[Bug target/106585] New: RISC-V: Mis-optimized code gen for zbs

["kito at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106585

            Bug ID: 106585
           Summary: RISC-V: Mis-optimized code gen for zbs
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kito at gcc dot gnu.org
  Target Milestone: ---
            Target: riscv

Command:
$ riscv64-unknown-elf-gcc foo.c -o - -S -O3 -march=rv64imafdc_zbb_zbs

```c
int foo(int rs1, int rs2) {
  return (rs1 & ~(1<<rs2));
}
```

Current code gen:
```asm
foo:
        li      a5,1
        sllw    a5,a5,a1
        andn    a0,a0,a5
        sext.w  a0,a0
        ret
```

And even worth if compile without zbb
```asm
foo:
        li      a5,1
        sllw    a5,a5,a1
        andn    a0,a0,a5
        sext.w  a0,a0
        ret
```

clang code gen:
```
foo:
        bclr    a0, a0, a1
        sext.w  a0, a0
        ret
```