Re: Question about conds attribute for *thumb2_alusi3_short

[Chung-Lin Tang <cltang at codesourcery dot com>]

On 13/6/24 äå11:43, Tom de Vries wrote:
> Richard,
> 
> I've noticed that f.i. *thumb2_alusi3_short has no explicit setting of the conds
> attribute, which means the value of the conds attribute for this insn is nocond:
> ...
> (define_insn "*thumb2_alusi3_short"
>   [(set (match_operand:SI          0 "s_register_operand" "=l")
>         (match_operator:SI 3 "thumb_16bit_operator"
> 	 [(match_operand:SI 1 "s_register_operand" "0")
> 	  (match_operand:SI 2 "s_register_operand" "l")]))
>    (clobber (reg:CC CC_REGNUM))]
>   "TARGET_THUMB2 && reload_completed
>    && GET_CODE(operands[3]) != PLUS
>    && GET_CODE(operands[3]) != MINUS"
>   "%I3%!\\t%0, %1, %2"
>   [(set_attr "predicable" "yes")
>    (set_attr "length" "2")]
> )
> ...
> 
> AFAIU, this insn is either:
> - conditional, and does not modify cc, or
> - unconditional, and sets cc.
> So the clobber of CC in the RTL conservatively describes both cases.
> 
> It seems to me the logical conds setting for the conditional case is nocond, set
> (or perhaps clob) for the unconditional case. So, is this a more accurate value
> of conds for this insn:
> ...
>    (set (attr "conds")
>         (if_then_else
>           (match_test "GET_CODE (PATTERN (insn)) == COND_EXEC")
>           (const_string "nocond")
>           (const_string "set")))]
> ...
> ?
> 
> Is there a generic need to have this attribute accurate for all insns?

Following this thread that Tom pointed to me earlier in internal discussion:
http://gcc.gnu.org/ml/gcc-patches/2012-02/msg00723.html

If the short-CC-clobbered form is selected very late now, I think this
pattern simply is (or should) not be used for the conditional (within
IT-block) case. It should simply be set to "clob". Predicable might be
set to "no" as well...

Chung-Lin