[llvm-commits] Patch: generalize vector shuffle

[Duncan Sands]

Hi Mon Ping,

> >> +//===---- LegalizeTypesUtils.cpp - Utilities for Legalization of  
> >> types
> >
> > Why not only do it in LegalizeTypes?
>
> Are you asking why these utilities are not part of LegalizeTypes  
> instead of placing them in their own class?  If so, LegalizeDAG would  
> need access to the utility...

why does LegalizeDAG need access to this at all?  At some point I'm
going to start removing all type legalization code from LegalizeDAG.
Not quite yet, I admit!  However is there really much point in adding
new type legalization code to LegalizeDAG?

> The changes in LegalizesTypes are needed to take advantage of  
> generalized the vector shuffle.   I should have copied my original  
> email for the patch to this last patch as an introduction.   With  
> these changes, we try to keep as much as the original vector program  
> (after optimization) structure all the way to the backend.  The  
> incoming program uses generalize vector shuffles, in SelectionDAG  
> building, we normalize, and then in Legalization, we convert any of  
> the illegal normalized shuffles to concat, extract sub vectors, etc.   
> Before, legalization would break it down to insert/extracts which we  
> had a hard time rebuilding.   For examples like transposing a vector,  
> this allows us to generate much better code.  Sorry about the confusion!

if I understand right, the changes to LegalizeTypes/LegalizeDAG are
logically independent of the generalization of vector shuffle (and must
be, because this code never sees generalized vector shuffles!): they
would already make sense without the vector shuffle generalization.
Maybe you can break them out of the patch and submit them separately.
For example, the EXTRACT_SUBVECTOR part could go in at once (with the
small cleanups I mentioned), and likewise for the vector shuffle
legalization, after a bit more cleaning/simplifying/reviewing.

Just a thought,

Duncan.