r =3D f(1); +long* p =3D g(1); diff --git a/gcc/testsuite/g++.dg/cpp0x/auto9.C b/gcc/testsuite/g++.dg/cpp0= x/auto9.C index 8d77b0b3667..a3f9be521d6 100644 --- a/gcc/testsuite/g++.dg/cpp0x/auto9.C +++ b/gcc/testsuite/g++.dg/cpp0x/auto9.C @@ -22,7 +22,7 @@ struct A struct A2 { operator auto () -> int; // { dg-error "invalid use of|trailing return= type" } - operator auto*() -> int; // { dg-error "invalid use of|trailing return= type" } + operator auto*() -> int; // { dg-error "invalid use of|trailing return= type|cannot be overloaded" } }; =20 template struct B diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr80471.C b/gcc/testsuite/= g++.dg/cpp2a/concepts-pr80471.C index d5fa5a536d3..6ea6164b417 100644 --- a/gcc/testsuite/g++.dg/cpp2a/concepts-pr80471.C +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr80471.C @@ -18,6 +18,6 @@ int main() { int i; static_assert(is_same< decltype(f(i)), int& >, ""); - static_assert(is_same< decltype(g(i)), int >, ""); + static_assert(is_same< decltype(g(i)), int& >, ""); static_assert(is_same< decltype(z(i)), int& >, ""); } diff --git a/libcc1/libcp1plugin.cc b/libcc1/libcp1plugin.cc index b466b34bee3..00449f43b52 100644 --- a/libcc1/libcp1plugin.cc +++ b/libcc1/libcp1plugin.cc @@ -3343,10 +3343,7 @@ plugin_get_expr_type (cc1_plugin::connection *self, if (op0) type =3D TREE_TYPE (op0); else - { - type =3D make_decltype_auto (); - AUTO_IS_DECLTYPE (type) =3D true; - } + type =3D make_decltype_auto (); return convert_out (ctx->preserve (type)); } =20 --=20 2.25.0.191.gde93cc14ab