[Bug tree-optimization/106883] New: SLSR may generate signed wrap

[Bug tree-optimization/106883] New: SLSR may generate signed wrap

[kristerw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106883

            Bug ID: 106883
           Summary: SLSR may generate signed wrap
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
  Target Milestone: ---

SLSR may generate new signed wrap for cases where the original did not wrap.
This can be seen in the function f from gcc.dg/tree-ssa/slsr-19.c:

int
f (int c, int s)
{
  int x1, x2, y1, y2;

  y1 = c + 2;
  x1 = s * y1;
  y2 = y1 + 2;
  x2 = s * y2;
  return x1 + x2;
}

SLSR optimizes this to

int f (int c, int s)
{
   int y1;
   int x2;
   int x1;
   int _7;
   int slsr_9;

   <bb 2>:
   y1_2 = c_1(D) + 2;
   x1_4 = y1_2 * s_3(D);
   slsr_9 = s_3(D) * 2;
   x2_6 = x1_4 + slsr_9;
   _7 = x1_4 + x2_6;
   return _7;

Calling f(-3, 0x75181005) does not make any operation wrap in the original
function, but slsr_9 overflow in the optimized code.

[Bug tree-optimization/106883] SLSR may generate signed wrap

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106883

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-09-08
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |wrong-code
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed - thanks for reporting!  Since there's a VRP pass after SLSR it might
be possible to craft a testcase that fails at runtime.