[m-rev.] for review: bug compiler abort on dep_par_14b.m

[Peter Wang]

Branches: main

Fix a bug causing the compiler to abort on tests/par_conj/dep_par_14b.m when
--intermod-opt was enabled (allowing superfluous calls to par_builtin.get be
deleted).

The problem could occur if a parallel conjunction was inside a disjunction.
A variable that was dead in the disjunct containing the parallel conjunction
may be required in a later disjunct, but this was not taken into account so
the stack slot holding the variable might then be erroneously reused.

compiler/live_vars.m:
	Make the variables which may become live again on backtracking past
	the parallel conjunction (ResumeVars0) part of the set of variables
	which need their own stack slots during execution of a parallel
	conjunction, so the stack slot allocator won't reuse their slots.


Index: compiler/live_vars.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/live_vars.m,v
retrieving revision 1.129
diff -u -r1.129 live_vars.m
--- compiler/live_vars.m	6 Jan 2007 09:23:37 -0000	1.129
+++ compiler/live_vars.m	30 Apr 2007 05:34:29 -0000
@@ -206,8 +206,10 @@
         % or nonlocal to the parallel conjunction. Nonlocal variables that are
         % currently free, but are bound inside one of the conjuncts need a
         % stackslot because they are passed out by reference to that stackslot.
+        % Variables needed on backtracking must be available in a stackslot
+        % past the parallel conjunction as well.
         goal_info_get_code_gen_nonlocals(GoalInfo0, NonLocals),
-        set.union(NonLocals, !.Liveness, LiveSet),
+        LiveSet = set.union_list([NonLocals, !.Liveness, ResumeVars0]),
 
         InnerNonLocals = LiveSet `set.union` OuterNonLocals,
         InnerParStackVars0 = parallel_stackvars(InnerNonLocals, [], set.init),
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