[llvm-commits] CVS: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp LegalizeDAG.cpp SelectionDAG.cpp SelectionDAGISel.cpp TargetLowering.cpp

[Dan Gohman]

>> We overload ISD::FADD and quite a lot of others. Why not  
>> ISD::ConstantFP too?
> 
> Fair enough, after pondering on it, I agree with you.  The proposed  
> semantics are that a ConstantFP (and also a normal Constant?) produce  
> the splatted immediate value?

Constant sounds good too. And UNDEF, for that matter. And yes, that's the
semantics I mean.

> If so, this sounds fine.  This should also reduce codegen memory  
> usage for many common cases, a very nice bonus :)

:)

> Please add a dag combine xform from build_vector [c,c,c,c] ->  
> constantfp and friends.

I sketched out some of the code for this. One question that's come up so far is
whether if the vector has some undef elements but all the non-undef elements
are equal it should still be folded. My initial preference is to still fold it,
since that lets things like isBuildVectorAllZeros become trivial to unnecessary,
but it is a pessimization in some obscure cases.

Dan

-- 
Dan Gohman, Cray Inc.