beam_utils: Extend live_opt/1 to recalculate live registers in allocs

The code generator uses conservative liveness information. Therefore
the number of live registers in allocation instructions (such as
test_heap/2) may be too high. Use the actual liveness information
to lower the number of live register if it's too high.

The main reason we want to do this is to enable more optimizations
that depend on liveness analysis, such as the beam_bool and beam_dead
passes.

1 files changed, 24 insertions, 0 deletions

diff --git a/lib/compiler/test/bs_construct_SUITE.erl b/lib/compiler/test/bs_construct_SUITE.erl
index 9ab76449c7..a393aaeffd 100644
--- a/lib/compiler/test/bs_construct_SUITE.erl
+++ b/lib/compiler/test/bs_construct_SUITE.erl
@@ -360,6 +360,11 @@ in_catch(Config) when is_list(Config) ->
     ?line <<255>> = small(255, <<1,2,3,4,5,6,7,8,9>>),
     ?line <<1,2>> = small(<<7,8,9,10>>, 258),
     ?line <<>> = small(<<1,2,3,4,5>>, <<7,8,9,10>>),
+
+    <<15,240,0,42>> = small2(255, 42),
+    <<7:20>> = small2(<<1,2,3>>, 7),
+    <<300:12>> = small2(300, <<1,2,3>>),
+    <<>> = small2(<<1>>, <<2>>),
     ok.
 
 small(A, B) ->
@@ -381,6 +386,25 @@ small(A, B) ->
     end,
     <<ResA/binary,ResB/binary>>.
 
+small2(A, B) ->
+    case begin
+	     case catch <<A:12>> of
+		 {'EXIT',_} -> <<>>;
+		 ResA0 -> ResA0
+	     end
+	 end of
+	ResA -> ok
+    end,
+    case begin
+	     case catch <<B:20>> of
+		 {'EXIT',_} -> <<>>;
+		 ResB0 -> ResB0
+	     end
+	 end of
+	ResB -> ok
+    end,
+    <<ResA/binary-unit:1,ResB/binary-unit:1>>.
+
 nasty_literals(Config) when is_list(Config) ->
     case erlang:system_info(endian) of
 	big ->