Re: [AArch64][SVE 13/32] Add an F_STRICT flag

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 23/08/16 10:14, Richard Sandiford wrote:
> SVE predicate operands can appear in three forms:
> 
> 1. unsuffixed: "Pn"
> 2. with a predication type: "Pn/[ZM]"
> 3. with a size suffix: "Pn.[BHSD]"
> 
> No variation is allowed: unsuffixed operands cannot have a (redundant)
> suffix, and the suffixes can never be dropped.  Unsuffixed Pn are used
> in LDR and STR, but they are also used for Pg operands in cases where
> the result is scalar and where there is therefore no choice to be made
> between "merging" and "zeroing".  This means that some Pg operands have
> suffixes and others don't.
> 
> It would be possible to use context-sensitive parsing to handle
> this difference.  The tc-aarch64.c code would then raise an error
> if the wrong kind of suffix is used for a particular instruction.
> 
> However, we get much more user-friendly error messages if we parse
> all three forms for all SVE instructions and record the suffix as a
> qualifier.  The normal qualifier matching code can then report cases
> where the wrong kind of suffix is used.  This is a slight extension
> of existing usage, which really only checks for the wrong choice of
> suffix within a particular kind of suffix.
> 
> The only catch is a that a "NIL" entry in the qualifier list
> specifically means "no suffix should be present" (case 1 above).
> NIL isn't a wildcard here.  It also means that an instruction that
> requires all-NIL qualifiers can fail to match (because a suffix was
> supplied when it shouldn't have been); this requires a slight change
> to find_best_match.
> 
> This patch adds an F_STRICT flag to select this behaviour.
> The flag will be set for all SVE instructions.  The behaviour
> for other instructions doesn't change.
> 
> OK to install?
> 
> Thanks,
> Richard
> 
> 
> include/opcode/
> 	* aarch64.h (F_STRICT): New flag.
> 
> opcodes/
> 	* aarch64-opc.c (match_operands_qualifier): Handle F_STRICT.
> 
> gas/
> 	* config/tc-aarch64.c (find_best_match): Simplify, allowing an
> 	instruction with all-NIL qualifiers to fail to match.

OK.

R.

> 
> diff --git a/gas/config/tc-aarch64.c b/gas/config/tc-aarch64.c
> index 165ab9a..9591704 100644
> --- a/gas/config/tc-aarch64.c
> +++ b/gas/config/tc-aarch64.c
> @@ -4182,7 +4182,7 @@ find_best_match (const aarch64_inst *instr,
>      }
>  
>    max_num_matched = 0;
> -  idx = -1;
> +  idx = 0;
>  
>    /* For each pattern.  */
>    for (i = 0; i < AARCH64_MAX_QLF_SEQ_NUM; ++i, ++qualifiers_list)
> @@ -4194,9 +4194,6 @@ find_best_match (const aarch64_inst *instr,
>        if (empty_qualifier_sequence_p (qualifiers) == TRUE)
>  	{
>  	  DEBUG_TRACE_IF (i == 0, "empty list of qualifier sequence");
> -	  if (i != 0 && idx == -1)
> -	    /* If nothing has been matched, return the 1st sequence.  */
> -	    idx = 0;
>  	  break;
>  	}
>  
> diff --git a/include/opcode/aarch64.h b/include/opcode/aarch64.h
> index 1e38749..24a2ddb 100644
> --- a/include/opcode/aarch64.h
> +++ b/include/opcode/aarch64.h
> @@ -598,7 +598,9 @@ extern aarch64_opcode aarch64_opcode_table[];
>  #define F_OD(X) (((X) & 0x7) << 24)
>  /* Instruction has the field of 'sz'.  */
>  #define F_LSE_SZ (1 << 27)
> -/* Next bit is 28.  */
> +/* Require an exact qualifier match, even for NIL qualifiers.  */
> +#define F_STRICT (1ULL << 28)
> +/* Next bit is 29.  */
>  
>  static inline bfd_boolean
>  alias_opcode_p (const aarch64_opcode *opcode)
> diff --git a/opcodes/aarch64-opc.c b/opcodes/aarch64-opc.c
> index 322b991..d870fd6 100644
> --- a/opcodes/aarch64-opc.c
> +++ b/opcodes/aarch64-opc.c
> @@ -854,7 +854,7 @@ aarch64_find_best_match (const aarch64_inst *inst,
>  static int
>  match_operands_qualifier (aarch64_inst *inst, bfd_boolean update_p)
>  {
> -  int i;
> +  int i, nops;
>    aarch64_opnd_qualifier_seq_t qualifiers;
>  
>    if (!aarch64_find_best_match (inst, inst->opcode->qualifiers_list, -1,
> @@ -864,6 +864,15 @@ match_operands_qualifier (aarch64_inst *inst, bfd_boolean update_p)
>        return 0;
>      }
>  
> +  if (inst->opcode->flags & F_STRICT)
> +    {
> +      /* Require an exact qualifier match, even for NIL qualifiers.  */
> +      nops = aarch64_num_of_operands (inst->opcode);
> +      for (i = 0; i < nops; ++i)
> +	if (inst->operands[i].qualifier != qualifiers[i])
> +	  return FALSE;
> +    }
> +
>    /* Update the qualifiers.  */
>    if (update_p == TRUE)
>      for (i = 0; i < AARCH64_MAX_OPND_NUM; ++i)
>