[llvm] [SLP] Compute a shuffle mask for getGatherCost (PR #85330)

[Philip Reames via llvm-commits]

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@@ -10526,6 +10527,7 @@ InstructionCost BoUpSLP::getGatherCost(ArrayRef<Value *> VL,
     if (!UniqueElements.insert(V).second) {
       DuplicateNonConst = true;
       ShuffledElements.setBit(I);
+      ShuffleMask[I] = I;
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preames wrote:

Clearly it is time for me to stop for the day.  I wrote the correct code here - and then managed to commit the wrong version.  Oops.  Will push a corrected version tomorrow. 

https://github.com/llvm/llvm-project/pull/85330