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, 2 insertions, 2 deletions

diff --git a/lib/compiler/src/beam_bool.erl b/lib/compiler/src/beam_bool.erl
index f9a08f8718..359fdb6d3c 100644
--- a/lib/compiler/src/beam_bool.erl
+++ b/lib/compiler/src/beam_bool.erl
@@ -238,9 +238,9 @@ extend_block(BlAcc0, Fail, [{block,Is0}|OldAcc]) ->
     end;
 extend_block(BlAcc, _, OldAcc) -> {BlAcc,OldAcc}.
 
-extend_block_1([{set,[_],_,{bif,_,{f,Fail}}}=I|Is], Fail, Acc) ->
+extend_block_1([{set,[{x,_}],_,{bif,_,{f,Fail}}}=I|Is], Fail, Acc) ->
     extend_block_1(Is, Fail, [I|Acc]);
-extend_block_1([{set,[_],As,{bif,Bif,_}}=I|Is]=Is0, Fail, Acc) ->
+extend_block_1([{set,[{x,_}],As,{bif,Bif,_}}=I|Is]=Is0, Fail, Acc) ->
     case safe_bool_op(Bif, length(As)) of
 	false -> {Acc,reverse(Is0)};
 	true -> extend_block_1(Is, Fail, [I|Acc])