[LLVMdev] IR Passes and TargetTransformInfo: Straw Man

[Krzysztof Parzyszek]

On 7/31/2013 1:02 PM, Shuxin Yang wrote:
>
> You might argue  running LICM early will miss the opportunities created
> by permutation. True.
> But, now that permutation has detailed dep-test result, it clearly
> understand which mem-access
> is invariant w.r.t which nest loop, why not move them to right place.

Because the next nest optimization would have to deal with it again.  As 
long as we are working on high-level structures, like loop nests, the 
details (such as invariance of some expression) should not concern us. 
That would be a job for a subsequent, lower-level pass (e.g. working on 
a single loop at a time).

-K

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