Re: [PATCH v7 2/9] Fix pro_and_epilogue for sibcalls at -O0

[Andi Kleen <ak@linux.intel.com>]

>      @@ -6557,7 +6558,7 @@ rest_of_handle_thread_prologue_and_epilogue
>      (function *fun)
>       {
>         /* prepare_shrink_wrap is sensitive to the block structure of the
>      control
>            flow graph, so clean it up first.  */
>      -  if (optimize)
>      +  if (cfun->tail_call_marked || optimize)
>           cleanup_cfg (0);
> 
>         /* On some machines, the prologue and epilogue code, or parts
>      thereof,
>      @@ -6579,7 +6580,7 @@ rest_of_handle_thread_prologue_and_epilogue
>      (function *fun)
> 
>         /* Shrink-wrapping can result in unreachable edges in the epilogue,
>            see PR57320.  */
>      -  cleanup_cfg (optimize ? CLEANUP_EXPENSIVE : 0);
>      +  cleanup_cfg ((cfun->tail_call_marked || optimize) ? CLEANUP_EXPENSIVE
>      : 0);
> 
>    I think this makes -g -O0 with musttail useless. Make sure if you have a
>    musttail function call in the ir that it does not change the cfg for -O0
>    case which adds extra jumps specifically for debugging. 

It looks like the second hunk (CLEANUP_EXPENSIVE) is not actually
needed. I just tested and at least ARM works without it. I will drop it.

But the first one is needed.

Do you still have the concern only with the first? AFAIK without
CLEANUP_EXPENSIVE there will be much less changes to branches.

-Andi