general dst() aliasing
general dst() aliasing

Clarity refactors: rename alias_reg() to try_alias() and add in_reg().

Let dst() hint what register to try_alias(), and use this anywhere
aliasing is safe and we have an argument that's either already in a
register or is guaranteed to be pulled back into one, e.g r(x).

Cases like vsqrtps(dst(), any(x)) are somewhat interesting, in that if x
is in a register, it is a good thing to alias, but if it's on the stack,
it's better to just vsqrtps directly into the new register.

Change-Id: I05ecb78f660e9e4ea0df44f03e5de03b85a49cc7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/285086
Reviewed-by: Herb Derby <9e12a3d2bbf73546e47cc9958f6ba8f3215b7eaf@google.com>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>

google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia