Re: [PATCHv2 1/2] aarch64: Do not give ABI change diagnostics for _BitInt(N)

[Richard Sandiford <richard.sandiford@arm.com>]

"Andre Vieira (lists)" <andre.simoesdiasvieira@arm.com> writes:
> This patch makes sure we do not give ABI change diagnostics for the ABI 
> breaks of GCC 9, 13 and 14 for any type involving _BitInt(N), since that 
> type did not exist before this GCC version.
>
> ChangeLog:
>
> 	* config/aarch64/aarch64.cc (bitint_or_aggr_of_bitint_p): New function.
> 	(aarch64_layout_arg): Don't emit diagnostics for types involving
> 	_BitInt(N).
>
> diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> index 1ea84c8bd7386e399f6ffa3a5e36408cf8831fc6..b68cf3e7cb9a6fa89b4e5826a39ffa11f64ca20a 100644
> --- a/gcc/config/aarch64/aarch64.cc
> +++ b/gcc/config/aarch64/aarch64.cc
> @@ -6744,6 +6744,33 @@ aarch64_function_arg_alignment (machine_mode mode, const_tree type,
>    return alignment;
>  }
>  
> +/* Return true if TYPE describes a _BitInt(N) or an angreggate that uses the
> +   _BitInt(N) type.  These include ARRAY_TYPE's with an element that is a
> +   _BitInt(N) or an aggregate that uses it, and a RECORD_TYPE or a UNION_TYPE
> +   with a field member that is a _BitInt(N) or an aggregate that uses it.
> +   Return false otherwise.  */
> +
> +static bool
> +bitint_or_aggr_of_bitint_p (tree type)
> +{
> +  if (!type)
> +    return false;
> +
> +  if (TREE_CODE (type) == BITINT_TYPE)
> +    return true;
> +
> +  /* If ARRAY_TYPE, check it's element type.  */
> +  if (TREE_CODE (type) == ARRAY_TYPE)
> +    return bitint_or_aggr_of_bitint_p (TREE_TYPE (type));
> +
> +  /* If RECORD_TYPE or UNION_TYPE, check the fields' types.  */
> +  if (RECORD_OR_UNION_TYPE_P (type))
> +    for (tree field = TYPE_FIELDS (type); field; field = TREE_CHAIN (field))
> +      if (bitint_or_aggr_of_bitint_p (TREE_TYPE (field)))
> +	return true;
> +  return false;
> +}
> +
>  /* Layout a function argument according to the AAPCS64 rules.  The rule
>     numbers refer to the rule numbers in the AAPCS64.  ORIG_MODE is the
>     mode that was originally given to us by the target hook, whereas the
> @@ -6767,12 +6794,6 @@ aarch64_layout_arg (cumulative_args_t pcum_v, const function_arg_info &arg)
>    if (pcum->aapcs_arg_processed)
>      return;
>  
> -  bool warn_pcs_change
> -    = (warn_psabi
> -       && !pcum->silent_p
> -       && (currently_expanding_function_start
> -	   || currently_expanding_gimple_stmt));
> -
>    /* HFAs and HVAs can have an alignment greater than 16 bytes.  For example:
>  
>         typedef struct foo {
> @@ -6907,6 +6928,18 @@ aarch64_layout_arg (cumulative_args_t pcum_v, const function_arg_info &arg)
>  	      && (!alignment || abi_break_gcc_9 < alignment)
>  	      && (!abi_break_gcc_13 || alignment < abi_break_gcc_13));
>  
> +
> +  bool warn_pcs_change
> +    = (warn_psabi
> +       && !pcum->silent_p
> +       && (currently_expanding_function_start
> +	   || currently_expanding_gimple_stmt)
> +      /* warn_pcs_change is currently used to gate diagnostics in case of
> +	 abi_break_gcc_{9,13,14}.  These however, do not apply to _BitInt(N)
> +	 types as they were only introduced in GCC 14.  */
> +       && (!type || !bitint_or_aggr_of_bitint_p (type)));

How about making this a new variable such as:

  /* _BitInt(N) was only added in GCC 14.  */
  bool warn_pcs_change_le_gcc14
    = (warn_psabi && !bitint_or_aggr_of_bitint_p (type);

(and keeping warn_pcs_change where it is).  In principle, warn_pcs_change
is meaningful for any future ABI breaks, and we might forget that it
excludes bitints.  The name is just a suggestion.

OK with that change, thanks.

Richard

> +
> +
>    /* allocate_ncrn may be false-positive, but allocate_nvrn is quite reliable.
>       The following code thus handles passing by SIMD/FP registers first.  */
>  
> @@ -21266,19 +21299,25 @@ aarch64_gimplify_va_arg_expr (tree valist, tree type, gimple_seq *pre_p,
>        rsize = ROUND_UP (size, UNITS_PER_WORD);
>        nregs = rsize / UNITS_PER_WORD;
>  
> -      if (align <= 8 && abi_break_gcc_13 && warn_psabi)
> +      if (align <= 8
> +	  && abi_break_gcc_13
> +	  && warn_psabi
> +	  && !bitint_or_aggr_of_bitint_p (type))
>  	inform (input_location, "parameter passing for argument of type "
>  		"%qT changed in GCC 13.1", type);
>  
>        if (warn_psabi
>  	  && abi_break_gcc_14
> -	  && (abi_break_gcc_14 > 8 * BITS_PER_UNIT) != (align > 8))
> +	  && (abi_break_gcc_14 > 8 * BITS_PER_UNIT) != (align > 8)
> +	  && !bitint_or_aggr_of_bitint_p (type))
>  	inform (input_location, "parameter passing for argument of type "
>  		"%qT changed in GCC 14.1", type);
>  
>        if (align > 8)
>  	{
> -	  if (abi_break_gcc_9 && warn_psabi)
> +	  if (abi_break_gcc_9
> +	      && warn_psabi
> +	      && !bitint_or_aggr_of_bitint_p (type))
>  	    inform (input_location, "parameter passing for argument of type "
>  		    "%qT changed in GCC 9.1", type);
>  	  dw_align = true;