[PATCH] D59995: [LV] Exclude loop-invariant inputs from scalar cost computation.

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.





================
Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:1343
+    if (VF > 1 && Scalars.find(VF) == Scalars.end())
+      return true;
+
----------------
Ayal wrote:
> Ahh, is it better to assume we can vectorize V, contrary to the above comment?
> Ahh, is it better to assume we can vectorize V, contrary to the above comment?

Ah sorry for the change, I missed adding an explanation here. Assuming vectorization here seems to be in line with the old behavior and switching it causes a bunch of unit-test failures. I agree it would be safer to assume scalarizing, but the current cost model seems to expect the optimistic choice here.

I might be worth investigating flipping it as a follow-up, but I think it will require some additional work to make sure other places in the cost model are in sync with the new assumption? 


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