From fd9b5ae4193fbab66093c88728c0dbeaa3b57312 Mon Sep 17 00:00:00 2001
From: Hans Bolinder <hasse@erlang.org>
Date: Mon, 27 Aug 2018 13:14:29 +0200
Subject: dialyzer: Improve handling of complex guards

See also https://bugs.erlang.org/browse/ERL-680.

The right associative short circuit expressions 'andalso' and 'orelse'
are expanded by the Compiler (see v3_core) into 'case' expressions. If
parentheses are used to enforce left associativeness, variables are
introduced, and the time needed by Dialyzer increases exponentially.

Rather than trying to fix Dialyzer itself, v3_core now rewrites
repeated use of 'andalso' ('orelse') into right associative
expressions before creating the 'case' expressions.
---
 lib/compiler/src/v3_core.erl | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

(limited to 'lib/compiler/src/v3_core.erl')

diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 3b746ab5bf..c9517c3e51 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -328,14 +328,16 @@ gexpr({protect,Line,Arg}, Bools0, St0) ->
             Anno = lineno_anno(Line, St),
 	    {#iprotect{anno=#a{anno=Anno},body=Eps++[E]},[],Bools0,St}
     end;
-gexpr({op,L,'andalso',E1,E2}, Bools, St0) ->
+gexpr({op,_,'andalso',_,_}=E0, Bools, St0) ->
+    {op,L,'andalso',E1,E2} = right_assoc(E0, 'andalso', St0),
     Anno = lineno_anno(L, St0),
     {#c_var{name=V0},St} = new_var(Anno, St0),
     V = {var,L,V0},
     False = {atom,L,false},
     E = make_bool_switch_guard(L, E1, V, E2, False),
     gexpr(E, Bools, St);
-gexpr({op,L,'orelse',E1,E2}, Bools, St0) ->
+gexpr({op,_,'orelse',_,_}=E0, Bools, St0) ->
+    {op,L,'orelse',E1,E2} = right_assoc(E0, 'orelse', St0),
     Anno = lineno_anno(L, St0),
     {#c_var{name=V0},St} = new_var(Anno, St0),
     V = {var,L,V0},
@@ -2054,6 +2056,19 @@ fail_clause(Pats, Anno, Arg) ->
 	     body=[#iprimop{anno=#a{anno=Anno},name=#c_literal{val=match_fail},
 			    args=[Arg]}]}.
 
+%% Optimization for Dialyzer.
+right_assoc(E, Op, St) ->
+    case member(dialyzer, St#core.opts) of
+        true ->
+            right_assoc2(E, Op);
+        false ->
+            E
+    end.
+
+right_assoc2({op,L1,Op,{op,L2,Op,E1,E2},E3}, Op) ->
+    right_assoc2({op,L2,Op,E1,{op,L1,Op,E2,E3}}, Op);
+right_assoc2(E, _Op) -> E.
+
 annotate_tuple(A, Es, St) ->
     case member(dialyzer, St#core.opts) of
         true ->
-- 
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