ARM: More intrinsics

[Andrew Haley]

On 03/15/2012 04:09 AM, pcpa at mandriva.com.br wrote:
>> Xerxes noticed an inconsistency in my patch.  I've removed the unused
>> masks, and redefined the condition in the atomic operations to use ETT
>> (else, true, true) rather than the confused encoding I used before.
>>
>> So, it's now
>>
>> +      it(codebuf, COND_EQ, IT_MASK_ETT);
>>
>> instead of
>>
>> -      it(codebuf, COND_NE, IT_MASK_TEE);
>
>   I feel there is something bogus here, because the first condition
> should be 'T' always, and the mask is based on bit 0 of the test
> condition. Talking this because I wrote support for arm thumb jit
> recently.

Well, that's how the ARM asm describes it, but that's not what
the encodings really do.  It's a shame they chose to describe it
in that way.

>> I had to do this because it's the only way the encodings make any
>> sense.  There isn't really any encoding for TEE that works with
>> COND_NE: it has to be expressed in the binary as COND_EQ:ETT.
>> (If cond is true, don't do X, but do Y and Z.)
>
>   For easier viewing instead of pointing to some link, the code I use
> to encode it* is:
>
> static void
> _tcit(jit_state_t *_jit, unsigned int tc, int it)
> {
>     int		c;
>     int		m;
>     c = (tc >> 28) & 1;
>     assert(!(tc & 0xfffffff) && tc != ARM_CC_NV);
>     switch (it) {
> 	case THUMB2_IT:		m =   1<<3; 			break;
> 	case THUMB2_ITT:	m =  (c<<3)| (1<<2);		break;
> 	case THUMB2_ITE:	m = (!c<<3)| (1<<2);		break;
> 	case THUMB2_ITTT:	m =  (c<<3)| (c<<2)| (1<<1);	break;
> 	case THUMB2_ITET:	m = (!c<<3)| (c<<2)| (1<<1);	break;
> 	case THUMB2_ITTE:	m =  (c<<3)|(!c<<2)| (1<<1);	break;
> 	case THUMB2_ITEE:	m = (!c<<3)|(!c<<2)| (1<<1);	break;
> 	case THUMB2_ITTTT:	m =  (c<<3)| (c<<2)| (c<<1)|1;	break;
> 	case THUMB2_ITETT:	m = (!c<<3)| (c<<2)| (c<<1)|1;	break;
> 	case THUMB2_ITTET:	m =  (c<<3)|(!c<<2)| (c<<1)|1;	break;
> 	case THUMB2_ITEET:	m = (!c<<3)|(!c<<2)| (c<<1)|1;	break;
> 	case THUMB2_ITTTE:	m =  (c<<3)| (c<<2)|(!c<<1)|1;	break;
> 	case THUMB2_ITETE:	m = (!c<<3)| (c<<2)|(!c<<1)|1;	break;
> 	case THUMB2_ITTEE:	m =  (c<<3)|(!c<<2)|(!c<<1)|1;	break;
> 	case THUMB2_ITEEE:	m = (!c<<3)|(!c<<2)|(!c<<1)|1;	break;
> 	default:		abort();
>     }
>     assert(m && (tc != ARM_CC_AL || !(m & (m - 1))));
>     is(0xbf00 | (tc >> 24) | m);
> }

LOL!  That's just the sort of thing I was trying to avoid!  :-)

I'd love to use this, but I think I probably can't.  I could use this
idea for just the couple of conditions I actually use, though, without
requiring copyright assignment.

Thanks,
Andrew.