[PATCH] D98210: [ARM] Add VREV MVE shuffle costs

[Dave Green via Phabricator via llvm-commits]

dmgreen added inline comments.


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Comment at: llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp:1222
+
+    if (!Mask.empty()) {
+      std::pair<int, MVT> LT = TLI->getTypeLegalizationCost(DL, Tp);
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RKSimon wrote:
> Why aren't you just using TTI::SK_Reverse?
Thanks for taking a look. A VREV is a little different from a SK_Reverse, as far as I understand, although for some of the tests it happens to match both. A vrev mask will reverse lanes in a block, not the whole register. So they have masks like <3, 2, 1, 0, 7, 6, 5, 4> or <1, 0, 3, 2, 5, 4, 7, 6>.

In MVE there are  vrev16.8, vrev32.8, vrev32.16, vrev64.8, vrev64.16 and vrev64.32. The way I think of them is that taking a 128 bit legal vector, they reverse the bits in the first number, then reverse back in the second.


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  https://reviews.llvm.org/D98210/new/

https://reviews.llvm.org/D98210