[Bug c++/63619] New: warning: deleting ‘void*’ is undefined has no -W flag

[Bug c++/63619] New: warning: deleting ‘void*’ is undefined has no -W flag

[fuscated at gmail dot com]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63619

            Bug ID: 63619
           Summary: warning: deleting ‘void*’ is undefined has no -W flag
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fuscated at gmail dot com

Save this snippet in delete_void.cpp
int main() {
    void *a=new char[100];
    delete [] a;
    return 0;
}

$ g++ -fdiagnostics-show-option delete_void.cpp 
delete_void.cpp: In function ‘int main()’:
delete_void.cpp:3:12: warning: deleting ‘void*’ is undefined
  delete [] a;
            ^
The compiler poroduces a warning, but doesn't allow the user to turn it into
error and thus such bugs cannot be detected at compile time.
>From gcc-bugs-return-464673-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Wed Oct 22 16:25:05 2014
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From: "evstupac at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/63620] New: RELOAD lost SET_GOT dependency on Darwin
Date: Wed, 22 Oct 2014 16:25:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc620

            Bug ID: 63620
           Summary: RELOAD lost SET_GOT dependency on Darwin
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: evstupac at gmail dot com
                CC: law at redhat dot com, vmakarov at redhat dot com
            Target: Darwin

Created attachment 33782
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id3782&actioníit
reproducer

For the attached tests even with fix in pr63618 SET_GOT is deleted on Darwin.

For some reason there are no dependency between:

(RELOAD PASS)

(insn/f 43 6 2 2 (parallel [
            (set (reg:SI 0 ax [87])
                (unspec:SI [
                        (const_int 0 [0])
                    ] UNSPEC_SET_GOT))
            (clobber (reg:CC 17 flags))
        ]) 679 {set_got}
     (expr_list:REG_EQUIV (unspec:SI [
                (const_int 0 [0])
            ] UNSPEC_SET_GOT)
        (expr_list:REG_CFA_FLUSH_QUEUE (nil)
            (nil))))

and

(insn 46 17 47 3 (set (reg:SI 0 ax [93])
        (plus:SI (reg:SI 0 ax [87])
            (const:SI (unspec:SI [
                        (symbol_ref/u:SI ("*LC0") [flags 0x2])
                    ] UNSPEC_MACHOPIC_OFFSET)))) elim_setgot_darwin.c:20 213
{*leasi}
     (expr_list:REG_EQUAL (symbol_ref/u:SI ("*LC0") [flags 0x2])
        (nil)))

And at 231r.ce3 SET_GOT is deleted which lead to incorrect code.

The issue reproduced on Darwin only, however it can be reproduced at cross
build configured as:
../configure --target=x86_64-apple-darwin11 --prefix=...
--enable-languages=c,c++ --enable-bootstrap=no

To reproduce we need only cc1:

gcc/cc1 elim_setgot_darwin.c -m32 -fPIE -O2 -msse4.2 -mtune=corei7 -fno-inline
-fdump-rtl-all

[Bug c++/63619] warning: deleting ‘void*’ is undefined has no -W flag

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63619

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-10-22
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, this is a very good candidate for wanting a -Werror=xxx option

[Bug c++/63619] warning: deleting ‘void*’ is undefined has no -W flag

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63619

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The simplest fix would be:

--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -478,7 +478,7 @@ delete_sanity (tree exp, tree size, bool doing_vec, int
use_global_delete,
   /* Deleting ptr to void is undefined behavior [expr.delete/3].  */
   if (VOID_TYPE_P (TREE_TYPE (type)))
     {
-      warning (0, "deleting %qT is undefined", type);
+      warning (OPT_Wdelete_incomplete, "deleting %qT is undefined", type);
       doing_vec = 0;
     }

Although it's possible someone would want deleting void to be an error but not
deleting an incomplete type (because it's only undefined to delete an
incomplete type if it has a non-trivial destructor or a custom deallocation
function).

[Bug c++/63619] warning: deleting ‘void*’ is undefined has no -W flag

[fuscated at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63619

--- Comment #3 from Teodor Petrov <fuscated at gmail dot com> ---
We already use -Werror=delete-incomplete, so it will be easier for us, because
it will just work.

But if you ask me (as a user) it is best to just change the standard to force
these two as errors. I know this will never happen, but I have to murmur about
it.

BTW: Thanks for looking at this in such a short time :)

[Bug c++/63619] warning: deleting ‘void*’ is undefined has no -W flag

[fuscated at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63619

--- Comment #4 from Teodor Petrov <fuscated at gmail dot com> ---
FYI: clang fixed the same issue by adding it to -Wdelete-incomplete

[Bug c++/63619] warning: deleting ‘void*’ is undefined has no -W flag

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63619

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Thu Oct 23 21:07:49 2014
New Revision: 216599

URL: https://gcc.gnu.org/viewcvs?rev=216599&root=gcc&view=rev
Log:
PR c++/63619

gcc/cp:
    PR c++/63619
    * decl2.c (delete_sanity): Use OPT_Wdelete_incomplete in warning.

gcc/testsuite:
    PR c++/63619
    * g++.dg/warn/Wdelete-incomplete-3.C: New.
    * g++.dg/warn/Wdelete-incomplete-4.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wdelete-incomplete-3.C
    trunk/gcc/testsuite/g++.dg/warn/Wdelete-incomplete-4.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl2.c
    trunk/gcc/testsuite/ChangeLog