[PATCH] D92178: [InstructionCost] Change LoopVectorizationCostModel::getInstructionCost to return InstructionCost

[David Sherwood via Phabricator via llvm-commits]

david-arm added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:5441
     VectorizationCostTy C = expectedCost(ElementCount::getFixed(i));
-    std::pair<unsigned, unsigned> VectorCost = {C.first, i};
+    std::pair<InstructionCost, unsigned> VectorCost = {C.first, i};
     LLVM_DEBUG(dbgs() << "LV: Vector loop of width " << i
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ctetreau wrote:
> I think you can get rid of these pairs if you just check validity before assigning it.
OK. I guess the problem is that we could start off with an invalid cost (ScalarCost) and get another Invalid cost in the loop too. I think we could get rid of the pairs, but it just makes the main loop more complicated that's all. What I could do is add this in the main loop:

  if (!C.first.isValid())
    continue
  if (!ScalarCost.isValid())
    MinCost = C.first;
  // Both costs are now valid.
  // ... use MinCost and C somehow ...

The other thing I was trying to do is move from using a float to represent the MinCost in the loop, to using an InstructionCost (integer based) instead. If I get rid of the pairs then it makes more sense to revert to using a float for MinCost I think, since then division (and hence a fractional cost) is involved.

I can try adding control flow to the loop like above?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D92178/new/

https://reviews.llvm.org/D92178