[PATCH] D32706: [AArch64] Consider widening instructions in cast cost calculation

[Evandro Menezes via Phabricator via llvm-commits]

evandro added a comment.

In https://reviews.llvm.org/D32706#746087, @mssimpso wrote:

> OK, yes I see that now. I missed it on the first look! What do you think about adding a new sub-target feature for this then? Something like "FastWideningOps"? We could condition this TTI change on the feature to prevent it from hurting performance on Exynos. And regarding your last point, you could then later use it to guide instruction selection to not generate the widening ops if the non-widening versions (with added extends) are more profitable.


Please, not yet another feature.  It should be possible, methinks, to `getSubtarget().getSchedModel()` to compare the relative costs.

Do you have a publicly available benchmark where this change is meaningful so that I can evaluate it better?  For I haven't seen any change in our workloads after this change.  Maybe, in the end, it doesn't matter; or maybe it's not that common.


https://reviews.llvm.org/D32706