From a1243173ed98d1006914337b94f28c9594bd8b02 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 15 Jan 2015 17:17:11 +0100
Subject: Fix handling of binary map keys in comprehensions

The translation of list comprehension with a map pattern
with a big literal binary as key such as:

  lc(L) ->
    [V || #{<<2:301>> := V} <- L].

would generate Core Erlang code where an unbound variable
were referenced:

  'lc'/1 =
    fun (L) ->
      letrec
        'lc$^0'/1 = fun (_cor4) ->
           case _cor4 of
             <[~{~<_cor1,V>}~|_cor3]> when 'true' ->
               let <_cor5> = apply 'lc$^0'/1(_cor3)
                 in [V|_cor5]
             <[_cor2|_cor3]> when 'true' ->
               apply 'lc$^0'/1(_cor3)
             <[]> when 'true' ->
               []
           end
      in let <_cor1> = #{#<2>(301,1,'integer',['unsigned'|['big']])}#
         in apply 'lc$^0'/1(L)

In the map pattern in the 'case' in the 'letrec', the key is the
variable '_cor1' which should be bound in the enclosing environment.

It is not.

There is binding of '_cor1', but in the wrong place (at the end of
the function). Because of the way v3_kernel translates letrecs,
the code *happens* to work.

The code will break if Core Erlang optimizations were strengthened
to more aggressively eliminate variable bindings that are not used,
or if the translation from Core Erlang to Kernel Erlang were changed.

Correct the translation so that '_cor1' is bound in the environment
enclosing the 'letrec':

  'lc'/1 =
    fun (L) ->
      let <_cor1> = #{#<2>(301,1,'integer',['unsigned'|['big']])}#
        in letrec
          'lc$^0'/1 = fun (_cor4) ->
            case _cor4 of
              <[~{~<_cor1,V>}~|_cor3]> when 'true' ->
                let <_cor5> = apply 'lc$^0'/1(_cor3)
                  in [V|_cor5]
              <[_cor2|_cor3]> when 'true' ->
                apply 'lc$^0'/1(_cor3)
              <[]> when 'true' ->
                []
            end
      in apply 'lc$^0'/1(L)

Unfortunately I was not able to come up with a test case that
demonstrates the bug.
---
 lib/compiler/src/v3_core.erl | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 612660c2d6..b861de3bbb 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -105,7 +105,8 @@
 -record(iset,      {anno=#a{},var,arg}).
 -record(itry,      {anno=#a{},args,vars,body,evars,handler}).
 -record(ifilter,   {anno=#a{},arg}).
--record(igen,      {anno=#a{},acc_pat,acc_guard,skip_pat,tail,tail_pat,arg}).
+-record(igen,      {anno=#a{},ceps=[],acc_pat,acc_guard,
+		    skip_pat,tail,tail_pat,arg}).
 
 -type iapply()    :: #iapply{}.
 -type ibinary()   :: #ibinary{}.
@@ -1011,7 +1012,8 @@ fun_tq({_,_,Name}=Id, Cs0, L, St0, NameInfo) ->
 %% lc_tq(Line, Exp, [Qualifier], Mc, State) -> {LetRec,[PreExp],State}.
 %%  This TQ from Simon PJ pp 127-138.  
 
-lc_tq(Line, E, [#igen{anno=GAnno,acc_pat=AccPat,acc_guard=AccGuard,
+lc_tq(Line, E, [#igen{anno=GAnno,ceps=Ceps,
+		      acc_pat=AccPat,acc_guard=AccGuard,
                       skip_pat=SkipPat,tail=Tail,tail_pat=TailPat,
                       arg={Pre,Arg}}|Qs], Mc, St0) ->
     {Name,St1} = new_fun_name("lc", St0),
@@ -1046,7 +1048,7 @@ lc_tq(Line, E, [#igen{anno=GAnno,acc_pat=AccPat,acc_guard=AccGuard,
     Fun = #ifun{anno=LAnno,id=[],vars=[Var],clauses=Cs,fc=Fc},
     {#iletrec{anno=LAnno#a{anno=[list_comprehension|LA]},defs=[{{Name,1},Fun}],
               body=Pre ++ [#iapply{anno=LAnno,op=F,args=[Arg]}]},
-     [],St4};
+     Ceps,St4};
 lc_tq(Line, E, [#ifilter{}=Filter|Qs], Mc, St) ->
     filter_tq(Line, E, Filter, Mc, St, Qs, fun lc_tq/5);
 lc_tq(Line, E0, [], Mc0, St0) ->
@@ -1071,7 +1073,8 @@ bc_tq(Line, Exp, Qs0, _, St0) ->
 			    args=[Sz]}}] ++ BcPre,
     {E,Pre,St}.
 
-bc_tq1(Line, E, [#igen{anno=GAnno,acc_pat=AccPat,acc_guard=AccGuard,
+bc_tq1(Line, E, [#igen{anno=GAnno,ceps=Ceps,
+		       acc_pat=AccPat,acc_guard=AccGuard,
                        skip_pat=SkipPat,tail=Tail,tail_pat=TailPat,
                        arg={Pre,Arg}}|Qs], Mc, St0) ->
     {Name,St1} = new_fun_name("lbc", St0),
@@ -1109,7 +1112,7 @@ bc_tq1(Line, E, [#igen{anno=GAnno,acc_pat=AccPat,acc_guard=AccGuard,
     Fun = #ifun{anno=LAnno,id=[],vars=Vars,clauses=Cs,fc=Fc},
     {#iletrec{anno=LAnno#a{anno=[list_comprehension|LA]},defs=[{{Name,2},Fun}],
               body=Pre ++ [#iapply{anno=LAnno,op=F,args=[Arg,Mc]}]},
-     [],St4};
+     Ceps,St4};
 bc_tq1(Line, E, [#ifilter{}=Filter|Qs], Mc, St) ->
     filter_tq(Line, E, Filter, Mc, St, Qs, fun bc_tq1/5);
 bc_tq1(_, {bin,Bl,Elements}, [], AccVar, St0) ->
@@ -1245,8 +1248,9 @@ generator(Line, {generate,Lg,P0,E}, Gs, St0) ->
                                 ann_c_cons(LA, Skip, Tail)}
                        end,
     {Ce,Pre,St4} = safe(E, St3),
-    Gen = #igen{anno=#a{anno=GA},acc_pat=AccPat,acc_guard=Cg,skip_pat=SkipPat,
-                tail=Tail,tail_pat=#c_literal{anno=LA,val=[]},arg={Ceps++Pre,Ce}},
+    Gen = #igen{anno=#a{anno=GA},ceps=Ceps,
+		acc_pat=AccPat,acc_guard=Cg,skip_pat=SkipPat,
+                tail=Tail,tail_pat=#c_literal{anno=LA,val=[]},arg={Pre,Ce}},
     {Gen,St4};
 generator(Line, {b_generate,Lg,P,E}, Gs, St0) ->
     LA = lineno_anno(Line, St0),
-- 
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