[PATCH] D149946: [LoongArch] Define `ual` feature and override `allowsMisalignedMemoryAccesses`

[Xi Ruoyao via Phabricator via cfe-commits]

xry111 added a comment.

In D149946#4324877 <https://reviews.llvm.org/D149946#4324877>, @SixWeining wrote:

> In D149946#4324803 <https://reviews.llvm.org/D149946#4324803>, @xen0n wrote:
>
>> From a LoongArch developer's perspective, it may be better to only enable UAL for LA464 and other supporting models, instead of for the generic `loongarch64` model too. This is because although all server- and desktop-class LoongArch models have UAL, the embedded-class (Loongson-1 and Loongson-2 series' older models) doesn't, and some of them e.g. Loongson 2K1000LA are readily available on the market so they're arguably relevant. We don't want to generate misaligned memory accesses for those systems only to fall back to much slower emulation later.
>
> If so, CPUs that support UAL will not benefit from this feature in default build (i.e. without -march or -mcpu or -mtune being specified).
>
> Does `generic` model mean the `lowest` model or the `most popular` model?

Technically `generic` should mean the `lowest`.  But as a desktop user, frankly I don't want to pay the extra cost for 2K models.


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