RE: [Ping] [PATCH, 7/10] aarch64: add function to output ccmp insn

["Zhenqiang Chen" <zhenqiang dot chen at arm dot com>]

> -----Original Message-----
> From: Richard Henderson [mailto:rth@redhat.com]
> Sent: Sunday, October 12, 2014 12:52 PM
> To: Zhenqiang Chen; gcc-patches@gcc.gnu.org
> Subject: Re: [Ping] [PATCH, 7/10] aarch64: add function to output ccmp
insn
> 
> On 10/11/2014 09:11 AM, Richard Henderson wrote:
> > On 09/22/2014 11:45 PM, Zhenqiang Chen wrote:
> >> +static unsigned int
> >> +aarch64_code_to_nzcv (enum rtx_code code, bool inverse) {
> >> +  switch (code)
> >> +    {
> >> +    case NE: /* NE, Z == 0.  */
> >> +      return inverse ? AARCH64_CC_Z : 0;
> >> +    case EQ: /* EQ, Z == 1.  */
> >> +      return inverse ? 0 : AARCH64_CC_Z;
> >> +    case LE: /* LE, !(Z == 0 && N == V).  */
> >> +      return inverse ? AARCH64_CC_N | AARCH64_CC_V : AARCH64_CC_Z;
> >> +    case GT: /* GT, Z == 0 && N == V.  */
> >> +      return inverse ? AARCH64_CC_Z : AARCH64_CC_N | AARCH64_CC_V;
> >> +    case LT: /* LT, N != V.  */
> >> +      return inverse ? AARCH64_CC_N | AARCH64_CC_V : AARCH64_CC_N;
> >> +    case GE: /* GE, N == V.  */
> >> +      return inverse ? AARCH64_CC_N : AARCH64_CC_N | AARCH64_CC_V;
> >> +    case LEU: /* LS, !(C == 1 && Z == 0).  */
> >> +      return inverse ? AARCH64_CC_C: AARCH64_CC_Z;
> >> +    case GTU: /* HI, C ==1 && Z == 0.  */
> >> +      return inverse ? AARCH64_CC_Z : AARCH64_CC_C;
> >> +    case LTU: /* CC, C == 0.  */
> >> +      return inverse ? AARCH64_CC_C : 0;
> >> +    case GEU: /* CS, C == 1.  */
> >> +      return inverse ? 0 : AARCH64_CC_C;
> >> +    default:
> >> +      gcc_unreachable ();
> >> +      return 0;
> >> +    }
> >> +}
> >> +
> >
> > I'm not overly fond of this, since "code" doesn't map 1-1.  It needs
> > the context of a mode to provide a unique mapping.
> >
> > I think it would be better to rearrange the existing aarch64_cond_code
> > enum such that AARCH64_NE et al are meaningful wrt NZCV.  Then you can
> > use
> > aarch64_get_condition_code_1 to get this mapping.
>
> Slight mistake in the advice here.  I think you should use
> aarch64_get_conditional_code_1 to get an aarch64_cond_code, and use that
> to index an array to get the nzcv bits.

Thanks for the comments. Patch is updated.
 
> Further, does it actually make sense to store both nzcv and its inverse,
or
> does it work to use nzcv and ~nzcv?
 
Flag GE checks N == V and LT checks N != V. We can no distinguish them with
nzcv and ~nzcv

Since aarch64_output_ccmp is removed as your comments, the patch is combined
with [PATCH, 8/10] aarch64: ccmp insn patterns. Please find the updated
patch in later email.

Thanks!
-Zhenqiang