From: Jason Merrill <jason@redhat.com>
To: Marek Polacek <polacek@redhat.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>, Jakub Jelinek <jakub@redhat.com>
Subject: Re: [PATCH v2] c++: constexpr error with fn redecl in local scope [PR111132]
Date: Thu, 4 Apr 2024 23:56:27 -0400 [thread overview]
Message-ID: <37d7a173-92e2-4fdd-b3b1-14e867f568e1@redhat.com> (raw)
In-Reply-To: <Zg80hQRRH_SKAMCf@redhat.com>
On 4/4/24 19:15, Marek Polacek wrote:
> On Thu, Apr 04, 2024 at 05:28:22PM -0400, Jason Merrill wrote:
>> On 4/4/24 14:43, Marek Polacek wrote:
>>> On Wed, Apr 03, 2024 at 01:14:46PM -0400, Jason Merrill wrote:
>>>> On 4/2/24 13:52, Marek Polacek wrote:
>>>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?
>>>>>
>>>>> -- >8 --
>>>>> We evaluate constexpr functions on the original, pre-genericization bodies.
>>>>> That means that the function body we're evaluating will not have gone
>>>>> through cp_genericize_r's "Map block scope extern declarations to visible
>>>>> declarations with the same name and type in outer scopes if any". Here:
>>>>>
>>>>> constexpr bool bar() { return true; } // #1
>>>>> constexpr bool foo() {
>>>>> constexpr bool bar(void); // #2
>>>>> return bar();
>>>>> }
>>>>>
>>>>> it means that we:
>>>>> 1) register_constexpr_fundef (#1)
>>>>> 2) cp_genericize (#1)
>>>>> nothing interesting happens
>>>>> 3) register_constexpr_fundef (foo)
>>>>> does copy_fn, so we have two copies of the BIND_EXPR
>>>>> 4) cp_genericize (foo)
>>>>> this remaps #2 to #1, but only on one copy of the BIND_EXPR
>>>>> 5) retrieve_constexpr_fundef (foo)
>>>>> we find it, no problem
>>>>> 6) retrieve_constexpr_fundef (#2)
>>>>> and here #2 isn't found in constexpr_fundef_table, because
>>>>> we're working on the BIND_EXPR copy where #2 wasn't mapped to #1
>>>>> so we fail. We've only registered #1.
>>>>>
>>>>> It should work to use DECL_LOCAL_DECL_ALIAS (which used to be
>>>>> extern_decl_map). We evaluate constexpr functions on pre-cp_fold
>>>>> bodies to avoid diagnostic problems, but the remapping I'm proposing
>>>>> should not interfere with diagnostics.
>>>>>
>>>>> This is not a problem for a global scope redeclaration; there we go
>>>>> through duplicate_decls which keeps the DECL_UID:
>>>>> DECL_UID (olddecl) = olddecl_uid;
>>>>> and DECL_UID is what constexpr_fundef_hasher::hash uses.
>>>>>
>>>>> PR c++/111132
>>>>>
>>>>> gcc/cp/ChangeLog:
>>>>>
>>>>> * constexpr.cc (get_function_named_in_call): If there's
>>>>> a DECL_LOCAL_DECL_ALIAS, use it.
>>>>
>>>> Perhaps this function should use cp_get_fndecl_from_callee, and this change
>>>> should be made there instead?
>>>
>>> It doesn't seem that get_function_named_in_call can use cp_get_fndecl_from_callee,
>>> (or be replaced with cp_get_callee_fndecl_nofold). We can get e.g. a CALL_EXPR
>>> whose CALL_EXPR_FN is a TEMPLATE_ID_EXPR, and get_function_named_in_call
>>> returns the TEMPLATE_ID_EXPR whereas cp_get_fndecl_from_callee would return
>>> null:
>>>
>>> if (TREE_CODE (fn) == FUNCTION_DECL)
>>> return fn;
>>> tree type = TREE_TYPE (fn);
>>> if (type == NULL_TREE || !INDIRECT_TYPE_P (type))
>>> return NULL_TREE;
>>
>> Why couldn't this function use cp_get_fndecl_from_callee and return the
>> original argument if that function returns null?
>
> It could. (The lambda below could have been a goto but either should be fine.)
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?
OK.
> -- >8 --
> We evaluate constexpr functions on the original, pre-genericization bodies.
> That means that the function body we're evaluating will not have gone
> through cp_genericize_r's "Map block scope extern declarations to visible
> declarations with the same name and type in outer scopes if any". Here:
>
> constexpr bool bar() { return true; } // #1
> constexpr bool foo() {
> constexpr bool bar(void); // #2
> return bar();
> }
>
> it means that we:
> 1) register_constexpr_fundef (#1)
> 2) cp_genericize (#1)
> nothing interesting happens
> 3) register_constexpr_fundef (foo)
> does copy_fn, so we have two copies of the BIND_EXPR
> 4) cp_genericize (foo)
> this remaps #2 to #1, but only on one copy of the BIND_EXPR
> 5) retrieve_constexpr_fundef (foo)
> we find it, no problem
> 6) retrieve_constexpr_fundef (#2)
> and here #2 isn't found in constexpr_fundef_table, because
> we're working on the BIND_EXPR copy where #2 wasn't mapped to #1
> so we fail. We've only registered #1.
