[Development] Updating x86 SIMD support in Qt

[Edward Welbourne]

On Wednesday, 19 January 2022 00:13:32 PST Lars Knoll wrote:
>> AVX is only used by a couple of classes in Qt Core and the drawhelper
>> in Qt Gui. Qt Gui already does runtime detection, so it would be only
>> about adding that to the methods in Qt Core.

Thiago Macieira (19 January 2022 17:48) replied:
> That's a misconception. AVX and especially AVX2 introduce a lot of
> codegen opportunities for the compilers, which they've been able to
> use for years.

Is the difference here:
* We have code that overtly conditions on the availability of CPU
  features (for example in the places Lars mentioned) vs
* The compiler can achieve some optimizations, on which we currently
  miss out, if we pass a relevant command-line option telling it to do
  so (or omit one telling it not to) ?

(Hoping you'll educate me if I'm being dense.)

	Eddy.