[Bug c++/44783] implement -ftemplate-backtrace-limit=

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |brian.amberg at unibas dot
                   |                            |ch

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-25 15:16:30 UTC ---
*** Bug 48667 has been marked as a duplicate of this bug. ***

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-09-26
                 CC|                            |jason at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2011-09-26 18:29:15 UTC ---
Makes sense to me.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|gcc-bugs at gcc dot gnu.org |
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-10-17 18:15:46 UTC ---
On it.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[gredner at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

Gabriel Redner <gredner at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gredner at gmail dot com

--- Comment #4 from Gabriel Redner <gredner at gmail dot com> 2012-02-13 01:06:56 UTC ---
Is there any progress on this issue?  This bug is a major impediment when
debugging template-heavy code.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-13 08:56:41 UTC ---
I may well get to it but at this point will be for 4.8.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

--- Comment #6 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-02-13 17:09:50 UTC ---
Any of you has a minimal self-contained testcase? The ones I used when
implementing this, no longer need this option. Thanks.

This is my totally untested but compiles patch. Probably it needs some tuning.


Index: gcc/c-family/c.opt
===================================================================
--- gcc/c-family/c.opt  (revision 184150)
+++ gcc/c-family/c.opt  (working copy)
@@ -1033,10 +1033,14 @@ C++ ObjC++ Ignore Warn(switch %qs is no 

 ftabstop=
 C ObjC C++ ObjC++ Joined RejectNegative UInteger
 -ftabstop=<number>     Distance between tab stops for column reporting

+ftemplate-backtrace-limit=
+C++ ObjC++ Joined RejectNegative UInteger Var(template_backtrace_limit)
Init(10)
+Specify number of template instantiations notes for a single warning or error
+
 ftemplate-depth-
 C++ ObjC++ Joined RejectNegative Undocumented Alias(ftemplate-depth=)

 ftemplate-depth=
 C++ ObjC++ Joined RejectNegative UInteger
Index: gcc/cp/error.c
===================================================================
--- gcc/cp/error.c      (revision 184150)
+++ gcc/cp/error.c      (working copy)
@@ -3072,14 +3072,15 @@ print_instantiation_partial_context (dia
        n_total++;
       }

   t = t0;

-  if (n_total >= 12) 
+  if (template_backtrace_limit &&
+      n_total > template_backtrace_limit) 
     {
-      int skip = n_total - 10;
-      for (n = 0; n < 5; n++)
+      int skip = n_total - template_backtrace_limit;
+      for (n = 0; n < template_backtrace_limit/2; n++)
        {
          gcc_assert (t != NULL);
          if (loc != t->locus)
            print_instantiation_partial_context_line (context, t, loc,
                                                      /*recursive_p=*/false);

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot
                   |                            |com

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-14 11:14:18 UTC ---
Thanks Manuel. Thus, I'm going to test your patch. Was wondering, maybe we want
the nit: 'n_total > template_backtrace_limit + 2' n the condition, in order to
keep by default exactly the current behavior?

Otherwise, shall I send the patch to the mailing list for you? Thanks again.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-14 12:36:57 UTC ---
Created attachment 26658
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26658
Draft

This is a slightly tweaked and extended version of the patch which I actually
booted and tested.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

--- Comment #9 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-02-14 14:27:40 UTC ---
(In reply to comment #7)
> Thanks Manuel. Thus, I'm going to test your patch. Was wondering, maybe we want
> the nit: 'n_total > template_backtrace_limit + 2' n the condition, in order to
> keep by default exactly the current behavior?

This is why I wanted a testcase. The ones that are in the testsuite from when I
added this behaviour do not trigger the "skipping message" anymore, since later
I implemented recognizing the recursive template (which is much nicer IMHO). So
we need a testcase that triggers this (like a very deep instantiation or
something that the recursion detection cannot handle).

n_total >= 12 == n_total > template_backtrace_limit + 1

The +1 is basically giving enough space, so at least we always print 2 template
instantiations, one before and one after the "skipping". However, if
template_backtrace_limit=1 and n_total = 2, should we print just 1 (new patch)
or still 2 (old behavior)? This was not a problem before because
template_backtrace_limit was always 10.

> Otherwise, shall I send the patch to the mailing list for you? Thanks again.

Yes, please. Feel free also to edit it or completely modify it. Thanks.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

--- Comment #10 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-14 14:44:03 UTC ---
Agreed about the testcase, of course.

By the way, for the actual dejagnu testcase, a few weeks ago I noticed that
apparently testing for 'note:' is pretty weak, like if additional notes are
emitted (additional in the sense that there is no corresponding dg-message to
match) that doesn't lead to failure. Did you see anything like that?

Anyway, about the code, if I understand correctly your explanation, 'n_total >
template_backtrace_limit + 1' would lead to the exact same default behavior we
have now, but appears to misbehave a little when template_backtrace_limit == 1
and n_total == 2 because we really want 1 note in that case, that is what the
user really asked, right? Then probably what you wrote in the draft is fine,
but I don't have a strong opinion, really, I only noticed something 'weird'
going on with that condition and decided to ask.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

--- Comment #11 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-02-14 16:26:10 UTC ---
(In reply to comment #10)
> By the way, for the actual dejagnu testcase, a few weeks ago I noticed that
> apparently testing for 'note:' is pretty weak, like if additional notes are
> emitted (additional in the sense that there is no corresponding dg-message to
> match) that doesn't lead to failure. Did you see anything like that?

Any number of notes will be matched by a single "note:" test, since the
testsuite does not detect duplicates. There is PR about this somewhere.

