[PATCH 1/2] Cost model: Add check for reverse shuffles to CostModel analysis

[Nadav Rotem]

LGTM!  A few minor comments:

There is an extra line break here. 

+
+static bool isReverseVectorMask(SmallVector<int, 16> &Mask) {
+  for (unsigned i = 0, MaskSize = Mask.size(); i < MaskSize; ++i)
+    if (Mask[i] != (int)(MaskSize - 1 - i))
+      return false;
+  return true;
+}
+

We should also check for -1's in the mask. 

+    if (NumVecElems == Mask.size() &&
+        isReverseVectorMask(Mask))


The expression above can fit in one line. 


Thanks,
Nadav