[PATCH] D116688: [SLP]Excluded external uses from the reprdering estimation.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added a comment.

In D116688#3226015 <https://reviews.llvm.org/D116688#3226015>, @vporpo wrote:

> This is obviously a contrived example, but it highlights the issue. It still holds if you replace the loads with other instructions of the same opcode that lead to a similar situation requiring tie-breaking using the cost of external uses.

If the instructions are the same, they will be combined. If the instructions are different, still better to choose the instruction with the higher score, even if it is externally used (we may have a deeper graph, which is still better for the vectorization). There is only one relevant case - if the instructions are very-very similar (their scores are equal). If the instruction is externally used, it still might be vectorized as part of another tree. The only preference here - instruction with a single use (or all vectorized users) and instruction with many uses, I believe. We can check for something like this and consider instruction with a single use (or all vectorized users) as a better choice rather than the instruction with not all vectorized users.


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