[PATCH] D79162: [Analysis] TTI: Add CastContextHint for getCastInstrCost

[Pierre van Houtryve via Phabricator via llvm-commits]

Pierre-vh added a comment.

In D79162#2013748 <https://reviews.llvm.org/D79162#2013748>, @dmgreen wrote:

> We (ARM/MVE) need to do the same thing for the cost of gather and interleaved loads. Whether the sext/zext is free there is equally variable. The way that I would have imagined this is a enum that can be one of the types of loads that the vectorizer produces (Normal, Masked, Interleave, Gather, Expanded?). There probably needs to be an option for None or Unknown too. I understand that you tried this before but ran into trouble? Can you speak to what kinds of problems you ran into doing things that way?


Yes, I originally tried an enum with one entry per "kind" of load/store, as you said. It was working fine, but I felt that it was a bit confusing, as each entry had a different meaning based on the opcode. For instance, I had the `MaskedVector` entry, which, for most casts, meant that the operand was a masked load, but for truncs meant that the single user of the cast is a masked store. ,What if another target needs to deal with truncs of masked loads or something like that ? They wouldn't be able to use that API, they'd have to hack it. (I don't know if this will ever come up, I'm just trying to think about all of the use cases for this enum)
With the current format of the enum, it's a clearer IMHO, there is no ambiguity, and any target can add their specific case in there and deal with it in the backend.

Of course, both versions work equally well, I'm fine with both.


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https://reviews.llvm.org/D79162