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View File 0131-v3_kernel-Stop-ensuring-one-return-value-in-k_try.patch of Package erlang (Project home:Ledest:erlang:20)

From c896f08f5c028b1e31290e6a5502597401acd39f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 6 Feb 2018 06:28:05 +0100
Subject: [PATCH 2/3] v3_kernel: Stop ensuring one return value in #k_try{}

For unclear reasons, v3_kernel attempts to guarantee that #k_try{}
always has at least one return value, even if it will never be
used. I said "attempts", because the handler block that is executed
when an exception is caught does not have the same guarantee. That
means that if an exception is thrown, the return value will not
actually be set.

In practice, however, this is not a problem for the existing code
generator (v3_codegen). The generated code will still be safe.
If we are to rewrite the code generator to generate an SSA-based
intermediate format, this inconsistency *will* cause problems
when creating phi nodes.

While at it, also remove an unecessary creation of new variables
in generation of #k_try_enter{}.
---
 lib/compiler/src/v3_kernel.erl | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/lib/compiler/src/v3_kernel.erl b/lib/compiler/src/v3_kernel.erl
index fd73e5a7dc..dfe8d26afb 100644
--- a/lib/compiler/src/v3_kernel.erl
+++ b/lib/compiler/src/v3_kernel.erl
@@ -2377,12 +2377,11 @@ uexpr(#k_try{anno=A,arg=A0,vars=Vs,body=B0,evars=Evs,handler=H0},
 	    {A1,Au,St2} = ubody(A0, {break,Avs}, St1),
 	    {B1,Bu,St3} = ubody(B0, Br, St2),
 	    {H1,Hu,St4} = ubody(H0, Br, St3),
-	    {Rs1,St5} = ensure_return_vars(Rs0, St4),
 	    Used = union([Au,subtract(Bu, lit_list_vars(Vs)),
 			  subtract(Hu, lit_list_vars(Evs))]),
-	    {#k_try{anno=#k{us=Used,ns=lit_list_vars(Rs1),a=A},
-		    arg=A1,vars=Vs,body=B1,evars=Evs,handler=H1,ret=Rs1},
-	     Used,St5}
+	    {#k_try{anno=#k{us=Used,ns=lit_list_vars(Rs0),a=A},
+		    arg=A1,vars=Vs,body=B1,evars=Evs,handler=H1,ret=Rs0},
+	     Used,St4}
     end;
 uexpr(#k_try{anno=A,arg=A0,vars=Vs,body=B0,evars=Evs,handler=H0},
       return, St0) ->
@@ -2390,13 +2389,11 @@ uexpr(#k_try{anno=A,arg=A0,vars=Vs,body=B0,evars=Evs,handler=H0},
     {A1,Au,St2} = ubody(A0, {break,Avs}, St1),	%Must break to clean up here!
     {B1,Bu,St3} = ubody(B0, return, St2),
     {H1,Hu,St4} = ubody(H0, return, St3),
-    NumNew = 1,
-    {Ns,St5} = new_vars(NumNew, St4),
     Used = union([Au,subtract(Bu, lit_list_vars(Vs)),
 		  subtract(Hu, lit_list_vars(Evs))]),
-    {#k_try_enter{anno=#k{us=Used,ns=Ns,a=A},
+    {#k_try_enter{anno=#k{us=Used,ns=[],a=A},
 		  arg=A1,vars=Vs,body=B1,evars=Evs,handler=H1},
-     Used,St5};
+     Used,St4};
 uexpr(#k_catch{anno=A,body=B0}, {break,Rs0}, St0) ->
     {Rb,St1} = new_var(St0),
     {B1,Bu,St2} = ubody(B0, {break,[Rb]}, St1),
-- 
2.16.3