minor change to common.m

[Simon TAYLOR]

Estimated hours taken: 0.1

compiler/common.m
	Avoid creating X = X assignment unifications.

Index: common.m
===================================================================
RCS file: /home/staff/zs/imp/mercury/compiler/common.m,v
retrieving revision 1.40
diff -u -r1.40 common.m
--- common.m	1997/05/21 02:13:17	1.40
+++ common.m	1997/05/21 07:35:00
@@ -576,7 +576,12 @@
 common__create_output_unifications(NonLocals, InstMap, InstMapDelta, 
 		[OutputArg | OutputArgs], [OutputArg2 | OutputArgs2],
 		Goals, RecomputeAtomic0, RecomputeAtomic) :-
-	( set__member(OutputArg, NonLocals) ->
+	( 
+		set__member(OutputArg, NonLocals),
+		% This can happen if the first cell was created with a
+		% partially instantiated deconstruction.
+		OutputArg \= OutputArg2	
+	->
 		Unification = assign(OutputArg, OutputArg2),
 		instmap__lookup_var(InstMap, OutputArg2, Inst0),
 		% Check if OutputArg2 was local to the call or deconstruction