Android and compatibility with deprecated armv7 instructions

[Måns Rullgård]

Arnd Bergmann <arnd at arndb.de> writes:

> On Friday 04 July 2014 20:24:05 Mark Brown wrote:
>> 
>> Another question I think it's worth asking is what the use case for 32
>> bit mode is other than preexisting binaries - I guess there's a case for
>> smaller binaries giving better cache utilisation?
>
> If you wanted that, you'd probably run x32-mode (or whatever it gets called
> on ARM64), which I'd expect to also be more efficient ;-)
>
> Seriously, backwards-compatibility is the only reason I can think of
> really, but that doesn't /have/ to mean existing binaries; there is a large
> amount of source code that can readily be compiled to any CPU as long as
> it's little-endian 32-bit.

There's also a lot of code that has been heavily optimised for 32-bit
ARM but doesn't (yet) have the same level of optimisation for ARM64, so
even if it builds and works for ARM64, it won't be nearly as fast.

-- 
Måns Rullgård
mans at mansr.com