[Beignet] [PATCH v2] fix llvm.trunc.float instruction bug.

[Zhigang Gong]

Should be RNDD, please see the difference between the two definitions below:

Libm trunk():
  These functions round x to the nearest integer not larger in *absolute* value.

Llvm.trunc:
The ‘llvm.trunc.*‘ intrinsics returns the operand rounded to the nearest integer not larger in magnitude than the operand.


> -----Original Message-----
> From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of
> Song, Ruiling
> Sent: Friday, January 16, 2015 10:36 AM
> To: Luo, Xionghu; beignet at lists.freedesktop.org
> Cc: Luo, Xionghu
> Subject: Re: [Beignet] [PATCH v2] fix llvm.trunc.float instruction bug.
> 
> Should be RNDZ. The llvm.trunc is same as libm trunc(), which means rounding
> toward zero.
> 
> > -----Original Message-----
> > From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf
> > Of xionghu.luo at intel.com
> > Sent: Thursday, January 15, 2015 7:05 PM
> > To: beignet at lists.freedesktop.org
> > Cc: Luo, Xionghu
> > Subject: [Beignet] [PATCH v2] fix llvm.trunc.float instruction bug.
> >
> > From: Luo <xionghu.luo at intel.com>
> >
> > float to float trunc should use RNDU IR instruction.
> >
> > v2: fix typo. should be RNDD instead of RNDU.
> > Signed-off-by: Luo <xionghu.luo at intel.com>
> > ---
> >  backend/src/llvm/llvm_gen_backend.cpp | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/backend/src/llvm/llvm_gen_backend.cpp
> > b/backend/src/llvm/llvm_gen_backend.cpp
> > index 53dec0a..ee5b6a3 100644
> > --- a/backend/src/llvm/llvm_gen_backend.cpp
> > +++ b/backend/src/llvm/llvm_gen_backend.cpp
> > @@ -3310,11 +3310,9 @@ error:
> >              ir::Type srcType = getType(ctx, llvmSrcType);
> >              GBE_ASSERT(srcType == dstType);
> >
> > -            const ir::Register tmp = ctx.reg(getFamily(ir::TYPE_S32));
> >              const ir::Register dst = this->getRegister(&I);
> >              const ir::Register src = this->getRegister(I.getOperand(0));
> > -            ctx.CVT(ir::TYPE_S32, srcType, tmp, src);
> > -            ctx.CVT(dstType, ir::TYPE_S32, dst, tmp);
> > +            ctx.RNDD(dstType, dst, src);
> >            }
> >            break;
> >            case Intrinsic::copysign:
> > --
> > 1.9.1
> >
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