[M68k] Failure to optimize out function prologue and epilogue/omit frame pointer

[GabrielRavier]

void f(){}

With -O3, GCC outputs this:

f():
  rts

LLVM outputs this:

f(): ; @f()
  link.w %a6, #0
  unlk %a6
  rts

[GabrielRavier]

(PS: I've just realized this can be accomplished by explicitly providing -fomit-frame-pointer on the command line, but even so it seems like it should be activated by default, unless there's a specific reason not to ? I looked around a bit and could not find any)

[llvmbot]

@llvm/issue-subscribers-backend-m68k

Author: Gabriel Ravier (GabrielRavier)

```cpp void f(){} ```

With -O3, GCC outputs this:

f():
  rts

LLVM outputs this:

f(): ; @<!-- -->f()
  link.w %a6, #<!-- -->0
  unlk %a6
  rts

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: Gabriel Ravier (GabrielRavier)

```cpp void f(){} ```

With -O3, GCC outputs this:

f():
  rts

LLVM outputs this:

f(): ; @<!-- -->f()
  link.w %a6, #<!-- -->0
  unlk %a6
  rts