[m-rev.] diff: document problem with puzzle_detism_bug

[Zoltan Somogyi]

Document the cause of the failure of the puzzle_detism_bug test case.

compiler/instmap.m:
compiler/mode_util.m:
	Document the problem in the places in the code that are responsible for
	it.

compiler/handle_options.m:
	Add a dump verbosity alias that was helpful in tracking down the
	problem.

tests/hard_coded/puzzle_detism_bug.m:
	Add a comment pointing to the source of the bug.

Zoltan.

Index: compiler/instmap.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/instmap.m,v
retrieving revision 1.34
diff -u -r1.34 instmap.m
--- compiler/instmap.m	14 Jun 2004 04:16:10 -0000	1.34
+++ compiler/instmap.m	7 Dec 2004 14:05:44 -0000
@@ -982,9 +982,26 @@
 	),
 	(
 		inst_merge(InstA, InstB, yes(VarTypes ^ det_elem(Var)),
-			ModuleInfo0, Inst, ModuleInfoPrime)
+			ModuleInfo0, Inst1, ModuleInfoPrime)
 	->
+		% XXX Given instmap__lookup_var(InstMap, Var, OldInst),
+		% we should probably set Inst not directly from Inst1, but
+		% from a conjunction of OldInst and Inst1. If OldInst says that
+		% Var is bound to f, and Inst1 says that it is bound to g,
+		% Inst should be `unreachable', not bound(g). If OldInst says
+		% that Var is bound to f or g, and Inst1 says that it is bound
+		% to g or h, Inst should say that it is bound(g).
+		%
+		% If there is an invariant to the effect that such situations
+		% are not supposed to arise, then it is being broken, due to
+		% the XXX in recompute_instmap_delta_unify in mode_util.m.
+		%
+		% At present, I believe that the cases we mishandle here can
+		% arise only after inlining, as in puzzle_detism_bug.m in
+		% tests/hard_coded. -zs
+
 		ModuleInfo1 = ModuleInfoPrime,
+		Inst = Inst1,
 		map__det_insert(InstMapping0, Var, Inst, InstMapping1)
 	;
 		term__var_to_int(Var, VarInt),
Index: compiler/mode_util.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/mode_util.m,v
retrieving revision 1.158
diff -u -r1.158 mode_util.m
--- compiler/mode_util.m	14 Jun 2004 04:16:22 -0000	1.158
+++ compiler/mode_util.m	7 Dec 2004 13:40:44 -0000
@@ -343,11 +343,6 @@
 %-----------------------------------------------------------------------------%
 
 inst_lookup(ModuleInfo, InstName, Inst) :-
-	inst_lookup_2(InstName, ModuleInfo, Inst).
-
-:- pred inst_lookup_2(inst_name::in, module_info::in, (inst)::out) is det.
-
-inst_lookup_2(InstName, ModuleInfo, Inst) :-
 	(
 		InstName = unify_inst(_, _, _, _),
 		module_info_insts(ModuleInfo, InstTable),
@@ -429,7 +424,7 @@
 			ground(Uniq, none), Inst)
 	;
 		InstName = typed_inst(Type, TypedInstName),
-		inst_lookup_2(TypedInstName, ModuleInfo, Inst0),
+		inst_lookup(ModuleInfo, TypedInstName, Inst0),
 		map__init(Subst),
 		propagate_type_into_inst(Type, Subst, ModuleInfo, Inst0, Inst)
 	).
@@ -1263,6 +1258,12 @@
 		goal_info_get_instmap_delta(GoalInfo, OldInstMapDelta),
 		instmap__lookup_var(InstMap, Var, InitialInst),
 		( instmap_delta_search_var(OldInstMapDelta, Var, FinalInst1) ->
+			% XXX we need to merge the information in InitialInst
+			% and FinalInst1. In puzzle_detism_bug, InitialInst
+			% has a var bound to one function symbol (james), while
+			% FinalInst1 has it bound to another (katherine).
+			% The correct final inst is thus `unreachable', but
+			% we don't return that.
 			FinalInst = FinalInst1
 		;
 			% it wasn't in the instmap_delta, so the inst didn't
Index: compiler/handle_options.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/handle_options.m,v
retrieving revision 1.210
diff -u -r1.210 handle_options.m
--- compiler/handle_options.m	2 Sep 2004 04:31:36 -0000	1.210
+++ compiler/handle_options.m	7 Dec 2004 11:32:29 -0000
@@ -1981,6 +1981,7 @@
 
 convert_dump_alias("ALL", "abcdfgilmnprstuvCDIMPTU").
 convert_dump_alias("all", "abcdfgilmnprstuvCMPT").
+convert_dump_alias("allD", "abcdfgilmnprstuvCDMPT").
 convert_dump_alias("most", "bcdfgilmnprstuvP").
 convert_dump_alias("trans", "bcdglmnstuv").
 convert_dump_alias("codegen", "dfnprsu").
cvs diff: Diffing tests/hard_coded
Index: tests/hard_coded/puzzle_detism_bug.m
===================================================================
RCS file: /home/mercury/mercury1/repository/tests/hard_coded/puzzle_detism_bug.m,v
retrieving revision 1.1
diff -u -r1.1 puzzle_detism_bug.m
--- tests/hard_coded/puzzle_detism_bug.m	2 Dec 2004 08:03:57 -0000	1.1
+++ tests/hard_coded/puzzle_detism_bug.m	7 Dec 2004 14:05:50 -0000
@@ -6,7 +6,14 @@
 % 	Uncaught Mercury exception:
 % 	Software Error: inappropriate determinism inside a negation
 %
-% The problem goes away when `--no-inlining' is enabled.
+% The problem goes away when inlining is disabled.
+%
+% The cause of the problem is that the recomputation of instmap_deltas after
+% inlining generates incorrect results. See the XXXs in the predicate
+% merge_instmapping_delta_2 in instmap.m and in recompute_instmap_delta_unify
+% in mode_util.m. There is no easy fix, since there seems to be no existing
+% predicate that takes two insts and computes the intersections of all the
+% bound insts inside them.
 %
 %----------------------------------------------------------------------------%
 
cvs diff: Diffing tests/hard_coded/exceptions
cvs diff: Diffing tests/hard_coded/purity
cvs diff: Diffing tests/hard_coded/sub-modules
cvs diff: Diffing tests/hard_coded/typeclasses
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