[PATCH] D100865: [COST] Improve shuffle kind detection if shuffle mask is provided.

[Dave Green via Phabricator via llvm-commits]

dmgreen added inline comments.


================
Comment at: llvm/include/llvm/CodeGen/BasicTTIImpl.h:753
+    case TTI::SK_PermuteTwoSrc:
+      if (ShuffleVectorInst::isSelectMask(Mask))
+        return TTI::SK_Select;
----------------
ABataev wrote:
> dmgreen wrote:
> > Some of these Mask functions do not handle all sizes of mask. Do we need to be careful about shuffles that changesLength?
> Here we don't have info about length changes, looks like all these functions use the size of the Mask array as vector factor.
I may have the wrong impression of what is going on exactly, but I think it's about the elements being out of range for the mask size.
(Hopefully) Try this example:
https://godbolt.org/z/WWrPbPxcW


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100865/new/

https://reviews.llvm.org/D100865