Re: [PATCH] arm64/io: Don't use WZR in writel

[Robin Murphy]

On 18/03/2019 17:30, Marc Gonzalez wrote:
> On 18/03/2019 18:19, Robin Murphy wrote:
>
> > For the context bank reset, yes, I am assuming that no complier will
> > ever be perverse enough to detect that cfg is not written after the
> > NULL check and immediately reallocate it to XZR for no good reason.
> > I'd like to think that assumption is going to hold for the reasonable
> > scope of this particular workaround, though.
>
> I'm not sure I understand the above paragraph.
>
> In code such as:
>
> 	if (val == 0) foo(val);
>
> gcc's algorithm is likely to figure out that the code is equivalent to
>
> 	if (val == 0) foo(0)
>
> and perform constant-propagation, etc.
>
> Is that what we're talking about?

As may already be apparent, the way I expect compilers to behave, and 
the way compilers actually behave, are two overlapping but distinct sets 
of concepts...

Robin.