Re: [PATCH v2 4/7] exec: Use const alias for TARGET_PAGE_BITS_VARY

[Peter Maydell]

On Fri, 25 Oct 2019 at 21:43, Richard Henderson
<address@hidden> wrote:
>
> On 10/25/19 10:51 AM, Peter Maydell wrote:
> >> + * We want to declare the "target_page" variable as const, which tells
> >> + * the compiler that it can cache any value that it reads across calls.
> >> + * This avoids multiple assertions and multiple reads within any one user.
> >> + *
> >> + * This works because we initialize the target_page data very early, in a
> >> + * location far removed from the functions that require the final results.
> >
> > I have to say that this feels like a worryingly large amount
> > of magic. Is this actually guaranteed to work by the compiler?
>
> Yes.

I'm curious to know how the compiler engineers define
"very early" and "far removed" -- in my experience they
usually prefer to be more precise than that :-)

thanks
-- PMM