[Bug tree-optimization/102634] New: Optimization in dom2 pass makes wrong signed integer overflow inference

[Bug tree-optimization/102634] New: Optimization in dom2 pass makes wrong signed integer overflow inference

[mk.aard.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102634

            Bug ID: 102634
           Summary: Optimization in dom2 pass makes wrong signed integer
                    overflow inference
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mk.aard.gcc at gmail dot com
  Target Milestone: ---

Created attachment 51563
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51563&action=edit
Sample code which fails. Integer with 'NaN' handling user type using min
integer value as NaN

Compiled using GCC 10.2.1 on Debian 11 Bullseye, amd64:

g++ -c -O2 -std=c++17 example.cpp

This generates the following assembly for strange_code() (see attached .ii)

00000000000000d0 <strange_code()>:
  d0:   55                      push   %rbp
  d1:   48 83 ec 10             sub    $0x10,%rsp
  d5:   48 c7 44 24 08 00 00    movq   $0x0,0x8(%rsp)
  dc:   00 00 
  de:   48 8d 6c 24 08          lea    0x8(%rsp),%rbp
  e3:   48 89 ef                mov    %rbp,%rdi
  e6:   e8 00 00 00 00          callq  eb <strange_code()+0x1b>
  eb:   48 89 ef                mov    %rbp,%rdi
**ee:   48 be 00 00 00 00 00    movabs $0x8000000000000000,%rsi
  f5:   00 00 80 
  f8:   e8 00 00 00 00          callq  fd <strange_code()+0x2d>
  fd:   48 83 c4 10             add    $0x10,%rsp
 101:   b8 01 00 00 00          mov    $0x1,%eax
 106:   5d                      pop    %rbp
 107:   c3                      retq

The use of 0x8000000000000000 as the argument for the second call we believe is
an incorrect optimization.

Although -fwrapv resolves this issue for us, and bug reporting guidelines
indicate that -fwrapv fixes are likely user error, I and several teammates have
been unable to find any signed integer overflow issues in the example provided.
As far as we can tell, each usage of the problematic value avoids any operation
which could cause overflow.

I apologize that the example isn't smaller, changing virtually anything in it
causes the issue to go away.

[Bug tree-optimization/102634] Optimization in dom2 pass makes wrong signed integer overflow inference

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102634

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=98513
         Resolution|---                         |DUPLICATE
      Known to fail|                            |10.2.0
             Status|UNCONFIRMED                 |RESOLVED
      Known to work|                            |10.3.0

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed already in GCC 10.3.0, a dup of bug 98513.

*** This bug has been marked as a duplicate of bug 98513 ***