Commentary Cmm page (Observations and Areas for Improvement)
p.tanski at gmail.com
Tue Nov 28 09:37:13 EST 2006
On Nov 24, 2006, at 2:50 AM, Simon Peyton-Jones wrote:
> Peter Tanski wrote:
>> I was trying to determine the grounds for when a side-effecting
>> primop would be inlined and when it would be coded as a separate
> That's a matter for the implementation, not the C--, or Cmm,
> specification. The user should not care. The implementer makes
> the usual cost/performance/complexity trade-off, and decides. I
> think there is no more to it than that.
Quite so. The wiki is intended for implementers, in this case those
who would be interested in implementing new Cmm primitive operators.
> If you are asking what GHC's current code-generator's decisions
> are, concerning this choice, I couldn't tell you without looking at
> the code!
According to nativeGen/MachCodeGen.hs, out-of-line primitive
operators (usually floating point operations) seem to be foreign
calls. I suppose a possible addition to Cmm, such as primitive
operators with exceptions, might be inlined but I haven't looked
carefully at the trade-offs.
On a somewhat related note, it has been a long holiday weekend (lots
of company, no spare time) so I got a slow start redoing the Cmm
language wiki page. It should be done fairly soon.
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