[PATCH] D142456: [AArch64][CostModel]: Add costs for zero/sign extend.

[David Sherwood via Phabricator via llvm-commits]

david-arm added a comment.

Hi @hassnaa-arm, so the confusing aspect here is that the throughput in the cost model is kind of the inverse of the throughput that's sometimes talked about in optimisation guides, which doesn't help. So in that optimisation guide you referenced earlier I believe that a high throughput is essentially a 'good thing', whereas in the vectoriser cost model a high value means the opposite. Suppose you took the inverse of the throughput (2), then it would be 1/2, but the cost has to be an integer so we can just round up to 1.


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