[Bug target/81736] New: Unnecessary save and restore frame pointer with -fno-omit-frame-pointer

["hjl.tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81736

            Bug ID: 81736
           Summary: Unnecessary save and restore frame pointer with
                    -fno-omit-frame-pointer
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: ubizjak at gmail dot com
  Target Milestone: ---
            Target: x86-64

[hjl@gnu-4 tmp]$ cat y.i
extern int i;

int foo (void)
{
return i;
}

[hjl@gnu-4 tmp]$ gcc -S -O3 y.i -fno-omit-frame-pointer                
[hjl@gnu-4 tmp]$ cat y.s
        .file   "y.i"
        .text
        .p2align 4,,15
        .globl  foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movl    i(%rip), %eax
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        popq    %rbp
        .cfi_def_cfa 7, 8
        ret
        .cfi_endproc
.LFE0:
        .size   foo, .-foo

There is no need to save and restore frame pointer since stack is untouched.