From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 1734) id A04D8388981F; Fri, 25 Mar 2022 14:15:31 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A04D8388981F MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Marek Polacek To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-7815] c++: alignas and alignof void [PR104944] X-Act-Checkin: gcc X-Git-Author: Marek Polacek X-Git-Refname: refs/heads/trunk X-Git-Oldrev: 8570cce7c705f2ec3ffaeb8e47d58af22a075ebd X-Git-Newrev: d0b938a7612fb7acf1f181da9577235c83ede59e Message-Id: <20220325141531.A04D8388981F@sourceware.org> Date: Fri, 25 Mar 2022 14:15:31 +0000 (GMT) X-BeenThere: gcc-cvs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 25 Mar 2022 14:15:31 -0000 https://gcc.gnu.org/g:d0b938a7612fb7acf1f181da9577235c83ede59e commit r12-7815-gd0b938a7612fb7acf1f181da9577235c83ede59e Author: Marek Polacek Date: Wed Mar 23 17:12:29 2022 -0400 c++: alignas and alignof void [PR104944] I started looking into this PR because in GCC 4.9 we were able to detect the invalid struct alignas(void) S{}; but I broke it in r210262. It's ill-formed code in C++: [dcl.align]/3: "An alignment-specifier of the form alignas(type-id) has the same effect as alignas(alignof(type-id))", and [expr.align]/1: "The operand shall be a type-id representing a complete object type, or an array thereof, or a reference to one of those types." and void is not a complete type. It's also invalid in C: 6.7.5: _Alignas(type-name) is equivalent to _Alignas(_Alignof(type-name)) 6.5.3.4: "The _Alignof operator shall not be applied to a function type or an incomplete type." We have a GNU extension whereby we treat sizeof(void) as 1, but I assume it doesn't apply to alignof, at least in C++. However, __alignof__(void) is still accepted with a -Wpedantic warning. We still say "invalid application of 'alignof'" rather than 'alignas' in the void diagnostic, but I felt that fixing that may not be suitable as part of this patch. The "incomplete type" diagnostic still always prints '__alignof__'. PR c++/104944 gcc/cp/ChangeLog: * typeck.cc (cxx_sizeof_or_alignof_type): Diagnose alignof(void). (cxx_alignas_expr): Call cxx_sizeof_or_alignof_type with complain == true. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/alignas20.C: New test. Diff: --- gcc/cp/typeck.cc | 21 +++++++++++++++------ gcc/testsuite/g++.dg/cpp0x/alignas20.C | 26 ++++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 6 deletions(-) diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc index 516fa574ef6..26a7cb4b50d 100644 --- a/gcc/cp/typeck.cc +++ b/gcc/cp/typeck.cc @@ -1873,9 +1873,9 @@ compparms (const_tree parms1, const_tree parms2) } -/* Process a sizeof or alignof expression where the operand is a - type. STD_ALIGNOF indicates whether an alignof has C++11 (minimum alignment) - or GNU (preferred alignment) semantics; it is ignored if op is +/* Process a sizeof or alignof expression where the operand is a type. + STD_ALIGNOF indicates whether an alignof has C++11 (minimum alignment) + or GNU (preferred alignment) semantics; it is ignored if OP is SIZEOF_EXPR. */ tree @@ -1899,6 +1899,13 @@ cxx_sizeof_or_alignof_type (location_t loc, tree type, enum tree_code op, else return error_mark_node; } + else if (VOID_TYPE_P (type) && std_alignof) + { + if (complain) + error_at (loc, "invalid application of %qs to a void type", + OVL_OP_INFO (false, op)->name); + return error_mark_node; + } bool dependent_p = dependent_type_p (type); if (!dependent_p) @@ -2132,11 +2139,13 @@ cxx_alignas_expr (tree e) /* [dcl.align]/3: When the alignment-specifier is of the form - alignas(type-id ), it shall have the same effect as - alignas(alignof(type-id )). */ + alignas(type-id), it shall have the same effect as + alignas(alignof(type-id)). */ return cxx_sizeof_or_alignof_type (input_location, - e, ALIGNOF_EXPR, true, false); + e, ALIGNOF_EXPR, + /*std_alignof=*/true, + /*complain=*/true); /* If we reach this point, it means the alignas expression if of the form "alignas(assignment-expression)", so we should follow diff --git a/gcc/testsuite/g++.dg/cpp0x/alignas20.C b/gcc/testsuite/g++.dg/cpp0x/alignas20.C new file mode 100644 index 00000000000..01a55f3d4a4 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/alignas20.C @@ -0,0 +1,26 @@ +// PR c++/104944 +// { dg-do compile { target c++11 } } +// { dg-options "-Wpedantic" } + +struct inc; + +struct alignas(inc) S1 { }; // { dg-error "invalid application" } +struct alignas(void) S2 { }; // { dg-error "invalid application" } + +template +struct alignas(T) S4 {}; // { dg-error "invalid application" } + +template +struct alignas(T) S5 {}; // { dg-error "invalid application" } + +S4 s1; +S5 s2; + +void +g () +{ + auto s1 = alignof(void); // { dg-error "invalid application" } + auto s2 = alignof(const void); // { dg-error "invalid application" } + auto s3 = __alignof(void); // { dg-warning "invalid application" } + auto s4 = alignof(inc); // { dg-error "invalid application" } +}