[m-rev.] trivial diff: workaround cygwin C compiler bug

[Fergus Henderson]

On 30-Jan-2003, Mark Brown <dougl at cs.mu.OZ.AU> wrote:
> Is it the case that an asm volatile statement will be generated in any
> grade where the internal label tables will be used?

The asm volatile statements are generated in "asm_*" grades.

In "none*" and "reg*" grades, function pointer addresses
are used rather than label addresses, and for those the C
standard guarantees that distinct functions will have
distinct addresses, so asm volatile statements aren't needed.

There might be problems for "jump*" and "fast*" grades.
However, there might also be all sorts of other problems with those
grades; they aren't really maintained anymore.
They are not tested in our nightly tests.

Now that we have the "hlc*" grades, "jump*" and "fast*"
are not going to beat the "hlc*" grades for raw performance,
so their main advantage is just that debugging is a bit faster,
on obscure architectures where we don't support asm_fast.gc
or asm_jump.gc.  But they have slow start-up times, since the
initialization code needs to page the whole program in,
so they're not great even for that.  I don't think we should
worry too much about them.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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