[Bug c/126753] New: GCC emitting useless AND instruction when setting a bool from processor flags

[contact at ivanchev dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126753

            Bug ID: 126753
           Summary: GCC emitting useless AND instruction when setting a
                    bool from processor flags
           Product: gcc
           Version: 16.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: contact at ivanchev dot net
  Target Milestone: ---

See this example https://godbolt.org/z/5nfr1vscn

I am compiling

#include <stdint.h>
#include <stdckdint.h>
#include <stdbool.h>

uint32_t func(uint32_t a, uint32_t b, bool *overflow) {
    uint32_t res;
    *overflow = ckd_add(&res, a, b);
    return res;
}

with `-m32 -O2`.

GCC emits a useless AND after setting the boolean var from the CARRY flag:

        setc    BYTE PTR [edx]
        and     BYTE PTR [edx], 1

This seems to happen for all flags and I'm seeing it across a broad range of
cases.