[Bug target/76774] atomics on PPC: inconsistent widths for an _Atomic(_Bool) and for atomic_compare_exchange_strong on it

Peter.Sewell at cl dot cam.ac.uk gcc-bugzilla@gcc.gnu.org
Tue Aug 16 10:22:00 GMT 2016


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=76774

--- Comment #4 from Peter Sewell <Peter.Sewell at cl dot cam.ac.uk> ---
(In reply to Andrew Pinski from comment #3)
> What code were you expecting anyways?

I hadn't noticed how recent the other-size LL/SC were.  But then I would have
expected a 4-byte representation for _Atomic(_Bool) on the older machines, to
minimise the amount of code between the lwarx and stwcx; would that have some
other disadvantage?  

I don't think the code you've got is functionally wrong on normal h/w.  We
noticed this running in a semantics-based emulator that's very picky about
reading from uninitialised memory, but on normal h/w the extra memory will
AFAICS always be mapped and be within the same reservation granule.


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