> Anyway, about the code, if I understand correctly your explanation, 'n_total >
> template_backtrace_limit + 1' would lead to the exact same default behavior we
> have now, but appears to misbehave a little when template_backtrace_limit == 1
> and n_total == 2 because we really want 1 note in that case, that is what the
> user really asked, right? Then probably what you wrote in the draft is fine,
> but I don't have a strong opinion, really, I only noticed something 'weird'
> going on with that condition and decided to ask.

So I used the testcase testsuite/g++.dg/cpp0x/noexcept15.C to play a bit. 

I noticed that my earlier version never prints "skipping 1 instantiation
contexts". Now I recall that this was done on purpose. It seems pointless to
print a line "skipping 1" instead of the actual instantiation context. Also, we
don't have to deal with singular/plural. ;-)

However, this means that in some cases, we would actually print one more than
the limit. If we just say that the limit is a limit not the exact number
printed, a workaround is to print one less in that case. So:

limit n_total printed skipped
5     5       5       0
5     7       5       2
5     6       4       2

I also added the option name to the message for convenience (clang also does
this if I recall correctly).


-  if (n_total >= 12) 
+  if (template_backtrace_limit &&
+      n_total > template_backtrace_limit) 
     {
-      int skip = n_total - 10;
-      for (n = 0; n < 5; n++)
+      int skip = n_total - template_backtrace_limit;
+      int head = template_backtrace_limit/ 2;
+      /* Avoid skipping just 1. If so, skip 2.  */
+      if (skip == 1)
+       {
+         skip = 2;
+         head = (template_backtrace_limit - 1) / 2;
+       }
+      
+      for (n = 0; n < head; n++)
        {
          gcc_assert (t != NULL);
          if (loc != t->locus)
            print_instantiation_partial_context_line (context, t, loc,
                                                      /*recursive_p=*/false);
          loc = t->locus;
          t = t->next;
        }
-      if (t != NULL && skip > 1)
+      if (t != NULL && skip > 0)
        {
          expanded_location xloc;
          xloc = expand_location (loc);
          if (context->show_column)
            pp_verbatim (context->printer,
-                        _("%s:%d:%d:   [ skipping %d instantiation contexts
]\n"),
+                        _("%s:%d:%d:   [ skipping %d instantiation contexts,
use -ftemplate-backtrace-limit=0 to disable ]\n"),
                         xloc.file, xloc.line, xloc.column, skip);
          else
            pp_verbatim (context->printer,
-                        _("%s:%d:   [ skipping %d instantiation contexts
]\n"),
+                        _("%s:%d:   [ skipping %d instantiation contexts, use
-ftemplate-backtrace-limit=0 to disable ]\n"),
                         xloc.file, xloc.line, skip);

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-14 16:45:20 UTC ---
> Any number of notes will be matched by a single "note:" test, since the
> testsuite does not detect duplicates. There is PR about this somewhere.

I'm not sure the issue is just about duplicates. I know that. I'm afraid there
is more, like if a testcase doesn't have *any* dg-message markup it can pass,
like the actual *text* in a dg-message doesn't matter, things like that. I can
easily provide examples of the former, probably as easily the latter too.

> > Anyway, about the code, if I understand correctly your explanation, 'n_total >
> > template_backtrace_limit + 1' would lead to the exact same default behavior we
> > have now, but appears to misbehave a little when template_backtrace_limit == 1
> > and n_total == 2 because we really want 1 note in that case, that is what the
> > user really asked, right? Then probably what you wrote in the draft is fine,
> > but I don't have a strong opinion, really, I only noticed something 'weird'
> > going on with that condition and decided to ask.
> 
> So I used the testcase testsuite/g++.dg/cpp0x/noexcept15.C to play a bit. 
> 
> I noticed that my earlier version never prints "skipping 1 instantiation
> contexts". Now I recall that this was done on purpose. It seems pointless to
> print a line "skipping 1" instead of the actual instantiation context. Also, we
> don't have to deal with singular/plural. ;-)
> 
> However, this means that in some cases, we would actually print one more than
> the limit. If we just say that the limit is a limit not the exact number
> printed, a workaround is to print one less in that case. So:
> 
> limit n_total printed skipped
> 5     5       5       0
> 5     7       5       2
> 5     6       4       2
> 
> I also added the option name to the message for convenience (clang also does
> this if I recall correctly).

Ok. I'm going to regtest the updated draft. Note, in general '&&' goes always
in a new line; also cut & pasting in the trail often leads to diffs hard to
manage, better attaching, imo.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #26658|0                           |1
        is obsolete|                            |

--- Comment #13 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-15 15:55:26 UTC ---
Created attachment 26664
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26664
Draft 2

As regtested.

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

--- Comment #14 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-03-15 09:57:35 UTC ---
Author: paolo
Date: Thu Mar 15 09:57:29 2012
New Revision: 185424

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=185424
Log:
/c-family
2012-03-15  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    PR c++/44783
    * c.opt (ftemplate-backtrace-limit) Add.

/cp
2012-03-15  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    PR c++/44783
    * error.c (print_instantiation_partial_context): Use
    template_backtrace_limit.

/doc
2012-03-15  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    PR c++/44783
    * doc/invoke.texi [C++ Language Options]: Document
    -ftemplate-backtrace-limit.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c.opt
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/error.c
    trunk/gcc/doc/invoke.texi

[Bug c++/44783] implement -ftemplate-backtrace-limit=

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44783

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.8.0

--- Comment #15 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-03-15 09:59:46 UTC ---
Done.