Using memory above TOS

bart@time.cirl.uoregon.edu (Barton C. Massey) writes:


| Thomas Charles CONWAY <conway@rimmer.cs.mu.OZ.AU> wrote that
| the Mercury compiler uses an optimization that depends on a
| word above TOS (the Top Of the Stack) not being munged.
[...]
| IMHO this isn't very "safe".
[...]
| For a language like Mercury, in which there's an explicit
| runtime system and signal handlers are not directly implemented
| by the user, optimizations which use memory above TOS may be
| acceptable.


The reason that the optimization is safe in Mercury is that the Mercury
compiler generates code which uses its own stack rather than the C
stack. Since we're using our own stack, we're free to do what we
please with it, without any danger of interference from the OS.


Indeed, it is possibly misleading to say that signal handlers are not
directly implemented by the user in Mercury. Although Mercury doesn't
have any direct support for signal handlers, is in fact possible for
Mercury code to install signal handlers using the C interface.


--
Fergus Henderson <fjh@cs.mu.oz.au>
WWW: <http://www.cs.mu.oz.au/~fjh>
PGP: finger fjh@128.250.37.3
--

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