[Bug tree-optimization/110896] New: [12/13/14 Regression] gcc.dg/ubsan/pr81981.c is xfailed

[Bug tree-optimization/110896] New: [12/13/14 Regression] gcc.dg/ubsan/pr81981.c is xfailed

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110896

            Bug ID: 110896
           Summary: [12/13/14 Regression] gcc.dg/ubsan/pr81981.c is
                    xfailed
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: diagnostic, xfail
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 24639
  Target Milestone: ---

The original issue in PR 81981 is fixed. The problem here is we don't even warn
without -fsanitize=undefined too.
Testcase from that PR:
```
int foo (int i)
{
  int t[1], u[1];
  int n = 0;

  if (i)
    {
      t[n] = i;
      u[0] = i;
    }

  return t[0] + u[0];
}

```
we don't warn about `u[0]` being unintinialized with just `-O2 -Wall -Wextra`
starting in GCC 12 via r12-4625 (the fix for pr102681). That is the issue is
unrelated to -fsanitize=undefined now.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639
[Bug 24639] [meta-bug] bug to track all Wuninitialized issues

[Bug tree-optimization/110896] [12/13/14 Regression] gcc.dg/ubsan/pr81981.c is xfailed

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110896

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.4

[Bug tree-optimization/110896] [12/13/14 Regression] gcc.dg/ubsan/pr81981.c is xfailed

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110896

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-08-04

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
We simplify this to t[0] * 2 (by luck, so it could also be u[0] * 2) which
means we lose track of the use of the other variable.

Value numbering stmt = t$0_4 = PHI <t$0_13(D)(2), t$0_15(3)>
Setting value number of t$0_4 to t$0_4 (changed)
Making available beyond BB4 t$0_4 for value t$0_4
Value numbering stmt = u$0_12 = PHI <u$0_14(D)(2), u$0_16(3)>
Marking CSEd to PHI node t$0_4 = PHI <t$0_13(D)(2), t$0_15(3)>
Setting value number of u$0_12 to t$0_4 (changed)
...
Replaced redundant PHI node defining u$0_12 with t$0_4
gimple_simplified to _9 = t$0_4 * 2;

early uninit sees conditional init of the memory and so refrains from
diagnosing this.

I suppose this is kind-of a duplicate of the many missed uninit diagnostics
because of CCP optimistic propagation (and only because we don't do optimistic
copyprop we do not have even more such cases).

[Bug tree-optimization/110896] [12/13/14 Regression] gcc.dg/ubsan/pr81981.c is xfailed

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110896

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
                 CC|                            |law at gcc dot gnu.org