Re: [PATCH try 2 resend] [i386] Remove warnings for ignoring -mcall-ms2sysv-xlogues.

[Bernd Edlinger <bernd dot edlinger at hotmail dot de>]

On 06/11/17 22:35, Daniel Santos wrote:
> I appear to have forgotten to cc gcc-patches, sorry about that.
> 
> There are currently three cases where we issue a warning when disabling
> -mcall-ms2sysv-xlogues for a function, but I never added a proper
> warning, so there's no mechanism for disabling it.  This is something
> that I meant to address sooner.  I'm thinking that it's better to just
> remove the warning entirely and document these cases, rather than adding
> a new warning.  Any thoughts?
> 
> These are the conditions:
> 
> * the use of -fsplit-stack,
> * the use of static call chains (not sure if we can ever have that), and
> * if the function calls __buildin_eh_return.
> 
> Some of these cases can likely be supported, but they are just on the
> "not yet tested" list.
> 
> 2017-06-11  Daniel Santos  <daniel.santos@pobox.com
> 
> 	* config/i386/i386.c (warn_once_call_ms2sysv_xlogues): Remove.
> 	(ix86_compute_frame_layout): Don't call warn_once_call_ms2sysv_xlogues.
> 	(ix86_expand_call): Likewise.
> 

Your change log should also mention the changed doc/invoke.texi


> Thanks,
> Daniel
> 
> Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
> ---
>   gcc/config/i386/i386.c | 26 +++-----------------------
>   gcc/doc/invoke.texi    | 25 ++++++++++++++++++++-----
>   2 files changed, 23 insertions(+), 28 deletions(-)
> 
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index d5c2d46bf5e..2dc6e53c765 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -12772,18 +12772,6 @@ ix86_builtin_setjmp_frame_value (void)
>     return stack_realign_fp ? hard_frame_pointer_rtx : virtual_stack_vars_rtx;
>   }
>   
> -/* Emits a warning for unsupported msabi to sysv pro/epilogues.  */
> -static void warn_once_call_ms2sysv_xlogues (const char *feature)
> -{
> -  static bool warned_once = false;
> -  if (!warned_once)
> -    {
> -      warning (0, "-mcall-ms2sysv-xlogues is not compatible with %s",
> -	       feature);
> -      warned_once = true;
> -    }
> -}
> -
>   /* When using -fsplit-stack, the allocation routines set a field in
>      the TCB to the bottom of the stack plus this much space, measured
>      in bytes.  */
> @@ -12814,18 +12802,10 @@ ix86_compute_frame_layout (void)
>         gcc_assert (TARGET_SSE);
>         gcc_assert (!ix86_using_red_zone ());
>   
> -      if (crtl->calls_eh_return)
> +      if (crtl->calls_eh_return || ix86_static_chain_on_stack)
>   	{
>   	  gcc_assert (!reload_completed);
>   	  m->call_ms2sysv = false;
> -	  warn_once_call_ms2sysv_xlogues ("__builtin_eh_return");
> -	}
> -
> -      else if (ix86_static_chain_on_stack)
> -	{
> -	  gcc_assert (!reload_completed);
> -	  m->call_ms2sysv = false;
> -	  warn_once_call_ms2sysv_xlogues ("static call chains");
>   	}
>   
>         /* Finally, compute which registers the stub will manage.  */
> @@ -29290,9 +29270,9 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1,
>   	  else if (ix86_function_ms_hook_prologue (current_function_decl))
>   	    ;
>   
> -	  /* TODO: Cases not yet examined.  */
> +	  /* TODO: Compatibility not yet examined.  */
>   	  else if (flag_split_stack)
> -	    warn_once_call_ms2sysv_xlogues ("-fsplit-stack");
> +	    ;
>   
>   	  else
>   	    {
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index c1168823af7..eec02b43a4f 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -25389,11 +25389,26 @@ using the function attributes @code{ms_abi} and @code{sysv_abi}.
>   @opindex mno-call-ms2sysv-xlogues
>   Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a
>   System V ABI function must consider RSI, RDI and XMM6-15 as clobbered.  By
> -default, the code for saving and restoring these registers is emitted inline,
> -resulting in fairly lengthy prologues and epilogues.  Using
> -@option{-mcall-ms2sysv-xlogues} emits prologues and epilogues that
> -use stubs in the static portion of libgcc to perform these saves and restores,
> -thus reducing function size at the cost of a few extra instructions.
> +default, the instructions for saving and restoring these registers are emitted
> +inline, resulting in fairly lengthy pro- and epilogues.  Using
> +@option{-mcall-ms2sysv-xlogues} emits pro- and epilogues that use stubs in the
> +static portion of libgcc to perform these saves and restores, thus reducing
> +function size at the cost of executing a few extra instructions.  This cost is
> +theoretically mitigated or eliminated by reduced instruction cache utilization,
> +temporal locality of the stubs, and the stubs' use of MOV instructions over
> +PUSH and POP.
> +
> +This option is not supported with SEH, so it is completely unavailable on
> +Windows.  It is also silently disabled if a function:
> +
> +@enumerate
> +@item is built with @option{-mno-sse2} or @option{-fsplit-stack},
> +@item has @code{__attribute__ ((ms_hook_prologue))}, or
> +@item either throws an exception or explicitly calls @code{__builtin_eh_return}.
> +@end enumerate
> +
> +Support for @option{-fsplit-stack} and @code{__builtin_eh_return} may be
> +added at some time in the future, but has not yet been tested.
>   
>   @item -mtls-dialect=@var{type}
>   @opindex mtls-dialect
>