[Bug c++/49118] New: Endless operator-> chain causes infinite loop

[Bug c++/49118] New: Endless operator-> chain causes infinite loop

[potswa at mac dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

           Summary: Endless operator-> chain causes infinite loop
           Product: gcc
           Version: 4.5.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: potswa@mac.com


When the "drill-down" behavior is used to chain operator-> calls, a cycle in
the chain causes an immediate error message, but an endless acyclic chain
causes the compiler to hang, very slowly consuming memory.

Minimal case:

template< int n >
struct a { 
    a< n+1 > operator->() { return a< n+1 >(); }
};

int main() {
    a<0>()->x;
}

Suggested fix: If operator-> returns a template specialization, consider its
instantiation to be nested. This existing error message and limit-mechanism
would be appropriate:

error: template instantiation depth exceeds maximum of 500 (use
-ftemplate-depth-NN to increase the maximum) instantiating ‘struct a<500>’

[Bug c++/49118] Endless operator-> chain causes infinite loop

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-05-23 07:44:01 UTC ---
For the record, ICC (EDG that is) misbehaves the same way, at least the
versions to which I have access. Maybe clang does something different?

[Bug c++/49118] Endless operator-> chain causes infinite loop

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-05-23 08:22:00 UTC ---
nope, same behaviour for clang 2.8

[Bug c++/49118] Endless operator-> chain causes infinite loop

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.05.23 10:58:00
     Ever Confirmed|0                           |1

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-23 10:58:00 UTC ---
Confirmed at least.

[Bug c++/49118] Endless operator-> chain causes infinite loop

[potswa at mac dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

--- Comment #4 from David Krauss <potswa at mac dot com> 2011-05-26 03:37:44 UTC ---
Created attachment 24359
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24359
Patch fixes behavior but error message repeats twice.

I implemented the suggested fix, but the resulting error message repeats the
part about "template instantiation depth exceeds maximum" twice. The template
backtrace appears after the error, not before as with a usual nesting problem.
Is there something I'm obviously doing wrong here?

Here are the most relevant lines from the attached patch.

/* For diagnostic purposes, pretend that the chain is nested. */
if (CLASS_TYPE_P (chain_type) && CLASSTYPE_TEMPLATE_INFO (chain_type))
  push_tinst_level (chain_type);

[Bug c++/49118] Endless operator-> chain causes infinite loop

[potswa at mac dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

David Krauss <potswa at mac dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #24359|0                           |1
        is obsolete|                            |

--- Comment #5 from David Krauss <potswa at mac dot com> 2011-05-26 03:43:41 UTC ---
Created attachment 24360
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24360
replace crufty previous patch

See this patch instead. Previous unintentionally captured unrelated
development.

[Bug c++/49118] Endless operator-> chain causes infinite loop

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-05-26 09:41:10 UTC ---
Maybe Jason can give you some tips, better sending the patch to the mailing
list for that, though, Bugzilla isn't meant for patches. CC Jason.

[Bug c++/49118] Endless operator-> chain causes infinite loop

[potswa at mac dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

--- Comment #7 from David Krauss <potswa at mac dot com> 2011-05-26 11:05:12 UTC ---
Yes, I'll likely do that in a few days… just wanted to put the code in "safe
holding," just in case.

[Bug c++/49118] Endless operator-> chain causes infinite loop

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-10 05:18:40 UTC ---
Author: jason
Date: Fri Jun 10 05:18:36 2011
New Revision: 174889

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174889
Log:
    PR c++/49118
    * typeck2.c (build_x_arrow): Push fake template context
    to produce diagnostic on acyclic endless operator-> drill-down.
    * call.c (build_new_op): Change Boolean overload status
    value to a pointer to the overload function.
    * cp-tree.h: Likewise.
    * typeck.c: Likewise.
    * parser.c: Likewise.
    * decl2.c: Likewise.
    * pt.c: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/template/arrow1.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/decl2.c
    trunk/gcc/cp/parser.c
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/cp/typeck2.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/49118] Endless operator-> chain causes infinite loop

[potswa at mac dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

--- Comment #9 from David Krauss <potswa at mac dot com> 2011-06-10 05:25:08 UTC ---
Thanks!

On Jun 9, 2011, at 10:18 PM, jason at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

[Bug c++/49118] Endless operator-> chain causes infinite loop

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.0

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2011-07-01 00:55:36 UTC ---
Fixed for 4.7.

[Bug c++/49118] Endless operator-> chain causes infinite loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49118

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |basil at list dot ru

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-25 22:45:10 UTC ---
*** Bug 56449 has been marked as a duplicate of this bug. ***