On Wed, Nov 14, 2018 at 05:50:39AM -0600, Segher Boessenkool wrote:
> > You mean for all local hard register variables living across function calls
> > save them into temporary and restore them around the calls?
> > One issue is that those variables aren't in SSA form, so liveness analysis
> > is harder. And, would we want to have an exception for the stack pointer?
> > I mean there is no need for register void *sp __asm ("rsp"); to be
> > saved/restored that way, it shouldn't change value across function calls.
> > Plus, as has been mentioned, function calls aren't the only issue here,
> > e.g. division/modulo etc. that require specific hard registers might clobber
> > them too.
>
> I was thinking put them in pseudos always, just copy them to the hard reg
> right before the asm statements that use them (and the other way around,
> for outputs).
Wouldn't that break all the code that does:
void *
retsp (void)
{
register void *sp __asm ("sp");
return sp;
}
(or any other (usually fixed) reg, where the user code expects to just
read the value of that register)?
Storing uninitialized value into it would break the program miserably.
Jakub
