[PATCH] D75689: [VectorCombine] fold extract-extract-op with different extraction indexes

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/VectorCombine.cpp:119
+      return true;
+
+    // If we are extracting from 2 different indexes, then 1 operand must be
----------------
So essentially we are assuming that this is the optimal cost model.
Can we assert that?
```
int ExpensiveExtractCost = std::max(Extract0Cost, Extract1Cost);
(void)ExpensiveExtractCost;

// FIXME: introduce TargetTransformInfo::SK_Splat.
assert(TTI.getShuffleCost(TargetTransformInfo::SK_PermuteSingleSrc, VecTy) + CheapExtractCost
       <=
       TTI.getShuffleCost(TargetTransformInfo::SK_Broadcast, VecTy) + ExpensiveExtractCost
);
```


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  https://reviews.llvm.org/D75689/new/

https://reviews.llvm.org/D75689