[Beignet] [PATCH 3/3] add llvm intrinsic call translate.

[Song, Ruiling]

Sorry, I previously thought it was for integer to integer truncation.
For the floating point llvm.trunc to nearest integer, you need use RNDZ.
When you convert from float to 32bit integer, numbers larger than 2^31 will get wrong result.
Floating point value range is larger than integer.

> -----Original Message-----
> From: Zhigang Gong [mailto:zhigang.gong at linux.intel.com]
> Sent: Thursday, January 15, 2015 4:13 PM
> To: Song, Ruiling; Luo, Xionghu; beignet at lists.freedesktop.org
> Cc: Luo, Xionghu
> Subject: RE: [Beignet] [PATCH 3/3] add llvm intrinsic call translate.
> 
> 
> 
> > -----Original Message-----
> > From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf
> > Of Song, Ruiling
> > Sent: Thursday, January 15, 2015 4:00 PM
> > To: Luo, Xionghu; beignet at lists.freedesktop.org
> > Cc: Luo, Xionghu
> > Subject: Re: [Beignet] [PATCH 3/3] add llvm intrinsic call translate.
> >
> > > +          case Intrinsic::trunc:
> > > +          {
> > > +            Type *llvmDstType = I.getType();
> > > +            Type *llvmSrcType = I.getOperand(0)->getType();
> > > +            ir::Type dstType = getType(ctx, llvmDstType);
> > > +            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);
> > Why do we need to convert to TYPE_S32 to convert from TYPE_S32 to
> dstType?
> This is what llvm.trunc's purpose:
> 
> ‘llvm.trunc.*‘ Intrinsic
> 
> Syntax:
> 
> This is an overloaded intrinsic. You can use llvm.trunc on any floating point
> or vector of floating point type. Not all targets support all types however.
> 
> declare float     @llvm.trunc.f32(float  %Val)
> declare double    @llvm.trunc.f64(double %Val)
> declare x86_fp80  @llvm.trunc.f80(x86_fp80  %Val)
> declare fp128     @llvm.trunc.f128(fp128 %Val)
> declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128  %Val)
> Overview:
> 
> The ‘llvm.trunc.*‘ intrinsics returns the operand rounded to the nearest
> integer not larger in magnitude than the operand.
> 
> >
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