[m-dev.] poor code generation for field accesses

[Fergus Henderson]

Currently we seem to generate poor code for field accesses,
in at least some situations.
Here's an example, from the Mercury ICFP2000 submission.
For the following source (line 256 of renderer.m),

	snd(Intersection)^object_id \= IgnoreId

which is equivalent to 

	\+ (
		snd(Intersection)^object_id = IgnoreId
	),

we generate code

	\+ (
		V_24 <= intersection(IgnoreId, _, _, _, _), % construction
		V_40 <= snd(Intersection),		    % function call
		V_24 = V_40                                 % unification
	)

This is bad, because the initial unification with V_24 is a
construction, which allocates memory.

-- 
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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