From a6edfacf112f3048630bbd002b1eb8d933ebb2df Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Wed, 25 May 2016 06:15:18 +0200
Subject: beam_utils: Simplify handling of 'return' to eliminate uncovered line

Y registers are killed by the deallocate/1 instruction, so there is no
need to handle Y register in the return/1 instruction in
check_liveness/3.

There is also no need to keep check_liveness_live_ret/3 since it
is only used in one place.
---
 lib/compiler/src/beam_utils.erl | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

(limited to 'lib')

diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index 47703b4aa3..cc5bb4b98b 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -324,8 +324,11 @@ check_liveness(R, [{deallocate,_}|Is], St) ->
 	{y,_} -> {killed,St};
 	_ -> check_liveness(R, Is, St)
     end;
-check_liveness(R, [return|_], St) ->
-    check_liveness_live_ret(R, 1, St);
+check_liveness({x,_}=R, [return|_], St) ->
+    case R of
+	{x,0} -> {used,St};
+	{x,_} -> {killed,St}
+    end;
 check_liveness(R, [{call,Live,_}|Is], St) ->
     case R of
 	{x,X} when X < Live -> {used,St};
@@ -534,14 +537,6 @@ check_liveness_at(R, Lbl, #live{lbl=Ll,res=ResMemorized}=St0) ->
 check_liveness_ret(R, R, St) -> {used,St};
 check_liveness_ret(_, _, St) -> {killed,St}.
 
-check_liveness_live_ret({x,R}, Live, St) ->
-    if
-	R < Live -> {used,St};
-	true -> {killed,St}
-    end;
-check_liveness_live_ret({y,_}, _, St) ->
-    {killed,St}.
-
 check_liveness_fail(_, _, _, 0, St) ->
     {killed,St};
 check_liveness_fail(R, Op, Args, Fail, St) ->
-- 
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