diff: bug fix for recompute_instmap_delta on switches

[Fergus Henderson]

Hi Simon,

Can you please review this change?

(As well as fixing up the bugs, I'm going to clean up the code a bit,
but I'll commit that as a separate change.)

Fix some bugs that caused the compiler to generate incorrect code in
certain cases.

compiler/mode_util.m:
	Fix bugs in recompute_instmap_delta_cases.
	The old code was passing the wrong instmap to
	instmap_delta_bind_var and in the recursive call.
	It was passing the instmap _after_ the implicit
	functor test unification at the start of the case.
	For example, for a switch like this:

		% Point 0
		(
			Var has functor f/1
			% Point 1
			Case
		;
			...
		)
		
	it was passing the instmap at point 1 rather than the instmap
	at point 0.

compiler/instmap.m:
	Fix a bug in instmap_delta_bind_var.  It was inserting the new inst
	for a switch variable in the instmap delta only if it had changed
	from point 1 in the above example, but it should have been inserting
	it if it had changed from point 0.

Index: instmap.m
===================================================================
RCS file: /home/staff/zs/imp/mercury/compiler/instmap.m,v
retrieving revision 1.8
diff -u -r1.8 instmap.m
--- instmap.m	1997/06/11 09:00:05	1.8
+++ instmap.m	1997/06/16 06:04:37
@@ -387,14 +387,15 @@
 		ModuleInfo = ModuleInfo0
 	;
 		InstmapDelta0 = reachable(InstmappingDelta0),
+		instmap__lookup_var(InstMap, Var, OldInst),
 		( map__search(InstmappingDelta0, Var, Inst0) ->
 			Inst1 = Inst0
 		;
-			instmap__lookup_var(InstMap, Var, Inst1)
+			Inst1 = OldInst
 		),
 		bind_inst_to_functor(Inst1, ConsId, Inst,
 			ModuleInfo0, ModuleInfo),
-		( Inst \= Inst1 ->
+		( Inst \= OldInst ->
 			instmap_delta_set(InstmapDelta0, Var,
 				Inst, InstmapDelta)
 		;
Index: mode_util.m
===================================================================
RCS file: /home/staff/zs/imp/mercury/compiler/mode_util.m,v
retrieving revision 1.90
diff -u -r1.90 mode_util.m
--- mode_util.m	1997/06/11 05:37:56	1.90
+++ mode_util.m	1997/06/16 05:52:33
@@ -1735,7 +1735,7 @@
 	recompute_instmap_delta(Atomic, Goal0, Goal,
 		InstMap, InstMapDelta0),
 	instmap_delta_bind_var_to_functor(Var, Functor,
-		InstMap, InstMapDelta0, InstMapDelta),
+		InstMap0, InstMapDelta0, InstMapDelta),
 	{ Case = case(Functor, Goal) }.
 recompute_instmap_delta_cases(Atomic, Var, [Case0 | Cases0], [Case | Cases],
 		InstMap0, NonLocals, InstMapDelta) -->
@@ -1745,11 +1745,11 @@
 	recompute_instmap_delta(Atomic, Goal0, Goal,
 		InstMap, InstMapDelta0),
 	instmap_delta_bind_var_to_functor(Var, Functor,
-		InstMap, InstMapDelta0, InstMapDelta1),
+		InstMap0, InstMapDelta0, InstMapDelta1),
 	{ Case = case(Functor, Goal) },
 	recompute_instmap_delta_cases(Atomic, Var, Cases0, Cases,
-		InstMap, NonLocals, InstMapDelta2),
-	merge_instmap_delta(InstMap, NonLocals, InstMapDelta1,
+		InstMap0, NonLocals, InstMapDelta2),
+	merge_instmap_delta(InstMap0, NonLocals, InstMapDelta1,
 		InstMapDelta2, InstMapDelta).
 
 %-----------------------------------------------------------------------------%

-- 
Fergus Henderson <fjh at cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3         |     -- the last words of T. S. Garp.