InlineEvaluator implementation question

[Mark Mitchell]

--On Monday, December 16, 2002 04:55:52 PM +0100 Richard Guenther 
<rguenth at tat.physik.uni-tuebingen.de> wrote:

> Hi!
>
> Does anyone remember why we create copies of the LHS and RHS inside
> the KernelEvaluator<InlineKernelTag>::evaluate() methods (within
> ReductionEvaluator<InlineKernelTag>::evaluate() is similar code)? I.e.
> there is code like
>
>   template<class LHS,class Op,class RHS,class Domain>
>   inline static void evaluate(const LHS& lhs,const Op& op,const RHS& rhs,
>                               const Domain& domain,WrappedInt<1>)
>   {
>     CTAssert(Domain::unitStride);
>     PAssert(domain[0].first() == 0);
>     LHS localLHS(lhs);
>     RHS localRHS(rhs);
>     int e0 = domain[0].length();
>     for (int i0=0; i0<e0; ++i0)
>       op(localLHS(i0),localRHS.read(i0));
>   }

I'm pretty sure that this copy allowed some C++ compilers (KCC) to see
that some parts of lhs/rhs were loop-invariant, and then hoist references
to those fields out of the loop.  (The compiler can see that nothing can
modify localLHS; it's less obvious to it that nothing can modify rhs
since it doesn't know what else might point to that location.)

-- 
Mark Mitchell                mark at codesourcery.com
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