v3_core: Improve code generation for guards

When translating guards to Core Erlang, it is sometimes necessary
to add an is_boolean/1 guard test. Here is an example when it is
necessary:

  o(A, B) when A or B ->
    ok.

That would be translated to something like:

  o(A, B) when ((A =:= true) or (B =:= true)) and
      is_boolean(A) and is_boolean(B) ->
    ok.

The is_boolean/1 tests are necessary to ensure that the guard
fails for calls such as:

  o(true, not_boolean)

However, because of a bug in v3_core, is_boolean/1 tests were
added when they were not necessary. Here is an example:

  f(B) when not B -> ok.

That would be translated to:

  f(B) when (B =:= false) and is_boolean(B) -> ok.

The following translation will work just as well.

  f(B) when B =:= false -> ok.

Correct the bug to suppress those unnecessary is_boolean/1 tests.

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 0941ad5dd5..7c229210a0 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -469,7 +469,8 @@ unforce_tree([#iset{var=#c_var{name=V},arg=Arg0}|Es], D0) ->
     unforce_tree(Es, D);
 unforce_tree([#icall{}=Call], D) ->
     unforce_tree_subst(Call, D);
-unforce_tree([Top], _) -> Top.
+unforce_tree([#c_var{name=V}], D) ->
+    gb_trees:get(V, D).
 
 unforce_tree_subst(#icall{module=#c_literal{val=erlang},
 			  name=#c_literal{val='=:='},