[Beignet] [PATCH] GBE: fix one potential bug in UnsignedI64ToFloat.

[Zhigang Gong]

On Thu, May 08, 2014 at 03:28:34AM +0000, Yang, Rong R wrote:
> 
> 
> -----Original Message-----
> From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of Zhigang Gong
> Sent: Tuesday, May 06, 2014 12:48 PM
> To: beignet at lists.freedesktop.org
> Cc: Gong, Zhigang
> Subject: [Beignet] [PATCH] GBE: fix one potential bug in UnsignedI64ToFloat.
> 
> Set exp to a proper value to make sure all the inactive lanes flag bits are 1s which satisfy the requirement of the following ALL16/ALL8H condition check.
> 
> Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
> ---
>  backend/src/backend/gen_context.cpp | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/backend/src/backend/gen_context.cpp b/backend/src/backend/gen_context.cpp
> index 00cbf1d..f014295 100644
> --- a/backend/src/backend/gen_context.cpp
> +++ b/backend/src/backend/gen_context.cpp
> @@ -907,6 +907,10 @@ namespace gbe
>                                              GenRegister mantissa, GenRegister tmp, GenRegister flag) {
>      uint32_t jip0, jip1;
>      GenRegister dst_ud = GenRegister::retype(dst, GEN_TYPE_UD);
> +    p->push();
> +      p->curr.noMask = 1;
> +      p->MOV(exp, GenRegister::immud(24)); // make sure the inactive lane is 1 when check ALL8H/ALL16H condition latter.
> >>>>>>Why move 24 to exp. It should initialize to -1 for inactive lane. When all exp is -1 here, ALL8H/ALL16H can jump out the function. So ALL8H/ALL16H is a optimization, and inactive lane should stop this jump.

      p->CMP(GEN_CONDITIONAL_G, exp, GenRegister::immud(23));
      p->curr.predicate = GEN_PREDICATE_NORMAL;
      p->CMP(GEN_CONDITIONAL_L, exp, GenRegister::immud(32));  //exp>23 && high!=0
      p->ADD(tmp, exp, GenRegister::immud(-23));
      ...
      p->curr.predicate = GEN_PREDICATE_ALIGN1_ALL8H/ALL16H;
      p->JMPI(GenRegister::immud(0));

The algorithm will check whether all channels are between (23, 32).
If it is, then it jump some instructions.

I initialize all channels to 24, so that all the inactive lanes cound satisfy the above checking.
And if all the active lanes are also within the range, then we can really jump over those instructions.

Is there anything wrong?
> 
> 
> +    p->pop();
>      p->FBH(exp, high);
>      p->ADD(exp, GenRegister::negate(exp), GenRegister::immud(31));  //exp = 32 when high == 0
>      p->push();
> --
> 1.8.3.2
> 
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