[Bug c++/49115] New: invalid return value optimization (?) when exception is thrown and caught

[Bug c++/49115] New: invalid return value optimization (?) when exception is thrown and caught

[arnej at pvv dot ntnu.no]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

           Summary: invalid return value optimization (?) when exception
                    is thrown and caught
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: arnej@pvv.ntnu.no


we have some code that started failing when I tried upgrading our tool chain to
GCC 4.5.2; it gets stale data in an object when an exception is thrown during
assignment.

It looks to me like return value optimization will cause the object constructor
to be optimized away, but I'm not totally certain if that is the actual
problem, nor what the C++ language guarantees in this situation.

A self-contained test program is below, failing for me on x86_64 using:

GNU C++ (GCC) version 4.5.2 (x86_64-unknown-linux-gnu)
    compiled by GNU C version 4.5.2, GMP version 4.3.2, MPFR version 3.0.1, MPC
version 0.9

----- test program follows -----

extern "C" { extern long write(int, const void *, unsigned long); }

struct MyException {};
int simfail = 7;

struct Data {
    int nr;
    Data() : nr(66) {}
};

Data getData(int i) {
    if (simfail == i) throw MyException();
    Data data;
    data.nr = i;
    return data;
}

bool verify() {
    char bad[7] = "BAD x\n";
    for (int i = 0; i < 10; i++) {
        Data data;
        try {
            data = getData(i);
        } catch (MyException& e) {
            if (data.nr != 66) {
                bad[4] = '0' + data.nr;
                write(2, bad, 6);
                return false;
            }
        }
    }
    return true;
}

int main(int, char **) {
    simfail = 4;
    return verify() ? 0 : 1;
}

[Bug tree-optimization/49115] invalid return value optimization (?) when exception is thrown and caught

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011.05.22 20:33:26
          Component|c++                         |tree-optimization
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1
      Known to fail|                            |4.7.0

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-22 20:33:26 UTC ---
Confirmed.  Reduced testcase:

extern "C" void abort (void);
struct MyException {};
struct Data {
    int nr;
    Data() : nr(66) {}
};
Data __attribute__((noinline,noclone)) getData(int i)
{
  if (i) throw MyException();
  Data data;
  data.nr = i;
  return data;
}
int main(int, char **)
{
  Data data;
  try {
      data = getData(1);
  } catch (MyException& e) {
      if (data.nr != 66)
        abort ();
  }
}

what happens is that the store to data.nr from the constructor call in
main is DCEd.  Looks like an alias issue to me.  Mine.

[Bug tree-optimization/49115] [4.5/4.6 Regression] invalid return value optimization (?) when exception is thrown and caught

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.4.5, 4.7.0
   Target Milestone|---                         |4.5.4
            Summary|invalid return value        |[4.5/4.6 Regression]
                   |optimization (?) when       |invalid return value
                   |exception is thrown and     |optimization (?) when
                   |caught                      |exception is thrown and
                   |                            |caught
      Known to fail|4.7.0                       |4.5.3, 4.6.0

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-23 12:11:14 UTC ---
Fixed on trunk sofar.  Works with 4.4.

[Bug tree-optimization/49115] invalid return value optimization (?) when exception is thrown and caught

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-23 12:08:45 UTC ---
Author: rguenth
Date: Mon May 23 12:08:41 2011
New Revision: 174066

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174066
Log:
2011-05-23  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/49115
    * tree-ssa-alias.c (stmt_kills_ref_p_1): If the assignment
    is not necessarily carried out, do not claim it kills the ref.
    * tree-ssa-dce.c (mark_aliased_reaching_defs_necessary_1): Likewise.

    * g++.dg/torture/pr49115.C: New testcase.

Added:
    trunk/gcc/testsuite/g++.dg/torture/pr49115.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-alias.c
    trunk/gcc/tree-ssa-dce.c

[Bug tree-optimization/49115] [4.5/4.6 Regression] invalid return value optimization (?) when exception is thrown and caught

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug tree-optimization/49115] [4.5/4.6 Regression] invalid return value optimization (?) when exception is thrown and caught

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-06-17 11:27:41 UTC ---
Author: rguenth
Date: Fri Jun 17 11:27:37 2011
New Revision: 175148

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175148
Log:
2011-06-17  Richard Guenther  <rguenther@suse.de>

        Backport from mainline
        2011-05-23  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/49115
    * tree-ssa-alias.c (stmt_kills_ref_p_1): If the assignment
    is not necessarily carried out, do not claim it kills the ref.
    * tree-ssa-dce.c (mark_aliased_reaching_defs_necessary_1): Likewise.

    * g++.dg/torture/pr49115.C: New testcase.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/torture/pr49115.C
Modified:
    branches/gcc-4_6-branch/gcc/ChangeLog
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_6-branch/gcc/tree-ssa-alias.c
    branches/gcc-4_6-branch/gcc/tree-ssa-dce.c

[Bug tree-optimization/49115] [4.5 Regression] invalid return value optimization (?) when exception is thrown and caught

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #6 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-07-04 13:25:39 UTC ---
Fixed.

[Bug tree-optimization/49115] [4.5 Regression] invalid return value optimization (?) when exception is thrown and caught

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49115

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-07-04 13:25:24 UTC ---
Author: rguenth
Date: Mon Jul  4 13:25:21 2011
New Revision: 175812

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175812
Log:
2011-07-04  Richard Guenther  <rguenther@suse.de>

        Backport from mainline
        2011-05-23  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/49115
    * tree-ssa-dce.c (mark_aliased_reaching_defs_necessary_1): Likewise.

    * g++.dg/torture/pr49115.C: New testcase.

Added:
    branches/gcc-4_5-branch/gcc/testsuite/g++.dg/torture/pr49115.C
Modified:
    branches/gcc-4_5-branch/gcc/ChangeLog
    branches/gcc-4_5-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_5-branch/gcc/tree-ssa-dce.c