Eliminate crash in beam_bool

beam_bool would crash when attempting to optimize BEAM code similar
to this code:

  bif '=:=' Reg1 SomeValue => y(0)
  bif '=:=' Reg2 {atom,true} => x(2)
  bif '=:=' Reg3 {atom,true} => x(3)
  bif 'or' x(2) x(3) => x(2)
  is_eq_exact Fail x(2) {atom,true}

The problem is that the first instruction that assigns a value to a Y
register. beam_bool:ssa_assign/2 will not accept a Y register
argument.

We could change ssa_assign/2 to accept a Y register, but that would
only cause the entire optimization to be rejected later because the Y
register is alive in the code that follows. Therefore, a better
solution is to modify extend_block/3 so that the instruction that
assign to Y registers are not added to the block. That is, the
optimizer will only operate on the following code:

  bif '=:=' Reg2 {atom,true} => x(2)
  bif '=:=' Reg3 {atom,true} => x(3)
  bif 'or' x(2) x(3) => x(2)
  is_eq_exact Fail x(2) {atom,true}

Usually the optimization will succeed, rewriting the four instructions
to a select_val instruction.

Assembly code such as the above can be produced by code similar to:

  Y = Something == SomethingElse,
  case Y of
     Condition; OtherCondition ->
       . . .
  end,
  . . .,
  Y.

Reported-by: http://bugs.erlang.org/browse/ERL-143
Reported-by: José Valim

1 files changed, 33 insertions, 2 deletions

diff --git a/lib/compiler/test/beam_bool_SUITE.erl b/lib/compiler/test/beam_bool_SUITE.erl
index 413d03b0ff..84d634e5ca 100644
--- a/lib/compiler/test/beam_bool_SUITE.erl
+++ b/lib/compiler/test/beam_bool_SUITE.erl
@@ -22,7 +22,7 @@
 -export([all/0,suite/0,groups/0,init_per_suite/1,end_per_suite/1,
 	 init_per_group/2,end_per_group/2,
 	 before_and_inside_if/1,
-	 scotland/1]).
+	 scotland/1,y_registers/1]).
 
 suite() ->
     [{ct_hooks,[ts_install_cth]}].
@@ -34,7 +34,8 @@ all() ->
 groups() ->
     [{p,[parallel],
       [before_and_inside_if,
-       scotland
+       scotland,
+       y_registers
       ]}].
 
 init_per_suite(Config) ->
@@ -127,3 +128,33 @@ do_scotland(Echo) ->
 	Echo = placed).
 
 found(_, _) -> million.
+
+
+%% ERL-143: beam_bool could not handle Y registers as a destination.
+y_registers(_Config) ->
+    {'EXIT',{badarith,[_|_]}} = (catch baker(valentine)),
+    {'EXIT',{badarith,[_|_]}} = (catch baker(clementine)),
+
+    {not_ok,true} = potter([]),
+    {ok,false} = potter([{encoding,any}]),
+
+    ok.
+
+%% Thanks to Quickcheck.
+baker(Baker) ->
+    (valentine == Baker) +
+	case Baker of
+	    Baker when Baker; Baker ->
+		Baker;
+	    Baker ->
+		[]
+	end.
+
+%% Thanks to Jose Valim.
+potter(Modes) ->
+    Raw = lists:keyfind(encoding, 1, Modes) == false,
+    Final = case Raw of
+		X when X == false; X == nil -> ok;
+		_ -> not_ok
+	    end,
+    {Final,Raw}.