[m-rev.] for review: Fix compiler abort during liveness detection.

[Peter Wang]

[I'm not certain of the fix]

The compiler would abort during liveness detection on an if-then-else goal
with an unreachable Then branch, due to the Then goal not having its
liveness-related fields initialised.  Bug #51.

compiler/liveness.m:
	    As above.

tests/valid/Mercury.options:
tests/valid/Mmakefile:
tests/valid/bug51.m:
	    Add test case.

NEWS:
	    Announce the change.
---
 NEWS                        |  1 +
 compiler/liveness.m         |  4 +++-
 tests/valid/Mercury.options |  1 +
 tests/valid/Mmakefile       |  1 +
 tests/valid/bug51.m         | 56 +++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 tests/valid/bug51.m

diff --git a/NEWS b/NEWS
index b7979b9..29f21ca 100644
--- a/NEWS
+++ b/NEWS
@@ -13,6 +13,7 @@ This is a bug-fix release.
 * We have added a workaround for a problem that was preventing the
   asm_fast grades working with GCC 4.8.  (Bug #293)
 * Fix inst for constant type_infos.  (Bug #297)
+* Fix compiler abort during liveness detection.  (Bug #51)
 
 
 NEWS for Mercury 13.05.1
diff --git a/compiler/liveness.m b/compiler/liveness.m
index e077a87..9e99ea7 100644
--- a/compiler/liveness.m
+++ b/compiler/liveness.m
@@ -443,7 +443,9 @@ detect_liveness_in_goal(Goal0, Goal, Liveness0, FinalLiveness, LiveInfo) :-
             CondDelta = goal_info_get_instmap_delta(CondInfo),
             ( instmap_delta_is_unreachable(CondDelta) ->
                 LivenessThen = LivenessCond,
-                Then1 = Then0
+                % Initialize liveness-related fields.
+                detect_liveness_in_goal(Then0, Then1,
+                    LivenessCond, _LivenessThen, LiveInfo)
             ;
                 detect_liveness_in_goal(Then0, Then1,
                     LivenessCond, LivenessThen, LiveInfo)
diff --git a/tests/valid/Mercury.options b/tests/valid/Mercury.options
index 590209f..daa185b 100644
--- a/tests/valid/Mercury.options
+++ b/tests/valid/Mercury.options
@@ -40,6 +40,7 @@ MCFLAGS-ambig_pred		= --type-check-constraints
 MCFLAGS-ambig_types		= --type-check-constraints
 MCFLAGS-ambig_stress_test	= --type-check-constraints
 MCFLAGS-builtin_false		= --intermodule-optimization
+MCFLAGS-bug51			= -O3
 MCFLAGS-bug85			= -O0 --deforestation
 MCFLAGS-bug100                  = --halt-at-warn
 MCFLAGS-bug128                  = -O5 --loop-invariants
diff --git a/tests/valid/Mmakefile b/tests/valid/Mmakefile
index 6df4698..20bf60b 100644
--- a/tests/valid/Mmakefile
+++ b/tests/valid/Mmakefile
@@ -67,6 +67,7 @@ OTHER_PROGS= \
 	any_inst_merge \
 	any_matches_bound \
 	big_foreign_type \
+	bug51 \
 	bug85 \
 	bug100 \
 	bug128 \
diff --git a/tests/valid/bug51.m b/tests/valid/bug51.m
new file mode 100644
index 0000000..797bcb2
--- /dev/null
+++ b/tests/valid/bug51.m
@@ -0,0 +1,56 @@
+% The compiler would abort during liveness detection on an if-then-else goal
+% with an unreachable Then branch, due to the Then goal not having its
+% liveness-related fields initialised.
+
+:- module bug51.
+:- interface.
+
+:- import_module io.
+
+:- pred main(io::di, io::uo) is det.
+
+%-----------------------------------------------------------------------------%
+%-----------------------------------------------------------------------------%
+
+:- implementation.
+
+:- import_module list.
+
+:- type fruit
+    --->    apple
+    ;       banana.
+
+main(!IO) :-
+    my_map(make, [apple], Xs),
+    do(Xs, !IO).
+
+:- pred my_map(pred(L, M), list(L), list(M)).
+:- mode my_map(pred(in, out) is det, in, out) is det.
+
+my_map(_, [], []).
+my_map(P, [H0 | T0], [H | T]) :-
+    P(H0, H),
+    my_map(P, T0, T).
+
+:- pred make(fruit::in, fruit::out) is det.
+
+make(X, X).
+
+:- pred do(list(fruit)::in, io::di, io::uo) is det.
+
+do([], !IO).
+do([X | Xs], !IO) :-
+    ( Xs = [_ | _] ->
+        S = "1"
+    ;
+        S = "2"
+    ),
+    (
+        X = apple
+    ;
+        X = banana,
+        io.write_string(S, !IO)
+    ).
+
+%-----------------------------------------------------------------------------%
+% vim: ft=mercury ts=4 sts=4 sw=4 et
-- 
1.7.12.1