[PATCH] Include legalization cost when computing scalarization cost

[Raul Silvera]

Thanks, Arnold. I think that's a good point. This overhead is not limited
to scalarization, but to any use of these instructions.

I'll update my patch with your suggestions (with .first) unless others have
objections.


On Thu, Mar 6, 2014 at 6:48 PM, Arnold Schwaighofer <aschwaighofer at apple.com
> wrote:

>
> On Mar 6, 2014, at 5:11 PM, Raul Silvera <rsilvera at google.com> wrote:
> > Index: lib/CodeGen/BasicTargetTransformInfo.cpp
> > ===================================================================
> > --- lib/CodeGen/BasicTargetTransformInfo.cpp
> > +++ lib/CodeGen/BasicTargetTransformInfo.cpp
> > @@ -20,7 +20,6 @@
> > #include "llvm/Analysis/TargetTransformInfo.h"
> > #include "llvm/Target/TargetLowering.h"
> > #include <utility>
> > -
> > using namespace llvm;
> >
> > namespace {
> > @@ -206,12 +205,19 @@
> >                                             bool Extract) const {
> >   assert (Ty->isVectorTy() && "Can only scalarize vectors");
> >   unsigned Cost = 0;
> > -
> > -  for (int i = 0, e = Ty->getVectorNumElements(); i < e; ++i) {
> > -    if (Insert)
> > -      Cost += TopTTI->getVectorInstrCost(Instruction::InsertElement,
> Ty, i);
> > -    if (Extract)
> > -      Cost += TopTTI->getVectorInstrCost(Instruction::ExtractElement,
> Ty, i);
> > +  VectorType *VecTy = cast<VectorType>(Ty);
> > +  std::pair<unsigned, MVT> LT =
> > +      getTLI()->getTypeLegalizationCost(VecTy->getElementType());
> > +
> > +  for (int i = 0, e = VecTy->getVectorNumElements(); i < e; ++i) {
> > +    if (Insert) {
> > +      Cost += LT.first *
> > +              TopTTI->getVectorInstrCost(Instruction::InsertElement,
> VecTy, i);
> > +    }
> > +    if (Extract) {
> > +      Cost += LT.first *
> > +              TopTTI->getVectorInstrCost(Instruction::ExtractElement,
> VecTy, i);
> > +    }
>
> Why do we want to do it at this (higher) level? I think,
> getVectorInstrCost() should have included the type legalization cost of the
> scalar type.
>
> unsigned BasicTTI::getVectorInstrCost(unsigned Opcode, Type *Val,
>                                       unsigned Index) const {
>     return getTLI().getTypeLegalizationCost(Ty->getScalarType()).second;
> }
>
>


-- 
 Raúl E. Silvera
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