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Re: missed PTA optimization?
Am Dienstag, den 11.02.2020, 21:43 +0100 schrieb Richard Biener:
> On February 11, 2020 9:32:14 PM GMT+01:00, "Uecker, Martin" <Martin.Uecker@med.uni-goettingen.de>
> wrote:
> >
> > In the following example, it seems
> > that 'bar' could be optimized to
> > return '1' and every else could be
> > optimized away. Or am I missing
> > something?
>
> p might be still NULL when bar is called.
>
> > Do I need to add
> > some specific compiler flags?
>
> -fipa-pta
This does not appear to change anything. Also
if I initialize p to the address of 'a', this
changes nothing.
For the second function, I get:
p = { ESCAPED NONLOCAL }
> But we simply do not implement turning pointer dereference into direct accesses when points to
> says it would be possible. And yes, the NULL case can probably be ignored (though we generally
> support catching NULL dereferences with signal handlers), or at least speculated away with a well
> predicted branch.
>
> Any situation where doing the above is profitable?
No, just trying to understand what is happening.
(clang does this optimization).
Best,
Martin
> >
> >
> > static int a = 1;
> > static int *p;
> >
> > extern
> > void foo(void)
> > {
> > p = &a;
> > }
> >
> > extern
> > int bar(void)
> > {
> > return *p;
> > }
> >
> >
> > thank you,
> > Martin
>
>