for review: fix a bug in value numbering reported by Simon

[Zoltan Somogyi]

Fix a bug in value numbering reported by Simon.

compiler/vn_block.m:
	Restore a previously commented block of code, whose job is to force
	the flushing of any stack slot that holds the saved value of a nondet
	control register or stack slot. The rationale for this code used
	to be the handling of cuts in nondet code; now it is the handling
	of hijackings.

tests/hard_coded.{m,exp}:
	A cut-down and inlined version of Simon's test case, which fails
	without the change to vn_block and succeeds with it.

tests/Mmakefile:
	Enable the new test case, and require that it be compiled with
	value numbering.

Zoltan.

Index: compiler/vn_block.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/vn_block.m,v
retrieving revision 1.56
diff -u -u -r1.56 vn_block.m
--- vn_block.m	1998/07/29 08:53:49	1.56
+++ vn_block.m	1998/08/25 05:12:52
@@ -203,27 +203,25 @@
 	vn_util__rval_to_vn(Rval, Vn, VnTables0, VnTables1),
 	vn_util__lval_to_vnlval(Lval, Vnlval, VnTables1, VnTables2),
 	vn_table__set_desired_value(Vnlval, Vn, VnTables2, VnTables),
-	vn_util__find_specials(Vnlval, Specials),
-%	vn_util__find_specials(Vnlval, LeftSpecials),
-%	(
-%		% Assignments of this form occur in the setup for commit.
-%		% We must record the left hand side (which will be a stackvar)
-%		% as a must flush location, because liveness will not force
-%		% it to be flushed. The reason for this is that livemap.m
-%		% may be confused by an incr_sp and assignment to a similarly
-%		% numbered stackvar in later code into thinking that this
-%		% assignment is redundant.
-%		Rval = lval(SubLval),
-%		( SubLval = curfr
-%		; SubLval = maxfr
-%		; SubLval = redoip(_)
-%		; SubLval = redofr(_)
-%		)
-%	->
-%		Specials = [Vnlval | LeftSpecials]
-%	;
-%		Specials = LeftSpecials
-%	),
+	vn_util__find_specials(Vnlval, LeftSpecials),
+	(
+		% Assignments of this form occur in hijacking.
+		% We must record the left hand side (which will be a stackvar
+		% or framevar) as a must flush location, because liveness will
+		% not force it to be flushed. The reason for this is that
+		% we do not properly include temporary slots (such as those
+		% used by hijacking) in livevals annotations.
+		Rval = lval(SubLval),
+		( SubLval = curfr
+		; SubLval = maxfr
+		; SubLval = redoip(_)
+		; SubLval = redofr(_)
+		)
+	->
+		Specials = [Vnlval | LeftSpecials]
+	;
+		Specials = LeftSpecials
+	),
 	set__insert_list(Liveset0, Specials, Liveset).
 vn_block__handle_instr(call(Proc, Return, Info, CallModel),
 		Livemap, Params, VnTables0, VnTables, Liveset0, Liveset,
Index: tests/hard_coded/Mmakefile
===================================================================
RCS file: /home/mercury1/repository/tests/hard_coded/Mmakefile,v
retrieving revision 1.38
diff -u -u -r1.38 Mmakefile
--- Mmakefile	1998/07/29 08:56:59	1.38
+++ Mmakefile	1998/08/25 08:50:11
@@ -58,6 +58,7 @@
 	nested3 \
 	no_fully_strict \
 	no_inline \
+	nondet_ctrl_vn \
 	nullary_ho_func \
 	parent \
 	parent2 \
@@ -88,7 +89,7 @@
 
 # The following is required to make the test cases
 #	nested, nested2, and nested3
-# work reliabily with parallel makes -- without this they occaisionally fail.
+# work reliabily with parallel makes -- without this they occasionally fail.
 RM_C = :
 
 #-----------------------------------------------------------------------------#
@@ -100,6 +101,7 @@
 MCFLAGS-ho_order	=	--optimize-higher-order
 MCFLAGS-ho_order2	=	--optimize-higher-order
 MCFLAGS-no_fully_strict	=	--no-fully-strict
+MCFLAGS-nondet_ctrl_vn	=	--optimize-value-number
 MCFLAGS-rnd		=	-O6
 
 # In grade `none' with options `-O1 --opt-space' on kryten
Index: tests/hard_coded/nondet_ctrl_vn.exp
===================================================================
RCS file: nondet_ctrl_vn.exp
diff -N nondet_ctrl_vn.exp
--- /dev/null	Wed May 28 10:49:58 1997
+++ nondet_ctrl_vn.exp	Tue Aug 25 20:51:00 1998
@@ -0,0 +1 @@
+test failed: OK.
Index: tests/hard_coded/nondet_ctrl_vn.m
===================================================================
RCS file: nondet_ctrl_vn.m
diff -N nondet_ctrl_vn.m
--- /dev/null	Wed May 28 10:49:58 1997
+++ nondet_ctrl_vn.m	Tue Aug 25 18:47:42 1998
@@ -0,0 +1,41 @@
+% This is a regression test. The 1998 August 24 version of the compiler
+% generated incorrect code for this module, the bug being that the value
+% numbering pass did not properly flush stack slots that hold the old values
+% of hijacked nondet control slots.
+%
+% This is a cut-down version of cut_test.m
+
+:- module nondet_ctrl_vn.
+
+:- interface.
+
+:- import_module io.
+
+:- pred main(io__state::di, io__state::uo) is det.
+
+:- implementation.
+
+:- import_module int.
+
+main -->
+	( { middle(100) } ->
+		io__write_string("test succeeded: BUG.\n")
+	;
+		io__write_string("test failed: OK.\n")
+	).
+
+:- pragma no_inline(middle/1).
+:- pred middle(int::in) is semidet.
+
+middle(A0) :-
+	(
+		A is A0 + 10
+	;
+		A is A0 + 20
+	),
+	A > 200,
+	(
+		B is A
+	;
+		B is A * 2
+	).