[Bug c/93781] New: Optimizer produces suboptimal code related to -ftree-vrp

[zhongyunde at huawei dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93781

            Bug ID: 93781
           Summary: Optimizer produces suboptimal code related to
                    -ftree-vrp
           Product: gcc
           Version: 9.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhongyunde at huawei dot com
  Target Milestone: ---

For the following code, we can known the value C000003FE is always less then 5,
so the return value should be true.
test base on the x86-64 gcc 9.2 on https://gcc.godbolt.org/, so get complicated
assemble.

unsigned int foo (unsigned int arg)
{
  int C00000400 = arg - 3;
  unsigned int C000003FE = 4;
  int C000003FF = 0x1 << arg;

  if (C00000400 < 0)
     C000003FE = C000003FF;

  return C000003FE < 5;
}