>
> It should work to use DECL_LOCAL_DECL_ALIAS (which used to be
> extern_decl_map). We evaluate constexpr functions on pre-cp_fold
> bodies to avoid diagnostic problems, but the remapping I'm proposing
> should not interfere with diagnostics.
>
> This is not a problem for a global scope redeclaration; there we go
> through duplicate_decls which keeps the DECL_UID:
> DECL_UID (olddecl) = olddecl_uid;
> and DECL_UID is what constexpr_fundef_hasher::hash uses.
>
> PR c++/111132
>
> gcc/cp/ChangeLog:
>
> * constexpr.cc (get_function_named_in_call): Use
> cp_get_fndecl_from_callee.
> * cvt.cc (cp_get_fndecl_from_callee): If there's a
> DECL_LOCAL_DECL_ALIAS, use it.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/constexpr-redeclaration3.C: New test.
> * g++.dg/cpp0x/constexpr-redeclaration4.C: New test.
> ---
> gcc/cp/constexpr.cc | 10 ++++------
> gcc/cp/cvt.cc | 18 ++++++++++++++++--
> .../g++.dg/cpp0x/constexpr-redeclaration3.C | 13 +++++++++++++
> .../g++.dg/cpp0x/constexpr-redeclaration4.C | 14 ++++++++++++++
> 4 files changed, 47 insertions(+), 8 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C
>
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index fa346fe01c9..410ccdf597f 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -702,16 +702,14 @@ build_constexpr_constructor_member_initializers (tree type, tree body)
>
> /* We have an expression tree T that represents a call, either CALL_EXPR
> or AGGR_INIT_EXPR. If the call is lexically to a named function,
> - retrun the _DECL for that function. */
> + return the _DECL for that function. */
>
> static tree
> get_function_named_in_call (tree t)
> {
> - tree fun = cp_get_callee (t);
> - if (fun && TREE_CODE (fun) == ADDR_EXPR
> - && TREE_CODE (TREE_OPERAND (fun, 0)) == FUNCTION_DECL)
> - fun = TREE_OPERAND (fun, 0);
> - return fun;
> + tree callee = cp_get_callee (t);
> + tree fun = cp_get_fndecl_from_callee (callee, /*fold*/false);
> + return fun ? fun : callee;
> }
>
> /* Subroutine of check_constexpr_fundef. BODY is the body of a function
> diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
> index cbed847b343..db086c017e8 100644
> --- a/gcc/cp/cvt.cc
> +++ b/gcc/cp/cvt.cc
> @@ -1001,8 +1001,22 @@ cp_get_fndecl_from_callee (tree fn, bool fold /* = true */)
> {
> if (fn == NULL_TREE)
> return fn;
> +
> + /* We evaluate constexpr functions on the original, pre-genericization
> + bodies. So block-scope extern declarations have not been mapped to
> + declarations in outer scopes. Use the namespace-scope declaration,
> + if any, so that retrieve_constexpr_fundef can find it (PR111132). */
> + auto fn_or_local_alias = [] (tree f)
> + {
> + if (DECL_LOCAL_DECL_P (f))
> + if (tree alias = DECL_LOCAL_DECL_ALIAS (f))
> + if (alias != error_mark_node)
> + return alias;
> + return f;
> + };
> +
> if (TREE_CODE (fn) == FUNCTION_DECL)
> - return fn;
> + return fn_or_local_alias (fn);
> tree type = TREE_TYPE (fn);
> if (type == NULL_TREE || !INDIRECT_TYPE_P (type))
> return NULL_TREE;
> @@ -1013,7 +1027,7 @@ cp_get_fndecl_from_callee (tree fn, bool fold /* = true */)
> || TREE_CODE (fn) == FDESC_EXPR)
> fn = TREE_OPERAND (fn, 0);
> if (TREE_CODE (fn) == FUNCTION_DECL)
> - return fn;
> + return fn_or_local_alias (fn);
> return NULL_TREE;
> }
>
> diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C
> new file mode 100644
> index 00000000000..2b41b456fc3
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C
> @@ -0,0 +1,13 @@
> +// PR c++/111132
> +// { dg-do compile { target c++11 } }
> +
> +constexpr bool bar(void) {
> + return true;
> +}
> +
> +constexpr bool foo() {
> + constexpr bool bar(void);
> + return bar();
> +}
> +
> +static_assert(foo(), "");
> diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C
> new file mode 100644
> index 00000000000..c58247218c6
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C
> @@ -0,0 +1,14 @@
> +// PR c++/111132
> +// { dg-do compile { target c++11 } }
> +
> +constexpr bool bar(void) {
> + return true;
> +}
> +
> +constexpr bool bar(void);
> +
> +constexpr bool foo() {
> + return bar();
> +}
> +
> +static_assert(foo(), "");
>
> base-commit: 27b6d081f68528435066be2234c7329e31e0e84f
prev parent reply other threads:[~2024-04-05 3:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-02 17:52 [PATCH] " Marek Polacek
2024-04-03 17:14 ` Jason Merrill
2024-04-04 18:43 ` Marek Polacek
2024-04-04 21:28 ` Jason Merrill
2024-04-04 23:15 ` [PATCH v2] " Marek Polacek
2024-04-05 3:56 ` Jason Merrill [this message]
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