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Re: SPARC, register renaming, __builtin_return_address
At 11:24 14.05.2001, Mark Mitchell wrote:
> >>>>> "Franz" == Franz Sirl <Franz.Sirlfirstname.lastname@example.org> writes:
> Franz> At 01:50 14.05.2001, Mark Mitchell wrote:
> >> - The manual explicitly documents __builtin_return_address
> >> being guaranteed to return the correct value only when the
> >> index is 0.
> >> Therefore, the test-case is semi-bogus.
> Franz> Nope, cause if __builtin_return_address(n) with n>=1
> Franz> doesn't work on a target, it has to return 0 and then the
> Franz> comparisons in the testcase are valid.
>Nope, because it doesn't have to consistently do that. There's
>nothing in the documentation that says that it couldn't do it for 1
>sometimes, but not other times. That might make sense; maybe you
>can't unwind past optimized stack frames, for example.
Hehe, I thought you would argue that way. But if we do the way you say, we
have to deal with the situation that b_r_a(1) sometimes works and sometimes
not, depending on the surrounding code. This would probably mean to
introduce a proper warning for the user during compilation, since this
isn't like normal code which might change behaviour under optimization if
the user isn't careful, this is a compiler builtin und I believe the user
can expect it to work _uniformly_ under all circumstances. If not, we have
to unambiguously document it that way and introduce a compilation time
But I think that's not worth it, it's easy for the targets to either return
0 if they don't support b_r_a(1) or force a valid stackframe otherwise. The
whole purpose of the testcase is to test for uniform behaviour for b_r_a(1).