[Bug rtl-optimization/100087] New: Redundant extend with compare against zero for baseline Armv8-M

[acoplan at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100087

            Bug ID: 100087
           Summary: Redundant extend with compare against zero for
                    baseline Armv8-M
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: acoplan at gcc dot gnu.org
  Target Milestone: ---

For the following:

_Bool eq0(int x)
{
    return x == 0;
}

with -march=armv8-m.base -O2 we generate:

eq0:
        rsbs    r3, r0, #0
        adcs    r0, r0, r3
        uxtb    r0, r0
        bx      lr

but the uxtb is redundant.