From 1cac7619bf9892f571f855a424b5542c3c1aaf81 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20H=C3=B6gberg?= <john@erlang.org>
Date: Tue, 5 Mar 2019 15:14:01 +0100
Subject: beam_validator: Refactor type conflict resolution

The current type conflict resolution works well for the example
case in the comment, but doesn't handle branched code properly,
consider the following:

  {label,2}.
    {test,is_tagged_tuple,{f,ignored},[{x,0},3,{atom,r}]}.
    {allocate_zero,2,1}.
    {move,{x,0},{y,0}}.
    %% {y,0} is known to be {r, _, _} now.
    {get_tuple_element,{x,0},2,{x,0}}.
    {'try',{y,1},{f,3}}.
    %% ... snip ...
    {jump,{f,5}}.
  {label,3}.
    {try_case,{y,1}}.
    %% {x,0} is the error class (an atom), {x,1} is the error term.
    {test,is_eq_exact,{f,ignored},[{x,0},{y,0}]}.
    %% ... since tuples and atoms can't meet, the type of {y,0} is
    %% now {atom,[]} because the current code assumes the type
    %% we're updating with.
    {move,{x,1},{x,0}}.
    {jump,{f,5}}.
  {label,5}.
    %% ... joining tuple (block 2) and atom (block 3) means 'term',
    %% so the get_tuple_element instruction fails to validate
    %% despite this being unrechable from block 3.
    {test_heap,3,1}.
    {get_tuple_element,{y,0},1,{x,1}}.
    {put_tuple2,{x,0},{list,[{x,1},{x,0}]}}.
    {deallocate,2}.
    return.

This commit kills the state on type conflicts, making unreachable
instructions truly unreachable.
---
 lib/compiler/test/beam_validator_SUITE_data/merge_undefined.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

(limited to 'lib/compiler/test/beam_validator_SUITE_data/merge_undefined.S')

diff --git a/lib/compiler/test/beam_validator_SUITE_data/merge_undefined.S b/lib/compiler/test/beam_validator_SUITE_data/merge_undefined.S
index 481d55045d..aa344807e4 100644
--- a/lib/compiler/test/beam_validator_SUITE_data/merge_undefined.S
+++ b/lib/compiler/test/beam_validator_SUITE_data/merge_undefined.S
@@ -15,8 +15,9 @@
     {select_val,{x,0},{f,1},{list,[{atom,gurka},{f,3},{atom,delete},{f,4}]}}.
   {label,3}.
     {allocate_heap,2,6,2}.
-    %% The Y registers are not initialized here.
     {test,is_eq_exact,{f,5},[{x,0},{atom,ok}]}.
+    %% This is unreachable since {x,0} is known not to be 'ok'. We should not
+    %% fail with "uninitialized y registers" on erlang:exit/1
     {move,{atom,nisse},{x,0}}.
     {call_ext,1,{extfunc,erlang,exit,1}}.
   {label,4}.
@@ -29,6 +30,7 @@
     {call_ext,2,{extfunc,io,format,2}}.
     {test,is_ne_exact,{f,6},[{x,0},{atom,ok}]}.
   {label,5}.
+    %% The Y registers are not initialized here.
     {move,{atom,logReader},{x,1}}.
     {move,{atom,console},{x,0}}.
     {call_ext,2,{extfunc,debug,filter,2}}.
-- 
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